An experimental bone defect healing with hydroxyapatite coating plasma sprayed on carbon/carbon composite implants

Hydroxyapatite coatings with proper thickness were coated on fusion-cage-like carbon fiber reinforced carbon composite implants for bone tissue reconstruction by the plasma spraying technique. Autogenously bone filled fusion-cage-like implants were grafted in hybrid goats' tibia for 328 days. By means of X-ray photography, histological observation and scanning electron microscopy, the biological behaviors of the coating were compared with the pure carbon fiber reinforced carbon composites and the bone defect healing effect of the implants was evaluated. The results indicated that hydroxyapatite coating has more obvious osteoconductive effect than the pure carbon fiber reinforced carbon composites with surface bioinert. The calcium and phosphorus ions leached from HA provide a suitable biological mineralization environment that accelerates the metabolism of bone, the osteoblast differentiation and collagen synthesis. The coating can significantly speed up the bone defect healing process and improve the surface bioactivity of carbon fiber reinforced carbon composites.     

SiC Coatings for Carbon/Carbon Composites Fabricated by Vacuum Plasma Spraying Technology

SiC coatings for carbon/carbon (C/C) composites have been prepared by the combination process of vacuum plasma spraying technology and heat treatment. The SiC coatings were formed by the reaction of C/C substrates with as-sprayed silicon coatings deposited by vacuum plasma spraying. The preparation temperature and the thickness of original silicon coatings have great influence on the microstructure and the thickness of the synthesized SiC coatings. The results indicated that a continuous and dense SiC coating has been produced on the surface of C/C substrates. The SiC coatings prepared at 2073 K with the silicon coatings of 230 μm thickness, exhibited a low mass loss of 2.56% in the plasma jet with temperature about 2473 K and duration of 420 s in atmosphere. The present results implied that vacuum plasma spraying technology combined with heat treatment was an acceptable method for synthesis of protective SiC coatings for C/C composites.     

预应力热处理对羟基磷灰石涂层相组成和结合强度的影响

设计不同角度的斜面工业纯钛柱,采用等离子法制备羟基磷灰石涂层,设计工装使涂层在预加相同正应力和不同切应力条件下进行热处理.利用电子拉伸实验机进行剪切结合强度测试,利用X射线衍射仪检测涂层的相组成与结晶度,探讨应力条件下热处理对涂层组成和涂层/基体结合强度的影响.研究表明:热处理中预加应力可以提高涂层的结晶度和涂层/基体的剪切结合强度.     

炭/炭复合材料声电沉积钙磷生物活性涂层的生长机理

通过声电沉积在炭/炭复合材料表面制备钙磷生物活性涂层,采用SEM（带EDAX）,XDR,FTIR研究电沉积时间对钙磷生物活性涂层的形貌、结构和组成的影响.实验结果表明：沉积初始先在炭/炭表面形成无定形层,片状磷酸氢钙（DCPD）在其表面生长,随着电沉积时间的延长,逐渐向针状的羟基磷灰石Ca10（PO4）6（OH）2（HA）转变,涂层厚度和n（Ca）/n（P）不断增加,涂层的结晶度和电解液的pH值下降.涂层为缺钙磷灰石.同时探讨了在炭/炭复合材料表面钙磷生物活性涂层的生长机理.     

The Influence of Spray Parameters on the Characteristics of Hydroxyapatite In-Flight Particles,Splats and Coatings by Micro-plasma Spraying

