Low temperature stress relief and martensitic decomposition in selective laser melting produced Ti6Al4V
Gerrit Matthys Ter Haar, Thorsten Hermann Becker
Abstract
This study contributes to the limited understanding of the initial stages of martensite decomposition and stress relief of SLM-produced Ti6Al4V. Samples are annealed at a temperature range of 427–610°C for hold times ranging from 5 minutes and 30 hours. Stress relief is measured through x-ray diffraction, while phase transformation is observed using microscopy and x-ray diffraction techniques. Tensile tests and hardness measurements are used to obtain mechanical properties. Key findings of this study are that ultra-fine vanadium-rich precipitates form at α’ dislocations and grain boundaries during preliminary phase transformation. While initial formation of vanadium-rich precipitates results in the embrittlement of the material, further growth of these precipitates into measurable β-phase is extremely slow but allows for an improvement of material ductility. The study reveals that phase transformation is incomplete after 30 hours at 610°C. While an increase in annealing temperature accelerates phase transformation and improves ductility, this comes at a cost of material strength.