CN113549780B - Powder metallurgy refractory multi-principal-element high-entropy alloy and preparation method thereof - Google Patents
Powder metallurgy refractory multi-principal-element high-entropy alloy and preparation method thereof Download PDFInfo
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C1/00—Making non-ferrous alloys
- C22C1/04—Making non-ferrous alloys by powder metallurgy
- C22C1/045—Alloys based on refractory metals
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
- B22F3/02—Compacting only
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
- B22F3/02—Compacting only
- B22F3/04—Compacting only by applying fluid pressure, e.g. by cold isostatic pressing [CIP]
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
- B22F3/10—Sintering only
- B22F3/1003—Use of special medium during sintering, e.g. sintering aid
- B22F3/1007—Atmosphere
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C1/00—Making non-ferrous alloys
- C22C1/04—Making non-ferrous alloys by powder metallurgy
- C22C1/045—Alloys based on refractory metals
- C22C1/0458—Alloys based on titanium, zirconium or hafnium
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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- C22C30/00—Alloys containing less than 50% by weight of each constituent
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F2201/00—Treatment under specific atmosphere
- B22F2201/20—Use of vacuum
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F2998/00—Supplementary information concerning processes or compositions relating to powder metallurgy
Abstract
The invention relates to the technical field of powder metallurgy preparation of refractory metal materials; specifically discloses a preparation method of powder metallurgy refractory multi-principal-element high-entropy alloy, which specifically comprises the following steps: step S1: sieving refractory metal element powder with a 300-mesh sieve, and mixing by adopting a multi-element powder mixing mode to obtain a mixture; the mixture is at least four elements of T i, Zr, Hf, V, Nb, Ta, Cr, Mo and W; the atomic percentage of each element in the mixture is 5-35%; the total percentage is 100%. Step S2: pressing and forming to obtain a pressed blank; step S3: and (4) performing vacuum high-temperature solid-phase sintering to obtain a sintered block. The method has the advantages of easily-regulated components, high production efficiency and near-net-shape forming, and the prepared powder metallurgy refractory multi-principal-element high-entropy alloy has stable structure and performance and low cost, and has remarkable advantages in the research and development of high-performance powder metallurgy refractory multi-principal-element high-entropy alloy and the flexible batch production of multi-shape variety products.
Description
Technical Field
The invention belongs to the technical field of powder metallurgy preparation of refractory metal materials, and particularly relates to a powder metallurgy refractory multi-principal-element high-entropy alloy and a preparation method thereof.
Background
The existing refractory multi-principal-element high-entropy alloy block preparation method mainly comprises an electric arc melting casting process and a powder metallurgy mechanical alloying and discharge plasma sintering process. The two processes are mostly used for preparing refractory multi-principal-element high-entropy alloy at laboratory level, but face a plurality of problems when being put into large-scale mass production. The problems with both processes are illustrated below.
At present, the most common method for preparing refractory multi-principal-element high-entropy alloy block materials is an arc melting casting process, but the process is quite complicated (such as patent document (NbMoTaW)100-xMxThe refractory high-entropy alloy and the preparation method thereof, and the application publication No. CN109182877A, the grant No. CN 109182877B). The process usually needs to be repeatedly smelted, at least four times are generally needed, and some times or even more than ten times of repeated smelting are needed to obtain the multi-element alloyed ingot. The reason for this is that the high melting point of the refractory elements and the large difference in melting point between the elements must be melted repeatedly to achieve alloying. However, even through such complicated operations, the process is very difficult in controlling the uniformity of the ingot structure and the stability of the component distribution of the refractory multi-principal-element high-entropy alloy, and due to factors such as large component melting point difference and non-uniform melt solidification thermal field, the problem of non-uniform cast structure or macro component segregation is easily caused, which seriously affects the stability of product performance and makes it difficult to make the refractory multi-principal-element high-entropy alloy have good service performance. Especially when elements with higher melting point, such as W, Ta, are added or the content of the elements is increased, the melting temperature of an alloy system is greatly increased, and the alloy is melted and alloyedAnd homogenization of the composition will be more difficult. For systems with large melting point difference, the melting temperature is higher than the boiling point of partial components, for example, the melting point of W reaches 3410 ℃, which exceeds the boiling point of Ti 3277 ℃, the boiling point of V is 3407 ℃ and the boiling point of Cr is 2671 ℃, and the component system containing the elements can cause burning loss of the low-boiling-point components in the melting process, thereby causing the components to deviate from the design expectation, and limiting the freedom of designing the component system of the refractory multi-principal-element high-entropy alloy material. In addition, the arc melting casting process can only obtain a 'button ingot' with a small size (the diameter is generally not more than 40mm at present), the shape is irregular, the ingot is required to be machined to meet the shape requirement of an application product, and the refractory multi-principal-element high-entropy alloy generally has high strength, hardness and wear resistance, so that the machining difficulty is higher than that of the conventional alloy material. Meanwhile, the machining undoubtedly reduces the utilization rate of refractory metal materials and increases the product cost.
