Nickel-titanium (NiTi) alloys are widely used as orthopedic implants because of their excellent shape memory effect; however, their inadequate corrosion resistance, nickel ion release, and limited bioactivity still hinder further clinical application. In this study, micro-arc oxidation (MAO) was employed to construct oxide coatings on NiTi alloy substrates, taking the concentration of calcium acetate in the electrolyte (0-3 g/L) as the key process variable. The effects of calcium acetate concentration on the coating microstructure, mechanical properties, corrosion resistance, and in vitro mineralization behavior were systematically investigated. The results demonstrate that changes in calcium acetate concentration markedly affect the discharge characteristics and film-forming quality, among which the coating prepared at 2 g/L (denoted as X2) exhibits the most favorable overall performance. Specifically, compared with the calcium-acetate-free control, the coating thickness of the X2 sample increases from 18.36 mu m to 22.44 mu m (a 22.2% increase), while the average pore size and surface porosity decrease by 29.8% and 26.6%, respectively, indicating a significantly improved coating compactness. This structural densification translates into superior mechanical performance and protective capability: the microhardness of the X2 sample reaches 370.2 HV (approximately 6.9% higher than that of the control), and the interfacial bonding strength increases to 20.34 N (an improvement of about 33.2%). Meanwhile, the corrosion resistance is substantially enhanced, as evidenced by a 53.8% reduction in corrosion current density to 5.96 x 10-8 A/cm2 and an approximately 3.5-fold increase in polarization resistance. After immersion in Hanks' solution for 14 days, the cumulative release of Ni ions from X2 is reduced by 44.4% compared with the control, with a concentration of only 20 mu g/L. In addition, Ca incorporation promotes the in situ formation of a beta-Ca3(PO4)2 phase within the coating; in particular, the 2 g/L group can induce the formation of a continuous reticulated hydroxyapatite (HA) layer during in vitro immersion, exhibiting the best mineralization capability among all samples. These findings indicate that rational regulation of calcium acetate concentration enables the synergistic enhancement of mechanical stability, physical barrier function, and bioactivity of MAO coatings, thereby providing optimized process parameters for the surface modification of NiTi implants.

This study investigated the growth mechanism of microarc oxidation ceramic coatings on AZ91D magnesium alloy by sequentially treating it in silicate and zirconate electrolyte systems. The distribution patterns of Si and Zr elements were examined to understand the growth mechanism. The results showed that the distribution of Si and Zr elements in the SZ ceramic coatings changed with increasing termination voltage of microarc oxidation. The growth mechanism of microarc oxidation ceramic coatings on magnesium alloys involved the reaction between Si and Zr elements from the electrolyte and Mg elements from the substrate to form molten oxides under the high-temperature and high-pressure conditions of microarc oxidation discharge. At lower termination voltages, some of the molten oxides remained near the discharge channels or the film/substrate interface, resulting in inward growth of the ceramic coating. As the termination voltage increased, some of the molten oxides were ejected outward through the discharge channels, facilitating outward growth of the ceramic coating. The inclusion of silicon elements compared to zirconium elements will significantly increase the concentration of oxygen vacancies in the ceramic membrane, enhancing the electrical conductivity of the ceramic membrane while reducing its corrosion resistance.

In this paper, ZnO-containing coatings were prepared on the surface of AZ31B magnesium alloy by a simple one-step micro-arc oxidation method using zinc gluconate as the zinc source. The microstructure, elemental distribution, phase composition and chemical composition of the coatings were analyzed by scanning electron microscopy (SEM), energy spectrometry (EDS), X-ray diffractometry (XRD) and X-ray photoelectron spectroscopy (XPS), potentiodynamic polarization tests and electrochemical impedance spectroscopy were carried out in simulated body fluids to study the corrosion behavior of the coatings. The results show that introducing Zn2+ into the coatings reduces the number of pores and changes the microstructure of the coatings, resulting in improving corrosion resistance. In addition, the corrosion current density of the coatings prepared by adding 6 g/L of zinc gluconate was approximately two orders of magnitude lower than that of the coatings prepared without adding zinc gluconate. ZnO-containing coating is successfully synthesized in situ on the surface of AZ31B magnesium alloy using zinc gluconate as the zinc source and micro-arc oxidation method. The formation of ZnO not only increases the thickness of the coating but also reduces its porosity, which blocks corrosive ions from entering the coating and further improves the corrosion resistance of the coating.image

