CN106270532A - Yittrium oxide tungsten functionally gradient material (FGM) and preparation method thereof and the application in manufacturing alloy melting crucible - Google Patents

Abstract

The invention relates to an yttrium oxide-tungsten gradient material, a preparation method thereof and an application in manufacturing a crucible for alloy melting. The gradient material includes an yttrium oxide layer and a plurality of transition layers, and the volume fractions of yttrium oxide and tungsten in the mth transition layer are according to C _Wm = 1‑C _Ym and Calculation, where C _Ym and C _Wm are respectively the volume fraction of yttrium oxide and tungsten in the m transition layer; m is a natural number from 1 to (n-1); l is the total thickness of the multiple transition layers; n is The total number of layers of the yttrium oxide layer and each transition layer is n≥3; H _i is the thickness of the i-th layer, and H _m is the thickness of the m-th transition layer. The method comprises weighing tungsten powder and yttrium oxide powder; laying corresponding layers with each powder, forming and sintering. The gradient material has high thermal conductivity and density, low thermal expansion coefficient, excellent corrosion resistance and excellent thermal shock resistance, and can be widely used in superalloy smelting; the method is simple in process, easy to operate, low in energy consumption, and environmentally friendly friendly.

Description

Yttrium oxide-tungsten gradient material, preparation method thereof and crucible for alloy melting application in

technical field

The invention belongs to the field of materials. Specifically, the invention relates to a yttrium oxide-tungsten gradient material, a preparation method thereof, and an application in manufacturing a crucible for alloy melting.

technical background

With the development of science, some metals and alloy materials with special properties are widely used in the automobile industry, aerospace, electrical and electronics, chemical industry, petroleum, national defense and military industry, etc. Including magnesium alloy, aluminum alloy, nickel alloy, copper alloy, uranium alloy, etc. For these alloy materials, high purity is required during use to ensure performance. Therefore, the smelting of alloys has important national value. Due to the advantages of high temperature resistance, good thermal shock resistance, easy processing and low price, graphite material has become an important and commonly used crucible and mold material in metal smelting. In the refining of active metals, the method of coating the surface of graphite crucibles can be used to replace precious metal crucibles and ceramic crucibles. However, studies have found that there are disadvantages such as poor bonding between the matrix and the lining, and difficulty in balancing the thermal shock resistance and erosion resistance of the lining under high temperature environments or thermal shock conditions. The research on graphite crucibles also mainly focuses on the selection of coating materials and the exploration of spraying process.

Commonly used coating materials include refractory oxides (Al ₂ O ₃ , MgO, CaO, ZrO ₂ , Y ₂ O ₃ , YSZ (7-8% Y ₂ O ₃ )) and nitrides (TiN, ZrN , HfN), there are some carbides. In addition, there are zirconates such as MgZrO ₂ and CaZrO ₂ and Al ₂ TiO ₅ . Los Alamos reported that when the laboratory uses graphite or high-temperature oxide-coated metal molds to melt metals, the oxide coatings used are usually MgO or Al ₂ O ₃ , but the effect is not good. Vasconcelos' results showed that no chemical reaction occurred between TiN and the molten alloy at 1700K. A. Shankar used the magnetron sputtering method to prepare graphite crucibles with TiN, ZrN and HfN coatings. The coating thickness was 3.62-3.85 μm, and calculated the Gibbs free energy of the reaction between coating materials and superalloys. The calculation results showed that In the temperature range below 1500 °C, the coating material can maintain good chemical stability with the alloy. Condon JB et al. studied the coating of nearly 50 kinds of ceramic materials (including metal oxides, nitrides, carbides, borides, silicides), and designed a superalloy melting reactivity experiment. Most of the metal oxides are in the alloy reaction. maintained good chemical stability. Among them, the Y ₂ O ₃ coating has the best alloy corrosion resistance and the best thermal stability. Zhang Xian, Cheng Laifei and others performed thermodynamic calculations on the chemical reactions between Y ₂ O ₃ , CaO, BeO, Ce ₂ O ₃ , MgO, ZrO ₂ and other coating or lining materials and metals at high temperatures. _The results show that in the temperature range _of 1200K～1900K, Y ₂ O ₃ , CaO, BeO and Ce ₂ O ₃ will not chemically react with the superalloy, and have good thermochemical stability. Stability is the best. However, Y ₂ O ₃ has a large coefficient of thermal expansion and low high-temperature mechanical properties, so using pure Y ₂ O ₃ as a material for a high-temperature alloy melting crucible cannot meet the application requirements.

Pure W has high thermal conductivity, low thermal expansion coefficient, excellent corrosion resistance, thermal shock resistance and neutron radiation resistance. However, as a melting crucible material, due to the interdiffusion between metals, it will inevitably have a certain impact on the melting and concentration of the alloy.

Toshiba Corporation of Japan has developed a WY ₂ O ₃ composite material. This material has high strength and high corrosion resistance and is used for melting rare earth metals. Compared with ordinary graphite crucibles, the service life of composite material crucibles is 10 times longer. times; within 1000°C, the flexural strength reaches 800MPa, more than 5 times that of pure W, and the content of rare earth metal impurities after smelting drops to one-tenth. However, the WY ₂ O ₃ composite material developed by Toshiba Corporation in Japan produces high thermal stress during the preparation and service of the transfer material, which leads to insufficient thermal shock resistance and erosion resistance.

