Search

In this study, Mo 2 FeB 2 -based cermet coating has been attempted to produce by electrospark deposition (ESD) process on a high speed steel substrate. Microstructural morphology, elementary distribution, phase constitute, microhardness, and wear resistance of the coating were investigated by scanning electron microscopy (SEM), electron probe microanalysis (EPMA), X-ray diffraction (XRD), microhardness measurement and tribological test. The SEM and EPMA results show that the coating is dense, metallurgically bonded to the substrate, and has an average thickness of 48.1 μm. Moreover, a discernible composition transition zone appeared between the coating and the substrate. The XRD patterns reveal a microstructural transformation from Mo 2 FeB 2 phase and binder phase (ferrite) of the cermet to amorphous phase and martensitic phase of the coating during the deposition, and the martensitic phase has nanocrystalline structure (31.7 nm). Such microstructure of the coating results in higher microhardness, lower friction coefficient, and better wear resistance than the high speed steel substrate. The main wear types for the coating are abrasive wear and fatigue wear. [ABSTRACT FROM AUTHOR]

To improve the corrosion resistance of micro-arc oxidation (MAO) treated Mg alloy wires, carbon (C) nanoparticles were added to the silicate electrolyte to fabricate C-containing composite coatings. Comparisons of microstructure, corrosion resistance and mechanical properties of uncoated wires, MAO-C-free coated wires and MAO-C coated wires were performed. The results indicated that the surface layers of Mg alloy wires treated with MAO were primarily composed of MgO and Mg 2 SiO 4 phases and demonstrated porous morphologies. The C nanoparticles in the electrolyte were capable of incorporating into composite coatings, forming a dense composite coating microstructure and resulting in the formation of a small amount of MgAlO 4 and Mg 3 SiO 4 F 2 , which improve corrosion resistance in static and dynamic immersion environments. Measurements of mechanical properties demonstrated that the MAO-C coated wires retained a high tensile strength of 180 MPa, even after dynamic immersion for 50 days, and possessed better corrosion resistance than the wires coated with MAO-C-free coating. The effects of shear stress and localized environment changes resulting from the flowing corrosive media were proposed as two mechanisms that accelerated corrosion in a dynamic immersion environment. [ABSTRACT FROM AUTHOR]

Obtaining excellent mechanical properties and high electrical conductivity for ceramic/metal composites is of great significance. In this study, the Ti 3 SiC 2 /Cu composite coatings (20 wt% and 50 wt% Ti 3 SiC 2) were prepared by plasma spraying with the agglomerated Ti 3 SiC 2 /Cu powders. The effects of Ti 3 SiC 2 content on the microstructure, mechanical properties, electrical conductivity and tribological properties of the coatings were analyzed. The results showed that besides the primary compound region, the diffusion and decomposition zones also coexisted within the coatings. The 20 wt% Ti 3 SiC 2 /Cu composite coating showed a denser microstructure with the highest microhardness of 224 HV 0.1 , whereas higher fracture toughness was obtained for the 50 wt% Ti 3 SiC 2 /Cu coating (1.26 MPa•m1/2). Moreover, the 20 wt% and 50 wt% Ti 3 SiC 2 /Cu composite coatings had considerably high electrical conductivity, with the values of 7.9 × 106 S/m and 4.3 × 106 S/m, respectively. Compared to dry friction, the friction coefficient of the coating increased under current-carrying condition, and the wear of the tribo-pairs was accelerated. Generally, the main wear mechanisms of the 50 wt% Ti 3 SiC 2 /Cu composite coating under dry friction and current-carrying conditions are the adhesion wear, abrasive wear and fatigue wear. • Ti 3 SiC 2 /Cu composite coatings were prepared by supersonic plasma spraying. • Effects of Ti 3 SiC 2 content on the coating microstructure and properties were investigated. • Friction and wear properties of the 50 wt% Ti 3 SiC 2 /Cu composite coating under current-carrying condition were analyzed. [ABSTRACT FROM AUTHOR]