In the current study, a HA/TiO2 composite coating is effectively fabricated on a Ti-13Nb-13Zr alloy using the plasma electrolytic oxidation (PEO) technique. Electrolytes with different Ca/P contents are selected to study the evolution of phase composition and microstructure of PEO coating. The relationship between Ca/P contents and the wear resistance and corrosion resistance of the coatings are evaluated. The Ca/P-30 g coating exhibits the best performance with Ca/P≈1.66. The average thickness and roughness of the coating manufactured by this system are about 159 µm and 1.591 µm. The HA/TiO2 coatings akin to honeycomb have analogous pore size and uniform distribution, and the phase composition is mainly anatase. Compared with the substrate, the corrosion current density decreases by 19.65

This study investigates the impact of static tensile loads on magnesium (Mg) alloys with and without ceramic coatings in simulated body fluids (SBF) using a combination of numerical simulation and experimental methods. The surface of an AZ31B Mg alloy was treated with a ceramic coating via micro-arc oxidation (MAO). Subsequently, bare Mg-alloy and MAO ceramic-coated specimens were subjected to static tensile stress testing using a tensiometer. After immersion for 12 h in SBF, the surface morphology and electrochemical corrosion of the stressed specimens were analysed. Notably, under the same tensile stress, the Mg alloy in the SBF exhibited more severe corrosion damage than the ceramic-coated specimen. Furthermore, there was a direct correlation between the corrosion rate of the ceramic coating and the magnitude of the applied tensile stress. Overall, the MAO ceramic coating exhibited superior corrosion resistance compared to the bare Mg alloy, even after undergoing static tensile stresses. The study demonstrates that MAO ceramic coatings can enhance the corrosion resistance of biodegradable Mg implants by protecting them from the combined effects of bodily stresses and fluids.

Biomedical materials have excellent mechanical properties, stability and biocompatibility, and are widely used in dentistry, orthopedics, medical devices and other fields. However, various infection problems obviously occur in the current use of biomedical materials, which are severely harmful for human health and life safety. Micro-arc oxidation technology can construct antibacterial film on the surface of biomedical metal materials such as titanium and magnesium, which is one of the surface modification technologies to effectively solve the infection problem. In this paper, the research status and mechanism of particle incorporation into micro-arc oxide film were summarized. On this basis, the latest development of antibacterial surface constructed by the incorporation of Ag, Ag2O, Cu, CuO, ZnO and other metal particles into micro-arc oxidation film in recent years was reviewed. The effects of particle incorporation on corrosion resistance and wear resistance of micro-arc oxidation film were described. Meanwhile, the application and development of micro-arc oxidation antibacterial film with particle incorporation were prospected.

HA/TiO2 composite coatings were prepared on Ti-13Nb- 13Zr alloy by micro-arc oxidation. By changing the ratio of Ca/P in the electrolyte, the phase composition and microstructure changes, as well as the effects of different Ca/P ratios on the wear resistance, corrosion resistance and in vitro biological activity of micro-arc oxidation coating were studied. The results show that the coating roughness and porosity increase with the increase of electrolyte Ca/P ratio. The coating phase is mainly composed of anatase and rutile, and the rutile phase content increases with the increase of Ca/P ratio of electrolyte. The coating thickness of CA35 prepared with 35 g/L calcium acetate electrolyte is 80.59 mu m and the surface Ca/ P ratio is 1.98, showing the best wear and corrosion resistance. Compared with the substrate, the average friction coefficient of CA35 coating is about 0.19, which decreases by 43%. The corrosion resistance of the coating was tested by Pt reference electrode and 0.9wt% NaCl test solution. The corrosion current density of CA35 coating is 4.94 mu A/cm2, and the corrosion potential is - 221.73 mV. The CA35 coating produces the fastest mineralized products in Kokubo solution. It is proved that increasing the Ca/P ratio of electrolyte can effectively promote the formation of HA and improve the wear resistance. In addition, the influence mechanism of Ca/P ratio on coating properties was discussed.

As light alloys have inherent friction and corrosion problems, an appropriate ceramic coating is often needed to resolve these problems in tribological and corrosive environments. In this work, the optimized pore structure of MoS2/Al2O3 self-lubricating ceramic coating was designed by in-situ synthesis of MoS2 combined with plasma electrolytic oxidation (PEO) and regulating the duty cycle. The evolution of pore structure was investigated by X-ray computed tomography. It is found that the power supply delivers more energy in each cycle as the duty cycle increases, resulting in larger discharge channels and ejecting more molten material. The change of the pore shape from connected to isolated and the decreasing of porosity through decreasing the duty cycle, which was caused by the narrowing of discharge channel and reduction of molten oxide ejection are acquired. The isolated pores structure is conducive to superior corrosion resistance, which can blocks the penetration of corrosive medium. Additionally, MoS2/Al2O3 coating exhibit a 75% reduction in coefficient of friction over traditional PEO coatings. This coating preparation approach is expected to provide a newly strategy to optimize the pore structure of the self-lubricating ceramic coating by regulating electrical parameters.