Chinese patent application CN200910046508.4 discloses a crucible for melting titanium. The crucible is coated with a composite coating on the inner surface of the graphite crucible. The composite coating has a three-layer structure of an inner layer, a transitional gradient coating and an outer layer. The inner layer is a thin SiC layer, the transition layer is composed of one of high temperature stable compound yttrium oxide, calcium zirconate or cerium sulfide and one of refractory metal tungsten, molybdenum or tantalum, the outer layer is high temperature stable compound yttrium oxide, One of calcium zirconate or cerium sulfide, the transition gradient coating is composed of powder of one of high-temperature stable compound yttrium oxide, calcium zirconate or cerium sulfide and one of refractory metal tungsten, molybdenum or tantalum The powder is mixed in different mass ratios and prepared by thermal spraying method (laser cladding, plasma spraying, etc.), from the inside to the outside, based on the mass ratio of high-temperature stable compounds and refractory metals, the first sub-layer is 1: 3. The second sublayer is 1:1, and the third sublayer is 3:1. However, this crucible is based on graphite and needs to be coated with a thin layer of SiC on the inner layer, so it cannot be used for melting metals or alloys sensitive to C. In addition, the proportion of high-temperature stable oxide and refractory metal in the sub-three layers of the transition layer in the crucible is only a simple increase and decrease, and the optimal matching of the thermal stress of the target material is not achieved by optimizing the gradient distribution function of the target material. Therefore, there are still obvious interlayer interfaces between the inner layer, the transition gradient coating and the outer layer, and between the sub-tertiary layers, resulting in thermal stress mismatch phenomenon generated during preparation and use, and reducing the stability of the entire material component. Thermomechanical properties especially reduce the thermal shock resistance of the component.

In order to improve the service temperature and the refining purity of the superalloy, and take into account the thermal shock resistance and corrosion resistance, the present invention proposes to use a Y ₂ O ₃ -W gradient material with a layered gradient transition structure to meet the above performance requirements. Y ₂ O ₃ -W gradient materials can give full play to the high temperature thermochemical stability of Y ₂ O ₃ ceramics and the advantages of high strength and high thermal conductivity of W metal; and Y ₂ O ₃ -W gradient materials with layered gradient transition structure It can effectively relieve and transfer the thermal stress generated in the process of material preparation and service, thereby prolonging the service life of the material.

The material prepared by the invention can be widely used in the field of high-purity rare earth alloy smelting, has good thermal shock resistance and corrosion resistance, has simple preparation process, low energy consumption, and is environmentally friendly, and has broad industrial application prospects.

Contents of the invention

The present invention provides a yttrium oxide-tungsten gradient material in a first aspect, the gradient material includes a yttrium oxide layer and a plurality of transition layers, and the yttrium oxide layer is located in the transition layer with the largest yttrium oxide content. One side of the layer, counting from the side of the layer with the largest tungsten content in the multiple transition layers, the multiple transition layers include the 1st, 2nd, ..., n-1 layers, the yttrium oxide layer Be the nth layer; the volume fraction of the yttrium oxide of the mth transition layer and the volume fraction of tungsten in the multiple transition layers are calculated according to the following formula:

${\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; Y</span>}\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; =</span>{<span\; class="notranslate">\; (</span>\frac{{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}}{\mathrm{<span\; class="notranslate">\; l</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 1.5</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

C _Wm ＝1-C _Ym (2)

${\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; =</span>\underset{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; m</span>}}{<span\; class="notranslate">\; \&Sigma;</span>}}{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>$

in:

C _Ym is the volume fraction of the yttrium oxide in the mth transition layer; C _Wm is the volume fraction of the tungsten in the m transition layer; m is the natural number of 1 to (n-1); 1 is described a plurality of transition layers The total thickness; n is the total number of layers of the yttrium oxide layer and each transition layer and n≥3; H _i is the thickness of the i-th layer, and H _m is the thickness of the m-th transition layer.

In a second aspect, the present invention provides a method for preparing the gradient material described in the first aspect of the present invention, the method comprising the following steps:

(a) According to the size and the number of layers of the gradient material, take the required tungsten powder and yttrium oxide powder;

(b) Use yttrium oxide powder and composite powder composed of yttrium oxide powder and tungsten powder, and tungsten powder to lay up the yttrium oxide layer, the transition layer and the tungsten layer respectively in the mold to form a composite material layup green body, and lay the layers Simultaneously or after forming and sintering, the gradient material is thus produced.

The third aspect of the present invention also provides the application of the gradient material described in the first aspect or the gradient material prepared by the method described in the second aspect in manufacturing a crucible for alloy melting.

After the gradient material of the present invention undergoes 15 to 25 cyclic thermal shocks at 1200°C to 1600°C, the material does not have interlayer peeling and fracture failure; and the material can resist instantaneous laser power of 50 to ^80MW /m2 Thermal shock, the surface of the material has no obvious damage under the in-situ irradiation of plasma with an online average electron density of 1-1.5×10 ¹³ /cm ³ , and has high thermal conductivity, high density, low thermal expansion coefficient, excellent corrosion resistance, Characterized by excellent thermal shock resistance. The invention ensures that the prepared gradient material has good ablation resistance, improves the thermal shock resistance and high-temperature mechanical properties of the composite material, avoids pollution in the melting process of precious metals and high-temperature alloys, and can be widely used in the field of high-purity alloy melting. It is especially suitable for manufacturing multifunctional melting crucibles, especially the core parts of alloy melting crucibles. The method of the invention has the advantages of simple process, low energy consumption, environmental friendliness and broad industrial application prospect.

