RESIDUAL STRESSES IN A MULTILAYER SYSTEM OF COATINGS

Residual stresses present in coatings are known to adversely affect coating adhesion and wear resistance, particularly in diamond coatings. Insertion of an appropriate intermediate layer between the coating and the substrate has been used to improve adhesion and wear resistance. In this study, the multilayer structures consisted of diamond/molybdenum carbide/molybdenum (substrate) and diamond/diamond-aluminum nitride/molybdenum carbide/molybdenum (substrate). Diamond was deposited via hot filament chemical vapor deposition, and AlN by laser physical vapor deposition. The residual stresses in the multilayer system of coatings were measured using x-ray diffraction and Raman spectroscopy and compared to theoretical calculations. The sign of residual stresses in the diamond, molybdenum carbide and molybdenum were consistent with the expected sign due to thermal expansion mismatch. Raman analysis indicated that the diamond layer possessed compressive residual stresses, which increased near the molybdenum substrate/coating interface. The interposing AlN layer in the multilayer diamond sample may have provided enhanced adhesion for a given stress level relative to a sample without this interposing layer as the multilayer diamond sample did not delaminate.