Influence of Cryogenic Treatment on Microstructure and Mechanical Properties of Ti6Al4V Alloy

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JMEPEG https://doi.org/10.1007/s11665-020-05177-y

Influence of Cryogenic Treatment on Microstructure and Mechanical Properties of Ti6Al4V Alloy Fatih Hayati C¸akir

and Osman Nuri C¸elik

(Submitted July 1, 2020; in revised form September 18, 2020; Accepted: 25 September 2020) Cryogenic treatment is an emerging application that can make signiﬁcant changes in many materials. In this study, shallow (2 80 °C) and deep (2 196 °C) cryogenic treatment was applied to Ti6Al4V alloy. Additionally, aging treatment and supplementary deep cryogenic treatment were also performed. Tensile tests were done to observe the effects of cryogenic treatment on the mechanical properties and formability of Ti6Al4 alloy. According to the results of these tests, it was observed that the cryogenic treatment had a positive inﬂuence on the plasticity properties of Ti6Al4V alloy. For the 24-h and 36-h deep cryo-treated samples, the uniform plastic deformation region (UPDR) was extended 5 and 8.3% compared to untreated sample, respectively. However, this improvement in plasticity observed in samples treated with cryogenic treatment for 36 h led to a decrease in yield strength by 2%. Microstructural and XRD analysis was performed to characterize the microstructural changes that happened with the effect of applied heat treatments. The characterization study shows that with the application of cryogenic treatment internal structure of the material changed, the b phase ratio of the alloy decreased from 8.1 to 5.6% with 36-h deep cryogenic treatment. The unstable b phase was transformed into a phase and stable b phase. The experimental study shows that cryogenic treatment improves the plasticity and toughness of Ti6Al4V alloy at room temperature and regulates the microstructure and reduces the residual stress. Keywords

characterization, cryogenic treatment, mechanical properties, Rietveld analysis, Ti6Al4V, XRD

1. Introduction Heat treatment is an effective way to tailor material properties for desired applications. There are many traditional heat treatment procedures for titanium alloys. The advantages and disadvantages of these procedures are mostly known. In the literature, there are many studies about the effect of traditional heat treatments on titanium alloys such as annealing, quenching aging on mechanical properties; however, the studies about the cryogenic treatment of titanium alloys are limited. Hence, the cryogenic treatment is a relatively new method. Cryogenic treatment is generally applied as additional heat treatment to parts in near-ﬁnal shape. This sub-zero treatment generally takes long soaking times that might alter the microstructure and mechanical properties. Since the applied heat treatment affects the a/b phase ratio, shape, and distribution of phases in the structure, it can be said that mechanical properties are also signiﬁcantly affected by the application of heat treatments. In the study of Gu et al., the effects of cryogenic treatment on the plastic properties of Ti6Al4V alloy at room temperature and static conditions w

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