HIGH-HARDNESS COMPOSITE OXIDE DISPERSION-STRENGTHENED TUNGSTEN ALLOY AND PREPARATION METHOD THEREOF

Abstract

A high-hardness composite oxide dispersion-strengthened tungsten alloy and a preparation method thereof are disclosed. The high-hardness composite oxide dispersion-strengthened tungsten alloy consists essentially of a tungsten phase, and nano-scale Y.sub.2O.sub.3 and ZrO.sub.2 particles dispersed in the tungsten phase, wherein there is a Y—Zr—O ternary phase structure at a coherent/semi-coherent interface.

Claims

1. A high-hardness composite oxide dispersion-strengthened tungsten alloy, consisting essentially of a tungsten phase, and nano-scale Y.sub.2O.sub.3 and ZrO.sub.2 particles dispersed in the tungsten phase, wherein there is a Y—Zr—O ternary phase structure at a coherent/semi-coherent interface in the high-hardness composite oxide dispersion-strengthened tungsten alloy.

2. The high-hardness composite oxide dispersion-strengthened tungsten alloy as claimed in claim 1, consisting essentially of 0.25% of Y.sub.2O.sub.3, 0.1% of ZrO.sub.2, and a balance of tungsten.

3. A method for preparing the high-hardness composite oxide dispersion-strengthened tungsten alloy as claimed in claim 1, comprising preparation of a composite powder dissolving yttrium nitrate, zirconium nitrate, and surfactant triethanolamine, with a certain proportion, in an appropriate amount of deionized water respectively, and stirring to be dispersed uniformly respectively, to obtain an aqueous yttrium nitrate solution, an aqueous zirconium nitrate solution, and an aqueous triethanolamine solution respectively; mixing the aqueous yttrium nitrate solution, the aqueous zirconium nitrate solution, and the aqueous triethanolamine solution, to obtain a mixed solution; heating while stirring the mixed solution to 100° C., pouring a solution of ammonium metatungstate dissolved in deionized water thereto, and continuing heating while stirring until that the resulting mixture becomes transparent; adding a solution of an appropriate amount of oxalic acid thereto, stirring the resulting solution at 140° C. until that the solution is completely volatilized, to obtain a precipitated block, i.e. a precursor; drying the precursor, and grinding the dried precursor, to obtain a precursor powder; and reducing the precursor powder in a hydrogen atmosphere, to obtain a W—Y.sub.2O.sub.3—ZrO.sub.2 composite powder; sintering of the W—Y.sub.2O.sub.3—ZrO.sub.2 composite powder loading the W—Y.sub.2O.sub.3—ZrO.sub.2 composite powder into a graphite mold and compacting, putting the loaded graphite mold into a spark plasma sintering furnace, applying a pre-pressure to the W—Y.sub.2O.sub.3—ZrO.sub.2 composite powder, vacuuming the spark plasma sintering furnace, and subjecting the W—Y.sub.2O.sub.3—ZrO.sub.2 composite powder to a two-stage heat-preservation sintering; and cooling the sintered W—Y.sub.2O.sub.3—ZrO.sub.2 composite powder in the spark plasma sintering furnace to ambient temperature, to obtain a block of the W—Y.sub.2O.sub.3—ZrO.sub.2 alloy.

4. The method as claimed in claim 3, wherein reducing the precursor powder in a hydrogen atmosphere comprises subjecting the precursor powder to a two-stage pyrolysis, which comprises first heating the precursor powder to 500-600° C., and maintaining at the temperature for 60-80 minutes, and further heating to 800-900° C., and maintaining at the temperature for 100-120 minutes.

5. The method as claimed in claim 3, wherein the two-stage heat-preservation sintering comprises a first stage heat-preservation sintering, which is performed at 750-850° C. for 5-10 minutes; and a second stage heat-preservation sintering, which is performed at 1500-1600° C. for 1-3 minutes.

6. The method as claimed in claim 3, wherein before the first stage heat-preservation sintering, the pre-pressure is not more than 14 MPa, and when the first stage heat-preservation sintering starts, the pre-pressure starts increasing, and after the first stage heat-preservation sintering, the pre-pressure increases up to 50-100 MPa at a constant rate.

