Temperaturberechnung an den Artikulationsflächen beim künstlichen Hüftgelenk

In hip replacement the wear rate is reduced when using femoral heads and acetabular cups made of alumina ceramics. It is proposed to use Y‐TZP zirconia ceramics. The process on the articulating surfaces head/cup are not totally understood, especially the temperature rise due to frictional heating. Alumina is a stable material, no problems are expected. When using Y‐TZP its phase transition may be triggered due to frictional heating and the leaching out of yttria. The model proposed by Blok, Jaeger and Kuhlmann‐Wilsdorf was used to calculate the flash temperature under in vivo conditions. The surface temperature of the wear couple Y‐TZP/Y‐TZP was higher than the one for alumina/alumina.     

Berechnung der Blitztemperaturen der Mikrokontakte in künstlichen Hüftgelenken unter Benutzung des Kontaktmodells von Greenwood – Williamson

Calculation of Flash Temperatures of Micro‐Contacts in Artificial Hip Joints by Using the Contact Model of Greenwood – Williamson In hip replacement the wear rate is reduced when using femoral heads and acetabular cups made of alumina ceramics. The use of zirconia ceramics (Y‐TZP) is discussed controversy. The process on the articulating surfaces head / cup are not totally understood, especially the temperature rise due to frictional heating. Alumina is a stable material, no problems are expected. When using Y‐TZP, friction temperature can be higher then the coagulate temperature of synovia or the phase transition is induced. The model proposed by Kuhlmann – Wilsdorf was used to calculate the flash temperature under in vivo conditions of micro‐contacts at the different articulating surfaces. The real contact conditions were calculated with the analytical contact model of Greenwood – Williamson. The surface temperature of the wear couple Y‐TZP/Y‐TZP was higher than the one for alumina/alumina.     

Three-body abrasive wear behaviour of orthopaedic implant bearing surfaces from titanium debris

The abrasive wear behaviour of several orthopaedic bearing materials was characterized for fully conformal, reciprocating sliding contact against ultra-high molecular weight polyethylene (UHMWPE). The bearing surfaces investigated were nitrogen ion implanted Ti–6Al–4V, TiN coated Ti–6Al–4V, Ti–6Al–4V, F-799 Co–Cr–Mo, yttria-stabilized zirconia and a Zr–2.5Nb alloy with a zirconia ceramic surface. The third-body debris was introduced as either Ti–6Al–4V particles or oxidized titanium powder (black debris). The wear tests were performed in deionized water with the third-body debris entrapped between the UHMWPE and the hard bearing surface. Surface profilometry measurements, scanning electron microscopy (SEM) and optical microscopy showed the severity of damage to the hard bearing surfaces to increase with decreasing hardness. The abrasion damage to the UHMWPE increased as the roughness of the opposing, hard bearing surface increased. Surface profilometry and energy dispersive spectroscopy (EDS) also showed oxidized titanium (black debris) to form an adherent transfer layer on all of the hard bearing surfaces. Nitrogen ion implantation of Ti–6Al–4V was ineffective in reducing wear of both the Ti–6Al–4V substrate and the UHMWPE. Solid yttria-stabilized zirconia and zirconia-coated Zr–2.5Nb showed no evidence of abrasion damage and produced the least amount of UHMWPE wear. These results are attributed to the high hardness and excellent wear resistance of zirconia and the excellent wettability of ZrO₂ due to its relatively high ionic character in comparison to metals and covalently bonded compounds.     

Wear Performance of Dental Materials: A Comparison of Substructure Ceramics,Veneering Ceramics,and Non‐Precious Alloys

The aim of this in vitro study was to compare the two‐body wear resistance of different dental ceramics and non‐precious alloys. Two‐body wear tests were performed in a chewing simulator with steatite antagonists. A pin‐on‐block design with a vertical load of 50 N for 1.2 × 10⁵ cycles (f = 1.6 Hz; lateral movement: 1 mm, mouth opening: 2 mm) was used for the wear test. Surface roughness R_a (SP6, Perthen‐Feinprüf, G) and wear depth were determined using a 3D‐Profilometer (Laserscan 3D, Willytec, G). Scanning electron microscopy (Quanta FEG 400, FEI, NL) was applied for evaluating wear performance of both, materials and antagonists. Statistics: one‐way ANOVA (α = 0.05). The in vitro wear test showed that the wear performance of dental materials is strongly influenced by the type of material (ceramic, zirconia, or alloy). Zirconia and alloy provided low wear in contrast to glass‐ceramic systems. In contradiction to common expectations, hard zirconia and alloy systems showed even lower antagonistic wear than glass‐ceramics.     

