Microstructure and corrosion properties of laser clads of magnesium base alloys for laser generated cylinder liners

Reciprocating electrolyte jet with prefabricated-mask machining micro-dimple arrays on cast iron cylinder liner

In order to better determine the applicable working conditions of Al-Si alloy cylinder liners and cast-iron cylinder liners, their tribological performance and scuffing resistance are discussed in this paper. After wear and scuffing tests, it was found that cast-iron cylinder liners had better wear resistance and better scuffing resistance, but poor friction performance. Al-Si alloy cylinder liners had weaker wear resistance and scuffing resistance, but excellent friction performance. The wear mechanism of cast-iron cylinder liners is slight adhesive wear, and they are suitable for traditional fuel engines and turbocharged engines with high load, high power, and high stability. The wear mechanism of Al-Si alloy cylinder liners was a mixture of adhesive wear and abrasive wear, and they are suitable for engines that are lightweight, efficient, and energy-saving, and operate at high speeds.

To improve the marine corrosion resistance of stainless steel coatings fabricated by high-velocity oxyfuel (HVOF) spraying with a gas shroud attachment, the molybdenum (Mo) content of stainless steel was increased to form coatings with a chemical composition of Fe balance-18mass%Cr-22mass%Ni-2∼8mass%Mo. These coatings were highly dense, with <0.1 vol.% in porosity, and less oxidized, with 0.5 mass% in oxygen content at most. The corrosion mechanism and resistance of the coatings were investigated by electrochemical measurement, chemical analysis, and statistical processing. The general corrosion resistance of the coatings in 0.5 mol/dm3 sulfuric acid was improved with increases in Mo content, and the corrosion rate could be decreased to 8.8 × 10−2 mg/cm2 per hour (∼1 mm/year) at 8 mass% Mo. The pitting corrosion resistance of the coatings in artificial seawater was improved with increases in Mo content and was superior to that of the 316L stainless steel coating. The crevice corrosion resistance of the coatings in artificial seawater was improved and the number of rust spots at 4 mass% Mo was decreased to 38% of that for the 316L coating. Accordingly, Mo is highly effective in improving the corrosion resistance of the stainless steel coatings by HVOF spraying.

Experiments were carried out with different process parameters to investigate the effects of used parameters on corrosion resistance of TiN coatings obtained. In experiments, TiN imitation gold decoration coatings were prepared on 1Cr13 pen-point and brass chromium plating pen-coil by multi-arc ion plating method. The phase composition of TiN coatings was measured by x-ray diffraction. The corrosion resistance of TiN coatings was tested by salt-mist and artificial-sweat experiments. The relationship between corrosion resistance of coatings and process parameters were analyzed. Therefore, the optimum process parameters were achieved suitable for plating coatings on substrates of 1Cr13 pen-point and brass chromium plating pen-coil with good imitation gold. Imitation gold plating layers obtained have good gloss, corrosion resistance, high hardness, wear resistance, and easy to maintain. The results showed that the corrosion resistance of coatings is more easily influenced by changes of PN2 and Vbom than that of matrix-bias voltage. The TiN coatings are of resistant to corrosion no matter they are in single or multi phase structure. The optimum parameters of achieving good corrosion resistance of TiN coatings are PN2=0.48Pa, Vbom=400V，bias=-20V. Under the optimum conditions, the obtained surface corrosion resistance state of the coatings can reach at least eight grades, even above ten grades.

In order to determine the influence of process parameters such as the optimal heating method, heating temperature, and time on the corrosion resistance of zinc iron alloy coatings, and to maximize their corrosion resistance while ensuring coating quality, a study was conducted on the influence of heating process on the corrosion resistance of zinc iron alloy coatings. Prepare coatings on steel-based materials using hot dip method, adjust the auxiliary plating and immersion temperatures, and test the corrosion resistance of coatings at different temperatures. After completing the coating preparation, test the corrosion resistance of the coating under two heating processes, namely, heating furnace and laser, as well as the corrosion morphology and corrosion rate of the coating under different heating temperatures. Calculate the corrosion loss of the coating under different heating durations. The experimental results show that the corrosion resistance of the coating is better when the auxiliary plating and immersion temperatures are 70 and 450°C, respectively. When the laser heating process is selected and the heating temperature does not exceed 450°C, the corrosion resistance of the coating is higher. Once the temperature is exceeded, the corrosion resistance of the coating decreases, and with the increase of heating time, the corrosion resistance of the coating will decrease. When the heating time is 14 min, the mass loss of the coating reaches 0.011 g. And in the electrochemical corrosion test, after soaking for 18 days, the polarization resistance value of the zinc iron alloy coating decreased to 987.8 Ω·cm2, achieving complete failure.

The objective of this study is to characterize and understand the evolutionary processes that the effect of surface texture has on the tribology properties of the Chrom-Keramik-Schicht (CKS) piston ring/cast iron cylinder liner system under high intensifying. Surface dimple textures with an area density of 3–9% were prepared on the CKS piston ring by YAG laser, and the antifriction and antiscuffing properties were tested on a reciprocating test rig at 200 °C and 80 MPa. The minimum friction coefficient and wear loss were both obtained at the area density of 5%, compared with the untextured cylinder liner–piston ring (CLPR). The friction coefficient decreased by 0.013 to 0.086, and the wear loss for the piston ring and cylinder liner decreased by 41% and 46%, respectively. The sharp decrease of the friction force induced by surface polishing of the cylinder liner is taken as a sign to indicate the cylinder scuffing under starved lubrication. The scuffing time for the piston ring/cylinder liner system reached a maximum value of 18 min at an area density of 3%, which is extended about 41% compared with that of the untextured piston ring. The dimple surface texture on the piston ring could extend the scuffing time by delaying the occurrence of polishing behavior on the surface of cylinder liner. It is found that the retarded surface polishing played a major role for the modification of the antiscuffing property of the friction pairs according to the friction curves and wear morphologies.

