CN114457272A - A kind of high entropy alloy and its laser cladding repair method of tungsten-based powder alloy die-casting mold - Google Patents

Abstract

The invention discloses a high-entropy alloy and a method for repairing a tungsten-based powder alloy die-casting die by laser cladding thereof, and aims to apply a high-energy-density laser beam to heat and melt high-entropy alloy powder to form a wear-resistant and high-temperature-resistant high-entropy alloy repairing coating on the worn surface of the tungsten-based powder alloy die-casting die, so that the size and the function of the die are recovered and reused, and the performance of the surface of the die is improved. The high-entropy alloy consists of Co, Cr, Fe, Ni and W, or Mo or Nb is adopted to replace W. The core technology of the invention is that the high-entropy alloy components and the related process and method are used for regulating and controlling the microstructure and the structure of the high-entropy alloy components. The repairing layer prepared by the process and the method has higher wear resistance and thermal conductivity, and the thermal diffusivity value is increased along with the increase of the temperature.

Description

High-entropy alloy and method for repairing tungsten-based powder alloy die-casting mold by laser cladding

technical field

The invention relates to a high-entropy alloy and a method for repairing a tungsten-based powder alloy die-casting mold by laser cladding. A high-energy-density laser beam is used to heat and melt the high-entropy alloy powder, and the high-entropy alloy powder is rapidly solidified and metallurgically combined with a matrix to form a repair layer on the surface. The locally damaged surface of the base powder alloy die-casting mold is repaired, so that the size and function of the mold can be restored and reused, and the performance of the mold can be improved, which belongs to the field of material science and engineering.

Background technique

In 2004, researchers such as Ye Junwei and Cantor B took the lead in breaking through the traditional research framework and proposed a new alloy design concept, that is, multi-principal element high-entropy alloys. It is composed of five or more elements in an atomic ratio of 1:1 or approximately 1:1, with each element having a composition between 5% and 35%. This alloy is not prone to form brittle intermetallic compounds, but instead forms body-centered cubic, face-centered cubic, nanostructures, and even amorphous structures with simple crystal structures. High-entropy alloys have high-entropy effect in thermodynamics, lattice distortion effect in structure, hysteresis diffusion effect in kinetics, and cocktail effect in performance. Therefore, high-entropy alloys have high hardness, excellent wear resistance and good corrosion resistance. properties, high temperature oxidation resistance, thermal stability and other advantages. The preparation techniques of high-entropy alloy coatings include thermal spraying, sputtering and laser cladding. There are many restrictions; the thickness of the laser cladding high-entropy alloy coating can reach the millimeter level, which greatly exerts the advantages of the mechanical properties of the high-entropy alloy. The application of high-entropy alloys, especially as surface coatings, has always been the focus of engineers and technicians.

