Microstructure And Crack Propagation Behavior Of In-situ （TiB+TiC+La₂0₃）/IMI834 Titanium Matrix Composites

Discontinuously reinforced titanium matrix composites（DRTMCs）shows great application potential due to easy-fabrication,low-cost and superior mechanical properties.In the present work,TiB+TiC+La₂O₃reinforced IMI834 composites were used to investigate the effect of reinforcement on microstructure,tensile properties and crack propagation behavior through microstructure observation,tensile tests and crack propagation tests at room temperature.We finally brought up modules for tensile fracture and crack propagation to illustrate how the reinforcements work in the tensile tests and crack propagation tests.In-situ synthetized TiB+TiC+La₂O₃ reinforced IMI834 composites were fabricated via the method of vacuum consumable furnace.Basket wave structure was formed after hot working and aging.Reinforcements of TiB（short fibers）,TiC（equiaxed particles）and La₂O₃（Nano-scale particles）are dispersed homogenously in TMCs.Some reinforcements are found broken or fractured,introducing defects like holes in TMCs.With the increase of the reinforcement volume fraction,the microstructure is refined and the aspect ratio of TiB whiskers is increased.With the increase of reinforcement volume fraction,the tensile strength and the elongation decreased.The best tensile property is obtained in TMCs of 0.5 vol.%,whereas TMCs of 2.5 vol.%and 5 vol.%display brittle fracture without evident plastic yielding.Such phenomenon is closely related to the reinforcements and the defects.There are more defects in higher reinforcement volume fraction TMCs,which tend to initiate micro cracks and lead to micropores coalescence.So the increase of reinforcement volume fraction is bad for the improvement of mechanical properties and responsible for the brittle fracture.Intergranular cracking and transgranular cracking are both observed along the crack path,and there are second crack initiated in the propagation process.With the increase of reinforcement volume fraction,the crack path gets more straight and the number of second cracks decreases.Reinforcements and defects play an important role in the crack propagation process by diverting cracks propagation direction and initiating second cracks.