Improved adhesion of polycrystalline diamond films on copper/carbon composite surfaces due to in situ formation of mechanical gripping sites

Diamond coatings are investigated for thermal management, wear protection and corrosion resistance in harsh environments. In power electronic industries, copper (Cu), which shows high thermal conductivity, is considered as a promising substrate for diamond based heat-spread materials. However, the coefficient of thermal expansion (CTE) mismatch between diamond and Cu induces thermo-mechanical stresses that affect the integrity of the diamond-Cu assembly. In fact, diamond films deposited on Cu substrates tend to peel-off upon cooling due to the compressive stresses present at the diamond-Cu interface. This investigation is focused on the growth of polycrystalline diamond thin films onto Cu/carbon fibers (CFs) composite materials, using combustion flame chemical vapor deposition (CVD). It has been found that increased CF content in the Cu/CF materials leads to a reduced CTE improving, hence, the adhesion between the diamond film and the Cu/CF substrate and reduces Cu/CF-diamond interfacial residual thermal stresses. At a CF content of 40% in volume, the residual thermal stress of the diamond film deposited on the Cu/CF composite is lower than that on bare Cu and adapted with CVD diamond growth. Naturally engineered composite surfaces have enhanced the adhesion of the diamond film on the composite substrate via mechanical interlocking.