Abstract:
To address the issue of low hardness and limited service life of Invar alloy in practical applications, this study employs the double-glow plasma surface alloying (DGPSA) technique to fabricate Mo and CoCrFeNiMn hard coatings on the surface of Invar alloy. The phase structure, microstructure, and element distribution of the two coatings are investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDS). The effects of loading strain rate on surface hardness, elastic modulus, and creep behavior of the two hard coatings are systematically studied via nanoindentation. The thickness of the Mo coating is approximately 8.3 μm, with a dense and uniform internal structure and a body-centered cubic (BCC) structure. The CoCrFeNiMn coating is about 10 μm thick, with some internal porosity, and exhibits a face-centered cubic (FCC) structure. Nanoindentation experiments reveal that the hardness of the Mo and CoCrFeNiMn coatings is 15.49 GPa and 8.18 GPa, respectively, while their elastic modulus are 278.7 GPa and 227.12 GPa. Both hard coatings significantly enhance the surface hardness and elastic modulus of the Invar alloy, and both exhibit sufficient toughness. The hardness of both coatings increases with increasing strain rate, showing a pronounced strain rate sensitivity, while the elastic modulus remains relatively stable. Additionally,the creep behavior of both coatings is influenced by the applied strain rate, with nanoindentation creep primarily governed by dislocation motion. The modification effect of the Mo coating is superior to that of the CoCrFeNiMn coating.
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