高性能陶瓷人工髋关节材料摩擦磨损研究发展

陶瓷已经在人工髋关节假体制作中获得一定的应用,并且有更大的潜力以待开发.对于陶瓷人工髋关节假体,其摩擦磨损性能是决定其寿命的最重要的性能之一,而体外的摩擦磨损测试对于确定其摩擦磨损性能有着重要意义.本文综述了国内外对于氧化铝、氧化锆、氮化硅和碳化硅四种陶瓷的摩擦磨损性能的研究结果,并且结合作者的工作对其进行评论.     

Characterization of ion beam modified ceramic wear surfaces using Auger electron spectroscopy

An investigation of the surface chemistry and morphology of the wear surfaces of ceramic material surfaces modified by ion beam mixing has been conducted using Auger electron spectroscopy and secondary electron microscopy. Studies have been conducted on ceramic/ceramic friction and wear couples made up of TiC and NiMo-bonded TiC cermet pins run against Si₃N₄ and partially stabilized zirconia disc surfaces modified by the ion beam mixing of titanium and nickel, as well as unmodified ceramic/ceramic couples in order to determine the types of surface changes leading to the improved friction and wear behaviour of the surface modified ceramics in simulated diesel environments. The results of the surface analyses indicate that the formation of a lubricating oxide layer of titanium and nickel, is responsible for the improvement in ceramic friction and wear behaviour. The beneficial effect of this oxide layer depends on several factors, including the adherence of the surface modified layer or subsequently formed oxide layer to the disc substrate, the substrate materials, the conditions of ion beam mixing, and the environmental conditions.     

Einfluss der Mikrostruktur auf das Verschleiß‐ verhalten der hartanodisierten Aluminium‐legierungen EN AW‐6082 und EN AW‐7075

Microstructural effect on the wear behaviour of the hard‐anodised aluminium alloys EN AW‐6082 and EN AW‐7075 The suitability of hard‐anodising of high‐strength Al alloys (EN AW‐7075‐T651) for the fabrication of protective coatings which are also applicable on screws was investigated. A medium‐strength AlSi1MgMn alloy (AA60682‐T6), generally rated as applicable for anodising, was used as reference material. After possible setting phenomena of a screw joint, the load‐bearing surface of the screw can be subjected to an oscillating relative movement. The damaging tribological load was simulated in an oscillation wear test. The resulting wear appearances have revealed that the untreated oxide coatings on the EN AW‐6082 substrate are not capable of providing protection against tribological load. Since hot‐water sealing increases the hardness of the coating but also contains the technology‐induced risk of softening the substrate material, other tribological protection methods have been looked for. The analysis of the tribological tests (characterisation of the structure and the resulting properties of the material, measurement of the wear amount and analysis of the wear appearance) have shown that the films sealed with wax emulsion on both substrate materials are the most promising candidates for the application of devices under oscillation wear. The obtained roughness, friction coefficients and hardness values confirm the positive behaviour of the anodically oxidised EN AW‐7075‐T651 alloy under the chosen tribological load.     

Ein Sterilisationsprozess kann die Eigenschaften von Biokeramik verändern

Sterilization can change properties of bioceramics Bioceramics made of bioinert alumina or zirconia and bioactive hydroxyapatite are well established implant materials. Implants have to be cleaned and sterilized. When sterilized some bioceramics change their color. This may effect their properties. No decrease of mechanical strength is observed when sterilizing alumina and the novel ceramic biocomposite AMC (Alumina Matrix Composite) with steam or Co⁶⁰ Gamma irradiation. When sterilizing Y‐TZP zirconia with steam a decrease of strength is observed.     

