Microstructural alterations within thermal spray coatings during highly loaded diesel engine tests




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НазваниеMicrostructural alterations within thermal spray coatings during highly loaded diesel engine tests
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Automotive

Microstructural alterations within thermal spray coatings during highly loaded diesel engine tests. The good wear characteristics of thermal spray coatings are related to structural, productional, and topographical properties. Finally, the alteration of the microstructure in different contact zones is essential for mild wear conditions that will guarantee a long-life cycle because it reveals the ability of the material to adjust to the current load situation. Previous studies have shown that in diverse tribosystems an in situ formation of a nanocrystalline layer together with mechanical mixing maintains long-lasting, wear resistant surfaces with low wear rates. This investigation exemplifies results from a cylinder that was run in a road test motor. The relevant piston ring positions that fully describe the tribosystem have to be defined at the combustion chamber (CC), top dead centre (TDC), stroke and bottom dead centre (BDC). Transmission electron microscopy (TEM) and energy-filtered transmission electron microscopy (EFTEM) are used to analyse these contact zones in terms of microstructure and chemistry. Nanocrystalline surface layers up to a thickness of 100 nm occurred in all areas of contact whereas subsurface zones revealed differing microstructural changes. Thus the influence of thermal impact and different mechanical load conditions in a motor cylinder are evident. EFTEM elemental mappings verify the incorporation of elements that stem from lubrication or combustion residues. © 2009 Elsevier B.V. All rights reserved.

M. Hahn, R. Theissmann, B. Gleising, W. Dudzinski and A. Fischer, Institute of Product Engineering, Material Science and Engineering, University of Duisburg

Essen

Germany. Cited: Wear, 267(5-8), Jun 15 2009, p 916-924 [in ISSN 0043-1648.


Oxygen-diffused titanium as a candidate brake rotor material. Titanium alloys are one of several candidate materials for the next generation of truck disk brake rotors. Despite their advantages of lightweight relative to cast iron and good strength and corrosion resistance, titanium alloys are unlikely to be satisfactory brake rotor materials unless their friction and wear behavior can be significantly improved. In this study, a surface engineering process - oxygen diffusion (OD) - was applied to titanium rotors and has shown very encouraging results. The oxygen-diffused Ti-6Al-4V (OD-Ti64) was tested on a sub-scale brake tester against a flat block of commercial brake lining material and benchmarked against several other Ti-based materials, including untreated Ti-6Al-4V (Ti64), Ti-based metal matrix composites (MMCs), and a thermal spray-coated Ti alloy. With respect to friction, the OD-Ti64 outperformed all other candidate materials under the imposed test conditions with the friction coefficient remaining within a desirable range of 0.35-0.50, even under the harshest conditions when the disk surface temperature reached nearly 600 °C. In addition, the OD-Ti64 showed significantly improved wear-resistance over the untreated Ti64 and was even better than the Ti-based composite materials. © 2009 Elsevier B.V.

J. Qu, P.J. Blau and B.C. Jolly, Materials Science and Technology Division, Oak Ridge National Laboratory

Oak Ridge, TN 37831-6063

United States. Cited: Wear, 267(5-8), Jun 15 2009, p 818-822 [in ISSN 0043-1648.


Flame sprayed V-doped TiO2 nanoparticles with enhanced photocatalytic activity under visible light irradiation. V-doped TiO2 (V-TiO2) nanoparticles were prepared by a simple one-step flame spray pyrolysis (FSP) technique. The obtained samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), electron paramagnetic resonance (EPR) spectra, UV-vis absorption spectroscopy, and nitrogen adsorption-desorption methods. Benefiting from the short residence time and high quenching rate during the flame spray process, V4+ ions are successfully incorporated into the crystal lattice of TiO2. It reveals that V doping favors the primary particle size growth as well as the increase of rutile content in the products. The photocatalytic activity of the V-TiO2 samples under UV and visible light irradiation were evaluate by the photocatalytic degradation of methylene blue (MB) and 2,4-dichlorophenol (2,4-DCP), respectively. It was found that V doping enhances the photocalytic activity under both UV and visible light irradiation. Especially, under visible light irradiation, the degradation rate of 2,4-dichlorophenol over 1%V-TiO2 is two times higher than that over undoped TiO2. The photocatalytic mechanisms for V-TiO2 samples under UV and visible light irradiation were tentatively discussed. © 2009 Elsevier B.V. All rights reserved.

