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The relationship between structure and mechanical, tribological and corrosion properties of coatings is investigated by adjusting the annealing time (750 °C for 1–10 h). Results exhibit that the coatings mainly consist of Ni(Mo) and Mo 2 C, and MoC is formed after long time annealing (≥4 h). The hardness of coatings decreases from 9.3 GPa to 5.9 GPa with the extension of annealing time, and the inversion relationship between strength and toughness (0.19–0.17) is observed owing to the decline of elastic recovery. The highest wear rate of coatings is about 13.6 × 10−6 mm3 N−1 m−1, and most of them under the applied load of 1.96 N and 3.92 N are in the range of 2.1–6.3 × 10−6 mm3 N−1 m−1. Meanwhile, the wear resistance of coatings annealed for 1–4 h is better than those annealed for longer time (6–10 h), and the change of it is proportional to the hardness and elasticity recovery. In addition, the corrosion resistance of coatings in 3.5 wt% NaCl solution decreases with annealing time due to the grain growth, the uneven distribution of composition and the increase of porosity. • Effect of structural changes on anti-wear and corrosion properties of coatings is studied. • Traditional inversion relation between strength and toughness is broken due to the graphitization of diamonds. • The wear mechanism of coatings is mainly abrasive. • Coatings with high hardness and elastic recovery has higher wear resistance. • Grain growth, uneven distribution of composition and increase of porosity lead to reduced corrosion resistance. [ABSTRACT FROM AUTHOR]

• Diamond/matrix interface of composite annealed at 450 °C becomes wide. • Graphitization of diamonds and precipitation of Mo 2 C are detected at 750 °C. • Traditional Archard model is broken due to the lubrication of Mo 2 C and the increase in elasticity. • Composite with wide diamond/matrix interfaces has the lowest corrosion resistance. • Precipitation of MoNi and Mo 2 C improves the corrosion resistance of composites. Ni–18 at.% Mo/21 vol% diamond composites are prepared on steel substrates by electrodeposition. Influence of annealing temperature (450–750 °C) on the microstructure, phase composition, hardness, tribological properties and corrosion resistance of composites is analyzed. Results show that matrix grain grows from 7 nm to 38.4 nm with the increasing temperature. Wide and amorphous particle/matrix (P/M) interface is observed at 450 °C due to Mo segregation, improving hardness (11.3 GPa) and wear resistance of composites. However, the uneven distribution of composition at P/M interface leads to the occurrence of local corrosion and the reduction of corrosion resistance. MoNi and Mo 2 C intermetallics are precipitated in composites while the temperature is ≥480 °C and 681 °C, respectively. Phase transition decreases Mo segregation at P/M interface and causes the disappearance of amorphous P/M interface, which inhibits local corrosion and improves corrosion resistance. Meanwhile, the consumption of Mo, the graphitization of diamonds and the growth of grains cause the softening of composites. However, composite annealed at 750 °C with the lowest hardness (6.2 GPa) has the lowest wear rate (3.4 × 10−6 mm3 N−1 m−1), which breaks the traditional Archard model attributing to the lubrication of Mo 2 C. [ABSTRACT FROM AUTHOR]

Ni Mo alloys with various Mo contents are prepared by electrodeposition in sulfate–citrate acid solutions under different temperature, pH, stirring rate, current density and MoO 4 2− concentration. Influences of Mo content on the grain size, hardness and wear resistance are studied. Results show that the increase in Mo content decreases the deposition rate of Ni Mo alloys prepared at a constant temperature. As–prepared alloys are composed of nanocrystalline Ni(Mo) solid solution when Mo is less than 24.4 at.%. The grain size of alloys decreases with the increment of Mo content. Amorphous phase appears in deposits when Mo content exceeds 24.4–27.3 at.%. Hardness and wear resistance of alloys firstly increases with Mo content, and then it has a decline due to the formation of amorphous. Additionally, Hall–Petch (HP) relationship is found in deposits as the grain size decreases from 12.4 nm to 7.9 nm, and then the inverse HP relationship appears with the further decrease in grain size to 1.5 nm. Meanwhile, traditional Archard law is found in Ni Mo alloys with Mo content in the range of 6.3–27.3 at.%. Additionally, HP breakdown causes a variation of wear resistance at the critical grain size of 7.9 nm. • Nanocrystalline and amorphous Ni–Mo alloys are obtained at different experimental conditions. • Plastic deformation of nanocrystalline Ni–Mo alloys is mediated by GBs. • Hall–Petch and its inverse relations are obtained in Ni–Mo alloys. • Critical grain size of Hall–Petch breakdown is 7.9 nm, smaller than that in pure Ni. • Hall–Petch breakdown is manifested in a variation of wear resistance in Ni–Mo alloys. [ABSTRACT FROM AUTHOR]

