Li Bin Niu

Center distance and pouring temperature on in-situ synthesis of WCP/Fe composite coating

Tungsten carbide (WC) particles can be in-situ synthesized through the reaction between tungsten wires and molten of gray cast iron. The different composite coatings were obtained by adjusting the pouring temperature and the center distance of tungsten wires, and were comparatively observed by X-ray diffraction, scanning electron microscopy, and two-body abrasive wear tests. The results show that the intensities of the WC peaks increase by the increasing pouring temperature, and firstly become strong and then weak by the increasing center distance. In case of the pouring temperature 1 400 °C and the center distance 0.5 mm, the formed WC particles present quadrilateral and triangle-structure and are homogenously distributed in the matrix. The wear rate of the composite coatings for stable center distance gradually increases by increasing the loads, however, at a constant pouring temperature, it firstly decreases from 5.91 to 2.97 mg/cm2·h, and slightly increases to 3.98 mg/cm2·h by increasing the center distance.

Impact Abrasive Wear Resistance of High-Chromium Cast Iron Bars Reinforced Hadfield Steel Matrix Composite

Hadfield steel matrix composite, reinforced by high-chromium (Cr) cast iron bars, was fabricated by inserting high-Cr alloy flux-cored welding wires into Hadfield steel molten at 1500 °C. The characteristics for water-quenched composite were investigated and compared with those of reference Hadfield steel. The results show that flux-cored welding wires could be melted by heat capacity of Hadfield steel molten and transformed into high-Cr cast iron bar reinforcements after solidification. The reinforcements of water-quenched composite consist of martensite, eutectic M7C3 carbides and residual austenite. With the increasing of impact energy, the impact wear rate of the composite firstly decreases, and then increases slightly, therefore, the composite is more available to the conditions of low and medium impact energy. The reason is it can combine fully advantages of the outstanding toughness of Hadfield steel, and high hardness of high-Cr cast iron.

The Study of Carbon Materials Prepared by Zhaotong Anthracite under Ultra-High Temperature

In this paper, reporting a new way to directly prepare quality of carbon materials such as artificial graphite, like-graphitization carburant and senior carbonaceous reductant et al ,which is prepared from anthracite under ultra-high temperature without any other additional process and catalyst. The chemical composition of carbon materials was analysed ; the electrical resistivity was tested; the composition of phase and the graphitization degree was tested by XRD; the microstructure was characterized by SEM and the degree of crystallization and crystal defect was characterized by the Raman diffraction spectrum. At the same time, the graphitization method was discussed during ultra-high temperature. The results show that good carburant and carbonaceous reductant can be prepared by anthracite which was graphitization under ultra-high temperature ;The microstructure of carbon materials which was prepared by anthracite that was graphitization during ultra-high temperature is more ordered than that of raw anthracite, its graphitization degree also increase significantly; When the ultra-high graphitization temperature is above 2600 °C, carbon materials which is like to pure graphite have a small amount of structural defects and distortion; the high quality carbon materials prepared by graphitization method under ultra-high temperature ,it is a simple process with low cost and high added value, and its prospects of application is broad.

New practical method of homogeneous dispersion of multi-walled carbon nanotubes (MWCNTs) into Mg matrix composites

It is difficult to disperse multi-walled carbon nanotubes (MWCNTs) into Mg matrix composites homogeneously due to the high specific surface energy between MWCNTs. This would affect the mechanical properties of magnesium matrix composites reinforced by MWCNTs tremendously. The key is to overcome MWCNTs aggregate together, and gain the homogeneous dispersion of MWCNTs. Moreover, the density difference of Mg matrix and MWCNTs is another problem which prevents MWCNTs from dispersing homogeneously into Mg matrix composites. In order to solve these problems, a new practical method of homogeneous dispersion of carbon nanotubes into Mg matrix composites was presented basing on combination the tow step ball milling and ultrasonication dispersion methods. First, a certain amount of MWCNTs was ball-milled in ethanol solution contain 5 wt.% sodium stearate at various rotation speeds (100 rpm-300 rpm) and ball-milled times (0.5 H-2 H) to break MWCNTs hard aggregation. Second, MWCNTs which were subjected to the ball-milling were dispersed further in ethanol solution containing (SDS, DBS) using ultrasonication method. Third, the Mg powers were mixed with good dispersion of carbon nanotubes solution and ball-milled for 1 H to make MWCNTs coated uniformly on the surface of the magnesium substrate. The results were mainly examined by field emission scanning electron microscopy (SEM). It was found that MWCNTs were dispersed well and some of these MWCNTs had directional arrangement. Furthermore, MWCNTs were homogeneously dispersed into Mg matrix composites. These results suggest that this method has good application for magnesium matrix composites reinforced by carbon nanotubes.

