• The tungsten heavy alloys is treated by solid surface carburization method. The results show that the two carburization layers can be obtained at 950℃ for 5 h in solid carburetant.（be composed of Activated carbon and carbonate） Hardness of HV388 to HV525 can improve surface hardness effectively.  ^[1]

                                          Table 1. The hardness of sample

• The even and compact Ir coating was deposited on Ta-10 W alloy substrate by arc ion plating. The oxidation resistance and thermal shock resistance of Ir coating at high temperature was studied. Results show that the Ir coating can keep protecting Ta-10 W alloy substrateat at 800 ℃ and 1 100 ℃. The light oxidation occurs and bowrn oxides appear on surface after 20 h. At 1 900 ℃, the oxidation resistance of life reaches 10 hours and above. Under temperature change from room temperature to (1 900± 50) ℃, the times of the thermal shock is 1 000 over cycles.^[2]

   

• Electroless Ni plating was carried out on the sur face of tungsten alloy by using nickel sulfate as main salt, sodium hypophosphite as reducer and sodium citrate as main complexing agent. The results of orthogonal test reveal obvious effect of pH value on deposition rate , and the optimal process conditions were obtained in combination with practical production as follows: 30 g/L of nickel sulfate, 25 g/L of sodium hypophosphite, 20 g/L of sodium citrate, tempe rature of 85 ℃and pH value of 4. 0. It is demonstrated that the surface of the plated part after heat treatment at 700 ℃has no grain boundary and evident defects , and has the most uniform and densest structure. The immension test shows that the plated sample after heat treatment has the greatest corrosion resistance, followed by the plated sample. The process has advantages of stable bath and deposit with good adhesion.^[3]

                                       Table 2. The mass changes of samples in three kinds of media

   

• Nanocrystalline layer of a certain thickness has been prepared on the surface of tungsten copper alloy by a supersonic fine particles bombarding(SFPB) method. Micro-hardnesses of the sample's nano layer significantly increase by about40%~60%while the conductivity decreases slightly. The formation of the arc can be inhibited and extinguished rapidly for achieving the arc erosion resistance.^[4]

  

  Figure 1. Surface hardness testing curve of Cu W70 after SFPB:(a) microindentation of longitudinal section and (b) curve of hardness with different depths 

[1].Wang ling, li shukui, song xiugang. Surface carburizing of high-density tungsten alloys(2007) . Acta ordnance sinica,(06):730-732.

[2]. Li haiqing, yan xubo, xu fangtao, Chen daoyong, zhang xuhu. Preparation and high-temperature oxidation performance of iridium coating on tantalum-tungsten alloy surface(2008) . Aerospace materials technology, 48(06):40-44.

[3].Zhang ying, wang xiaoxuan, li tao, han zhenhua. Electroless nickel plating on tungsten alloy surface(2006) . Electroplating and finishing,(03):8-12.

[4].Liu bing, Chen wenge, zhang zhijun. Nano-surface and performance analysis of tungsten-copper alloy(2015) . Rare metal materials and engineering,44(12):3188-3191.

[5] Meiling Zhou, Tieyong Zhou. (1984, Dec). Study on Deformation and Microstructure of Tungsten in Rotary Forging Process. Journal CSIMM, 4, (2), 11-17

[6] Shuisheng Xie, Zutang Wang. (1990, June). Numerical Simulation and Experimental Study on New Process of Tungsten Rod Processing. Beijing Nonferrous Metals Research Institute & Tsinghua University.

[7] Peiqing Feng. (1982, June). Defect Analysis of Twisting and Forging of Tungsten. Zhejiang Hengshan Iron and Steel Plant.

[8] Zhihong Zhan. (1986). Trends in the development of tungsten processing technology. Changsha Nonferrous Metallurgy Design and Research institute

[9] Xiaowei Yang, Gaolin Li, Fei Wang, Yu Wu. (2014). Research on Rolling Process of Large Size Tungsten Plate. Xi'an Noble Rare Metal Materials Co., Ltd.

[10] Jie Ma, Jinghua Chang, Congzeng Wang, Luyan Wang. (2017, Dec). Study on chemical vapor deposition tungsten ingot process. China Surface Engineering, 20, (6), 19-24