Advanced Materials Research Vols. 538-541

Abstract: It has attracted very strong interests in enhancing the wear resistance of the TiAl intermetallic alloy. In this paper, both plasma-sprayed conventional and nanostructured ZrO₂-7wt.%Y₂O₃ thermal barrier coatings (TBCs) were prepared on TiAl alloy, and microhardness of coating were investigated. Meanwhile, the dry sliding friction tests on the substrate, the traditional coating, and the nanostructured coating were evaluated by ball-on-disk tribometer at room temperature. The results show that the microhardness of nanostructured coating is higher than that of the conventional one. Lower friction coefficient and higher wear resistance than the original TiAl alloy is achieved in the coatings under wear test conditions. Due to the existence of nanostructured microstructures, the nanostructured coating exhibits the lowest friction coefficient, and the best wear resistance. The wear mechanism of the original TiAl substrate is severe adhesive wear. However, the wear mechanisms of the TBCs are mild ploughing and severe adhesion.

Abstract: Copper is infiltrated on 0Cr18Ni9 austenitic stainless steel surface by Double Glow Plasma technology, the surface copper content is about 3.5%, content of Cr in metal infiltration layer reaches up to 29.2%. Under the conditions of normal pressure and temperature, corrosion resistance of stainless steel samples which copper infiltrated on surface was researched in 1 mol/L NaOH solution by measurement method of electrochemical. The result shows that, corrosion resistance of copper-infiltrated stainless steel is about 1.67 times higher than untreated sample in 1 mol/L NaOH solution.

Abstract: A novel Plasma Emission Monitoring (PEM) controlled N2-O2 dual gas reactive dcMS method is proposed for deopsiting TiAlON and TiMoAlON solar absorber coatings. Working in a 'cheated' feedback mode, the PEM controller ensures smooth & precise control of O/N ratio in obtained oxy-nitrides without occuring of serious target poisoning. The coatings have three functional layers including the infrared reflector, the absorbing layer, and the antireflection layer. The absorbing layers of the two kinds of coatings are both designed to have a gradually change Al and/or O content. However, the TiAlON coatings have a single TiAlON absorber layer while the TiMoAlON have a tandem absorber composed of a Mo doped TiAlN layer and a Mo doped TiAlON layer. Single-crystal silicon chips and glass slides are used as substrates to deposit the coatings and to characterize the photothermal conversion properties and thermal stability of the coatings by using SEM, UV-visible-near infrared photospectrometer, and solar spectrum emissiometer. The experimtal results show that the tandem TiMoAlON coating exhibits superior theraml stability up to 550oC. After annealing in air at 500oC for 8hrs, it exhibits higher absorptance than as-deposited status. The annealed TiMoAlON coating has a broad absorbing peak covering 400-800nm, which is beneficial to collect the majority energy in solar radiation. Due to its higher absorptivity and lower normal emissivity than the TiAlON coatings, the TiMoAlON coating yields a high solar selectivity (α/ε≈19) at room temperature. However, at 500oC, its ε value increases from 0.05 to about 0.25 which might attribute to its excessive thicknesses of the sublayers. The above results demonstrate that the proposed method is a convenient way for preparing high performance oxy-nitride solar absorber coatings which are suitable for non-vacuum high temperature photothermal applications.

Abstract: The surface of commercial TiO2 nanoparticles was modified by titanate coupling agent, JSC(isopropyl tricarboxytate titanate), FTIR spectrum confirmed that organic functional groups were successfully grafted onto the surface of TiO2 nanoparticles. The SEM micrographs indicated that the aggregation of modified TiO2 was reduced and most of the particles were approximately 20 nm.

Abstract: The rehealing ability of the oxide scales on sputter-deposited Ni-based K52 nanocrystalline coatings after pitting corrosion had been studied by polarization curves in 3.5% NaCl solution. The results indicated that the oxide scales formed on the nano-coatings exhibited excellent rehealing ability after pitting corrosion, and the rehealing oxide scales still had high corrosion resistance. The rehealing ability was declined with longer immersion time in the chloride solution. EDX analyses revealed that the oxide scales within the pits were composed of mixed-oxides. The mixed-oxides were made up of two layers: the external oxide layer was composed of Cr₂O₃ and TiO₂ and the internal oxide layer was Al₂O₃.

Abstract: The SiO2-ZrO2-Al2O3-Cr2O3 film is coated on the surface of stainless steel using analytical reagent TEOS, ZrOCl2·8H2O, Al(NO3)3·9H2O and Cr(NO3)3·9H2O as precursor and basing on mole ratio to calculate through Sol-gel method. The phase transformation behavior，erosion resistance，thermal shock resistance and abrasion resistance of ceramic coating by different heat treatment are studied. The results show that: 1)The SiO2-ZrO2-Al2O3-Cr2O3 gel coatings has non-crystalline structure after the treatment at 700°C and 800°C. New substance is not created below 700°C 2) The stainless steel substrate with ceramic coating has a higher erosion resistance at high temperature (700°Cand 800°C)than that without coating.3) Thermal shock resistance of the samples treated in 700°C is the best which has reached within 17-21cycles (900°C, air cooling). 4) The stainless steel substrate with ceramic coating has a higher abrasion resistance than that without coating. The samples treated at 700°Cand 800°C have the best abrasion resistance.

Abstract: The pyrite in the nature, due to the differences of the semiconductor properties caused by crystal structure and the presence of defects, will be bound to seriously affect the surface state and surface-activity of the mineral, eventually make the process of electrochemical reaction and flotation behavior change in the solution. Starting from the microscopic point of view, this article would study the affect mechanism of crystal structure and defects on the pyrite surface properties and the electrochemical reaction process. Studies have shown, because of the existence of the strong Fe-S covalent bond and determinate equilibrium defects, make the Fermi level and valence state of partial surface element change, accordingly lead to special semiconductor and surface properties of pyrite, ultimately affect the process of pyrite electrochemical flotation.

Abstract: The ceramic coatings, on the substrate of LY12 Al alloy, were prepared by micro-arc oxidation (MAO) technique with different electrical source parameters. The microstructure and tribological properties of the resulting micro-arc oxidation ceramic coatings(MAOC) were tested and analyzed by Nano-scratch tester, Micro-hardness tester and ball-on-disk friction tester etc. The results indicate that the thickness, roughness, micropore sizes and wear-resistance of MAOC increase with impulse frequency decreasing, however, the porosity is correspondingly reduced.

Abstract: The yttrium stabilized zirconia (YSZ) thermal barrier coatings (TBCs) were fabricated by plasma spraying on the surface of H13 hot work die steel and then were remelted by a transverse flow CO₂ laser. The phase compositions, microstructure and thermal shock resistance of the as-sprayed and laser remelted coatings were investigated by means of X-ray diffraction (XRD), scanning electron microscopy (SEM) and thermal shock tests. The results showed that the quality of laser remelted coating was improved obviously. Also, the thermal shock resistance of the TBCs was improved dramatically by laser surface remelting.

Abstract: In this paper, the mechanism of surface low defect in sheet metal stamping is studied. Firstly, we simulate the forming procedure of a stamping component by Finite Element Method (FEM) to observe the growth of surface low defect. And then, we establish an analytical model and deduce the critical stress for local buckling. Finally, we take advantage of the critical stress to detect local buckling areas in the component. The FE simulation result shows that during springback the non-uniform displacement in the thickness direction forms surface low. Moreover, the detected local buckling area agrees with the experimental surface low area. This indicates that the essence of surface low phenomenon is panel’s local buckling under the residual compressive stress during springback.