Microstructures and mechanical properties of TiAl matrix composites with multi-precipitates quasi-continuous network reinforced structures

A novel quasi-continuous network reinforced structure that consists of borides and carbides in B4C/TiAl matrix composites was innovatively designed for the strengthening at high temperatures. Simultaneously, impacts of such reinforced structures on microstructures and mechanical properties of the composites have been unveiled. TiAl matrix units in B4C/TiAl composites are duplex microstructures which are composed of (α2+γ) colonies and γ grains. The ascent of B4C contents triggers off the formation of network reinforced structures in the layers of TiAl matrix units. With B4C contents increasing to 0.1wt.%, elasticity modulus and ultimate compressive strengths of B4C/TiAl composites are upgraded from 10.944GPa and 723.10MPa to 16.052GPa and 774.611MPa. As B4C contents reach at 5.0wt.%, elasticity modulus and ultimate compressive strengths further soar to 17.244GPa and 799.19MPa. Borides and carbides within the quasi-continuous network reinforced structures are unfolded as stripe and needle shaped TiB with B27 structure and Ti2AlC particles with MAX structure. Parts of Ti2AlC particles take TiB as cores to nucleate and grow. Moreover, TiC phases usually act as the cores for the nucleation of Ti2AlC particles. The orientation relationships of such reinforcements represent as [011]TiC//[010]TiB, (1-11)[011]TiC//(0006) [-2110]Ti2AlC, [100]TiB//[0001]Ti2AlC, [010]TiB//[-2110]Ti2AlC and [001]TiB//[01-10]Ti2AlC. The fractures of TiB are usually along or perpendicular to [010]TiB direction. Meanwhile, the fracture surfaces of TiB are always parallel to (100)TiB or (010)TiB planes. Additionally, dislocations slip through Ti2AlC particles and lead to separation and sliding of staking planes (0001)Ti2AlC within Ti2AlC lattices. TiB and Ti2AlC with alternative distribution can stabilize the network reinforced structures and upgrade properties of B4C/TiAl composites.