Einsatz von Hartstoffbeschichtungen bei Spindellagern

Application of hard surface coatings for spindle bearings The demands on modern Machine Tools ascends continuously with the requirements of the production for high quality and short‐time processings. Particularly the increase of the processing‐ and removal times of the last years dues to higher loads of the main spindle bearing. The bearing as a central machine component characterises the performance of the Machine Tool for the cutting process and defines the reliability of the main spindle. The majority of the applicated spindle bearings are ball bearings. A large amount of the spindle fall‐outs is caused by a non adequate or defecitive lubrication and is effected by the tribological properties of the bearing elements. For the reduction of friction and wear nowadays several materials, coatings and lubrication additives are applied. Actual researches focus on the development of hard surface coatings (a‐C:H:W) with a nano structure for the rolling contact of ball bearings to increase their reliability. In this article the test of nano structured hard surface coating systems for the reduction of friction, warming and wear are presented. Thus the coating systems are verificated for the application in spindle bearings by pretesting. According to the evaluation the inner and outer raceway of standard‐hybrid bearings are coated and the adhesion in reference to rotational speed, resistance and wear performance at high acceleration is analysed. Concluding the emergency running properties at dry‐running condition is evaluated to identify the field of application for the coatings.     

Mechanical characterization of anti-infectious,anti-allergic,and bioactive coatings on orthopedic implant surfaces

In total joint replacement much effort has been made to reduce implant loosening. We investigated different implant coatings (copper integrated titanium dioxide (TiO₂–Cu), titanium nitride (TiN), plasma polymerized allylamine (PPAAm), and calcium phosphate (CaP)) regarding the adhesion strength and wear resistance. Standardized scratch and adhesive tests were applied. Abrasive wear was measured with artificial bone and bone cement using a special testing machine. All tested coatings have higher bonding strengths than the 22 N/mm² required for medical implant surface coatings by ASTM standard 4711-F. Using bone cement, wear testing revealed higher wear rates in most cases. Polished surfaces reduce the amount of wear, whereas rough surfaces highly increase the wear rate due to three-body wear, especially ceramic surfaces. In general, the application of bone cement in conjunction with modified implant surfaces can lead to an increase in wear rate.     

Friction and wear characteristics of binary and ternary zirconia ceramics

The friction and wear behaviour of binary and ternary zirconia ceramics was studied in an unlubricated environment over a range of loads and sliding speeds. In these tests, ternary zirconia ceramics based on the ZrO₂-CeO₂-Y₂O₃ system were seen to show very low friction coefficients and wear rates compared with the other binary zirconia systems investigated, with a coefficient of friction typically about 50% that of other (binary) zirconia ceramics, and a wear rate of about 1% of that of tetragonal yttria-doped zirconia. During slide testing of zirconias a transition from a low wear regime to a high wear regime was observed with increasing sliding velocity and load. SEM was used to identify the wear mechanisms.     

On the properties of plasma-sprayed oxide and metal-oxide coatings

Alumina (with 3% TiO₂), zirconia (with 13% Y₂O₃) and powder mixtures of zirconia (with 13% Y₂O₃) and molybdenum (in the proportions 70%:30% and 30%:70%) were plasma sprayed under standard conditions onto several steel substrates. Intermediate Ni-Cr metal layers were used.The adhesive strength of the coatings under static and dynamic stress and the thermal shock resistance were tested as well as the wear and corrosion resistance, the porosity and other properties of these oxide and oxide-metal compound layers. In all the tests the number of samples tested was sufficient for reliable average results to be determined.Resistance against friction and against abrasion, sometimes in combination with corrosion, can be controlled by the use of pure oxide layers or, depending on the type of chemical reactions and mechanical behaviour, of oxide-molybdenum compounds. Some theoretical aspects of the behaviour of the coatings tested will be discussed.A knowledge of the mechanical, thermal and corrosion behaviour of the sprayed layers and the interfaces enables selections for practical use. The results reported are part of an industry-sponsored test program for industrial applications of plasma-sprayed coatings.     

