Ti3SiC2/Cu composites with different contents of Cu were fabricated by mechanical alloying and spark plasma sintering method. The phase composition and structure of the composites were analyzed by X-ray diffractometry and scanning electron microscopy equipped with energy dispersive spectroscopy. The mechanical and tribological properties of Ti3SiC2/Cu composites were tested and analyzed compared with monolithic Ti3SiC2 in details. The results show that the Cu leads to the decomposition of Ti3SiC2 to produce TiCx, Ti5Si3Cy, Cu3Si, and TiSi2Cz. The friction coefficient and wear rate of the composites are lower than that of monolithic Ti3SiC2, which is ascribed to the fixing effect of hard TiCx, Ti5Si3Cy, and Cu3Si to inhibit the abrasive friction and wear. However, at elevated temperatures (ranging from room temperature to 600 °C) the friction and wear of the composites are higher than those at room temperature. Plastic flowing and tribo-oxidation wear accompanied by material transference contribute to the increased friction and wear at elevated temperatures.

An attempt has been made to improve the corrosion behavior of WE43 magnesium alloy by laser surface melting (LSM) using a 10 kW continuous-wave CO2 laser. The microstructure evolution of WE43 alloy after LSM treatment was analyzed by using scanning electron microscopy, energy-dispersive spectroscopy and metallographic microscope. The corrosion resistance of specimens was assessed by electrochemical and immersion tests. Results showed that the LSM treated WE43 alloy presented a uniform microstructure with refined grains, enriched alloying elements and redistributed intermetallic compounds. The LSM treatment effectively improved corrosion resistance of WE43 alloy, which was mainly associated with enrichment of alloying elements in α-Mg matrix and uniform distributions of the refined Mg14Nd2Y phase.

Plasma electrolytic oxidation (PEO) was performed on a laser surface melting (LSM) modified AZ91 Mg alloy. The effect of LSM pre-treatment on the long-term corrosion resistance of the PEO coated AZ91 alloy was evaluated. Results showed that the LSM pretreatment had a negligible effect on the phase composition and microstructure of the PEO coatings. However, after LSM pretreatment, the long-term corrosion resistance of the PEO coated AZ91 alloy revealed a large enhancement. This was mainly ascribed to the improved corrosion resistance of the substrate resulting from the change of microstructure characteristics induced by the LSM treatment. This provided an alternative approach to improve the long-term corrosion resistance of the PEO coated Mg alloy by appropriate surface modified pretreatment of substrates.

•The incorporation of Al restrains the decomposition of Ti3SiC2.•The wear rates of TCASc are lower than those of Ti3SiC2 at RT and 200 °C.•Negative wear rate was found for Ti3SiC2 at 800 °C due to tribo-oxidation.•The incorporated phase of AlCu reinforces the bonding of Ti3SiC2 grains.•Abrasive wear and tribo-oxides films lubrication are the main wear mechanisms.Dense Ti3SiC2/Cu/Al/SiC composites (TCASc) were successfully produced by powder metallurgy/spark plasma sintering (SPS). The composition and microstructure of the composites were analyzed by X-ray diffractometry and scanning electron microscopy equipped with energy dispersive spectroscopy. The tribological properties of the TCASc sliding against Si3N4 ball at temperatures ranging from room temperature (RT) to 800 °C were investigated in comparison with those of Ti3SiC2 (TSC). The tribology tests were conducted on dry sliding tribometer by ball-on-disk configuration. The wear mechanisms were discussed in detail. The results show that the main phases of the composite include TSC, AlCu, SiC, and Al2O3. The incorporation of Al could inhibit the decomposition of TSC. The hardness and flexural strength of the composite are slightly lower than those of TSC. The tribological properties of TCASc and TSC are intensively dependent on temperature. The tribological properties of TCASc are better than those of TSC at room and medium temperatures (wear rate, WR, of TSC at RT and 200 °C: (8.63±0.37)×10−4 and (2.15±0.18)×10−3 of TCASc (5.31±0.55)×10−4 and (1.12±0.02)×10−3 mm3/N·m, respectively), while the wear properties of TCASc are not better than that of TSC at 400–800 °C (WR at 600 °C, for example, for TSC: (9.7±1.4)×10−5 and TCASc (2.27±0.15)×10−4 mm3/N·m, respectively). Abrasive wear dominates the wear mechanisms at RT and 200 °C for TCASc. The incorporated phases of AlCu, SiC, and Al2O3 reinforce the bonding of TSC grains and nail the surrounding soft TSC matrix under the cyclic stress. At high temperature, dynamic-equilibrium tribo-oxides layers show the lubricating and wear-reduction effects contributing to the decreasing friction and wear for both TSC and TCASc. The adhesive wear resulting from the plastic flow is one of the reasons of the higher WR of TCASc than that of TSC.

