High-temperature tensile and high cycle fatigue properties of inconel 625 alloy manufactured by laser powder bed fusion

Abstract

High-temperature tensile and high cycle fatigue properties of hot isostatic pressed LPBF Inconel 625 (laser powder bed fusion, HIPed LPBF 625) were investigated and then compared to conventional wrought Inconel 625. HIPed LPBF and wrought alloys show similar microstructural characteristics in average grain size, defects, fraction of special grain boundaries, and grain morphologies. However, Al2O3 and TiN phase was found (without carbides) in HIPed LPBF 625, and various stoichiometry of carbides (without Al2O3) were identified in wrought 625. The yield and tensile strengths and elongation at fracture of both alloys have similar values at room temperature. At 650 °C, elongation at fracture of HIPed LPBF 625 significantly decreases compared to that of wrought 625. HIPed LPBF 625 also has a lower high-cycle fatigue limit of 500 MPa (at 107 cycles without fracture) and shorter life in low-stress conditions compared to wrought 625. The relatively higher sulfur content in HIPed LPBF 625 (33 ppm) is suggested as the reason for lower fatigue endurance at 650 °C. The LPBF (or additive manufacturing), which uses powder feedstock, is vulnerable to impurity concentration increases, elemental contamination control is critical in the initial powder and LPBF process.