A further insight into pores in plasma sprayed hydroxyapatite coating

Pores in hydroxyapatite (HA) coatings affect their mechanical and biological performances, and so far pore characteristic and formation mechanism are not fully understood. In the present study, microstructural observations on plasma sprayed HA coating have been carried out, indicating that globular pores exist commonly on coating surface, cross-sectional facet and fracture surface. Analysis of HA particles plasma sprayed into water shows that hollow HA spheres were formed, and the hollow spheres will transform into globular pores when they impact onto the substrate.     

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.     

Ti-6Al-4V基体上等离子喷涂羟基磷灰石涂层的热-力耦合和残余应力

基于热弹塑性理论建立了等离子喷涂羟基磷灰石涂层的热-力耦合模型。一方面,通过引入变形对温度的影响项对经典的Fourier瞬态热传导方程进行了修正,另一方面,在考虑了温度软化效应、应变硬化效应、和应变率强化效应后,采用适用于高温、高应变率条件下的Johnson-Cook模型作为本构方程。基于上述耦合模型,采用有限元方法对涂层内的残余应力场进行了模拟,同时还模拟了基体预热温度以及涂层厚度对残余应力的影响。为了验证数值模拟的可靠性,还采用“材料去除”的实验技术测试了涂层在界面处的残余应力。结果表明：在界面边缘有明显的应力集中;适当提高基体的预热温度有利于减小残余应力;涂层的残余应力随厚度的增加而增大。     

Phase composition and in-vitro bioactivity of plasma sprayed calcia stabilized zirconia coatings

Zirconia coatings stabilized with different calcia content (12.8 mol%, 16 mol% and 30 mol%) were fabricated on titanium alloy substrates using atmospheric plasma spraying technology. The in-vitro bioactivity of coatings was evaluated by simulated body fluid (SBF) soaking test. The morphology and phase composition of the coatings were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), micro Raman spectroscopy, energy dispersive spectrometry (EDS) and infrared spectroscopy (IR). The results showed that the apatite was formed on the surface of the calcia stabilized zirconia coatings soaked in SBF for 28 days and the formation ability of apatite decreased with the increase in calcia content of the coating. The bioactivity of zirconia coatings was thought to be related to the Zr-OH formed on their surfaces during the phase transformation in the presence of water. Osteoblast-like MG63 cells were cultured on the surfaces of the coatings to evaluate their cytocompatibility. Results showed that MG63 cell grew and proliferated well on all coating surfaces, indicating that plasma sprayed calcia stabilized ZrO₂ coatings were cytocompatible.     

Effects of power level on characteristics of vacuum plasma sprayed hydroxyapatite coating

In this study, hydroxyapatite coatings were obtained with a vacuum plasma spray system at different power levels that were achieved by altering the plasma current and voltage. The effects of spray power level on coating characteristics were investigated. X-ray diffraction was used to identify the crystallinities of as-sprayed coatings, Electron Probe Microanalysis was employed to detect the surface chemical composition of as-sprayed coatings and Scanning Electron Microscopy revealed the microstructure. The results indicated that spray power greatly affected the crystallinity, chemical composition, and microstructure of as-sprayed hydroxyapatite coatings, which were linked to the melting state of hydroxyapatite powder. Presently at School of Materials Science and Engineering, Shanghai Jiaotong University, 1954 Huashan Road, Shanghai 200030, Republic of China.     

Experimental design of plasma spraying and laser treatment of hydroxyapatite coatings

Plasma spray process of hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂, HA) followed by laser treatment of obtained coatings were optimized by an advanced statistical planning of experiments. The full factorial design of 2⁴ experiments was used to find effects of four principal parameters, i.e. electric power, plasma forming gas composition, carrier gas flow rate and laser power density onto microstructure of hydroxyapatite (HA) coatings and powders and depth of laser melted zone. The SAS and Statgraphics commercial softwares have been applied to obtain the mathematical model of influence of process parameters onto experimental responses. The chosen responses were the fraction of HA crystal phase and two phases of its decomposition α-tricalcium phosphate (Ca₃(PO₄)₂, α-TCP), tetracalcium phosphate (Ca₄P₂O₉, TTCP) and, on the other hand, the depth of laser melted zone in the coating. The two most important factors influencing these responses are electric power supplied to torch, laser power density. Laser power density is very important for the depth of laser melted zone. The crystal phase content of powders and coatings was determined using X-ray diffraction (XRD) quantitative analysis. The morphologies of coatings surfaces, cross-sections were characterized using scanning electron microscope (SEM).     