Therefore, the current arc melting casting process has the defects of low production efficiency, poor stability of organization and performance, limited material component system, low material utilization rate, high cost and the like in the batch production process of refractory multi-principal-element high-entropy alloy block products. Some researches adopt induction melting casting (such as patent document: a light refractory high-entropy alloy and a preparation method thereof), suspension melting casting (such as patent document: a refractory multi-principal-element high-entropy alloy and a preparation method thereof), and suspension melting casting (such as patent document: a refractory multi-principal-element high-entropy alloy and a preparation method thereof, and an application publication number: CN109112380A, an authorization publication number: CN 109112380B), but all of the methods also face similar problems to the arc melting casting process. To solve this problem, "powder metallurgy refractory multi-principal element high-entropy alloys" were produced. The powder metallurgy mechanical alloying and discharge plasma sintering process can fundamentally avoid the occurrence of coarse structures and macro segregation in the electric arc melting process, has large performance promotion space and good stability, and is concerned by many researches (such as patent documents: a preparation method of NbZrTiTa refractory high-entropy alloy powder and NbZrTiTa refractory high-entropy alloy powder, application publication No. CN109108273A, an authorization publication No. CN 109108273B), but still faces many problems in the application process.
At present, mechanical alloying is used for processing raw material powder in almost all reports about the preparation method of the powder metallurgy refractory multi-principal-element high-entropy alloy, although the high-energy ball-milling mechanical alloying can achieve the effects of forced alloying and homogenization, the severe cold welding phenomenon between the powder and a ball-milling tank and between the powder and grinding balls is easily generated in the high-energy ball-milling process, and the problems of low powder yield and limited yield are caused. The cold welding can be relieved to a certain extent by adding some process control agents (such as absolute ethyl alcohol, n-heptane and the like), but the effect is limited, the cold welding problem cannot be completely avoided, and a subsequent procedure for removing the process control agents is required to be added. In the ball milling process, the ball milling tank and the milling balls are inevitably worn, and the wear products enter refractory multi-principal-element high-entropy alloy powder to cause impurity contamination and influence the product quality. In addition, the surface activity of the powder after mechanical alloying is greatly improved, which increases the use safety risk of the originally inflammable refractory active powder in production, and especially increases the difficulty of controlling the safety risk when the components contain elements such as Ti, Zr, Hf and the like.
At present, most discharge plasma sintering equipment is single-cavity station equipment for scientific research, the batch production efficiency is very low, the shape and the size of a formed block are also greatly limited (currently, only a wafer-shaped or cylindrical sample with the diameter not more than 60mm can be prepared), and the requirement of large-scale industrial production is difficult to meet. And the spark plasma sintering equipment is very expensive and has high maintenance cost. In addition, the graphite mold is mainly used in the spark plasma sintering, the graphite mold has large loss and short service life in the use process, can be repeatedly used for several times and even can be damaged once, the product cost is increased, and the production efficiency is reduced. Carbon elements in the graphite mold are easy to react with refractory metal elements at high temperature, so that carbon pollution of refractory multi-principal-element high-entropy alloy is caused, and the product quality is influenced. Some studies have adopted a hot-pressing sintering method (for example, patent document: preparation method of VNbMoTaW high-entropy alloy application publication No. CN111411249A.), but the hot-pressing sintering process also faces similar problems to the spark plasma sintering process when put into mass production.
At present, the scale batch production of the refractory multi-principal-element high-entropy alloy by using the preparation method is difficult or very high in cost, and the application and popularization of the refractory multi-principal-element high-entropy alloy material are limited.
Disclosure of Invention
The invention aims to solve the technical problem of providing a powder metallurgy refractory multi-principal-element high-entropy alloy and a preparation method thereof; the method has the advantages of easily-regulated components, high production efficiency and near-net-shape forming, the prepared powder metallurgy refractory multi-principal-element high-entropy alloy has stable structure and performance, the market maturity of related equipment is high, the cost is low, and the method has remarkable advantages in research and development of the high-performance powder metallurgy refractory multi-principal-element high-entropy alloy and flexible batch production of multi-shape variety products.
The technical problem to be solved by the invention is as follows:
the preparation method of the powder metallurgy refractory multi-principal-element high-entropy alloy specifically comprises the following steps:
step S1: sieving refractory metal element powder with a 300-mesh sieve, and mixing by adopting a multi-element powder mixing mode to obtain a mixture;
the mixture is at least four elements of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo and W;
the atomic percentage of each element in the mixture is 5-35%; the total percentage is 100%.
Step S2: pressing and forming to obtain a pressed blank;
step S3: and (4) performing vacuum high-temperature solid-phase sintering to obtain a sintered block.
In some possible embodiments, the step S1 specifically refers to:
pouring refractory metal element powder into a mixer to mix under the protection of protective gas, wherein the mixing time is 20-40 hours.
In some possible embodiments, the press forming in step S2 is rigid press forming; wherein the pressing pressure is more than or equal to 800MPa, and the pressure maintaining time is 5-15 seconds.
In some possible embodiments, the press forming in step S2 is cold isostatic press forming; wherein the pressing pressure is 150MPa-300MPa, and the pressure maintaining time is 10 minutes-20 minutes.
