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To optimise spray parameters for fabricating well-bonded and less decarburised coatings, the morphologies and cross-sectional microstructures of powders and splats, in addition to the microstructure, phase constitution, and mechanical properties of high-velocity oxy-fuel (HVOF)-sprayed WC–Cr 3 C 2 –Co coatings were systematically investigated. Significantly influenced by spray parameters, splat morphologies vary from ellipsoids to well-flattened pies with some ejectors or stripes on their periphery and a splat/substrate interface with good contact. Splat microstructures vary homogeneously from a minimal hard phase to non-uniform structures with some dense surface layers and smoothly outlined hard phases or to non-uniform structures with rough surfaces and angular hard phases. The coating microstructure evolves from a non-lamellar structure with many pores to a lamellar structure with a well-contacted interface and a smooth surface hard phase. The coatings mainly consist of the WC hard phase and a small fraction of decarburised and amorphous phases, in addition to Co, Cr 3 C 2 , Cr 7 C 3 , Cr 2 O 3 , and Cr 2 O 5. Porosity and WC retention index vary from 0.89 ± 0.11 to 2.32 ± 1.75% and from 84.68 to 94.48%, respectively. Microhardness, elastic modulus, fracture toughness, adhesive strength, and wear rate of the coatings vary from 7.03 ± 0.64 to 11.96 ± 0.94 GPa, from 77.64 ± 13.77 to 244.73 ± 65.75 GPa, from 1.23 ± 0.1 to 2.66 ± 0.66 MPa m1/2, from 18.54 ± 1.21 to 63.84 ± 8.01 MPa, and from 1.38 ± 0. 32 to 3.54 ± 0.79 × 10−2 mg/(N⋅m), respectively. [ABSTRACT FROM AUTHOR]

The (WC-Co)-Ni composite coatings were fabricated by high velocity oxygen fuel (HVOF) spraying process using (WC-Co)-Ni powders prepared through blending agglomerated WC-Co powder with Ni powder. Microstructure and phase composition of the coatings deposited with different content of Ni powders were characterized using scanning electronic microscopy (SEM) and X-ray diffraction (XRD), respectively. The microhardness, elastic modulus and fracture toughness of the coatings were tested by indentation method. The wear properties of the coatings sliding in dry and wet conditions as well as under different applied loads were tested using a modified pin-on-disc tester. Experimental results showed that the microstructure of HVOF sprayed (WC-Co)-Ni composite coating was exhibited some lamella features consisted of deformed WC-Co splats and even distributed Ni splats, which was significantly influenced by the Ni content in original powders. Phase constitutions of the coatings mainly consisted of WC, W 2 C, Co, Ni and a little of Co 6 W 6 C, which were related to the Ni content in original powders. Microhardness, elastic modulus, fracture toughness and wear rate of the coatings were varied from 435.5 ± 34.7 to 708.7 ± 43.3 Hv0.3, from 58.9 ± 10.3 to 135.0 ± 82.7 GPa from 1.07 ± 0.11 to 2.41 ± 0.09 MPa m1/2 and from 0.15 to 0.4 mg•(Nm)−1, respectively. The abrasive wear of the coating occurred mainly in the form of gouging and peeling off in addition to a little of plastic deformation. [ABSTRACT FROM AUTHOR]

