Direct rolling of as-cast Ti-6Al-4V modified with trace additions of boron

Trace boron additions to titanium alloys produce an order of magnitude reduction in as-cast grain size, leading to the possibility of significant simplification of ingot breakdown and thermomechanical processing procedures. In this study, the boron modified titanium alloy Ti-6Al-4V + 0.1B (wt.%) was hot rolled from the cast + HIP condition to thickness reductions of 50% and 75% in multi-step rolling sequences. Baseline alloys (without boron) in the cast and wrought (mill product) states were also processed under identical conditions for comparison. After 50% reduction in thickness at 750-950 degrees C (1382-1742 degrees F), the deformation behavior of cast Ti-6Al-4V + 0.1B is not noticeably different from that of standard Ti-6Al-4V mill product, whereas cast Ti-6Al-4V without boron exhibited extensive cracking. The boron-containing alloy could be deformed further to 75% reduction in thickness at 950 degrees C (1742 degrees F) without producing any macroscopic defects. The alpha phase shows a tendency to globularize during heat treatment after a 50% reduction in thickness to produce an equiaxed microstructure. The potential, therefore, exists for the production of slab and sheet stock with an equiaxed microstructure by directly rolling the as-cast titanium alloys modified with trace boron additions. (c) 2007 Elsevier B.V. All rights reserved.