Abstract
In this study, diamond-copper composites were prepared with ZrC/Zr-coated diamond powders by spark plasma sintering. The magnetron sputtering technique was employed to coat the diamond particles with a zirconium layer. After heat treatment, most of the zirconium reacted with the surface of diamond and was transformed into zirconium carbide. The remaining zirconium on the zirconium carbide surface formed the outer layer. Owing to the method used to produce the ZrC/Zr-coated diamond in this study, the maximum thermal conductivity (TC) of 609 W·m−1·K−1 was obtained for 60 vol. % diamond-copper composites and the corresponding coefficient of thermal expansion (CTE) reached as low as 6.75 × 10−6 K−1. The bending strength of 40 vol. % ZrC/Zr-coated diamond-copper composites reached 255.95 MPa. The thermal and mechanical properties of ZrC/Zr-coated diamond-copper composites were substantially superior to those of uncoated diamond particles. Excellent properties can be attributed to the strengthening of the interfacial combination and the decrease in the interfacial thermal resistance due to the improvement associated with the ZrC/Zr coating. Theoretical analysis was also proposed to compare the thermal conductivities and CTE of diamond-copper composites fabricated with these two kinds of diamond powders.
Highlights
Conventional electronic packaging materials such as W/Mo-Cu [1], SiCp -Cu/Al [2,3] all display limited thermal conductivities (TCs)
Zirconium reacted with the diamond surface, and the inner ZrC layer thereon formed firm chemical bonding
As diamond surfaces were physically coated with zirconium and a slight carbonization reaction occurred on the diamond surface during heat treatment, the diamond particles maintained good surface morphology
Summary
Conventional electronic packaging materials such as W/Mo-Cu [1], SiCp -Cu/Al [2,3] all display limited thermal conductivities (TCs). The alloying elements inevitably diffuse into the copper matrix, which greatly reduces the TC of diamond-copper composites Another method is to coat diamond with B [17,18], Ti [19,20], Cr [21,22], Mo [23,24,25,26], or W [27,28,29,30] by vacuum micro-deposition, molten salt bath, or magnetron sputter deposition. Small quantities of zirconium can form a thin ZrC layer with diamond, and the remaining elemental residue resides in the copper, which can reduce the thermal diffusivity of the matrix. With rapid sintering by spark plasma sintering (SPS), the outer zirconium layer partly diffused into the copper matrix, so the copper matrix and zirconium layer had good interfacial adhesion With this well-designed coating layer on the surface of diamond particles, both the coating layer with diamond and copper matrix effectively combined. With the small size particles filling in the gaps of larger ones, the density of the composite can be effectively increased
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