Hydroxyapatite (HA) is one of the most important bioceramic materials used in medical implants. The structure of HA coatings is closely related to their manufacturing process. In the present study, HA coatings were deposited on Ti-6Al-4V substrate by micro-plasma spraying. Results show that three distinct HA coatings could be obtained by changing the spraying power from 0.5 to 1.0 kW and spraying stand-off distance from 60 to 110 mm: (1) high crystallinity (93.3%) coatings with porous structure, (2) high crystallinity coatings (86%) with columnar structure, (3) higher amorphous calcium phosphate (ACP, 50%) coatings with dense structure. The in-flight particles melting state and splat topography was analyzed to better understand the formation mechanism of three distinct HA coatings. Results show that HA coatings sprayed at low spraying power and short stand-off distance exhibit high crystallinity and porosity is attributed to the presence of partially melted particles. High crystallinity HA coatings with (002) crystallographic texture could be deposited due to the complete melting of the in-flight particles and low cooling rate of the disk shape splats under higher spraying power and shorter SOD. However, splashed shape splats with relative high cooling can be provided by increasing SOD, which leads to the formation of ACP.     

Functionally graded carbon nanotubes/hydroxyapatite composite coating by laser cladding

Functionally graded carbon nanotubes/hydroxyapatite (CNTs/HA) composite coatings have been fabricated by laser cladding technique using CNTs/HA composite powders. As the feedstock for laser deposition, CNTs/HA composite powders were prepared by ball-milling different weight ratios (1%, 3% and 5%) of CNTs with HA powders. CNTs/HA composite coatings were fabricated with CNTs/HA composite powders and functionally graded coating was fabricated by sequentially depositing different CNTs/HA composite coatings on pure titanium. The phase composition, microstructure, micro-hardness, bonding strength and in vitro cellular responses of the composite coatings and the functionally graded composite coating were studied. The results show that the crystallinity of CNTs/HA composite coatings increased with increasing amount of CNTs in the powder mixture. The CNTs were dispersed homogeneously in the coatings to form an interconnected web and the cylinder graphic structure of CNTs was not changed after laser irradiation. Compared with pure HA coating, the maximum increase of the micro-hardness of CNTs/HA composite coatings was 46.8% and the micro-hardness of the functionally graded coating increased gradually through the thickness of this coating. Furthermore, the bonding strength of the functionally graded coating was nearly twice higher than that of pure HA coating. The in vitro cellular biocompatibility tests reveal that the functionally graded composite coating has comparable in vitro bioactivity with pure HA coating.     

Metallic coating of aerospace carbon/epoxy composites by the pulsed gas dynamic spraying process

A method for applying metallic coatings to high fibre volume fraction aerospace carbon/epoxy polymer matrix composites is presented. The pulsed gas dynamic spraying process was used for depositing zinc coatings on composites featuring a thin layer of copper particles co-cured into the laminate. No surface preparation was required on the cured substrates prior to spraying hence no damage was induced in brittle carbon fibres. Polymer matrix composite substrates with an added layer of co-cured copper particles were manufactured using a standard autoclave process. External substrate heating was not required. Metal powder and epoxy degradation were avoided through low process temperatures. Satisfactory cohesive and adhesive characteristics, low porosities and good microhardness values were obtained for a range of coating parameters. Microhardness and porosity of coatings deposited on polymer matrix composites compared well with those of similar coatings deposited on metallic substrates.     

Influence of hydrothermal temperature on hydroxyapatite coating transformed from monetite on HT-C/C composites by induction heating method

Hydrothermal post-treatment was used to convert monetite coating fabricated by induction heating method on H₂O₂ treated C/C (HT-C/C) composites to an adherent HA coating. The monetite coatings were hydrothermally treated for 4 h at 373 K, 403 K, 423 K, and 453 K in a 50 mL autoclave. After hydrothermal post-treatment, the structure, morphology and the chemical composition of these HA coatings were characterized with XRD, FTIR SEM and EDS. A scratch test was conducted to measure the strength of the adhesion of the coatings to the HT-C/C substrate. The results showed that the degree of crystallinity and the Ca/P ratio of the HA coatings increased with increasing hydrothermal temperature. The submicron-level morphology and adhesion of the HA coatings were highly affected by the hydrothermal temperature. From the results, it can be suggested that 423 K was the best hydrothermal treatment temperature for the HA coatings which were transformed from the monetite coatings produced by the induction heating method on HT-C/C composites.     

