The preparation and structure of superhard films of TaN, TaC and Ta(N,C) have been researched extensively since the 1980s because of their important properties, such as high melting point, high hardness, oxidation resistance, corrosion resistance, high chemical stability etc. [14 ] . These properties are certainly related to the material structure [5, 6]. Among these, the hardness is a measure of a material's ability to resist applied load against plastic deformation. The microhardness, Hv, can be regarded as being determined by the bonding type and strength, which are reflected in the shear modulus, and, at the same time, as being determined by the configuration parameters of crystal defects, such as the dislocation substructure and so on [7, 8]. However, the establishment of the quantitative constitution equation between the microhardness and the dislocation substructure has been attempted by many people even in dreams in the past 40 years. The objective of the study reported here was to resume this kind of effort. Of course, the dislocation substructure parameter must first be measured, then the parameters can be taken into a certain quantitative constitutive equation. The real values of microhardness are usually obtained by the indentation method, which creates some damage and plastic deformation and is influenced by the substrate. How to avoid influence from the subst, ate is a serious problem. TaN, TaC and Ta(N,C) films er coatings are generally made by the plasma vapour deposition (PVD) method. Ion beam assisted deposition (IBAD) has been used successfully to prepare superhard films of TaN, TaC and Ta(N,C) with good adhesion and homogeneity in this study. These films were deposited ente Wl8Cr4V steel and Fe (99.99%) substrates in a triode-sputtering system. Pre-vacuum varied from 1 x 10 -4 to 5 x 10 -4 torr and the pressure of argen was controlled at 1 x 10 .3 torr (1 torr = 1.333 x 102 Pa). The substrate temperature was higher than 400 °C. The deposition rate was about 9 nmmin -1. The IBAD was carried out using argen (99.99%) ions as a sputtering source, tantalum (99.99%) as target, and nitrogen (99.99%), carbon and a mixture of nitrogen and carbon as len sources. Before sputtering, the system was pumped to about 8 x 10 .6 torr. The technical parameters are listed in Table I. The thickness of the prepared thin films was about 200 nm. The measurements of microhardness Hvm were