Description of drawings

Fig. 1 is a schematic diagram of an embodiment of the gradient material of the present invention, the uppermost layer (the layer in contact with the alloy to be smelted) is the yttrium oxide layer (i.e. the nth layer, n=9 in this embodiment, i.e. the ninth layers), the transition layer includes n-1 layers, that is, 8 layers, and the calculation from bottom to top is the first layer, the second layer, ..., the n-1th layer (that is, the eighth layer), and the bottom side is the transition layer The tungsten-rich side of the transition layer is the yttrium oxide-rich side opposite the tungsten-rich side.

detailed description

As mentioned above, the present invention provides a yttrium oxide-tungsten gradient material in the first aspect, the gradient material includes a yttrium oxide layer and a transition layer, the gradient material includes a yttrium oxide layer and a plurality of transition layers, the The yttrium oxide layer is located on the side of the layer with the largest yttrium oxide content in the multiple transition layers, counting from the side of the layer with the largest tungsten content in the multiple transition layers, and the multiple transition layers include the first 1, 2, ..., n-1 layers, the yttrium oxide layer is the nth layer; the volume fraction of yttrium oxide and the volume fraction of tungsten in the mth transition layer in the plurality of transition layers are calculated according to the following formula:

${\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; Y</span>}\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; =</span>{<span\; class="notranslate">\; (</span>\frac{{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}}{\mathrm{<span\; class="notranslate">\; l</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 1.5</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

C _Wm ＝1-C _Ym (2)

${\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; =</span>\underset{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; m</span>}}{<span\; class="notranslate">\; \&Sigma;</span>}}{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>$

in:

C _Ym is the volume fraction of the yttrium oxide in the mth transition layer; C _Wm is the volume fraction of the tungsten in the m transition layer; m is the natural number of 1 to (n-1); 1 is described a plurality of transition layers Total thickness; n is the total number of layers of the yttrium oxide layer and each transition layer and n≥3; H _i is the thickness of the i-th layer, H _m is the thickness of the m-th transition layer, x _m is as shown in formula (3) , that is, the distance between the middle position of the mth transition layer in the thickness direction and the outer surface (the surface away from the yttrium oxide layer) of the layer with the largest tungsten content among the plurality of transition layers.

The present invention is based on the requirements of the size of the crucible material, thermal stress matching, thermal shock resistance and alloy corrosion resistance, and also fully considers the properties of yttrium oxide and tungsten materials, and calculates the ratio of yttrium oxide and tungsten in each transition layer according to the above formula The dosage and distribution are used to prepare gradient materials that meet the expected performance requirements.

In some preferred embodiments, the total number of layers of the gradient material is 3≤n≤15, for example, n is 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13 , 14 or 15, and for example, 5≤n≤11 or 5≤n≤10.

The present invention has no particular limitation on the thickness of each layer in the transition layer, as long as the gradient material can have expected performance. But preferably, the thickness of each layer in the transition layer can be independently 0.5mm to 3mm and all values or sub-ranges in between, such as 0.5mm, 1.0mm, 1.1mm, 1.2mm, 1.3mm, 1.4 mm, 1.5cm, 1.6mm, 1.7mm, 1.8mm, 1.9mm, 2.0mm, 2.1mm, 2.2mm, 2.3mm, 2.4mm, 2.5mm, 2.6mm, 2.7mm, 2.8mm, 2.9mm or 3.0mm.

The present invention has no particular limitation on the thickness of the yttrium oxide layer, as long as the gradient material can have expected performance. Preferably, however, the thickness of the yttrium oxide layer may independently be 0.5 mm to 3 mm and all values or subranges therebetween, such as 0.5 mm, 1.0 mm, 1.1 mm, 1.2 mm, 1.3 mm, 1.4 mm, 1.5 cm, 1.6mm, 1.7mm, 1.8mm, 1.9mm, 2.0mm, 2.1mm, 2.2mm, 2.3mm, 2.4mm, 2.5mm, 2.6mm, 2.7mm, 2.8mm, 2.9mm or 3.0mm. .

In some optional implementation manners, the gradient material may further include a tungsten layer on the tungsten-rich side. The present invention has no particular limitation on the thickness of the tungsten layer, and the thickness of the tungsten layer can be 0.01mm to 3.0mm and all values or sub-ranges therebetween, such as 0mm, 0.01mm, 0.05mm, 0.1mm, 0.2 mm, 0.3mm, 0.4mm, 0.5mm, 0.6mm, 0.7mm, 0.8mm, 0.9mm, 1.0mm, 1.1mm, 1.2mm, 1.3mm, 1.4mm, 1.5mm, 1.6mm, 1.7mm, 1.8mm, 1.9mm, 2.0mm, 2.1mm, 2.2mm, 2.3mm, 2.4mm, 2.5mm, 2.6mm, 2.7mm, 2.8mm, 2.9mm or 3.0mm.

In some embodiments, the tungsten, such as tungsten in the tungsten layer (if present), or such as tungsten in the transition layer (not counting the yttrium oxide in the transition layer), which The purity may independently be 90% by mass or higher, such as 90, 91, 92, 93, 94, 95, 96, 97, 98, 99 or 99.9% by mass, preferably 98% by mass or higher.

In some other embodiments, the purity of the yttrium oxide, for example, the yttrium oxide in the yttrium oxide layer or the yttrium oxide in the transition layer (the tungsten in the transition layer is not counted) can independently be 90 mass % or more, for example, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99 or 99.9 mass % or more, preferably 98 mass % or more.

In a second aspect, the present invention provides a method for preparing the gradient material described in the first aspect of the present invention, the method comprising the following steps:

(a) According to the size and the number of layers of the gradient material, take the required tungsten powder and yttrium oxide powder;

(b) Use yttrium oxide powder and composite powder composed of yttrium oxide powder and tungsten powder in a mold (such as a graphite mold), and tungsten powder is used to lay up an yttrium oxide layer, a transition layer and a tungsten layer respectively to form a composite material laminated body , and molding and sintering are carried out at the same time as or after lamination, thereby preparing the gradient material.

In some embodiments, the particle size of the tungsten powder used to form the tungsten layer (if any) and the particle size of the tungsten powder used to form the transition layer are independently 0.1 μm to 10 μm, for example 0.1 μm , 0.2, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10 μm.

