Comparison of self-mated hardmetal coatings under dry sliding conditions up to 600 °C

Hardmetal coatings prepared by high velocity oxy-fuel (HVOF) spraying represent an advanced solution for surface protection against wear. In the current systematic study the high-temperature oxidation and unidirectional sliding wear in dry and lubricated conditions were studied. Results for a series of experiments on self-mated pairs in dry conditions as part of that work are described in this paper. Coatings with nominal compositions WC-10%Co4%Cr, WC-(W,Cr)₂C-7%Ni, Cr₃C₂-25%NiCr, (Ti,Mo)(C,N)-29%Ni and (Ti,Mo)(C,N)-29%Co were prepared with an ethylene-fuelled DJH 2700 HVOF spray gun. Electrolytic hard chromium (EHC) coatings and bulk (Ti,Mo)(C,N)-15%NiMo (TM10) hardmetal specimens were studied for comparison. The wear behaviour was investigated at room temperature, 400 and 600 °C. For the coatings sliding speeds were varied in the range 0.1–1 m/s for a wear distance of 5000 m and a normal force of 10 N. In some cases the WC- and (Ti,Mo)(C,N)-based coatings showed total wear rates (sum of wear rates of the rotating and stationary samples) of less than 10^?6 mm³/Nm, i.e., comparable to values typically measured under mixed/boundary conditions. Coefficients of friction above 0.4 were found for all test conditions. The P × V values as an engineering parameter for coating application are discussed. The microstructures and the sliding wear behaviour of the (Ti,Mo)(C,N)-based coatings and the (Ti,Mo)(C,N)-15%NiMo hardmetal are compared.     

High temperature tribology of ceramics

The friction and wear behaviour of self-mated couples of MgO---ZrO₂, Al₂O₃ and two types of SiSiC were studied under dry sliding conditions in a special pin-on-disc high temperature tribometer. The temperature was varied between 25 and 1000°C, and the sliding speed from 0.03 m s⁻¹ to 3 m s⁻¹. The morphology of the worn surfaces was studied by means of SEM, and their phase distribution by X-ray diffraction and TEM analyses. The results show that the wear coefficients of all couples mostly increase with increasing temperature and sliding velocity. The wear of MgO---ZrO₂ is influenced by tribo-induced phase transformations while α-Al₂O₃ retains its original structure for all test conditions. For SiSiC delamination and fatigue of the interface Si/ß-SiC predominate. At higher temperatures and sliding velocities tribo-oxidation is effective. The friction coefficients lie between 0.5 and 1.0 under steady-state conditions but for short test durations lower values can occur. The couple SiSiC/SiSiC has low friction coefficients at low sliding velocities and temperatures, even if the steady-state region is reached.     

Schäden wälzbeanspruchter DLC‐Schichten auf Stahlsubstraten unterschiedlicher Härte

Damages of slip‐rolling tested DLC coatings on steel substrates of different hardness Extremely hard diamond coatings on hard SSiC substrates, various hard DLC coatings on 100Cr6 substrates (HRC60) as well as selected DLC coatings on unhardened steel substrates (HRC20) were tested under slip‐rolling conditions. Unadditivated paraffin oil was used as a lubricant. The tests were carried out in an Amsler type twin disc tester at initial maximum pressures of P₀=2.3 GPa according to Hertz. The tests were terminated after n=1.000.000 revolutions (endurance tests: n=10.000.000 revolutions) or if a coherent damaged area of A>1 mm² occurred. The slip‐rolling tests showed that the SSiC had a supportive influence on the diamond coatings which, however, failed due to fractures in the substrate. At least two of the DLC coatings on 100Cr6 substrates (HRC60) withstood the slip‐rolling test for up to n=10.000.000 revolutions with nearly no visible damage. These coatings deposited onto a soft, nitrogen alloyed steel (HRC20) were able to adjust to the deformation of the substrate without major damaged areas (A>1 mm²).     

