Gas Flow Rate and Scanning Speed influence on microstructure and Microhardness Property of Laser Metal Deposited Titanium-alloy

Laser metal deposition process is an additive manufacturing technology that is capable of producing three dimensional components as well as repair of an existing worn out components. Processing parameters play an important role on the resulting properties of the processed materials using the laser metal deposition process. This study investigates the influence of gas flow rate and scanning speed on the microstructural and microhardness properties of laser metal deposited Ti6Al4V, an important titanium alloy used in the aerospace industries. Nd-YAG laser was used in this work with the maximum laser power of 4.0 kW. The laser power used was 3.0 kW and the powder flow rate of 2.88 g/min was maintained throughout the experiments. The scanning speed was set between 0.01 and 0.04 m/s while the gas flow rate was varied between 1 and 4 l/min. The microstructures of the samples were studied using optical microscope while the microhardness profiling was conducted using microhardness indenter. The results showed that, as the scanning speed was increased, the microstructure changed from fine basketweave structure to coarse martensitic structure. The microhardness was found to increase with increasing scanning speed. By increasing the gas flow rate results in decrease in microhardness values while the microstructure was observed to change from martensitic structure to basketweave structure. The result from this study is especially useful in repair application in order to achieve the desired properties.