In order to decrease wear losses between piston rings and cylinder liners and improve the partner adaptability, laser cladding and electroplating techniques were adopted to form coatings on the surfaces of piston rings made of nodular cast iron. Fe-based composite layers reinforced by in situ particles were formed by laser cladding using preplaced FeCSiB alloy powders on nodular cast iron matrix. The chromium-plated layers were formed on the nodular cast iron matrix. By simulating the operating conditions of piston rings and cylinder liners in the diesel engine, the Optimal SRV tests were carried out using laser cladding and chromium-plated strengthening piston rings as upper samples and segments of grey cast iron cylinder liners as lower samples. The morphologies of worn scars were observed with optical microscopy and scanning electron microscopy (SEM). The SRV tests show that laser cladding processes reduce the wear depth of both the piston rings and the partner cylinder liners，have the lower friction coefficient (0.067∼0.085), which reduces with the increase of wear time. It can be concluded that the piston rings processed by laser strengthening have good wear resistance and extensive partner adaptability and the mechanism is slightly scratching. The results demonstrate that the friction coefficient (0.1170～0.1332) between the chromium-plated rings and cast iron cylinder liners increased with the increase of wear time in the same conditions and the wear mechanism is severe adhesive wear.

Effects of ultrasonic impact treatment on the corrosion resistance of laser-cladded CrMnFeCoNi high-entropy alloy coatings

A Ni-Cr thick film doping with nano-MoS2 particles doping was electrodeposited on the textured surface of the ductile iron cylinder liner to enhance the tribology performance of piston ring-cylinder liner(PR-CL) friction pair. The circular texture was prepared on the cylinder liner surface, which is characterized with the depth of 50 μm, the diameter of 350 μm, and the 10 % area density. The dop-ing concentration of nano-MoS2 particles was 1-5 g/L and the current density for electrodeposition was 2-6 A/dm2. The morphologies and element distribution of electro-deposition films in the mi-cro-dimples indicated that the Ni-Cr-MoS2 composite film were successfully deposited into the inte-rior of the micro-texture and the micro-texture still maintains the original morphological characteris-tics. A reciprocating friction test was carried out to evaluate the effect of Ni-Cr-MoS2 composite film (TNMF) combined with surface texture on the tribology properties of cylinder liner. The lubricating oil is 4652D. The coefficient of friction (COF) of the TNMF cylinder liner reduced from 0.143 to 0.127 and the wear loss decreased from 7.6 mg to 6.9 mg, compared with the uncoated cast iron (UC) cylinder liner. The scuffing time of TNMF cylinder liner extended from 19 min to 65 min. The syn-ergistic effects with the solid lubricant release from composite film, and lubricant reservation and debris capture of the micro-texture play the dominant role for the enhancement in tribology proper-ties of PR-CL friction pair.

The characterization and corrosion resistance of cerium chemical conversion coatings for 304 stainless steel

Effect of magnetic field on corrosion protection efficacy of Ni-W alloy coatings

The collaborative effect of carbon-borides and the redistribution of Ni, Cr and Mo on the corrosion and wear resistance of NiCrMoCB coatings

High-entropy alloy (HEA) coatings on the surface of low-alloy steel by laser cladding can improve the corrosion and wear resistance, and the performance can be further improved by adding the Cr element. However, the effect of Cr content on the microstructure, hardness, wear and corrosion resistance of the coatings on the welded joint has not been completely understood in the literature. This paper aims at revealing the influence of Cr content on the microstructure and properties of laser-cladded FeCoCrxNiAl HEA on different regions of Q345 welded structure. The results indicate that FeCoCrxNiAl HEA coating has good metallurgical bonding with the Q345 welded surface. The increase of Cr element content in the powder plays an important role in energy absorption of powder and substrate, affecting the dilution rate and diffusion of Fe from the substrate to HEA coating. The HEA coating is mainly composed of the face-centered cubic phase (FCC) and body-centered cubic phase (BCC). When x = 1.5, the actual Cr element content of coating is the highest, which promotes the formation of hard brittle phase BCC, and subsequently affects the hardness and wear resistance of the sample. Meanwhile, the corrosion resistance increases and then decreases, and reaches the highest when x = 1.5. Due to the existence of Cr and other elements with good corrosion resistance in the HEA coating, a dense oxide film can be formed in 3.5 wt.% NaCl solution and neutral salt spray environment to prevent the corrosion from continuing, which can effectively improve the corrosion resistance of each region of the welded joint, and the protective efficiencies on the weld bead (WB), heat-affected zone (HAZ) and base metal (BM) are 99.1, 98.4 and 96.6%, respectively.

The effect of laser energy density on the geometric characteristics, microstructure and corrosion resistance of Co-based coatings by laser cladding

Optimization of thermal control and corrosion resistance of PEO coatings on 7075 aluminum alloy by frequency alteration