Advanced Materials Research Vols. 291-294

Abstract: NiCrBSi coating was prepared on the surface of 45 steel by CO₂ laser. The microstructure of the clad layer was characterized by SEM、EDS and XRD. The microhardness and wear resistance of the laser clad layer was examined. The results show that laser clad layer can be achieved under technical processing parameters and that the good metallurgical bonding is formed between the coating and substrate. The coating is uniform, continuous and free of pores and cracks. The microstructure of the coating is mainly composed of g-Ni, Ni₃B, CrB and Cr₂₃C₆ particles. The microhardness of the coating (500～650HV_0.2) is distinctly higher than that of the substrate(240～250 HV_0.2). The clad layer is reinforced by particles and grain-refining, resulting in greatly increase in wear resistance comparing with 45 steel.

Abstract: Microstructures and properties of plasma surfaced NiCrBSi+20%WC/12Co layer prepared on the die steel (H13) substrate were investigated. The study showed that the interface boundary existed between the layer and substrate. Compared with the typical microstructures of welded joint, the similar columnar grains in the layer perpendicular to the interface line were observed, which were never seen in the plasma sprayed coating. The conclusion could be drawn that the bonding between the NiCrBSi+20%WC/12Co layer and H13 substrate belonged to the metallurgical cohesion. The XRD analysis showed that the main phases in the layer included γ-(Fe, Ni), Cr₇BC₄, Ni₄B₃, Cr₇C₃ and Co₇W₆, which brought higher strength and higher hardness to the surfaced layer than the H13 substrate.

Abstract: Thermal sprayed WC-based coatings are widely used in modern industry, especially in excellent wear-resistant-demanding fields, due to their high hardness and superior mechanical properties. WC-Co is a typical representative of the coatings, usually used as the protective layers of shaft, pump sleeve intine, etc. WC-Co coatings were prepared on low carbon steel substrate using high velocity oxygen fuel (HVOF) technology, under different distance ranging from 160 to 240 mm. The influence of the spraying distance on coating hardness was investigated and discussed. The results reveal that, the cross-sectional hardness of the HVOF WC-Co coatings depend not only on the spraying distance, but also on the indentation position. The average microhardness for all the coatings was obviously enhanced. The highest one (1793.6 Hv) was produced with a distance of 240 mm. Due to the heat effect of the flame, the hardness for all coatings varies with the distance from indentation to coating/substrate interface.

Abstract: Al₂O₃-TiO₂-ZrO₂-CeO₂ coatings formed via a plasma spray approach. The optimal spray parameters of plasma sprayed nano-structured coating were determined by orthogonal experimental design, based on porosity, bond strength of the coatings and the partly melted(PM) zone percentage. Microstructure of the plasma sprayed nanostructured Al₂O₃-TiO₂-ZrO₂-CeO₂ coating sprayed on the optimal spray parameters was analyzed. Wear map was established by wear experiments. The results show, nanostructured coating contains fully melted (FM) zone and PM zone, the increasing of the critical plasma spray parameter (CPSP) promote the decreasing of the PM zone percentage and the increasing of the bond strength of the coatings. The composition phases of the powder reacted to each other during the plasma spraying process. FM and PM zone resulted from fully melted droplets and partly melted particles respectively. Nanosized crystals and amorphous particles exist in the PM zone, liquid phase sintering is taken place in the PM zone. The main wear mechanism of plasma spraying coatings are plastic deformation and microplow, microfracture and grain spalling, fracture and delamination at different normal load and sliding speed in dry friction.

Abstract: The presence of Mg addition in bath has been shown to improve the corrosion resistance of the hot-dip Al-Zn alloy coating while adhesion of coating degrades. And the underlying mechanism of the additive effects was not very clear. In this work, first-principles method has been used to investigate the effect of Mg addition on thickness of Galvalume coating. The optimized geometric configurations, total energy and electronic charge distributions for the Mg substitution in Fe₂Al₅ and FeAl₃ phases were obtained. And results indicated that the most favorable sites for Mg substitution in both Fe₂Al₅ and FeAl₃ phases are Al positions. Bonding energy and charge density results show that the addition Mg could not form Mg-Al bond and has little effect on the thickness of alloy layer.

