Pulsed magnetron sputtering of chromium boride films from loose powder targets

Transitional metal boride coatings are attracting increasing interest, due to the fact that they combine high hardness with good wear and corrosion resistance. In the case of sputtering, boride coatings are often deposited from powder-metallurgically-prepared, usually brittle, ceramic targets, which often suffer from cracking caused by overheating. In addition, any change in composition requires the manufacture of a new solid target. Although chromium borides are recognised to have excellent resistance to corrosive-wear, very few descriptions of their properties have appeared in the scientific literature, to date. In this study, therefore, chromium boride coatings were deposited by the pulsed magnetron sputtering (PMS) of loosely packed blended powder targets. Sputtering of a target having Cr:B atomic ratio of 1:2 produced CrB0.92 films. Additional boron incorporated into the target enabled the deposition of crystalline films with the CrB2 structure and a strong (001) texture. These films appeared to be crystalline and fully dense with no discernible structural features or defects. The hardness of the stoichiometric pulsed magnetron sputtered CrB2 films was found to be of the order of 39 GPa. However, excess or deficit of boron in the film resulted in lower hardness values. On the other hand, DC magnetron sputtering of the same target produced low quality, X-ray amorphous films. Comparisons of coatings produced by continuous DC and pulsed DC clearly demonstrate the significant impact of the pulsed sputtering process on the structure and properties of these coatings. Further investigation of the pulsing parameters showed their importance in terms of deposition rate and film stress.