Thermo-chemical treatment of nickel composite layers containing titanium
Andrzej Serek, Antoni Budniok Uniwersytet Śląski, Instytut Fizyki i Chemii Metali, ul. Bankowa 12, 40-007 Katowice
Annals 2 No. 3, 2002 pages 58-62
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abstract In order to improve of utilitarian properties of the nickel layers, the layers were co-deposited from baths containing solid metal particles of different oxides (TiO2, Sc2O3, NiO), carbides, nitrides or PTFE. Incorporating into a metall matrix the component in powder form and its embedding into a matrix structure allows to obtain a new kind of composite material. Therefore, the present study was undertaken in order to obtain the galvanic composite layers containing embedded titanium grains into crystalline or amorphous matrix. Electrodeposition of Ni+Ti and Ni-P+Ti composite was carried out in the nickel galvanic bath to which 40 g/dm3 of titanium powder was added. Electrodeposition process was carried out on a steel substrate (018 A1IT). Thermo-chemical treatment of obtained composite layers was conducted at nitrogen atmosphere at a temperature of 1093 K for 6÷48 hours. After treatment the structural analysis, the surface morphology, microhardness and the percentage volume fraction of selected TiN phase was investigated. The phase composition of the layers was studied by the X-ray diffraction method. It was ascertained that the thermal treatment of the Ni+Ti layers leads to production of a new kind of composite layers containing TiN, Ni3Ti and NiTi phases (Fig. 1a), where the thermal treatment of the Ni-P+Ti layers produces layers containing TiN, Ni5P2, Ni3Ti and NiTi phases in the nickel matrix (Fig. 1b). The quantity of those phases depends on time of the thermal treatment. The surface morphology after thermal treatment was investigated by Nikon stereoscopic microscope and Svistmet computer system. Obtained layers show the mat, rough metallic surface with places of gold colour (Fig. 2a, b). Depending on thermal treatment time at 1093 K the different surface morphology are produced. This indicates that chemical reaction in solid state in the layer took place. It allows to determine the percentage of volume fraction of selected TiN phase. It was proved that the composite layers Ni+Ti and Ni-P+Ti contain about 46 and 30% TiN respectively (Fig. 3). Additionally the micro-hardness of the obtained coatings was calculated. The micro-hardness of the Ni+Ti and Ni-P+Ti layers after thermal treatment is higher then the values before the thermal treatment. The highest micro-hardness are observed after 48 hours of nitridation. The micro-hardness of the Ni+Ti and Ni-P+Ti layers depends on time of thermal treatment (Fig. 4). Using the microscopic observation the thickness of the diffusion layers obtained after thermal treatment from cross-sections were evaluated (Figs 5, 7). The thickness of those diffusion layers increase non linearly with annealing time (Fig. 6). It means that in the layers the different chemical reaction and phase transformations occur. In conclusion it is stated that after thermo-chemical treatment obtaining of the Ni+Ti and Ni-P+Ti layers are possible in new kind of composite which contains TiN, Ni3Ti and NiTi or additionally Ni5P2 phases embedded in the nickel matrix. These layers exhibit that their structure is based on a nickel matrix