Advancing nanograined/ultrafine-grained structures for metal implant technology: Interplay between grooving of nano/ultrafine grains and cellular response

Nanograined/ultrafine-grained (NG/UFG) metals provide surfaces that are different from conventional coarse-grained polycrystalline metals because of the high fraction of grain boundaries. In the context of osseointegration of metal implants, grooving of nanograins/ultrafine grains by electrochemical grooving is a potential approach to increase the biomechanical interlocking and anchorage with consequent enhancement of cellular response. The primary objective of the research described here is to advance science and technology of metal implants by making a relative comparison of osteoblast response of grain boundary grooved and planar NG/UFG surfaces. The NG/UFG substrates were obtained using an ingenious concept of controlled phase reversion and the grain boundaries were electrochemically treated to induce grooving of large fraction of grain boundaries of NG/UFG substrate. Experiments on the effect of grooving of grain boundaries of NG/UFG metal indicated that cell attachment, proliferation, viability, morphology, and spread are favorably modulated and significantly different from planar (non-grooved) NG/UFG substrates. Furthermore, immunofluorescence studies demonstrated stronger vinculin signals associated with actin stress fibers in the outer regions of the cells and cellular extensions on electrochemically grooved NG/UFG substrate. These observations are indicative of accelerated response of cell–substrate interaction and activity. The differences in the cellular response of planar and grain boundary grooved NG/UFG surface are attributed to favorable surface topography that accelerates the cellular activity.     

Effect of substrate rotation on structure, hardness and adhesion of magnetron sputtered TiB2 coating on high speed steel

Titanium diboride (TiB₂) coatings have been deposited on stationary and rotating high speed steel substrates by magnetron sputtering of a TiB₂ target. The structure and hardness of the coatings and the coating–substrate adhesion have been investigated by X-ray diffraction, field emission scanning electron microscopy, nanoindentation and microscratch tests. The results show that substrate rotation has a significant effect on these structural and properties features. It was found that, with substrate rotation, the TiB₂ coating exhibits a columnar structure with random orientation and relatively low hardness and coating–substrate adhesion. On the other hand, without substrate rotation, the TiB₂ coating shows a strong (001) texture with dense, equiaxed grain structure. The hardness and coating–substrate adhesion of the coatings deposited on stationary substrates are much higher than those deposited on rotating substrates. The observed phenomena are discussed in terms of the energy of the sputtered flux, which varies with the substrate–target distance during deposition.     

Structure, mechanical properties and corrosion resistance of nanocomposite coatings deposited by PVD technology onto the X6CrNiMoTi17-12-2 and X40CrMoV5-1 steel substrates

This article presents the research results on the structure and mechanical properties of nanocomposite coatings deposited by PVD methods on the X6CrNiMoTi17-12-2 austenitic steel and X40CrMoV5-1 hot work tool steel substrates. The tests were carried out on TiAlSiN, CrAlSiN and AlTiCrN coatings. It was found that the structure of the PVD coatings consisted of fine crystallites, while their average size fitted within the range 11–25 nm, depending on the coating type. The coatings demonstrated columnar structure and dense cross-sectional morphology as well as good adhesion to the substrate, the latter not only being the effect of adhesion but also by the transition zone between the coating and the substrate, developed as a result of diffusion and high-energy ion action that caused mixing of the elements in the interface zone. The critical load L _C2 lies within the range 27–54 N, depending on the coating and substrate type. The coatings demonstrate a high hardness (~40 GPa) and corrosion resistance.     

The interplay between osteoblast functions and the degree of nanoscale roughness induced by grain boundary grooving of nanograined materials

From the perspective of osseointegration, nanograined/ultrafine-grained (NG/UFG) metals provide surfaces that are different from conventional coarse-grained (CG) polycrystalline metals because of the high fraction of grain boundaries. We describe here the interplay between the cellular response and grain boundary grooving as a potential approach to enhance osteoblast functions and facilitate the biomechanical interlocking and anchorage. This is accomplished by making a relative comparison of osteoblast response of NG/UFG grains electrochemically grooved to different depths to induce different degree of nanoscale roughness with planar NG/UFG surfaces, under identical biological environment. Electrochemically grooved NG/UFG structures indicated significant attachment and proliferation, and consequently enhanced modulation of cellular response that was significantly different from planar (non-grooved) NG/UFG substrate. Consistent with cell attachment and proliferation, immunofluorescence microscopy and computational analysis indicated stronger vinculin signals associated with actin stress fibers in the outer regions of the cells and cellular extensions on electrochemically-grooved NG/UFG substrates. These observations are indicative of accelerated response of cell-substrate interaction and activity. The behavior is attributed to average nanoscale roughness and high surface hydrophilicity of the nanoengineered surface.     

