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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 To investigate the wear behavior of bioceramic coating, two-body abrasive wear of air-plasma sprayed (APS) hydroxyapatite (HA) coating was studied in different conditions including: i) in simulated body fluid (SBF) and in dry conditions, and ii) sliding on Al 2 O 3 abrasive paper, HA, polycarbonate (PC) and polyurethane (PU), as well as iii) on different applied loads. Cross-sectional microstructures and worn surface morphologies of the coating were examined by scanning electron microscopy (SEM). Phase constitutions were analyzed by X-Ray diffraction (XRD). Microhardness, elastic modulus, fracture toughness and bond strength of the coating were investigated. It was revealed that, under the load of 20 N and sling on different counterpart materials, the wear rates of the coating varied from 24.09 × 10−2to 0.25 × 10−2 mg/Nm in SBF and varied from 13.54 × 10−2 to 0.05 × 10−2 mg/Nm in dry condition, respectively. The accumulated weight loss of the coating sliding on HA in SBF increased from 3.1 to 7.9 mg as the applied load increased from 5 N to 20 N. As sliding on Al 2 O 3 in dry condition and/or under high load, the abrasive wear of the coating dominantly occurred in the form of ploughing and peeling off of splats. As sliding on PC, PU and HA in SBF, the adhesive wear of the coating mainly occurred in the form of exfoliation. [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 reduce the decarburization of WC, the core-shell WC-16Cr 3 C 2 -10Co4Ni-La 2 O 3 (named as WC-Cr 3 C 2 -CoNiLa in following) powder was prepared through second agglomeration and spray granulation process and deposited using high velocity oxygen fuel (HVOF) spraying. Microstructure and phase constitutions of the deposited coating were characterized using scanning electronic microscopy (SEM) with energy dispersive spectrometer (EDS) and X-ray diffraction (XRD), respectively. Microhardness, elastic modulus, and fracture toughness of the coating were tested by indentation method. Wear properties of the coating under different applied loads were evaluated by two body dry sliding wear using a pin-on-disc tester. Experimental results showed that the HVOF sprayed WC-Cr 3 C 2 -CoNiLa coating was mainly consisted of WC, Cr 3 C 2 , Co, Ni phases and a little of Cr 2 O 3 without any WC decarburized phases including W 2 C, M 6 C and M 12 C). Most of WC carbide in the coating presented a round outline with the average particle size of 0.54 ± 0.35 μm and average crystal sizes 401 ± 91.41 Å in different crystal orientation index. The coating presented dense microstructure with the porosity about 1.16 ± 0.39%, and some lamella features with well bonded interfaces of carbide particles/binder phase, inter-splats and coating/substrate. Microhardness, elastic modulus, fracture toughness and wear rate of the coatings were 12.57 ± 0.52 Hv0.3, 153.91 ± 31.66 GPa, 5.31 ± 0.51 MPa⋅m1/2 and 6.67*10−3-11.11*10−3 mg/(Nm) when the applied load increased form 5 N to 15 N, respectively. The abrasive wear of the coating occurred mainly in the form of gouging and plastic deformation as well as peeling off carbide particles. • Core-shell WC-Cr 3 C 2 -CoNiLa powder made by second agglomeration and spray granulation. • Core-shell structural particle results to little WC decarburize and well melting of binder phase. • WC-Cr 3 C 2 -CoNiLa coating exhibits compact WC/binder, splat/splat, coating/substrate interfaces. • Coating exhibits reduced WC particle size with some crystal growth, well melted/deformed Cr 3 C 2. • The Coating exhibits higher microhardness, facture toughness as well as wear resistance. [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 the corrosion resistance and bioactivity of biodegradable Mg alloy substrate, novel Zn-HA/Zn double-layer coatings with different HA/Zn ratios in weight were deposited on AZ91D substrates by cold spraying. Phase compositions and microstructures of as-sprayed coatings and coatings after corrosion tests were analyzed by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). Electrochemical corrosion behaviors of both Zn-HA/Zn double-layer coatings were investigated in Hanks' simulated body fluid using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). Results showed that both the pure Zn coating and HA/Zn composite coatings presented the similar phase compositions with their primary powders in addition to Zn oxidizations. Zn powders were plastically deformed and partially oxidized due to its low melting point, while HA powders were mainly crashed into fragments and hill-like splats. Both Zn under layer and HA/Zn upper layer were well bonded and presented dense structures, differences in HA/Zn upper layers were related to the HA/Zn ratios. Potentiodynamic polarization and EIS measurements illustrated that the cold-sprayed Zn-HA/Zn double-layer coatings not only improve the corrosion resistance of Mg alloy substrates, but also enhance its bioactivity due to the HA existed in composite upper layer. [ABSTRACT FROM AUTHOR]

To compare with enhancing effects of TiO 2 and ZrO 2 reinforcement particles in hydroxyapatite (HA) coatings, HA/TiO 2 and HA/ZrO 2 composite coatings have been deposited on 316 L stainless steel substrates by high-velocity suspension flame spray (HVSFS) technique with the addition contents of 10 wt% and 30 wt% for both TiO 2 and ZrO 2 . Phase structures and compositions of all coatings were analyzed by X-ray diffraction (XRD) and Fourier-transform infrared spectroscopy (FTIR). Surface morphologies and microstructures were characterized by scanning electron spectroscopy (SEM). Vickers hardness, Young's modulus, tensile strength, wear rate and corrosion resistance were also measured and compared for both HA/TiO 2 and HA/ZrO 2 composite coatings. Results show that TiO 2 particles induced thermal decompositions of HA in HA/TiO 2 composite coatings rather than ZrO 2 in HA/ZrO 2 composite coatings. Both the HA/TiO 2 and HA/ZrO 2 composite coatings exhibited rough surfaces with spherical/flattened splats and nanoparticle agglomerates as well as bonded coating/substrate interfaces. Although mechanical properties of all composite coatings were improved with increasing addition contents of reinforcements, HA/TiO 2 composite coatings showed slightly higher mechanical properties than HA/ZrO 2 composite coatings at the same addition content due to higher melting degrees of HA/TiO 2 powders. Both HA/TiO 2 and HA/ZrO 2 composite coatings exhibited comparable and increased corrosion-resist performances in Hanks' simulation body fluids compared to the bare substrate. [ABSTRACT FROM AUTHOR]

In order to improve the mechanical and electrochemical properties of hydroxyapatite (HA) coating, nanostructured HA/Ti (nHA/Ti) composite coatings with different Ti contents of 30, 50 and 70 wt% were deposited on 316L stainless steel (SS) substrates by high-velocity suspension flame spray (HVSFS) and compared to HVSFS-deposited nanostructured HA (nHA) coatings. Microstructures and phase compositions of as-sprayed coatings were analyzed by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The deposition mechanism of nanostructured HA/Ti composite coatings was also examined. Microhardness and Young's modulus were measured. Electrochemical corrosion behaviors of all coatings were tested in Hanks’ simulated body fluid using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). Results showed that the nHA/Ti composite coatings contained HA and Ti in addition to some Ti-O compounds. Compared to nHA coatings, nHA/Ti composite coatings presented dense and typical lamella structures formed mostly by flattened splats. Microhardness and Young's modulus of nHA/Ti composite coatings increased with increasing Ti content. Potentiodynamic polarization and EIS measurements illustrated that nHA/Ti composite coatings had excellent corrosion resistance compared to nHA coatings and bare SS substrate. [ABSTRACT FROM AUTHOR]