The influence of hydrogen on the synthesis of γ-TiAl alloys containing Nb, Cr and Mn by non-traditional Hydride Cycle method

Abstract

This work describes a new technology for synthesis of Ti-47.5Al-2Cr/Mn-2Nb alloys by sequential applying two methods: Self-propagating High-temperature Synthesis (SHS) of metal hydrides, and Hydride Cycle (HC) formation of metal alloys from obtained hydrides. Four compositions are synthesized: Ti-47.5Al-2Cr-2Nb, Ti-47.5Al-2Mn-2Nb, Ti-47.5Al-2Cr-2Mn-2Nb and Ti-47.5Al-1Cr-1Mn-2Nb. To get the alloy by the developed method, titanium and niobium hydrides are first synthesized in SHS; then alloys of the specified compositions are produced in HC from these hydrides. The influence of doping additives Cr, Mn and Nb on several characteristics of the alloys is defined. Tetragonal γ-TiAl phase was synthesized, containing 11–22% of hexagonal α₂-Ti₃Al phase. Thermograms of HC processes, DTA curves, and the absence of melting traces on the surface of the samples indicate a solid-phase diffusion mechanism of the reaction of formation of all studied compositions in HC. The advantages of this method over traditional ones are: diminishing of operating temperatures from 1800-2600 to 600–1000 °C, and of process duration from tens to 1.0–2 h; single-stage and environmentally friendly process of formation of multicomponent alloys of a given chemical and phase composition, without multiple re-melting. These advantages ensure lower energy consumption and low manufacturing cost of alloys.