Influences of boron contents on microstructures and mechanical properties of as-casted near α titanium alloy

Abstract

Ti-6.5Al-2.5Sn-9Zr-0.5Mo-0.25Si-1Nb-1W-0.1Er-xB (x = 0, 0.1, 0.2, 0.4, 0.6 and 0.8 wt%) with different boron contents are fabricated for investigation. Influences of boron element and its amounts on phase constitutions, microstructures, textures and compression mechanical properties are carefully studied. With the increasing boron additions, contents of TiB phase increase, and the maximum intensities of textures decrease. Microstructures are significantly and continuously refined after adding boron element and with the increasing boron additions, and turning point of refinement rates for different microstructural parameters is found at 0.2 wt% boron content. Strengths increase monotonously, while elongations increase firstly and decrease afterwards. The maximum value of elongation is acquired at boron content of 0.2 wt%. On the premise of ensuring plasticity, 0.2 wt% boron content is the most appropriate amount for microstructural refinement and mechanical properties enhancement for current near α titanium alloys. Meanwhile, aspect ratios of TiB whiskers increase with the increasing boron contents. Lots of near equiaxed α grains or α grains with irregular morphologies are discovered around TiB phase. Distorted and twisted α grain boundaries are also obviously detected in boron containing alloys. Moreover, premature fracture of alloys containing TiB whiskers is largely influenced by the fracture of these brittle reinforcements.