医用镁合金等离子喷涂羟基磷灰石涂层研究

为了提高医用镁合金的表面耐蚀性和生物相容性,采用等离子喷涂技术在镁合金表面制备羟基磷灰石(HA)涂层.研究结果表明,镁合金表面所制备的HA涂层与基体结合牢固,界面无裂纹、气孔等缺陷.相组成为生物相容性较好的HA和少量的Ca3(PO4)2(TCP),显微组织具有层状特征,涂层表面存在一些有利于骨长人的孔隙.涂层的弹性模量约为19.825 GPa,接近骨的弹性模量,涂层表面硬度为300～350 HV.腐蚀试验和钙磷沉积试验结果表明HA涂层具有较好的耐蚀性和骨诱导性.     

Preparation and characterization of plasma sprayed Ni3Al-hBN composite coating

Ni₃Al-hBN composite powders were manufactured by spray drying technology, and then plasma sprayed to form the coatings. The influence of hBN addition amount on the flowability and apparent density of the composite powders, as well as the mechanical and tribological properties of the as-sprayed coatings was evaluated. The results indicate that the spherical powders with uniformly distributed compositions are successfully manufactured by spray drying technology. Both the flowability and apparent density of the Ni₃Al-hBN powders, as well as the bond strength and hardness of the composite coatings decrease with the increase of hBN content. Addition of hBN less than 10 wt.% reduces the friction coefficient and brittle fracture of the coatings, which is beneficial to improve the tribological properties of the Ni₃Al-hBN composite coatings. However, high hBN addition, damaging the bond in the coating, will deteriorate the wear resistance of the coating. The Ni₃Al-hBN composite coating containing 10%hBN shows the optimum properties combining strength and hardness with tribological properties.     

Effect of Ti-OH formation on bioactivity of vacuum plasma sprayed titanium coating after chemical treatment

The effect of Ti-OH groups on bioactivity of NaOH treated titanium coating was investigated in this paper. The NaOH-heat treatment was also applied to modify the titanium coating for comparison. The results show that the amount of Ti-OH groups was important to induce apatite formation on the treated titanium coating. When the NaOH treated titanium coating was exposed to SBF, it released Na⁺ ions from the sodium titanate layer on its surface into the SBF via exchanging with H₃O⁺ ions in the fluid and Ti-OH groups were rapidly formed on the surface. So the NaOH treated titanium coating has good bioactivity in simulated body fluid (SBF). The amount of Ti-OH groups on the titanium coating was reduced after heat treatment, so the bioactivity of NaOH-heat treated titanium coating was obviously affected.     

Preparation and bioactivity evaluation of bone-like hydroxyapatite nanopowder

Calcium phosphate ceramic such as hydroxyapatite (HA) is good candidate for bone substitutes due to their chemical and structural similarity to bone minerals. The bone mineral consists of tiny hydroxyapatite crystals in the nanoregime. Nanostructured hydroxyapatite is also expected to have better bioactivity than coarser crystals. This paper reports on the preparation and in vitro evaluation of bone-like hydroxyapatite nanopowder. The sol–gel prepared hydroxyapatite nanopowder was characterized for its phase purity, chemical homogeneity and bioactivity. Fourier transform infrared (FTIR) spectroscopy was used to identify the functional groups. X-ray diffraction (XRD) analysis was carried out to study the phase composition, crystallinity and the crystallite size of hydroxyapatite nanopowders that were sintered at different temperatures. The in vitro test was performed in a stimulated body fluid (SBF) medium. The changes of the pH of SBF medium were measured at pre-determined time intervals using a pH meter. The dissolution of calcium ions in SBF medium was determined by an atomic absorption spectrometer (AAS). FTIR result combined with the X-ray diffraction exhibited single phase of hydroxyapatite with carbonate peaks in the FTIR spectrum. The results indicate that increasing the sintering temperature increases the crystallinity and the crystallite size of hydroxyapatite nanopowders. Photomicrograph of transmission electron microscopy (TEM) showed that the obtained powder after sintering at 600 °C is composed of hydroxyapatite nanoparticles (20–30 nm). Dissolution rate of hydroxyapatite nanopowders was higher than conventional hydroxyapatite powders and closer to biological apatite due to its nanostructure dimensions. It was concluded that sol–gel prepared hydroxyapatite nanopowders had superior bioresorption and similar chemical and crystal structure to natural bone apatite.     

The effect of plasma spraying power on the structure and mechanical properties of hydroxyapatite deposited onto carbon/carbon composites

This paper deals with the effect of plasma spraying power on hydroxyapatite (HA) coatings on carbon/carbon composites (C/C composites). The microstructure and phase composition of the as-sprayed coatings have been examined by scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. The shear strength of the HA coatings–C/C substrates was detected on a RGD-5 tensile testing machine. Results indicate that the melting extent and the shear strength of the coatings were evidently improved with the increasing of spraying power. Moreover, the amount of decomposed phases is increased and the content of crystalline HA of coatings was slightly changed. Observation of fracture surfaces shows that carbon fiber bundles can bond well with HA coatings using 40 kW spraying power.     

