Correlation between microstructure and deformation mechanism in Ti_(66)Nb_(13)Cu_8Ni_(6.8)Al_(6.2) composites at ambient and elevated temperatures

摘要

In this study, Ti66Nb13Cu8Ni6.8Al6.2 composites with equiaxed and Widmanstatten microstructure matrixes were prepared by sintering amorphous and crystalline powder, respectively. The alloy with Widmanstatten structure exhibits lower yield and fracture strengths at ambient temperature but higher values at elevated temperatures compared with that with equiaxed structure. Microscopic deformation mechanisms of the alloys with different microstructures were investigated by scanning electron microscope (SEM), transmission electron microscope (TEM) and numerical simulation. The results indicate that the profuse dislocation pile-ups and formation of nanotwins in the beta-Ti matrix contribute to the high room-temperature strength and plasticity of the composite with equiaxed beta-Ti structure matrix, while stress concentration and cracking in the interior of acicular (Cu, Ni)Ti-2 phases in Widmanstatten structure matrix deteriorates plastic deformation capacity of the alloy. The higher strength and plasticity for the composite with Widmanstatten structure matrix at elevated temperature is ascribed to dislocation pile-ups around grain boundaries of beta-Ti and acicular (Cu, Ni)Ti-2 phases and the curving of acicular (Cu, Ni)Ti-2 phases inside Widmanstatten structure matrix. The results obtained provide some guidelines to design high-temperature alloy with excellent properties for structural applications.