Effect Of Al(Cr) On Mechanical Properties And Oxidation Behavior Of Ta-based Alloys

Superalloys are important materials for aerospace and nuclear industry.With the development of industry and science,engines and nuclear equipment need more higher temperature performance materials.Ta based alloy has remarkable high strength at high temperature,but its application is limited by its?pesting?oxidation resistance at high temperature.Designing and producing multicomponent Ta based alloys are research focus in order to improve mechanical properties and oxidation resistance of alloys.In this paper,Ta-Nb-Ti ternary alloy and Ta-Nb-Ti-Al(Cr)quaternary alloy were prepared by spark plasma sintering method.The phase composition,microstructure and compression properties of alloys were studied,and the oxidation behavior of the alloys were studied by cyclic oxidation method.After then,the alloys were treated by heat treatment.The compressive mechanical properties and oxidation resistance of the alloy before and after heat treatment were compared,and the following results were obtained:(1)All densified alloys with BCC structure were prepared at 1600?.The additive of Al reduces the ductility and increases the strength of the alloy,the total elongation decreases from 33.7%to 9.8%with the addition of Al from 0 to 4wt%,and the tensile strength increases from 1649 Mpa to 1732 Mpa at the seem time.(2)Oxidation experiments at 900?and 1000?show that the oxidation kinetics of ternary alloy obeyed linear kinetic.The addition of Al increase oxidation resistance,while the effect of Cr is not clearly.The kinetic of all alloys was governed by linear law kinetics.In ternary alloy,Nb element is severely segregation.In Ta-Nb-Ti-Cr quaternary alloys Cr and Nb elements are concentrated.After oxidation,the formation of Nb₂O₅ causes destructive fracture and crack in the oxide layer,which reduces the oxidation resistance of ternary alloy and Ta-Nb-Ti-Cr quaternary alloys.(3)After heat treatment,the compressive mechanical properties and oxidation resistance of quaternary alloy are improved significantly.The tensile strength of the alloy with Al addition increases from 1732 Mpa to 1886 Mpa,and that of the alloy with Cr increases from 1650 Mpa to 2069 Mpa.The yield strength and tensile strength of the alloy with Cr addition are higher than those with Al addition.(4)After heat treatment,the oxidation kinetics curves of alloys with Cr addition no longer obeyed linear kinetic,while those of alloys with Al addition followed approach parabola kinetic.The segregation of Cr and Nb elements in ternary alloy and Ta-Nb-Ti-Cr quaternary alloys was distributed evenly after heat treatment,which improves oxidation resistance.The results of this study show that addition of Al and Cr elements in Ta base alloy can improve the oxidation resistance of the alloy,and heat treatment obviously improve on the performance of quaternary alloys.After heat treatment,Ta-Nb-Ti-Cr alloy has better mechanical properties and oxidation resistance.