The article presents a model and derives analytical expressions forHelmholtz free energy, the nearest neighbor distance, isothermal compressibility,the thermal expansion coefficient, the heat capacities at constant volume andconstant pressure as functions of temperature, concentration of interstitial atoms,and film’s thickness for an interstitial binary alloy with a BCC structure based onthe statistical moment method (SMM). The theoretical results are applied tonumerical calculations for films of W and WSi. The temperature and interstitialatom concentration dependences of thermodynamic quantities for the alloy WSi’sfilm are similar to those for the metal W film. When the film thickness increases toabout 40 nm, the thermodynamic properties of the film approach those of the bulkmaterial. The SMM numerical results for W agree well with experimental data andother calculation results. Other SMM numerical results are new and predict futureexperimental results.The article presents a model and derives analytical expressions forHelmholtz free energy, the nearest neighbor distance, isothermal compressibility,the thermal expansion coefficient, the heat capacities at constant volume andconstant pressure as functions of temperature, concentration of interstitial atoms,and film’s thickness for an interstitial binary alloy with a BCC structure based onthe statistical moment method (SMM). The theoretical results are applied tonumerical calculations for films of W and WSi. The temperature and interstitialatom concentration dependences of thermodynamic quantities for the alloy WSi’sfilm are similar to those for the metal W film. When the film thickness increases toabout 40 nm, the thermodynamic properties of the film approach those of the bulkmaterial. The SMM numerical results for W agree well with experimental data andother calculation results. Other SMM numerical results are new and predict futureexperimental results.