Investigation of the Static and Dynamic Mechanical Properties of the Base Metal and Weld Zone of Haynes ۲۵ Alloy

This work presents a comprehensive investigation of the high cycle fatigue behavior of Haynes ۲۵ 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 ۶۵۰ MPa, an ultimate tensile strength of ۱۰۵۰ MPa, and an outstanding elongation of ۵۷% at room temperature. The fatigue limit was determined by test method as ۲۰۰ MPa for lifetimes exceeding ۱۰⁸ 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 ۶۶۰ MPa and ۹۶۵ MPa, respectively, with a fatigue limit of ۱۷۵ 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 ۲۵ 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.

کلیدواژه ها:

Haynes ۲۵ ، Cobalt based ، Fatigue ، Strength ، Fractography