In some possible embodiments, the step S3 specifically includes the following steps:
step S31: loading the pressed blank into a sintering furnace, performing vacuum high-temperature solid phase sintering, and keeping the vacuum degree to be less than or equal to 1 × 10- 3Pa；
Step S32: the temperature of the pressed blank is raised to the sintering temperature TsAnd keeping the temperature for 180-420 minutes;
step S33: and cooling to obtain a sintered block, namely a product of the powder metallurgy refractory multi-principal-element high-entropy alloy.
In some possible embodiments, the step S31 specifically refers to:
after the pressed blank is loaded into a sintering furnace, vacuumizing is firstly carried out, then protective gas is filled into the furnace for cleaning, and then high vacuum is pumped until the vacuum degree is less than or equal to 1 multiplied by 10-3And sintering is started after Pa.
In some possible embodiments, the sintering temperature TsThe calculation formula of (A) is as follows: t iss＝α·Tm；
Wherein: t is a unit ofmThe melting temperature of the refractory multi-principal-element high-entropy alloy of a corresponding component system;
alpha is a temperature index, and alpha is not less than 3/4 and not more than 6/7.
In some possible embodiments, the sintering furnace is a metal tungsten heater or a metal molybdenum heater.
In some possible embodiments, the purity of each refractory metal element powder is 99.7% or more.
The powder metallurgy refractory multi-principal-element high-entropy alloy is prepared by the method.
Compared with the prior art, the invention has the beneficial effects that:
the preparation method has the advantages of simple process, low cost, high efficiency, good stability, near-net-shape forming, high flexibility on the size and shape of the product, and suitability for large-scale batch production;
the powder metallurgy refractory multi-principal-element high-entropy alloy prepared by the method has the advantages of fine microstructure, uniform component distribution, stable phase structure and excellent performance;
the raw material powder is processed by adopting a multi-component powder mixing mode, so that the element powder of each component is easy to obtain, and the alloy components are easy to adjust; the mixing process can completely avoid the problems of cold welding, low powder yield, abrasion, impurity pollution and the like of high-energy ball milling mechanical alloying, and can mix a large amount of materials, and the powder yield can reach 100%; the activity of the powder before and after mixing is basically the same, and compared with the mechanical alloying powder with extremely high activity, the safety risk control is easier; the strength, hardness and work hardening degree of the element powder are less than those of the alloy powder, so that the element powder is easier to press and form; the component gradient formed by the multi-component powder is beneficial to diffusion and promotes densification;
the invention adopts a rigid mould pressing or cold isostatic pressing mode to carry out press forming; the limitation on the shape and size is smaller compared to arc melting casting and spark plasma sintering; in the actual production, automatic pressing and a furnace for batch production of a plurality of workpieces are matched, so that the production efficiency can be very high;
the invention adopts a vacuum high-temperature solid-phase sintering mode to carry out alloy homogenization and densification of the pressed blank;
according to the invention, the metal tungsten heating element or the metal molybdenum heating element is used as the sintering furnace, so that carbon pollution caused by the graphite mold can be avoided; the synchronous sintering of a plurality of workpieces in one furnace can greatly improve the production efficiency;
the equipment used in the invention has better market maturity and lower cost, does not need expensive spark plasma sintering equipment, has high flexibility on the size and the shape of the product, and is more suitable for large-scale batch production.
Drawings
FIG. 1 is a photograph of the microstructure of an alloy prepared according to the present invention at a sintering process parameter of 1500 ℃ for 60 minutes;
FIG. 2 is a photograph of the microstructure of an alloy prepared according to the present invention at a sintering process parameter of 1500 ℃ for 180 minutes;
FIG. 3 is a microstructure photograph of an alloy prepared according to the present invention at a sintering process parameter of 1500 ℃ for 300 minutes;
FIG. 4 is an XRD spectrum of an alloy prepared at 1500 ℃ X60 minutes, 1500 ℃ X180 minutes, 1500 ℃ X300 minutes respectively according to the sintering process parameters in the example of the present invention;
FIG. 5 is a schematic view of the surface of the sample prepared in comparative example 1;
FIG. 6 is a schematic view of the anatomical surface of the sample prepared in comparative example 1;
FIG. 7 is a schematic diagram of the alloy sample prepared at 1800 ℃ for 300 minutes in the example sintering process and the gasket being welded together;
FIG. 8 is a schematic representation of a sintered compact prepared at 1500 ℃ for 300 minutes in the example sintering process;
FIG. 9 is a schematic representation of a sintered compact prepared with the sintering process parameters of 1500 ℃ for 420 minutes in the examples.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention more apparent, the embodiments of the present invention will be described in detail and completely with reference to the accompanying drawings. All other embodiments, which can be obtained by a person skilled in the art without any inventive step based on the embodiments of the present invention, are within the scope of the present invention. Thus, the detailed description of the embodiments of the present invention provided below is not intended to limit the scope of the invention as claimed, but is merely representative of selected embodiments of the invention.
