Shaoqun Jiang

In situ synthesis of Fe-based alloy clad coatings containing TiB2–TiN–(h-BN)

Fe-based alloy coatings containing TiB2–TiN–(h-BN) were synthesized in situ on Q235 steel substrates by a plasma cladding process using the powders of Fe901 alloy, Ti, and h-BN as raw materials. The effects of Ti/h-BN mass ratio on interfacial bonds between the coating and substrate along with the microstructures and microhardnesses of the coatings were investigated. The results show that the Ti/h-BN mass ratio is a vital factor in the formation of the coatings. Free h-BN can be introduced into the coatings by adding an excess amount of h-BN into the precursor. Decreases in the Ti/h-BN mass ratio improve the microstructural uniformity and compactness and enhance the interfacial bonds of the coatings. At a Ti/h-BN mass ratio of 10/20, the coating is free of cracks and micropores, and mainly consists of Fe-Cr, Fe3B, TiB2, TiN, Ti2N, TiB, FeN, FeB, Fe2B, and h-BN phases. Its average microhardness in the zone between 0.1–2.8 mm from the coating surface is about Hv0.2 551.5.

Bonding characteristics of the Al2O3-metal composite coating fabricated onto carbon steel by combustion synthesis

The fabrication of an alumina-metal composite coating onto a carbon steel substrate by using a self-propagating high-temperature synthesis technique was demonstrated. The effects of the type and thickness of the pre-coated layer on the binding structure and surface quality of the coating were systematically investigated. The macrostructure, phase composition, and bonding interface between the coating and the substrate were investigated by scanning electronic microscopy (SEM), X-ray diffraction (XRD), and energy-dispersive X-ray spectrometry (EDS). The diffraction patterns indicated that the coating essentially consisted of α-Al2O3, Fe(Cr), and FeO·Al2O3. With an increase in the thickness of the pre-coated working layer, the coating became more smooth and compact. The transition layer played an important role in enhancing the binding between the coating and the substrate. When the pre-coated working layer was 10 mm and the pre-coated transition layer was 1 mm, a compact structure and metallurgical bonding with the substrate were obtained. Thermal shock test results indicated that the ceramic coating exhibited good thermal shock resistance when the sample was rapidly quenched from 800°C to room temperature by plunging into water.

Influence of Grinding Particle Size on Structure and Electrical Properties of La0.67Sr0.33MnO3−δ Compound

In this article, the influences of grinding particle size on the structure and electrical transport properties of La0.67Sr0.33MnO3−δ compound have been investigated. The compound was prepared by gel combustion process followed by grinding for different duration time. It was found that the lattice parameters, unit-cell volume, strain, oxygen deficiency, and temperature dependence of resistivity ρ–T increase with decreasing particle size. The ρ–T growth can be explained by the increasing contribution of the grain boundary effect, strain, and even oxygen deficiency. The electrical transport mechanism over the whole temperature range of 100–400 K was thoroughly described by applying the phase separation model around the phase transition temperature TP. This model was subsequently employed to calculate the ρ–T at high temperature up to 1000 K. The result showed there was a second phase transition at a typical temperature T*>TP, which could be attributed to the relaxation of small polarons to large ones. This relaxation occurred at lower temperatures when the particle size decreased. It might be due to the decrease in conduction bandwidth caused by the defects arisen during the grinding.

Friction and Wear Properties of ZrO2–Al2O3 Composite with Three Layered Structure Under Water Lubrication

Zirconia–Alumina (ZrO2–Al2O3) composite with three layered structure was prepared, and its friction and wear properties under water lubrication were investigated. The results indicate that the layered composite exhibited better tribological properties comparing with ZrO2–Al2O3 mono-layered composite at same tested conditions. Good combination of toughness and strength as well as subsequently excellent friction and wear properties were mainly contributed to the residual stress of the layered composite, which caused by thermal mismatch of sintering between layers through special design of compositions and structure. Friction coefficient and wear rate of the layered composite decreased with increment of load and/or velocity. The change of tribological properties was also relative to wear mechanisms, micro-cutting, and abrasive wear were main mechanisms at lower load and/or lower velocity but fatigue wear caused by plastic deformation became dominant at higher load and/or higher velocity.

Si-STEEL THIN-STRIP PREPARED BY TWIN-ROLL CONTINUOUS CASTING

The fabrication process of Si-steel thin-strip by twin-roll continuous casting was described and the quality of the obtained Si-steel thin-strip was measured. Si-steel strips with 0.5–6.5 wt.% Si content were successfully prepared, and proper parameters including pouring temperature, height of molten pool, casting speed and pouring head mode were optimized, and their mechanisms were discussed. The relationship between quality factors of Si-steel including cracks, strip thickness, impurity and process parameters such as Si content and so on were discussed. The morphologies of the strips with different Si content were studied.