A binary beta titanium superalloy containing ordered-beta TiFe, alpha and omega

Alpha beta titanium alloys excel for aeroengine applications but are typically limited to -550 degrees C. An alternative strategy is reinforcement with the ordered-beta TiFe intermetallic, toward 'beta-Ti superalloys', however, there has been minimal study of TiFe precipitation in the binary system. Here, a Ti-20Fe (at.%) alloy was homogenised at 1050 degrees C in the beta-Ti phase field and aged at 600 degrees C where the Fe supersaturation promoted TiFe precipitation. Curiously, as the TiFe volume fraction increased, the alloy hardness decreased, due to an interplay of mechanisms: (1) Fe solid solution strengthening, which reduces as the beta-Ti Fe content falls to 16.2% on ageing; (2) omega precipitation strengthening, as omega-like incommensurate modulated domains were identified by transmission electron microscopy in the homogenised beta-Ti parent phase and are suggested to change in size and structure after ageing, resulting in reduced omega-strengthening; (3) softening as softer TiFe and alpha-Ti phases precipitate from the harder omega-strengthened beta-Ti parent phase. (C) 2021 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Automated summary

This study investigates the precipitation of TiFe in a binary titanium-iron system, showing that Fe supersaturation promotes TiFe precipitation but leads to a decrease in alloy hardness as TiFe volume fraction increases. The change in hardness is influenced by multiple mechanisms, including Fe solid solution strengthening, omega precipitation strengthening, and softening caused by the precipitation of softer TiFe and alpha-Ti phases from the harder omega-strengthened beta-Ti parent phase.