Microstructure characteristics and enhanced properties of network-structured TiB/(TA15-Si) composites via rolling deformation at different temperatures

Abstract

Discontinuously reinforced titanium matrix composites (DRTMCs) with network structure have attracted much attention in recent years due to their superior strengthening effect and ductility. To figure out their microstructure characteristics of the as-rolled network-structured composites under different rolling temperatures, hot rolling deformation processes at α+β region, upper α+β region, β region were performed on a series of TiB whiskers reinforced Ti–6.5Al–2Zr–1Mo–1V–0.3Si (TA15) composites (TiB/TA15–Si). The results showed that with the increase of rolling temperature, primary α (αp) phases and silicides gradually decreased, while transformed β (βT) phases, secondary α (αs) phases and TiB aspect ratio gradually increased, which is attributed to the phase transformation, Si dissolution and lower deformation resistance. And the silicides were fractured into several parts at 900 °C due to the low solid solubility and excessive growth. Besides, the composite rolled at α+β region exhibited dominant dynamic recrystallization (DRX) of α phase, while the composite rolled at β region presented an elongated deformation of prior β phase inside the network and DRX behavior near the network. With the increasing rolling temperature, the composites showed an increasing trend in strength and a decreasing trend in ductility. The composite rolled at 1100 °C can obtain better overall ultimate tensile strengths of 1260 MPa (at RT), 843 MPa (at 600 °C), 729 MPa (at 650 °C) and 595 MPa (at 700 °C), which increased by 13.4%, 38.2%, 36.3%, 21.9% compared with those of the as-sintered composite, respectively. The superior strengthening mechanism of the as-rolled composites can be mainly attributed to grain refining of the matrix and load transfer of TiB.