SiC/SiC–YAG–YSZ oxidation protective coatings for carbon/carbon composites

SiC/SiC–YAG–YSZ coatings were prepared by pack cementation, chemical vapor deposition and slurry painting on carbon/carbon (C/C) composites. The microstructures and oxidation behavior of coatings were investigated. The results show that the coatings displayed good oxidation and thermal shock resistance due to a dense glassy layer with silicates formed on the coating of SiC–YAG–YSZ. The weight gain rate of coated C/C composites was 1.77% after oxidation for 150 h at 1773 K. SiC in outer coating can promote the formation of oxygen diffusion barrier and lead to the optimum oxidation resistance for the coatings, compared with YSZ and YAG.     

多孔体制备工艺对C/C-SiC复合材料弯曲性能的影响

以针刺整体炭毡为坯体,采用CVD和树脂浸渍／炭化混合法增密制备了4种C／C多孔体,然后熔硅浸渗C／C多孔体制备了C／C-SiC复合材料;研究了不同炭涂层、高温热处理对C／C-SiC复合材料弯曲强度和断裂方式的影响。结果表明：热解炭涂层可减少制备过程中炭纤维的损伤,具有适中的界面结合强度,使复合材料的弯曲强度达到161．5MPa,表现出良好的“假塑性”;适当选择高温热处理工艺可制备弯曲性能较高,具有一定“假塑性”的C／C-SiC复合材料。     

Cold spray deposition of a WC-25Co cermet onto Al7075-T6 and carbon steel substrates

This work focussed on the deposition of wear-resistant and corrosion-resistant WC-25Co cermet powders on carbon steel and aluminium (Al7075-T6) substrates by cold gas spraying (CGS). The unique combination of mechanical, physical and chemical properties of WC-Co cermets has led to their widespread use for the manufacture of wear-resistant parts. X-ray diffraction tests were run on the powder and coatings to determine possible phase changes during the spraying process. The bonding strength of the coatings was measured by adhesion tests (ASTM C633-08). The sliding (ASTM G99-04) and abrasive (ASTM G65-00) wear resistance of the coatings were also studied. Corrosion resistance was determined by electrochemical measurements and salt fog spray tests (ASTM B117-03). CGS achieved thick, dense and hard WC-25Co coatings on both aluminium alloy Al7075-T6 and carbon steel substrates, with excellent tribological and electrochemical properties. We thus conclude that this method is very competitive compared with conventional thermal spraying techniques, giving thick, dense and hard coatings on both aluminium alloy Al7075-T6 and carbon steel substrates, with excellent tribological and electrochemical properties.     

Anti-oxidation behavior of chemical vapor reaction SiC coatings on different carbon materials at high temperatures

To protect carbon materials from oxidation, SiC coatings were prepared on carbon/carbon(C/C) composites and graphite by chemical vapor reaction. SEM and XRD analyses show that the coatings obtained are composed of SiC grains and micro-crystals. The influence of different carbon substrates on oxidation behavior of coated samples was investigated, and then their oxidation mechanisms were studied. Oxidation test shows that the SiC coated graphite has a better oxidation resistance than SiC coated C/C composites at high temperatures (1 623 K and 1 823 K). In the oxidation process, the oxidation curves of SiC coated C/C composites are linear, while those of SiC coated graphite follow a quasi-parabolic manner. The oxidation mechanism of the former is controlled by chemical reaction while the latter is controlled by oxygen diffusion based on the experimental results. The variation of oxidation behavior and mechanism of SiC coatings on two kinds of carbon substrates are primarily contributed to their structure differences.     

A MoSi2/SiC oxidation protective coating for carbon/carbon composites

To protect carbon/carbon (C/C) composites against oxidation, a MoSi₂ outer coating was prepared on pack-cementation SiC coated C/C composites by a hydrothermal electrophoretic deposition. The phase composition, microstructure and oxidation resistance of the prepared MoSi₂/SiC coatings were investigated. Results show that hydrothermal electrophoretic deposition is an effective route to achieve crack-free MoSi₂ outer coatings. The MoSi₂/SiC coating can protect C/C composites from oxidation at 1773 K for 346 h with a weight loss of 2.49 mg cm⁻² and at 1903 K for 88 h with a weight loss of 5.68 mg cm⁻².     

