On the construction of wear maps for Y-TZP dental ceramics in aqueous environments: pH, exposure time and impact angle effects

The object of this work was to evaluate the particulate erosion performance of Y-TZP (Yttria Tetragonal Zirconia Polycrystalline), used in the construction of artificial teeth, at various pH values, impact angles and exposure times. The results showed that the highest degradation recorded was in acidic environments. However, the incubation time to high wastage was also affected by impact angle and exposure time. Wear maps were constructed, based on the results, identifying wastage regimes for the material as a function of the exposure conditions. In addition, a wear map was generated based on the observed phase transformations for the material.     

Wear prediction of ceramics

Advanced ceramics are increasingly being used for wear applications. Wear prediction of ceramics has become an important subject in these arenas. Ceramic wear is a complex function of microstructure, grain size and shape, grain boundary toughness, and the operating conditions. Wear prediction, therefore, needs to address not only the amount of wear for a given range of operating conditions, it also needs to address the location of wear transitions, and the onset of different dominant wear mechanisms. This paper reviews the various wear models developed by the authors over the years to predict wear, wear transitions, and wear under different mechanisms for ceramics. Finally, we investigate the feasibility of modeling across a range of materials and operating condition using a concept of contact severity and material property normalization process. This results in a model capable of predicting wear of ceramics to ±1 order of magnitude using only the material property and operating parameters.     

The transition of mild to severe wear of ceramics

The transition of mild to severe wear of ceramics depends on the operating conditions (normal load, velocity and temperature) and material properties (like grain size, mechanical and thermal material properties). Adachi et al. [Wear 203-204 (1997) 291] introduced the transition of mild to severe wear of ceramics by defining a mechanical severity parameter based on the work of Hamilton [Proc. Inst. Mech. Eng. 197C (1983)] and a thermal severity parameter based on the work of Ashby et al. [Tribol. Trans. (34) (1991) 577]. Metselaar et al. [Wear 249 (2001) 962] improved the thermal severity parameter using the temperature model introduced by Bos [Frictional heating of tribological contacts, Ph.D. Thesis, University of Twente, 1995]. Better prediction of wear transition in the region where the transition is dominated by thermally induced wear was achieved. The combination of the mechanical severity parameter and the thermal severity parameter for Peclet number (Pe) higher than 2 is presented in this paper. This model is verified experimentally and gives an improved prediction of the mild to severe wear transition of ceramics.     

材料磨损与微电子机械系统中的磨损现象

磨损是材料和机械失效的主要原因之一。本文介绍了近年来材料磨损性能材料的进展,磨损的几种破坏机制以及相应的磨损理论模型,并介绍了MEMS中磨损研究的现状。     

The effects of work material on tool wear

Wear maps showing the wear behaviour of titanium carbide (TiC)-coated cemented carbide tools during dry turning of various types of steel have been presented in earlier studies. The maps have demonstrated that tool wear rates vary with cutting speeds and feed rates used. They have also shown that there is a range of cutting conditions, called the safety zone, within which tool wear rates are the lowest. This paper further examines, using the wear mapping methodology, the effects of different grades of steel workpieces on the wear of TiC-coated carbide tools. Wear maps constructed for the machining of AISI 1045 and 4340 steels show that flank wear is generally more severe when machining the AISI 4340 grade, especially at high cutting speeds and feed rates. Nevertheless, the contour and location of the safety zone on the wear maps for both grades of steels correspond to that revealed in previous work on general steel grades.     

Wear Characteristics of Diamond Tools in Machining Ceramics

Wear characteristics of natural diamonds used to machine ceramic materials at a depth of cut of 2 μm and a speed of 1600 m/min were investigated. The diamond tools used for the machining tests were inspected using the Laue back reflection technique and scanning electron microscopy (SEM). Wear characteristics of the diamond tools appeared to be influenced by the material properties of the ceramics being machined, the build-up on the tips of the diamond tools, and the crystallographic orientations of the diamond crystals. Three wear patterns were identified: single-flat wear, double-flat wear, and micro-chipping wear. The single-flat and double-flat wear patterns were primarily observed in machining silicon nitride and alumina; the microchipping wear pattern was observed in machining silicon carbide. The wear rate for the microchipping pattern was found to be one to two orders of magnitude higher than those for other wear patterns. Silicon nitride wore the diamond tools faster than alumina did; however, it often formed built-up lips which reduced the wear of the diamond tools.     

