Different effects of multiscale microstructure on fatigue crack growth path and rate in selective laser melted Ti6Al4V

Abstract

During the selective laser melting (SLM) process of Ti6Al4V, a special structure can be formed with columnar prior β grains along the building direction and fully martensitic α 0 within the β grain. To investigate the influence of such special structure on the fatigue crack growth (FCG) rate, Ti6Al4V specimens fabricated by SLM were heat-treated at two different temperatures in this study. The columnar grains were retained, and the martensite was decomposed when heat-treated below the β transus. It is found that all the SLM features were removed when heat-treated above the β transus. FCG rate tests were subsequently performed at room temperature, and it was found that the prior β grains affected the macroscopic fracture morphology, but there was no discernible influence on the FCG rate. The morphology of the α phase affected the crack growth path and the FCG rate. Changes in the strengthtoughness relationship induced by heat treatment can help understand the decrease in the FCG rate.

Effects of build direction and microstructure on fatigue crack growth behavior of Ti6Al4V fabricated by laser powder bed fusion

“…It has also been suggested that the most critical factor controlling strength and FCG is α′/α slat thickness 22 . Zhao et al 23 examined the effect of β‐grains on the crack extension rate and proposed that prior β‐grains affected the macroscopic fracture morphology but had no significant effect on the FCG rate.…”

Effect of laser‐scan strategy on microstructure and fatigue properties of 316L additively manufactured stainless steel

“…24 Although numerous studies have reported the effect of laser-scan strategy on microstructure of 316L LPBF parts, none of them have investigated the impact of such modifications on the fatigue behavior; however, there is a need to explore it, as the microstructure can have a strong influence on fatigue crack initiation mechanisms. [28][29][30][31] The control of the microstructure allowed by the laser-scan strategy provides an interesting way to study the microstructural influence on fatigue. Numerous studies have reported the influence of energetic parameters on defect occurrence, 22,[32][33][34][35] and have investigated the impact of LPBF defects on fatigue behavior [36][37][38][39][40][41] ; however only few studies have investigated the microstructure-defect interplay using the laser-scan strategy as the controlling parameter.…”

“…Although numerous studies have reported the effect of laser‐scan strategy on microstructure of 316L LPBF parts, none of them have investigated the impact of such modifications on the fatigue behavior; however, there is a need to explore it, as the microstructure can have a strong influence on fatigue crack initiation mechanisms 28–31 . The control of the microstructure allowed by the laser‐scan strategy provides an interesting way to study the microstructural influence on fatigue.…”