几种生物陶瓷材料的裂纹扩展特性

采用破坏力学中的双扭矩实验法，研究了玻璃陶瓷、云母陶瓷、氧化铝陶瓷、氧化锆陶瓷材料分别在大气、水环境中的静负荷和循环负荷下的裂纹扩展特征，阐明了水环境和循环负荷对材料裂纹扩展特性（KI－V特征）的影响。所研究的材料在水环境下的裂纹扩展速度均加快，但玻璃陶瓷和氧化锆陶瓷材料更为明显。在静负荷下这几种材料的裂纹扩展阻力由小到大的次序为：玻璃陶瓷（N－0），玻璃陶瓷（N－11），云母陶瓷，氧化锆陶瓷和氧化铝陶瓷，对于氧化铝和氧化锆陶瓷材料在循环负荷下的裂纹扩展速度均明显加快。     

Surface morphology,tribological properties and in vitro biocompatibility of nanostructured zirconia thin films

Deposition of nanostructured and low-wear zirconia (ZrO₂) thin films on the metallic component of a total joint implant is envisaged to reduce wear of the soft ultra-high molecular weight polyethylene (UHMWPE) counterpart. In this work, morphological surface features, wear resistance and in vitro-biocompatibility of zirconia thin films deposited by the novel Pulsed Plasma Deposition (PPD) method have been investigated. Film thickness, roughness and wettability were found to be strongly dependent on deposition gas pressure. Interestingly, wear rate of UHMWPE disks coupled to zirconia-coated titanium spheres was only poorly correlated to the contact angle values, while film roughness and thickness seemed not to affect it. Furthermore, wear of UHMWPE, when coupled with zirconia coated-titanium spheres, significantly decreased with respect to uncoated spheres under dry or NaCl-lubricated conditions; besides, when using bovine serum, similar results were obtained for coated and uncoated spheres. Finally, suitable mesenchymal stem and osteoblast cells adhesion, proliferation and viability were observed, suggesting good biocompatibility of the nanostructured zirconia films. Taken together, the results shown in this work indicate that zirconia thin films deposited by the PPD method deserve further investigations as low-wear materials for biomedical applications such as total joint replacement.     

Latest progress on tribological properties of industrial materials

Wear is closely related to friction and lubrication; the study of these three subjects is known as tribology. In science and technology it is concerned with interacting surfaces in relative motion. Soft or hard film coating, alloying and composite structuring have all been developed to control wear and friction. This is achieved by improving materials and surfaces with some characteristics that improve resistance to friction and wear. In recent years, several new solid lubricant and modern lubrication concepts have been developed to achieve better lubricity and longer wear life in demanding tribological applications. Most of the traditional solid lubricants were prepared in the form of metal, ceramic and polymer–matrix composites. They have been used successfully in various engineering applications. Recent progress in thin-film deposition technologies has led to the synthesis of new generations of self-lubricating coatings with composite or multilayered architectures, by using multiplex surface treatments. In this study, typical wear behaviors of representative materials of metallic alloys, ceramics, polymeric materials, and composites are reviewed in relation to their friction behaviors. Additionally, modeling for the wear prediction is outlined.     

Corrosion and wear behavior of alumina coatings obtained by various methods

Alumina coatings are widely used in a range of industrial applications to improve corrosion protection, wear and erosion resistances, and thermal insulation of metallic surfaces. Refined alumina surfaces with long-term use are obtained from various efficient and adjustable processes. It can be seen that costefficient arc-sprayed Al coatings post-treated by plasma-electrolytic oxidation (PEO) form Al₂O₃ -layers with remarkable corrosion protection, hardness, bonding strength, and abrasion resistance, as well as with the extended service time. The properties of these coatings are compared with alumina coatings obtained by flame spraying and atmospheric plasma spraying.     

