Advanced Materials Research Vols. 139-141

Abstract: In this paper, the TiN/TiAlN duplex coatings were deposited on SKH51 tool steel by means of multi-arc ion plating. By means of SEM, Vickers microhardness tester and scratch tester, the effect of target current levels on the surface morphology and mechanical properties of TiN/TiAlN duplex coatings on SKH51 tool steel was studied. During deposition, the effect of target current on microstructure and mechanical properties is responsible for the number, energy of emission target particles and distribution of target droplets. It was found that the thickness and microhardness of coatings, and the number of droplets with diameter more than 2 m increased with target current increasing. The adhesion force between coating and substrate reaches a peak value of 40.5N at 70A. From application view, it is better to control the Ti-Al target current density at 9.88x10-3 A/mm2.

Abstract: By the combined process of hot-dip aluminum and micro-arc oxidation, multilayer ceramic coatings were obtained on the surface of commercial 080A15 steel plates. The microstructures and chemical elements of the coatings were investigated by means of scanning electron microscopy (SEM) and energy-dispersive spectrometry (EDS), respectively. The results show that the conversion coating on the surface of 080A15 steel plate is mainly composed of three layers, they are the outer layer of alumina ceramic coating, the middle layer of pure aluminum, and the inner layer of FeAl intermetallic compound. The FeAl intermetallic compound layer appears as branch-like to grow into the steel substrate. The alumina ceramic layer is a porous structure attached on the pure aluminum layer. The distribution of composition elements on the interface between the each layer is gradient transition, which is one of metallurgical adhesive characteristics.

Abstract: A method for tin (Sn) film prepared by electroless plating on the surface of Cu substrate was realized, the silvery-white and semi-bright film has been obtained. The deposition mechanism is discussed and summed up period of replacement reaction, co-deposition period of Cu and Sn, and period of self-catalyzed deposition of Sn. The deposition process takes place because of the change of Cu and Sn potential when thiourea is added into the bath. That the film thickness increases linearly with the rise of plating times proves that the continuous self-catalyzed deposition of Sn has been realized, and the possibility of immersion plating is also excluded. The diffraction peak of Cu phase in the film becomes weaker and weaker, and that of Sn phase becomes stronger and stronger with increasing plating times. Additives B and C can play a role of grain refinement.

Abstract: 9Cr2Mo steel is widely used as measuring and cutting tool steel. The friction and wear behavior of 9Cr2Mo steel was investigated under dry friction and solid lubricant by wear tester. The experiment results show that the friction coefficient of 9Cr2Mo steel is 0.34~0.58 under dry friction and 0.035~0.06 under solid lubricant. With the increase of load , the friction coefficient decreases and the wearing capacity increases under two kinds of conditions. The wearing capacity of 9Cr2Mo steel under solid lubricant is great lower than it under dry friction. The friction process is smooth under solid lubricant. It indicated that the solid lubricant took effect in antifriction and antiwear of 9Cr2Mo steel.

Abstract: A theoretical model has been developed for the mechanical seals with a laser-textured porous seal face. By means of variable dimensionless steps, parametric analysis has been performed to obtain dimensionless liquid film pressure by the finite difference method. Liquid film pressure profiles over the pore column have be achieved by the computer program MATLAB. It is found from calculating results that average liquid film pressure increases with increase of the rotational speed, liquid viscosity and reduction of liquid film thickness. Hydrodynamic effect produced by micro-pores decreases with increase of fluid pressure. In addition, the effect of the pore area density and depth over diameter ratio on the liquid film pressure is very significant. Optimum values of these parameters can maximize the average liquid film pressure.

