Key Engineering Materials Vols. 353-358

Abstract: Mo-Cr diffusion layer on carbon steels are prepared by double glow plasma surface metallurgy and then treated by ultra-saturated carbonization, quenching and tempering. The content of component is roughly that of high-speed steels (HSS). The results showed that the depth of coating is over 100μm and the content of Mo, Cr alloyed layer is about 20% and 10% respectively. Surface carbon content is over 2.0% after ultra-saturated carbonization. The carbides of the alloyed layer are fine and dispersed, without coarse eutectic ledeburite. X-ray diffraction showed that the carbides are M6C, M2C, M23C6 etc. SEM analyse indicated that the dimension of surface carbide is less 1μm. The abrasion experimental results showed that the relative wear resistance of the treated sample was 2.38 times as that of quenched GCr15.

Abstract: High quality TiN/Ti multi-layers have been successfully obtained on a carbon steel substrate by double glow plasma surface alloying technique (DGP). The TiN/Ti multi-layers consists of deposition layer and diffusion layer, and then on its surface TiN film (PVD) is deposited to form TiN/TiN/Ti compound multi-layers. In addition, studies were carried to compare TiN/Ti multi-layers, TiN/TiN/Ti compound multi-layers and TiN film (PVD) directly deposited on the surface of the carbon steel and their microhardness and dry friction-abrasion properties were also investigated. The results show that the thickness of TiN/Ti multi-permeated layers is above 10*m; Ti and N concentrations change gradually along the depth of alloying layer. TiN/Ti multi-layers and substrates are metallurgically bonded. Preferred orientation of TiN/Ti multi-layers is crystal surface (200). The hardness of the TiN/Ti multi-permeated layers ranges up 2200HV, its average friction coefficient is lower, abrasion crack is shallower and wear resistance better.

Abstract: Laser cladding technique was used to form Ni3(Si,Ti) intermetallic coating by Nb addition on Ni-based superalloy substrate. The coating was investigated by optical microscopy and X-ray diffraction (XRD). The clad coating was dense, compact and smooth. An excellent bonding between the coating and the substrate was ensured by a strong metallurgical interface. Ni3(Si,Ti) phase was detected in all of the claddings, and NbNi3, Nb3Ni2Si were detected in Nb additional experiments. The peaks intensity of Nb3Ni2Si and NbNi3 increased with the increasing of Nb content. The Ni3Nb and Nb3Ni2Si were formed when Nb was beyond its solubility in the L12 Ni3(Si,Ti). The average microhardness of the coating was improved with the increasing of the Nb content. The microhardness was up to 530Hv when the atom percentage of Nb addition reached 5%, and it was much greater than that of Ni-based superalloy substrate.

Abstract: CrxN coatings are deposited on the substrates with low temperature using a Teer UDP 550 Close Field Unbalanced Magnetron Sputter Ion Plating system (CFUBMSIP). The effect of applied power on Cr targets related to sample temperature is studied. When the applied power of Cr targets is lower than 1.1KW, the depositing temperature could be controlled at about 180°C. Scratch test shows no coating detachment at the end of scratch track up to 85N load. All results of Rockwell-C indentation indicate that CrxN coating holds good bonding strength. Pin-on-disc tests are performed to evaluate wear resistance of the coatings and no any wear loss can be detected after 6000s and 1800s of running. XRD profile demonstrates that the coating deposited in this study is CrxN.

Abstract: The microstructure of Ag/TiO2 and Ag/Ti/TiO2 multilayer system are investigated by AFM and TEM, and their interfaces are analyzed by the means of spectroscopic ellipsometry (SE). The results show that the multilayer has a sharp interface without interdiffusion and interface reaction products. AFM surface roughness analysis indicates a 2-nm titanium transition layer can improve surface quality of silver films, because it is enabled to change silver island dimension and distribution and improve coverage of silver films on Ti/TiO2 substrate. This can be attributed to titanium ׳s strong oxygen affinity and good wettability to titanium dioxide. The optical properties test of TiO2/Ag/TiO2 multilayer demonstrates surface plasma resonance (SPR) absorption shifts towards long wave region with the increasing of the total thickness of dielectrics.

