| Surface modification of a copper substrate can obtain a variety of excellent performance, such as high temperature resistance, wear resistance and corrosion resistance. Plasma cladding, as an advanced surface modification technique, can prepare coating with low dilution rate, dense structure and good metallurgical combination between coating and substrate. However, this technique used to prepare coating on copper substrate has not been reported. Using Ni powder and Al powder as cladding materials, this paper made a first attempt to prepare Ni-Al intermetallic compound coating on pure copper substrate by plasma cladding. Considering the poor wettability of Ni-Al intermetallic compound on copper substrate and the presence of stress singularity at the interfacial region, the Ni/Ni-Al intermetallic compound coatings were prepared, by means of joining the Ni transition layer in between Ni-Al layer and copper substrate, and the Fe and Y2O3 were added in the Ni-Al layer. The phase composition, the interfacial bonding, microstructure, composition, microhardness and wear resistance were tested. The main results are as follows:(1) Plasma cladding Ni/Ni-Al intermetallic compound coating orthogonal experiments were carried out Using L9(33) orthogonal table with three factors including working current, scanning speed, argon flow rate. The results show that argon flow rate (C), the most profound effect on the coating appearance quality and working current (A) influence on the coating interfacial bonding and microhardness most significantly. The optimum parameters:working current is 150 A, scanning speed is 10 cm/min, argon flow rate is 1 L/min.(2) Preparig Ni/Ni-Al coatings by plasma cladding with the optimum parameters, the research results are as follows:in-situ synthesized single-phase of NiAl intermetallic compound is obtained. The coating is dense and crack-free. The Ni transition layer form a metallurgical bond with copper substrate. The microstructure change from the substrate to the surface is planar grain→columnar grain→disordered dendrite→quiaxed grain. In the frictional wear test, Ni-Al coating does not appear brittle fracture, but appears the furrows of the abrasive wear characteristics, the wear is caused by multiple plastic deformation leading to fracture.(3) In the Ni-Al coatings with different Fe content, the main phase is single-phase NiAl, Fe as the solute atoms in NiAl solid solution. Microstructure of the coatings are mainly the dendrite; Ni, Al, Fe, Cu elements exist obvious transition gradient at the interface, the coating and copper substrate form a metallurgical bonding. With the increase of Fe content, the dendrites are gradually refined; thickness of the Ni transition layer narrows because of the lower melting point of Ni-Al-Fe ternary alloy; Microhardness of the coating increases first and then decreases, when the Fe content is 15at.%, the maximum microhardness is obtained. The wear resistance of the Ni-Al coatings added with Fe is significantly improved, the highest wear resistance of coating is 6.5 times over that of the coating without Fe.(4) The phase composition of Ni-Al coatings with different Y2O3 content change with the increase of Y2O3 content. When the Y2O3 content is less than 1.5wt.%, the single-phase intermetallic compound NiAl can be obtained. When the Y2O3 content is 2.0wt.%, the NiAl phase and M3Al phase exist in Ni-Al coating. With the increase of Y2O3 content, Ni-Al coating micro structure is refined, obtaining the dispersed precipitation; Ni, Al, Cu elements change from the coating area to interfacial region and the dilution of cladding materials from the substrate is reduced; Due to the alloy fluidity enhancement, Ni transition layer disappears; The average microhardness of the coating increase. The wear resistance of the Ni-Al coatings added with rare earth is significantly improved, the highest wear resistance of coating is 8.7 times over that of the coating without Y2O3. |
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