NOVEL ALLOY MATERIAL WITH HIGH STRENGTH AND TOUGHNESS AND ITS FABRICATION METHOD OF SEMI-SOLID SINTERING

Abstract

The present invention belongs to the technical field of the preparation of alloy materials, and discloses a high strength and toughness alloy material, a method for preparing the alloy material by semi-solid sintering, and application thereof. The preparation method comprises the three steps of mixing powders, preparing alloy powders by high-energy ball milling, and semi-solid sintering of alloy powders, the key point lies in the two-step sintering, wherein the temperature is heated to less than the initial melting temperature of the lowest-temperature melting peak of the alloy powder, under the sintering pressure conditions, and carried out a sintering densification treatment; after pressure release, the temperature is heated to the sintering temperature Ts, and maintained at the same temperature, and a semi-solid processing is carried out, with a sintering temperature Ts: Tsthe initial melting temperature of the lowest-temperature melting peak of the alloy powder, Tsthe initial melting temperature of the highest-temperature melting peak of the alloy powder. By using the present method, a variety of high melting point alloy systems comprising such as Ti-based, Ni-based alloy system, and the like are carried out a semi-solid processing, so as to obtain an alloy material with a novel microstructure such as nanocrystalline, ultra-fine crystalline, fine crystalline or bimodal structure, and the like, and having excellent performances, which can be widely used in the fields of aerospace, military, instruments and the like.

Claims

1. A method for preparing a high strength and toughness alloy material by semi-solid sintering, characterized by particularly comprising the steps and process conditions as follows: step 1: mixing powders elementary substance powders are placed in proportion into a powder mixing machine according to the designed alloy composition, and mixed to uniform; step 2: preparing alloy powders by high-energy ball milling the homogenously mixed powders are placed into a ball mill to carry out high-energy ball milling, until forming alloy powders with nanocrystalline or amorphous structure; step 3: semi-solid sintering of alloy powders the alloy powders loaded in a sintering mould are consolidated by a powder metallurgy technology, the sintering temperature Ts is selected, the sintering is carried out by two-step process, wherein the temperature is heated to less than the initial melting temperature of the lowest-temperature melting peak of the alloy powder under sintering pressure conditions, and the alloy powders are carried out sintering densification treatment; after pressure release, the temperature is heated to the sintering temperature Ts, and maintained at the same temperature, and a semi-solid processing is carried out, with process conditions as follows: the sintering temperature Ts:Tsthe initial melting temperature of the lowest-temperature melting peak of the alloy powder Tsthe initial melting temperature of the highest-temperature melting peak of the alloy powder; the sintering pressure of 20500 MPa; cooling, so as to obtain a high strength and toughness alloy material.

2. A method for preparing a high strength and toughness alloy material by semi-solid sintering according to claim 1, characterized in that when the sintering mould used is a graphite mould, the sintering pressure in step 3 is 3050 MPa; and when the sintering mould used is a tungsten carbide mould, the sintering pressure in step 3 is 50500 MPa.

3. A method for preparing a high strength and toughness alloy material by semi-solid sintering according to claim 1, characterized in that the powder metallurgy technology in step 3 is any one of powder extrusion, powder hot pressing, powder rolling, powder forging and spark plasma sintering.

4. A method for preparing a high strength and toughness alloy material by semi-solid sintering according to claim 1, characterized in that the elementary substance powders in step 1 are the powders prepared by atomization process, electrolysis process or hydrogenation-dehydrogenation process.

5. A method for preparing a high strength and toughness alloy material by semi-solid sintering according to claim 1, characterized in that the high strength and toughness alloy material prepared in step 3 is carried out a post-heat treatment.

6. A method for preparing a high strength and toughness alloy material by semi-solid sintering according to claim 1, characterized in that the high strength and toughness alloy material prepared in step 3 is carried out an annealing treatment.

7. A high strength and toughness alloy material, characterized in that the high strength and toughness alloy material is obtained by the method for preparing a high strength and toughness alloy material by semi-solid sintering according to claim 1.

8. A high strength and toughness alloy material according to claim 7, characterized in that the high strength and toughness alloy material is Ti-based, Ni-based, Zr-based, Cu-based, Co-based, Nb-based, Fe-based, Mn-based, Mo-based or Ta-based alloy system.

9. A high strength and toughness alloy material according to claim 7, characterized in that the structure of the high strength and toughness alloy material comprises nanocrystalline, ultra-fine crystalline, fine crystalline or dual-scale structure.

10. (canceled)

Description

BRIEF DESCRIPTION OF THE FIGURES

[0040] FIG. 1 is a differential scanning calorimetry curve of the high-energy ball milled alloy powders prepared in example 1.

[0041] FIG. 2 is a scanning electron microscope image of a high strength and toughness titanium alloy with a bimodal structure prepared in example 1.