The design and preparation of antifriction coating on the surface of aluminum alloy is one of the key technologies to improve the friction properties of aluminum alloy components. For the current problem of easy wear of aluminum alloy structural parts, nano-MoS2 was synthesized in situ on the surface of 6063 aluminum alloy by one-step micro-arc oxidation method to prepare MoS2/Al2O3 composite ceramic coating with antifriction effect. The effect of sulfur concentration on the composition, morphology and friction properties of the coating was discussed. The friction reducing mechanism of the coating was analyzed. The results show that the self-lubricating composite ceramic coating containing MoS2 is successfully prepared on the surface of 6063 aluminum alloy by micro-arc oxidation. The friction coefficient of the coating decreases first and then increases with the increase of the sulfur salt concentration. When the sulfur concentration in the electrolyte is 15 g/L, the friction coefficient of the coating is 0.15, which is reduced by 76% compared with the conventional micro-arc oxidation coating. The MoS2 in the coating is distributed on the surface and inside of the coating. Under the action of contact and extrusion with the friction pair, a uniformly distributed MoS2 lubricating film is formed, showing good antifriction performance.

The pores formed by molten material ejection from the discharge channel and rapidly solidification during plasma electrolytic oxidation (PEO) act as passageways for corrosive particles. The overall porosity and pore shape, the inevitable features of ceramic coatings, are main factors that determines the corrosion resistance. In this work, we propose a novel approach that utilizes the advantages of graphene oxide (GO) to alter the pore shape and plasma discharge to effectively reduce the overall porosity. Simultaneously, the overall porosity and pore shape were deconstructed by X-ray microscopy. We found that the GO additive not only formed covalent bonds with the metal oxide, limiting the amount and distribution of molten oxide, but also changed the discharge form of the plasma reaction. The obtained coating exhibited an ultra-low surface porosity (1.10%), ultra-low overall porosity (2.11 vol%), and high aspect ratio (0.7-0.8), which are lowered for 94.8%, 90.9%, and increased for 66.9% than that of the traditional coating, respectively. The ultra-low porosity eliminates channels inside the coating and reduces the number of corrosive ions invading the substrate, resulting in superior corrosion resistance.

Inconel 718高温合金具有优异的高温力学性能以及良好的耐热腐蚀性能,被广泛应用于航空航天、燃气轮机、核电及化石等领域.近年来,凭借自由设计和近净成型等特点,激光增材制造技术在Inconel 718等复杂精密零部件的制造领域具有不可替代的作用.激光增材制造技术是一个快速加热与冷却的过程,得到的合金枝晶/胞晶和析出相的尺寸比传统制备工艺更加细小,且表现出跨尺度的多级分层结构,呈现出独特的力学性能相关性.随着人们对激光增材制造Inconel 718高温合金的广泛研究,目前Inconel 718合金的力学性能可以达到甚至超过锻件的水平.然而,激光增材制造的Inconel 718合金内部往往存在显著的凝固织构和较大的残余拉应力,使得合金的力学性能呈各向异性且疲劳持久性能较差,在一定程度上限制了激光增材制造技术的推广应用.因此,需从跨尺度组织结构角度入手,通过工艺参数调控和后处理技术,实现ln-conel 718合金的高质量增材制造.本文归纳总结了激光选区熔化和激光立体成形技术在制备Inconel 718合金方面的研究进展,围绕"工艺参数-显微组织结构-力学性能"的本构关系,重点阐述了不同增材制造工艺及加工参数对Inconel 718中枝晶生长、析出相、晶粒结构以及残余应力等显微组织结构和力学性能的影响,并讨论了激光增材制造Inconel 718高温合金面临的难题及其解决措施.

