Study On Processes And Performance Of Plasma Ni-Cr Alloying On TiAl Surface

TiAl alloys are one of the most promising high temperature structural materials due to their advantages,such as low density,high melting point and good mechanical property.However,their insufficient wear resistance and oxidation resistance become the major obstacles for their wide applications.This paper studied plasma Ni-Cr alloying on TiAl surface by double glow discharge plasma surface alloying process.The effects of each parameter were researched and the typical parameter was obtained.The component,microstructure and microhardness in the alloying layer under the typical processing condition were tested.The behaviors of high-temperature oxidation resistance and wear resistance under the typical processing condition were analysed.The research results show that:1.The weight gain of the Ni-Cr alloying samples in air at 650℃for 100h is more than the weight gain of the TiAl substrate.The oxide film consists of Al₂O₃,TiO₂ and NiCr₂O₄.The oxide film is dense and has oxidation resistance.2.The oxidation rate of the Ni-Cr alloying samples in air at 900℃is obvious slower than the oxidation rate of the TiAl substrate.The TiAl substrate and the Ni-Cr alloying samples for different oxidation time 5h, 20h,100h were tested.The tests indicate that:the oxide film of TiAl mainly consists of TiO₂ and Al₂O₃,but the content of Al₂O₃ is few for 5h, 20h.100h.The structure of the oxide film is loose and the oxidation resistance is bad.But the oxide film of the Ni-Cr alloying samples consists of TiO₂,A1203,NiCr₂O₄,Cr₂O₃ and NiO for 5h,20h.100h. Al₂O₃ and NiCr₂O₄ and Cr₂O₃ have good oxidation resistance.The oxide film is dense and has strong cohesion with the substrate.3.The oxidation rate of the Ni-Cr alloying samples in air at 1000℃is still slower than the oxidation rate of the TiAl substrate.But the oxidation resistance of the Ni-Cr alloying samples at 1000℃is insufficient by observing the surface morphology and morphology of cross-section.4.The average friction coefficient and wear volume and specific wear rate and wear width of the Ni-Cr alloying samples are smaller than TiAl substrate's in high-temperature wear test.Plasma Ni-Cr alloying on TiAl surface can reduce the friction coefficient and improve the wear resistance.5.The friction coefficient of the Ni-Cr alloying samples is little more than TiAl substrate's in fretting wear.But the wear volume and wear range of the Ni-Cr alloying samples are smaller than TiAl substrate's. Plasma Ni-Cr alloying on TiAl surface can not reduce the friction coefficient,but improve the wear resistance.