Laser assisted cold spray of 15-5 PH stainless steel in a designed and developed setup

Laser Assisted Cold Spray (LACS), a hybrid deposition process can be used to deposit crack free coatings in solid state with high compressive residual stress for variety of materials. However, high gas consumption rate, high maintenance cost, and costly experimental set-up often restricts its widespread usage in industries. The present work attempts to address these challenges. A novel design for a compact supersonic nozzle has been concep-tualized and fabricated. The nozzle is designed for 2 Mach gas velocity having Converging- Diverging-Barrel (C-D-B) typed shape in which powders are injected in the barrel zone where the gas pressure ratio is minimum. Thus, it can be used with any commercially available low gas pressure powder feeder. The flow characteristics of the gas jet coming out of the nozzle have been characterized using a simple yet accurate home-built experimental setup. Gas velocity measured at the 5 mm standoff distance was similar to 550 m/s, which compared well with the supersonic gas velocity estimated by measuring the gas jet temperature at the nozzle exit. Crack-free deposition of 15-5 PH Stainless Steel up to 220 mu m layer thickness and an average compressive residual stress of 372 MPa was obtained on SS304 substrate. Substantial increase in hardness and scratch hardness,1.5 times and 2.5 times respectively, of the coating was obtained as compared to those of the substrate material. The coating could sustain upto 60 N load without producing any cracks during scratch test.