Tungsten-based powder alloy is a composite material composed of tungsten as the hard phase and nickel, copper or nickel and iron as the binder phase. It has high thermal conductivity, high strength, high density, low thermal expansion coefficient and excellent corrosion resistance. , oxidation resistance and impact toughness and other properties, it is one of the best materials for manufacturing high-precision molds and die-casting molds. Tungsten-based powder alloys are used to produce non-ferrous metal die-casting molds. Due to their ultra-high thermal conductivity and low thermal expansion coefficient, they can refine non-ferrous metal structures and improve the performance and dimensional accuracy of non-ferrous metal die-casting parts. During the die-casting production of tungsten-based powder alloy die-casting molds, the molten non-ferrous metal liquid enters the mold cavity at high pressure, high temperature and high speed, causing severe impact and erosion on the surface of the cavity, resulting in tungsten-based powder alloy die-casting molds. Corrosion, wear and cracks occur on the surface of the cavity; during the filling process, molten metal, impurities and slag also have complex chemical effects on the surface of the mold cavity, accelerating the corrosion, wear and cracks on the surface of the mold cavity; in addition, The friction between the mold and the casting during the mold opening and demolding process also aggravates the wear of the mold surface cavity. Relevant literatures at home and abroad believe that thermal wear is one of the main reasons for the failure of tungsten-based powder alloy die-casting molds. Excessive wear on the cavity surface of tungsten-based powder alloy die-casting molds will lead to excessive size and unqualified surface quality of liquid non-ferrous metal pressed parts. The high price of tungsten-based powder alloy materials leads to high manufacturing costs of tungsten-based powder alloy die-casting molds; at the same time, mold processing and manufacturing are difficult, and mold repair and maintenance costs after production are also high. Therefore, timely repair of molds to prevent further damage to the mold, It can greatly reduce the mold cost of die casting production. The reasonable solution is to repair the locally damaged cavity surface of the mold through surface engineering technology, so that the size and function of the mold can be restored and reused and the performance of the mold surface can be improved. Currently, commonly used surface engineering techniques for engineering materials include physical vapor deposition (PVD), chemical vapor deposition (CVD), spark deposition, surfacing, cold welding, thermal spraying, and a variety of additive manufacturing technologies developed in recent years. The materials used for the repair layer are mostly alloys or ceramic materials. Alloy materials include self-fluxing alloy powders such as nickel-based, cobalt-based and iron-based alloy powders and the like. Ceramic materials include carbides, oxides, and silicide powders, among others. At present, when repairing the worn parts of the tungsten-based powder alloy die-casting mold cavity working surface, the main problem is that the chemical composition and properties of the repair layer and the base material are quite different, and the compatibility and bonding between the materials are poor. During the production process of the repaired tungsten-based powder alloy die-casting mold, the surface repair layer of the cavity is continuously eroded by the high pressure, high temperature and high speed of the molten metal. The heat first reaches a higher temperature and expands. After the mold is opened, the repair layer on the surface of the cavity is contacted with air and quenched and shrinks to generate tensile stress. This alternating stress circulates repeatedly and is easily generated at the interface between the repair layer and the base material. Cracks, with increasing production times, eventually lead to cracking and spalling of the repaired layer. The surface repair layer of the tungsten-based powder alloy die-casting mold cavity is both a working surface and a functional surface. Therefore, the material used for the repair layer must have similar thermal conductivity, low thermal expansion coefficient, and excellent corrosion resistance and oxidation resistance to tungsten-based powder alloy materials. performance and impact toughness. Therefore, how to improve the wear resistance and fatigue resistance of the repair layer of the tungsten-based powder alloy die-casting mold and its bonding strength with the matrix, prolong the service life of the mold, improve the utilization rate of the mold, and at the same time ensure the high thermal conductivity of the surface, Low expansion performance is an inescapable responsibility and a long-term and arduous task for scientific researchers.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a high-entropy alloy and a method for repairing a tungsten-based powder alloy die-casting mold by laser cladding. The entropy alloy powder is rapidly solidified to form a metallurgical bond with the matrix, and a wear-resistant and high-temperature-resistant high-entropy alloy repair coating is formed on the surface of the tungsten-based powder alloy die-casting mold cavity wear and failure to restore the size and function of the mold.

The core technology of a high-entropy alloy and a method for repairing a tungsten-based powder alloy die-casting mold by laser cladding described in the present invention is: high-entropy alloy composition and related processes and methods to control its microstructure and structure.

The chemical formula of the high-entropy alloy described in the present invention is CoCrFeNiW _x , 0.5≤x≤1, and is composed of Co, Cr, Fe, Ni and W, wherein Co, Cr, Fe and Ni have the same mole fraction, and the mole ratio is fixed as 1 : 1:1:1, the value of W is 0.5≤x≤1; the composition is calculated in atomic percentage (at%): cobalt (Co) 20%-22.2%, chromium (Cr) 20%-22.2%, iron ( Fe) 20%-22.2%, nickel (Ni) 20%-22.2%, tungsten (W) 11.1%-20%.

Further, the elements in the high-entropy alloy described in the present invention may be replaced by Mo or Nb, and the chemical formula of the high-entropy alloy is CoCrFeNiMo or CoCrFeNiNb. The molar ratio of each element in its composition is fixed at 1:1:1:1:1, in atomic percentage (at%): cobalt (Co) 20%, chromium (Cr) 20%, iron (Fe) 20%, Nickel (Ni) 20%, Molybdenum (Mo) 20%; or Cobalt (Co) 20%, Chromium (Cr) 20%, Iron (Fe) 20%, Nickel (Ni) 20%, Niobium (Nb) 20%. The high-entropy alloy related process of the present invention consists of two parts, one part is the preparation process of the high-entropy alloy powder; the other part is the laser cladding process of the wear-resistant high-entropy alloy repair coating.

