Comparison of the influence of molybdenum and chromium TIG surface alloying on the microstructure, hardness and wear resistance of ADI

In this study microstructures and wear resistance of different layers formed by tungsten inert gas (TIG) surface melting as well as molybdenum and chromium surface alloying of austempered ductile iron (ADI) were studied. Surface melting resulted in formation of a ledeburitic structure with the hardness up to 895 Vickers (HV) as compared to the 360 HV, that of ADI. Chromium surface alloying resulted in formation of two different structures depending on the chromium content of the layer. In the specimen with higher chromium content a hypereutectic structure consisting of primary (Fe,Cr)7C3 carbides and a eutectic matrix, with a hardness of 1080 HV, was formed. However, in the specimen with lower chromium content a ledeburitic structure with an acicular morphology comprised of (Fe,Cr)3C carbides, martensite and retained austenite with a hardness of 895 HV was produced. In molybdenum surface alloyed specimens the microstructure formed included cementite, (Fe,Mo)3C carbides, martensite and retained austenite. With the increase in the amount of molybdenum in the alloyed layer, the amount of (Fe,Mo)3C carbides increased resulting in raising the hardness from 855 to 1065 HV. The results also revealed that surface melting reduced the wear rate of the ADI by approximately 37%. In addition, chromium and molybdenum surface alloying also reduced the wear rate of ADI about 66 and 62% respectively.