Flexural destructive process of unidirectional carbon/carbon composites reinforced with in situ grown carbon nanofibers

Unidirectional carbon/carbon (C/C) composites modified with in situ grown carbon nanofibers (CNFs) were prepared by catalysis chemical vapor deposition. The effect of in situ grown CNFs on the flexural properties of the C/C composites was investigated by detailed analyses of destructive process. The results show that there is a sharp increase in the flexural load-displacement curve in the axial direction of the CNF-C/C composites, followed by a serrated yielding phenomenon similar to the plastic materials. The failure mode of the C/C composites modified with in situ grown CNFs is changed from the pull-out of single fiber to the breaking of fiber bundles. The existence of interfacial layer composed by middle-textured pyrocarbon, CNFs and high-textured pyrocarbon can block the crack propagation and change the propagation direction of the main crack, which leads to the higher flexural strength and modulus of C/C composites.     

The effect of partially carbonized fibers on the mechanical properties of carbon/carbon composites

The carbon/carbon (C/C) composite with satisfactory mechanical properties were obtained through introduction of partially carbonized fibers as a precursor. Applying this procedure the production cost of C/C composites may be significantly reduced. Stabilized PAN fibers were partially carbonized at temperatures ranging from 400 to 1000 °C and reinforced with phenolic resin, resole type. Cured composite were carbonized up to 1000 °C in an inert atmosphere. Monofilament tensile test strength, Young's modulus and tensile strength of partially carbonized fibers were determined. Mechanical properties of carbon/carbon composites (flexural strength and flexural modulus) determined by using three-point bending test. The effect of partially carbonized fibers on the mechanical properties of C/C composites was examined by scanning electron microscope (SEM) through analysis of the fracture surface. The C/C composite reinforced with partially carbonized fibers at 600 °C showed quite satisfactory flexural strength. This confirms assumptions that through co-carbonization of partially carbonized fibers and resin C/C composite with suitable mechanical properties could be obtained.     

PIP工艺制备2D C/SiC复合材料Z-向穿刺工艺

针对2D C/SiC复合材料存在碳布层间缺乏纤维增强,层间结合较差的问题,提出通过Z-向穿刺工艺提高碳布层间结合,克服材料使用时可靠性不高的问题,并比较了穿刺工艺对复合材料微观结构和力学性能的影响.结果表明,通过Z-向穿刺工艺制得试样2D C/SiC-Z_(pin)的弯曲强度、弯曲模量和剪切强度分别为247.8 MPa、37.8 GPa和32.1 MPa,而未穿刺试样2D C/SiC的弯曲强度、弯曲模量和剪切强度分别只有219.3 MPa、34.4 GPa和23.3 MPa,由此可见,采用Z-向穿刺工艺能明显提高复合材料的力学性能.微观结构分析认为,试样力学性能提高的根本原因在于采用Z-向穿刺纤维加强了碳布层间结合,使材料具有较好的整体性,克服了复合材料层间结合较弱对力学性能带来的不利影响.     

Preparation and mechanical properties of carbon/carbon composites with high textured pyrolytic carbon matrix

Short carbon fiber felts with an initial porosity of 89.5% were deposited by isobaric, isothermal chemical vapor infiltration using natural gas as carbon source. The bulk density of the deposited carbon/carbon (C/C) composites was 1.89 g/cm³ after depositing for 150 h. The microstructure and mechanical properties of the C/C composites were studied by polarized light microscopy, X-ray diffraction, scanning electron microscopy and three-point bending test. The results reveal that high textured pyrolytic carbon is deposited as the matrix of the composites, whose crystalline thickness and graphitization degree highly increase after heat treatment. A distinct decrease of the flexural strength and modulus accompanied by the increase of the toughness of the C/C composites is found to be correlated with the structural changes in the composites during the heat treatment process.     

