In this study we examine the structure and mechanical properties of ternary carbide films, with the objective of understanding the role that residual stress, density, grain size, texture and crystallinity play in determining film hardness. The main variables we used to alter film structure are the nominal film compositions and substrate bias voltage. The systems examined here are Ti-Hf-C and Hf-Si-C, and are compared to previous work on Ti-Si-C. The Hf-Si-C films show hardness levels above that of HfC alone. Residual stress measurements show a compressive stress to be present, with the exception of the -25V sample where the stress was tensile. However, compositional analysis of the biased samples by XPS reveals that Si content in the films is reduced by the application of substrate bias. Consistent with this, the films with higher bias have larger grain sizes and better crystallinity. For the Ti-Hf-C films, the results for hardness vs. bias are consistent with known stress and densification effects of the bias, and values are consistent with rule-of-mixtures expectations.