•Tribological properties of laser cladding NiAl intermetallic compound coating were investigated at elevated temperatures.•The glaze layer acts as a wear-resistant solid lubricant to reduce the friction and wear of laser cladding NiAl coating.•The wear mechanism is abrasive wear below 500 °C, and transforms to adhesive wear and oxidation wear at 500 °C and above.Tribological properties, phase compositions and wear mechanisms of laser cladding NiAl coating were investigated from room temperature to 1000 °C under air atmosphere environment. The results showed that a glaze layer composed of NiO, Ni2O3, Al2O3 and NiAl2O4 phases as well as Ni3Al phase were formed on worn surface under high temperature, which act as a solid lubricant and anti-wear material improving the tribological properties of NiAl coating at elevated temperatures. The wear mechanism is dominated by abrasive wear below 500 °C, and transforms to plastic deformation and adhesive wear at 500 °C up to 700 °C and oxidation wear at 900 °C and above, owing to formation of new oxide phase during tribochemical reaction.

•NiCrAlY/Cr3C2 (NiCr)/V2O5/Ag2O coating was prepared by laser cladding.•Silver vanadate produced by mechanical alloying and decomposed by laser cladding•Silver vanadate reproduced by tribo-chemical reaction•The coating exhibits excellent tribological properties at elevated temperatures.•Reproduced silver vanadate contributes to improving of tribological properties.Self-lubricating coating NiCrAlY/Cr3C2 (NiCr)/V2O5/Ag2O was prepared by laser cladding. Two different kinds of contrast samples were prepared in order to verify the excellent tribological properties of the composite coating. The composition and microstructure of the composite coating were characterized by X-ray diffractometry, scanning electron microscopy with energy spectrum analyzer (SEM-EDS). The tribological behavior of the coating from 25 °C to 800 °C was evaluated by a ball-on-disk tribometer and dual-mode 3D surface profiler, the corresponding wear mechanism of the composite coating was investigated by Raman spectroscopy. It has been found that the composite coating shows better tribological properties than the compared coatings when the temperature higher than 400 °C, the friction coefficient of composite coating was 0.143 and the wear rate was 2.86 × 10− 5 mm3/Nm at 800 °C. All these can be attributed to formation of the self-lubricant Ag3VO4 and AgVO3 with lamella structure on the worn surface. The wear mechanism of the composite coating is dominated by plastic deformation, delamination and adhesive wear at elevated temperature.

•Profuse micro-sized β-phases precipitated in T6-treated AZ91 alloy.•AZ91 alloy had better corrosion resistance after T6 treatment.•T6 treatment improved the corrosion resistance of PEO coated AZ91 alloy.AZ91 Mg alloy was treated by solid solution and ageing heat treatment (T6), followed by plasma electrolytic oxidation (PEO). The microstructure and corrosion behavior of the T6, PEO and T6-PEO treated AZ91 alloy as well as the as-received one were investigated using scanning electron microscopy, X-ray diffraction and corrosion tests, respectively. The chemical compositions of the naturally formed oxide film on sample surface were determined by X-ray photoelectron spectroscopy. Especially, the effect of T6 treatment on the corrosion behavior of the bare and PEO treated specimens was evaluated. Results showed that the T6 treatment resulted in the formation of high density fine β-phase in α-Mg matrix and enhanced the corrosion resistance of AZ91 alloy. Meanwhile, the T6-PEO treated alloy had much better corrosion resistance than the PEO treated one, due to the combined effects of reduced defects of PEO coating and improved corrosion resistance of the T6 treated substrate.

•Ag-MoO3 contained NiCrAlY based composite coating was prepared by laser cladding.•Phase transformation during laser cladding and tribo-chemical reactions was studied.•Tribological behavior and mechanism from room temperature to 800 °C were investigated.Ag-MoO3 contained NiCrAlY based composite coating was successfully prepared on GH4169 stainless steel substrate by high energy ball milling and laser cladding. The microstructure and phase transformation were investigated by scanning electron microscopy (SEM) equipped with energy dispersive spectroscopy (EDS) and X-ray diffraction spectrum (XRD). The tribological behavior and mechanism from room temperature to 800 °C were investigated. Results showed that MoO3 in the composite powders transformed to Mo2C reinforcement under the high energy density of laser, and a series of opposite transformation occurred during friction process. The coating showed the lowest friction coefficient and low wear rate at 600 °C and 800 °C due to the generation of Ag2MoO4 during tribo-chemical reactions and the formation of lubrication glaze on the worn surface. Ag made effective lubrication when the temperature rose up to 200 °C. The coating displayed a relatively high friction coefficient (about 0.51) at 400 °C, because though MoO3 (oxidation products of Mo2C) and Ag2MoO4 were detected on the worn surface, they could not realize effective lubrication at this temperature. Abrasive wear, adhesive wear and plastic deformation contributed to the increased friction and wear.