The Effect Of Zr And Co On The Microstructure And Mechanical Propeties Of TiAl Based Alloys

Ti Al based alloys are new high-temperature structural materials with low density and high specific strength, so it has broad application prospects in aero-engine fabrication and automotive field. However, it also has some disadvantages, e.g. poor plasticity at room temperature and weak machinability, restricting its comprehensive application. Alloying is one of the efficient ways to improve the room-temperature ductility and other mechanical properties. The contained of Nb and Zr in Ti Al-based alloys improve the strength. With large amounts of Zr replacing the site of Ti, the solution strengthing can improve the strengths of Ti Al based alloys largely. The content of Co can change the electron structure and elastic properties of Ti Al alloys, which lea to the improve of the plasticity. However, the studies about the effects of different content of Zr and Co on the Ti43 Al and Ti47 Al alloys are necessary to be further researched.The experimental alloys with different contents of Zr and Co in Ti43Al、Ti43Al6Nb、Ti47Al and Ti47Al6 Nb are prepared by multi-function vacuum arc melting furnace. This paper mainly study the macrostructure, microstructure, microstructure evolution, phase composition and micro-segregation by SEM, EDS, XRD analysis. The room-temperature compression strength and plastic deformation are studied to figure out the effect of Zr and Co on the mechanical properties of Ti Al alloys. Also the fracture morphology is also researched by secondary electron imagines in SEM and the fracture mechanism have been studied.The results show that, with refining microstructure and improved room-temperature compression strength, Zr have a good effect on Ti43 Al and Ti43Al6 Nb alloys, while the plastic deformation doesn’t have obvious improvement. The microstructure of Ti43 Alx Zr is columnar and the microstructure of Ti43Al6 Nbx Zr presents an exchange from dendrites to equiaxial grain, and the alloys of highest compression strength is Ti43Al5 Zr and Ti43Al6Nb2.5Zr. Ti43Al-5Zr have the highest compression strenghs, which have a improving of 81.71% with 1685 MPa. With an improving of 9.25% in compression strength, the Ti43Al6Nb2.5Zr alloy have a mean width of columnar of 486.11μm,which has declined 199.6μm from the Ti43Al6 Nb alloy.Except for Ti47Al0.5Zr, the mechanical properties of Ti47 Alx Zr and Ti43Al6 Nbx Zr are both declined, and the segregation is the top reason to leading this. The compression strength and pastic deformation of Ti47Al0.5Zr are 2158.03 MP and 35.24%,improving 9.46% and 7.64% respevtively.Also, Co have a good effect on Ti43 Al and Ti43Al6 Nb alloys with highest mechanical properties of Ti43Al2.5Co and Ti43Al6Nb1 Co both in compression strength and plastic deformation. Ti43Al-2.5Co alloy has improved 142.78% and 205.92% in compression strength ang plasticdeformation, and the exact gigures are 2251.10 MPa and 28.42%.Since of massive segregation, the mechanical properties of Ti47 Alx Co and Ti47Al6 Nbx Co are declining. But the alloy of Ti47Al-1Co have a little improve from 1971.5MPa to 2041.14 MPa.In general, the effect of Zr and Co on Ti43 Al is better than Ti47 Al. The content of Zr can separate out a phase of(Zr, Ti)-Al, which can refine te grain. The addition of Co in Ti Al alloys can bring a tepical structure named “massive microstructure”, Also there are two precipitated-phases, consisting of Ti-Co and Al-Co. A balanced amount of B2 can refine the microstructure and improve the compression strength. With an excess of B2, the microstructure insists of severe segregation, which leading to a inclining of mechanical properties. With amount of translamellar fracture surface, interlamellar fracture surface and rivermarkings, brittle fracture is the main character of Ti Al alloys, though the ductility of some alloys have been improved.