CN118726776A - A TiAl alloy prepared by using a high melting point refractory metal casting mold and a preparation method thereof - Google Patents

Abstract

The present invention discloses a method for preparing a TiAl alloy by using a high melting point refractory metal as a casting mold and a preparation method thereof. In the present invention, the casting mold can be prepared by selecting a high melting point refractory metal niobium, or tantalum, or tungsten or its alloy. Among them, the casting mold is suitable for vacuum induction shell melting, vacuum non-consumable electrode arc melting, vacuum consumable electrode arc melting, electron beam melting, plasma beam melting, composite melting and other methods, and is directly cast and formed. It can also be used for directional solidification to prepare single crystal or columnar crystal samples. The casting mold can also be used as a crucible and applied to vacuum induction melting or vacuum resistance heating melting systems. The TiAl alloy prepared using the casting mold does not contain non-metallic impurities, thereby avoiding the introduction of non-metallic impurities that leads to a decrease in alloy strength, plasticity and other properties, while realizing the alloying of the TiAl alloy and improving the comprehensive properties of the alloy such as strength, high temperature strength, room temperature plasticity and oxidation resistance.

Description

A TiAl alloy prepared by using a high melting point refractory metal casting mold and a preparation method thereof

Technical Field

The present invention relates to the field of casting technology, and in particular to a TiAl alloy prepared by using a high-melting-point refractory metal casting mold and a preparation method thereof.

Background Art

TiAl intermetallic compounds have long-range ordered atomic arrangement, coexistence of metallic bonds and covalent bonds in the crystal, and the characteristics of both metals and ceramics. It is a new type of lightweight heat-resistant structural material with broad application prospects in the fields of aerospace and civil industry. TiAl alloys not only have low density, high specific strength and specific stiffness, corrosion resistance, and wear resistance, but also have excellent oxidation resistance and creep properties. By comparing with high-temperature structural materials at different temperatures, it is found that in the temperature range of 600-900°C, TiAl alloys have higher specific strength than nickel-based high-temperature alloys and titanium alloys; and have higher specific modulus at all temperatures, even 50% to 70% higher than titanium alloys. The excellent high-temperature comprehensive performance of TiAl alloys makes it possible to replace traditional Ni, Fe, Co-based high-temperature alloys and materials used in high temperatures in the automotive and aerospace industries, and is called the "future alloy."

For traditional titanium alloy parts and other materials, casting is a production technology that has been deeply developed. For the casting of TiAl alloys, traditional casting equipment currently used in aviation-grade titanium alloys and nickel alloys can also be used. Casting is the most economical means to produce industrial-grade near-net-shape TiAl alloy parts. At present, the main methods for preparing TiAl alloys are investment casting, metal mold gravity casting, centrifugal casting, anti-gravity low-pressure casting, and directional solidification. However, the molds used in the current casting methods will mostly cause non-metallic impurities in the castings, which will adversely affect their strength, plasticity and other properties. Ordinary metals have poor high temperature resistance. For example, the melting point of steel is about 1500℃ and the melting point of copper is 1084℃, which cannot meet the casting requirements of high-melting-point TiAl-based alloys.

Summary of the invention

The present invention aims to provide a method for casting a TiAl alloy using a high melting point refractory metal mold. By using a high melting point refractory metal mold to cast the TiAl alloy, the TiAl alloy can be alloyed without introducing non-metallic impurities, thereby improving the comprehensive properties of the alloy such as strength and high temperature resistance.

The technical solution of the present invention is:

A method for preparing a TiAl alloy using a high-melting-point refractory metal casting mold. The high-melting-point refractory metal is used as a casting mold to prepare the TiAl alloy, or as a crucible to prepare the TiAl alloy, or as a crucible and a casting mold at the same time to prepare the TiAl alloy.

Furthermore, a high melting point refractory metal is used as a casting mold to prepare a TiAl alloy, and the method comprises the following steps:

Step 1: Put the TiAl alloy raw materials with expected composition into the smelting system in proportion;

Step 2, melting the TiAl alloy at a temperature of 1400-2200° C. under a vacuum state of 10 ^-1 -10 ^-4 Pa;

Step 3: After the mixture is completely melted, keep it warm for 5-20 minutes, and then cast it into a high melting point refractory metal mold;

Step 4: Solidify for 3-30 minutes. After solidification, demould and remove from the mold, cut off the edges, and obtain the alloy ingot.

