Influence of 2D forging processes and boron contents on the microstructures and mechanical properties of near α titanium alloys

Abstract

2D forging processes are adopted to tailor the microstructures and mechanical properties of near α titanium alloys with different boron contents and the evolutions of the microstructures and mechanical properties of the acquired alloys are carefully characterised. Maximum texture intensities decrease with increasing boron contents, thereby illustrating the improvements in the homogeneity of the microstructures. The distribution of TiB whiskers in the 3D space exhibits a near-columnar arrangement around boundaries of squashed and elongated prior β grains along the stretching direction. Increases in the contents of equiaxed α grains with increasing TiB contents are ascribed to enhancements in recrystallisation due to the promotion effects of the TiB phase and increases in β transus temperatures. Boron exhibits excellent refinement effects on the alloy matrices, and the refinement degree increases with increasing boron contents. The proportions of low-angle grain boundaries decrease whilst the corresponding proportions of high-angle grain boundaries increase with increasing boron contents. The ultimate and yield strengths of the alloys increase at room temperature (RT) and 650 °C. Elongations exhibit a decreasing trend at RT but are maintained at 650 °C. At RT, cleavage fractures of the TiB whiskers determine the evolution law of elongation. The fracture characteristics of alloy matrices exhibit a transformation from a mixture of tearing lamellae and dimples to dimples only. At 650 °C, the alloy matrices are characterised by ductile fractures with numerous dimples. Er containing particles facilitate the fracture of alloy through cooperative effects with TiB whiskers.