In other embodiments, the particle size of the yttrium oxide powder used to form the yttrium oxide layer and the particle size of the yttrium oxide powder used to form the transition layer are independently 0.1 μm to 8 μm, for example, 0.1, 0.2 , 0.5, 1, 2, 3, 4, 5, 6, 7 or 8 μm.

In some embodiments, the composite powder can be prepared by ball milling wet mixing, wherein the dispersion medium and the dispersant are used as the mixing medium, and the mixing time is 6 hours to 24 hours (such as 6, 12, 18 or 24 hours), Then, for example, the mixed medium is removed by evaporating the mixed medium such as ethanol in an open drying oven or a vacuum distillation system to obtain a mixed powder, and then the mixed powder is passed through a 120-mesh sieve to obtain a uniformly mixed composite powder.

The present invention has no special limitation on the dispersion medium and dispersant used in ball milling wet mixing, but in some preferred embodiments, the dispersion medium can be selected from the group consisting of water, ethanol, methanol and xylene. In the present invention, there is no special limitation on the amount of the dispersion medium, as long as it can disperse the yttrium oxide powder and tungsten powder to be dispersed. In other embodiments, the dispersant may be selected from the group consisting of polyethylene, polyacrylic acid, glycerin, and copolymers formed by copolymerization of polycarboxylic acid and polysiloxane. In the present invention, there is no special limitation on the amount of the dispersion medium, as long as it can disperse the yttrium oxide powder and/or tungsten powder to be dispersed. However, in some preferred embodiments, the concentration of the dispersant in the dispersion liquid may be 0.5 mol% to 3 mol%, such as 0.5, 1, 2, or 3 mol%.

In some optional embodiments, the composite powder can be prepared by ball milling dry mixing, wherein ceramic balls or cemented carbide balls are used as the mixing medium, and the mixing time is 12 hours to 48 hours (for example, 12, 18, 24 , 30, 36, 42 or 48 hours), and then passed through a 120 mesh sieve to obtain a uniformly mixed composite powder.

Optionally, the composite powder can be granulated after preparation to achieve better shaping.

In some embodiments where layup, shaping and sintering are achieved simultaneously, the composite layup body can be laid up with respective powders for the respective layers by means of a plasma spraying equipment equipped with a powder feeder . The working pressure of the spray gun of the plasma spraying equipment can be 0.1～0.5MPa (such as 0.1, 0.2, 0.3, 0.4 or 0.5MPa), and the moving speed of the spray gun can be 20～50mm/s (such as 20mm/s, 30mm/s s, 40mm/s or 50mm/s), the powder feeding rate of the powder feeder can be 5-20g/min (such as 5, 10, 15 or 20g/min), and the spraying temperature can be 1600-2000℃ or in between Any numerical value or range, for example, 1600, 1700, 1800, 1900 or 2000° C., thereby realizing forming and sintering while laying layers.

In an embodiment in which layer laying, molding and sintering are performed sequentially, the layer laying can be done by hand laying, tape casting and the like. For example, in the case of tape laying, it can be laid by casting at room temperature, then dried at 80 to 150°C (80, 90, 100, 110, 120, 130, 140, or 150°C), and Debinding is carried out at 120-350° C. (120, 150, 200, 250, 300 or 350° C.), so as to lay the composite material ply body. Then, the green body is formed and sintered in sequence. The molding can be realized by cold pressing at room temperature and/or cold isostatic pressing. The pressure of the room temperature cold pressing can be 5 to 50 MPa, for example, 5, 10, 20, 25, 30, 35, 40, 45 or 50 MPa. The pressure of the cold isostatic pressing may be 50-200 MPa (for example, 50, 100, 150 or 200 MPa). Sintering can be performed by hot-press sintering or pressureless sintering. The sintering temperature of hot-press sintering can be 1600-2000°C or any value or range in between, such as 1600, 1700, 1800, 1900 or 2000°C. One-way pressure or two-way pressure can be used during hot-press sintering Pressurization, the applied pressure is 10MPa to 50MPa or any value or range therebetween, such as 10, 20, 30, 40 or 50MPa, and the sintering holding time is 1 hour to 5 hours, such as 1, 2, 3, For 4 or 5 hours, the cooling rate is 5°C/min to 10°C/min, such as 5, 6, 7, 8, 9 or 10°C/min, and the sintering atmosphere can be argon, nitrogen or vacuum. The sintering temperature of the pressureless sintering can be any value or range between 1600°C and 2000°C, for example, 1600, 1700, 1800, 1900 or 2000°C. The holding time of pressureless sintering is 1 hour to 5 hours, such as 1, 2, 3, 4 or 5 hours, and the cooling rate is 5°C/min to 10°C/min, such as 5, 6, 7, 8, 9 or 10°C/min, the sintering atmosphere can be argon, nitrogen or vacuum.

In the third aspect, the present invention also provides the gradient material described in the first aspect or the gradient material prepared by the method described in the second aspect used in the manufacture of crucibles, such as crucibles for melting high-temperature metals or alloys, especially crucibles for melting alloys Applications.

The present invention will be further described below by way of illustration, but these examples are only for the purpose of illustration, and should not be construed as limiting the protection scope of the present invention.