The smelting system in step 1 includes but is not limited to vacuum induction melting, vacuum resistance heating melting, vacuum induction shell melting, vacuum non-consumable electrode arc melting, vacuum consumable electrode arc melting, electron beam melting, plasma beam melting and composite melting.

In step 3, the high melting point refractory metal casting mold is prepared using high melting point refractory metals including but not limited to niobium, tantalum, tungsten, or their alloys. The casting mold and crucible can be processed according to the required shape and size.

Furthermore, the high melting point refractory metal is used as a crucible to prepare a TiAl alloy, and the method comprises the following steps:

Step 1: Put the TiAl alloy raw material with the expected composition into a high melting point refractory metal crucible according to proportion, and put it into a smelting system;

Step 2: Under a vacuum state of 10-1-10-4 Pa, the TiAl alloy is melted at a melting temperature of 1400-2200°C to completely melt the alloy;

Step 3: After the melted alloy solidifies and cools, turn the alloy over and repeat the smelting 3-6 times;

Step 4: Take out the alloy after smelting.

Furthermore, in step 1, the high melting point refractory metal crucible is prepared by using high melting point refractory metals including but not limited to niobium, tantalum, tungsten, or alloys thereof, and the crucible can be processed according to the required shape and size.

Furthermore, the smelting system in step one includes but is not limited to vacuum induction melting, vacuum resistance heating melting, vacuum induction shell melting, vacuum non-consumable electrode arc melting, vacuum consumable electrode arc melting, electron beam melting, plasma beam melting and composite melting.

Furthermore, the high melting point refractory metal is used as a crucible and a casting mold to prepare a TiAl alloy, and the method comprises the following steps:

Step 1: Process the high melting point refractory metal mold according to the required shape and size, load the TiAl alloy raw material or ingot into the mold, and place it in a directional solidification system, evacuate to 10 ^-1 -10 ^-4 Pa, and then fill the system with high-purity argon protective gas;

Step 2: Use an induction heating or resistance heating system to melt the alloy in the crucible;

Step 3: After the TiAl alloy is completely melted and kept warm for a certain period of time, the high melting point refractory metal is used as a metal mold to directionally solidify the TiAl alloy in a directional solidification system;

Step 4: heat treat the prepared sample at a temperature of 880-1390°C for a holding time of 0.5-100h, followed by furnace cooling.

Furthermore, in step one, the high melting point refractory metal mold is prepared using high melting point refractory metals including but not limited to niobium, tantalum, tungsten, or their alloys. The mold and crucible can be processed according to the required shape and size, and the cross-sectional shape is a circular ring, a square ring, or a complex shape, and the wall thickness is 1-20 mm.

Furthermore, in step three, the directional solidification holding temperature is 1200-2000° C., the holding time is 5-120 min, and the pulling rate is 1-100 μm/s.

The present invention also relates to a method for preparing a TiAl alloy by using a high melting point refractory metal casting mold prepared by the method described in the above claims.

Beneficial effects:

The molds used in the current method for preparing TiAl alloys will mostly cause non-metallic impurities to form in the castings, thereby adversely affecting the properties such as strength and plasticity. The TiAl alloy prepared by the present invention adopts a high melting point refractory metal casting mold, which overcomes the disadvantage of introducing non-metallic impurities in the current preparation of TiAl alloys, and the casting mold is suitable for various methods for preparing TiAl alloys, such as vacuum induction shell melting, vacuum non-consumable electrode arc melting, vacuum consumable electrode arc melting, electron beam melting, plasma beam melting, composite melting and other direct casting forming methods, and can also be applied to directional solidification, for preparing TiAl alloy columnar crystals or single crystals, and can also be used as a crucible, and applied to vacuum induction melting or vacuum resistance heating melting systems. The TiAl alloy cast using the casting mold does not contain non-metallic impurities, avoiding the influence of non-metallic impurities on the room temperature performance of the TiAl alloy. In addition, the casting mold can be used to alloy the alloy while casting the TiAl alloy, further improving the performance of the TiAl alloy. And the shape of the TiAl alloy prepared using the casting mold is not limited, and the shape of the casting mold only needs to be processed according to the requirements to form the TiAl alloy in one step. The performance of the TiAl alloy obtained by this method is not only not affected by non-metallic impurities, but can also be further improved, which has important commercial value.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a microstructure diagram of a Ti48Al alloy prepared by using a niobium high melting point refractory metal casting mold in the present invention;

FIG2 is a microstructure diagram of a Ti49Al3Ta alloy prepared by using an alloy of niobium and tantalum as a high melting point refractory metal casting mold in the present invention;

