In this study, NiAl-Al2O3-WC nanocomposite has been synthesized from the Al-NiO-W-C powder mixture by mechanical alloying and subsequent heat treatment. Phase development and structural changes were studied by X-ray diffraction technique, field-emission gun scanning electron microscopy, and transmission electron microscopy. XRD results showed that NiO was disappeared after 1 h milling and NiAl, Al2O3, and W2C phases were formed and after 20 hours of mechanical alloying, NiAl and W2C were the only phases that seen in the XRD results and no phase development was observed. So, for access to desired compounds, 20 h milled powder thermally treated at 1200 ˚C for 3 hours, and XRD and TEM results confirmed the formation of NiAl-WC-Al2O3 nanocomposite with an average size of less than 100 nm. In the following, to achieve the best available conditions for coating by spark plasma sintering process, samples of nanocomposite were prepared under different sintering temperatures and holding times and were eva‎luated in terms of microstructure, density, hardness, roughness and corrosion behavior. Finally, the coating was carried out at 1100 ° C, under uniaxial pressure 60 MPa for 10 min. NiAl-WC-Al2O3 composite coating was successfully manufactured on steel substrate (St37) by spark plasma sintering method and were eva‎luated in terms of microstructure, corrosion behavior and mechanical properties. The results showed that steel substrate and coating was strongly interconnected and no separation and porosity were observed in their interface. The images of scanning electron microscopy showed that composite coatings with the thickness of 500 μm were obtained for all samples. Microhardness test showed that microhardness of the composite coating reached over 800 Vickers and the hardness increased more than 4.5 times compared to the steel substrate. The results of corrosion polarization showed that the corrosion resistance of coated samples exhibits nobler than St37 steel substrate in 3.5 wt.% NaCl solution. Wear analysis also showed that the wear rate of coated specimens was on average 10 times lower than that of uncoated specimens. However, increasing the temperature is effective in increasing the wear rate but in this composite, with increasing temperature up to 400 ° C and the formation of lubricant layer on the composite, the wear rate is reduced to minimum amount. Also, the coefficient of friction for coated specimens in all test conditions was less than uncoated specimens.

مرتضي شمعانيان اصفهاني، مسعود عطاپور

عبدالمجيد اسلامي، حميدرضا سليمي جزي