Scanning speed and powder flow rate influence on the properties of laser metal deposition of titanium alloy

Abstract

Ti4Al4V is an important aerospace alloy because of its excellent properties that include high strength-to-weight ratio and corrosion resistance. In spite of these impressive properties, processing titanium is very challenging which contributes to the high cost of the material. Laser metal deposition, an important additive manufacturing method, is an excellent alternative manufacturing process for Ti6Al4V. The economy of this manufacturing process also depends on the right combination of processing parameters. The principal aim of this study is to know the optimum processing parameters that will result in deposit with sound metallurgical bonding with the substrate with proper mechanical property and better surface finish. This will help to reduce the need for expensive secondary finishing operations using this manufacturing process. This study investigates the influence of scanning speed and the powder flow rate on the resulting properties of the deposited samples. Microstructure, microhardness, and surface finish of Ti6Al4V samples were produced using the laser metal deposition process over a range of scanning speeds, ranging from 0.02 to 0.12 m/s, and powder flow rate, ranging from 0.72 to 6.48 g/min. The microstructure, microhardness, and surface finish were characterized using optical microscopy, Metkon hardness tester, and Jenoptik surface analyzer, respectively. These process parameter variations were mapped with the microstructure, the microhardness, and surface roughness. The microstructures were found to change from the thick lath of basket woven to martensitic microstructure as the scanning speed and the powder flow rate were increased. The microhardness and the surface roughness were found to increase as the scanning speed and the powder flow rate were increased. It can be concluded that in order to minimize the surface roughness while maintaining a moderate microhardness value, the optimum scanning speed is about 0.63 m/s while the powder flow rate should be maintained at 2.88 g/min. The laser power and the gas flow rate should also be fixed at 3 kW and 2 l/min, respectively.