HfB2 and Hf–B–N hard coatings by chemical vapor deposition

Hard, dense and conformal hafnium diboride (HfB2) thin films were obtained by CVD from the precursor Hf[BH4]4 at deposition temperatures ≤ 350 °C. As-deposited films were X-ray amorphous but transformed to a nanocrystalline structure after being annealed at 700 °C. Amorphous HfB2 films exhibited a respectable hardness of 20 GPa; the hardness increased in the nanocrystalline state to 40 GPa. Ternary Hf–B–N films, which consisted of a mixture of HfB2, HfN and BN were obtained by adding atomic nitrogen to the growth flux. The formation of the softer a-BN phase produced a drop in the hardness and modulus values. A multilayer HfB2/Hf–B–N exhibited a good combination of high hardness (33 GPa) and low elastic modulus (300 GPa).