[0042] FIG. 3 is a transmission electron microscopy image of a high strength and toughness titanium alloy with a bimodal structure prepared in example 1.

[0043] FIG. 4 is a stress-strain curve of a high strength and toughness titanium alloy with a bimodal structure prepared in example 1.

DETAILED DESCRIPTION

[0044] The present invention is further described in details below in combination with the examples and drawings, but the embodiments of the present invention are not limited thereto.

EXAMPLE 1

Preparation of a High Strength and Toughness Titanium Alloy with a Bimodal Structure

[0045] The method for preparing bimodal titanium alloy by semi-solid sintering comprises the steps of:

[0046] Step 1: Mixing Powders

[0047] Ti.sub.62Nb.sub.12.2Fe.sub.13.6Co.sub.6.4Al.sub.5.8 alloy system is selected, the powders are formulated according to the mass ratio of the selected alloy system, the elementary substance powders with an average particle size of 75 m prepared with atomization process are selected in the present example, but the powder raw materials of the present invention are not limited thereto, the elementary powders may also be the powders prepared by other processes such as electrolysis process, and the like, and there are no specific limitations on the particle size, both fine powder and relatively large particle size powder are available. The abovementioned elementary powders are mixed to uniform in a powder mixing machine. The preferred alloy system in the present example is Ti-based alloy system, but the alloy systems selected in the present invention are not limited thereto, and Ni-based, Zr-based, Cu-based, Co-based, Nb-based, Fe-based, Mn-based, Mo-based, Ta-based alloy system, and the like can also be selected.

[0048] Step 2: Preparation of Alloy Powders by High-Energy Ball Milling

[0049] The homogenously mixed powders are placed in a planetary ball mill (QM-2SP20) under argon protection to carry out high-energy ball milling, wherein the barrel body and ball milling medium, such as the grinding ball material, etc., are all made of stainless steel, the grinding balls have diameters of 15, 10, and 6 mm respectively, with a weight ratio of 1:3:1. The high energy ball milling has process parameters as follows: ball-milling barrel is filled with high purity argon (99.999%, 0.5 MPa) for protection; ratio of ball to powder is 8:1, rotating speed is 2 s.sup.1, about 3 g powders are taken every 10 h in a glove box under argon atmosphere to carry out the tests, such as X-ray diffraction (XRD), differential scanning calorimetry (DSC) analysis and the like, until after the ball milling time is 70 hours, the XRD detection shows that the structure of the powders which are ball milled for 70 h is about 90% by volume of -Ti nanocrystalline surrounded by amorphous phase, the DSC curve in FIG. 1 shows that the powders which are ball-milled for 70 hours have two melting peaks with endothermic peak temperatures of 1125 and 1180 respectively, in the heating process.

[0050] Step 3: Semi-Solid Sintering of Alloy Powders

[0051] 20 g alloy powders prepared in step 2 are taken and put into a graphite sintering mould with a diameter of 120 mm, the alloy powders are pre-pressed to 50 MPa via positive and negative graphite electrodes, and vacuumized to 10.sup.2 Pa, then filled with high-purity argon gas for protection; and the rapid sintering is carried out by pulse current, with the process conditions as follows:

[0052] the sintering device: Dr. Sintering SPS-825 spark plasma sintering system

[0053] sintering mode: pulse current

[0054] a duty ratio of the pulse current: 12:2

[0055] a sintering temperature Ts: 1100 C.

[0056] a sintering pressure: 50 MPa

[0057] a sintering time: the temperature is heated to 1050 C. under 50 MPa pressure in 10 minutes, the temperature is heated to 1100 C. under the pressure release condition in 1 minutes and maintained at the same temperature for 5 minutes.

[0058] After sintering, a high strength and toughness titanium alloy material with a bimodal structure having a diameter of 20 mm (if the mould size is larger, the size of the prepared alloy material is also larger), and a density of 5.6 g/cm.sup.3 is obtained. The scanning electron microscope image in FIG. 2, shows that the microstructure comprises the micron-sized (CoFe)Ti.sub.2 phase region and the micron-sized mixed matrix. The transmission electron microscope image in FIG. 3 shows that the micron-sized mixed matrix is consisted of nano-sized TiFe surrounded by nano-sized -Ti, therefore, the alloy has a bimodal structure of micron crystalline (CoFe)Ti.sub.2 and nanocrystalline -Ti and TiFe; the stress-strain curve in FIG. 4 shows that the compressive yield strength and fracture strain of the titanium alloy material with the bimodal structure are 1790 MPa and 19% respectively.

[0059] The abovementioned examples are the preferred embodiments of the present invention, but the embodiments of the present invention are not limited thereto, any other changes, modifications, alternatives, combination, simplification, which are all the equivalent replacement modes, made without departing from the spirit and principles of the invention, should be embraced within the scope of the present invention.