Preparation method of high melting point differential alloy powder for 3D printing

Abstract

The present invention relates to the technical field of high entropy alloys, and discloses a method for preparing high melting point difference alloy powder for 3D printing, comprising the following steps: Step 1, powder metallurgy semi-alloying: alloying single elements with lower mixing enthalpy by hot pressing sintering or hot isostatic pressing sintering; Step 2, plasma complete alloying: secondary alloying of the alloyed elements with single elements with higher melting points by plasma rotating electrode atomization. This technical solution solves the problem of high melting point difference, and the low melting point elements and the adjacent higher melting point elements are partially alloyed in situ by powder metallurgy to form an "intermediate alloy". During the plasma rotating electrode atomization process, the intermediate alloy in the rod material is alloyed with the adjacent higher melting point elements under the action of plasma energy, thereby avoiding the low melting point elements from burning or evaporating due to excessive temperature or energy, and achieving a uniform structure of the refractory high entropy alloy powder and controllable composition.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of high-entropy alloys, and particularly relates to a preparation method of high-melting-point differential alloy powder for 3D printing. BACKGROUND

[0002] In the current 3D printing industry, metal 3D printing accounts for a considerable proportion, and with the increasing maturity of metal 3D printing technology and the substantial reduction in cost, the application range, depth and scale are constantly breaking through. For example, in the field of aerospace, metal 3D printing has entered the stage of mass production from manufacturing test samples; in the field of dentistry, 3D printed metal crowns have become a routine means for dental technicians; in the field of orthopedics, 3D printed metal implants are being used on a large scale; in the field of molds, heat sinks and other fields, 3D printing is replacing traditional processes; and in the field of automobiles, there is great application potential to be tapped. Due to the particularity of 3D printing in the manufacturing process, the metal powder required is also different from the traditional powder metallurgy method.

[0003] At present, the mainstream 3D printing metal powder preparation methods include gas atomization (GA), plasma rotating electrode process (PREP), plasma atomization (PA) and plasma spheroidization (PS) and the like. When preparing refractory high-entropy alloys based on 3D printing technology, the initial metal materials mainly include single metal mixed powder and high-entropy alloy powder. Due to the differences in physical properties such as melting point, particle size and density of multiple single element powders, it is difficult to achieve uniform distribution of elements during the preparation process, which easily leads to composition segregation, unstable phase formation, particle inclusions and other problems, resulting in cracks, pores and other defects, which affects the preparation effect and alloy performance.

[0004] Plasma rotating electrode process (PREP) is a centrifugal atomization technology commonly used to produce high purity spherical titanium powder. The basic principle is that the metal or alloy is made into a consumable electrode, the end surface of the consumable electrode is melted into a liquid film by plasma arc, and the liquid film is spun out to form liquid droplets under the action of rotating centrifugal force. The molten droplets are further broken under the action of shear stress by friction with Ar gas in the atomization chamber. Subsequently, the droplets are rapidly cooled and solidified into spherical powder under the action of surface tension. PREP uses a consumable electrode, and the prepared powder has the advantages of clean surface, high sphericity, few associated particles, no hollow / satellite powder, good flowability, high purity, low oxygen content, narrow particle size distribution, etc. It is suitable for metal 3D printing. Moreover, this technology does not use high-speed inert gas to atomize the metal liquid stream, avoiding the formation of hollow powder and satellite powder particles caused by "umbrella effect". Therefore, compared with gas atomization, the PREP prepared powder has less hollow powder and satellite powder, and the sphericity of the PREP prepared powder can reach more than 99.5%. However, the particle size distribution of the powder prepared by this method is relatively narrow, mainly between 50-150 μm, and there are problems of large powder size and low fine powder yield. In addition, the PREP powder preparation process has high dependence on the quality of the rod. The refractory high-entropy alloy rod prepared by casting method cannot meet the performance requirements of the PREP powder preparation process for component uniformity and mechanical strength of the rod. Especially when the melting point difference between the alloy components is large, the cast rod is prone to component segregation, cracks, porosity and other defects, and cannot meet the requirements of high-speed rotating centrifugal powdering. SUMMARY

[0005] The present application aims to provide a preparation method of high melting point difference alloy powder for 3D printing to solve the problem that in the prior art, when preparing a refractory high-entropy alloy rod, the cast rod is prone to component segregation, cracks, porosity and other defects when the melting point difference between the alloy components is large.

