Investigation On Preparation Of Cu-(Cr)-(W) Binary And Ternary Composite Coatings On Copper Substrate Surface By Mechanical Alloying

As a novel method of material surface treatment technology, surface mechanical alloying not only can be used for the preparation of nanometer grain layer of bulk materials, also can be used for the fabrication of material surface coating. During the process of preparation of coating with mechanical alloying method, under the collisions and roller compactions of the high energy balls, metal powder particles undergo continuous and repeated extrusion deformation, cold welding, fracture and re-cold welding process. Meanwhile, the surface of substrate material and the powder particles are activated, which can lead to the deformed powder particles deposit on the substrate to form a coating. According to this principle, composite alloy coatings are prepared on the pure copper substrate, in order to improve the surface properties of pure copper substrate.There are three main experimental parts in this paper, which including the Cr-Cu binary composite coating, the Cr-Cu/W-Cu double layer composite coating and Cu-Cr-W ternary composite coating. The first part is about the preparation of Cr-Cu binary composite coating, which focused on the effects of Cu/Cr powder ratio on the coating surface morphology, structure and performance. The second part studied the preparation of Cr-Cu/W-Cu double layer composite coating, the bonding between the two dissimilar coatings need to be taken into account, thus the annealing treatment of the inner Cr-Cu coating was studied to figure out the effects on the forming of the bi-layer coating. The influences of the outer W-Cu coating fabricated under different milling speed on the structure and morphology of the double-layer coating were also studied. In the last part of the work, the Cu-Cr-W ternary composite coating was prepared, which mainly discussed the effects of different original powder ratios and milling parameters on the formability and performance of the Cu-Cr-W ternary composite coating. And the formation mechanism of the Cu-Cr-W composite coating fabricated under different ball milling time parameter was discussed in this part.Scanning electron microscope(SEM), energy dispersive X-ray spectroscopy(EDS) and X-ray diffraction(XRD) were used to investigate the micro-structured morphologies, chemical compositions and phase structures of the as-fabricated coatings. Micro-hardness test, scratch adhesion test and friction and wear experiment were carried out to inspect the properties of coatings.According to the experimental results, the increase of Cu content on the one hand could improve the combination performance of Cr-Cu coating, but on the other hand would reduce the mechanical properties of the coating. The composition range of Cu was in 30~50 wt. %, which could obtain a Cr-Cu coating with perfect formability. When the annealing temperature of inner Cr-Cu coating reached 800 ? and the ball milling speed to prepared the outer of W-Cu coating was 350 rpm, the as-prepared Cr-Cu/W-Cu bi-layer composite coating had relatively higher coating quality. The best preparation parameters of Cu-Cr-W ternary composite coating were powder ratio of 40 wt. % Cu-Cr-W, ball milling speed of 300 rpm and ball milling time of 7 h. The hardness testing and friction and wear experimental results showed that the as-prepared Cu-Cr-W coating could greatly improve the surface performance of the substrate material.