Study On The Microstructure And Mechanical Properties Of In-Situ Synthesized Al₂O₃/TiAl Composite Materials

TiAl-based alloys are considered an important alternative to nickel-based high-temperature structural materials due to their excellent properties such as high specific strength,excellent oxidation and corrosion resistance,high melting point,and low density.They provide a high-performance and highly reliable material choice for aerospace and other fields and are widely used in the manufacture of various critical components.However,the deformation resistance of TiAl-based alloys at high temperatures is relatively low,which limits their application in high-temperature environments.Therefore,it is of great significance to study how to improve the high-temperature strength of TiAl-based alloys,which can expand their application fields.In this article,the mechanical properties of the alloy were improved by introducing strengthening phases through direct addition or in-situ synthesis.Among them,the strengthening phase synthesized in-situ has excellent bonding with the matrix,making it more stable and improving its mechanical properties.Therefore,this study used powder metallurgy technology to introduce Al₂O₃ particles into the Ti-45Al-8Nb alloy matrix through in-situ synthesis,preparing Al₂O₃/TiAl composite materials,and studying their micro structure and mechanical properties.The main conclusions of this study are as follows.（1）Through vacuum hot-press sintering technology,this study successfully prepared an Al₂O₃/TiAl composite material.The material used Ti-45Al-8Nb pre-alloy powder,TiO₂ nanofibers,TiO₂ nanoparticles,and Al₂O₃ particles as the reinforcing phase.The matrix phase of the composite material is composed of equiaxed γ phase and lamellarγ/α2 phase,and a good metallurgical bond is formed between the matrix phase and the reinforcing phase.（2）By adding different amounts of TiO₂ nanofibers and powders to pre-alloy powders,in situ synthesis of Al₂O₃ ceramic particles can be achieved through vacuum hot-press sintering,which generates at the grain boundaries of the matrix and effectively inhibits grain growth,refining the size of the grains.As the amount of TiO₂ increases,the grain size of the matrix gradually decreases,but the generated Al₂O₃ also tends to aggregate,which decreases the mechanical properties of the TiAl composite material.By observing the morphology of the mixed powders,it can be found that TiO₂ nanofibers can be effectively dispersed on the surface of the pre-alloy powders,while TiO₂ nanoparticles tend to aggregate on the surface,leading to the agglomeration of subsequently synthesized Al₂O₃ particles,which affect the performance of the composite material.（3）Studies have shown that the high-temperature tensile strength of Al₂O₃/TiAl composite materials decreases with decreasing strain rate.By adding TiO₂ nanofibers and nanopowder to the mixed powder,the high-temperature tensile strength of the composite material can be gradually improved.Research on the high-temperature tensile properties of composite materials with different contents of TiO₂ nanofibers and nanoparticles added showed that the composite material with TiO₂ nanofibers exhibited superior mechanical properties.When 0.25 wt.%of TiO₂ fibers are added,the strength and toughness of the composite material are both improved,exhibiting the best comprehensive performance.Under conditions of 900℃ and a strain rate of 1×10-3 s-1,the tensile strength of the composite material is 466 MPa and the elongation is 69.0%.Compared with Ti-45Al-8Nb alloy,the tensile strength and elongation of the composite material are increased by 84 MPa and 7.7%,respectively.（4）The high-temperature compressive rheological stress peak of Al₂O₃/TiAl composite material with added TiO₂ nanofibers increases with the increase of the applied strain rate.Meanwhile,this composite material is a negative temperature-sensitive material,and the increase in temperature will decrease the rheological stress peak of different alloy components.In the preparation process,adding TiO₂ nanofibers can improve the peak rheological stress of the composite material.However,too fast strain rate can cause too short plastic deformation time,resulting in uneven internal deformation of the structure,local stress concentration,and ultimately sample cracking.（5）This study established a high-temperature deformation constitutive equation for Al₂O₃/TiAl composite materials,which was based on the high-temperature compression peak rheological stress of samples prepared by adding 0.25 wt.%TiO₂ nano fibers.ε=e24.23[sinh（0.0909σ）]4.47 exp（-318808/RT）...