Effect of argon-nitrogen mixing gas during magnetron sputtering on titanium interlayer deposition with TiB2 coatings on high speed steel

It has been a common practice that in the deposition of a ceramic coating onto a substrate, a thin titanium interlayer is used to improve the adhesion between the coating and the substrate. But the structure and strength of the interlayer play an important role in determining the adhesion strength of the coating. This work involves the deposition of titanium diboride (TiB2) based nanostructured coatings on high speed steel substrates. A titanium interlayer was applied by sputtering a titanium target in pure argon atmosphere and in argon-nitrogen gas mixtures to affect nitrogen doping of the interlayer. Structural and properties analysis revealed that various contents of nitrogen gas in argon-nitrogen gas mixture during deposition by magnetron sputtering has significant effect on the adhesion between the TiB2 coating and the high speed steel substrate. There exists an optimum degree of nitrogen incorporation in the interlayer that results in the maximum enhancement in adhesion. The beneficial effect of nitrogen gas mixing is discussed in terms of the modified structure and increased hardness of the interlayer, which provides stronger support for mechanical loading.