Microstructureand High Temperature Oxidation Resistance Of Micro-alloying Tial Based Alloy With High Nb Content

The as-cast and heat treated microstructure of B, Hf, Y micro-alloyed TiAl based alloywith high Nb content was investigated. The results show that the as-cast microstructure ofTi-45Al-8Nb alloy is refined greatly alloyed by B、Y and the most obvious refined effectowned by adding B,Y and Hf. However,the part element enrichment is serious by adding anexcess of Hf. Both of Ti-45Al-8Nb and Ti-45Al-8Nb-0.2B-0.3Y alloys get the nearlylamellar microstructure heated by the process of1310℃/1h+900℃/30min/AC,while thealloys adding Hf get the microstructure between the duplex and the nearly lamellar.Thisphenomenon indicates that Hf can enhance the temperature of Tα in some extent and enlargethe region of α+γ.The perfect microstructure of TiAl based alloys with high Nb content cangained by the ways of micro-alloying united heat treatment.It is demonstrated that theprocess of1310℃/4h+900℃/30min/AC can get better lamellar microstructure and the β(B2)segregation is eliminated obviously at the same time.0.3at.%Y and0.5at.%Hf adding canproduce the most ideal lamellar microstructure of TiAl based alloys.The characterization and morphologies of oxidation scales of high Nb-containing TiAlbased alloys were studied and the oxidation kinetics curves were drawn at900℃in the staticair for300h in order to explore the effects of alloying elements.The results show thatTi-45Al-8Nb alloy has a poor property of oxidation resistance for the reason of its scale isloose and falling off easily in high temperature during the research.The alloys addingmoderate B and Y can decrease the size of oxidation products and form continuous denseA12O3scale,they can also improve the adhesion between oxidation scale and the matrix toimprove the oxidation resistance of TiAl based alloys in some content.The formationmechanism of scale is changed micro-alloying by Hf,and the element can reduce the interioroxidation rate.The TiAl based alloys can form continuous dense A12O3scale and improve theadhesion of the scale united adding B、 Y and Hf to improve the oxidationresistance.However,the alloys appear serious interior oxidation because the excrescent Hfadding can increase the path of duffusion. The alloys added0.5at.%Hf and1.0at.%Hf show better property of oxidation resistance.