To Develop Mo-W-Si-N Coating On The Molybdenum Materials Based On The Heat Matching

Molybdenum(Mo) and its metal products are extensively used in the aerospace industry 、 high temperature furnaces industry 、 glass manufacturing industry 、electronic elements industry and so on due to its high melting point(2617 °C)、 high abrasive resistance、corrosion resistance、good thermal conductivity and electrical conductivity. While, the characteristics formed volatile MO3 occured above 600 °C in air restricts its potentialities for widespread. Therefore, the high temperature heating element made by molybdenum can only be used in the vacuum or protective atmosphere. Therefore, it is a great significance to study and improve the high temperature oxidation resistance performance of molybdenum. Surface protected coating method not only can maintain the performance of molybdenum and its alloys,but also improve the high temperature oxidation resistance.Ihe surface high temperature oxidation resistance coating system on molybdenum and its alloy contains: heat resistant alloy coating 、 oxide coating 、aluminide coating、 silicide coating. Considering the oxidation resistance and high temperature structural strength, molybdenum disilicide(Mo Si2) coating system has become the focus for improving the high temperature oxidation resistance of molybdenum and its alloys. Studies have shown that Mo Si2 coating can improve the high temperature oxidation resistance of molybdenum and its alloys, the work temperature and service life strongly depends on the spread of the Si, the work temperature and service life have been improved by alloying W on Mo Si2 coating system. The matching of Mo Si2 coating system and the thermal expansion coefficient of molybdenum substrate(8.5×10-6/ ℃ and 5.8×10-6/ ℃, respectively) isalso the key factors for affecting the service life of the coating, N element can change the microstructure of coating material and improve the heat matching of substrate and coating; But the thermal matching between molybdenum and Mo Si2 coating alloyed W need further research.The paper is based on the research that W alloying Mo Si2 coating can improve the high temperature oxidation resistance of the coating, preparing Mo-W-Si-N coating materials with different contents of WSi2 and Si3N4 by vacuum sintering process and the spark plasma sintering through the determination of different ratio of thermal expansion coefficient of composite materials, and exploring the thermal expansion coefficient matching mechanism of molybdenum substrate and coating material with different contents of WSi2 and Si3N4. Obtained the following results:1. The best preparation technology for Mo-W-Si-N coating material by vacuum sintering: milling time: 4h, binder content: 4%, pressure: 180 MPa, the sintering temperature: 1500℃, heat preservation: 2h. The best preparation technology for spark plasma sintering process: the sintering temperature: 1550 ℃, pressure preservation: 10 min, axlepressure: 25 MPa.2. Adding a small amount of WSi2/Si3N4 can reduce the thermal expansion coefficient of Mo-W-Si-N coating material. The thermal expansion coefficient of the coating material close to the pure molybdenum when the coating material with WSi2 volume fraction of 6% and Si3N4 volume fraction of 30%.3. Based on the influence mechanism of Si3N4/WSi2 to the thermal expansion coefficient of composite material, prepare molybdenum matrix composites with WSi2 of 6vol.% and Si3N4 of 4vol.%, 20 vol.%, 30 vol.%, 40 vol.%, and conducte the thermal shock test at room temperature to 1100℃with the molybdenum matrix composites. Tests show that the molybdenum matrix coating material with 6vol.%WSi2 and 30 vol.% Si3N4 has the best matching with pure molybdenum as the coating material has the best thermal shock performance.