Further, a high-entropy alloy and its laser cladding repairing process and method for a tungsten-based powder alloy die-casting mold described in the present invention are to prepare a high-entropy alloy repair coating with wear-resistance and high-temperature resistance by means of laser cladding, Include the following steps:

The first step is to prepare high-entropy alloy powder. The purity of the metals Co, Cr, Fe, Ni, W, Mo and Nb used in the high-entropy alloy are all greater than 99.9%, and the particle size of the metal powder is 20-50 μm; according to the designed composition, an electronic balance with an accuracy of 0.0001g is used to massage The metal powders of Co, Cr, Fe, Ni and W (Mo or Nb) were accurately weighed and put into the ball mill jar, and three kinds of zirconia balls with diameters of 10mm, 5mm and 3mm were used. The weight ratio is 5:3:5; the powder is mixed uniformly and vacuum ball milled, the ball-to-material ratio is 15:1, the ball milling speed is 350r/min, and the ball milling is more than 20h to obtain high-entropy alloy powder;

The second step is to mechanically treat the worn parts of the working surface of the tungsten-based powder alloy die-casting mold cavity to remove the fatigue layer and residual stress layer, and to remove surface oxides and various dirt;

In the third step, the high-entropy alloy powder prepared in the first step is uniformly coated on the surface of the pretreated substrate to form a pre-layer with a thickness of 0.8-1.2mm, and the high-entropy alloy powder is heated by a fiber continuous laser. A high-entropy alloy cladding layer is obtained on the surface of the cavity of the alloy die-casting mold. The high-energy density fiber continuous laser, the process parameters of the laser cladding obtained by optimization are: laser power 1600W, scanning speed 4mm/s, spot diameter 3.5mm, separation distance The coke amount is 30mm, the protective gas is argon, and the gas flow is 15L/min.

The novelty of high-entropy alloys is that they consist of a mixture of elements in equal or approximately equal proportions. There are 37 main elements of high-entropy alloys, of which Co, Cr, Fe, and Ni are used in high-entropy alloys in a proportion of more than 70%, which can form more than 480 high-entropy alloy systems. Refractory elements such as Mo, Nb, V, and Zr are also common elements in high-entropy alloys. There are many kinds of high-entropy alloys, and the high-entropy effect is the main factor regulating their microstructure and structure. The amount of alloying elements and processing conditions have a significant effect on its microstructure. The structural differences of high-entropy alloys present different structural properties and functional characteristics. A high-entropy alloy and its laser cladding repairing process and method for a tungsten-based powder alloy die-casting mold according to the present invention, firstly adopt a mechanical alloying method and a high-energy planetary ball mill to prepare the required high-entropy alloy powder, and then A high-energy-density laser beam is used to form a high-entropy alloy coating on the worn surface of a tungsten-based powder alloy die-casting die. The elements of tungsten, iron and nickel in the high-entropy alloy coating are the same as those of the base material, and cobalt, chromium, molybdenum and niobium elements also have good compatibility with the tungsten-based powder alloy, which ensures that the formed high-entropy alloy coating and the base material Elemental diffusion and good metallurgical bonding between them. The chromium element in the high-entropy alloy coating ensures the good oxidation resistance and corrosion resistance of the coating, and the nickel, cobalt, molybdenum and niobium elements ensure the good high-temperature performance of the high-entropy alloy coating; the thermal conductivity of tungsten and molybdenum is extremely high. The addition of tungsten or molybdenum to the strong, high-entropy alloy coating can greatly increase the thermal conductivity of the coating, thereby improving the performance of die-casting to produce non-ferrous metal castings. The high-entropy alloy coating of the present invention has good thermal stability, wear resistance, red hardness, thermal conductivity, oxidation resistance and corrosion resistance, and is similar to the linear expansion coefficient of tungsten-based powder alloy. The compatibility and bonding between the materials are good. Laser cladding the wear-resistant, high-temperature, high-entropy alloy coating on the surface of the tungsten-based powder alloy can improve the wear resistance and high-temperature performance of the tungsten-based powder alloy die-casting mold. Characterized by scanning electron microscopy, the microstructure of the wear-resistant high-entropy alloy coating exhibits a typical dendritic structure. It can be seen from the phase identification of the X-ray diffraction pattern of the coating that the high-entropy alloy coating is mainly composed of a body-centered cubic solid solution (similar to W in a body-centered cubic structure) and a small amount of Fe-Ni face-centered cubic solid solution, with a typical high Entropy alloy phase structure. Due to the high-entropy effect and rapid laser solidification, the high-entropy alloy coating has high thermal stability and is suitable for working conditions in the process of die-casting non-ferrous metals.

