Narrow Results

SiC and SiO₂ nano-particles were co-deposited with electroless NiP coating onto API-5L-X65 steel substrates with 7g/L load of nano-particles in the bath at pH 4.6 ± 0.2 and temperature of 90 ± 2°C. The hardness and corrosion resistance of the composite coatings were measured using micro-hardness, polarization and electrochemical impedance spectroscopy techniques, respectively. Moreover, the structure of the composite coatings was investigated by means of X-ray diffraction (XRD) technique, while their morphologies and elemental compositions were analyzed using a scanning electron microscope (SEM) equipped with an energy dispersive spectrometer (EDS). Results showed that co-deposited nano-particles caused an increase in the hardness of the composite coatings. Corrosion tests showed that addition of nano-SiO₂ particles improved corrosion resistance of electroless Ni-P coatings in salty atmosphere but addition of nano-SiC particles decreased, due to the agglomeration of SiC nano-particles together with an increase in the porosity of the composite coatings.

Electroless composite coatings have been vastly used in various industries during last decades due to their good properties, such as corrosion and wear resistance, hardness and uniform thickness. In this paper, co-deposition of TiO₂ nano-particles with Nickel-Phosphorus electroless coatings on API-5L-X65 steel substrates was investigated. Surface morphology and composition of coatings were studied via SEM and EDX, respectively. XRD analyses showed that these coatings had amorphous structure with TiO₂ crystalline particles. TiO₂ nano-particles increased microhardness of coatings. Corrosion resistance of these coatings was tested using linear polarization in 0.5M sulfuric acid electrolyte. Results showed that NiP-TiO₂ electroless composite coatings increased corrosion resistance of substrates.

The present study considers the tribological behavior and corrosion resistance of electroless Ni-B-W coatings deposited on AISI 1040 steel substrates. Coating is characterized using scanning electron microscopy, energy dispersive X-ray analysis and X-ray diffraction technique. In as-deposited condition, coatings are found to be amorphous. On heat treatment, precipitation of crystalline Ni (1 1 1) and its borides take place. For as-deposited coating, the microhardness is obtained as $\sim$759HV${}_{100}$ which increases to $\sim$1181HV${}_{100}$ and $\sim$1098HV${}_{100}$ when heat treated at 350${}^{\circ }$C and 450${}^{\circ }$C, respectively. Incorporation of W in Ni-B coating results in an increase of hardness by 89HV${}_{100}$ in as-deposited condition. Heat treatment also results in increase in crystallite size of Ni (1 1 1). Wear rate and coefficient of friction (COF) of the coatings are evaluated on a pin-on-disc setup under both dry and lubricated sliding conditions. Wear resistance is observed to improve on heat treatment with an increase in crystallite size while COF deteriorates. However, in as-deposited condition, wear rate and COF of Ni-B-W coatings improve by $\sim$5 and $\sim$3 times, respectively, compared with Ni-B coatings. Wear and friction performance of the coatings are enhanced under lubrication due to the columnar structure of the coatings that retain lubricants. Corrosion resistance of Ni-B-W coating in 3.5% NaCl solution gets improved on heat treatment.

Improved of chemical corrosion resistance of silicon nitride (Si₃N₄) ceramics is strongly desired. However, there is not enough information on chemical corrosion at present. In this paper, corrosion resistance of two kinds of Si₃N₄ based ceramics with different additives developed for bearing material was investigated. One of the specimens is composed of Si₃N₄-Y₂O₃-Al₂O₃-AlN-TiO₂, the other of Si₃N₄-SiC-MgAl₂O₄-SiO₂-TiO₂. A corrosion test was conducted under conditions of 240h-soaking at 30°C and 100h-soaking at 80°C in acid and base solutions. The weights of both specimens after soaking were confirmed to decrease with decreasing concentration of sulfuric acid. The bending strength also decreased in proportional to the weight change. Contrary to the results in acid solutions, the weights of the specimens decreased with increasing concentration of sodium hydroxide solutions. The weight changes at 80°C were much larger than those at 30°C. The extent of corrosion was found to depend on the composition of the ceramics. Specimens with additives of Y₂O₃, Al₂O₃, AlN, and TiO₂ tended to corrode more easily than those with SiC, MgAlO₄, SiO₂ and TiO₂. A correlation between the weight loss and the bending strength was established.

Stainless steels are attractive due to its high strength, high chemical stability, low gas permeability and wide selection of alloys. However, stainless steels are prone to corrosion where SO4^2- and F^- are released from the membrane in the PEFCs, which, as a result, will shorten the age of the bipolar plates and exert a negative influence on the function of the cells. Therefore, great attention is given on high-nitrogen austenitic stainless steels (HNASS) which have lower costs and good localized corrosion resistance. The effects of the different F- concentration on the corrosion behavior in the high nitrogen austenitic stain steel were investigated through polarization curve measurement and electrochemical impedance spectroscopy. The results show that the corrosion resistance of the experimental steel is the best in the 0.05 mol/L SO42- (pH 5.5) + 2 ppm F- solution. As the F- concentration increases, the passivation film of the experimental steel becomes thicker and denser, leading to stronger corrosion resistance.

The yearly production of hot stamped automotive parts is increasing due to several advantages over the conventional cold forming processes, such as allowing the manufacture of components of much higher strength and of more complex geometries. Hot stamping of uncoated boron steel results in the formation of a loose oxide on the steel surface. This oxide has to be subsequently removed by shot blasting for satisfactory painting. In this paper, a method to avoid shot blasting is presented. The method is based on a chemical pre-treatment allowing anchoring of the formed oxide to the steel surface during hot stamping. Characterization by Scanning Electron Microscopy (SEM) as well as results from adhesion tests and a cyclic corrosion test of the produced material indicate that the scale adhesion is unaffected by subsequent process steps (cleaning, phosphating, and painting). The results also indicate that the corrosion properties of the hot stamped material are directly affected by scale adhesion; improved adhesion results in improved corrosion resistance. Furthermore, the chemical pre-treatment allows more rapid heating than non-modified material.

