CN105543749A - High-entropy alloy gradient stress modification technology - Google Patents

Abstract

The invention relates to a gradient stress plastic modification method specially aimed at damage control and fine structure regulation of high-entropy alloy material characteristics. The purpose of the invention is to solve the problem that the as-cast structure of the high-entropy alloy is dominated by coarse dendrites and its comprehensive mechanical properties are poor. The preparation method mainly includes: preparing high-entropy alloy ingots, homogenizing heat treatment, simulation, sheath forging, and obtaining high-entropy alloy ingots. When processing the high-entropy alloy ingot, the present invention mainly adopts a preset variable-section sheath to effectively control the internal stress state of the high-entropy alloy material during the process, and form a gradient three-dimensional compressive stress combined with deformation characteristics. Finally, the invention can effectively inhibit the initiation and expansion of microcracks induced by lattice distortion, refine crystal grains, improve comprehensive mechanical properties, and realize effective modification of high-entropy alloys.

Description

High Entropy Alloy Gradient Stress Modification Technology

technical field

The invention relates to a plastic modification method specially aimed at damage control and fine structure regulation of high-entropy alloy material characteristics.

Background technique

With the development of modern industry, people put forward higher and higher requirements for materials in terms of temperature, strength, hardness and wear resistance. Although people continue to try to develop new processing technologies and design new material components to compensate Insufficient performance of materials, but the inherent defects of this traditional alloy design have seriously restricted the development of the industry. It is against this background that people have broken the traditional alloy design concept and adopted the concept of multi-principal alloy to design a new type of alloy system, high-entropy alloy.

High-entropy alloys are different from traditional alloys based on one or two elements as the main elements, and the traditional material design concept of improving the microstructure and properties of the alloy by adding a small amount of other elements. In high-entropy alloys, each principal element has a high, but The mole fraction does not exceed 35%, forming a multi-element collective effect, showing excellent comprehensive mechanical properties, among which the quasi-static yield strength of AlCoCrFeNiTi _0.5 can reach 2.26GPa, the fracture strength is 3.0GPa, and the compressive plasticity is 23%, which is much higher than the current conventional Material.

However, the as-cast structure of high-entropy alloys is dominated by coarse dendrites, which seriously affects their comprehensive mechanical properties. Especially under dynamic impact conditions, fractures are easily induced, and there are huge engineering hidden dangers.

Plastic processing can effectively break coarse dendrites, refine grains, and improve the microstructure and mechanical properties of materials. However, in order to improve the mechanical properties of high-strength high-entropy alloys, it is often necessary to add more elements with large atomic radius, resulting in severe crystal distortion and cracking during plastic processing.

In view of this, the present invention proposes a targeted gradient stress plastic modification technology. According to the composition of high-entropy alloy materials and the characteristics of the geometric structure of the ingot, the design and processing of the ingot whose cross-sectional geometric size adapts to the ingot changes according to a certain rule Billet sheathing, by applying a variable-section sheath to the high-entropy alloy ingot, effectively controls the internal stress distribution of the ingot during plastic processing, forms a gradient three-dimensional compressive stress specific to the characteristics of the deformation process, and effectively inhibits the microscopic deformation of the high-entropy alloy during deformation. The initiation and propagation of cracks complete the fine and effective control of the microstructure of high-entropy alloys, realize efficient plastic modification, and effectively improve the serviceability of high-entropy alloys.

Contents of the invention

The purpose of the present invention is to provide a gradient stress plastic modification method for high-entropy alloy service requirements. According to the thermal processing characteristics of high-entropy alloys, the preset variable-section sheath is used to effectively control the stress state inside the high-entropy alloy material during the deformation process, forming a gradient three-dimensional compressive stress combined with the deformation characteristics, and effectively suppressing the microscopic deformation induced by lattice distortion. The initiation and propagation of cracks, the refinement of grains, the improvement of comprehensive mechanical properties, and the effective modification of high-entropy alloys.