Low conductivity plasma sprayed thermal barrier coating using hollow psz spheres: Correlation between thermophysical properties and microstructure

Life and thermal properties of plasma sprayed TBCs - widely used in gas turbine engines - are closely related to the microstructure of the ceramic top coating. Especially, the thermal behaviour of this coating is induced by the void shapes and networks which are in turn determined by both the spraying conditions and the feedstock material.A specific hollow yttria partially stabilised zirconia powder was produced in a one-step process by spray drying and an experimental statistical design study was conducted to investigate the influence of spraying variables (primary and secondary gas flow rates, arc current, spraying distance, spraying angle and traverse speed) on structure and properties of resulting plasma sprayed coatings. The coatings were characterized with respect to deposition efficiency, roughness, porosity and thermal conductivity. A reduction of 25% of the thermal conductivity was achieved by improving the spray and powder parameters. A quantitative characterization of the porous structure using image analysis of polished cross-sections was implemented. The parameters that have relevant influence on the coating porous structure were identified, and their relative importance was determined. An attempt was made to identify morphological criteria of the porous network (coarse/fine porosity ratio, cracks total length, cracks orientation) correlating with the thermal conductivity values.     

微束等离子喷涂制备羟基磷灰石涂层

采用微束等离子喷涂系统制备羟基磷灰石涂层,通过扫描电子显微分析(SEM)和X射线衍射分析(XRD)对涂层形貌、相组成和结晶度进行了研究.结果表明,随着喷涂电流和离子气流量的增加,羟基磷灰石粒子的熔化和撞击后的铺展更充分,在70～130 mm范围内随着喷涂距离的增加粒子熔化程度增加.适当的喷涂工艺条件下微束等离子喷涂制备羟基磷灰石涂层的结晶度可以相当或高于传统大气等离子喷涂制备的涂层,有利于涂层在体液环境中稳定性的提高.     

Laser-assisted laser ablation method for high-quality hydroxyapatite coating onto titanium substrate

Hydroxyapatite (HAp) coating on titanium (Ti) or Ti alloy implant materials is one of the important technologies for improving the bioactivity of their surface. We recently developed a new HAp coating method using two laser beams, laser-assisted laser ablation method (LALA method). In this method, two excimer lasers were used. One laser beam from KrF laser, the ablation laser, is used for ablation of a HAp target. The other beam from ArF laser, the assist laser, is used to irradiate a Ti substrate surface during formation of the HAp coating. The assist laser plays an important role in the formation of a crystalline HAp coating and improves the strength of adhesion to the Ti substrate.The coating quality varied with the timing of the assist laser irradiation. A coating deposited with a long assist laser delay contained a large amorphous component. High-quality coatings were obtained with delay time between 2 and 10 μs.Using the present method, we succeeded in fabricating thin (≤1 μm) HAp coatings with high crystallinity and high adhesion strength.     

等离子喷涂Al2O3与Cr2O3涂层性能的研究

对等离子喷涂Ａｌ２Ｏ３、Ｃｒ２Ｏ３涂层耐蚀性和耐磨性的试验研究表明,在３．５％ＮａＣｌ介质中,Ａｌ２Ｏ３涂层耐蚀性优于Ｃｒ２Ｏ３涂层;在滑动磨损条件下,Ｃｒ２Ｏ３涂层的耐磨性优于Ａｌ２Ｏ３涂层。     

新型铝青铜及其喷涂层中Ce元素的作用(英文)

采用一次共装熔炼、砂型铸造Al含量超过Cu-Al二元合金共析点的新型铝青铜合金Cu-14Al-4.5Fe,在45#中碳钢表面制备铝青铜等离子喷涂层。通过扫面电镜、X射线衍射分析、电子探针、透射电镜和显微硬度计分析Ce元素对新型铝青铜合金及喷涂层表面组织形貌和维氏硬度的影响。结果表明:添加0.6%Ce到铸态合金及喷涂层可以使细化的κ相均匀分布于基体,并提高材料硬度。等离子喷涂层快速凝固,保留铝青铜涂层中Fe元素的过饱和固溶体,避免生成(α+γ2)共析相。含Ce喷涂层中的堆垛层错是提高材料力学性能的因素。     

Characteristics of the nanostructures in thermal sprayed hydroxyapatite coatings and their influence on coating properties