[0006] To achieve the above-mentioned purpose, the present application adopts the following technical scheme: a preparation method of high melting point difference alloy powder for 3D printing, comprising the following steps:

[0007] Step one, powder metallurgy semi-alloying: using hot-pressing sintering or hot-isostatic-pressing sintering to alloyize the single-element with low mixing enthalpy;

[0008] Step two, plasma complete alloying: using plasma rotating electrode process to secondary alloyize the alloyed elements with high melting point single-element.

[0009] Preferably, as an improvement, in step one, the hot-pressing sintering conditions are as follows: hot-pressing sintering temperature is 0.5-0.7Tm, pressure is 10-100 MPa, and holding time is 20-40 min.

[0010] Preferably, as an improvement, in step one, the hot isostatic sintering temperature is 0.5-0.7Tm, the pressure is 10-100 MPa, and the holding time is 20-40 min.

[0011] Preferably, as an improvement, in step one, before hot pressing sintering or hot isostatic sintering, the elemental substance powders are mixed uniformly.

[0012] Preferably, as an improvement, the melting point difference of the elemental substance powders is ≥1000℃.

[0013] Preferably, as an improvement, in step two, the plasma rotating electrode atomization conditions are: the rod diameter is 50-80 mm, the rotating speed is 10000-32000 r / min, the plasma torch working current is 700-1600 A, the gas flow is 10-40 m 3 / h, and the rod-torch distance is 10-40 mm.

[0014] Preferably, as an improvement, in step two, the plasma rotating electrode atomization conditions are: the rod diameter is 60 mm, the rotating speed is 20000 r / min, the plasma torch working current is 1000 A, the gas flow is 20 m 3 / h, and the rod-torch distance is 30 mm.

[0015] The principle and beneficial effects of the technical solution are: in the technical solution, in view of the problem in the prior art that when preparing refractory high-entropy alloy rods, when the melting point difference between alloy components is large, low-melting-point elements are evaporated and lost during processing, thereby causing the cast rods to easily have component segregation, cracks, porosity and other defects, the preparation process of high-melting-point-difference alloy powder is optimized as a whole, a powder metallurgy-plasma step-by-step alloying method is used to prepare refractory high-entropy alloys with a high component melting point difference, the advantages of powder metallurgy and plasma rotating atomization are combined, the uniformity of the components is ensured by using powder metallurgy first, and then the sphericity of the metal powder is ensured by using plasma rotating atomization. During the development of the technical solution, to ensure the uniformity of the rods obtained by sintering, the sintering process is one of the key points and difficulties of the solution, through optimization of the sintering process and parameters, the sintering temperature can be ensured to be below the melting point of the alloy, thereby reducing energy consumption and reducing the loss of alloy elements.

[0016] The beneficial effects of the technical solution are:

[0017] (1) The technical solution solves the problem of high melting point difference. Low melting point elements and adjacent higher melting point elements are partially in-situ alloyed by powder metallurgy to form "intermediate alloy". In the process of plasma rotating electrode atomization, the intermediate alloy in the rod material and the adjacent higher melting point elements are alloyed under the action of plasma energy, avoiding the burning or evaporation of low melting point elements due to excessive temperature or energy. Through the first step of partial element in-situ alloying and the second step of micro-region gradient alloying, the uniform organization and controllable composition of refractory high-entropy alloy powder are realized.

[0018] (2) The technical solution has the advantage of high-quality powder forming. The plasma arc is used as a heat source to continuously melt the end face of the high-speed rotating metal rod. Under the action of centrifugal force, the molten metal droplets fly out and rapidly solidify under the cooling action of inert gas (argon or helium). The prepared powder is pure, has narrow particle size distribution, high sphericity, good flowability, low oxygen content, and rarely has hollow powder and satellite powder, which is an ideal powder for 3D printing. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 The preparation method flow chart of the high melting point difference alloy powder for 3D printing in the embodiment of the present application.

