Mechanism of nanoscale TiB whisker improving the high-temperature strength and plasticity of TA15 matrix composite

Abstract

This study employs low-energy ball milling with hot press sintering technique to fabricate network-structure TA15 matrix composites with TiB₂ of different sizes (5 μm, 0.5 μm, and 100 nm). For 5 μm or 0.5 μm TiB₂, in-situ synthesized TiB whisker (TiBw) exhibit rod-like morphology with aspect ratio of 7.8 or 7.5, forming quasi-continuous networks at primary β phase boundaries to induce heterogeneous nucleation of primary α (α_p). Their room-temperature yield strength and elongation are 890 MPa and 7.7 %, 896 MPa and 8.2 %, respectively. Meanwhile, their high-temperature strength at 600 °C is 518 MPa and 543 MPa. However, when the size of TiB₂ is reduced to 100 nm, TiBw exhibited a much smaller diameter accompanied by a remarkably high average aspect ratio of 16.2, leading to the formation of a needle-like morphology. The morphological transformation of TiBw is governed by its nucleation sites and the concentration gradient of B atomic diffusion. This needle TiBw/TA15 composite exhibits a very good room-temperature yield strength of 1135 MPa and high-temperature properties of 589 MPa in strength and 16.4 % in fracture strain at 600 °C. The enhanced high-temperature elongation stems from TA15 matrix softening, which reduces crack propagation resistance and promotes crack deflection into the matrix.