Yaser Vahidshad,
Volume 21, Issue 0 (IN PRESS 2024)
Abstract
This work presents a comprehensive investigation of the high cycle fatigue behavior of Haynes 25 cobalt-based superalloy and its welds produced by pulsed continuous-wave (CW) laser welding. The alloy, manufactured through vacuum induction melting and electroslag remelting followed by rolling and annealing, exhibited a yield strength of 650 MPa, an ultimate tensile strength of 1050 MPa, and an outstanding elongation of 57% at room temperature. The fatigue limit was determined by test method as 200 MPa for lifetimes exceeding 10⁸ cycles, highlighting its excellent resistance to cyclic loading. For the weld zone, fabricated under optimized pulsed CW laser parameters, the yield and ultimate tensile strengths were 660 MPa and 965 MPa, respectively, with a fatigue limit of 175 MPa. Advanced microstructural analyses using OM, SEM, EBSD, and XRD revealed an austenitic FCC matrix with carbide precipitates, predominantly (W, Cr)₇C₃ and M₆C, decorating both the matrix and grain boundaries. Fatigue crack initiation in the base metal was associated with carbide clusters near the surface, while in the weld zone it was strongly linked to near-surface gas porosity defects. These findings not only establish fundamental fatigue benchmarks for Haynes 25 but also provide the first direct insights into the microstructural origins of fatigue damage in its laser-welded joints, thereby addressing a critical knowledge gap for its deployment in high-temperature and cyclic-loading environments.
Yaser Vahidshad, Karen Abrinia,
Volume 22, Issue 3 (September 2025)
Abstract
Selective laser melting (SLM) is a widely used additive manufacturing method for 3D-printing metal parts. This study investigates how SLM parameters affect the density, microstructure, and mechanical properties of maraging steel 300. A process window was developed, revealing that maximum density and minimal porosity are achieved when laser energy density exceeds 50 J/mm³. Optimal parameters—100 mm/s scan speed, 20 μm layer thickness, 0.15 mm hatch distance, Stripe scanning strategy, and XZ build direction—were identified. Optimal processing reduced porosity, increased martensite content, and enhanced strength, reaching 1064 MPa and improving by 75% to 1862 MPa after aging and solution treatment. Strength gains were attributed to the uniform dispersion of nano-sized precipitates (such as Ni(Mo)3 and Ni(Ti, Al)3) within the martensitic matrix. Additionally, it was found that higher cooling rates further improve the mechanical strength of heat-treated parts.