FIG3 is a microstructure diagram of a Ti50Al3Nb alloy single crystal prepared by using a tantalum high melting point refractory metal casting mold in the present invention;

FIG4 is a microstructure diagram of columnar crystals of Ti49Al alloy prepared by using a niobium high melting point refractory metal casting mold in the present invention;

FIG5 is a microstructure diagram of a Ti53Al alloy prepared in a tungsten high melting point refractory metal crucible according to the present invention;

FIG. 6 is a microstructure diagram of a Ti50Al4W alloy prepared by using an alloy of tungsten and tantalum as a high melting point refractory metal crucible in the present invention.

DETAILED DESCRIPTION

The present invention discloses a method for preparing a TiAl alloy by using a high-melting-point refractory metal casting mold. The high-melting-point refractory metal is used as a casting mold to prepare the TiAl alloy, or as a crucible to prepare the TiAl alloy, or as a crucible and a casting mold at the same time to prepare the TiAl alloy.

The TiAl alloy is prepared by using a high melting point refractory metal as a casting mold. The specific implementation method is as follows: niobium, tantalum, tungsten, or their alloys are selected to prepare a high melting point refractory metal casting mold in the desired shape. The high purity raw material of the TiAl alloy with the expected composition is placed in the smelting system, the smelting furnace is closed, the vacuum is sealed to 10 ^-1 -10 ^-4 Pa, induction heating or resistance heating is turned on, the smelting temperature is 1400-2200°C, and after complete melting, it is kept warm for 5-20 minutes and then cast into a high melting point refractory metal casting mold. The solidification time is 3-20 minutes. After the solidification is completed, the mold is removed and the edge part is cut off to obtain an alloy ingot.

The specific implementation method of using a high melting point refractory metal as a crucible to prepare a TiAl alloy is as follows: niobium, tantalum, tungsten, or an alloy thereof is selected to prepare a high melting point refractory metal crucible in the desired shape. The high purity raw material of the TiAl alloy of the expected composition is placed in a high melting point refractory metal crucible and placed in a smelting system, the smelting furnace is closed, the vacuum is sealed to 10 ^-1 -10 ^-4 Pa, induction heating or resistance heating is turned on, the smelting temperature is 1400-2200°C, the material is fully melted and evenly fused, and the alloy is turned over after cooling, and the smelting is repeated 3-6 times to ensure that the material is evenly fused, and the alloy is taken out after cooling.

The high melting point refractory metal is used as a crucible and a casting mold to prepare TiAl alloy, and the specific implementation method is as follows:

Step 1: Select the expected TiAl alloy single crystal composition and size. According to the multi-element alloy phase diagram and the diffusion rate of the casting elements in the TiAl alloy melt, select the appropriate alloy composition, casting composition and size for processing, load the TiAl alloy raw material or ingot into the casting mold, and put it into the directional solidification system, evacuate to 10 ^-1 -10 ^-4 Pa, and then fill the system with 0.03-0.05MPa high-purity argon protective gas.

Step 2: Turn on the heating system, use a high melting point refractory metal as a crucible, heat and keep the sample warm by induction heating or resistance heating to melt the alloy in the crucible, the holding temperature is 1200-2000°C, the holding time is 5-120min, and the heating rate is 5-15°C/min.

Step 3: After the heat preservation is completed, a high melting point refractory metal is used as a casting mold to directionally solidify the TiAl alloy at a pulling rate of 1-100 μm/s.

Step 4: heat-treat the obtained sample at a temperature of 880-1390°C for 0.5-100h, and use furnace cooling to cool the sample.

Example 1

Niobium is selected as a high melting point refractory metal casting mold, and the high melting point refractory metal casting mold is processed according to the required shape and size. The alloy composition used in the experiment is Ti48Al, and the purity of its metal components is 99.999%. The raw materials are placed in a vacuum induction shell melting system, the melting furnace is closed, the vacuum is sealed to ^10-1 Pa, the resistance heating is turned on, the temperature is raised to 1400℃, and the temperature is kept for 5 minutes to ensure that the metal is completely melted. The molten metal is cast into the casting mold, solidified for 3 minutes, demolded and taken out, the edges are cut off, and the alloy ingot is obtained. Its organization diagram is shown in Figure 1.

