Influence of laser power and powder feed rate on the microstructure evolution of laser metal deposited Ti-5553 on forged substrates

In this work, titanium blocks of Ti-5Al-5Mo-5V-3Cr (Ti-5553) have been Laser Metal Deposited (LMD) on forged substrate of the same alloy under varying laser power and powder feed rates. The microstructure has been characterized using optical microscopy, scanning electron microscopy and Electron backscatter diffraction (EBSD) techniques. Microstructure was predominantly large columnar beta-grains aligned with the build direction interspersed with fine equiaxed beta-grains. Increase in the powder feed rate was found to reduce the average beta-grain size and promoted clusters of fine grains to be retained during the deposition of subsequent layers. Increase in the laser power also reduced the average beta grain size and promoted greater nano-scaled alpha precipitates at the substrate interface and initial deposited layers which significantly increased the microhardness in this area. Dendrites exist due to micro-segregation of solutes during rapid solidification which create preferential regions for alpha nucleation. A difference in texture was observed between specimens manufactured with varying laser powers: a low laser power produced a cube texture and a higher laser power produced a < 001 > // BD fibre texture.