7. The method as claimed in claim 5, wherein before the first stage heat-preservation sintering, the pre-pressure is not more than 14 MPa, and when the first stage heat-preservation sintering starts, the pre-pressure starts increasing, and after the first stage heat-preservation sintering, the pre-pressure increases up to 50-100 MPa at a constant rate.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0027] FIG. 1 shows a scanning electron microscope image of W—Y.sub.2O.sub.3—ZrO.sub.2 composite powder after reducing. It can be seen from FIG. 1 that among the W—Y.sub.2O.sub.3—ZrO.sub.2 composite precursor powder prepared by the method according to the present disclosure, larger particles have a particle size of about 200 nm, and smaller particles have a particle size of about 50 nm. The increase in the surface area of the powder is conducive to improving the sintering activity.

[0028] FIG. 2 shows a scanning electron microscope image of the fracture surface of the W—Y.sub.2O.sub.3—ZrO.sub.2 composite material. It can be seen from FIG. 2 that the grains have a size of about 1.5 μm, and that there are many fine particles and pits after pulling out, indicating that the finely dispersed second phase is evenly distributed in the tungsten matrix. In the present disclosure, the size of the grain (namely grain size) is measured according to GBT6394-2017.

[0029] FIG. 3 shows a transmission electron microscope image of a block of tungsten-based composite material after sintering. It can be seen from FIG. 3 that second-phase particles on the grain boundaries have a larger particle size of about 200 nm, while intracrystalline second-phase particles have a smaller particle size of about 50 nm.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Example 1

[0030] In this example, the composite oxide dispersion-strengthened tungsten alloy was prepared according to the following procedure:

[0031] Step 1, Preparation of a Composite Powder

[0032] The mass ratio of reaction raw materials was calculated by converting the mass percentages of alloy components in the alloy composition, and a precursor powder was prepared by a wet chemical method, in which nitrate(s) containing Y.sup.3+ and Zr.sup.4+ was added to the ammonium metatungstate solution. Yttrium nitrate (Y(NO.sub.3).sub.3.6H.sub.2O, from Aladdin, with a purity of not less than 99.9%), zirconium nitrate (Zr(NO.sub.3).sub.4.5H.sub.2O, from Aladdin), and surfactant triethanolamine (C.sub.16H.sub.22N.sub.4O.sub.3, with a purity of not less than 99%) were dissolved in an appropriate amount of deionized water respectively, and they were stirred for a period of time respectively, obtaining an aqueous yttrium nitrate solution, an aqueous zirconium nitrate solution, and an aqueous triethanolamine solution respectively. The three kinds of solutions were mixed, obtaining a mixed solution. The mixed solution was heated while stirring to 100° C., and a solution of ammonium metatungstate (AMT, from Aladdin, with a purity of 99.95%) dissolved in an appropriate amount of deionized water was poured thereto, and the heating was continued while stirring until that the resulting mixture becomes transparent. Finally a solution with an appropriate amount of oxalic acid (C.sub.2H.sub.2O.sub.4, analytically pure) was added thereto, and the resulting solution was stirred at 140° C. until that the solution was completely volatilized, obtaining a precipitated block, i.e. a precursor. The precursor was dried, and the dried precursor was ground, obtaining a precursor powder. The precursor powder was reduced in a hydrogen atmosphere, obtaining a composite powder of W—Y.sub.2O.sub.3—ZrO.sub.2, in which the precursor powder was poured uniformly into a combustion boat, and the combustion boat was placed in a tube furnace, and the precursor powder was reduced by a two-stage pyrolysis in a hydrogen atmosphere with a hydrogen purity greater than or equal to 99.999%.

[0033] In this step, yttrium nitrate, zirconium nitrate, triethanolamine, and oxalic acid were added in an amount of 0.6%, 0.3%, 6%, and 38.5%, respectively, based on the mass of ammonium metatungstate; and

[0034] the process that the precursor powder was reduced in a hydrogen atmosphere was performed by a two-stage pyrolysis, i.e. first heating to 600° C., and maintaining at the temperature for 60 minutes; and further heating to 800° C., and maintaining at the temperature for 120 minutes.