Example 1

The number of layers of the composite material is preset to be n=5, and the uppermost layer of the material is Y ₂ O ₃ layers with a thickness of 2 mm. The transition layer is 4 layers, and the thickness of each layer is 2mm. Calculate the volume ratio of each transition layer according to the above formulas (1) to (3) according to the yttrium oxide powder with an average particle size of 1 μm and a purity of 98% and the tungsten powder with an average particle size of 0.2 μm and a purity of 98%. The components of each layer from top to bottom are:

_81.8vol .% _Y2O3-18.2vol .%W, _49.4vol .% _Y2O3-50.6vol .%W,

_23vol .% _Y2O3-50.0vol .%W, _4.4vol .% _Y2O3-95.6vol .%W,

According to the pre-designed gradient structure, each powder is put into the graphite mold layer by layer, cold-pressed at room temperature, and the pressure is 5MPa; after 200MPa cold isostatic pressing, it is directly sintered in a vacuum hot-pressing sintering furnace to obtain Y ₂ O ₃ -W gradient material. The process parameters of vacuum pressureless sintering are: heat preservation at 1800°C for 1 hour, vacuum degree of 1.3×10 ^-2 Pa, and cooling rate of 5°C/min.

The density of the composite material reaches 96.8%, and the bending strength tested by the three-point bending method at room temperature is 532.0MPa. It can resist instantaneous laser thermal shock with a power of about 50MW/m ² , and there is no obvious damage to the surface of the material under the in-situ irradiation of plasma with an online average electron density of 1-1.5×10 ¹³ /cm ³ .

Example 2

The number of layers of the composite material is preset to be n=5, and the uppermost layer of the material is Y ₂ O ₃ layers with a thickness of 2 mm. The transition layer is 4 layers, and the thickness of each layer is 2mm. Calculate the volume ratio of the transition layer according to the formulas (1) to (3) above with the yttrium oxide powder with an average particle size of 1 μm and a purity of 98% and the tungsten powder with an average particle size of 0.2 μm and a purity of 98%. The components of the transition layer from top to bottom are:

_81.8vol .% _Y2O3-18.2vol .%W, _49.4vol .% _Y2O3-50.6vol .%W,

_23vol .% _Y2O3-50.0vol .%W, _4.4vol .% _Y2O3-95.6vol .%W,

Put the powder into the graphite mold layer by layer according to the pre-designed gradient structure, and cold press at room temperature with a pressure of 5 MPa. Then, direct hot-press sintering in a vacuum hot-press sintering furnace to prepare the Y ₂ O ₃ -W gradient material. The process parameters of the vacuum hot pressing sintering are: heat preservation at 1500°C for 1 hour, pressure at 30MPa, vacuum degree at 1.3×10 ^-2 Pa, and cooling rate at 10°C/min.

The density of the composite material reaches 97.6%, and the bending strength tested by the three-point bending method at room temperature is 535.2MPa. In a cyclic thermal shock furnace, after 15 cycles of thermal shock between 1200°C and 1600°C, the prepared Y ₂ O ₃ -W gradient material has no interlayer peeling and fracture failure, and its performance meets the alloy Service performance of melting crucible materials.

Example 3

The number of layers of the composite material is preset to be n=5, and the uppermost layer of the material is Y ₂ O ₃ layers with a thickness of 2 mm. The transition layer is 4 layers, and the thickness of each layer is 2mm. Calculate the volume ratio of the transition layer according to the formulas (1) to (3) above with the yttrium oxide powder with an average particle size of 2 μm and a purity of 99% and the tungsten powder with an average particle size of 0.5 μm and a purity of 98%. The components of the transition layer from top to bottom are:

_81.8vol .% _Y2O3-18.2vol .%W, _49.4vol .% _Y2O3-50.6vol .%W,

_23vol .% _Y2O3-50.0vol .%W, _4.4vol .% _Y2O3-95.6vol .%W,

According to the volume content of the pre-designed transition layer, it is put into the powder feeder of thermal spraying one by one, and the powder is sprayed layer by layer by the plasma spraying process to prepare the Y ₂ O ₃ -W gradient material. The process parameters are: arc heating at 1600°C, the working pressure of the spray gun is 0.5-1.0MPa, the moving speed of the spray gun is 30mm/s, and the powder feeding volume of the powder feeder is 15g/min.

The density of the composite material reaches 95.3%, and the bending strength tested by the three-point bending method at room temperature can reach 524.0MPa. In a cyclic thermal shock furnace, after 15 cycles of thermal shock between 1200°C and 1600°C, the prepared Y ₂ O ₃ -W gradient material has no interlayer peeling and fracture failure, and its performance meets the alloy Service performance of melting crucible materials.

Example 4

The number of layers of the composite material is preset to be n=9, and the uppermost layer of the material is Y ₂ O ₃ layers with a thickness of 2 mm. The transition layer is 8 layers, and the thickness of each layer is 1mm. Calculate the volume ratio of the transition layer according to the formulas (1) to (3) above with the yttrium oxide powder with an average particle size of 2 μm and a purity of 99% and the tungsten powder with an average particle size of 0.5 μm and a purity of 98%. The components of the transition layer from top to bottom are:

_91.0vol .% _Y2O3-9.0vol .%W, _73.2vol .% _Y2O3-26.8vol .%W,

_57.0vol .% _Y2O3-43.0vol .%W, _42.2vol .% _Y2O3-57.8vol .%W,

_29.0vol .% _Y2O3-71.0vol .%W, _17.5vol .% _Y2O3-82.5vol .%W,

_8.2vol .% _Y2O3-91.8vol .%W, _1.6vol .% _Y2O3-98.4vol .%W,

According to the pre-designed gradient structure, the powder is put into the graphite mold layer by layer, cold-pressed at room temperature, and the pressure is 5MPa; after 200MPa cold isostatic pressing, it is directly sintered without pressure in a vacuum hot-pressing sintering furnace to obtain Y ₂ O ₃ -W gradient material. The process parameters of vacuum pressureless sintering are: heat preservation at 1900°C for 1 hour, argon protection, and cooling rate of 10°C/min.