B. Tian, C. Li, F. Gu, H. Jiang, Y. Hu and J. Zhang, Key Laboratory for Ultrafine Materials, Ministry of Education, School of Materials Science and Engineering

Shanghai, 200237

China. Cited: Chemical Engineering Journal, 151(1-3), Aug 15 2009, p 220-227 [in ISSN 1385-8947.


Biomaterials

Cladding of titanium/fluorapatite composites onto Ti6Al4V substrate and the in vitro behaviour in the simulated body fluid. To improve the bioactivity of Ti6Al4V alloy, an innovative cladding method has been developed to bond a Ti/fluorapatite (FA) composite onto the alloy for load-bearing applications. With the aid of a silver interlayer and external pressure during sintering, a defect-free interface between the composite and the substrate was obtained. The fabricated materials were bioactive and could induce the nucleation and formation of bone-like carbonated apatite after immersed in the simulated body fluid (SBF). Functional ions, such as Ag+ and F-, were released from the materials during immersion, which could impart favourable activities for the implant. This work demonstrated that a simple and novel method could be applied to enhance functionalities of Ti alloys for load-bearing implant applications. Crown Copyright © 2009.

H. Ye, X.Y. Liu and H.P. Hong, Faculty of Engineering, The University of Western Ontario

London, Ont. N6A 5B8

Canada. Cited: Applied Surface Science, 255(18), Jun 30 2009, p 8126-8134 [in ISSN 0169-4332.


A novel graded bioactive high adhesion implant coating. One method to increase the clinical success rate of metal implants is to increase their bone bonding properties, i.e. to develop a bone bioactive surface leading to reduced risks of interfacial problems. Much research has been devoted to modifying the surface of metals to make them become bioactive. Many of the proposed methods include depositing a coating on the implant. However, there is a risk of coating failure due to low substrate adhesion. This paper describes a method to obtain bioactivity combined with a high coating adhesion via a gradient structure of the coating. Gradient coatings were deposited on Ti (grade 5) using reactive magnetron sputtering with increasing oxygen content. To increase the grain size in the coating, all coatings were post annealed at 385 °C. The obtained coating exhibited a gradual transition over 70 nm from crystalline titanium oxide (anatase) at the surface to metallic Ti in the substrate, as shown using cross-section transmission electron microscopy and X-ray photoelectron spectroscopy depth profiling. Using scratch testing, it could be shown that the adhesion to the substrate was well above 1 GPa. The bioactivity of the coating was verified in vitro by the spontaneous formation of hydroxylapatite upon storage in phosphate buffer solution at 37 °C for one week. The described process can be applied to implants irrespective of bulk metal in the base and should introduce the possibility to create safer permanent implants like reconstructive devices, dental, or spinal implants. © 2009 Elsevier B.V. All rights reserved.

U. Brohede, S. Zhao, F. Lindberg, A. Mihranyan, J. Forsgren, M. Stromme and H. Engqvist, Division for Nanotechnology and Functional Materials, Department of Engineering Sciences, The Angstrom Laboratory

751 21 Uppsala

Sweden. Cited: Applied Surface Science, 255(17), Jun 15 2009, p 7723-7728 [in ISSN 0169-4332.


