Shengqiang Ma

Investigations on Microstructures and Two-body Abrasive Wear Behavior of Fe–B Cast Alloy

The microstructures of Fe–B alloys containing different carbon and boron concentrations have been investigated. The solidification microstructures of Fe–B alloy consist of the eutectic boride, pearlite, and ferrite. Borides precipitate along the grain boundary during the formation of eutectic. After heat treatment, the phases in Fe–B alloy are composed of the boride and martensite. With increase of carbon and boron concentrations, the Rockwell hardness of Fe–B alloy becomes larger. Meanwhile, by using a pin-on-disk abrasion tester, the effects of carbon and boron concentrations on the wear behaviors including ploughing depth, roughness, and wear weight loss under different loads have been studied. The results show that the wear resistance of Fe–B alloy with higher carbon and boron concentrations is comparable with the high chromium white cast iron.

Parametric effects of residual stress in pulsed d.c. plasma enhanced CVD TiN coatings

In order to design coatings with optimized wear and corrosion performance, knowledge of residual stress in hard coatings and its dependence on the processing parameters is required. In the present paper, TiN coatings deposited onto tool steels using pulsed d.c. plasma enhanced chemical vapor deposition were investigated. The processing parameters, including pulse voltage, pulse frequency and pre-nitriding time were varied. The residual stress was measured with X-ray diffraction and the interfacial adhesion between the coating and the substrate was evaluated using both indentation test (Pc) and scratch test (Lc). It was found that the residual stress and the adhesion could be adjusted by the processing parameters, and a correlation between these two properties was established. It was also evident that the residual stresses in coating deposited in the industrial-scale pulsed d.c. plasma CVD facility were much smaller than in those deposited in a conventional laboratory-scale chamber with d.c. power.

Investigations on Microstructures and Three-Body Abrasive Wear Behaviors of Fe–B Cast Alloy Containing Cerium

Abstract The effect of the element cerium on the microstructure and wear behavior of Fe–B cast alloy was investigated by scanning electron microscope, transmission electron microscope, X-ray diffraction analysis, Leica digital image analysis, hardness tester and abrasion tester. The microstructures of as-cast Fe–B alloy are composed of the phase ferrite, pearlite and eutectic boride. Moreover, the as-cast eutectic boride structures in Fe–B alloy containing cerium are finer than that in the alloy having no cerium. After heat treatment, the average boride area and wear weight loss of the alloy containing cerium are lower than these of the alloy having no cerium. Before the formation of primary austenite, cerium can combine with oxygen to form Ce2O3. Ce2O3 can act as nuclei of primary austenite, promoting the refinement of austenite and borides during solidification, and improve the wear property of Fe–B alloy.

Effects of Erosion Angle on Erosion Properties of Fe-B Alloy in Flowing Liquid Zinc

The effect of erosion angle on erosion behavior of the as-cast Fe-B alloy in flowing liquid zinc was investigated. The results show that the erosion rate of Fe-B alloy decreases linearly with increasing erosion angle. The erosion resistance of Fe-B alloy is better than that of 316L stainless steel, which is attributed to the favorable barrier effect of net-like Fe2B that resists erosion by flowing liquid zinc. Meanwhile, the ductile matrix can provide support in preventing borides from spalling and borides cause barrier effect on flowing liquid zinc during liquid zinc erosion, which shows a synergistic erosion-corrosion behavior between the matrix and borides. Moreover, an increase in erosion angle can cause a decrease in the removal effect of the flowing liquid zinc scouring component on the erosion compounds. Therefore, the quantity of erosion compounds increases at the erosion interface, weakening the mass transfer process and decreasing the erosion rate of the Fe-B alloy.

Interface Structure and Wear Behavior of Cr26 Ferrous Matrix Surface Composites Reinforced with CTCP

Using cast tungsten carbide particles (CTCP) and reduced iron powders as raw materials, the porous ceramic preforms with honeycomb, strip, and layer structure, respectively, were prepared by loose sintering process; then, the CTCP/Cr26 ferrous matrix composites were fabricated by casting infiltration process. The microstructure of the composites was analyzed by SEM, XRD, and EDS. The results show that a sintered shell forms as a result of the reaction of Fe and W2C in the CTCP during loose sintering process; the inner part of the shell around the CTCp consists of WC and Fe3W3C phases, while the outer part between the particles is dominated by Fe3W3C. Therefore, the strength of preforms is enhanced because the particles are connected with each other by sintered shell. During casting infiltration process, a transition layer constituted by WC and Fe3W3C formed at the interface of CTCp and the matrix due to the dissolution and precipitation of the sintered shell in the high-temperature liquid iron. The three-body abrasive wear behavior of the composites was investigated. The result shows the wear resistance of honeycomb structure composite is comparable to that of whole layer (WL) structure composite, which is three times of heat-treated Cr26. However, the honeycomb structure composite has higher performance/cost ratio owing to the lower CTCp volume fraction and higher strength and toughness compared with the WL structure composite.