Example 2

An alloy of niobium and tantalum is selected as a high melting point refractory metal mold, and the high melting point refractory metal mold is processed according to the required shape and size. The alloy composition used in the experiment is Ti49Al3Ta, and the purity of its metal components is 99.999%. The raw materials are placed in a vacuum electron beam melting system, the melting furnace is closed, the vacuum is sealed to 10 ^-4 Pa, the induction heating is turned on, the temperature is raised to 1800℃, and the temperature is kept for 20 minutes to ensure that the metal is completely melted. The molten metal is cast into the mold, solidified for 30 minutes, demolded and taken out, the edges are cut off, and the alloy ingot is obtained. Its organization diagram is shown in Figure 2.

Example 3

The alloy composition used in the experiment is Ti50Al3Nb, and the purity of its metal components is 99.999%. Under the protection of high-purity Ar gas, it is melted in a vacuum induction suspension furnace and cast into a steel mold. The alloy of Ф15mm is cut, polished, cleaned and dried for use. A tantalum high melting point refractory metal mold with an inner diameter of 15mm, a length of 240mm and a wall thickness of 20mm is selected, and a seed crystal with a composition of Ti50Al3Nb is selected. Its sheet direction is the same as the growth direction. It is placed in the metal mold together with the TiAl alloy ingot. The seed crystal is located between the pull rod and the alloy ingot, and is placed in the metal crystal growth system. The vacuum degree is ^10-1 Pa and filled with high-purity argon protective gas. Adjust the induction heating power supply, heat up to 1200℃, and keep warm for 5min, start directional solidification, and control the directional solidification growth rate to 1μm/s. It is heat treated at a heat treatment temperature of 880℃, keep warm for 0.5h, and then cool with the furnace. The longitudinal section of the cylindrical sample was analyzed, and it was found that the lamellar direction of the TiAl alloy single crystal was consistent with the growth direction, and its organization diagram is shown in FIG3 .

Example 4

The alloy composition used in the experiment is Ti49Al, and the metal components are prepared with a purity of 99.999% and a total mass of 1200g. A blade-shaped niobium high-melting-point refractory metal mold is selected, and its wall thickness is 20mm. The metal material is placed in the mold and placed in the metal crystal growth system, the vacuum degree is evacuated to ^10-4 Pa, and high-purity argon protective gas is filled. Adjust the resistance heating power supply, heat the sample, raise the temperature to 2000℃, and keep it warm for 120min, start directional solidification, and control the directional solidification growth rate to 100μm/s. After the pulling is completed, a blade-shaped sample is obtained. It is heat treated at a heat treatment temperature of 1390℃, kept warm for 100h, and then cooled with the furnace. The longitudinal section of the sample is analyzed, and it is found that a well-arranged columnar crystal structure is obtained, and its organization diagram is shown in Figure 4.

Example 5

Tungsten was selected as a high melting point refractory metal crucible. The alloy used in the experiment was Ti53Al, and the purity of its metal components was 99.999%. The raw materials and the crucible were placed in a vacuum consumable electrode arc melting system, the melting furnace was closed, the vacuum was sealed to 10 ^-1 Pa, and the resistance heating was turned on. The melting temperature was 1500°C, so that the material was fully melted and fused evenly. At the same time, magnetic stirring could be turned on. After melting and cooling, the reverse side was carried out, and the melting was repeated 3 times to ensure that the material was evenly fused. After the alloy was completely cooled, the alloy was taken out. Its organization diagram is shown in Figure 5.

Example 6

An alloy of tungsten and tantalum is selected as a high melting point refractory metal crucible. The alloy composition used in the experiment is Ti50Al4W, and the purity of its metal components is 99.999%. The raw materials and the crucible are placed in a vacuum electron beam melting system, the melting furnace is closed, the vacuum is sealed to 10 ^-4 Pa, and the induction heating is turned on. The melting temperature is 1800℃, so that the material is fully melted and fused evenly. At the same time, magnetic stirring can be turned on. After melting and cooling, the reverse side is carried out. The melting is repeated 6 times to ensure that the material is evenly fused. After the alloy is completely cooled, the alloy is taken out. Its organization diagram is shown in Figure 6.

The above contents are only preferred embodiments of the present invention and are not intended to limit the implementation scheme of the present invention. A person skilled in the art can easily make corresponding changes or modifications based on the main concept and spirit of the present invention. Therefore, the protection scope of the present invention shall be based on the protection scope required by the claims.

