Microstructural Control of Fatigue Behaviour in a Novel  Titanium Alloy

Bache Bache,Davey Davey,Thomas Thomas,Davies Davies,Berment-Parr Berment-Parr

doi:10.3390/met9111200

Bache Bache, Davey Davey + Show 3 more

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https://doi.org/10.3390/met9111200

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Abstract

The novel titanium alloy TIMETAL® 407 (Ti-407) has been developed as an alternative to Ti-6Al-4V (Ti-6-4), for applications that demand relatively high ductility and energy absorption. Demonstrating a combination of lower strength and greater ductility, the alloy introduces a variety of cost reduction opportunities, including improved machinability. Thermo-mechanical processing and its effects on microstructure and subsequent mechanical performance are characterised, including a detailed assessment of the fatigue and crack propagation properties. Demonstrating relatively strong behaviour under high-cycle fatigue loading, Ti-407 is nevertheless susceptible to time-dependent fatigue effects. Its sensitivity to dwell loading is quantified, and the associated deformation and fracture mechanisms responsible for controlling fatigue life are explored. The intimate relationship between thermo-mechanical processing, micro-texture and fatigue crack initiation through the generation of quasi-cleavage facets is highlighted. Consistent fatigue crack growth kinetics are demonstrated, independent of local microstructure.

Highlights

Titanium alloys continue to dominate engineering applications where a combination of strength, corrosion resistance and low density are key design requirements
The combined high-cycle fatigue (HCF), low-cycle fatigue (LCF) and dwell fatigue data generated from TIMETAL® 407 (Ti-407) are plotted in Figure 6, with least squares, best fit trend lines superimposed to the LCF and HCF data sets
The novel α + β titanium alloy Ti-407 has shown good HCF strength, relative to yield properties, and provided better HCF strength compared to previous forms of Ti-6-4 assessed by this laboratory [27], without compromising ductility, machinability and manufacturing properties

Summary

Introduction

Titanium alloys continue to dominate engineering applications where a combination of strength, corrosion resistance and low density are key design requirements. These factors are of greatest pertinence to the aerospace industry, where the relatively high material cost can be justified by the highly specific properties on offer. Applications where impact resistance and energy absorption are essential would benefit from relative improvements in ductility. This has led to the development of a novel α + β alloy [Ti-0.85Al-3.9V-0.15O-0.25Si-0.25Fe], designated as TIMETAL®

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Conclusion