Schichten in der Kunststoffverarbeitung. Mittels MSPVD abgeschiedene CrxN-Schichten eröffnen neue Möglichkeiten für den Verschleißschutz von Plastifiziereinheiten

Coatings in polymer processing Cr_xN coatings produced by PVD-magnetron sputtering (MSPVD) open units For several years hard coatings have been used in plastic processing. The reduction of adhesion and contamination effects play a more and more important role besides the wear protection of injection moulds and extrusion tools. Applications of hard coatings in the field of highly stressed screws and barrels of plastification units are very seldom. In these cases the tribological effects are very intense so that the demanded wear resistance of hard coatings in the range 10μm is not sufficient. Different hard coatings based on titanium and chromium were tested according to their applicability for wear protection of screws in plastification units. Thickness, hardness, internal stresses and adhesion of the coatings were studied. Afterwards tribological tests in a model testing unit were investigated. Here the coatings were studied under tribological conditions, similar to those in a real plastification unit. The Cr_xN multilayer coatings showed extremely better wear resistance than the titanium based coatings. For this reason the Cr_xN coatings were optimized by help of the deposition parameters. These optimized coatings have been investigated according to their applicability for different polymers in comparison to other coating systems. First tests of CrCN/TiCN coated screw elements in practice showed very pleasing results. The test in practice with the optimized Cr_xN multilayer coating has yet to take place, but in the model tests the Cr_xN coatings showed excellent results.     

Tribological characterization of microarc oxidized alumina coatings for biological applications

Coatings with high wear and corrosion resistance are desirable in tribological and biological applications. In an attempt to develop such coatings, we used microarc oxidation (MAO) method to generate noble coatings of alumina on aluminum alloys. This paper reports our tribological investigations on these coatings with a pin-on-disk tribometer in synthetic biofluid. The frictional behavior and wear mechanisms were studied through surface characterization using a scanning electron microscope and a surface profilometer. It was found that the MAO coatings were highly wear resistant in the biofluid environment. The frictional behavior depends on the relative hardness of the ball-on-disk materials. The increased α-Al₂O₃ and γ-Al₂O₃ phases with an increase in the current intensity were found to reduce the friction.     

SURFACE MODIFICATION ISSUES FOR ORTHOPAEDIC IMPLANT BEARING SURFACES

In total joint replacement, generally a polished metal surface articulates against an ultra high molecular weight polyethylene (UHMWPE) counter bearing surface. Metals used include 316L stainless steel, Co-Cr-Mo alloy, and Ti-6AI-4V alloy (particularly with a hardened N⁺ ion implanted surface). Minimizing friction and UHMWPE wear is of prime concern for long-term performance. Additionally, it is desirable to minimize metal ion release which results from constant removal and reformation of passive surface oxides and oxyhydroxides during articulation. Long term effects from the presence of potentially toxic or carcinogenic ions of Cr, Co, Mo, Ni, V, and Al are not well known. Inert ceramic bearing surfaces eliminate this issue and are also resistant to potential three-body wear from bone cement debris or potential stray porous metal coating material. However ceramic (Al₂O₃ and ZrO₂) materials are only available for total hip replacement. For total knee replacement, ft is too difficult and expensive to manufacture a monolithic ceramic knee surface, thus various surface coating methods are being investigated. These methods include plasma sprayed Al₂O₃ and ZrO₂, TiN and amorphous diamond like coatings via PVD/CVD methods, and in-sKu oxidation. In other cases, the existing metal surfaces are simply hardened using methods such as N⁺ ion implantation and oxygen or nitrogen diffusion hardening. This paper reviews the limitations of existing total joint systems and the effectiveness of various surface modification methods of orthopaedic implant bearing surfaces on friction, abrasion, UHMWPE wear, and metal ion release.     

Fabrication and evaluation of SixNy coatings for total joint replacements

Wear particles from the bearing surfaces of joint implants are one of the main limiting factors for total implant longevity. Si(3)N(4) is a potential wear resistant alternative for total joint replacements. In this study, Si(x)N(y)-coatings were deposited on cobalt chromium-discs and Si-wafers by a physical vapour deposition process. The tribological properties, as well as surface appearance, chemical composition, phase composition, structure and hardness of these coatings were analysed. The coatings were found to be amorphous or nanocrystalline, with a hardness and coefficient of friction against Si(3)N(4) similar to that found for bulk Si(3)N(4). The low wear rate of the coatings indicates that they have a potential as bearing surfaces of joint replacements. The adhesion to the substrates remains to be improved.