Laser assisted cold spray of AISI 4340 steel

Abstract

Laser assisted cold spray (LACS) of AISI 4340 steel, with sample deposited thicknesses between 1.7 mm and 3.5 mm, was accomplished by combining an infrared (940 nm wavelength) 4 kW laser with a VRC Metal Systems Gen III cold spray instrument. In situ laser heating of the substrate increased the deposition efficiency of the high strength 4340 steel from 48% to 72%. The increased surface temperature from 400 °C to 950 °C also increased the median ferrite grain size from 0.51 μm to 2.2 μm. As the ferrite grain size increased, the hardness decreased from 561 HV to 466 HV; however, at higher surface temperatures (738 °C and 950 °C) the creation of martensite occurred and compensated the lost hardness with the hardness returning to values of 532 HV and 592 HV respectively. In addition, LACS with increased laser power changed the impact behavior of particles from particle flattening to substrate penetration. Increased laser power also resulted in micro-scale oxidation during deposition.