The microstructures, tribo-mechanical properties of the fabricated NiAl/Cr 2 AlC composite coatings with various additions of self-made Cr 2 AlC were comparatively investigated. The results indicated that appropriate addition (10 wt%) of Cr 2 AlC could improve the microstructure, hardness, bending strength and tribological performance of the coatings. However, excessive addition of Cr 2 AlC led to the loose structure, decreased bending strength and adhesive strength of the coatings. The added Cr 2 AlC played a critical role of lubrication and wear resistance at low and medium temperatures due to its layered structure, leading to the low COFs and wear rates. At higher temperatures, the Cr 2 AlC accompanied with the generated oxides such as Al 2 O 3 , Cr 2 O 3 and NiO played a critical role of antifriction and anti-wear, resulting in the significant reduced COFs and wear rates. The NiAl/Cr 2 AlC composite coating with the Cr 2 AlC addition of 10 wt% exhibited excellent tribological performance from room temperature to 800 °C. • The stoichiometric ratio Cr 2 AlC powders were successfully obtained. • The Cr 2 AlC played a critical role of lubrication due to its layered structure. • The Cr 2 AlC could enhance the coatings' mechanical and tribological properties. • The lubrication of generated oxides could account for the lower COF at 800 °C. [ABSTRACT FROM AUTHOR]

The microstructures, mechanical properties and corrosion resistance of 2060 AL-Li alloy subjected to laser shock peening (LSP) with power densities of 3, 4 and 5 GW·cm−2 were investigated comprehensively. Microhardness, residual stress, wear resistance and fatigue life were tested on LSP alloys to analyze the mechanical properties and the corrosion behavior was investigated by electrochemical test. X-ray diffraction (XRD) and field emission transmission electron microscopy (FE-TEM) were used to investigate the surface microstructure evolution. The results show that LSP leads to a high magnitude of surface compressive residual stress and a significant increase of dislocation density near the surface in the plastic deformation layer. Additionally, with the increase of laser power density, the microhardness, compressive residual stress and surface roughness increase, while the friction coefficient and wear rate decrease compared to pristine alloy. The fatigue life of the sample with a laser power density of 4 GW·cm−2 reaches the highest value of 6.00 × 104 times, approximately twice that of the pristine sample (2.98 × 104 times), which is mainly attributed to the surface residual compressive stress, high density dislocations and surface hardening owing to the LSP. The corrosion resistance of the LSP alloys modestly decreases in a 3.5% NaCl solution compared with pristine alloy, which mainly ascribes to the increase of surface roughness. Laser shock peening with a GW cm−2 level power density is employed to form high residual compressive stress and increase the dislocation density near the surface layer of the 2060 Al Li alloy. The LSP alloys with power densities of 4 GW cm−2 achieved the highest fatigue life of 6 × 104 times at a maximum cyclic stress of 330 MPa, which is far higher than that of the pristine alloy. [Display omitted] • Laser shock processing is employed to modify the 2060 Al Li alloy. • The high-density dislocation density is obtained near the surface layer of the 2060 Al Li alloy. • High residual compressive stress is formed on the alloy surface. • The microstructure, friction properties and fatigue life of 2060 Al Li alloy are improved. [ABSTRACT FROM AUTHOR]

Alloyed layer with gradient structure was prepared on the surface of 20Cr2Ni4A steel by lanthana-bearing supersonic fine particle bombarding (SFPB). Microstructure features of the surface layer were characterized. Subsequently, the samples were carburized in an ECM vacuum furnace. Based on the experimental observations, the mechanism of promoting the diffusion of carbon atoms by lanthana-bearing SFPB was proposed. It mainly involves the promotion of the structure obtained by lanthana-bearing SFPB on the adsorption and diffusion of carbon atoms during carburization. The promotion mechanism of the rare earth in the alloying layer on carbon atom diffusion was analyzed from the aspects of accelerating mechanism of carbon source decomposition by rare earth, subsurface diffusion channel mechanism and driving force. Experimental evidence and related mechanisms show that, the structure formed by the step of austenitization during carburization and the existence of rare earth are necessary to promote the diffusion of carbon atoms. Therefore, our research results clarify the promotion mechanism of lanthana-bearing SFPB treatment on the diffusion of carbon atoms in the carburizing process, and further useful to adjust the surface structure to promote the application of pretreatment technology in surface modification. [Display omitted] • A surface alloying layer is prepared by lanthana-bearing SFPB. • The alloying layer presents texture characteristics and gradient structure. • The alloying layer improves the interstitial atom diffusion significantly. • Microstructure evolution mechanism for promoting atom diffusion is proposed. [ABSTRACT FROM AUTHOR]