In the drawings of the present invention, it should be understood that different technical features which are not mutually substituted are shown in the same drawing only for the convenience of simplifying the drawing description and reducing the number of drawings, and the embodiment described with reference to the drawings does not indicate or imply that all the technical features in the drawings are included, and thus the present invention is not to be construed as being limited thereto.
The specific meanings of the above terms in the present invention can be understood by those skilled in the art according to specific situations.
The present invention will be described in detail below.
The preparation method of the powder metallurgy refractory multi-principal-element high-entropy alloy specifically comprises the following steps:
step S1: sieving refractory metal elements with a 300-mesh sieve; mixing the powder in a multi-element powder mixing mode to obtain a mixture;
the mixture is at least four elements of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo and W;
the atomic percentage of each element in the mixture is 5-35%; the total percentage is 100%;
step S2: pressing and forming to obtain a pressed blank;
step S3: and (4) performing vacuum high-temperature solid-phase sintering to obtain a sintered block.
The invention adopts a multi-element powder mixing mode to process raw material powder.
The method uses element powder with higher purity for mixing, and is different from high-energy ball milling mechanical alloying in that the method only mixes multi-element powder without grinding, and has the following advantages:
(1) the element powder of each component is easy to obtain, and the alloy components are easy to adjust;
(2) the mixing process can completely avoid the problems of cold welding, low powder output, abrasion impurity pollution and the like of high-energy ball-milling mechanical alloying, and can mix a large amount of materials, wherein the powder output can reach 100%;
(3) the activity of the powder before and after mixing is basically the same, and compared with the mechanical alloying powder with extremely high activity, the safety risk control is easier;
(4) the strength, hardness and work hardening degree of the element powder are less than those of the alloy powder, so that the element powder is easier to press and form;
(5) the composition gradient formed by the multi-component powder is favorable for diffusion and promotes densification.
The invention utilizes the characteristic of multi-principal-element high-entropy effect, and the effect is favorable for multi-element powder mixing-pressing-vacuum high-temperature solid-phase sintering process. The high temperature phase of each refractory metal component is transformed into the BCC structure, where the diffusion rate of the atoms is relatively fast (several orders of magnitude faster than in the FCC structure). The multi-principal-element high entropy effect simultaneously promotes the system to tend to form a single-phase BCC structure, which can further strengthen the diffusion homogenization and improve the densification degree. Thanks to the effect, the tolerance of vacuum high-temperature solid-phase sintering to the difference of the mixing uniformity of the multi-component powder is higher, and even if the local micro-area mixing of the multi-component powder is not uniform, the uniform distribution of alloy components can be realized through the full diffusion of sintering.
In some possible embodiments, the step S1 specifically refers to:
and pouring the refractory metal element powder into a mixer to mix under the protection of protective gas, wherein the mixing time is 20-40 hours, and thus obtaining a mixture.
Preferably, the mixer is any one of a three-dimensional motion mixer, a V-shaped mixer and a double-cone mixer.
In some possible embodiments, the press forming in step S2 is rigid press forming; wherein the pressing pressure is more than or equal to 800MPa, and the pressure maintaining time is 5-15 seconds.
Preferably, when rigid press molding is adopted, the corresponding mold is a steel mold or a hard alloy mold.
In some possible embodiments, the press forming in step S2 is cold isostatic pressing; wherein the pressing pressure is 150MPa-300MPa, and the pressure maintaining time is 10 minutes-20 minutes.
Preferably, when cold isostatic pressing is used, a soft mold made of a polymer material is used as the corresponding mold.
The invention adopts rigid mould pressing or cold isostatic pressing to carry out press forming. The shape of the product can be realized by more flexible design of a pressing die, and the size of the product is smaller than the size specification of the hearth. This approach is less restrictive than the shape and size limitations of arc melting casting and spark plasma sintering. In the actual production, the automatic pressing and the batch production in one furnace are matched, and the production efficiency can be very high.
In some possible embodiments, the step S3 specifically includes the following steps:
step S31: loading the pressed blank into a sintering furnace, performing vacuum high-temperature solid phase sintering, and keeping the vacuum degree to be less than or equal to 1 × 10- 3Pa；
Step S32: the temperature of the pressed blank is raised to the sintering temperature TsAnd keeping the temperature for 180-420 minutes;
step S33: and cooling to obtain a sintered block, namely a product of the powder metallurgy refractory multi-principal-element high-entropy alloy.
In some possible embodiments, the step S31 specifically refers to:
loading the pressed blank into a sintering furnace, vacuumizing, filling protective gas to wash the furnace, and vacuumizing until the vacuum degree is less than or equal to 1 × 10-3After Pa, sintering was started.
Preferably, the protective gas is an inert gas, and can be nitrogen or argon.
In some possible embodiments, the sintering temperature TsThe calculation formula of (A) is as follows: t is a unit ofs＝α·Tm；
Wherein: t ismThe melting temperature of the refractory multi-principal element high-entropy alloy of a corresponding component system;
alpha is a temperature index, and alpha is not less than 3/4 and not more than 6/7.
In some possible embodiments, the sintering furnace is a metal tungsten heater or a metal molybdenum heater.