[0020] Figure 2 The Al 10 (Nb3TaTi3Zr) 90 Alloy stress-strain curve. DETAILED DESCRIPTION

[0021] The embodiments of the present application will be further described in detail below, but the embodiments of the present application are not limited thereto. If not specifically indicated, the technical means used in the following embodiments are conventional means known to those skilled in the art; the experimental methods used are conventional methods; the materials, reagents, etc. used can be obtained from commercial channels.

[0022] General description of the scheme:

[0023] As Figure 1 shown, a preparation method of high melting point difference alloy powder for 3D printing includes the following steps:

[0024] Step one, powder metallurgy semi-alloying: after mixing the elemental substance powders uniformly, the metal bond of the elemental substance is broken by means of hot-pressing sintering or hot-isostatic-pressing sintering of the powder metallurgy, the atoms between adjacent atoms diffuse mutually, the preferential alloying of the Al-Ti and Al-Zr alloys with lower mixing enthalpy is realized by adjusting the temperature and the pressure, and the high-melting-point Ta and Nb elements coexist with the generated alloys in the form of elemental powders. The hot-pressing sintering conditions are as follows: the hot-pressing sintering temperature is 0.5-0.7Tm, the pressure is 10-100 MPa, and the holding time is 20-40 min. The hot-isostatic-pressing sintering conditions are as follows: the hot-isostatic-pressing sintering temperature is 0.5-0.7Tm, the pressure is 10-100 MPa, and the holding time is 20-40 min.

[0025] Step two, plasma complete alloying: the secondary alloying of the Al-Ti and Al-Zr alloys and the high-melting-point Ta and Nb elements is carried out on the micro-regions of the cross section of the high-speed rotating rod under the action of the plasma energy, the completely alloyed molten droplets are formed, and the micro-region gradient alloying is realized layer by layer under the action of the high-speed rotating centrifugal force. The plasma rotating electrode atomization conditions are as follows: the rod diameter is 50-80 mm, the rotating speed is 10000-32000 r / min, the plasma torch working current is 700-1600 A, the gas flow is 10-40 m 3 / h, and the rod-torch distance is 10-40 mm.

[0026] Example 1

[0027] In this embodiment, the Al 10 (Nb3TaTi3Zr) 90 is taken as an example, and the test sample is prepared by the scheme of the present application, that is, powder sintering-plasma atomization, and the test sample is prepared by 3D printing. The specific preparation method is as follows:

[0028] Step one, powder metallurgy semi-alloying: after the elemental Al, Nb, Ta, Ti and Zr powders are mixed uniformly at a proportion of 8:27:9:27:9, the metal bond of the elemental substance is broken by means of hot-pressing sintering or hot-isostatic-pressing sintering of the powder metallurgy, the atoms between adjacent atoms diffuse mutually, the preferential alloying of the Al-Ti and Al-Zr alloys with lower mixing enthalpy is realized by adjusting the temperature and the pressure, and the high-melting-point Ta and Nb elements coexist with the generated alloys in the form of elemental powders. The sintering conditions are as follows: the sintering temperature is 1400℃, the sintering pressure is 20 Mpa, and the hot-pressing sintering time is 0.5 h.

[0029] Step two, plasma complete alloying: using the method of plasma rotating electrode atomization, under the action of plasma energy, the high-speed rotating bar section micro area, Al-Ti and Al-Zr alloy and high melting point Ta, Nb element secondary alloying, form complete alloying of molten droplets under the action of high-speed rotating centrifugal force, realize micro area gradient alloying layer by layer. The conditions of plasma rotating electrode atomization are: bar diameter 60mm, rotating speed 20000r / min, plasma torch working current 1000A, gas flow 20 cubic meters / h, bar-torch distance 30mm.

[0030] Example 2

[0031] The difference between this example and example 1 is that in this example, hot isostatic pressing sintering is used, and the sintering conditions are: sintering temperature is 1000℃, sintering pressure is 100Mpa, and sintering time is 20min. The conditions of plasma rotating electrode atomization are: bar diameter 80mm, rotating speed 10000r / min, plasma torch working current 700A, gas flow 40 cubic meters / h, bar-torch distance 10mm.

