Research On Microstructure Evolution And Compression Properties Of Two-Component Powder Metallurgy TiAl Alloy

As a lightweight structural material,TiAl alloy has the advantages of low density,high specific strength,specific stiffness and excellent high-temperature mechanical properties,making it an ideal choice for high-temperature structural materials.However,its low room temperature plasticity and poor hot workability limit its wide application.Therefore,this paper proposes to prepare TiAl alloy by powder metallurgy of two-component materials to form a bimodal structure in which the"soft phase"wraps the"hard phase",refine the structure and coordinate its plasticity and toughness,and obtain TiAl-based alloys with higher comprehensive properties.This article uses Ti-48Al-2Cr-2Nb（at%,the same below）and Ti-45Al-8Nb pre-alloyed powder as raw materials,through ball milling,hot pressing sintering,forging and heat treatment processes to prepare equiaxedγgrains wrapped layer The two-component two-state structure ofγ/α₂ lamellar clusters.Characterize the microstructure and phase of the material through analysis and testing methods such as scanning electron microscope（SEM）,energy spectrum analysis（EDS）,electron backscatter diffraction（EBSD）,and X-ray diffraction（XRD）,focusing on exploring the structure of different processes Evolution,and analyze the change law of alloy density and grain size.The room temperature compression test was performed on the obtained two-component two-state structure,the effect of its fracture type and strain rate on its compression performance was studied,the strain rate sensitivity and activation volume were calculated,and the deformation mechanism in compression deformation was determined.Microstructure analysis shows that:（1）Forging improves the density of the alloy without changing the sintered phase.Dynamic recrystallization occurs during the forging process to generate a fine recrystallized structure to achieve the effect of fine grain strengthening;（2）Under the heat treatment process of air cooling at1280℃for 30 minutes,the static recrystallization in the high-Nb area is small,and the static recrystallization in the low-Nb area is large,and finally the formation of equiaxedγgrains wrapped in lamellaγ/α₂ lamella cluster Component dual-state structure,plasticity and toughness have been greatly improved.（3）A uniformγ/α₂lamellar structure is obtained under the heat treatment process of 1350°C for 5minutes and air cooling.The different Nb element content makes the size of the lamellar clusters different,and the toughness is better.The mechanical properties test showed that:（1）The compactness of the sintered structure is poor,which is a mixed fracture of transgranular and intergranular;the forged structure is larger in size,which is a mixed fracture of cleavage fracture and shear fracture;heat treatment at 1280℃The composition of the structure is uniform,which is a mixed fracture of cleavage fracture and shear fracture.（2）Compared with the sintered structure,the yield strength and maximum compressive strength of the alloy after forging and heat treatment are increased by54%and 63.8%,respectively,and the elongation has increased.And it shows positive strain rate sensitivity,the activation volume is small,and the deformation mechanism is a dislocation slip mechanism.Based on the above research,this paper has prepared a two-component dual-state structure with equiaxedγgrains wrapped in lamellaγ/α₂ lamella clusters,and its room temperature plasticity and toughness are well matched.The design concept is TiAl alloy The improvement of room temperature plasticity provides an idea,which is beneficial to the wide application of TiAl alloy.