The density of the composite material reaches 98.0%, and the bending strength tested by the three-point bending method at room temperature is 537.0MPa. In a cyclic thermal shock furnace, after 20 cycles of thermal shock between 1200°C and 1600°C, the prepared Y ₂ O ₃ -W gradient material has no interlayer peeling and fracture failure, and its performance meets the alloy Service performance of melting crucible materials.

Example 5

The number of layers of the composite material is preset to be n=9, and the uppermost layer of the material is Y ₂ O ₃ layers with a thickness of 2 mm. The transition layer is 8 layers, and the thickness of each layer is 1mm. The yttrium oxide powder with an average particle size of 4 μm and a purity of 99% and the tungsten powder with an average particle size of 1 μm and a purity of 99% are used to calculate the volume ratio of the transition layer according to the above-mentioned formulas (1) to (3). The components of each layer from top to bottom are:

_91.0vol .% _Y2O3-9.0vol .%W, _73.2vol .% _Y2O3-26.8vol .%W,

_57.0vol .% _Y2O3-43.0vol .%W, _42.2vol .% _Y2O3-57.8vol .%W,

_29.0vol .% _Y2O3-71.0vol .%W, _17.5vol .% _Y2O3-82.5vol .%W,

_8.2vol .% _Y2O3-91.8vol .%W, _1.6vol .% _Y2O3-98.4vol .%W,

Put the powder into the graphite mold layer by layer according to the pre-designed gradient structure, and cold press at room temperature with a pressure of 5 MPa. Then, direct hot-press sintering in a vacuum hot-press sintering furnace to prepare the Y ₂ O ₃ -W gradient material. The process parameters of the vacuum hot pressing sintering are: heat preservation at 1600°C for 1 hour, pressure at 35MPa, argon protection, and cooling rate at 10°C/min.

The density of the composite material reaches 98.5%, and the bending strength tested by the three-point bending method at room temperature is 551.5MPa. It can resist instantaneous laser thermal shock with a power of about 60MW/m ² , and there is no obvious damage to the surface of the material under in-situ irradiation of plasma with an online average electron density of 1-1.5×10 ¹³ /cm ³ .

Example 6

The number of layers of the composite material is preset to be n=9, and the uppermost layer of the material is Y ₂ O ₃ layers with a thickness of 2 mm. The transition layer is 8 layers, and the thickness of each layer is 1mm. The yttrium oxide powder with an average particle size of 4 μm and a purity of 99% and the tungsten powder with an average particle size of 1 μm and a purity of 99% are used to calculate the volume ratio of the transition layer according to the above-mentioned formulas (1) to (3). The components of each layer from top to bottom are:

_91.0vol .% _Y2O3-9.0vol .%W, _73.2vol .% _Y2O3-26.8vol .%W,

_57.0vol .% _Y2O3-43.0vol .%W, _42.2vol .% _Y2O3-57.8vol .%W,

_29.0vol .% _Y2O3-71.0vol .%W, _17.5vol .% _Y2O3-82.5vol .%W,

_8.2vol .% _Y2O3-91.8vol .%W, _1.6vol .% _Y2O3-98.4vol .%W,

According to the volume content of the pre-designed transition layer, it is put into the powder feeder of thermal spraying one by one, and the powder is sprayed layer by layer by the plasma spraying process to prepare the Y ₂ O ₃ -W gradient material. The process parameters are: arc heating at 1700°C, the working pressure of the spray gun is 0.5-1.0MPa, the moving speed of the spray gun is 40mm/s, and the powder feeding volume of the powder feeder is 10g/min.

The density of the composite material reaches 96.8%, and the bending strength tested by the three-point bending method at room temperature is 540.5MPa. In a cyclic thermal shock furnace, after 20 cycles of thermal shock between 1200°C and 1600°C, the prepared Y ₂ O ₃ -W gradient material has no interlayer peeling and fracture failure, and its performance meets the alloy Service performance of melting crucible materials.

Example 7

The number of layers of the composite material is preset to be n=11, and the uppermost layer of the material is a Y ₂ O ₃ layer with a thickness of 2 mm. The transition layer is 10 layers, and the thickness of each layer is 0.8mm. Calculate the volume ratio of the transition layer according to the formulas (1) to (3) above with the yttrium oxide powder with an average particle size of 5 μm and a purity of 99.9% and the tungsten powder with an average particle size of 0.8 μm and a purity of 99%. The components of the transition layer from top to bottom are:

_92.6vol .% _Y2O3-7.4vol .%W, _78.4vol .% _Y2O3-21.6vol .%W,

_65.0vol .% _Y2O3-35.0vol .%W, _52.4vol .% _Y2O3-47.6vol .%W,

_40.8vol .% _Y2O3-59.2vol .%W, _30.2vol .% _Y2O3-69.8vol .%W,

_20.7vol .% _Y2O3-79.3vol .%W, _12.5vol .% _Y2O3-87.5vol .%W,

_5.8vol .% _Y2O3-94.2vol .%W, _1.1vol .% _Y2O3-98.9vol .%W,

Put the powder into the graphite mold layer by layer according to the pre-designed gradient structure, and cold press at room temperature with a pressure of 5 MPa. Then, directly carry out pressureless sintering in a vacuum hot-pressing sintering furnace to prepare Y ₂ O ₃ -W gradient material. The process parameters of the vacuum pressureless sintering are: heat preservation at 1850°C for 1 hour, vacuum degree of 1.2×10 ^-2 Pa, and cooling rate of 10°C/min.

The density of the composite material reaches 98.5%, and the bending strength tested by the three-point bending method at room temperature is 543.5MPa. In a cyclic thermal shock furnace, after 25 cycles of thermal shock between 1200°C and 1600°C, the prepared Y ₂ O ₃ -W gradient material has no interlayer peeling and fracture failure, and its performance meets the alloy Service performance of melting crucible materials.