The method and the post-treatment process are easy to operate, low in cost, and can obtain high-entropy alloy ingot materials with uniform and excellent microstructure properties, effectively improving its serviceability. The method can not only promote the mass use of high-entropy alloys, but also effectively Improve and control the mechanical properties of high-entropy alloys.

In order to solve the above-mentioned technical problems, the gradient stress modification method of the high-entropy alloy of the present invention is realized by the following technical solutions.

The first step: the production of the original blank of the high-entropy alloy. The high-entropy alloy bar is cut according to the size of the ingot, and then heated to an initial temperature of 1000°C-1100°C according to the composition of the high-entropy alloy, and then heat preservation is carried out according to the thickness of the bar 0.8-1min/mm. Keep warm for 12-100h, and cool down with the furnace to make its internal structure uniform.

The second step: the analysis and design of the envelope with variable cross-section. Combined with the composition and deformation characteristics of the selected high-entropy alloy, through calculation and simulation, the stress characteristics and laws of different parts of the ingot during the deformation process, especially the distribution of three-dimensional compressive stress and damage distribution, are obtained.

On this basis, combined with the material stress and damage characteristics, the sheath material is selected and the variable cross-section sheath structure is designed, the deformation of the high-entropy alloy under the condition of variable cross-section sheathing and the change of three-dimensional compressive stress and damage distribution are analyzed, and the variable cross-section is optimized. Envelope structure.

The third step: variable section wrapping processing. According to the design plan, the variable-section sheath is processed by a lathe or a machining center. In order to ensure the effective combination of the sheath and the high-entropy alloy ingot, it is necessary to ensure that the sheath has good processing accuracy. At the same time, in order to control the manufacturing cost, the material is conventional carbon Predominantly steel and stainless steel. The aspect ratio of the jacket is between 1:1 and 1.5:1.

The fourth step: high temperature gradient stress modification. Put the homogenized high-entropy alloy ingot into corresponding sheaths with different cross-sectional shapes at room temperature, and then place it in a heating furnace to raise the temperature and keep it warm. When the deformation temperature is reached, the high-entropy alloy with additional sheath is taken out for high-temperature plastic modification. The deformation temperature is about 1000°C-1100°C depending on the material, preferably 1100°C, and the strain rate is 0.01s ^-1 -0.1s ^-1 , preferably 0.05s ^-1 . First upsetting and then elongating, the amount of upsetting deformation should not be too large, and it needs to be returned to the furnace for heating after elongation, and at the same time ensure that the sheath and high-entropy alloy are closely combined during the deformation process to form an effective gradient three-dimensional compressive stress to suppress the deformation due to high The initiation and propagation of micro-cracks caused by severe lattice distortion of entropy alloys results in a high-entropy alloy ingot with finer grains, uniform structure, and excellent serviceability. According to the different high-entropy alloys, the material modified by the gradient stress of the variable cross-section sheath can be directly air-cooled or furnace-cooled.

Step five: Peel off. The variable cross-section sheath is stripped off by mechanical processing.

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

The as-cast structure of high-entropy alloys is dominated by coarse dendrites, which seriously affects its comprehensive mechanical properties. Especially under dynamic impact conditions, it is very easy to induce fracture, which has huge engineering hidden dangers and requires plastic processing modification. However, because high-strength high-entropy alloys often have severe crystal distortion, cracking is prone to occur during plastic processing. The compressive stress can be effectively increased by applying an external sheath, but due to the difference in ingot material and geometric size, the equal-section sheath cannot form an effective gradient compressive stress for the deformation process, and cannot effectively suppress cracking for high-entropy alloys with severe lattice distortion. Complete the crushing of coarse dendrites, refine the grains, improve the microstructure and mechanical properties of the material, and realize processing modification.

