Search

A biodegradable Mg/MgO composite coating was deposited onto AZ31B magnesium alloy by high-velocity suspension flame spraying technique using nano-sized MgO and micron-sized Mg powders. Phase constitution, microstructure, mechanical property and corrosion behavior of Mg/MgO composite coatings with different Mg/MgO ratios were investigated. Mg/MgO composite coatings with different Mg/MgO ratios presented rough and porous surfaces with typical features of solid-fluid co-deposition and exhibited well bonding coating/substrate interfaces with some pores within the coatings. Mg/MgO composite coatings prepared by co-deposition of Mg/MgO mixed powder were mainly composed of Mg rather than MgO indicating superior deposition of Mg. Microhardness, elastic modulus and tensile strength of Mg/MgO composite coatings were influenced by the Mg/MgO ratio. Mg/MgO composite coatings presented a limited corrosion protection for Mg alloy substrate after immersion in Hanks' simulated body fluid for different times. Corrosion behavior of Mg/MgO composite coatings was also discussed. This study proposed a strategy to prepare biodegradable Mg/MgO composite coating on metal substrates for potential applications in the implant field. [ABSTRACT FROM AUTHOR]

To slow down the corrosion rate and increase the bioactivity of magnesium alloys, biodegradable hydroxyapatite/magnesium (HA/Mg) composite coating was deposited onto AZ91D alloy substrate by high-velocity suspension flame spray technique using nano-sized HA and micron-sized Mg powders. Microstructures and phase constitutions of HA/Mg composite coating were analyzed by scanning electron microscopy and x-ray diffraction. Corrosion resistance of composite coating was also evaluated by potentiodynamic polarization test and electrochemical impedance spectroscopy in Hanks' balanced salt solution (HBSS). The result shows that the HA/Mg composite coating mainly consisted of Mg and HA in addition to a few of MgO phases. The coating showed a rough surface morphology with homogeneous elemental distribution and a lamellar structure in cross section as well as well-bonded coating/substrate interface. Mg particles presented superior deposition during spraying due to their higher melting degree compared to HA particles. AZ91D alloy substrate was significantly protected from corrosion in HBSS by the HA/Mg composite coating with Mg dissolution on surfaces of the composite coating. This strategy can offer a new route to fabricate HA/Mg composite coatings on other metal substrates for use in biodegradable implant fields. [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]

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 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]

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]