The invention adopts a vacuum high-temperature solid-phase sintering mode to carry out alloy homogenization and densification of the pressed blank. And a metal tungsten heating element or a metal molybdenum heating element is adopted, so that carbon pollution of the graphite mould can be avoided. The synchronous sintering of a plurality of batches in one furnace can greatly improve the production efficiency. Almost no liquid phase is generated in the solid phase sintering process, the preparation temperature is lower than that of smelting, and the method has obvious advantages in the preparation of refractory metal materials. High temperature is the most direct and effective means for strengthening the diffusion process, and can accelerate homogenization and promote densification. The vacuum can not only avoid pollution such as oxidation, but also remove physical adsorption on the surface of powder particles, activate diffusion interfaces and promote densification.
In some possible embodiments, the purity of each refractory metal element powder is 99.7% or more.
The preparation method has simple process, only has three process steps, avoids the complex smelting process of the electric arc smelting casting process, and can be shaped nearly cleanly.
Compared with the cast alloy prepared by the arc melting casting process, the powder metallurgy refractory multi-principal-element high-entropy alloy has the advantages of fine microstructure, uniform component distribution, stable phase structure and excellent performance.
The equipment used by the invention has better market maturity and lower cost, does not need expensive spark plasma sintering equipment, has high flexibility on the size and the shape of the product, and is more suitable for large-scale batch production.
The powder metallurgy refractory multi-principal-element high-entropy alloy is prepared by the method.
Example (b):
an example is a refractory multi-principal element high-entropy alloy containing Ti, Zr, Hf and Ta, wherein the atomic percentages of the components of Ti, Zr, Hf and Ta are respectively 28.33%, 28.33% and 15.01%. According to the data, the melting point T of the alloymAbout 1850 ℃ from the sintering temperature Ts＝α·TmCalculation of the sintering temperature TsThe range is 1387.5 ℃ -1585.7 ℃, and 1400 ℃ and 1500 ℃ in the range are taken as sintering temperatures for testing in order to facilitate setting of sintering process parameters. The sintering process parameters consisting of different sintering temperatures and holding times are set in the test, and are respectively 1500 ℃ multiplied by 60 minutes, 1500 ℃ multiplied by 180 minutes, 1500 ℃ multiplied by 300 minutes, 1500 ℃ multiplied by 420 minutes, 1400 ℃ multiplied by 300 minutes, 1300 ℃ multiplied by 300 minutes and 1800 ℃ multiplied by 300 minutes.
Firstly, preparation
Step S1: mixing the multi-element powder;
weighing commercially available Ti powder, Zr powder, Hf powder and Ta powder with the purity of more than or equal to 99.7 percent and the granularity of-300 meshes according to the formula of the components; and (3) putting the powder into a three-dimensional moving mixer, filling argon into a cavity of the mixer for protection, and mixing for 20-40 hours to obtain a mixture.
Step S2: pressing;
and filling the mixture into a square silica gel soft mold, vacuumizing and packaging, performing cold isostatic pressing at 150MPa for 10 minutes, and removing the silica gel soft mold after pressing is finished to obtain a formed pressed blank.
Step S3: vacuum high-temperature solid-phase sintering;
loading the pressed blank into a multi-atmosphere sintering furnace of a metal tungsten heating element, vacuumizing, filling argon for furnace washing, and vacuumizing to the vacuum degree of less than or equal to 1 × 10-3Starting sintering after Pa; the vacuum degree is kept less than or equal to 1 multiplied by 10 in the sintering process-3Pa; sintering is carried out according to set sintering process parameters, the temperature of the pressed blank is raised to 1500 ℃, heat preservation is carried out for 300 minutes, and a sintered block is obtained after cooling, namely the product of the powder metallurgy refractory multi-principal-element high-entropy alloy.
The preparation operations of step S1-step S3 were repeated, and the sintering process parameters in step S3 were changed to 1500℃ × 60 minutes, 1500℃ × 180 minutes, 1500℃ × 420 minutes, 1400℃ × 300 minutes, 1300℃ × 300 minutes, 1800℃ × 300 minutes, respectively, to obtain sintered cakes prepared with different sintering process parameters, respectively.
1500 ℃ x 60 minutes as described herein is specifically the sintering temperature 1500 ℃, the holding time 60 minutes; 1500 ℃ X180 minutes, 1500 ℃ X420 minutes, 1400 ℃ X300 minutes, 1300 ℃ X300 minutes, 1800 ℃ X300 minutes.
The sintering process parameters of 1500℃ × 60 minutes, 1500℃ × 180 minutes, 1500℃ × 300 minutes, 1500℃ × 420 minutes, 1400℃ × 300 minutes, 1300℃ × 300 minutes, 1800℃ × 300 minutes set in the test all achieve sintering of the pressed compact into a sintered block.