Compared with the prior art, the beneficial effects of the present invention are:

A high-entropy alloy and its laser cladding repair process and method for a tungsten-based powder alloy die-casting mold described in the present invention utilize a high-energy-density laser beam to repair the wear-resistant, high-temperature-resistant high-entropy alloy formed on the wear surface of the tungsten-based powder alloy The coating has a similar linear expansion coefficient with that of tungsten-based powder alloys, and the compatibility and bonding between the two are good; at the same time, it has high thermal conductivity, and the thermal diffusivity value increases with the increase of temperature.

Description of drawings

Fig. 1 is a scanning electron microscope (SEM) photograph of the bonding interface of the laser cladding high-entropy alloy coating on the surface of the tungsten-based powder alloy;

Fig. 2 is the scanning electron microscope (SEM) of the laser cladding high-entropy alloy coating on the surface of the tungsten-based powder alloy;

Figure 3 is the X-ray diffraction pattern (XRD) of the laser cladding high-entropy alloy coating on the surface of the tungsten-based powder alloy.

Detailed ways

The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are a part of the embodiments of the present invention, but not all of the embodiments. The examples listed below are only for further understanding and implementation of the technical solutions of the present invention, and do not constitute further limitations on the claims of the present invention, therefore. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

The method of the present invention is further explained in detail by the examples given below.

The high-entropy alloy and its laser cladding repairing process and method for a tungsten-based powder alloy die-casting mold according to the present invention are the application of high-energy-density laser beam heating to the wear failure of the working surface of the tungsten-based powder alloy die-casting mold cavity. The high-entropy alloy powder is melted and rapidly solidified to form a metallurgical bond with the matrix, and a wear-resistant and high-temperature-resistant high-entropy alloy repair coating is formed on the worn surface of the tungsten-based powder alloy die-casting mold, so that the mold can recover its size and function. The chemical formula of the wear-resistant and high-temperature-resistant high-entropy alloy coating is CoCrFeNiW _x , 0.5≤x≤1, composed of Co, Cr, Fe, Ni and W, wherein Co, Cr, Fe and Ni have the same mole fraction, and the value of W The value is 0.5≤x≤1. The element in the high-entropy alloy described in the present invention may take Mo or Nb to replace W.

A high-entropy alloy and its laser cladding repairing process and method for a tungsten-based powder alloy die-casting mold described in the present invention are to prepare a high-entropy alloy repair coating with wear resistance and high temperature resistance by means of laser cladding, including the following steps :

The first step is to prepare high-entropy alloy powder. The purity of the metals Co, Cr, Fe, Ni, W, Mo and Nb used in the high-entropy alloy are all greater than 99.9%, and the particle size of the metal powder is 20-50 μm; according to the designed composition, an electronic balance with an accuracy of 0.0001g is used to massage The metal powders of Co, Cr, Fe, Ni and W (Mo or Nb) were accurately weighed and put into the ball mill jar, and three kinds of zirconia balls with diameters of 10mm, 5mm and 3mm were used. The weight ratio is 5:3:5; the powder is mixed uniformly and vacuum ball milled, the ball-to-material ratio is 15:1, the ball milling speed is 350r/min, and the ball milling is more than 20h to obtain high-entropy alloy powder;

The second step is to mechanically treat the worn parts of the working surface of the tungsten-based powder alloy die-casting mold cavity to remove the fatigue layer and residual stress layer, and to remove surface oxides and various dirt;

In the third step, the high-entropy alloy powder prepared in the first step is uniformly coated on the surface of the pretreated substrate to form a pre-layer with a thickness of 0.8-1.2mm, and the high-entropy alloy powder is heated by a fiber continuous laser. A high-entropy alloy cladding layer is obtained on the surface of the cavity of the alloy die-casting mold. The high-energy density fiber continuous laser, the process parameters of the laser cladding obtained by optimization are: laser power 1600W, scanning speed 4mm/s, spot diameter 3.5mm, separation distance The coke amount is 30mm, the protective gas is argon, and the gas flow is 15L/min.

A high-entropy alloy and its laser cladding process and method for repairing a tungsten-based powder alloy die-casting mold according to the present invention, all the following examples are obtained by using the above-mentioned high-entropy alloy coating composition, process steps and parameters. The composition of the tungsten-based powder alloy of the present invention is calculated by mass percentage (Wt%): W: 97, N: 2.1, Fe: 0.9.

Examples are shown in Table 1 below.