There are generally two methods for depositing nanostructured coatings, retaining the nanostructures from starting feedstock and forming novel nanostructures through quenching. The present study utilized spray-dried nanostructured hydroxyapatite (nSD-HA) feedstock for coating/splat deposition. The nanostructures were characterized by transmission electron microscopy (TEM) and field emission scanning electron microscopy (FESEM). Results revealed that the rod-shaped nano-grains in the starting HA particles (< 500 nm in length and 40-70 nm in diameter) encountered two major experiences: enlargement due to unmelt state and reorganization due to melting-solidification. The molten part of the particles results in formation of spherical nanosized particles with grain sizes of 30-110 nm. TEM observation of the HA splats demonstrates consistent nanostructures. The unmelted part of individual nSD-HA particles showed significantly enlarged grains along radial direction (< 550 nm in length and < 400 nm in diameter). In addition, individual hexagonal grains were observed in the HVOF coating made from 30 ± 10 μm powder. The grains have the size of < 250 nm in height and < 50 nm in side length and are perpendicular to the coating/substrate interface. The nanostructures within the coatings contribute to an increased Young's modulus with up to 60.11 GPa, however, they showed detrimental effect on adhesion of the coatings. In vitro cell culturing revealed marked attachment and proliferation of the osteoblast cells on the nanostructured coatings. However, the results suggest that the nanostructures possess less importance than the phases (preferably high content of crystalline HA) on enhancing the cell proliferation.     

铝基表面等离子喷涂Al2O3-TiO2-Ta涂层的制备及防腐性能

采用等离子喷涂技术在铝基表面构建Al₂O₃-TiO₂涂层和Al₂O₃-TiO₂-Ta涂层。由于钽元素的引入,Al₂O₃-TiO₂-Ta涂层表面形貌更均匀、致密。同时钽金属具有极强的耐酸碱特性,因此,Al₂O₃-TiO₂-Ta涂层相对于Al₂O₃-TiO₂涂层具有更强的耐腐蚀性。Tafel曲线结果显示,Al₂O₃-TiO₂涂层使得基体的腐蚀电位仅正移了99.6 mV,Al₂O₃-TiO₂-Ta涂层使得铝基体腐蚀电位正移了208.9 mV。因此,由于耐蚀性极强的Ta金属的掺入,Al₂O₃-TiO₂涂层的防腐性得到了极大的增强,Al₂O₃-TiO₂-Ta涂层有效地防止铝合金腐蚀。     

Mechanical properties of suspension plasma sprayed hydroxyapatite coatings submitted to simulated body fluid

Home synthesized (HA) powder was formulated with water and alcohol to obtain a suspension used to plasma spray coatings onto titanium substrate. The deposition process was optimized and the resulting coatings were soaked in simulated body fluid (SBF) for the periods of 3, 7, 14, 28, and 60 days at controlled temperature of 37 °C. The microstructural research enabled to find in the as-sprayed deposits two characteristic zones: (i) dense zone corresponding to the lamellas, observed usually in thermally sprayed coatings; (ii) sintered zone containing fine hydroxyapatite grains corresponding to the fine solids from initial suspension. The sintered zone disappears after soaking in SBF and the pores get filled by the reprecipitated calcium phosphates. The adhesion of the soaked coatings to the substrate was characterized by the critical load in the scratch test and was about 10 to 12 N. The Young modules of the coatings were determined with help of depth-sensing indentation test by the use of the technique developed by Oliver and Pharr. The modules were not depending on the time of soaking and their mean values were 15.6 and 28.4 GPa, depending on the coating operational parameters. The scratch test enables to determine the hardness of the coatings, which remained fairly constant during the time of soaking in the range of 3 to 5 GPa. This hardness was compared to that the Martens microhardness which doubled with time of soaking to reach up to 1 GPa.     

微束等离子喷涂氧化锆增韧羟基磷灰石复合涂层

采用微束等离子喷涂方法,在Ti-6Al-4V基体上制备了羟基磷灰石 氧化锆(70HA-30ZrO2,质量分数,%)复合涂层.将复合涂层置于模拟体液中分别浸泡了3,7,14,28 d并观察表面磷灰石的生长情况以评价涂层生物活性.采用扫描电镜(SEM)和X射线衍射(XRD)分析技术对涂层浸泡前后的表面形貌和相组成进行了研究.结果表明,涂层中ZrO2主要以立方相存在;喷涂过程中羟基磷灰石(HA)出现了一定的分解,产生大量的α-Ca3(PO4)2杂质相.HA涂层熔化效果很好,但涂层中有未熔化的ZrO2颗粒.涂层在模拟体液中浸泡28 d后表面可以形成磷灰石,说明涂层具有很好的生物活性.