Thick tungsten coating on ferritic-martensitic steel applied with a vacuum plasma spray coating method

The characteristics of thick tungsten layers coated onto ferritic-martensitic (FM) steel blocks using a vacuum plasma spray system were investigated. Because of the large differences in thermal properties between tungsten and FM steel, it is difficult to coat a thick tungsten layer onto FM steel without delamination or detachment of the coated layer from the substrate. To avoid detachment of the tungsten layer from the FM steel surface, the optimization of the coating process was studied in this work. The tungsten layer having a 3.7. mm thickness was coated using 43. kW DC torch power at 16. kPa of chamber pressure with a mixture of argon, hydrogen, and helium. The adhesion between the coating layer and the FM steel was enhanced by inserting pre-heating process before coating process, which increased the penetration of molten tungsten droplets into the FM substrate. The hardness of the coating layer was about 380-400. HV, which was 80 to 95% of the hardness levels for commercial bulk tungsten monoblocks, and the porosity, purity, and morphology properties of the tungsten coating layer were also discussed. To evaluate the homogeneity of the layer bonding between the FM steel and the tungsten coating layer, an ultrasonic test was also performed.