Bias effects on the tribological behavior of cathodic arc evaporated CrTiAlN coatings on AISI 304 stainless steel

In this study, CrTiAlN coatings were deposited on AISI 304 stainless steel by cathodic arc evaporation under a systematic variation of the substrate bias voltage. The coating morphology and properties including surface roughness, adhesion, hardness/elastic modulus (H/E) ratio, and friction behavior were analyzed to evaluate the impact of the substrate bias voltage on the coating microstructure and properties. The results suggest that for an optimized value of the substrate bias voltage, i.e. − 150 V, the CrTiAlN coatings showed increased Cr content and improved properties, such as higher adhesion strength, hardness, and elastic modulus in comparison to the coatings deposited by other substrate bias voltage. Moreover, the optimum coatings achieved a remarkable reduction in the steel friction coefficient from 0.65 to 0.45.     

Development of nano-hydroxyapatite coating by electrohydrodynamic atomization spraying

Electrohydrodynamic atomisation (EHDA) spraying of a hydroxyapatite (HA) suspension consisting of nano-particles (nHA) has been used to produce a HA coating comprising of nanostructured surface topography. In EHDA the suspension is jetted from a needle under an electric field. Obtaining the stable cone-jet mode of EHDA is critical to improve the quality and optimise the morphology of HA coatings, therefore a systematic investigation of the effects of several key processing parameters, such as suspension flow rate, applied voltage and distance between the needle and substrate, and needle size was carried out in this work. The HA coatings processed under different spraying parameters were compared and then scored according to uniformity and microstructural integrity. It was found that all of these parameters had a very significant influence on the morphology of nHA coating prepared. Under an optimised processing condition, where a needle orifice diameter of 300 μm, kept at a distance of 20 mm from the substrate, a flow rate of 20 μL/min, and the applied voltage kept within 4.3 kV and 5.2 kV, a uniform nHA coating was obtained. This is a crucial step forward in obtaining advanced nano-hydroxyapatite coatings of high quality for biomedical applications by using EHDA spraying.     

Microstructure and mechanical properties of CrAlN coatings deposited by modified ion beam enhanced magnetron sputtering on AISI H13 steel

CrAlN coatings were deposited on silicon and AISI H13 steel substrates using a modified ion beam enhanced magnetron sputtering system. At the modified ion beam bombardment, the effects of bias voltage and Al/(Cr + Al) ratio on microstructure and mechanical properties of the coatings were studied. The X-ray diffraction data showed that all CrAlN coatings were crystallized in the cubic NaCl B1 structure, showing the (111), (200), and (220) preferential orientation. It is noted that the (111) diffraction peak intensity decreased and the peaks broadened as the bias voltage increased at the same ratio of Al/Cr targets power, which is attributed to the variation in the grain size and microstrain. The microstructure observation of the coatings by field emission scanning electron microscopy cross-section morphology shows that the columnar grain became more compact and dense with increasing substrate bias voltage and Al concentration. At a substrate bias voltage of −120 V and a Al/(Cr + Al) ratio of 40%, the coating had the highest hardness (33.8 GPa) and excellent adhesion to the substrate.     

等离子熔覆铁基涂层的组织及冲蚀磨损研究

采用等离子熔覆法制备了铁基涂层.研究了涂层的组织结构,测试了涂层的显微硬度及耐冲蚀磨损性能,并利用扫描电镜对涂层显微组织、冲蚀表面形貌进行了分析.结果表明:涂层显微硬度是基体材料不锈钢1Cr18Ni9Ti的2倍,最高达到550,涂层冲蚀后质量损失是不锈钢对比试样1Cr18Ni9Ti和0Cr13Ni5Mo的1/2左右.     

Composite ceramic-metal coatings by means of combined electrophoretic deposition and galvanic methods

A method based on the combination of electrophoretic and galvanic deposition techniques has been developed to fabricate metal-ceramic composite coatings on metallic substrates. A ZrO₂-Ni composite coating with interpenetrating microstructure was produced on stainless steel plates. For electrophoretic deposition of the ceramic component, a non-aqueous suspension consisting of zirconia nanoparticles, ethanol and addition of 4-hydroxybenzoic acid was optimised by electrokinetic sonic amplitude (ESA) measurements. The zirconia deposits were partially sintered to create an open porous structure (porosity = 40–50%), which was subsequently filled with Ni by galvanic deposition. The bonding strength between the composite coating and the stainless steel substrate was improved by a final heat-treatement at 950°C for 3 h which promoted the diffusion of Ni into the steel substrate and the formation of a diffusion interlayer. The high adhesion strength of the composite coating to the stainless steel substrate after the diffusion bonding heat-treatment was confirmed by 3-point flexural strength tests. The coating exhibited a homogeneous interpenetrating microstructure with hardness values >6 GPa.     

