Bronze is commonly used as a bearing material because of its superior wear resistance. In an effort to improve further its wear resistance, researchers have resorted to adding Ni/Cr. However, the wear property need not be improved for the entire bulk of the alloy, rather it is sufficient for many applications if it is enhanced to a certain depth from the surface. In this work, a surface alloying process using the gas tungsten arc as the heat source has been developed to make an in-situ alloy of Ni/Cr with bronze at the surface. A heat transfer model with an enhanced conductivity and mass transfer model with the eddy mass diffusivity were developed for the surface alloying process. The heat distribution parameters required for the heat transfer model were determined through a vision system based experimental method and the thermal efficiency of the heat source (arc) was determined by a combined experimental and simulation method. Parametric models of the heat distribution parameters and the thermal efficiency of the heat source relating with the process parameters were developed. The heat distribution parameters were dependent on the process parameters, while the thermal efficiency was found to be independent and around 74%. The heat transfer model was used to predict the modified layer and the mass transfer model was used to predict the concentration profile of the alloying element. The models were validated through experiments. The hardness of the Bronze surface increased from HV120 to HV185 in case of Ni and HV175 in case of Cr improving the wear property of the surface. The wear rate of Bronze decreased to one fourth of its value after surface alloying with Ni and the coefficient of friction remains 0.57. The gas tungsten arc heat source is able to modify and enhance the wear property of Bronze by alloying Ni/Cr at the surface and the simplified heat and mass transfer models were able to predict the concentration of the alloying element at the modified surface.
A. Sanjivi, “Process development for surface alloying of bronze with NI/CR using GTA heat source-modelling and validation”, Amrita Vishwa Vidyapeetham ( Amrita University), Coimbatore, 2013.