Example 8

The number of layers of the composite material is preset to be n=11, and the uppermost layer of the material is a Y ₂ O ₃ layer with a thickness of 2 mm. The transition layer is 10 layers, and the thickness of each layer is 0.8mm. Calculate the volume ratio of the transition layer according to the formulas (1) to (3) above with the yttrium oxide powder with an average particle size of 5 μm and a purity of 99.9% and the tungsten powder with an average particle size of 0.8 μm and a purity of 99%. The components of the transition layer from top to bottom are:

_92.6vol .% _Y2O3-7.4vol .%W, _78.4vol .% _Y2O3-21.6vol .%W,

_65.0vol .% _Y2O3-35.0vol .%W, _52.4vol .% _Y2O3-47.6vol .%W,

_40.8vol .% _Y2O3-59.2vol .%W, _30.2vol .% _Y2O3-69.8vol .%W,

_20.7vol .% _Y2O3-79.3vol .%W, _12.5vol .% _Y2O3-87.5vol .%W,

_5.8vol .% _Y2O3-94.2vol .%W, _1.1vol .% _Y2O3-98.9vol .%W,

Put the powder into the graphite mold layer by layer according to the pre-designed gradient structure, and cold press at room temperature with a pressure of 5 MPa. Then, direct hot-press sintering in a vacuum hot-press sintering furnace to prepare the Y ₂ O ₃ -W gradient material. The process parameters of the vacuum hot pressing sintering are: heat preservation at 1600°C for 1 hour, pressure at 40MPa, vacuum degree at 1.2×10 ^-2 Pa, and cooling rate at 10°C/min.

The density of the composite material reaches 98.8%, and the bending strength tested by the three-point bending method at room temperature is 548.0MPa. In a cyclic thermal shock furnace, after 25 cycles of thermal shock between 1200°C and 1600°C, the prepared Y ₂ O ₃ -W gradient material has no interlayer peeling and fracture failure, and its performance meets the alloy Service performance of melting crucible materials.

Example 9

The number of layers of the composite material is preset to be n=11, and the uppermost layer of the material is a Y ₂ O ₃ layer with a thickness of 2 mm. The transition layer is 10 layers, and the thickness of each layer is 0.8mm. The yttrium oxide powder with an average particle size of 4 μm and a purity of 99.9% and the tungsten powder with an average particle size of 1 μm and a purity of 99% are used to calculate the volume ratio of the transition layer according to the above formulas (1) to (3). The components of each layer from top to bottom are:

_92.6vol .% _Y2O3-7.4vol .%W, _78.4vol .% _Y2O3-21.6vol .%W,

_65.0vol .% _Y2O3-35.0vol .%W, _52.4vol .% _Y2O3-47.6vol .%W,

_40.8vol .% _Y2O3-59.2vol .%W, _30.2vol .% _Y2O3-69.8vol .%W,

_20.7vol .% _Y2O3-79.3vol .%W, _12.5vol .% _Y2O3-87.5vol .%W,

_5.8vol .% _Y2O3-94.2vol .%W, _1.1vol .% _Y2O3-98.9vol .%W,

According to the pre-designed volume content of the transition layer, a tape casting process is used to prepare a composite material green body with a composition gradient change at room temperature. After drying at 90°C and debinding at 280°C, a composite body with gradient composition was prepared. Cold pressing at room temperature, the pressure is 5MPa. After 200MPa cold isostatic pressing, a relatively dense composite body with gradient composition was prepared. The Y ₂ O ₃ -W gradient material is obtained by direct pressureless sintering in a vacuum hot-pressing sintering furnace. The process parameters of vacuum pressureless sintering are: heat preservation at 1800°C for 1 hour, vacuum degree of 1.3×10 ^-2 Pa, and cooling rate of 10°C/min.

The density of the composite material reaches 98.3%, and the bending strength tested by the three-point bending method at room temperature is 445.0MPa. It can resist instantaneous laser thermal shock with a power of about 70MW/m ² , and there is no obvious damage to the surface of the material under in-situ irradiation of plasma with an online average electron density of 1-1.5×10 ¹³ /cm ³ .

Example 10

The number of layers of the composite material is preset to be n=5, and the uppermost layer of the material is Y ₂ O ₃ layers with a thickness of 2 mm. The transition layer is 3 layers, and the thickness of each layer is 2mm. According to the order of calculation from the Y ₂ O ₃ layer, the volume ratio of yttrium oxide and tungsten in the first layer, the second layer and the third layer of the transition layer The order is 3:1, 1:1 and 1:3. The bottom layer is a tungsten layer with a thickness of 2mm. The yttrium oxide powder with an average particle size of 1 μm and a purity of 98% and the tungsten powder with an average particle size of 0.2 μm and a purity of 98% are mixed according to the above volume ratio, and the components of each layer from top to bottom of the transition layer are as follows:

75.0vol.% Y ₂ O ₃ -25.0vol.% W,

50.0vol.% Y ₂ O ₃ -50.0vol.% W,

_25.0vol .% _Y2O3-75.0vol .%W,

Put the powder into the graphite mold layer by layer according to the pre-designed gradient structure, and cold press at room temperature with a pressure of 5 MPa. Then, direct hot-press sintering in a vacuum hot-press sintering furnace to prepare the Y ₂ O ₃ -W gradient material. The process parameters of the vacuum hot pressing sintering are: heat preservation at 1500°C for 1 hour, pressure at 30MPa, vacuum degree at 1.3×10 ^-2 Pa, and cooling rate at 10°C/min.

