Metal Material Sintering Densification and Grain Size Control Method

Patent metadata

Field	Value
Publication number	US-2020198013-A1
Application number	US-202016793897-A
Country	US
Kind code	A1
Filing date	Feb 18, 2020
Priority date	Dec 24, 2018
Publication date	Jun 25, 2020
Grant date	—

Abstract

The present invention provides a method to achieve full densification and grain size control for sintering metal materials. First, raw material powder is deagglomerated to obtain deagglomerated powder with dispersion. The deagglomerated powder is granulated by spray granulation. The granulated particles are processed by high-pressure die pressing and cold isostatic pressing. The powder compact is sintered by two-step pressureless sintering. The first step is to heat up the powder compact to a higher temperature and hold for a short time to obtain 75-85% theoretical density; the second step is to cool down powder compact to a lower temperature and hold for a long time. The two-step sintering can decrease the sintering temperature, so that the powder compact can be densified at a lower temperature. Thus, the obtained refractory metal product is densified, with ultrafine grains, uniform grain size distribution, and outstanding mechanical properties.

First claim

What is the claim is:

1 . A metal material sintering densification and grain size control method, comprising the following steps:
first, processing raw material powder by deagglomeration to obtain deagglomerated powder with excellent dispersion; granulating the deagglomerated powder by spray granulation to improve powder flowability and density uniformity of powder compact and obtain granulated particles in an approximately spherical shape; processing the obtained granulated particles in an approximately spherical shape by high-pressure die pressing and cold isostatic pressing to obtain a powder compact; sintering the powder compact by two-step pressureless sintering, wherein the first step of sintering is to heat up the powder compact quickly to a specified temperature, hold the powder compact at the temperature for a short time and control the density at 75-85%, and the second step of sintering is to cool down the powder compact to a specified temperature and hold the powder compact at the temperature for a long time to further eliminate residual pores, so as to obtain high-density ultrafine grain metal.

2 . The method according to claim 1 , comprising the following steps:
S 1 : using metal powder as a raw material, and processing the raw material powder by deagglomeration with a high-speed helical blade mixer at 2,000-3,000 rpm blade rotation speed for 0.5-2 h, to obtain deagglomerated powder; S 2 : first, mixing a binder and deionized water homogeneously to prepare a solution A, in which the content of the binder is 5-15 wt. %; then, adding the deagglomerated raw material powder obtained in the step S 1 into the solution A and stirring the solution mechanically to a homogeneous state, so as to obtain a slurry; granulating the obtained slurry by spray granulation with a centrifugal atomizing drier at 8,000-15,000 r/min. rotation speed, 100-300 kPa atomizing pressure, and 90-150° C. drying temperature; loading the granulated powder into a tube heating oven and adding high-purity hydrogen into the tube heating oven for degreasing and reduction at 550-700° C. processing temperature, 5-10° C./min. heating rate, and holding for 60-120 min., to obtain granulated particles in an approximately spherical shape; S 3 : pressing the granulated powder by high-pressure die pressing at 700-1,000 MPa pressing pressure, and holding for 0.5-1.5 min. to obtain a preformed powder compact, loading the preformed powder compact into a jacketed mold and performing cold isostatic pressing at 200-280 MPa, and holding for 5-10 min., to obtain a powder compact; and S 4 : performing two-step sintering: first, in the first step of sintering, heating up the powder compact obtained in the step S 3 at a specified heating rate to a temperature T 1 and holding at the temperature T1, to obtain a one-step sintered compact; then, in the second step of sintering, cooling down the one-step sintered compact from the temperature T1 to a temperature T2 at a specified cooling rate, and holding at the temperature T2, so as to obtain a metal material with ultrafine grains finally, wherein, the temperature T2 is lower than the temperature T1 by 50-250° C., and the holding time for T1 in the first step is shorter than the holding time for T2 in the second step.

3 . The method according to claim 2 , wherein in the step S 1 , the metal powder comprises a refractory metal; the particle size of the deagglomerated powder is smaller than 0.5 μm.

4 . The method according to claim 2 , wherein in the step S 2 , the binder is polyvinyl alcohol, polyethylene glycol, stearic acid or paraffin; the solid content in the slurry is 60-85 wt. %.

5 . The method according to claim 2 , wherein in the step S 3 , the relative density of the powder compact is higher than 50%.

6 . The method according to claim 2 , wherein in the first step of sintering in the step S 4 , the powder compact is sintered in a hydrogen atmosphere by heating up the powder compact to the temperature T1 at 5° C./min heating rate, the temperature T1 is 1,200-1,500° C. and the holding time for T1 is 1-2 h.

7 . The method according to claim 2 , wherein in the second step of sintering in the step S 4 , the shielding gas atmosphere is hydrogen or argon gas atmosphere, the temperature is decreased from the temperature T1 to the temperature T2 at 15-25° C./min cooling rate, and the holding time for T2 is 10-60 h.

8 . The method according to claim 2 , wherein the density of the one-step sintered compact is 75-85%, the grain size is 0.5-1 μm, and the pore distribution is uniform.

9 . The method according to claim 2 , wherein the ratio of the obtained ultrafine grain metal grain size to the one-step sintered compact grain size is less than or equal to 1.5.

10 . The method according to claim 2 , wherein the density of the ultrafine grain metal is higher than 98%.

Assignees

• Univ Beijing Science & Technology

Inventors

• Zhang Lin
• Qu Xuanhui
• Li Xingyu
• Qin Mingli
• Dong Yanhao
• Li Ju
• Wang Guanghua
• Long Ying
• Zhong Wei

Classifications

• B22F1/05

  Metallic powder characterised by the size or surface area of the particles · CPC title

• B22F1/065

  Spherical particles · CPC title

• B22F1/142

  Thermal or thermo-mechanical treatment · CPC title

• B22F1/148

  Agglomerating · CPC title

• B22F1/10

  Metallic powder containing lubricating or binding agents; Metallic powder containing organic material · CPC title