Low-Energy Plasma Spray (LEPS) Deposition of Hydroxyapatite/Poly-ε-Caprolactone Biocomposite Coatings

Thermal spraying is widely employed to deposit hydroxyapatite (HA) and HA-based biocomposites on hip and dental implants. For thick HA coatings (>150 μm), problems are generally associated with the build-up of residual stresses and lack of control of coating crystallinity. HA/polymer composite coatings are especially interesting to improve the pure HA coatings' mechanical properties. For instance, the polymer may help in releasing the residual stresses in the thick HA coatings. In addition, the selection of a bioresorbable polymer may enhance the coatings' biological behavior. However, there are major challenges associated with spraying ceramic and polymeric materials together because of their very different thermal properties. In this study, pure HA and HA/poly-ε-caprolactone (PCL) thick coatings were deposited without significant thermal degradation by low-energy plasma spraying (LEPS). PCL has never been processed by thermal spraying, and its processing is a major achievement of this study. The influence of selected process parameters on microstructure, composition, and mechanical properties of HA and HA/PCL coatings was studied using statistical design of experiments (DOE). The HA deposition rate was significantly increased by the addition of PCL. The average porosity of biocomposite coatings was slightly increased, while retaining or even improving in some cases their fracture toughness and microhardness. Surface roughness of biocomposites was enhanced compared with HA pure coatings. Cell culture experiments showed that murine osteoblast-like cells attach and proliferate well on HA/PCL biocomposite deposits.     

The evaluation of powder processing on microstructure and mechanical properties of hydroxyapatite (HA)/yttria stabilized zirconia (YSZ) composite coatings

In clinical applications, the mechanical failure of HA-coated titanium alloy implants suffered at the interface of the HA coating and titanium alloy substrate will be a potential weakness in prosthesis. Yttria stabilized zirconia (YSZ) reinforced HA coatings have been proven to enhance the mechanical properties of the HA coating significantly and reduce the formation of calcium oxide (CaO). In this paper, HA/YSZ (30 wt.% YSZ) composite coatings were sprayed by the plasma technique. The effects of the powder processing–mechanical ball milling method and spheroidization method on the microstructure and mechanical properties of the HA/YSZ composite coatings were evaluated. The experimental results showed that the spheroidized powders melted better than the ball milled powders during plasma spraying and formed higher mechanical property coatings (1.6326±0.08 MPa m^−0.5 of fracture toughness, 58.59±2.91 GPa of elastic modulus and 43.42±2.53 MPa of tensile bond strength). HA/YSZ solid solution formed during deposition on the substrate, which played a very important role in the mechanical properties of the HA/YSZ composite coatings. Tensile bond strength tests showed that the fracture mode was cohesive and that failure occurred at the interface of HA and unmelted YSZ particles. The molten state of YSZ had a great influence on the properties of the HA/YSZ composite coatings.     

Study of fluorhydroxyapatite coatings on carbon/carbon composites

Fluorhydroxyapatite coatings were prepared on the surface of carbon/carbon composites using the combined action of ultrasonic-electrodeposition and ion exchange. The morphology, structure and composition of the prepared coatings after ion exchange were investigated by scanning electron microscopy, X-ray energy spectrum analysis, infrared spectroscopy and X-ray diffraction. Results show that the crystallinity of the coating as well as the intensity of the diffraction peaks (112) and (300) of hydroxyapatite increased, whereas the intensity of the diffraction peaks of tricalcium phosphate decreased. The small lamellar crystals were converted into large ones. The fluorine content in the coating was 4.59%. The bonding strength between the coating and the carbon/carbon matrix increased slightly after immersion, reaching 4.12 MPa. The mechanism of the ion exchange during which hydroxyapatite turned into fluorhydroxyapatite is discussed.