Abstract The present paper investigates the deposition behavior of cold spraying agglomerated hydroxyapatite (HA) particles on stainless steel (SS) and HA substrates; for that purpose, the surface morphologies and cross-section microstructures of splats were investigated and compared to that of original HA particles. Full characterization of the coating was performed through the evaluation of (i) phase constitutions, crystallographic structure and composition, and coating/substrate interface as well as (ii) nanohardness of the powder, microhardness, tensile strength and the abrasive wear properties of the coating. HA splats on both substrates exhibited cap-like shape morphology with rough surface, and had some ring grooves on surface and some radial stripes on periphery composing of tiny HA granules. The cross-section of HA splats presented an asymmetric ellipsoid morphology with a flat bottom surface and convex up surface as well as compact area near bottom interface. Bonding of splats/substrate interface was related to the splats size and substrate materials. CS HA coating possessed a dense and homogeneous microstructure with reduced pores and crystal size, similar chemical structures, phase constitutions and chemical compositions to original powder. These microstructure evolutions were related to the deformation behavior of HA splats, i.e. radial spreading and compacting in impact direction by the un-continuous moving of agglomerates or granules in low temperature. Microhardness, tensile strength and the abrasive wear rate of the coating were 59.0 ± 5.6 kg/mm2, 10.9 ± 1.1 MPa and 1.3 ± 0.2 × 10−1 mg/(m·N), respectively. Highlights • Cold sprayed HA splats deform in radial spreading and in impact direction tamping • HA splats can form a well contact interface to HA substrate • There exists unbond area in the center of HA splats / SS substrate interface • HA coatings possess non-lamella structure and well contact interface to substrate • HA coatings possess same phase, composition as powders and reduced crystal size • HA coatings possess well wear resistance against PU or PC [ABSTRACT FROM AUTHOR]

To investigate the effect of Cr 3 C 2 and Y 2 O 3 additions on cermet coatings, agglomerated and sintered multimodal WC-10Cr 3 C 2 –12Co and WC-10Cr 3 C 2 –12Co–1Y 2 O 3 cermet powders were deposited as new type of WC-based cermet coatings on plain carbon steel substrate by high velocity oxy-fuel flame spraying. Microstructures, phases, and mechanical properties of both WC-10Cr 3 C 2 –12Co and WC-10Cr 3 C 2 –12Co–1Y 2 O 3 coatings were examined and compared with those of WC-12Co coating. Results showed that WC-10Cr 3 C 2 –12Co and WC-10Cr 3 C 2 –12Co–1Y 2 O 3 cermet coatings presented homogeneous microstructures with multimodal carbide particles well distributed in binder matrix, and exhibited phases similar to the feedstock without decomposed phase. However, WC-12Co coating showed the existence of some serious decomposed phases including W 2 C and amorphous Co 3 W 3 C. Morphologies of individual splats on WC-Co substrate clearly demonstrated liquid–solid two phase deposition behaviors of three types of powders in which carbide particles were mainly present in solid state and Co in liquid state. Furthermore, fracture toughness, elastic modulus, and wear resistance of WC-10Cr 3 C 2 –12Co and WC-10Cr 3 C 2 –12Co–1Y 2 O 3 coatings were found to be higher than those of WC-12Co coating owing to synergistic effects of Cr 3 C 2 , Y 2 O 3 , and multimodal carbides. Surface morphologies of worn out WC-12Co, WC-10Cr 3 C 2 –12Co, and WC-10Cr 3 C 2 –12Co–1Y 2 O 3 coatings indicated that wear mechanism mainly included gouging and peeling off. [ABSTRACT FROM AUTHOR]

In order to improve mechanical properties of HA coatings, nano-structured HA/TiO 2 multilayer coatings composed of TiO 2 bond layer, HA/TiO 2 intermediate layer with different TiO 2 contents and HA top layer were prepared by a high velocity suspension flame spraying (HVSFS) method using nano-sized HA and TiO 2 powders. Phase constitution, compositions and microstructures were characterized by XRD, XPS, FTIR and SEM. Mechanical properties of multilayer coatings were investigated in comparison with the pure HA coating. Results show that multilayer coatings were mainly composed of HA and TiO 2 phases, and presented well-bonded coating/substrate interfaces and porous surfaces as well as graded chemical compositions in coating thickness. Microhardness and Young's modulus of HA/TiO 2 intermediate layers were increased with the TiO 2 contents due to its reinforcement, and HA/TiO 2 multilayer coatings revealed gradual mechanical properties from the TiO 2 bond layer to HA top layer. Tensile strengths of HA/TiO 2 double-layer coatings were improved due to TiO 2 reinforcement in comparison with the pure HA coating. Wear properties of HA/TiO 2 multilayer coatings were tested by a pin-on-disc method and were improved due to the presence of intermediate layers resulting in lower wear rates than that of the pure HA coating. [ABSTRACT FROM AUTHOR]