A high-entropy alloy and its laser cladding repairing process and method for a tungsten-based powder alloy die-casting mold according to the present invention, the technical indicators achieved by repairing a tungsten-based powder alloy die-casting mold according to the above-mentioned process steps and components:

(1) The hardness of the high-entropy alloy coating formed after repair is 1.3-1.9 times that of the tungsten-based powder alloy matrix;

(2) The hardness of the high-entropy alloy coating formed after the repair is 1.2-1.8 times that of the tungsten-based powder alloy matrix after being kept at 800 °C for 12 hours;

(3) The relative wear resistance of the high-entropy alloy coating formed after repair is 1.4-1.8 times that of the tungsten-based powder alloy matrix.

Table 1 Coating alloy composition and its performance index

Although embodiments of the present invention have been disclosed above, they are not limited to the applications set forth in the specification and embodiments. It can be fully adapted to various fields suitable for the present invention. Additional modifications can readily be implemented by those skilled in the art. Therefore, the invention is not to be limited to the specific details and illustrations herein shown and described, without departing from the general concept defined by the appended claims and the scope of equivalents.

Claims (3)

1. A high-entropy alloy and a method for repairing a tungsten-based powder alloy die-casting die by laser cladding thereof are characterized in that: the chemical formula of the high-entropy alloy is CoCrFeNiW_xX is more than or equal to 0.5 and less than or equal to 1, and consists of Co, Cr, Fe, Ni and W, wherein the Co, Cr, Fe and Ni have the same mole fraction, and the mole ratio is fixed as 1: 1: 1: 1, the value of W is more than or equal to 0.5 and less than or equal to 1; the components are at% in atomic percentage: 20 to 22.2 percent of cobalt, 20 to 22.2 percent of chromium, 20 to 22.2 percent of ferrum, 20 to 22.2 percent of nickel and 11.1 to 20 percent of tungsten.

2. The high-entropy alloy and the method for repairing the tungsten-based powder alloy die-casting die by laser cladding thereof according to claim 1, wherein the method comprises the following steps: the elements in the high-entropy alloy are Mo or Nb to replace W, and the chemical formula of the high-entropy alloy is CoCrFeNiMo or CoCrFeNiNb; the mol ratio of each element in the components is fixed as 1: 1: 1: 1: 1, at% in atomic percentage: 20% of cobalt, 20% of chromium, 20% of iron, 20% of nickel and 20% of molybdenum; or 20% of cobalt, 20% of chromium, 20% of iron, 20% of nickel (Ni) and 20% of niobium.

3. The high-entropy alloy and the method for repairing the tungsten-based powder alloy die-casting die by laser cladding thereof as claimed in claim 1 or 2, wherein the high-entropy alloy powder is prepared by adopting a mechanical alloying method, and the wear-resistant high-temperature-resistant high-entropy alloy coating is prepared by adopting a laser cladding method, and the method comprises the following specific steps:

firstly, preparing high-entropy alloy powder, wherein the purity of Co, Cr, Fe, Ni, W, Mo and Nb adopted by the high-entropy alloy is more than 99.9%, and the particle size of the metal powder is 20-50 mu m; accurately weighing Co, Cr, Fe, Ni and W or Mo or Nb metal powder according to the designed components by adopting an electronic balance with the precision of 0.0001g according to the molar ratio, putting the Co, Cr, Fe, Ni and W or Mo or Nb metal powder into a ball milling tank, and adopting three zirconia ball milling beads with the diameters of 10mm, 5mm and 3mm respectively, wherein the weight ratio of the three zirconia ball milling beads is 5: 3: 5; uniformly mixing the powder, and carrying out vacuum ball milling, wherein the ball-material ratio is 15: 1, ball milling at the rotating speed of 350r/min for more than 20 hours to obtain high-entropy alloy powder;

secondly, mechanically treating the worn part of the working surface of the die cavity of the tungsten-based powder alloy die-casting die, removing a fatigue layer and a residual stress layer, and removing surface oxides and various dirt;

and step three, uniformly coating the high-entropy alloy powder prepared in the step one on the surface of a pretreated matrix to form a preset layer with the thickness of 0.8-1.2mm, heating the high-entropy alloy powder by adopting an optical fiber continuous laser, and obtaining a high-entropy alloy cladding layer on the surface of a tungsten-based powder alloy die-casting die cavity, wherein the optical fiber continuous laser with high energy density is optimized to obtain the laser cladding process parameters as follows: the laser power is 1600W, the scanning speed is 4mm/s, the diameter of a light spot is 3.5mm, the defocusing amount is 30mm, the protective gas is argon, and the gas flow is 15L/min.

Images