Investigation On Alloying Method Of Pure Copper Surface Subjected To Surface Mechanical Attrition Treatment

Copper is one of the most common engineering materials and used widely in various fields because of its excellent mechanical and electrical properties. However, the hardness of pure copper material is bad, which is hard for its further use in some special fields. Cu-Ni alloy, Cu-Al alloy has many excellent properties, but due to its poor ductility at low temperature and toughness, meanwhile the preparation of equipment requirement is more strict, thus failing to play its due role. Metallic surface nanocrystallization can make metal hardness increase greatly; therefore nanocrystallization in the surface of pure copper has been widely concerned in recent years. If get both alloys and nanocrystalline layer in pure copper surface, then it will improve significantly the properties of pure copper materials and make it get more extensive application. Surface mechanical attrition treatment (SMAT) is the experimental method of using the projectile to spraying material surface, making a strong plastic deformation on material surface and achieving nanometer in grain size eventually. In this paper, different powder are added in pure copper material for SMAT treatment according to the principle, which can obtain the surface of pure copper material with alloy layer and find a new method of metal surface modification.In this paper, the rolling pure copper plate (99.8wt%>) was carried out stress relief annealing treatment, after polishing processing, adding nickel powder and aluminum powder subjected to SMAT treatment for120min and240min respectively. The composition distribution and microstructures of composite layers of samples were characterized by means of optical microscopic (OM), X-ray diffraction(XRD) and scanning electron microscopic (SEM).The concentration variation of Ni and Al element along the depth of the treated sample was examined by using X-ray energy dispersive spectrum (EDS). Using the Vickers hardness instrument to analyze hardness of all specimens; At the same time, corrosive nature was tested on specimens; Finally using the friction-abrasion testing machine to test friction wear properties of the tested sample. To find out material performance change of the experiment after adding nickel powder and aluminum powder subjected to SMAT. The experimental results are as follows:(1) Cu-Ni alloy layer was formed on the surface after adding nickel powder to the pure copper subjected to SMAT treatment. The thickness of35μm and50μm Cu-Ni alloyed layer, combining with matrix deformation layer closely, were synthesized with different treatment time of120min and240min respectively. EDS analysis results also show that Cu-Ni alloy layer and deformation layer of proceed samples appear resulted from mutual diffusion between copper atoms and nickel atoms, the binding force between the substrate and Cu-Ni alloyed layer is stronger.(2) Cu-Al alloy layer was formed on the surface after adding aluminum powder to pure copper subjected to SMAT treatment. The thickness of37μm and37μm Cu-Al alloyed layer, combining with matrix deformation layer closely, were synthesized with different treatment time of120min and240min respectively. EDS analysis results also show that Cu-Al alloyed layer and deformation layer of proceed samples appear resulted from reaction diffusion between copper atoms and aluminum atoms, the binding force between the substrate and Cu-Al alloyed layer is stronger.(3) Pure copper subjected to SMAT treatment after adding nickel powder for240min and120min, the surface hardness is302HV and274HV respectively, improving3and2.7times compared with the matrix. Pure copper subjected to SMAT treatment after adding aluminum powder for240min and120min, the surface hardness is324HV and320HV respectively, increasing3.3times compared with the substrate. As a result, alloy layer was formed after Nano crystallization and SMAT treatment, the hardness of the material had a lot of ascension.(4) Pure copper adding with nickel powder after240min SMAT treatment, the sample in the electrochemical polarization test shows that corrosion potential increase and corrosion current decrease, greatly improving the corrosion resistance of materials. And sample adding with nickel powder after120min by SMAT, the electrochemical polarization test shows that corrosion potential decrease, corrosion current increase slightly and its corrosion resistance is down a bit. Pure copper adding with aluminum powder after120min and240min SMAT treatment, two samples in the electrochemical polarization test shows that corrosion current increase a lot, the corrosion resistance material decrease obviously.(5) The sample that pure copper adding with nickel powder120min and240min by SMAT treatment, the friction and wear performance is greatly improved. The friction and wear performance after SMAT240min is more excellent than that after SMAT120min. The samples were formed after pure copper adding aluminum powder after120min and240min by SMAT treatment, its performance of friction and wear is improved under small load. But with the increase of load, performance of friction and wear didn’t have the obvious promotion effect which is similar with those of the substrate.