Effect of surface roughness, porosity, and a resorbable calcium phosphate coating on osseointegration of titanium in a minipig model. The aim of this study was to compare the osseointegration of four different implant surfaces in the Gottingen minipig femur model. They were prepared by glasspearlblasting (A), sandblasting (B) and titanium- plasma spraying (C and D). Surface D received additionally an electrochemically deposited layer of a resorbable calcium phosphate (CaP) layer, made mainly of brushite. Sample size was n = 20 per group. Implants were placed in the intertrochanteric and intercondylar sites of both femora. After 12 weeks, implant anchorage was measured by the pull-out test and histomorphometry measurements were carried out at the bone-implant interface. Implant anchorage was 0.7 ± 0.3 MPa for surface A, 3.2 ± 0.6 MPa for surface B, 6.5 ±1.5 MPa for surface C and 7.3 ±1.9 MPa for surface D. The differences between surfaces were statistically significant, with exception of C and D. The stiffness of the bone-implant interface showed no statistically significant difference between surfaces. After pull-out, surface A and B showed nearly no bone spots, while on surfaces C and D bone remains were found. Bone- implant contact was 1.9 ± 1.1% for surface A, 10.5 ± 3.6% for surface B, 22.4 ± 4.5% for surface C and 48.8 ± 4.5% for surface D. The differences were statistically significant. Implant location, intertrochanteric and intercondylar, did not affect the data. In this minipig model, rougher surfaces showed better osseointegration. After 12 weeks of healing, the resorbable CaP layer enhanced significantly the bone- implant contact but not the level of anchorage. The findings also suggest that the pull-out test should be critically evaluated to determine the shear strength between bone and porous surfaces. © 2008 Wiley Periodicals, Inc.

M.L.R. Schwarz, M. Kowarsch, S. Rose, K. Becker, T. Lenz and L. Jani, Laboratory for Biomechanics and Experimental Orthopedics, University Hospital Mannheim, University of Heidelberg

Germany. Cited: Journal of Biomedical Materials Research - Part A, 89(3), Jun 1 2009, p 667-678 [in ISSN 1549-3296.


A novel nano-porous alumina biomaterial with potential for loading with bioactive materials. Nano-porous alumina, with the potential for being loaded with bioactive materials, has been proposed as a novel material for coating implants. In this study, the shear strength of the interface between such nano-porous anodic aluminium oxide (AAO) coatings and titanium substrates, their biocompatibility, and their potential for pore loading have been investigated. An interface shear strength in excess of 29 MPa was obtained which is comparable with that of conventional plasma sprayed hydroxyapatite implant coatings. The viability and differentiation of MG63 osteoblastic cells co-cultured on the coating was found to be broadly comparable to that of similar cells co-cultured on conventional bioinert implant materials such as titanium and fully dense alumina. Extensive pore loading with silica nano-particles of different sizes and in different combinations was demonstrated throughout the thickness of AAO layers 1 μm and 60 μm thick. This work has demonstrated, that with suitable choice of pore filling materials, this novel coating might simultaneously combat infection, encourage bone regeneration, and secure fixation of the implant to bone. © 2008 Wiley Periodicals, Inc.

A.R. Walpole, Z. Xia, C.W. Wilson, J.T. Triffitt and P.R. Wilshaw, Department of Materials, University of Oxford

Oxford

United Kingdom. Cited: Journal of Biomedical Materials Research - Part A, 90(1), July 2009, p 46-54 [in ISSN 1549-3296.


Bone growth is enhanced by novel bioceramic coatings on Ti alloy implants. Calcium phosphate ceramics are widely used as coating materials to orthopedic implants and are found to enhance initial bony ingrowth by stimulating osseous apposition to the implant surface. In this study, two novel calcium orthophosphate materials were selected for coating onto the commonly used orthopedic implant material Ti-6Al- 4V. One was calcium alkali orthophosphate with the crystalline phase Ca10[K/Na](PO 4)7 with a small addition of SiO2 (AW-Si) and the other was calcium orthophosphate composed of 70 mol % fluorapatite, Ca10(PO4)6F2 and 30 mol % CaZr4(PO 4)6 (FA7Z). The coated implants were placed in cortical and cortico-cancellous bone of sheep femur for six weeks. Retrieved samples were tested for osseointegration and mechanical strength. It was found that both coatings produced enhanced bone/implant contact rate compared to the control when implanted in cortico-cancellous bone. This study demonstrates that the two coatings have the capability of encouraging bone growth, and hence the potential for being used as coating materials on Ti implants. © 2008 Wiley Periodicals, Inc.