Abstract: The high-phosphorus electroless Ni–P plating was coated on the surface of stainless steel. Five parameters, which have much effect on coating quality, were chosen to optimize the high-phosphorus electroless Ni–P plating technology in L₁₆(4⁵) orthogonal test. By means of x-ray diffraction and scanning electron microscopy, the morphologies and phase structures of coating were analyzed. Furthermore, the mechanical properties of coating were studied by micro-hardness tester and universal friction-wear testing machine. The results reveal that the optimal technical parameters are as follows: 20 g•L^-1 for NiSO₄, 23 g•L^-1 for NaH₂PO₂, 15 g•L^-1 for C₆H₅O₇Na₃•2H₂O, 8 g•L^-1 for H₂N-CH₂-COOH, 10g•L^-1 for CH₃COONa, 7 g•L^-1 for C₄H₆O₄, with PH value of 4.6, which leads to perfect coating quality. Besides, the P content is 11.64 wt.%, i.e. a high-P coating. The micro-hardness of the coating is 550.67 HV and the wear loss, 4.7×10^-3 g. The thermal shock test suggests that between coating and matrix exist a perfect cohesion, which is due to the homogenous and compact coating, with an amorphous structure, under the condition of the optimal technical parameters.

Abstract: Considering the thermally-growth oxide (TGO) that grows between ceramic coating and bond coat interface and surface topography of bond coat in a TBC system, the effect of residual stresses distribution by growth of TGO and cone interface topography in thermal barrier coating was calculated. The calculating result shows that the residual stress of TGO interface is affected by interface topography unit size and topography distribution density obviously. The stress between TGO and ceramic coating interface is greater than the stress between TGO and bond coat interface. Stress concentrates in topography center and the maximal value is 870MPa.The stress decreases with the increase of topography quantity.

Abstract: The effects of the hot-rolling process on microstructures and strength were investigated for two kinds of magnesium alloy Mg-Zn-Y and Mg-Zn-Y-Nd. In comparison with the as-cast alloys, the tensile strength of Mg-Zn-Y and Mg-Zn-Y-Nd both increases 45%, whereas their elongation decreases 73%, 60% via hot-rolling process, respectively. The results show that the dynamic recrystallization process and the pining effect of I-phase during hot rolling contribute to the fine-grained structure formation. The hot-rolling process has refined the grain size greatly.

Abstract: Two kinds of magnetron sputtering ZrAlN films containing 23%atAl were deposited. The first was multicomponent ZrAlN film, the second was structure gradient and mulilayer film, named superlattice ZrAlN film. The microstructure was studied by FESEM, TEM , XRD, its mechanical properties were evaluated by nano-indentation method. The fracture toughness of films were determined from the length of ‘radial cracks’ on the applied diamond identer load 1.96N. the results show that, multicomponent ZrAlN film has hardness value of 35GPa, fracutre toughness value of 1.97MPa·m^-0.5; while superlattice ZrAlN film has coresponding value of 40.1GPa and 3.17MPa·m^-0.5. TEM image illustrates the superlattice ZrAlN film period is 2.5nm, nanoidentation test shows superlattice film has higher elastic recovery parameter and lower plastic work.

Abstract: To effective integrate the bright-field and dark-field defect image information to solve the missed and false inspection problems due to incomplete information, according to the characteristic of strip steel surface defect image, a novel image fusion method is proposed. Firstly, the two original images are decomposed using Non-sub-sampled contourlet transform (NSCT) separately so that the low frequency coefficients and high frequency coefficients are obtained. To retain the important defect information, different methods are adapted to fuse high and low frequency coefficients. Finally, the fused image is obtained by performing the inverse NSCT on the combined coefficients. The experimental results show that the quantity of image information and image quality are highly improved. This method can effectively solve the problem of missed and false detection.