The influence of titanium nitride sputter deposition temperature on surface-hardened 2.5% silicon iron

Surface-hardened silicon iron (SiFe), with 2.5% Si, was sputter deposited with TiN by a reactive d.c. magnetron sputtering process. In this work we have studied the influence of the substrate temperature on the adhesion, hardness and the chemical composition of the TiN film and the substrate hardened structure during sputtering. Glow discharge optical spectrometry (GDOS) and electron microprobe analysis (EPMA), together with a scratch tester and a Vickers' hardness instrument, were used to study the chemical composition depth profiles, hardness and the critical load C_L at the TiN-substrate interface. The substrate surface hardness drops from 820 to 225 HV after TiN deposition as a result of decarburization of the SiFe surfaces. This drop in hardness level was found for all the substrate deposition temperatures, between 200 and 600 °C. The TiN surface hardness reached a maximum of 2700 HV at a substrate temperature of 300 °C and dropped to 1400 HV for a substrate temperature of 600 °C. At 200 °C substrate temperature the TiN surface hardness is 2100 HV which is considered to be a normal hardness for stoichiometric TiN film. GDOS chemical composition depth profiles show changes in the relative intensities at the interface when the substrate deposition temperature was at 400 and 550 °C for the elements carbon, nitrogen, titanium, silicon and iron. The O:Ti ratio increases from 200 to 300 °C and decreases between 300 and 500 °C. Above 500 °C, O:Ti starts to increase again. EPMA shows that the TiN surface hardness and critical load values reach a maximum when the interface C:Ti ratio is 0.1 at a deposition temperature of about 300 °C.