Abstract: Stellite 12/TiC/CaF2 composite coating has been successfully fabricated on copper substrate by a pulsed Nd:YAG laser system with preplacment powder bed to improve the absorbance of copper substrate to laser energy. Microstructures, phases and wear properties were studied by means of scanning electron microscopy (SEM), X-ray diffraction (XRD), dry sliding wear tester. The results showed that the existence phases of Co-based solid solution, Cr4Ni15W, TiC, Cr23C6, CaF2 and Ti8C5. The morphology of titanium carbide is mainly spherical and exists in two forms, one is TiC and the other is Ti8C5. The microhardness of the layers reveals a gradient variation along the cross section of the LSA layers. The friction coefficient of the coating is oscillating around approximately 0.17 because CaF2 is a solid lubricant because of the lamellar structure and softness and Titanium carbide is hard. The dry sliding wear testing shows the wear resistance of as-receive copper is significantly improved by laser cladding Stellite 12/TiC/CaF2 composite coating.

Abstract: The residual stress induced by Laser shock processing (LSP) can improve properties of fatigue crack growth. In this paper, the CT models of LSP and fatigue crack growth have been built. We experimented the TC4 alloy treated by LSP and fatigue crack growth and then simulated the fatigue crack growth. The results show that the values of simulations are conform to experiments. With the increment of peak pressures and overlapping rates, the fatigue lives have been increased, the fatigue crack growth rates have been descent. The fatigue lives have been 1.46-3.03 times compared with untreated by LSP, the fatigue crack growth rates have been 0.127-0.95 time compared with untreated by LSP, but to overlapping rates, it is not obvious with the improvement compared with peak pressures.

Abstract: The effect of laser shock processing (LSP) on bending fatigue performance of 7075-T651 aluminum alloy was studied. LSP was performed on fatigue testing specimens with optimized parameters. Stress-life fatigue data were generated for both shocked and as-machined conditions. The fatigue improvements of LSP were discussed accounting for the effect of residual stress. The results show that shocked specimens exhibited significantly improved fatigue performance, with as-machined specimens having a factor of 1.6-4.4 improvement in fatigue life (depending on fatigue stress level). The stability of the residual stress induced by LSP under cyclic load was particularly investigated by means of X-ray diffraction measurements. Residual stress relaxation was observed. And the higher the cyclic load, the higher the relaxation rate. Due to the cyclic creep effect, the residual stress decreases linearly with the logarithm of the number of cycles.

Abstract: . In order to improve the high temperature stability of casting mold, we carried out the RE Ion nitro-carbonizing technology test on the 4Cr5MoSiVl steel. This test was done by using high-power pulsed supply for the 4Cr5MoSiVl steel casting mold surface treatment under different temperatures, time period, atmospheric pressure, and RE contents. The optimization of these parameters makes the layer structure dense, toughness increased, specifically the surface hardness, wear resistance, high temperature oxidation resistance, and thermal fatigue properties of the treated layer significantly improved. A test with the use of this technology has been done for the 4Cr5MoSiVl steel automotive lamp aluminum casting mold. The mold service life of each mold time increased from 30,000 to 100,000. The experimental results show that by using 4%RE 520oC×2h, and 1.05KPa atmospheric pressure, the treated layer has optimal qualities, which can meet the requirements in practice.

Abstract: A composite layer was prepared on the Ti-6Al-4V alloy surface by ion nitriding, magnetron sputtering Mo and ion sulfurizing composite treatment technique. The phase structure, morphology, and cross-sectional element distribution of composite layer were analyzed. Friction and wear properties of composite layer were tested by MM-200 laboratory tester. XRD analysis showed that the composite layer was mainly comprised of Ti, Mo, MoS2, TiN, and transition layer. This composite layer is perfect wear-resistant surface due to existence of self-lubricating MoS2 on hard Mo and TiN layers with good anti-friction ability. Thereby, the results of friction and wear test showed that anti-wear performance of Ti-6Al-4V alloy after composite treatment was remarkably improved under dry and sliding conditions. Both the friction coefficient and the wear loss of the nitriding-Mo plating-sulfurizing layers were lower than that of the nitriding layer due to the formation of the MoS2 layer on Mo and TiN layers.