In view of this, the present invention proposes a targeted gradient stress plastic modification technology. According to the composition of high-entropy alloy materials and the characteristics of the geometric structure of the ingot, the design and processing of the ingot whose cross-sectional geometric size adapts to the ingot changes according to a certain rule Billet sheathing, by applying a variable-section sheath to the high-entropy alloy ingot, effectively controls the internal stress distribution of the ingot during plastic processing, forms a gradient three-dimensional compressive stress specific to the characteristics of the deformation process, and effectively inhibits the microscopic deformation of the high-entropy alloy during deformation. The initiation and propagation of cracks complete the fine and effective control of the microstructure of high-entropy alloys, realize efficient plastic modification, and effectively improve the serviceability of high-entropy alloys.

The invention uses the cast high-entropy alloy original billet, and obtains an ingot with fine grains, uniform structure and significantly improved comprehensive service ability through gradient stress modification, which can greatly reduce processing costs and improve material service ability. The variable cross-section covering material used in the present invention is easy to obtain, convenient and simple to process, and can be processed by ordinary lathes or processing centers, and the gradient stress modification process can be realized on processing equipment such as traditional hydraulic presses or forging hammers, which is simple, easy to implement, and easy to popularize application.

Description of drawings

Figure 1 is a flow chart of the process for preparing high-entropy alloy ingots.

detailed description

Taking AlCoCrFeNiTi as an example, this embodiment is a method for preparing an AlCoCrFeNiTi _0.5 high-entropy alloy ingot with uniform structure and significantly improved mechanical properties through high-temperature gradient stress modification technology. Specifically, it is completed according to the following steps:

(1) Prepare the high-entropy alloy AlCoCrFeNiTi _0.5 ingot: select the ingot of the high-entropy alloy whose composition is AlCoCrFeNiTi _0.5 , and the molar ratios of the six elements are Al:Co:Cr:Fe:Ni:Ti=1:1:1 :1:1:0.5.

(2) Homogenization heat treatment: perform homogenization heat treatment on the AlCoCrFeNiTi _0.5 high-entropy alloy ingot selected in step (1), the temperature of the homogenization heat treatment is 1000°C-1100°C, and then heat preservation according to the thickness of the ingot 0.8-1min/mm Treatment, the holding time of the homogenization heat treatment is 12h-100h, and then the ingot of the high-entropy alloy AlCoCrFeNiTi _0.5 is cooled with the furnace to obtain the ingot of the high-entropy alloy with uniform internal structure and composition.

(3) Deformation process simulation: Computer simulation of the deformation process is carried out by numerical simulation software to obtain the stress characteristics and laws of different parts of the ingot during the deformation process, especially the distribution law and damage distribution of the three-dimensional compressive stress.

(4) Envelope design: According to the simulation results in step (3), select the envelope material and design the envelope structure with variable cross-section. On this basis, optimize the cross-sectional structure and size of different positions of the envelope through simulation until it is formed The process has a relatively uniform three-dimensional compressive stress field.

(5) Sheathing processing: According to the structural size of the variable-section sheath obtained in step (4), the variable-section sheath is processed by a lathe and a machining center. The jacket material in this step is generally conventional carbon steel and stainless steel, and the aspect ratio of the jacket is between 1:1 and 1.5:1.

(6) High-temperature gradient stress modification: take out the high-entropy alloy AlCoCrFeNiTi _0.5 obtained by the homogenization heat treatment in step (2), and put it in the variable-section sheath processed in step (5), to obtain the high-entropy alloy AlCoCrFeNiTi _0.5 Ingots of pre-machined billets. The ingot is heated to 1050°C for upsetting modification. The strain rate is 0.05s ^-1 , upsetting first and then elongating. According to the different geometrical dimensions, it can be upset and one pull or two upsetting and two pulls per fire, and then reheated. After three fires, it was cooled to room temperature in air, and the sheath was peeled off by mechanical processing to obtain an AlCoCrFeNiTi _0.5 high-entropy alloy material with completely broken dendrites in the as-cast state, uniform structure and excellent mechanical properties.

The mold used in this step is a superalloy mold. In the modification process, it is necessary to ensure that the sheath and the high-entropy alloy are closely combined to form an effective gradient three-dimensional compressive stress. And the amount of upsetting deformation should not be too large, and it needs to be returned to the furnace for heating after drawing.

