Thermal stress in large area free-standing diamond films was remarkable during the post-deposition cooling of direct current (DC) arc plasma jet chemical vapor deposition (CVD) process.In this research,the stress release caused by delamination of Cr interlayer was of great importance to ensure the integrity of free-standing diamond film.The effects of Cr interlayer on Mo substrate,namely composite substrate,on thermal stress were investigated.Thermo-mechanical coupling analysis of the thermal stress was applied by finite element analysis (FEA) using ANSYS code.It was found that the interlayer could be destroyed first by the large thermal stress,and then the stress could be released and the probability of diamond film crack initiation would be reduced.The stress concentration at the bent edge of diamond film was also discussed.In addition,diamond films deposited on Mo substrates with and without Cr interlayer were prepared by DC arc plasma jet CVD system and experimental measurements were used to characterize these films.It was found that composite substrate could be an effective method of growing free-standing crack-free diamond films by DC arc plasma jet CVD system when there is no special requirement to the film strength. Thermal stress in large area free-standing diamond films was remarkable during the post-deposition cooling of direct current (DC) arc plasma jet chemical vapor deposition (CVD) process. In this research, the stress release caused by delamination of Cr interlayer was great importance to ensure the integrity of free-standing diamond film.The effects of Cr interlayer on Mo substrate, namely composite substrate, on thermal stress were investigated.Thermo-mechanical coupling analysis of the thermal stress was applied by finite element analysis (FEA) using ANSYS code. It was found that the interlayer could be destroyed first by the large thermal stress, and then the stress could be released and the probability of diamond film crack initiation would be reduced. The stress concentration at the bent edge of diamond film was Also discussed, in addition, diamond films deposited on Mo substrates with and without Cr interlayer were prepared by DC arc plasma jet CVD system and experimental measurements we re used to characterize these films. It was found that composite substrates could be an effective method of growing free-standing crack-free diamond films by DC arc plasma jet CVD system when there is no special requirement to the film strength.