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Mo2FeB2 coatings were fabricated by laser cladding with different pre-placed powder sizes. In the present research, a coaxial nozzle head coupled with a continuous fiber laser with a maximum power of 3 kW was used. The influence of powder size (~ 6 μm, ~ 13 μm, ~ 65 μm) on the morphology, microstructure, microhardness, wear resistance, and fracture toughness of the coating were discussed in this research. The morphology showed that coating obtained with ~ 6-μm powder size had excellent wettability and avoided obvious defects; microstructure revealed that the coating appeared particle agglomeration phenomenon with the increase of powder size. The coating obtained with ~ 6 μm had herringbone and feature structures to improve the density, and the bonding zone had typical columnar crystal and no cracks. The microhardness, wear resistance, and fracture toughness decreased as the increase of powder size. The optimal microhardness, COF, and fracture toughness of coating reached 1138.56 HV0.5, 0.59, 14.65 MPa·m1/2, respectively, when powder size was ~ 6 μm. The wear form of coatings was typical abrasive wear and adhesive wear; the fracture mechanism was transgranular fracture. The research can provide a reference for the preparation of Mo2FeB2 ternary boride coating. [ABSTRACT FROM AUTHOR]

WCoB-TiC composite coatings with in-situ formation of NbC were fabricated on the surface of an AISI 1045 substrate by laser cladding. The geometric characteristics, microstructure, microhardness, and fracture toughness of coatings were investigated by means of an optical microscope (OM), a scanning electron microscope (SEM), energy-dispersive spectroscopy (EDS), X-ray diffraction (XRD), an electron probe microanalyzer (EPMA), and a microhardness tester. In addition, the elastic constants and bulk property of the reinforced phases were investigated by first principles calculation. The results showed that a reliable metallurgical bonding was formed between the coating and the substrate and in-situ synthesized reinforcement phases of the coating consisted of WCoB, W2CoB2, TiC, NbC, (Nb,Ti,W)C, and traces of Nb2C. The dilution rate and porosity had a negative effect with the addition of Nb. According to the results of SEM, EDS, and EPMA, Nb was diffused uniformly in the TiC structure. The NbC phase had the highest hardness among all in-situ synthesized reinforcement phases, which reached 24.525 GPa, while Nb2C reflected the strongest metallicity. The microhardness and fracture toughness of the coating were increased firstly and then decreased following the increase of Nb content, and when the Nb addition was 4 wt%, the coating had the highest average microhardness and fracture toughness (1755.42 HV0.5, 8.23 MPa·m1/2, respectively). The microhardness and fracture toughness was 24% and 30% higher than that of the coating without Nb addition, respectively. From the crack propagation morphology of coatings, all coatings had fine transgranular fracture. [ABSTRACT FROM AUTHOR]

To study the influence of the three soluble salt ions of Mg2+, Cl−, and SO42− on the strength of salt-rich cement soil, an unconfined compression test was conducted on cement soil with different curing times to study the effect of the content of soluble salt ions on the strength of cement soil. X-ray diffraction and environmental scanning electron microscopy were used to study the influence of soluble salt ions on the microstructure and chemical composition of salt-rich cement soil and to reveal the mechanism of interaction between soluble salt ions and cement soil from macro and micro perspectives. The results show that the Mg2+, Cl−, and SO42− soluble salt ions have distinct adverse effects on the strength of cement soil samples. Moreover, with the increase in the content of soluble salt ions, the adverse effects become more apparent. The main reason for this phenomenon is that the high content of soluble salt ions consumes C–S–H and C–A–H gels and generates M–S–H, M–A–H, and a large number of crystals. M–S–H and M–A–H dispersed in C–S–H and C–A–H gels can reduce the cementing force of cement soil and the strength of salt-rich cement soil. [ABSTRACT FROM AUTHOR]

In this research, the TiC–Ni35A composite coating was fabricated on the AISI 1045 steel substrate by laser cladding process. The cross-sectional morphology, microstructure, microhardness, and wear resistance of coatings obtained under different laser energy densities (E) and TiC powder ratios (PR) were analyzed. According to the results, all the coating had a reliable metallurgical bonding with the AISI 1045 steel substrate. The X-ray diffraction (XRD) analysis revealed that the coating phases were Ni and TiC. The average microhardness of the Ni35A-80wt.% TiC coating reached up to 75.1 HRC. The minimum coefficient of friction of the composite coating was only about 30% of the AISI 1045 steel substrate. The wear form was mainly adhesive wear when altering the TiC powder ratios, while the wear form also contained abrasion wear under different energy densities. The ability of decomposition and re-nucleation of TiC was significantly improved with the increase of laser energy densities and the decrease of TiC powder ratios. The microhardness, wear resistance, and coefficient of friction of the composite coating were improved because of the TiC strengthening phase particles. Compared with the AISI 1045 steel substrate, the microhardness and wear resistance of the composite coating were increased by 5.3 times and 6.3 times, respectively. [ABSTRACT FROM AUTHOR]

Traditional isothermal aging treatments could not balance the relationship between mechanical properties and corrosion resistance of ultra-high-strength Al–Zn–Mg–Cu alloys. Therefore, the effect of non-isothermal aging (NIA) treatments on the microstructure and properties of TiC-TiB2 (BC) ceramic particles-reinforced spray-formed 7055 aluminum alloy tungsten inert gas (TIG) weld metal (WM) has been investigated. Weld joints were solid soluted at 475 °C for 2.5 h and quenched in water at 65 °C. Then, they were heated from 100 to 180 °C firstly at the rates of 60, 40, and 20 °C h−1 and cooled from 180 to 100 °C at the rate of 20 °C h−1. The results show that the mechanical properties of WM improve as the variable temperature rates decrease and its corrosion resistance deteriorates. The tensile strength of BC-20 is the best (580 ± 25 MPa), and the corrosion resistance of BC-60 is the best. The NIA treatments promote the formation of narrower precipitate free zones and finer-dispersed precipitates. Therefore, the mechanical properties (565 ± 25 MPa, 4.20 ± 0.21%) and corrosion resistance of BC-40 are excellent in the shorter aging time. [ABSTRACT FROM AUTHOR]