聚酰胺染色过程中的pH控制

酸性产及金属络合染料对聚酰胺染色通常都使用温度控制方法。温度的控制一般基于经验，并且常根据织物质量，色泽深度及使用设备来加以选择。在ＰＨ恒定工艺中这些裼 最优化过去已经描述过。为了增加染浴的竭染率并由此来改善染色的重现性和资源匀染性，在工艺操作中实施降低ＰＨ同时井高温度是切实可行的。要一文就这类ＰＨ滑动工艺的最优化作了概念。由于最佳的ＰＨ范围随着没的被染物而改变，因而本语文所述的方法也考虑到了这些     

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.     

The impact of biofuels on engine oil performance

The dilution of biogenic fuels into lubricating engine oils often leads to a shortening of the recommended oil drains (between 30% and 60%) and an increase in wear. The large number of overlapping and influencing factors, of which dilution and polymerization of fuel components in the engine oil are emphasised, makes it difficult to find a uniform solution to prevent failures in the various applications. Insofar single solutions for the different types of biofuels are needed. The contribution of base oil chemistry and additives as well as triboactive materials is featured to deal with the adverse effects of biofuels. In the frame of the European Commission (EC)‐funded project ‘cleanengine’, tentative engine oils based on esters with a content of renewables and polyglycols are formulated to increase the lubricant's tolerance in engines fuelled with biofuel‐based blends, with the aim of ensuring required lubricating and wear protection performance while keeping oil drain intervals unchanged. The present paper focuses on four‐stroke diesel applications, fuelled by biodiesel (fatty acid methyl ester — FAME) as well as by rapeseed oil and Jatropha oil (pure vegetable oils, triglycerides), together with relevant blends of those biofuels and conventional diesel fuel. This paper screens the functional profile (in particular rheological, toxicological, bio‐compatibility, tribological and biofuels affinity) of lube families with respect to biofuel contamination. Moreover, this is followed by the contributions of piston ring and liner materials as well as thin film coatings. Copyright © 2011 John Wiley & Sons, Ltd.     

Validierung der Beständigkeit von ZrO2‐Minikugeln gegenüber Heißdampfsterilisation

Validation of the Resistance of ZrO₂‐Mini Balls against Hot Vapour Sterilisation Mini‐balls are used in bearings of dental drills. As the bearings as well as the drills are hot vapour sterilised, the bearings are operated under non‐lubricated conditions. In the present study, Raman scattering experiments show that hot vapour sterilisations of Y₂O₃ stabilised ZrO₂‐Mini‐balls lead to a phase transition from tetragonal to monoclinic ZrO₂. This phase transition finally causes the failure of ZrO₂‐Mini‐balls under the tribological conditions typical for dental drills. If, however, the ZrO₂‐Mini‐balls are stabilised using CeO₂, such hot vapour sterilisation induced phase transitions could not be observed. Subsequent tribological experiments prove that CeO₂ stabilised ZrO₂‐Mini‐balls, produced in a Sol‐Gel process, are resistant to slip‐rolling conditions, if large pores can be avoided.     

Charakterisierung des tribologischen Verhaltens von keramischen Gleitpaarungen mit moderner Oberflächenanalytik

Characterization of the Tribological Behaviour of Ceramic Sliding Couples with Modern Surface Analysis Methods Dry friction and wear tests were performed in ambient atmosphere with various self-mated couples of SiC, Al₂O₃, Si₃N₄ and ZrO₂. The temperature was varied between 22 °C and 1000 °C and the sliding velocity between 0.03 m/s and 5 m/s. Normal force, temperature and sliding velocity are kept constant during the tests. The materials and wear mechanisms were characterized by various surface analytic methods – optical microscopy, scanning electron microscopy, transmission electron microscopy, electron microprobe analysis, IR-spectroscopy, X-ray diffraction, auger electron spectroscopy and X-ray photoelectron spectroscopy. High wear/low wear transitions could be explained. On the basis of these results new ceramic materials with lower friction and/or wear were selected or successful developed.