Hot forming technology can not only improve the impact resistance and safety performance of the car, but also reduce its weight, so it has become a popular research topic in China and abroad. Hot forming steel is divided into uncoated hot forming steel and coated hot forming steel. Hot stamping parts of coated hot forming steel do not need shot blasting treatment and have better corrosion resistance compared with uncoated hot forming steel, so coated hot forming steel has been used more widely. Al-Si coating is the most mature coating for hot forming steel, and the Zn coating hot forming steel is still in the research stage because of the narrow process window. This paper focuses on Masteel Al-Si coating hot forming steel, whose coating composition, matrix microstructure and mechanical properties before and after hot stamping is studied. The research shows that Masteel Al-Si coating hot forming steel has good performance, and it can meet the requirements of mainstream car manufacturers.

In this paper, the effect of the elemental content of aluminum in cermets on the electric conductivity and corrosion resistance of anodes was analyzed. The experimental results demonstrate that both corrosion resistance and electrical conductivity decrease when the elemental content of aluminum increases in the dense layer on the anodes’ surface. This can be attributed to the formation of FeAl₂O₄ and NiAl₂O₄ as production of FeAl₂O₄ and NiAl₂O₄ occur on the surface of the anodes during electrolysis.

Effects of solution treatment on the Mg-2Zn-0.4Zr-0.6Ce (wt.%) biomedical magnesium alloy have been studied through SEM, immersion test, electrochemical measure. The result shows, compared with as-cast alloy, the grain becomes coarse and the most of second phases dissolve for the quenched alloys. Meanwhile, solution treatment gives an enhancement in the corrosion resistance and electrochemical properties, which is attributed to the reduction of second phases and homogenization of alloying element. The corrosion rate of quenched alloys firstly decreases with the increasing temperature of solution treatment, when the temperature is up to 460 °C, the corrosion rate increases slightly. And the optimal corrosion rate is acquired at 450°C and is about 0.7293 mm·a⁻¹. Electrochemical measure shows: with the increasing temperature of solution treatment, the diameter of capacitive loop firstly increases and then decreases, I_corr first decreases and then increases.

The molybdate conversion coating for 6063 aluminum alloy was prepared with Na₂MoO₄·and K₂ZrF₆ via the dip process. The physical and chemical properties of conversion coating were analyzed by CuSO₄ dropping corrosion test, electrochemical impedance spectroscopy (EIS), scanning electron microscope (SEM) and energy-dispersive spectrometer (EDS). The optimized process conditions are as follows: Na₂MoO₄·2H₂O 6 g/L, K₂ZrF₆ 3 g/L, pH 3, temperature 40 °C, and reaction time 10 min. The conversion coating exhibits yellow color and consists of Mo, Zr, Mg, Al, O.

Hot formed part is widely used in the automotive industry to meet increasing requirements of safety and light weight. However, the corrosion protection is also a major aspect for automotive materials. For this reason, aluminized, galvanized and galvannealed hot forming steels were developed. Here the corrosion resistance of hot formed zinc-based coating was evaluated by cycle corrosion test. And it was compared with aluminum-silicon coated steel.

Properties and corrosion resistance of the electrophoretic paint films on two types of uncoated press-hardened 22MnB5 steels (cold-rolled and CSP hot-rolled) and an Al-Si steel based on 22MnB5 were compared in the present contribution. The physicochemical properties of the electrophoretic paint films on these three types of press-hardened steels were found to be proximal, and all meet the requirements of related standards of automobile manufacturers. The corrosion resistance of unpainted press-hardened samples of the three kinds of materials was found to be poor. The poor corrosion resistance of the Al-Si sample is related to the high iron concentration and the presence of microcracks in the coating after hot-stamping process.

In the present work, the electrochemical behavior of Mg-xCe-1Zn (x = 3, 8 and 13wt.%) alloys have been investigated. The alloys were fabricated by using a vacuum induction melting method under an argon atmosphere. Potentiodynamic polarization was carried out in 3.5% NaCl solution of pH 7.2 at room temperature to evaluate the corrosion properties of Mg-xCe-1Zn (x = 3, 8 and 13wt.%) alloys. The microstructure of the Mg-(3, 8 and 13wt.%)Ce-1Zn alloys were mainly consisted of α-Mg and eutectic Mg₁₂Ce phase. With the increase of Ce contents, the volume percent and size of the eutectic Mg₁₂Ce phase were increased. Results indicated that the corrosion rate of Mg-xCe-Zn alloy was increased by the excessive Ce addition.

Magnesium alloy is a promising candidate for use as biodegradable implant material. However, its corrosion rate is too fast in human body fluid. Thereby, improving corrosion resistance is an urgent problem for application of the magnesium alloy in the medical field. Presently, Mg-8.0Al-1.0Zn-xGd alloys were prepared. Effect of rare earth Gd on the microstructures and corrosion resistance of magnesium alloy were investigated. Results showed that the most of Al₃Gd particles, a high melting point rare earth compound, are distributed in β phases (Mg₁₇Al₁₂). With the increase of the content of Gd, the amount of precipitation of β phases increased and interconnected each other. Fine network-like β phases acted as corrosion barrier and effectively impeded the corrosion extending. The corrosion resistance improved with the increase of rare earth Gd.