Experimental Study of Hardness Property and Microstructure of TiZnNi Laser Deposited on Titanium Alloy

Abstract

The study is aimed at using laser cladding technique to deposit a thick coating of composite TiZnNi on titanium alloy Ti-6Al-4V substrate. The composite powder was mixed with Zinc (Zn), Nickel (Ni) and Titanium (Ti), in which the tubular mixer was used to prepare the mixture. The laser metal deposition technique that was employed in the process was used to control the heat input, which governed the resulting microstructure of the ZnNiTi coating that was produced. This was based on the analysis that was conducted. The results of the hardness obtained from the Vickers microindenter revealed that there was an improvement as the hardness measured for the cladded ZnNiTi layer was approximately 1396.90 HV0.1 and the hardness of the Ti-6Al4V substrate was measured to be 320.8 HV0.1. This improvement was attributed to the NiTi, Ni3Ti, hard Ni4Ti3 and intermetallic phases that formed, this was confirmed by the analysis done on the cladded layer by employing EDS and XRD. The grain form and structure as well as the mechanical properties of the cladded layer were significantly affected by the heat input from the laser beam. At higher scanning speed of 1.0 m/min, the coating and substrate being limitedly mixed, resulted in the cladded layer having a significantly higher hardness than the substrate, but some hardness values gradually reduced after the cladded layer towards the interface and heat affected zone. The behaviour of the coating hardness property was improved by 4.4 compared to the hardness of the uncoated titanium substrate. The characteristics of the hardness of the deposited coating was heavily affected by processing parameters, which the grain morphologies and concentration of phase composition formed were predominant in the result of the hardness properties. Industries of biomedical and mechanical components may implement the application of composite ZnNiTi coating since there was an improvement on the hardness characteristics, which is usually of major concern in industrial applications.