To improve the corrosion resistance of Mg alloy, Zn coating was formed by cold spraying technology followed by post shot-peening processing. The phase structure, microstructure, and corrosion properties of the cold-sprayed Zn coatings before and after shot peening process were all investigated. The cold-sprayed Zn coating presented a porous and roughness structure. However, the Zn coatings after shot peening illustrated densifications with flattened and elongated Zn particles on the top layer. The mass and thickness losses of Zn coatings after shot peening both increased with the impact pressure owing to the competition between the densification and the erosion of Zn coatings. The microhardness of Zn coatings after shot peening increased from 40 HV 0.025 to 64 HV 0.025 due to factors like densification structure, work hardening, and grain refinement. It also displayed decreasing profiles from the surface to the inner bulk. The anti-corrosion properties of Zn coatings after shot-peening were improved by about one fold when compared to the cold-sprayed Zn coating owing to the presence of compact top layers. The corrosion changes in behaviors of Zn coatings before and after shot peening were clarified by comparing the morphologies and phase structures after immersion in stimulated body fluid. In sum, the proposed simple post-processing strategy looks promising for improving the corrosion resistance of cold-sprayed Zn coatings modified Mg alloy substrates, which might be useful for future use in bone implants. • Cold-spayed Zn coatings were improved by shot peening with different pressures. • Flattening and elongated particles were observed in dense top layers after shot peening. • Zn coatings after shot peening showed increased microhardness with decreasing profiles. • Anti-corrosion properties of Zn coatings were increased by shot-peening. • Corrosion behaviors of different Zn coatings were discussed after immersion in SBF. [ABSTRACT FROM AUTHOR]

WC-Cr 3 C 2 -12Ni coatings, with Cr 3 C 2 weight content of 10% and 30%, were fabricated on steel substrate by high velocity oxy-fuel (HVOF) flame spraying technique, and microstructure, phase composition and mechanical properties of WC-Cr 3 C 2 -12Ni coatings prepared by different oxygen flows were investigated. The results reveal that phase compositions of WC-Cr 3 C 2 -12Ni coatings were mainly influenced by the Cr 3 C 2 content rather than the oxygen flow. WC-Cr 3 C 2 -12Ni coatings demonstrated low decarburization and decomposition of WC due to coarse WC gains and high in-flight particle velocities during HVOF. WC-Cr 3 C 2 -12Ni coatings exhibited low porosities and typical microstructures, where a mixture of fine and coarse WC grains was uniformly embedded in the Ni/Cr 3 C 2 matrix. The microhardness, indentation fracture toughness and elastic modulus of WC-Cr 3 C 2 -12Ni coatings were improved by coarse WC grains, Cr 3 C 2 addition and dense microstructure, which resulted in high wear resistances of WC-Cr 3 C 2 -12Ni coatings. The abrasive wear features with groove, peel-off and exposed/fractured WC grains were observed in WC-Cr 3 C 2 -12Ni coatings after dry-sliding wear. The relationship between microstructure and mechanical property of WC-Cr 3 C 2 -12Ni coatings was discussed from the viewpoints of powder properties and process parameters. • WC-Cr 3 C 2 -12Ni powder was home-made by agglomeration & sintering method. • WC-Cr 3 C 2 -12Ni coatings presented less decarburization and decomposition. • WC-Cr 3 C 2 -12Ni coatings exhibited dense microstructure and multi-sized carbide grains. • Cr 3 C 2 and oxygen flow influenced mechanical properties of WC-Cr 3 C 2 -12Ni coatings. • Relationship between structure and property of WC-Cr 3 C 2 -12Ni coatings was discussed. [ABSTRACT FROM AUTHOR]