Jianlin Chen

Corrosion behaviour of nanochromium coatings deposited by direct current magnetron sputtering

Chromium films are frequently used as corrosion resistant coatings. Chromium coatings with a columnar structure deposited by magnetron sputtering demonstrate poor corrosion resistance. In this paper, a nanochromium coating with a non-columnar structure was deposited on 316L stainless steel by a direct current magnetron sputtering technique. The grain size of chromium coatings with a pyramidal structure was 95 nm. The corrosion performance of the bare and chromium coated steel in 0·5M H2SO4 was examined using electrochemical impedance spectroscopy, polarisation and open circuit potential measurements. The results showed that the corrosion rate of nanochromium coatings was lower than that of uncoated steel by more than one order of magnitude. Electrochemical impedance spectra of the nanochromium coatings exhibited distinct characteristics in corrosive solution. No obvious degradation was observed for the coatings after 768 h exposure to the corrosive solution.

Effect of the Sic Particle Orientation Anisotropy on the Tensile Properties of a Spray-Formed Sicp/Al-Si Composite

The effects of the SiC particle orientation anisotropy on the tensile properties of spray-formed SiCp/Al-Si composites was investigated and compared with that of the unreinforced matrix alloy. The addition of SiC particles increased the elastic modulus but decreased ultimate tensile strength and elongation of an Al–Si alloy under peak-aged conditions. Microstructure disolayed a preferred orientation of the reinforcement particles, which were inclined to align parallel to the extrusion axis. Meanwhile, the degree of orientation anisotropy turned to be higher with larger reinforcement sizes particle. The elastic modulus, tensile strength and elongation in the longitudinal orientation (parallel to the extrusion axis) were higher than those in the transverse orientation (perpendicular to the extrusion axis). The fracture mechanism in a composite with 4.5 μm particles was attributed to interfacial debonding between SiC and matrix in the two orientations. However, in case of aluminum reinforced wild 20 μm particles, both cracking of SiC particles in the longitudinal orientation and the interfacial debonding in the transverse orientation played an important role in fracture.

ELECTROCHEMICAL CARBONITRIDING OF 316L STAINLESS STEEL IN MOLTEN SALT SYSTEM

This paper reports an electrochemical route for carbonitriding 316L stainless steel in molten salts. Carbonitriding process was accomplished in molten alkaline chloride (LiCl/KCl) with the addition of KNO2 at 480∘C using a three-electrode system in which a carbon sheet was the counter electrode. The carbonitriding layer of 316L stainless steel obtained by potentiostatic electrolysis was analyzed by several physical techniques. The results showed that a compact layer with a thickness of about 7μm formed after the treatment. According to X-ray diffraction analysis, chromium nitride and carbide formed on the surface of carbonitriding layer. The microhardness of the carbonitriding layer is HV 336, as compared to HV 265 for the substrate.

Effects of Substrate Temperature on the Corrosion Behaviour of Nanochromium Coatings Deposited by Direct Current Magnetron Sputtering

Nanochromium coatings were deposited on 316L stainless steel bipolar plates of a proton-exchange membrane fuel cell (PEMFC) by a direct current magnetron sputtering technique. The effect of substrate temperature on the corrosion resistance of nanochromium coatings was investigated. The corrosion performance of the bare and chromium-coated steel in a simulated environment of PEMFC (0.5 M H2SO4 + 2 ppm Fź) was studied using electrochemical impedance spectroscopy, polarisation, and open circuit potential measurements. The results showed that the corrosion rates of two nanochromium coatings deposited at 300°C and 500°C were lower than those of uncoated steel by more than one order of magnitude. Electrochemical impedance spectra of both nanochromium coatings exhibited distinct characteristics in corrosive solution. The nanochromium coating deposited at 500°C showed superior stability in the corrosive solution.

Investigation on compressive behavior of Cu-35Ni-15Al alloy at high temperatures

Microstructures and mechanical properties of Cu-35Ni-15Al alloy in cast and porous states were studied by scanning electron microscopy and compression tests. The influence of porosity, deformation temperature and loading rate on mechanical properties of the two kinds of alloys was investigated. The results show that the as cast alloy and porous alloys have almost the same phase constitution: Cu rich phase, Ni rich phase and K intermetallics. The yield strength of porous alloys increases continuously with decreasing porosity, the relationship between porosity and yield stress follows Gibson-Ashby equation. With decreasing deformation temperature, the yield strength of as cast alloy and porous alloy increase. With the increase of loading rate, the yield strength of these alloys shows an increasing trend. After compression, the microstructure of as cast alloy is more uniform, and porous alloys are more prone to have localized deformations.

Electrochemical Impedance Spectra for the Corrosion of Porous Cu-35mass%Ni-(5,10)mass%Cr Alloys in Molten (0.62Li,0.38K)2CO3 at 650 °C in Air

Abstract The electrochemical impedance spectra was employed to investigate corrosion behavior of porous Cu-35mass%Ni-5mass%Cr and Cu-35mass%Ni-10mass%Cr alloys in molten (0.62Li,0.38K)2CO3 at 650 °C in air. The results show that the Nyquist plots for the corrosion of two alloys are composed of two capacitive loops which indicate that localized corrosion occur for the total immersion time. The differential potential between Cu-rich phase and Cu-depleted phase contributes to galvanic corrosion of the alloys. As compared to porous Cu-35mass%Ni-5mass%Cr, porous Cu-35mass%Ni-10mass%Cr is more corrosion resistant, which is related with its smaller area fraction of the cathodic Cu-rich phase. In addition, crevice corrosion in the pores of the alloys promotes the micro-crack generation and expansion.