Laser metal deposition of Ti6Al4V: A study on the effect of laser power on microstructure and microhardness

Abstract

The effect of laser power on the resulting microstructure and microhardness of laser metal deposited Ti6Al4V powder on Ti6Al4V substrate has been investigated. The tracks were deposited using 99.6 % pure Ti6Al4V powder of particle size ranging between 150 - 200 µm on 99.6% Ti6Al4V substrate. The laser power was varied between 0.8 - 3.0 kW while the scanning speed, powder flow rate and the gas flow rate were kept at the values of 0.005 m/sec, 1.44 g/min and 4 l /min respectively. The microstructure and the microhardness were studied using the optical microscope and the Vickers hardness tester respectively. Layer band or macroscopic banding was observed in all the samples which is phenomenon as it was only reported in the literature for multi-layer deposits. The literature attributed re-melting of the previous layers by the succeeding layers as being responsible for their formation. This study has revealed that this band could be as a result of shrinkage happening in the fusion zone as a result of the interaction of the deposited powder and the melt pool created by the substrate material. This study also reveals the relationship between the microstructure, the average microhardness and the laser power which are comprehensively discussed. The higher the laser power, the lower the density of columnar prior beta grain structure. Also the average microhardness increases as the laser power increases.