Claims (10)

1. A method for preparing a TiAl alloy using a high-melting-point refractory metal mold, characterized in that the high-melting-point refractory metal is used as a mold to prepare the TiAl alloy, or as a crucible to prepare the TiAl alloy, or as a crucible and a mold at the same time to prepare the TiAl alloy. 2. The method for preparing a TiAl alloy using a high melting point refractory metal mold according to claim 1, wherein the high melting point refractory metal is used as a mold to prepare the TiAl alloy, and the method comprises the following steps: Step 1: Put the TiAl alloy raw materials with expected composition into the smelting system in proportion; Step 2: melting the TiAl alloy at a temperature of 1400-2200° C. under a vacuum state of 10 ^-1 -10 ^-4 Pa; Step 3: After the mixture is completely melted, keep it warm for 5-20 minutes, and then cast it into a high melting point refractory metal mold; Step 4: Solidify for 3-30 minutes. After solidification, demould and remove from the mold, cut off the edges, and obtain the alloy ingot. 3. The method of preparing TiAl alloy using high melting point refractory metal as casting mold according to claim 2 is characterized in that the smelting system in step 1 includes but is not limited to vacuum induction melting, vacuum resistance heating melting, vacuum induction shell melting, vacuum non-consumable electrode arc melting, vacuum consumable electrode arc melting, electron beam melting, plasma beam melting and composite melting. 4. The method of preparing a TiAl alloy using a high melting point refractory metal as a casting mold according to claim 2, wherein the high melting point refractory metal casting mold in step 3 is prepared using a high melting point refractory metal including but not limited to niobium, tantalum, tungsten, or an alloy thereof, and the casting mold can be processed according to a desired shape and size. 5. The method for preparing a TiAl alloy using a high melting point refractory metal casting mold according to claim 1, wherein the high melting point refractory metal is used as a crucible to prepare the TiAl alloy, and the method comprises the following steps: Step 1: Put the TiAl alloy raw material with the expected composition into a high melting point refractory metal crucible according to proportion, and put it into a smelting system; Step 2: Smelting the TiAl alloy at a temperature of 1400-2200° C. under a vacuum state of 10 ^-1 -10 ^-4 Pa to completely melt the alloy; Step 3: After the melted alloy solidifies and cools, turn the alloy over and repeat the smelting 3-6 times; Step 4: Take out the alloy after smelting. 6. The method of preparing TiAl alloy by using high melting point refractory metal as crucible according to claim 5, characterized in that in step 1, the high melting point refractory metal casting mold is prepared by using high melting point refractory metal including but not limited to niobium, tantalum, tungsten, or their alloys, and the crucible can be processed according to the required shape and size. 7. The method of preparing TiAl alloy by using high melting point refractory metal as crucible according to claim 5, characterized in that the smelting system in step 1 includes but is not limited to vacuum induction melting, vacuum resistance heating melting, vacuum induction shell melting, vacuum non-consumable electrode arc melting, vacuum consumable electrode arc melting, electron beam melting, plasma beam melting and composite melting. 8. The method for preparing a TiAl alloy using a high melting point refractory metal casting mold according to claim 1, wherein the high melting point refractory metal is used as both a crucible and a casting mold to prepare the TiAl alloy, and the method comprises the following steps: Step 1: Process the high melting point refractory metal mold according to the required shape and size, load the TiAl alloy raw material or ingot into the mold, and place it in a directional solidification system, evacuate to 10 ^-1 -10 ^-4 Pa, and then fill the system with high-purity argon protective gas; Step 2: Use an induction heating or resistance heating system to melt the alloy in the crucible; Step 3: After the TiAl alloy is completely melted and kept warm for a certain period of time, the high melting point refractory metal is used as a metal mold to directionally solidify the TiAl alloy in a directional solidification system; Step 4: heat treat the prepared sample at a temperature of 880-1390°C for a holding time of 0.5-100h, followed by furnace cooling. 9. The method of preparing TiAl alloy by using high melting point refractory metal as both crucible and casting mold according to claim 8, characterized in that in step 1, the high melting point refractory metal casting mold is prepared by using high melting point refractory metal including but not limited to niobium, tantalum, tungsten, or alloys thereof, and its shape can be processed according to the required shape and size, and the cross-sectional shape is a circular ring, a square ring or a complex shape, and its wall thickness is 1-20 mm. In step 3, the directional solidification holding temperature is 1200-2000° C., the holding time is 5-120 min, and the pulling rate is 1-100 μm/s. 10. A method for preparing a TiAl alloy using a high melting point refractory metal casting mold prepared by the method according to any one of claims 1 to 9.