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ABSTRACTSynthesis of the Cr2AlC MAX phase was investigated by mechanical alloying. Cr, Al, and C powders were milled and heat treated at temperature range of 500–1300°C for 1 h. X-ray diffraction and differential thermal analysis were used to study the reaction mechanisms and a scanning electron microscope was used to observe the microstructures. The Cr7C3and Cr–Al compounds were formed by reactions among the initial elements. These compounds transformed to the Cr2AlC phase by increasing the temperature. The maximum amount of Cr2AlC phase was equal to 97.23 wt.%, which was related to the sample with 45 h of ball milling and subsequent heat treatment at temperature of 700°C. DTA results showed a major exothermic peak at about 685°C, which represents the formation of the Cr2AlC . This indicates that most conversions are completed in a single stage, below the temperature of 800°C.

In this research, the effect of different bonding times on the microstructure and mechanical properties of the WC-Co/St52 joint created by the transient liquid-phase process at 1200°C using copper interlayer was investigated. For this purpose, bonding times of 1, 15, 30, and 45 min were used. The microstructure of the bonded samples was examined using an optical microscope as well as scanning electron microscope equipped with energy-dispersive X-ray spectroscopy. Microhardness and tensile-shear strength tests were carried out to evaluate the mechanical properties of the joints. The results showed that there were two main zones of isothermal and athermal solidification in the bonding region, which determined the properties of the bonding samples. The isothermal solidification zone contained a Fe-rich solid solution, which increased its volume fraction with increasing the bonding time. The athermal solidification zone also contained a Cu-rich solid solution phase. The presence of Fe-rich solid solution in the centerline of the all joints caused the same hardness in all joints. The maximum tensile-shear strength was related to the sample with bonding time of 15 min, because of the proper continuity in the microstructure and presence of optimal amount of Cu-rich solid solution phase in microstructure.

Physical vapor deposition (PVD) multilayered coatings with titanium nitride and chromium nitride top layers were deposited on UNS S17400 alloy in an attempt to improve the corrosion and corrosion-wear resistance of this stainless steel in corrosive environments. The coatings were produced in an industrial chamber by cathodic arc PVD on heat-treated and mechanically polished stainless steel specimens. The microstructures of the substrates and coatings were characterized by X-ray diffraction and scanning electron microscope equipped with an energy-dispersive X-ray spectroscopy system. To evaluate the corrosion and corrosion-wear resistance, reciprocating-sliding tribometer and electrochemical tests were conducted in 3.5% NaCl solution. The results showed that nitride coatings possess, in general, better corrosion and corrosion-wear resistance compared with bare S17400 substrates. Specimens with CrN top coating revealed a typical compact structure and superior corrosion resistance compared with substrate and TiN top coating. However, the sliding motion damaged the surface with some microcracks on the coating, which act as the diffusion channels for NaCl solution; both TiN and CrN top coats experienced approximately similar behavior in corrosion-wear open-circuit potential testing.