Effect of heat input on the microstructure of AlCoCrFeNi high entropy alloy coating deposited using gas tungsten arc welding

AlCoCrFeNi based high entropy alloy coatings were deposited on low carbon steel substrates using gas tungsten arc welding process in different heat inputs (two amperages of ۱۸۰ and ۲۱۰ A) and effects of heat input on the deposit microstructure was studied. The microstructural details were investigated by Optical Microscopy (OM), Field Emission Scanning Microscopy (FE-SEM) and X-ray Diffraction (XRD) analysis and microhardness testing. The result showed that the coating with the lowest heat input has petal dendritic morphology which includes two B۲ and A۲ face centered cubic structures and a Cr-rich strip-like structure in some parts of grain boundaries. By Increasing heat input a new Co-Cr rich phase appears besides the A۲ and B۲ phases. The morphology and amount of this phase are different in every area of the coating. The variations in microstructure and morphologies of the involved phases were explained based on the temperature gradient to growth rate ratio (G/R) and amount of the iron content. In all the coatings, the average hardness was higher than ۵۰۰ HV. Changes in heat input de not produce meaningful changes in the coating hardness.

Keywords:

AlCoCrFeNi high entropy alloy , Gas tungsten arc welding , Heat input , Microstructure.