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.
Hot isostatic pressing of nickel-based superalloys has important applications for manufacturing near-net shape parts such as turbine disks and jet engine parts, which have to operate at high temperatures. Finite element modelling can be used to predict deformation and densification behaviour of such superalloys. Thus, the cost and time of trial and error to obtain the required geometry of the part can be reduced, such that near-net shape parts can be manufactured more economically. Numerical simulations were carried out by implementing the model of ElRakayby and Kim into Abaqus-FEA. The model parameters (relative density functions f and c) for the nickel-based superalloy were obtained from the creep response and compressive strength of porous and solid powder compacts at high a temperature. The agreement between finite element calculations and the experimental data was good for densification, shape change and density distribution of nickel-based superalloy during hot isostatic pressing.
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