Abstract
Titanium alloys, such as Ti-6Al-4V, are extensively used in critical aerospace applications. Heat treatments are often conducted during forging processes to produce final microstructures which exhibit advantageous mechanical properties. However, high thermal gradients present during processing may lead to the generation of undesirable levels of residual stress. Stress relief can be achieved by conducting aging or annealing treatments at elevated temperatures, yet there is limited quantitative understanding of how holding temperature affects the evolution of residual stress. Stress relaxation testing was conducted between 500-750°C and the resulting response was modified to describe creep strain. This was implemented in DEFORM™ finite element analysis software to model the evolution of residual stress during solution treatment followed by aging between 500-750°C, with comparison against solutions which did not consider creep strain. Stress relaxation phenomena was found to have an important impact on the reduction of residual stress and needs to be considered when carrying out thermo-mechanical processing at elevated temperatures.
Highlights
Titanium alloys are often among selected materials for use in aerospace applications due to their favourable strength-to-weight ratio, as well as good temperature and corrosion resistance [1]
Water quenching leads to the formation of brittle martensite (α′), as well as high thermal gradients throughout the workpiece and in turn, high magnitudes of residual stress
The aim of the following work was to characterise the stress relaxation behaviour exhibited by Ti-6Al-4V over typical heat treatment temperatures of 500 to 750°C and determine the importance that this behaviour has on the evolution of residual stress through simulation in DEFORMTM finite element analysis (FEA) software
Summary
Titanium alloys are often among selected materials for use in aerospace applications due to their favourable strength-to-weight ratio, as well as good temperature and corrosion resistance [1]. Whilst higher aging temperatures promote stress decay, this may lead to partial dissolution of the bimodal microstructure formed during solution treatment; adversely affecting strength [1,4] This has led to the commercial application of various aging regimes with holding temperatures ranging from 500 to 750°C and above, and holding durations ranging from 0.5 to 24 hours [1,5,6]. Stress relaxation behaviour in Ti-6Al-4V is thought to be highly dependent on process history and significant variation in response has even been found between similar initial microstructures [5] This has led to the recommendation that material specific stress relaxation data is gathered prior to application in finite element analysis (FEA) software. The aim of the following work was to characterise the stress relaxation behaviour exhibited by Ti-6Al-4V over typical heat treatment temperatures of 500 to 750°C and determine the importance that this behaviour has on the evolution of residual stress through simulation in DEFORMTM FEA software
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