Secondly, performance test:
and (3) testing the density:
the density of the powder metallurgy refractory multi-principal-element high-entropy alloy prepared by testing different sintering process parameters by an Archimedes drainage method is shown in the following table 1:
| sintering process parameters | Agglomerate Density (g/cm)3) |
| 1500 ℃ for 60 minutes | 9.090 |
| 1500 ℃ for 180 minutes | 9.224 |
| 1500 ℃ for 300 minutes | 9.313 |
| 1500 ℃ for 420 minutes | 9.339 |
| 1400 ℃ for 300 minutes | 9.203 |
| 1300 ℃ for 300 minutes | 9.052 |
| 300 minutes at 1800 DEG C | 9.362 |
TABLE 1
And (3) hardness testing:
the alloy was ground and polished to a mirror surface, and microhardness was measured with a Vickers hardness tester under an indentation load of 0.5kgf for 15 seconds, with the results shown in Table 2 below:
| sintering process parameters | Hardness of sintered lump (kgf/mm)2) |
| 1500 ℃ for 60 minutes | 530.3 |
| 1500 ℃ for 180 minutes | 584.8 |
| 1500 ℃ for 300 minutes | 603.0 |
TABLE 2
Testing the compression fracture strength:
the sample specification for the compression test was a cuboid of 5mm x 9mm, the compression test loading rate was 0.5mm/min, and the results are given in table 3 below:
| sintering process parameters | Compression fracture Strength (MPa) of |
| 1500 ℃ for 60 minutes | 919 |
| 1500 ℃ for 180 minutes | 1631 |
| 1500 ℃ for 300 minutes | 1466 |
TABLE 3
The density and the compressive fracture strength of the sintered block with the sintering process parameter of 1500 ℃ multiplied by 60 minutes are lower because the sintering time is insufficient, the sintered block can not be fully densified, and the parameter is not suitable for preparing the denser powder metallurgy refractory multi-principal-element high-entropy alloy.
The density of the sintered block with the sintering process parameter of 1300 ℃ multiplied by 300 minutes is lower, because the sintering temperature is insufficient, the sintered block can not be fully densified, and the parameter is not suitable for preparing the denser powder metallurgy refractory multi-principal-element high-entropy alloy.
The sintered cake in fig. 8 is obtained under the sintering process parameter of 1500 ℃ x 300 minutes; the agglomerates in FIG. 9 are schematic representations of agglomerates prepared at a sintering process parameter of 1500 ℃ for 420 minutes;
as shown in fig. 7, the sintered cake with the sintering process parameter of 1800℃ × 300 min has a higher density, but because the sintering temperature is too high, the sintered cake is seriously sintered and welded with the crucible and the gasket contained in the furnace, so that it is difficult to separate the sintered cake product from the crucible and the gasket after the sintered cake is discharged, which is not favorable for the production of actual products, and the parameter is not suitable as the preferred sintering process parameter.
The powder metallurgy refractory multi-principal-element high-entropy alloy prepared by the sintering process parameters of 1500 ℃ multiplied by 180 minutes, 1500 ℃ multiplied by 300 minutes, 1500 ℃ multiplied by 420 minutes and 1400 ℃ multiplied by 300 minutes has higher density and can be used as the sintering process parameters of the powder metallurgy refractory multi-principal-element high-entropy alloy compact sintered block. Wherein, the sintering process parameters are that the hardness and the compression fracture strength of the sintered block are higher at 1500 ℃ multiplied by 180 minutes and 1500 ℃ multiplied by 300 minutes, and the two parameters can be used as the optimized sintering process parameters.
The density of the as-cast refractory multi-element high-entropy alloy of this composition produced by the arc-melting casting process is described in the prior art as 9.328g/cm3Hardness of 3720MPa (converted to 379.2 kgf/mm)2) The compressive fracture strength is 1314 MPa; thus, in contrast, the powder metallurgy refractory multi-principal component prepared by the method of the present invention is highThe entropy alloy has more excellent hardness and strength performance.
Microstructure and phase structure:
observing the microstructure of the sintering block with a scanning electron microscope under different sintering process parameters, wherein the microstructure of the sintering block is respectively a photograph of the microstructure of the sintering block at 1500 ℃ multiplied by 60 minutes, 1500 ℃ multiplied by 180 minutes and 1500 ℃ multiplied by 300 minutes in the sintering process parameters shown in figure 1, figure 2 and figure 3; the microstructure of the powder metallurgy refractory multi-principal-element high-entropy alloy is uniform and fine, and has a special heterogeneous microstructure which is in lamellar cross distribution, and the microstructure is favorable for improving the mechanical property of the alloy; it can also be seen that the sintered cakes having the sintering process parameters of 1500 ℃ x 180 minutes and 1500 ℃ x 300 minutes had fewer pores and were superior to the sintered cakes having the sintering process parameters of 1500 ℃ x 60 minutes. The combination of performance test data shows that the powder metallurgy refractory multi-principal-element high-entropy alloy with the sintering process parameters of 1500 ℃ multiplied by 180 minutes and 1500 ℃ multiplied by 300 minutes has higher compactness, uniform and fine microstructure and better mechanical property, so the two parameters can be used as the optimal sintering process parameters of the component system.