According to the different high-entropy alloys, the material modified by the gradient stress of the variable cross-section sheath can be directly air-cooled or furnace-cooled.

The advantage of this implementation mode:

(1) The high-entropy alloy component prepared by the high-temperature gradient stress modification method in this embodiment can effectively suppress the severe lattice stress of the high-entropy alloy due to the formation of an effective gradient three-dimensional compressive stress on the high-entropy alloy throughout the process. The initiation and expansion of micro-cracks caused by distortion results in a high-entropy alloy ingot with finer grains, uniform structure, and excellent serviceability.

(2) This embodiment can prepare larger-sized high-entropy alloy components, and the gradient stress modification process can be realized on processing equipment such as traditional hydraulic presses or forging hammers, which is simple and easy to popularize and apply.

Claims (2)

1. prepared a method for the high-performance high entropy alloy material of homogeneous microstructure by high-temperature gradient stress modification technology, specifically complete according to the following steps:

(1) for the requirement of Service Environment, the high-entropy alloy ingot casting required for preparation.

(2) homogenizing thermal treatment: the ingot casting of high-entropy alloy step (1) chosen carries out homogenizing thermal treatment, the heat treated temperature of homogenizing is 1000 DEG C-1100 DEG C, then isothermal holding is carried out according to ingot casting thickness 0.8-1min/mm, the heat treated soaking time of homogenizing is mainly chosen for 12h-100h, then furnace cooling, obtains the high-entropy alloy ingot casting of interior tissue homogenization of composition.

(3) deformation process analog simulation: carry out Computer Simulation to deformation process by simulation software, obtains stress characteristics and the rule of deformation process ingot blank different sites, especially the regularity of distribution of three-dimensional stress under compression and damage profile.

(4) jacket design: according to the analog simulation result in step (3), selects sheath material (being mainly conventional carbon steel or stainless steel) and designs variable cross-section wrapping structure.Cross section structure and the size of jacket different positions is optimized on this basis, until forming process has comparatively uniform three-dimensional compressive stress field by analog simulation.

(5) jacket processing: according to the variable cross-section wrapping structure size obtained in step (4), by lathe and machining center, processing can form the variable cross-section jacket of three-dimensional stress under compression in deformation process, and jacket aspect ratio is between 1:1 to 1.5:1.

(6) high-temperature gradient stress modification: homogenizing thermal treatment in step (2) is obtained high-entropy alloy AlCoCrFeNiTi _0.5be put in the variable cross-section jacket obtained of processing in step (5), obtain comprising high-entropy alloy AlCoCrFeNiTi _0.5the ingot blank of pre-manufactured blanks.Ingot blank is heated to high temperature modified processing temperature, carries out upsetting pull modification.Pull out after first upsetting, time processing of many fire, is cooled to room temperature after completing, and adopts mechanical workout to be peeled off by jacket, obtains the high entropy alloy material of homogeneous microstructure good mechanical performance.

2. a kind of method being prepared high-entropy alloy ingot blank by high-temperature gradient stress modification technology according to claim 1, be is characterized in that: in 1 step 4, jacket is the variable cross-section jacket that the sectional dimension designed according to deformation process ingot blank internal stress distribution has certain Changing Pattern; By applying variable cross-section jacket, 2 ensure that in deformation process, high-entropy alloy inside forms the gradient three-dimensional stress under compression field with good repair ability; The gradient three-dimensional stress under compression formed in 3 deformation processes can suppress to have germinating and the expansion of tiny crack in the high-entropy alloy deformation process of high lattice distortion, effectively completes the regulation and control that become more meticulous of high-entropy alloy microtexture; 4 compress adaptive microstress field broken as cast condition high-entropy alloy large dendritic crystal by having three-dimensional, improve homogeneity of structure, significantly improve high-entropy alloy service ability, the service ability especially under the extreme condition such as shock resistance.