Search

Abstract: Nanostructured Cr2N/Cu multilayer coatings were deposited periodically by a bipolar asymmetric reactive pulsed DC magnetron sputtering system. The crystalline structure of multilayer coatings was determined by a glancing angle X-ray diffractometer. Microstructures of thin films were examined by an atomic force microscopy (AFM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM), respectively. A nanoindenter, a micro Vickers hardness tester and pin-on-disk wear tests were used to evaluate the hardness, fracture toughness and tribological properties of the thin films, respectively. Electrochemical tests in 3.5 wt.% NaCl aqueous solution were performed to evaluate the corrosion resistance of multilayered coatings. The bilayer period of the nanostructured multilayer coatings were controlled within the range from 5 to 40 nm. It was found that the hardness increased with decreasing bilayer period and leveled off at small periods around 6–12 nm. The Cr2N/Cu multilayered coatings with bilayer periods of 5 and 6 nm exhibited a combination of high hardness, good tribological and good anticorrosion performance in this study. [Copyright &y& Elsevier]

Ternary Ni–P–W and Ni–P–Cr alloy molding coatings were fabricated by radiofrequency (RF) magnetron sputtering onto steel substrate, AISI 420 tool steel. Cycling annealing up to 500 °C was performed on various Ni–P-based coatings to simulate the cycling injection or press-molding process in practical use. The mechanical properties, including hardness and Young''s modulus of the alloy coatings, were evaluated by continuous stiffness measurement. It was observed that the ternary Ni–P–Cr and Ni–P–W coatings exhibited a maximum hardness up to 14 and 15.5 GPa under 8 and 12 h of annealing test at 500 °C, respectively. With long-term annealing up to 20 h at elevated temperature, the Ni–P-based coatings retained a steady hardness of 12 GPa. The influence of the third element introduction on the mechanical properties of the Ni–P-based coating was probed and discussed. The incorporation of W and Cr into the NiP-based coating exhibited superior mechanical behavior under elevated temperature environments as compared to Ni–P binary coating. In addition, the correlation between indentation penetration depth and mechanical behavior was also evaluated. Reliable hardness values of the coatings were extracted from the indentation range of 200–400 nm, while the gradual descent in hardness with increasing indentation depth was influenced by the substrate effect. [Copyright &y& Elsevier]

Abstract: In this study, CrN top coating with NiP and NiPAl alloy interlayers were fabricated by sputtering technique. The microstructure of the CrN/NiP-based composite coatings was controlled by process temperature during sputtering and post annealing procedures. The alloy NiP and NiPAl interlayers remained an amorphous feature as CrN top coating was deposited at 350°C. The higher CrN deposition temperatures hastened the crystallization of the NiP-based interlayer significantly. The NiPAl interlayer exhibited a higher crystallization temperature of 450°C as compared to that for binary NiP ones. Not only could the addition of Al in NiP layer increase the thermal stability of the composite coatings, but also improve the thermal resistance during CrN coating deposition. Through indentation behavior analysis, significant creep behavior was observed when the microstructure of the interlayer was amorphous or fully crystallized. On the other hand, under proper heat treatment, the creep phenomenon of the composite coatings was suppressed by the precipitation and crystallization of the NiP-based interlayer. [Copyright &y& Elsevier]