Structure and mechanical properties of PVD coatings deposited onto the X40CrMoV5-1 hot work tool steel substrate

This work presents the research results on the structure and mechanical properties of coatings deposited by PVD methods on the X40CrMoV5-1 hot work tool steel substrates. The tests were carried out on CrAlSiN, CrAlSiN+DLC, CrN and WC/a-C:H coatings. It was found that tested coatings have nanostructural character with fine crystallites, while their average size fitted within the range 3-13 nm, depending on the coating type. The coatings demonstrated a dense cross-sectional morphology as well as good adhesion to the substrate, the latter not only being the effect of interatomic and intermolecular interactions, but also by the transition zone between the coating and the substrate, developed as a result of diffusion that caused mixing of the elements in the interface zone and the compression stresses values. The critical load L_C2 lies within the range 45-55 N, depending on the coating type. The coatings demonstrate a high hardness (4000 HV).     

Effect of Cr interlayer on the adhesion and corrosion enhancement of nanocomposite TiN-based coatings deposited on stainless steel 410

Applications of hard protective nanocomposite coatings are frequently limited by insufficient adhesion related to high stress. In the present work, we study the effect of an intermediate Cr layer on top of the stainless steel 410 (SS410) substrate on the performance of the nanocomposite (nc) TiN-based coatings prepared by plasma enhanced chemical vapor deposition. The Cr layer was found to enhance the corrosion resistance of the SS410 substrate by a factor of 280 in terms of corrosion current, and to increase adhesion of the TiN coating by a factor of 4. We show that for the nc-TiN/a-SiN_x and nc-TiCN/a-SiCN coatings, the substantial improvement of the corrosion resistance can be attributed to the combination of the inertness of the Cr layer, and of the densely packed homogeneous nc structure of the nc coatings containing Si and/or C in comparison to columnar crystalline TiN coatings.     

一种易消除热水器不锈钢加热管结垢的镀金工艺

热水器不锈钢加热管易结垢,在硬水地区应用受到了限制.在不锈钢表面镀金可以解决结垢问题.由于不锈钢表面有一层致密的钝化膜,影响了镀金层与基体之间的结合力.采用特殊的前处理和预镀层作中间过渡层,能攻克结合力这一难关.     

Compositional and structural control in bone regenerative coatings

The development of a low-temperature method of producing bioactive coatings for medical implants has been shown to bypass the problems associated with high temperature processing routes, in particular the appearance of amorphous phases and non-stoichiometric hydroxyapatite (HA), and delamination of the coating from the substrate. An electric field/aqueous solution technique for producing adherent, crack-free calcium phosphate coatings on titanium and stainless steel substrates is described. The characteristics of the coating are a function of electrode spacing, supersaturation, temperature and current and voltage conditions. Scanning electron microscopy (SEM) characterized the surface morphology of the coatings, which were shown to be HA. The possibility of producing a coating of carbonate-substituted HA having the same chemical composition as bone apatite, and forming at physiological temperatures, has also been demonstrated. The size of the microstructure decreased and the morphology changed as the carbonate ion concentration in the calcium and phosphate ion solution increased. © 1999 Kluwer Academic Publishers     

磁/电场约束下钛合金表面羟基磷灰石/TiO_2复合生物涂层的制备

用恒电位阳极氧化法分别以硫酸和磷酸为电解液,在钛合金基体上制备出具有不同孔径大小和不同晶型的TiO2涂层. 外加磁场条件下,在TiO2涂层上电沉积形成纳米羟基磷灰石涂层.当垂直电场方向施加1T磁场时,在洛伦兹力影响下生长成羟基磷灰石生长成长度大约为200nm,直径大约为50nm的棒状晶粒;在磁场平行于电场的条件下,生成直径为50-70nm的粒状晶粒.纳米羟基磷灰石与多孔TiO2涂层之间几何形貌的匹配程度,影响复合涂层与钛合金基体的结合强度.当TiO2涂层的孔径大约为100 nm时,棒状羟基磷灰石晶粒与钛合金基体间的锁合更牢固,结合力更强.     

