Effect of laser surface treatment on microstructural evolution and mechanical properties of a Co–Cr–Fe–Ni–Mo medium–entropy alloy

Abstract

In this study, we explored the influence of laser surface treatment on the microstructural evolution and mechanical properties of a Co_17.5Cr_12.5Fe₅₅Ni₁₀Mo₅ medium-entropy alloy. After laser scanning on the cold-rolled alloy, a heterogeneous microstructure with Mo-rich μ-precipitates formed along the depth from the surface. Notably, laser processing parameters, including scanning speed and the number of scans, affected the macroscopic heterogeneity in the microstructure of the alloy, such as the thickness of the columnar, recrystallized, partially-recrystallized, and non-recrystallized layers. Furthermore, the microstructural features of the laser-treated alloys with a heterogeneous distribution of grains, cellular structures, and precipitates, contributed to the mechanical response of the alloys. As the heat input from the laser heat source increases, the grain coarsening and the absence of non-recrystallized layer have a greater impact on the strength of the laser-treated alloys, even if the precipitates distributed deeper from the surface. These microstructural modifications through laser surface treatment are linked to variations in the mechanical performance of the alloys, indicating that it can be an effective method to tailor the mechanical properties of structural materials.