Tribological property in vacuum of high speed steel modified with diamond-like-carbon coatings

The diamond-like-carbon (DLC) coatings were deposited on substrate of high speed steel by unbalanced magnetron sputtering. The tribological properties of the DLC coatings against GCr15 and Si₃N₄ balls were investigated in vacuum and in ambient environment, respectively. The microstructures of the worn surfaces involved after ball-on-disc friction and wear tests were characterized with scanning electron microscopy. The preliminary results show that the DLC coating significantly reduces the friction coefficient and improves the surface hardness and wear-resistance in air and in vacuum. In addition, the friction coefficient of the DLC coated substrate against GCr15 steel and Si₃N₄ balls in air was found to be lower than that in vacuum, possibly because of the adhesive wear, as shown by the rough wear-tracks, micro scraps and grains left by the test on the surfaces of DLC coatings and balls.