Siwei Tang

A comparative study on wear and corrosion behaviour of HVOF- and HVAF-sprayed WC–10Co–4Cr coatings

In this work, WC–10Co–4Cr coatings were separately deposited on 300M steel by high-velocity oxygen fuel (HVOF) and high-velocity air fuel (HVAF) spraying processes. Microstructure, porosity, micro-hardness, bonding strength, wear and corrosion resistance of the coatings after different processing were investigated and compared. The result shows that dense and homogeneous microstructure existed in both two WC–10Co–4Cr coatings. Owing to lower temperature flames and higher particle velocity in the HVAF process, the HVAF-sprayed WC–10Co–4Cr coating exhibited less decarburisation, lower porosity (0.74%), higher micro-hardness (1162 HV0.3) and bonding strength (74.68 MPa) than HVOF-sprayed WC–10Co–4Cr coating. In addition, wear and corrosion resistance of these two coatings were evaluated by sliding wear test and electrochemical corrosion test. The HVAF-sprayed WC–10Co–4Cr coating also exhibited excellent wear resistance and superior corrosion property than HVOF-sprayed WC–10Co–4Cr coating.

New method for preparing micron porous aluminium via powder metallurgy

ABSTRACT In this work, micron porous aluminium (Al) specimens with various porosities were successfully prepared via a cold pressing-vacuum sintering-dissolution process (SDP) with water-soluble granules as space holders. Effects of the parameters of the sintering process on microstructure, density, and hardness were investigated. Results show that SDP was used to synthesise open-cell porous aluminium with uniform holes and enabled easy control of the microstructure porosity of porous aluminium. We also found that vacuum sintering and the addition of magnesium (Mg) improved the sintered behaviours. Based on our findings, the optimised sintering parameters (temperature and time) for porous aluminium are 650°C and 270 min, respectively.

Evolution of Voids in Mg/Al Diffusion Bonding Process

Abstract The closure process of voids was very crucial for diffusion bonding, voids behaviors in Mg/Al bonding process were investigated, and the control mechanisms of diffusion at different predominant process parameters were discussed in this paper. Finite element simulation was utilized to investigate the influence of thermal residual stresses on the appearance of secondary voids. The results showed that: the dominant mechanism of void closure was plastic deformation in the initial stage of Mg/Al diffusion bonding. Numerical results indicated that secondary voids could be easily generated in the regions where tensile residual stress gradient achieves the maximum, corresponding to area that Al3Mg2 layer at the nearby Al/Al3Mg2 interface, the segregation of voids deteriorated the performances of the bonded joints.

Influence of Various Concentrations (TiC and TiN) on the Microstructure and Properties of Ti(CN)-Based Cermets Prepared by Spark Plasma Sintering

ABSTRACT The Ti(CN)-based cermets have been widely used for cutting tools in recent years due to their high hardness, temperature stability, chemical inertness, etc. In this work, Ti(CN)-based cermets were prepared by spark plasma sintering (SPS) at 1800°C for 10 min. Influence of various concentrations (TiC and TiN) on the microstructure and properties were investigated by X-ray diffraction, scanning electron microscope and nano mechanical comprehensive test system. Results show that the sintered cermets become more compact by SPS sintering. Both the transgranular and intergranular fracture are found in cermets of various concentrations. These fractures can obviously improve the hardness and elastic modulus; TiC0.7N0.3 has achieved the highest hardness of 45.29 GPa and elastic modulus of 653.42 GPa. GRAPHICAL ABSTRACT