[0032] Example 3

[0033] The difference between this example and example 1 is that in this example, hot isostatic pressing sintering is used, and the sintering conditions are: sintering temperature is 1400℃, sintering pressure is 10Mpa, and sintering time is 40min. The conditions of plasma rotating electrode atomization are: bar diameter 50mm, rotating speed 32000r / min, plasma torch working current 1600A, gas flow 10 cubic meters / h, bar-torch distance 40mm.

[0034] Comparative example 1

[0035] The control sample is prepared by 3D printing of elemental powder mixing, and the specific preparation steps are as follows:

[0036] Step one, mix the Al, Nb, Ta, Ti, Zr elemental powders with a ratio of 8:27:9:27:9 uniformly by vacuum mixing method.

[0037] Step two, print the sample by using powder laying 3D printing technology (prior art).

[0038] Mechanical property test

[0039] The samples prepared by example 1 and comparative example 1 are tested for mechanical properties, and the test method refers to national standards GB / T7314-2017 "Metal material compression test method at room temperature" and GB / T 4340-2009 "Metal material Vickers hardness test", and each group is repeated three times. The test results are shown in Table 1 and Figure 2As shown in the results, the mechanical properties of the test sample are better than those of the control sample.

[0040] Table 1

[0041]

[0042] The above-mentioned are only embodiments of the present application, and the specific technical solutions and / or common knowledge of the scheme are not described in detail. It should be pointed out that for those skilled in the art, without departing from the technical solutions of the present application, a number of modifications and improvements can be made, which should also be considered as the protection scope of the present application, and these will not affect the effect and practicality of the patent. The protection scope claimed in the present application should be subject to the content of its claims, and the specific implementation mode and the like recorded in the specification can be used to explain the content of the claims.

Claims

1. A method for preparing high melting point alloy powder for 3D printing, characterized in that: The elements are Al, Nb, Ta, Ti, and Zr single substance powders, comprising the following steps: Step 1, powder metallurgy semi-alloying: After uniformly mixing the elemental powders, the metal bonds of the elemental elements are broken by hot pressing or hot isostatic pressing powder metallurgy, and adjacent atoms diffuse into each other. By regulating the temperature and pressure, preferential alloying of Al-Ti and Al-Zr alloys with low mixing enthalpy is achieved, and the high-melting-point Ta and Nb elements still coexist with the alloy generated by the reaction in the form of single powders; the melting point difference of the elemental powders is ≥1000°C, and the conditions for hot pressing sintering are: hot pressing sintering temperature of 0.5-0.7Tm, pressure of 10-100MPa, and holding time of 20-40min; the conditions for hot isostatic pressing sintering are: hot isostatic pressing sintering temperature of 0.5-0.7Tm, pressure of 10-100MPa, and holding time of 20-40min; Step 2: Plasma complete alloying: Using the plasma rotating electrode atomization method, under the action of plasma energy, Al-Ti and Al-Zr alloys are secondary alloyed with high-melting-point Ta and Nb elements in the micro-area of ​​the high-speed rotating bar cross-section, forming fully alloyed molten droplets. Under the action of high-speed rotating centrifugal force, micro-area gradient alloying is achieved layer by layer.

2. The method for preparing a high melting point alloy powder for 3D printing according to claim 1, characterized in that: In step 1, before hot pressing or hot isostatic pressing, the element powders are mixed uniformly.

3. The method for preparing a high melting point alloy powder for 3D printing according to claim 2, wherein: In step 2, the conditions for plasma rotating electrode atomization are: rod diameter 50~80mm, rotation speed 10000~32000 r / min, plasma torch operating current 700~1600A, gas flow rate 10~40m 3 / h, torch distance 10~40mm.

4. The method for preparing high melting point alloy powder for 3D printing according to claim 3, characterized in that: In step 2, the conditions for plasma rotating electrode atomization are: rod diameter 60 mm, rotation speed 20000 r / min, plasma torch operating current 1000 A, gas flow 20 m 3 / h, torch distance 30mm.

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