Microstructure and High-Temperature Oxidation of Ni-Si3N4 Composite Coatings by Pulse Electrodeposition

Nickel matrix and Si3N4 micron particles were co-deposited on the aluminum alloy by pulse electro-deposition for high temperature performance. Meanwhile, the oxidation resistance was evaluated through the high temperature oxidation test. The phase structure, micrographs and components of the composite coatings were investigated by means of X-ray diffraction (XRD), scanning electron microscopy (SEM) together with energy dispersive spectroscopy (EDS) respectively. The results indicated that Si3N4 particles were uniformly distributed across the coating and there were no pores and cracks or other defects at the coating/substrate interface. Ni-Si3N4 composite coatings are characterized by pyramidal micro-crystallite structure. The thickness of Ni-Si3N4 composite coatings were up to 80 μm for 2h. The results also revealed that the Ni-Si3N4 composite coatings presented better oxidation resistance than the pure Ni coating and aluminum alloy at high temperature. After oxidation at 673 K for 8h, the oxidation resistance of Ni-Si3N4 composite coatings presented the improved oxidation resistance behavior compared to pure Ni and the aluminum alloy, respectively.

Effects of NaBH4 and Heat-Treat on Corrosion Resistance of Electroless Plating Ni-B Coating

Ni-B/Ni-B-B4C composite coatings on the substrate of medium-carbon steel (45#) were successfully fabricated by electroless plating in a low temperature bath. The corrosion resistance of Ni-B coating were examined by using electrochemical workstation. The results indicated that there are no pores and cracks and other defects at the interface between the substrate and composite coating. It was found that the corrosion resistance of Ni-B coating increased and then decreased with the addition of NaBH4 increasing, and the best addition in plating bath was about 0.9 g/L. While the corrosion resistance of Ni-B coating heat-treated at 400°C with NaBH4 addition 0.9 g/L was the worst.

Phase Transformation of Coal at High Temperature

Anthracite and bitumite were processed respectively at 1400°C,1700°C, 2000°C, 2200°C, 2400°C and 2600°C,and their chemical composition,resistivity,microstructure, phase composition,and the internal migration of molecular functional group were tested and characterized. The results indicate that moisture, ash and volatile in coal have gradually shifted and lost with the elevation of heat treatment temperature, while the higher temperature, the quicker and completer phase change. Heat treatment can make the coal transform from approximately insulative phase to conductive phase,. Furthermore, as the temperature increases, the conductive phase transformation effect is better. The higher the heat treatment temperature of coal, the more amorphous carbon transforming into crystalline carbon completely, but the less types of phases .

Corrosion Behavior of AZ91/AZ91-0.4%Nd Alloys in 3.5wt.% NaCl

The microstructure and corrosion behavior of commercial AZ91/AZ91-0.4%Nd alloys were investigated by OM, immersion test and weight-loss method. It was found that the number of Nd element in the AZ91 magnesium alloy has effect on the grain refining efficiency, the coarse β-Mg17Al12 phase distributed along the grain boundaries transformed into granular, and the granular or acicular Al3Nd phase precipitated in matrix. The addition of Nd element significantly reduces the corrosion rate of AZ91-0.4%Nd magnesium alloy, as a result the corrosion resistance of alloy was improved obviously.

Influence of Annealing Treatment on Precipitation of β-Mg17Al12 Phase of AZ80 Magnesium Alloy

The microstructure and element distribution of AZ80 magnesium alloy as-cast and after annealing treatment were studied by OM, SEM, XRD, EDS and TEM. The results show that the coarse divorced eutectic phase distributed along the grain boundary dissolve into Mg matrix during the isothermal process at 415°C for 24h. During the cooling process of annealing treatment, the lameller-shape β-Mg17Al12 nucleated preferentially in the grain near the boundary, then grows towards the neighbor grains with longitudinal direction, which precipitated from magnesium solid solution as perlite-type precipitation. When cooled to room temperature, the lameller-shape β-Mg17Al12 was uniformly distributed in the matrix, and the lamellar spacing inside β phase is about 1-2μm.

Influence of Solution Treatment on Atomic Diffusion and Mechanical Properties of AZ80 Magnesium Alloy

The atomic diffusion and mechanical properties of as-cast AZ80 magnesium alloy after solution treatment at different time were studied by OM,SEM,EDS as well as tensile testing. The results show that the coarse β-Mg17Al12 phase distributed along the grain boundaries as net microstructure is almost dissolved after solution treatment, and the content of Al that in the α-Mg matrix is well distributed with the solution time prolonged. Because of the β-Mg17Al12 phase reducing and granulating, the function of precipitates phase strengthening was depressed and the hardness (HB) of alloy dropped obviously. However, the tensile strength(σb ) and elongation(δ) enhanced remarkably and the yield strength (σ0.2) decreased slightly.