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

During the selective laser melting (SLM) process of Ti6Al4V, a special structure can be formed with columnar prior beta grains along the building direction and fully martensitic alpha' within the beta 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 beta transus. It is found that all the SLM features were removed when heat-treated above the beta transus. FCG rate tests were subsequently performed at room temperature, and it was found that the prior beta grains affected the macroscopic fracture morphology, but there was no discernible influence on the FCG rate. The morphology of the alpha phase affected the crack growth path and the FCG rate. Changes in the strength-toughness relationship induced by heat treatment can help understand the decrease in the FCG rate.

Automated summary

Through investigating the influence of a special structure formed during selective laser melting (SLM) process on fatigue crack growth (FCG) rate, it was found that the prior beta grains affected the macroscopic fracture morphology, but had no discernible influence on the FCG rate, while the morphology of the alpha phase affected the crack growth path and rate. Changes in the strength-toughness relationship induced by heat treatment helped understand the decrease in the FCG rate.