Tribological properties of in situ Fe3Al-20 wt% Al2O3 composites

The tribological properties of Fe3Al-20 wt% Al2O3 composites, prepared by means of mechanical alloying and plasma-activated sintering, were investigated under air atmosphere against GCr15 bearing steels from room temperature to 500 °C. It was found that the friction coefficient of the composites (at 200 °C/350 °C) decreased with increasing temperature and the value was lower than that of Fe3Al alloys at the same temperature, and the friction coefficient increased again at 500 °C. Moreover, the wear rates of all the pins and discs were low at the medium/high temperatures. The dominant wear mechanism of the composites is microplowing and a little oxidation wear at room temperature. However, at elevated temperatures, oxidation wear and a little microplowing are found to be the main wear mechanism. There is also spalling induced by microfracture at 500 °C. The in situ Fe3Al-20 wt% Al2O3 composites have excellent wear resistance at a wide temperature range.

Effect of Hot Forging on Microstructure and Abrasion Resistance of Fe-B Alloy

The effect of hot forging on the microstructure and abrasion resistance of Fe-B alloy was studied. The results showed that boride networks are broken down by hot forging. After hot forging, the hardness of Fe-B alloy increased marginally, and the toughness increased considerably. In the two-body abrasion test, unforged Fe-B alloy exhibited excellent wear resistance and soft abrasive tended to show higher wear resistance. When alloys were tested against very hard abrasives, the wear resistance of forged Fe-B alloy was similar to that of unforged Fe-B alloy, but in the case of soft abrasives the wear resistance of forged Fe-B alloy was lower than that of unforged Fe-B alloy.

Erosion–corrosion interaction of Fe–B alloy in flowing zinc

The effect of erosion angle on the erosion–corrosion interaction of Fe–3.5 wt-%B alloy in flowing zinc was investigated. The total erosion–corrosion rate decreased linearly, whereas the pure erosion rate fluctuated slightly with increasing erosion angle, which was strongly dependent on the erosion–corrosion interaction. At an erosion angle of 0°, liquid zinc corrosion damaged the sample surface and facilitated erosion, which in turn increased corrosion via the removal of corrosion products. As the erosion angle increased, corrosion products accumulated and Fe2B flaked and cracked in front of the erosion interface, which resulted, in turn, in increased obstruction to the diffusion of liquid zinc. Accordingly, the erosion–corrosion interaction was reduced, thereby resulting in a low material loss at high erosion angles.

Toughness characteristics of arc enhanced magnetron sputtered SiCN hard films

Abstract The toughness of arc enhanced magnetron sputtered SiCN hard films is determined using microindentation measurements. The effects of the chemical composition, hardness, and microstructure on the film toughness are investigated. The results show that the presence of Si and C affects the film microstructure. The films with the nanocrystalline/amorphous composite structure are highly resistant to cracking and the film toughness is almost proportional to hardness. Our data also reveal that SiCN films with smaller Si contents and larger C concentrations have better toughness albeit possessing high hardness of 37 GPa.

Asymmetrical reorientation of bimetallic core-shell nanowires.

The reorientation mechanism of core-shell nanowires is investigated and our theoretical studies reveal the significance of the structural configuration. In nanowires which have a larger lattice in the core region than in the shell, for example, Au-core and Pd-shell, the surface stress and interfacial stress may synergistically cause them to reorient spontaneously, but they can revert back to the original state upon an appropriate tensile loading. In contrast, the misfit interface is detrimental to spontaneous reorientation in nanowires which have a smaller lattice in the core than in the shell such as the Pd-core and Au-shell structure, but uniaxial tensile loading causes the nanowires to transform in another way. This asymmetrical reorientation is caused by the different intrinsic stress as well as distinctive slipping characteristics, namely partial slipping and perfect slipping in the compressive and tensile processes.