Methods And Experimental Study Of Modification Of Room Temperature Brittleness Of TiAl Alloys

TiAl alloy has excellent specific strength,creep resistance and oxidation resistance than Ti alloy and Ni-based alloy because of its low density,high melting point,high specific strength and specific modulus,low creep rate and outstanding high temperature oxidation resistance.So it is considered that TiAl alloy has the potential to replace the nickel-basedsuperalloy as a high temperature light alloy.However,its poor brittleness at room temperaturehas limited its wide application.Therefore,it has been a hot issue to improve the plasticity/toughness and strength of TiAl alloys alloys Therefore,nano-TiB₂ was used as the reinforcing phase in this experiment to study the effect of TiAl alloy on the mechanical properties and microstructure of TiAl alloy.At the same time,two kinds of alloy systems were designed,prepared by vacuum arc smelting method,and the mechanical properties of the alloy were improved by the method of heat treatment.The effect of alloying elements on TiAl was studied.（1）In this study,with the addition of nano-TiB₂,Ti-46Al（at%）-x（x is 0,0.5,1.0,1.5）vol%TiB₂ was prepared by planetary ball combined with SPS sintering method.The results show that TiAl composites have the relatively superior mechanical properties（1543MPa,19.4%）when the content of TiB₂ is 0.5 vol.%.The nano-TiB₂ has certain effect of grain refinement,but with the increase of TiB₂,The aggregation of nano-TiB₂ is more and more serious,and the nano-TiB₂ mainly concentrates at the grain boundary of the lamellar structure,which in turn deteriorate the mechanical property.（2）The effects of Mn,Nb and V alloying elements on the microstructure and mechanical properties of TiAl under cast conditions were investigated.The experimental results show that there are segregation of alloying elements under as-cast conditions,and because of the presence of Nb,there are B2 Phase,due to the segregation of elements and the presence of B2 phase,as well as the existence of defects under the as-cast,resulting in the material is still showing a lot of brittleness,the two materials XRD analysis,the main phase are TiAl,Ti₃Al,B2 Phase,while there are still AlNb₂,Al₃Ti_0.75Mn_0.18V_0.08,indicating that in the case of as-cast elements still exist in the case of non-uniform diffusion.TiB₂mainly distributed in the grain inside,as a heterogeneous nucleation of the particles,play a role in refining grain,and TiB₂ in the process of melting there is a phenomenon of re-melting.（3）The effects of different temperature on the microstructure and mechanical properties of TiAl alloy in Tγ_-solvus were investigated by heat treatment.The main phase of TiAl is TiAl,Ti₃Al,and B2 phase after heat treatment,and the B2 phase can not be completely eliminated after heat treatment.The possible reason is that Nb,Mn and V areβ-phase stable elements at high temperature The distribution of Mn and V elements in the matrix are more uniform after heat treatment,The compressive strength of the material after heat treatment is higher than that of the as-cast,but the overall compression ratio is not changed.In the second step heat treatment,when the heat treatment temperature is 1290℃Ti-44Al-5Nb-2Mn-3V-0.5TiB₂ alloy exhibit the best Comprehensive mechanical properties,the compressive strength reached 2083MPa,the strain reached 19%.