Molecular dynamic simulations of the growth and mechanical properties of Zr—Cu films

The binary Zr-Cu system is a paradigm for studying the atomistic structure-property relationships and glass transition due to its outstanding glass formation ability (GFA). Metallic glass (MG) thin films are mainly prepared using magnetron sputtering deposition methods. The outstanding mechanical properties of these MG thin films have gained the attention of the industry. In this study, molecular dynamic (MD) simulations were employed to investigate the growth of Zr_xCu_100-x(x=50, 70, and 90), with initial conditions similar to the experimental operating ones. The deposition process of the Zr-Cu system was performed on the Si (100) substrate. The simulated radial distribution functions (RDF) and X-ray diffraction (XRD) were adopted to analyze the phase of Zr-Cu films. Additionally, the correlation between GFA and five-fold local symmetry (FFLS) was discussed in depth. The mechanical properties of the deposited films and the effect of film thickness on the tensile process were also analyzed. The results show that the structure is composition-dependent. Both Zr₅₀Cu₅₀ and Zr₇₀Cu₃₀-deposited films exhibited amorphous properties with strong short range orders, whereas Zr₉₀Cu₁₀ -deposited film showed a perfect crystal characteristic. The positive correlation exists between GFA and degree of FFLS in binary Zr-Cu systems. Zr₉₀Cu₁₀ -deposited film has a Young's modulus of 100 GPa, which is larger than that of the other two deposited films. Deposited Zr-Cu MG films exhibited better ductility than crystalline ones. Herein, the failure strain of Zr-Cu MG films exceeded 40%. The correlation existed between GFA and mechanical strength. Deposited films with higher GFAs had greater strength at the same box size. Moreover, the Zr₅₀Cu₅₀ -deposited glass film had greater ultimate tensile strength than the near-eutectic glass film (Zr₇₀Cu₃₀). This study also shows that the deposited film exhibited a certain size effect. The size effect was detected, and when the thickness of the film was smaller, the tensile strength was greater. This study provides new ideas for the preparation of MG films with perfect mechanical properties.