Superplastic Behaviour of Ti54M and Ti64

Abstract

Even though TIMETAL-54M (Ti-5Al-4V-0.6Mo-0.4Fe or Ti54M) has been commercially available for over 10 years, further study of its superplastic properties is still required in order to assess its applicability within the aerospace industry as a potential replacement for other commercial titanium alloys such as Ti-6Al-4V (Ti64). Ti54M is expected to obtain superplastic characteristics at a lower temperature than Ti64 due to its lower beta-transus temperature. The superplastic forming (SPF) capability of alloys that can be formed at lower temperatures has always attracted the interest of industry as it reduces the grain growth and alpha-case formation, leading to longer life for costly high temperature resistant forming tools. In this work, the SPF characteristics of both Ti54M and Ti64 have been examined by conducting tensile tests according to the ASTM E2448 standard within a range of temperatures and strain values at a fixed strain rate of 1 × 10-4/S. A high strain rate sensitivity and uniform deformation at high strains are key indicators in selecting the optimum superplastic temperature. This was observed at 815˚C and 925˚C for Ti54M and Ti64 respectively. The tensile samples were water quenched to freeze their respective microstructure evolution following superplastic deformation and SEM images were captured for grain size and volume fraction of alpha-phase analyses. A slightly higher alpha-grain growth rate was observed during superplastic deformation of Ti64. The initial fine-grain microstructure of Ti54M (~1.6 micron) resulted in a final microstructure with an average grain size of ~3.4 micron and optimum the alpha/beta ratio. Both the fine-grained microstructure and increased amount of beta-volume fraction promotes the superplastic behaviour of Ti54M by grain boundary sliding (GBS). Thus superplastic properties were observed for Ti54M at a lower temperature (~100˚C) than for Ti64.

Grain Rotation Accommodated GBS Mechanism for the Ti-6Al-4V Alloy during Superplastic Deformation

“…Even in the deformations dominated by the diffusion creep mechanism, grain boundary sliding still can contribute 50 to 70% in the II region [15]. Thus, the GBS playing a dominant role in SPF has been extensively recognized [16,17].…”

An investigation of forming of Ti-6Al-4V at lower temperatures

“…For a long time, the aerospace sector has been forming Ti64 through SPF to obtain near-net complex shapes without springback and residual stresses. Typically, Ti64 is superplastically formed at optimum SPF conditions, with temperatures close to 900 °C [2][3][4]. The exposure of titanium alloys to air/Argon at a high temperature (>650°C) during the SPF process frequently results in surface oxidation [5].…”

A Study on Modelling the Superplastic Behaviour of Ti54M Alloy

“…The present work utilizes a microstructural-based power-law model to predict the superplastic behaviour of Ti54M alloy at 815 °C and compare it to the superplastic behaviour of Ti64 alloy at 925 °C. These temperatures were reported to be optimal for Ti54M and Ti64 alloys based on strain rate sensitivity values and uniform deformation conditions [7,8].…”

“…The parameters of the material model have been calculated based on material experimental data by means of a developed Matlab script for Ti54M and Ti64 alloys. The material experimental data used in this work are reported in the literature [7,8]. Mandal et al [7] studied the grain size evolution of Ti54M and Ti64 alloys under superplastic deformation for various test conditions.…”

“…The material experimental data used in this work are reported in the literature [7,8]. Mandal et al [7] studied the grain size evolution of Ti54M and Ti64 alloys under superplastic deformation for various test conditions. Gomez-Gallegos et al [8] investigated the mechanical and superplastic properties of Ti54M and Ti64 alloys at various temperatures via high temperature tensile tests.…”