An X-ray diffractometer is used for collecting XRD spectrograms of sintered blocks with sintering technological parameters of 1500 ℃ multiplied by 60 minutes, 1500 ℃ multiplied by 180 minutes and 1500 ℃ multiplied by 300 minutes, and the result is shown in figure 4; as can be seen from fig. 4, the XRD spectrograms of different sintering process parameters show consistent peak positions, and the phases of the powder metallurgy refractory multi-principal element high-entropy alloys prepared under different sintering process parameters are consistent and are all BCC + HCP structures. The result also shows that the phase structure stability of the powder metallurgy refractory multi-principal element high-entropy alloy is better.
Comparative example 1:
compared with the embodiment, the Fe element is added in the comparative example to form the refractory multi-principal-element high-entropy alloy containing Ti, Zr, Hf, Ta and Fe; wherein Ti, Zr, Hf, Ta and Fe account for 25.50%, 13.50% and 10.00% of the composition in atomic percentage, respectively. The sintering process parameter composed of the experimental sintering temperature and the heat preservation time is 1500 ℃ multiplied by 180 minutes.
Firstly, preparation
Step S1: mixing the multi-element powder;
commercially available Ti powder, Zr powder, Hf powder, Ta powder and Fe powder with the purity of more than or equal to 99.7 percent and the granularity of-300 meshes are weighed according to the formula of the components. And (3) putting the powder into a three-dimensional moving mixer, filling argon into a cavity of the mixer for protection, and mixing for 20-40 hours to obtain a mixture.
Step S2: pressing;
and filling the mixture into a square silica gel soft mold, vacuumizing and packaging, performing cold isostatic pressing at a pressing pressure of 150MPa for 10 minutes, and removing the silica gel soft mold after pressing to obtain a formed pressing blank.
Step S3: vacuum high-temperature solid-phase sintering;
loading the pressed blank into a multi-atmosphere sintering furnace of a metal tungsten heating element, vacuumizing, filling argon for furnace washing, and vacuumizing to the vacuum degree of less than or equal to 1 × 10-3And sintering is started after Pa. The vacuum degree is kept less than or equal to 1 multiplied by 10 in the sintering process-3Pa. And sintering according to the set sintering process parameters, raising the temperature of the pressed blank to 1500 ℃, preserving the heat for 180 minutes, and cooling to obtain a sintered block, namely the comparative alloy sample.
Thirdly, performance test:
and (3) testing the density:
the density of the alloy prepared according to the sintering process parameters was measured by Archimedes drainage method and found to be 9.121g/cm3。
And (3) hardness testing:
the alloy was polished to a mirror surface, and microhardness was measured with a Vickers hardness meter under a pressing load of 0.5kgf for 15 seconds, resulting in 505.7kgf/mm2。
Testing the compression fracture strength:
the sample specification for the compression test was a rectangular parallelepiped of 5mm × 5mm × 9mm, and the compression test loading rate was 0.5mm/min, and the result was 983 MPa.
The performance of the sample is lower than that of the alloy prepared by sintering process parameters of 1500 ℃ for 180 minutes in the embodiment. The sample sintered cake had a bubbling phenomenon as shown in fig. 5 and 6, and a large number of macroscopic holes were observed on the debranching surface, indicating that the sample had a low density.
Analyzing the cause, finding that Fe will affect the densification process of vacuum high temperature solid phase sintering, resulting in poor performance.
Comparative example 2:
compared with the refractory multi-principal element high-entropy alloy in the embodiment, the comparative alloy in the comparative example does not have the element components within the range of 5-35%, wherein the atomic percentages of Ti, Zr, Hf and Ta are 91.00%, 3.00% and 3.00%, respectively. The sintering process parameter composed of the experimental sintering temperature and the heat preservation time is 1500 ℃ multiplied by 180 minutes.
Firstly, preparation
Step S1: mixing the multi-element powder;
commercially available Ti powder, Zr powder, Hf powder and Ta powder with the purity of more than or equal to 99.7 percent and the granularity of-300 meshes are weighed according to the formula of the components. And (3) putting the powder into a three-dimensional moving mixer, filling argon into a cavity of the mixer for protection, and mixing for 20-40 hours to obtain a mixture.
Step S2: pressing;
and filling the mixture into a square silica gel soft mold, vacuumizing and packaging, performing cold isostatic pressing at a pressing pressure of 150MPa for 10 minutes, and removing the silica gel soft mold after pressing to obtain a formed pressing blank.
Step S3: vacuum high-temperature solid-phase sintering;
loading the pressed blank into a multi-atmosphere sintering furnace of a metal tungsten heating element, vacuumizing, filling argon for furnace washing, and vacuumizing to the vacuum degree of less than or equal to 1 × 10-3And sintering is started after Pa. The vacuum degree is kept less than or equal to 1 multiplied by 10 in the sintering process-3Pa. And sintering according to the set sintering process parameters, raising the temperature of the pressed blank to 1500 ℃, preserving the heat for 180 minutes, and cooling to obtain a sintered block, namely the sample of the comparison alloy.
