Microstructures and properties of W–Cu functionally graded composite coatings on copper substrate via high-energy mechanical alloying method

Abstract

In the present work, process of gradual addition of powders was proposed to prepare W–Cu functionally graded composite coatings on copper surface via high-energy mechanical alloying method using a planetary ball mill. The microstructures and elemental and phase composition of mechanically alloyed coatings were studied using scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy dispersive X-ray spectroscopy (EDS). Fully dense and uniform triple layer W–Cu (W–30wt.% Cu+W–15wt.% Cu+W–7wt.% Cu) functionally graded composite coatings was metallurgically bonded on the pure copper substrate, with an average thickness of ∼92μm. Microhardness test and friction and wear test were carried out to examine the mechanical properties of the coatings. The results showed that the maximum microhardness of the triple layer gradient coatings reached HV0.1 212, showing a threefold improvement upon the pure copper substrate. And the cross-sectional microhardness values of the processed sample changed gradually, which gave a proof for the cushioning and sustaining functions of the W–Cu functionally graded composite coatings. The friction coefficient of the as-fabricated triple layer W–Cu functionally graded composite coatings was 0.5 and the corresponding wear mass loss was only 2.8mg, which was obviously lower than that of the pure copper substrate. A reasonable formation mechanism of W–Cu functionally graded composite coatings prepared by process of gradual addition of powders via high-energy mechanical alloying method was presented.