Preparation And Properties Of Ta,Nb Alloyed Layer On ?-Ti Al By Plasma Surface Alloying Technology

Alloys based on?-TiAl have the advantages of low density,high melting point and good corrosion resistance.As one of the most potential alloys,it can be used in advanced aerospace and automobile engines.However,the defects such as poor high temperature oxidation resistance and wear resistance of?-TiAl limited its wider application.In this research,Ta and Nb alloyed layer were manufactured by double glow plasma surface alloying technology.That could effectively improve the surface performance of?-TiAl.The Ta alloyed layer had a thickness of 14?m,insist of deposite layer?10?m?and diffusion layer?4?m?.And the coating consisted of pure Ta.The Nb alloyed layer had a thickness of 12?m,insist of deposite layer?9?m?and diffusion layer?3?m?.And it consisted of pure Nb.Oxidation experiments were carried out for 100h to study the oxidation resistance of samples at700?,800?and 900?.In 700?and 800?,oxidation film of Ta alloyed layer was compact and well bonded to the?-TiAl.The oxidation product is maily Ta₂O₅,and Al₂O₃.In 900?,The oxidation product is Ta₂O₅,Al₂O₃ and TiO₂.The oxidation weight increase of Ta alloyed layer was minimum,which was 10.511mg/cm².That was about half of?-TiAl,which could effectively protected?-TiAl against oxidation.The oxidation product of Nb alloyed layer was Nb₂O₅,NbO₂,NbO and Al₂O₃ at700?.In 800?,the oxidation layer was continuous and compact.In 900?,The oxidation product is Nb₂O₅,NbO₂,NbO Al₂O₃ and TiO₂.The weight increase of Nb alloyed layer was 7.797mg/cm².The surface hardness of Ta alloyed layer was enhanced to 775.9HV_0.1,which was 2.4 times that of?-TiAl.And the surface hardness of Nb alloyed layer was 693.1HV_0.1.Throught the nano-indentation test,the Ta alloyed layer has high nano-hardness(DHT₁₁₅=740.146),the nano-hardness of Nb alloyed layer was DHT₁₁₅=740.146.Friction resistance experiments were carried out to study the wear resistance in different load,speed.and temperature.The results instructed that the wear mechanism of Ta alloyed layer at room temperature was adhesive wear,at high temperature was abrasive wear.The wear mechanism of Nb alloyed layer was abrasive wear.The wear volume and the wear rate of Ta and Nb alloyed layer were lower than?-TiAl substrate.Ta and Nb alloyed layer could effectively improve the wear resistance of?-TiAl.