The research of technological properties of the titanium alloy Ti-6Al-4V. Part 1. Microstructure and mechanical properties

Abstract

The paper describes the results of comprehensive studies of the microstructure, mechanical and technological properties (formability and weldability in the solid state) of the titanium sheet alloy VT6 (Ti-6Al-4V) with improved superplastic properties produced by PSC «VSMPO-AVISMA». In the first part the initial microstructure of the alloy and its mechanical properties over a wide temperature range from 650 to 900°C at strain rates of 4×10–4, 4×10–3 and 4×10–2 s–1 have been investigated. It is found that the initial microstructure of the sheet is uniform and ultrafine grained with an average size of 1.2 μm. The initial grain size of the microstructure is varied from 0.1 to 4 microns. Most of the grains have a size from 0.5 to 1.5 microns. Mechanical tensile tests revealed that the ultrafine grained titanium alloy VT6 possesses higher superplastic characteristics as compared with those of the standard VT6 sheet. The microstructure of deformed samples and data on changes in the grain size depending on the temperature and strain rate are investigated and represented. The comparison of the superplastic characteristics of the samples cut along and across to the rolling direction indicates the absence of anisotropy. The studied alloy exhibits the best superplastic properties at temperatures ranging from 700 to 850°C and strain rates of 4×10–4 – 4×10–3 s−1, which corresponds to the manifestation of the low-temperature superplasticity. Superplastic elongations are from 650 to 1075 %. That allows us to recommend the produced sheet alloy for development of low temperature processing methods based on superplastic forming and diffusion welding to manufacture the parts for aerospace industry.