C. Wang, G.A. Karlis, G.I. Anderson, C.R. Dunstan, A. Carbone, G. Berger, U. Ploska and H. Zreiqat, Biomedical and Tissue Engineering Research Unit, School of AMME, University of Sydney

Sydney, NSW 2006

Australia. Cited: Journal of Biomedical Materials Research - Part A, 90(2), August 2009, p 419-428 [in ISSN 1549-3296.


Development of novel thermal sprayed antibacterial coating and evaluation of release properties of silver ions. Several studies have addressed the use of antibacterial coating to reduce implantassociated infections. In this study, novel silver (Ag)-containing calcium-phosphate (CP) coating technology based on the thermal spraying method was developed. The coating's physical and chemical properties, in vitro antibacterial activity, hydroxyapatite (HA)-forming ability, and release of Ag ions were evaluated. An amorphous structure of the coating was confirmed by X-ray diffraction, and Ag residue in the coating was determined by elementary analysis. The coating showed strong antibacterial activity to methicillin-resistant Staphylococcus aureus in fetal bovine serum (FBS) along with HA-forming ability in simulated body fluid. Therefore, it is expected that the coating would confer antibacterial and bone bonding abilities to the implant surface. Time course release testing of Ag ions from the coating on immersion in FBS showed pronounced Ag release for up to 24 h after immersion, with consistent strong antibacterial activity at the early postoperative stage. In repeated testing, the amount of released Ag ions was about 6500 parts per billion (ppb, μg/L) for the first release test, after which it gradually decreased. However, retention of significant release of Ag ions after a sixth repeat implies that Ag release from the coating is slow in FBS. © 2008 Wiley Periodicals, Inc.

I. Noda, F. Miyaji, Y. Ando, H. Miyamoto, T. Shimazaki, Y. Yonekura, M. Miyazaki, M. Mawatari and T. Hotokebuchi, Research Department, Japan Medical Materials Corporation

Osaka 532-0003

Japan. Cited: Journal of Biomedical Materials Research - Part B Applied Biomaterials, 89(2), May 2009, p 456-465 [in ISSN 1552-4973.


Investigation of boundary conditions for biomimetic HA deposition on titanium oxide surfaces. To improve the clinical outcome of metal implants, i.e. earlier loading and reduction of the incidence of revision surgery, better bone bonding ability is wanted. One method to achieve this is to change the surface chemistry to give a surface that facilitates bone bonding in vivo, i.e. a bioactive surface. Crystalline titanium oxide has recently been proven to be bioactive in vitro and is an interesting option to the more common hydroxylapatite (HA) coatings on implants. A materials possible in vitro bioactivity is tested through soaking in simulated body fluid and studies of possible HA formation on the surface. For bioactive materials, the formed HA layer can also be used as a coating. The aim of the current paper is to investigate some boundary conditions for HA formation on crystalline titanium oxide surfaces regarding influence from coating thickness, soaking time and soaking temperature. The influence from soaking time and temperature on the HA growth were investigated on oxidised Ti samples, (24 h at 800°C) resulting in a rutile surface structure. The oxidised samples were tested at three temperatures (4, 37 and 65°C) and four times (1 h, 1 day, 1 week and 4 weeks). The influence from titanium coating thickness on the HA growth was investigated via depositing thin films of crystalline titanium dioxide on Ti plates using a reactive magnetron sputtering process. Four different PVD runs with coating thicknesses between 19 and 74 nm were tested. The soaking temperature had an effect on the HA formation and growth on both rutile surfaces and native oxide on Ti substrates. Higher temperatures lead to easier formation of HA. It was even possible, at 65°C, to grow HA on native titanium oxide from soaking in PBS. The coating quality was better for HA formed at 65°C compared to 37°C. All PVD-coatings showed HA growth after 1 week in PBS at 37°C, thus even very thin coatings of crystalline titanium oxide coatings are bioactive. © 2009 Springer Science+Business Media, LLC.

M. Lindgren, M. Astrand, U. Wiklund and H. Engqvist, Department of Engineering Sciences, Materials Science, Uppsala University

Uppsala

Sweden. Cited: Journal of Materials Science: Materials in Medicine, 20(7), July 2009, p 1401-1408 [in ISSN 0957-4530.


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