Jiangbo Cheng

Formation and Mechanical Properties of CoNiCuFeCr High-Entropy Alloys Coatings Prepared by Plasma Transferred Arc Cladding Process

Plasma transferred arc cladding process was used to fabricate CoNiCuFeCr multi-element alloys coatings. The experimental results show that the coating forms a face-centered-cubic solid solution phase. The microstructure of the coating is mainly composed of dendrite and discontinuous interdendritic segregation. The average hardness of the coating reaches 194.8 HV100. The nano-indentation testing indicates that the micro-hardness and elastic modulus of the coating are 3.64 GPa and 211 GPa, respectively. The CoNiCuFeCr high-entropy alloy coating has excellent wear and corrosion resistance. The wear resistance of the coating is about 1.7 times higher than that of Q235 steel substrate under the same wet sand rubber wheel abrasion testing conditions. In 1N hydrochloric acid solution, the coating presents lower icorr values in polarization curves and higher fitted Rf values in EIS plots than that of as-cast 304 stainless steel.

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.

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.