Abstract: The storage modulus, loss modulus, loss tangent (tanδ), stress and strain have been determined for painted steel specimens by dynamic mechanical analysis (DMA) operated in Dual Cantilever mode. Analysis of the composite system enabled the elastic modulus of the paint layer to be calculated and the result can be useful to analyze the mechanical properties of the coil coating. The calculation was found to be very sensitive to the geometry (especially thickness of the substrate and coating) and properties of the substrate and coating, leading to considerable variability in the calculated coating modulus. The DMA method was successful in detecting the glass transition temperature (Tg) as a peak in the tanδ curve. The value of Tg is sensitive to the preparation conditions (e.g. curing temperature) and composition of the paint. The results show that DMA in Dual Cantilever can be useful as a characterization tool for painted steel.

Abstract: Oxidation ceramic coating was directly synthesized on LY12 aluminium alloy by micro-arc oxidation (MAO) process in Na2SiO3 electrolyte solution with the Na2WO4-KOH-Na2EDTA addition. The corrosion resistance of the coating was tested using CS300P electrochemical corrosion workshop in 3.5% NaCl solution. Using the scanning electron microscopy (SEM) and X-ray diffraction (XRD), the cross-section microstructure, the surface morphology and the phase structure of the micro-arc oxidation ceramic coating were analyzed. The results showed that the corrosion resistance of the micro-arc oxidation ceramic coating in 3.5% NaCl solution was enhanced remarkably, the corrosion velocity was obviously slowed down. The thickness of micro-arc oxidation ceramic coating was about 11μm. The final phases in the coating were found to be α-Al2O3 and γ-Al2O3. The mechanism of the oxidation ceramic coating formation was investigated too.

Abstract: The CoNiCrAlY thermal barrier coating was prepared on the surface of TiAl alloy by plasma spraying technique. SEM observation shows that the bonding between thermal barrier coating and substrate is good. The surface hardness of TiAl alloy is improved, the microhardness of the coating surface is about 673HV after the oxidation test at 850°C. The oxidation tests at 850°C show that the oxidation resistance of the samples is improved remarkably. The surface morphology and microstructure of the thermal barrier coating are determined by SEM.

Abstract: The surface age alloy of Fe-Co-W-Mo was formed on 25Cr2Mo2V steel by double glow plasma surface alloying technique. The effects of processing parameters on the depth, composition and constituent phases of surface alloying layer were investigated. Results indicate that the plasma processing parameters influenced significantly the surface alloying process. The composition of the surface layer nears W11Mo7Co23Fe59wt%, the depth of the surface alloying layer is 150μm after processing at 1100°C for 6hr. The microstructure of the cross section was composed of three sub-layers, that is, the deposition layer, the diffusion layer and the matrix. The constituent phases of the deposition layer were Fe7W6 type μ phase Fe2W type laves phase, Fe3Mo and a little amount of M2C type carbide, that of the diffusion layer were α-Fe and some intermetallics.

Abstract: Surface modification is a promising technique to improve wear properties of titanium and titanium alloys by modifying either the surface composition or microstructure. Laser remelting and laser nitriding of commercial purity titanium were carried out under pure argon and pure nitrogen ambient, respectively. Characterization of the laser treated surface was done by optical microscopy, scanning electron microscopy (SEM), X-ray diffraction (XRD), microhardness tester. During laser irradiation heating, Ti exhibits a height activity and combines with N in the atmosphere of pure nitrogen forming TiN and TiN0.3, whereas Ti only transform into martensitic Ti in pure argon. The Vickers microhardnesses are greatly improved by laser remelting and laser nitriding.