[0035] Step 2, Sintering of the W—Y.sub.2O.sub.3—ZrO.sub.2 composite powder

[0036] The W—Y.sub.2O.sub.3—ZrO.sub.2 composite powder prepared in step 1 was loaded into a graphite mold and compacted. The loaded graphite mold was put into a spark plasma sintering furnace. A pre-pressure was applied to the W—Y.sub.2O.sub.3—ZrO.sub.2 composite powder. Then the spark plasma sintering furnace was vacuumed, and the W—Y.sub.2O.sub.3—ZrO.sub.2 composite powder was subjected to a two-stage heat-preservation sintering. After starting the sintering, the W—Y.sub.2O.sub.3—ZrO.sub.2 composite powder was heated to 800° C., and maintained at the temperature for 5 minutes; then the W—Y.sub.2O.sub.3—ZrO.sub.2 composite powder was heated to 1600° C., and maintained at the temperature for 60 seconds. The sintered W—Y.sub.2O.sub.3—ZrO.sub.2 composite powder was cooled in the spark plasma sintering furnace to ambient temperature, obtaining a block of the W—Y.sub.2O.sub.3—ZrO.sub.2 alloy. In this step, the pre-pressure was 14 MPa when the temperature was not higher than 800° C., and increased to 75 MPa at a constant rate during the process of maintaining at 800° C. for 5 minutes; the block obtained after cooling was a W—Y.sub.2O.sub.3—ZrO.sub.2 alloy with a grain size of 1.5 μm, a relative density of 98.7%, and a hardness of 703Hv.sub.0.2.

Example 2

[0037] In this example, the composite oxide dispersion-strengthened tungsten alloy was prepared according to the following procedure:

[0038] Step 1, Preparation of a Composite Powder

[0039] The mass ratio of reaction raw materials was calculated by converting the mass percentages of alloy components in the alloy composition, and a precursor powder was prepared by a wet chemical method, in which nitrate(s) containing Y.sup.3+ and Zr.sup.4+ was added to the ammonium metatungstate solution. Yttrium nitrate (Y(NO.sub.3).sub.3.6H.sub.2O, from Aladdin, with a purity of not less than 99.9%), zirconium nitrate (Zr(NO.sub.3).sub.4.5H.sub.2O, from Aladdin), and surfactant triethanolamine (C.sub.16H.sub.22N.sub.4O.sub.3, with a purity of not less than 99%) were dissolved in an appropriate amount of deionized water respectively, and they were stirred for a period of time respectively, obtaining an aqueous yttrium nitrate solution, an aqueous zirconium nitrate solution, and an aqueous triethanolamine solution respectively. Three kinds of solutions were mixed, obtaining a mixed solution. The mixed solution was heated while stirring to 100° C., and a solution of ammonium metatungstate (AMT, from Aladdin, with a purity of 99.95%) dissolved in an appropriate amount of deionized water was poured thereto, and the heating was continued while stirring until that the resulting mixture becomes transparent. Finally a solution with an appropriate amount of oxalic acid (C.sub.2H.sub.2O.sub.4, analytically pure) was added thereto, and the resulting solution was stirred at 140° C. until that the solution was completely volatilized, obtaining a precipitated block, i.e. a precursor. The precursor was dried, and the dried precursor was ground, obtaining a precursor powder. The precursor powder was reduced in a hydrogen atmosphere, obtaining a composite powder of W—Y.sub.2O.sub.3—ZrO.sub.2, in which the precursor powder was poured uniformly into a combustion boat, and the combustion boat was placed in a tube furnace, and the precursor powder was reduced by a two-stage pyrolysis in a hydrogen atmosphere with a hydrogen purity greater than or equal to 99.999%.

[0040] In this step, yttrium nitrate, zirconium nitrate, triethanolamine, and oxalic acid were added in an amount of 0.6%, 0.3%, 6%, and 38.5%, respectively, based on the mass of ammonium metatungstate; and

[0041] the reduction was performed by a two-stage pyrolysis, i.e. first heating to 550° C., and maintaining at the temperature for 70 minutes; and further heating to 850° C., and maintaining at the temperature for 110 minutes.

[0042] Step 2, sintering of the W—Y.sub.2O.sub.3—ZrO.sub.2 composite powder

[0043] The W—Y.sub.2O.sub.3—ZrO.sub.2 composite powder prepared in step 1 was loaded into a graphite mold and compacted. The loaded graphite mold was put into a spark plasma sintering furnace. A pre-pressure was applied to the W—Y.sub.2O.sub.3—ZrO.sub.2 composite powder. Then the spark plasma sintering furnace was vacuumed, and the W—Y.sub.2O.sub.3—ZrO.sub.2 composite powder was subjected to a two-stage heat-preservation sintering. After starting the sintering, the W—Y.sub.2O.sub.3—ZrO.sub.2 composite powder was heated to 750° C., and maintained at the temperature for 10 minutes; then the W—Y.sub.2O.sub.3—ZrO.sub.2 composite powder was heated to 1500° C., and maintained at the temperature for 3 minutes. The sintered W—Y.sub.2O.sub.3—ZrO.sub.2 composite powder was cooled in the spark plasma sintering furnace to ambient temperature, obtaining a block of the W—Y.sub.2O.sub.3—ZrO.sub.2 alloy. In this step, the pre-pressure was 14 MPa when the temperature was not higher than 750° C., and increased to 100 MPa at a constant rate during the process of maintaining at 750° C. for 10 minutes; the block obtained after cooling was a W—Y.sub.2O.sub.3—ZrO.sub.2 alloy with a grain size of 2 μm, a relative density of 98.5%, and a hardness of 691Hv.sub.0.2.