The characteristic plasma electrolytic oxidation (PEO) coating prepared by adjusting parameters has been widely used, while the design of coating close to human Ca/P=1.67 still needs further exploration. In this contribution, the hydroxyapatite (HA)/TiO 2 composite coating was successfully prepared on Ti-13Nb-13Zr alloy by controlling with different Ca/P (Ca/P-20g, Ca/P-25g and Ca/P-30g) in electrolyte solutions to optimize the friction and bio-corrosion property of the titanium alloy for biomedical applications. The results show that the Ca/P-30g coating shown the best comprehensive performance and Ca/P≈1.66. The morphology of the coating is typical honeycomb, and a large number of nucleation sites are generated at the edge of the microporous to preferentially form HA. Compared with the matrix, i corr decreased by 22.76%, E corr increased by 0.568V, and the average friction coefficient decreased by 77% to 0.19. More importantly, it is concluded that the formation of HA is the process of crystal growth and non-uniform nuclear, where nucleation is the gradual evolution of the HA phase from CaTiO 3 phase formed in electrolyte solution near the anode. The high concentration group reaction not only improved the HA formation rate, but also generated stable spherical structure. It has been proved that the high friction and bio-corrosion resistance of the coatings are associated with the insulation and physical shielding caused by the large accumulation of HA. Our research provides a new strategy to fabricate corrosion coating for titanium alloys, and is expected to open new avenues for designing titanium alloy components for biomedical conditions.

Intrinsic friction and corrosion issues of light alloys impede their application in tribological and corrosive environments, thus a proper ceramic coating is normally required to overcome these issues for practical engineering deployment. Here, we developed a new approach to fabricate controllable and self-lubricating nanocomposite coating by combining in-situ synthesis of MoS2 and plasma electrolytic oxidation (PEO) process. It is found that the coefficient of friction of this new coating is only about a quarter of the coatings obtained by traditional PEO process due to the self-lubricating characteristic of gradient MoS2. More importantly, this ceramic coating exhibits excellent interfacial strengthen through edge-pinning by noncoherent, which endows excellent tribological and adhesive properties. This facile technique provides a new strategy to fabricate self-lubricating ceramic coating for light alloys, and is believed to have great potential applications in wide engineering sectors and open new avenues for designing novel alloy systems for extreme conditions.

采用扫描电镜和电子背散射衍射等研究了激光重熔Inconel 718合金微观组织和显微硬度在不同热处理工艺与超声冲击强化(UIT)作用下的演化规律.结果表明:原始态重熔区(FZ)组织主要由γ枝晶干和Laves相组成;经固溶处理(SHT)后,Laves相大量溶解,元素偏析减弱,显微硬度降低;固溶+双时效处理(SDA)后,γ′和γ″强化相大量析出,显微硬度显著提升;而直接进行双时效处理(DA)时,由于时效温度不足以溶解Laves相,FZ形貌与原始态非常类似,但强化相γ′和γ″充分析出,使FZ显微硬度明显升高.之后,对原始态(AR)试样及热处理态试样表面进行UIT处理后,试样表层均出现严重塑性变形和压应力,位错密度显著增加,并产生了不同深度的硬化层.相比于AR和SHT样品,UIT处理对SDA和DA样品产生的强化效果减弱,这与γ′和γ″强化相的位错强烈交互作用有关.

The cracks will impact the toughness and wear properties in the coating formation process of micro-arc oxidation melting and cooling. This research used the ZrO2 to synthesize a ZrO2/MgO coating with self-repairing cracks, and investigated the effect of in-situ ZrO2 on the wear properties of the coating. It is found that the in-situ synthesized ZrO2 by micro-arc oxidation undergoes phase change in the high-temperature discharge channel to generate volume expansion, which causes microcracks in the zirconia interface and hinders the crack propagation at the crack tip, so as to realize the self-repairing coating crack. The ZrO2 content in the coating is controlled by controlling the content of zirconium source. When the in-situ ZrO2 content in the coating is 32%, the cracks of the ZrO2/MgO coating are finely dispersed, and the crack density is 63.4% lower than that of the traditional coating, the friction coefficient is reduced by 53.4%, the amount of wear is descended by 66.7%. It is believed that the in-situ synthesized ZrO2 realizes self-repairing of cracks during the coating preparation process, which can effectively reduce the friction coefficient and wear amount, and improve the surface wear properties of the ZrO2/MgO coating.

