Effect of heat treatment on microstructure and mechanical properties of selective laser melting GH4169 alloy at 650 ℃: in-situ SEM investigation

Abstract

The effect of heat treatment on the microstructure and high temperature mechanical properties of SLM GH4169 alloy was studied by using a self-developed in-situ high temperature tensile device. The results show that the grain morphology of as-built alloy changes from columnar crystal to equiaxed crystal after homogenization+solid solution+aging treatment （HSA）， coupling with Laves phase dissolution， and a large amount of γ′ and γ″ strengthening phase precipitates. At 650 ℃， the yield strength and tensile strength of the as-built sample are 574 MPa and 740 MPa， while the yield strength and tensile strength of HSA sample are 818 MPa and 892 MPa respectively， which are 42.5% and 20.1% higher than that of the deposited alloy. The deformation process can be further characterized by in-situ tensile testing. The surface grain undulation of the as-built sample gets larger， the coordinated deformation ability becomes stronger， and the plastic flow ability gets better.The cracks in the as-built sample are originated around the Laves phase， spreading along the dendrite towards the maximum shear stress， and shear fracture occurs after necking of the sample. In HSA samples， the cracks are initiated around carbides and propagating along the grain boundaries. The fracture mode is a mixed type， involving both intergranular and transgranular fractures.

Keywords

• gh4169 alloy
• selective laser melting
• high temperature in situ tensile
• heat treatment