Decomposition of deformed α′(α″) martensitic phase in Ti–6Al–4V alloy

Abstract

The process of martensitic α′( α″) phase decomposition in titanium alloys has not been sufficiently characterised in the literature – especially in terms of plastically deformed martensite. The research results of water-quenched Ti–6Al–4V alloy, subsequently cold deformed in compression test and tempered at the temperature range of 600–900°C for 1 and 2 h were presented in the paper. Light and scanning electron microscopy observations revealed the influence of plastic deformation on tempered martensite laths morphology – particularly at the temperature of 900°C – it favoured their fragmentation and spheroidisation. The effect of plastic deformation on characteristic temperatures of α′( α″)→ α + β phase transformation, phase composition and alloying elements distribution in phase constituents of Ti–6Al–4V alloy was identified and evaluated too. This paper is part of a thematic issue on Titanium. GRAPHICAL ABSTRACT

The effect of plastic deformation on martensite decomposition process in Ti-6Al-4V alloy

“…4). Microstructure in outer parts of compressed specimens -called "undeformed zones 1 " -is typical for martensite decomposition in Ti-6Al-4V alloy [12]. No significant changes in martensitic microstructure were detected by light microscopy method after deformation at 600ºC (Fig.…”

“…It is believed that the product of martensite decomposition in two-phase titanium alloys is a mixture of a and b phases [1][2][3]. Using XRD method, in previous investigation [12], it was confirmed that b phase was formed after 1 h tempering at the temperature range of 600-900ºC. In presented research XRD measurement were conducted in the central part of compressed specimens -in or close to the FLZ.…”

“…An innovative approach adopted in the recent research [12] was to evaluate the effects of cold plastic deformation on martensite decomposition in Ti-6Al-4V alloy. Water quenched alloy was compressed at room temperature and tempered at the temperature range of 600-900ºC.…”

Effect of stress relaxation on the evolution of residual stress during heat treatment of Ti-6Al-4V

“…Although stress relief is shown to improve on increasing temperature (Fig 4c), there is little improvement between 700 and 750°C as the process is effectively complete. Whilst this may appear beneficial in terms of reducing residual stress, aging at such temperatures would lead to thickening of secondary α and in turn, reduced strength [14]. Whilst annealing is commonly conducted in this region, lower temperatures are often selected for aging treatments.…”

Study on Transformation Mechanism and Kinetics of α’ Martensite in TC4 Alloy Isothermal Aging Process

“…The microstructure and mechanical behavior of TC4 alloy are very sensitive to the history of the thermomechanical deformation and thermochemical treatment [6][7][8][9]. Ahmed [10] found that the transformation mechanism of TC4 alloy is complete martensite, massive transformation and diffusion transformation with the cooling rate decreasing from 525 • C/s to 1.5 • C/s.…”