Effect of trace boron on the microstructural characteristics, hot-workability and mechanical properties of a high Mn-modified β-solidifying γ-TiAl intermetallic compound

Abstract

An isothermal compression simulation experiment under conditions of 1100∼1250 °C, 0.001–10 s⁻¹ was conducted to study the hot deformation behavior of the Ti–42Al–5Mn-0.3B (at. %) intermetallic compound, prepared by vacuum induction melting. A hot processing map and constitutive equation were established. Based on these findings, Ti–42Al–5Mn and Ti–42Al–5Mn-0.3B ingots were prepared using un-packing forging. The room temperature and high temperature tensile properties of the forged alloys were tested. The effects and mechanisms of trace B addition on the microstructures of the as-cast and forged alloys, hot-workability, as well as the mechanical properties of the forged alloys, were systematically analyzed. The results show that, regardless of the as-cast or forged conditions, the addition of 0.3 at. % B increases the α₂ phase content and decreases the γ phase content, with the influence being more pronounced in the as-cast condition than in the forged condition. In the as-cast condition, 0.3 at. % B addition not only eliminates the coarse Widmanstätten lamellar structure to form an equiaxed lamellar structure, but also reduces the content and size of the β_o phase. These microstructural changes result in lower flow stress and apparent activation energy (Q) for the B-containing alloy compared to the alloy without B, leading to improved hot workability. In the as-cast condition, curved flaky TiB with orthorhombic B27 structure precipitates and coexists with the B2 phase, which can be fragmented into dispersed particles or short rods during hot forging deformation. This fragmentation significantly refines the lamellar colony size and lamellar spacing, thus enhancing the strength and ductility of the alloy at both room and high temperatures.