纳米TiO2/Sb2O5涂层的光生阴极保护研究

采用溶胶凝胶法在304不锈钢表面制备了纳米TiO₂/Sb₂O₅叠层涂层. 用扫描电子显微镜（SEM）、X射线衍射（XRD）、X射线光电子能谱(XPS)对涂层表面形貌、晶体结构以及组成进行表征. 采用电化学方法研究涂层的光电化学性能与光生阴极保护特性. 结果表明,所制备的纳米TiO₂/Sb₂O₅叠层涂层表面连续、均匀、致密;XRD分析表明纳米TiO₂为锐钛矿型;XPS分析表明纳米涂层表面与内层均由Ti、Sb、O、C四种元素组成;稳定电位与极化曲线测试表明,在3%NaCl溶液中,纳米TiO₂/Sb₂O₅叠层涂层的光电化学性能低于纯纳米TiO₂涂层,但纳米TiO₂/Sb₂O₅涂层经紫外光照1h,停止紫外光照后的延时阴极保护作用可达4h. 通过研究分析,提出了一种新的纳米叠层涂层光生阴极保护作用机理.     

Mesoporous titania films with adjustable pore size coated on stainless steel substrates

Mesoporous layers of titania were prepared on stainless steel substrates of defined roughness by dip coating. Ordered arrays of micelles formed from amphiphilic block copolymers served as pore templates during film drying. Coating of the precursors solution on freshly grinded steel resulted in extensively fractured films with severely distorted templated porosity. In contrast, films produced on precalcined steel showed good integrity, high substrate coverage and narrow pore size distribution with pores interconnected and ordered in a short range. This difference in film quality and morphology was ascribed to the reaction between template polymers and metal ions leached from the steel of grinded substrate surfaces. Films were ca. 700 nm thick and composed of nanocrystalline titania. The pore size of titania coatings was varied between 5 and 16 nm employing polymer templates of different structure and molecular weight.     

Untersuchung der Einflüsse von Substratrauheit und Spritzpartikelgröße auf die Haftung thermisch gespritzter Schichten

About the influence of substrate roughness and spray particle size on the adhesion of thermal spray coatings The influence of substrate roughness and spray particle size on the adhesion of thermal spray coatings was researched systematically. In addition to established spray materials (Cr₂O₃, WCCo, NiCr) and spraying processes (atmospheric plasma spraying (APS), high velocity flame spraying (HVOF)) different substrate materials (steel, stainless steel, aluminum) were included in the research work as well.     

纳米Al2O3和TiO2改性有机硅涂层对304不锈钢高温氧化行为的影响

本文以纳米Al₂O₃和TiO₂为主要填料,采用物理混合方法制备了两种纳米改性有机硅涂料,将涂料喷涂于马口铁和304不锈钢表面并室温干燥,获得了两种涂层样品。测试了两种涂层的常规机械性能,研究了600℃空气中涂层对304不锈钢抗氧化性能的影响。结果表明：两种涂层均具有良好的附着力、柔韧性和耐冲击性能。两种涂层均能有效减缓304不锈钢在600℃下的氧化;当纳米Al₂O₃和TiO₂含量比例为4:1时,纳米改性有机硅涂层对304不锈钢的防护效果最佳。     

Fatigue Characteristics of Aircraft Materials with Ionic-Plasma Coatings

We study the effect of mono- and multilayer ionic-plasma titanium-nitride-titanium coatings on the fatigue strength of aircraft materials: 30KhGSA structural steel, 07Kh16N6 stainless steel, and VT22 high-strength titanium alloy. We show that the effect of ionic-plasma coatings on the fatigue limit depends on both the kind of material of the substrate (base) and the technology, i.e., the structure of the coating itself. The positive influence on the fatigue of the base of multilayer coatings as compared with monolayer is connected with the stresses arising in the course of spraying.     

爆炸喷涂Cr3C2-25NiCr涂层的微观结构及性能

为了使Cr_3C_2-NiCr涂层能够应用于水力机械表面,采用爆炸喷涂技术在0Cr13Ni4Mo不锈钢基材表面制备了Cr_3C_2-25NiCr涂层,通过扫描电镜(SEM)、X射线衍射仪(XRD)、金相分析仪、拉伸试验机、显微硬度计、摩擦磨损试验机、电化学工作站等手段研究分析了该涂层的微观形貌、孔隙率、结合强度、显微硬度、耐磨性能、耐蚀性能等。结果表明:爆炸喷涂Cr_3C_2-25NiCr涂层具有高致密结构,平均孔隙率仅为0. 76%,并且其结合强度高达82 MPa;涂层平均显微硬度为1 026 HV2 N,远高于基体;且在相同试验条件下,涂层的磨损量仅为基体的1/72;同时涂层还具有远高于基体的耐腐蚀性能。