Properties of boron carbide thin films deposited by pulsed laser deposition

Boron carbide (B4C) is the third hardest material known after diamond or ta-C and cubic boron nitride (c-BN). Due to its super-hardness and, moreover, its stability up to high temperatures and chemical stability against ferrous materials, it is an interesting material for use as wear resistant coatings, particularly in applications where diamond or ta-C films are not possible to use. Super-hard boron carbide coatings were produced using Pulsed Laser Deposition (PLD) and their mechanical properties were investigated in dependence of the laser fluence and the substrate temperature during deposition. While substrate temperature was found to have a significant influence on the hardness of the coatings, the influence of the ablation fluence was insignificant. At all fluences used, the indentation hardness increases from some 31 GPa at mom temperature up to 47 GPa at 500 degrees C. The Young's modulus was measured to be in the range of 470 to 600 GPa. The films show good adhesion on tungsten carbide but a poorer adhesion on cold working steel. The surface quality, however, was poor at film thicknesses sufficient for practical applications due to the incorporation of many droplets. In order to improve this, an approach was made using an alternative boron carbide target the results of which also are presented. The target was produced by depositing a several ten microns thick boron carbide film on a steel substrate using PLD. The films deposited using this target were found to have much less and much smaller droplets.