为了提高镁合金的表观装饰作用和耐腐蚀性能,在微弧氧化Zr盐溶液体系中通过加入不同的着色盐在AZ91D镁合金基体上制得微弧氧化黑色膜层.利用3nh色差仪、扫描电子显微镜(SEM)和X射线衍射仪(XRD)测定膜层的黑色程度、构成成分和结构形貌,利用电化学法对膜层的耐腐蚀性能进行研究.结果 表明:加入Fe盐后膜层的黑色程度最大,加入Cu-Fe盐的膜层黑色程度次之,加入Cu盐的黑色程度最小.不添加着色盐的膜层主要组成物质为MgO、Zr02和Zr(Si04);加入着色盐后膜层中增加了着色盐金属离子反应后形成的氧化物,该氧化物为膜层中的显色物质.着色盐的加入提高了膜层的自腐蚀电位,降低了自腐蚀电流密度,Zr盐溶液中加入着色盐后镁合金的耐腐蚀性能明显提高,其中加入Cu-Fe盐时黑色膜层的耐腐蚀性能最好.

Self-sealing pore is one of the important technologies to control the pore structure, improve the antifriction and corrosion resistance of micro-arc oxidation coating. In order to solve the problem that the poorer stability of physical sealing pore and expansion of sealing agent impacted the structure of the coating, this paper used the conductivity properties of graphene oxide to prepare GO/TiO2 self-sealing pore ceramic coatings with antifriction effect. The effect of graphene oxide concentration on pore structure and antifriction of ceramic coating was discussed. It is found that the electrochemical balance process of electrolyte is changed by adding graphene oxide, which contributes to controlling the pore structure of the GO/TiO2 coating. When graphene oxide concentration is 5 g/L, the porosity, pore size and average friction coefficient of the self-sealing pore ceramic coating (G5) are 3.6%, 2.5 mu m and 0.1, which decrease by 83.2%,78.4% and 87.5%, respectively, compared with the G0 coating. It is believed that the pore structure of micro-arc oxidation coating can be controlled through controlling graphene oxide concentration, which can affect the colloidal deposition and energy release. This provides a new idea for the preparation of antifriction self-sealing pore coating.

综合国内外钛合金微弧氧化生物膜制备的方法,主要阐述了电参数与电解液对钛合金微弧氧化生物膜结构以及性能的影响机制.脉冲电源下,电流对膜层的制备具有良好的调整作用,且得到的膜层厚度显著增大.膜层厚度随氧化电压的升高而增加时,膜层表面颜色与腐蚀电位也发生变化.增加脉宽,降低频率时,单脉冲放电能量随之增加,微弧氧化成膜速率显著加快.不同体系电解液制备的膜层表面粗糙度、微孔结构等存在差异.在电解液中引入银、锌、铜离子能有效改善植入物涂层表面细菌黏附引起的异物炎症问题,增强其抗菌作用.基于目前钛合金微弧氧化的研究进展,展望了该研究方向,对钛合金植入物在临床医学应用发展中具有积极的促进作用.

A SiC/TiN particle reinforced Ni-Mo nanocomposite coating was prepared on the surface of 6061 aluminum alloy by pulse electrodeposition technique. By introducing SiC and TiN nanoparticles into the coating and changing the average current density and duty cycle of electrodeposition, the microstructure of the composite coating was adjusted, and the film formation process and grain refinement mechanism of the nanoparticle-enhanced coating were analyzed. The relationship between the microstructure of composite coating and the corrosion resistance and wear resistance was studied. The results show that the addition of double nanoparticles results in a shift of the coating structure from conical to cellular, and the grain size is reduced from 29.86 nm to 22.79 nm. The coatings prepared at current density of 8 A.dm(-2) are the most homogeneous and dense with the highest SiC/TiN particle complexes of 1.3wt% and 3.1wt%, respectively. The coating exhibits (111) preferred orientation and' typical fcc structure, with nanoparticles uniformly dispersing in the Ni-Mo matrix. The corrosion behavior of the coatings was investigated by Tafel polarization and immersion test. Compared with the corrosion current density of Ni-Mo composite coating of 7.08 mu A/cm(2), the corrosion current densities of Ni-Mo/SiC-TiN nanocomposite coatings prepared at current densities of 4, 8, 12 A.dm(-2) and duty cycle of 40% and 60% are 4.68, 4.12, 5.75, 4.37 and 5.53 mu A/cm(2), which are reduced by 34%, 42%, 19%, 38% and 21%, respectively. In particular, the nanocomposite coatings prepared at the current density of 8 A.dm(-2) and the duty cycle of 20% exhibits the best corrosion resistance. Compared with Ni-Mo coating, the introduction of SiC/TiN particles significantly improves the wear resistance of the coating. In addition, the mechanism of pulsed co-deposition was discussed.