Example 3

[0044] In this example, the composite oxide dispersion-strengthened tungsten alloy was prepared according to the following procedure:

[0045] Step 1, Preparation of a Composite Powder

[0046] The mass ratio of reaction raw materials was calculated by converting the mass percentages of alloy components in the alloy composition, and a precursor powder was prepared by a wet chemical method, in which nitrate(s) containing Y.sup.3+ and Zr.sup.4+ was added to the ammonium metatungstate solution. Yttrium nitrate (Y(NO.sub.3).sub.3.6H.sub.2O, from Aladdin, with a purity of not less than 99.9%), zirconium nitrate (Zr(NO.sub.3).sub.4.5H.sub.2O, from Aladdin), and surfactant triethanolamine (C.sub.16H.sub.22N.sub.4O.sub.3, with a purity of not less than 99%) were dissolved in an appropriate amount of deionized water respectively, and they were stirred for a period of time respectively, obtaining an aqueous yttrium nitrate solution, an aqueous zirconium nitrate solution, and an aqueous triethanolamine solution respectively. Three kinds of solutions were mixed, obtaining a mixed solution. The mixed solution was heated while stirring to 100° C., and a solution of ammonium metatungstate (AMT, from Aladdin, with a purity of 99.95%) dissolved in an appropriate amount of deionized water was poured thereto, and the heating was continued while stirring until that the resulting mixture becomes transparent. Finally a solution with an appropriate amount of oxalic acid (C.sub.2H.sub.2O.sub.4, analytically pure) was added thereto, and the resulting solution was stirred at 140° C. until that the solution was completely volatilized, obtaining a precipitated block, i.e. a precursor. The precursor was dried, and the dried precursor was ground, obtaining a precursor powder. The precursor powder was reduced in a hydrogen atmosphere, obtaining a composite powder of W—Y.sub.2O.sub.3—ZrO.sub.2, in which the precursor powder was poured uniformly into a combustion boat, and the combustion boat was placed in a tube furnace, and the precursor powder was reduced by a two-stage pyrolysis in a hydrogen atmosphere with a hydrogen purity greater than or equal to 99.999%.

[0047] In this step, yttrium nitrate, zirconium nitrate, triethanolamine, and oxalic acid were added in an amount of 0.6%, 0.3%, 6%, and 38.5%, respectively, based on the mass of ammonium metatungstate; and

[0048] the reduction was performed by a two-stage pyrolysis, i.e. first heating to 500° C., and maintaining at the temperature for 80 minutes; and further heating to 900° C., and maintaining at the temperature for 100 minutes.

[0049] Step 2, Sintering of the W—Y.sub.2O.sub.3—ZrO.sub.2 composite powder

[0050] the W—Y.sub.2O.sub.3—ZrO.sub.2 composite powder prepared in step 1 was loaded into a graphite mold and compacted. The loaded graphite mold was put into a spark plasma sintering furnace. A pre-pressure was applied to the W—Y.sub.2O.sub.3—ZrO.sub.2 composite powder. Then the spark plasma sintering furnace was vacuumed, and the W—Y.sub.2O.sub.3—ZrO.sub.2 composite powder was subjected to a two-stage heat-preservation sintering. After starting the sintering, the W—Y.sub.2O.sub.3—ZrO.sub.2 composite powder was heated to 850° C., and maintained at the temperature for 8 minutes; then the W—Y.sub.2O.sub.3—ZrO.sub.2 composite powder was heated to 1550° C., and maintained at the temperature for 2 minutes. The sintered W—Y.sub.2O.sub.3—ZrO.sub.2 composite powder was cooled in the spark plasma sintering furnace to ambient temperature, obtaining a block of the W—Y.sub.2O.sub.3—ZrO.sub.2 alloy. In this step, the pre-pressure was 14 MPa when the temperature was not higher than 850° C., and increased to 50 MPa at a constant rate during the process of maintaining at 850° C. for 8 minutes; the block obtained after cooling was a W—Y.sub.2O.sub.3—ZrO.sub.2 alloy with a grain size of 2 μm, a relative density of 98.6%, and a hardness of 695Hv.sub.0.2.