Microstructural and microchemical characterization of Ni-Ta-Al-Cr-C coating layer on austenitic stainless steel AISI 310

Microstructural and microchemical characterization of Ni-Ta-Al-Cr-C coating layer, deposited by Gas Tungsten Arc Welding (GTAW) method on AISI 310 is presented. The layer was characterized by X-ray diffraction (XRD), light microscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and hardness measurements. Results obtained by XRD and TEM show that the coating layer consists of a γ-nickel matrix strengthened by the γ′-Ni3(Al,Ta) phase, MC and M7C3 carbides (of tantalum-and chromium-rich type, respectively). Growth mechanism, which depends on the cooling rate determines morphology of eutectic carbides. For slow growth rate MC carbides tend to be blocky, while for greater growth rate they exhibit a tendency to form more developed shapes. M7C3 carbides have a polygonal and reticulated plate morphology with different sizes. The γ′-Ni3(Al,Ta) phase has a spherical shape with few nanometers in diameter. The average hardness of the AISI 310 substrate is 174 ± 5 HV1, while the hardness of Ni-Ta-Al-Cr-C coating layer is 359 ± 31 HV1.