Ni-Mo coating with different Mo content is prepared by electrodeposition. The influences of Mo content and heat treatment on the structure, hardness, and wear and corrosion properties of coatings are studied. It is found that Ni-Mo coatings consist of nanocrystalline, and the grain size is ≤18.5 nm. MoNi intermetallic precipitates out when the annealing temperature is ≥ 499 °C. Both of the Mo content and the heat treatment are important to strengthen coatings. The highest hardness is about 10.3 GPa, corresponding to the Ni–19.1 at.% Mo coating after annealing at 500 °C. The lowest wear rate is about 2.1 × 10−4 mm3 N−1 m−1, which related to Ni–22 at.% Mo coating annealed at 450 °C. Additionally, Ni–16.7 at.% Mo coating after annealing at 450 °C shows the best corrosion resistance in 0.5 M H 2 SO 4. • Electrodeposited Ni–Mo coatings consist of nanocrystalline. • MoNi intermetallic precipitates out when the annealing temperature is ≥499 °C. • Optimum Mo content and heat treatment are important to strengthen coatings. • Wear resistance of Ni–Mo coatings increases with hardness. • Optimum Mo content for highest corrosion resistance behavior was obtained. [ABSTRACT FROM AUTHOR]

Ni–Mo/diamond composite coatings have been electrodeposited in a Ni–Mo electrolyte containing micron diamonds with five different sizes, respectively. The diamond content in coatings is in the range of 5–31 vol%. The grain size of as-annealed coatings is smaller than 10 nm. Microhardness of as-annealed coatings increases with the diamond content, and the highest hardness is about 15.4 GPa. The as-annealed coatings incorporated with 5 μm diamonds have supvderior wear resistance to that of the other coatings. The lowest wear rates of the as-annealed coating and the pin-on-disk system are about 2 × 10−6 and 5 × 10−6 mm3 N−1 m−1, respectively, which all correspond to the coating containing 31 vol% diamonds with the size of 5 μm. • Ni–Mo/micron diamond composite coating was prepared by electrodeposition. • Microhardness of the composite coatings increases with diamond content. • High diamond size and content are helpful improving the tribological performance of coatings. [ABSTRACT FROM AUTHOR]

WB 2 /Cr multilayer films with different modulation ratios (λ = 1, 3, 5, 7, 12, and 20) were deposited by a combination of direct-current and pulse direct-current magnetron sputtering, and the number of bilayers was fixed at ten. The effect of the modulation ratio on the microstructure, mechanical and tribological properties of the multilayer films was investigated in detail. X-ray diffraction demonstrates that a preferred orientation of WB 2 (101) and Cr (110) exists, and WB 2 (101) dominates the film's growth with increasing of modulation ratio. The TEM results show that the multilayer films consist of nanograins dispersed in an amorphous matrix in WB 2 layers and polycrystalline grains in Cr layers. The hardness increases with the increasing modulation ratio, and the maximum hardness (31.1 GPa) is obtained at λ = 20. The indentation toughness presents an opposite changing trend, and the maximum indentation toughness (1.264 MPa m1/2) is obtained in S1 at λ = 1 which conforms to the rule of mixture due to the relatively thick bilayer thickness (Λ = 160–192 nm). The wear mechanism is investigated, and the results suggest that the multilayer film with λ = 7 possesses the best wear resistance (2.06 × 10−7 mm3/Nm), benefiting from the balance of hardness and indentation toughness. [ABSTRACT FROM AUTHOR]