Fourthly, performance test:
and (3) testing the density:
the density of the alloy prepared according to the sintering process parameters was measured by Archimedes drainage method and found to be 5.198g/cm3。
And (3) hardness testing:
the alloy was polished to a mirror surface, and microhardness was measured with a Vickers hardness tester under a pressing load of 0.5kgf for 15 seconds, resulting in 329.3kgf/mm2。
Testing the compression fracture strength:
the specification of a sample for the compression test is a cuboid of 5mm × 5mm × 9mm, and the loading rate for the compression test is 0.5mm/min, and the result is 1189 MPa.
The hardness and compressive strength of the sample are both lower than those of the alloy prepared by the sintering process parameters of 1500 ℃ for 180 minutes in the examples. Although the alloy also has higher compactness, the mechanical property of the alloy is inferior to that of the powder metallurgy refractory multi-principal-element high-entropy alloy in the embodiment.
For analysis reasons, the refractory element components are not in the range of 5-35%, and better high-entropy solid solution strengthening and heterogeneous microstructure strengthening are difficult to form, so that the performance is poor.
The elements and the preparation method in the invention are adopted to prepare the refractory multi-principal-element high-entropy alloy, and the refractory multi-principal-element high-entropy alloy has the advantages of easily regulated components, high production efficiency and near net shape, and has the characteristics of stable structure and performance.
As can be seen from the comparison of FIGS. 5 to 9, the sintered cake prepared by the invention has good surface quality, no bubbling phenomenon and no welding with the crucible and the gasket; has excellent hardness and strength performance.
The invention is not limited to the foregoing embodiments. The invention extends to any novel feature or any novel combination of features disclosed in this specification and any novel method or process steps or any novel combination of features disclosed.
Claims (7)
1. The preparation method of the powder metallurgy refractory multi-principal-element high-entropy alloy is characterized by comprising the following steps of:
step S1: sieving refractory metal element powder with a 300-mesh sieve, and mixing by adopting a multi-element powder mixing mode to obtain a mixture; the purity of each refractory metal element powder is more than or equal to 99.7 percent; the method specifically comprises the following steps:
pouring refractory metal element powder into a mixer to mix under the protection of protective gas, wherein the mixing time is 20-40 hours; the mixer is any one of a three-dimensional moving mixer, a V-shaped mixer and a double-cone mixer;
the mixture is Ti, Zr, Hf and Ta;
the atomic percentage of each element in the mixture is 5-35%; the total percentage is 100%;
step S2: pressing and forming to obtain a pressed blank;
step S3: performing vacuum high-temperature solid-phase sintering to obtain a sintered block; wherein the sintering temperature is TsAnd keeping the temperature for 180-420 minutes; the sintering temperature TsThe calculation formula of (A) is as follows: t iss＝α·Tm；
Wherein: t ismThe melting temperature of the refractory multi-principal element high-entropy alloy of a corresponding component system;
alpha is a temperature index, and alpha is not less than 3/4 and not more than 6/7.
2. The method for preparing the powder metallurgy refractory multi-principal-element high-entropy alloy according to claim 1, wherein the press forming in the step S2 is rigid press forming; wherein the pressing pressure is more than or equal to 800MPa, and the pressure maintaining time is 5-15 seconds.
3. The method for preparing the powder metallurgy refractory multi-principal-element high-entropy alloy according to claim 1, wherein the press forming in the step S2 is cold isostatic press forming; wherein the pressing pressure is 150MPa-300MPa, and the pressure maintaining time is 10 minutes-20 minutes.
4. The method for preparing the powder metallurgy refractory multi-principal-element high-entropy alloy according to claim 1, wherein the step S3 specifically comprises the following steps:
step S31: loading the pressed blank into a sintering furnace, performing vacuum high-temperature solid phase sintering, and keeping the vacuum degree to be less than or equal to 1 × 10-3Pa；
Step S32: the temperature of the pressed blank is raised to the sintering temperature TsAnd preserving heat;
step S33: and cooling to obtain a sintered block, namely a product of the powder metallurgy refractory multi-principal-element high-entropy alloy.
5. The method for preparing the powder metallurgy refractory multi-principal-element high-entropy alloy according to claim 4, wherein the step S31 specifically includes:
loading the pressed blank into a sintering furnace, vacuumizing, filling protective gas to wash the furnace, and vacuumizing until the vacuum degree is less than or equal to 1 × 10-3And sintering is started after Pa.
6. The method for preparing the powder metallurgy refractory multi-principal-element high-entropy alloy according to claim 4, wherein the sintering furnace is a metal tungsten heating element or a metal molybdenum heating element.
7. A powder metallurgy refractory multi-principal element high-entropy alloy, characterized by being prepared by the method of any one of claims 1-6.
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| CN104263981A (en) * | 2014-09-17 | 2015-01-07 | 福建龙溪轴承(集团)股份有限公司 | Method for preparing powder metallurgy titanium alloy bar |
| CN111304479A (en) * | 2020-03-18 | 2020-06-19 | 南昌航空大学 | Preparation method of VCrNbMoW refractory high-entropy alloy |
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| CN104263981A (en) * | 2014-09-17 | 2015-01-07 | 福建龙溪轴承(集团)股份有限公司 | Method for preparing powder metallurgy titanium alloy bar |
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