The density of the composite material reaches 90.4%, and the bending strength tested by the three-point bending method at room temperature is 230.1MPa. In a cyclic thermal shock furnace, after 8 cycles of thermal shock between 1200°C and 1600°C, the prepared Y ₂ O ₃ -W gradient material has interlayer peeling and fracture failure, and its performance cannot meet the requirements of alloys. Service performance of melting crucible materials.

Claims (10)

1. A yttrium oxide-tungsten gradient material, characterized in that: The gradient material includes an yttrium oxide layer and a plurality of transition layers, the yttrium oxide layer is located on the side of the layer with the largest yttrium oxide content in the plurality of transition layers, and the tungsten content in the plurality of transition layers is the largest Counting from one side of the layer, the multiple transition layers include the 1st, 2nd, ..., n-1 layers, and the yttrium oxide layer is the nth layer; the mth transition layer in the multiple transition layers The volume fraction of yttrium oxide and the volume fraction of tungsten are calculated according to the following formula: ${\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; Y</span>}\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; =</span>{<span\; class="notranslate">\; (</span>\frac{{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}}{\mathrm{<span\; class="notranslate">\; l</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 1.5</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$ C _Wm ＝1-C _Ym (2) ${\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; =</span>\underset{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; m</span>}}{<span\; class="notranslate">\; \&Sigma;</span>}}{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>$ in: C _Ym is the volume fraction of the yttrium oxide in the mth transition layer; C _Wm is the volume fraction of the tungsten in the m transition layer; m is the natural number of 1 to (n-1); 1 is described a plurality of transition layers The total thickness; n is the total number of layers of the yttrium oxide layer and each transition layer and n≥3; H _i is the thickness of the i-th layer, and H _m is the thickness of the m-th transition layer. 2. The gradient material according to claim 1, characterized in that: The thickness of each of the n layers of gradient material is each independently 1 mm to 3 mm. 3. The method according to claim 1 or 2, characterized in that: The purity of the tungsten is independently above 90% by mass, preferably above 98% by mass; and/or The purity of the yttrium oxide is independently 90% by mass or higher, preferably 98% by mass or higher. 4 . The gradient material according to claim 1 , wherein the gradient material further comprises a tungsten layer on the tungsten-rich side, and the thickness of the tungsten layer is independently 0 to 3 mm. 5. A method for preparing the gradient material according to any one of claims 1 to 4, characterized in that the method comprises the steps of: (a) According to the size and the number of layers of the gradient material, take the required tungsten powder and yttrium oxide powder; (b) Use yttrium oxide powder and composite powder composed of yttrium oxide powder and tungsten powder, and tungsten powder to lay up the yttrium oxide layer, the transition layer and the tungsten layer respectively in the mold to form a composite material layup green body, and lay the layers Simultaneously or after forming and sintering, the gradient material is thus produced. 6. The method according to claim 5, characterized in that: The particle size of the tungsten powder used to form the tungsten layer and the particle size of the tungsten powder used to form the transition layer are independently 0.1 μm to 10 μm; and/or The particle size of the yttrium oxide powder used to form the yttrium oxide layer and the particle size of the yttrium oxide powder used to form the transition layer are independently 0.1 μm to 8 μm. 7. The method according to claim 5 or 6, characterized in that, the composite powder is made in one of the following ways: (1) Ball milling wet mixing method, using dispersion medium and dispersant as mixing medium, mixing time is 6 hours to 24 hours, then removing the mixing medium to obtain mixed powder, and then passing the mixed powder through a 120 mesh sieve to obtain a uniformly mixed compound powder; (2) Ball milling dry mixing method, using ceramic balls or cemented carbide balls as the mixing medium, the mixing time is 12 hours to 48 hours, and then passing through a 120 mesh sieve to obtain a uniformly mixed composite powder. 8. The method of claim 7, wherein: The dispersion medium is selected from the group consisting of water, ethanol, methanol and xylene; and/or The dispersant is selected from the group consisting of polyethylene, polyacrylic acid, glycerin, and copolymers of polycarboxylic acid and polysiloxane. Preferably, the concentration of the dispersant is 0.5 mol% to 3 mol%. 9. A method according to any one of claims 5 to 8, characterized in that: Layering is carried out by manual layering method or casting method to obtain the composite material layering body, and then the composite material layering body is subjected to room temperature cold pressing and/or cold isostatic pressing, and then hot Pressure sintering or pressureless sintering; or, spraying by plasma spraying equipment to achieve layup, shaping and sintering; Preferably, in the casting method, the composite material ply blank is prepared at room temperature, then dried at 80°C to 150°C, and debinding is performed at 120°C to 350°C, so as to prepare the composite material ply blank body; or, in the cold press forming, the pressure used is 5MPa to 50MPa; or, in the cold isostatic pressing, the pressure used is 50MPa to 200MPa; or, in the hot press sintering, sintering The temperature is 1600-2000°C, the pressurization method is one-way or two-way pressurization, the applied pressure is 10-50MPa, the sintering holding time is 1-5 hours, the temperature drop rate is 5-10°C/min, and the sintering atmosphere is argon , nitrogen or vacuum; or, in the pressureless sintering, the sintering temperature is 1600 to 2000°C, the sintering holding time is 1 to 5 hours, the temperature drop rate is 5 to 10°C/min, and the sintering atmosphere is nitrogen or argon or vacuum; or, the working pressure of the spray gun of the plasma spraying equipment is 0.1～0.5MPa, the moving speed of the spray gun is 20～50mm/s, the powder delivery rate of the powder feeder is 5～20g/min, and the temperature of spraying is 1600～2000℃. 10. Application of the gradient material according to any one of claims 1 to 4 or the gradient material prepared by the method according to any one of claims 5 to 9 in the manufacture of crucibles for alloy melting.