Tribological behavior of RH ceramics made from rice husk sliding against stainless steel,alumina, silicon carbide,and silicon nitride

The tribological behavior of rice husk (RH) ceramics, a hard, porous carbon material made from rice husk, sliding against stainless steel, alumina, silicon carbide, and silicon nitride (Si₃N₄) under dry conditions was investigated. High hardness of RH ceramics was obtained from the polymorphic crystallinity of silica. The friction coefficients for RH ceramics disks sliding against Si₃N₄ balls were extremely low (<0.1), irrespective of contact pressure or sliding velocity. Transfer films from RH ceramics formed on Si₃N₄ balls. Wear-mode maps indicated that the wear modes were powder formation under all tested conditions, resulting in low specific wear rates (<5×10⁻⁹ mm²/N).     

Wear mechanism maps of uncoated HSS tools drilling die-cast aluminum alloy

A map describing the flank wear characteristics of uncoated high-speed steel (HSS) tools is constructed under the condition of drilling die-cast aluminum alloy. Several wear mechanisms are revealed which describe different wear modes observed by SEM in uncoated HSS tools, including adhesive wear, adhesive and abrasive wear, abrasive wear, severely plastic flow, and thermal wear. In the map, there exists a minor wear region, which is called “safety cutting zone” to the HSS tools. This map will be a good reference for choosing suitable drilling parameters of uncoated HSS cutting tools.     

Sliding speed-temperature wear transition maps for Si3N4/iron alloy couples

The superior high temperature resistance of silicon nitride (Si₃N₄) based ceramics makes them suitable for tribological applications above room temperature or in high speed unlubricated sliding. There are some published works on the wear behaviour of Si₃N₄/metal alloys. However, experimental data are shown in a form that is not of direct use for engineers involved in materials selection. In the present work, Si₃N₄ pins were tested against tool steel and grey cast iron on a pin-on-disc tribometer. Ceramics were produced by hot-pressing and tested without lubrication at variable temperature and sliding speed. SEM/EDS and XRD analysis were used for chemical and microstructural characterisation of worn surfaces and wear debris. At low speeds (0.05–0.5 m s⁻¹) and room temperature, Si₃N₄ surfaces are polished-like due to a combination of humidity-assisted tribo-oxidation and abrasive action of very fine wear debris. At high sliding speeds (2–3.5 m s⁻¹), as well as for temperatures in the range 400–600°C, an extensive coherent tribolayer mainly composed by iron oxides spreads over the ceramic surfaces. Polishing and protection by adherent tribolayers are the mechanisms responsible for observed severe and mild wear regimes, respectively. Wear maps are constructed showing the transition of wear regimes in Si₃N₄/iron alloys contacts determined by constant flash temperature curves. Equations for calculation of bulk and flash contact temperatures in tribocontacts between dissimilar materials are deduced.     

Wear and friction behavior of alumina ceramics in aqueous solutions with different pH

It is well known that the wear and friction behavior of ceramics can be significantly improved by using them in water or humid air rather then a dry atmosphere. Accordingly, various ceramics have found many water-lubricated applications. In spite of this, the effect of the pH of the aqueous media on the wear and friction behavior has not been investigated in detail. In this study, we have investigated the wear behavior of alumina ceramics in different water-lubricated conditions with a range of pH values from 0.85 to 13. Based on the results of reciprocating sliding tests, we found that the wear can vary by as much as one order of magnitude and the coefficient of friction between 0.2 and 0.6, depending on the conditions. We also observed that significantly different wear surfaces are generated for different pH values, and these surfaces have a diverse effect on the wear and friction behavior. Wear mechanisms were established by employing surface topography analyses and scanning electron microscopy (SEM). The chemical and electrochemical effects under the selected tribological conditions are discussed to help explain the observed behavior. Our findings suggest that by varying the pH of a solution we can obtain low-wear and/or high-wear of alumina ceramics to suit the requirements of the process.     

Measurement of wear of carbon coated sliders using atomic force microscopy and Raman spectroscopy

Wear of carbon coated sub-ambient pressure “pico” sliders is investigated during sweep testing as a function of interference height, slider design and sliding distance using atomic force microscopy. The wear results from atomic force microscopy measurements are compared with wear measurements of the carbon overcoat using Raman spectroscopy. The effect of interference on wear and disk burnishing is studied using acoustic emission measurements and atomic force microscopy. The results show that wear of a slider is higher for larger interference height and higher stiffness of the air-bearing.     

The performance of TiN-coated high speed steel tool inserts in turning

While it is well known that thin, hard coatings can reduce tool wear and improve tool life and productivity, there is still little consensus over the degree of advantage coated tools have over their uncoated counterparts. This paper compares the behaviour of titanium nitride- (TiN-) coated and uncoated high speed steel (HSS) tool inserts during turning. Wear maps describing the crater wear characteristics of these tools are used to show that the extent of tool wear reduction due to the coatings depends strongly on the cutting speed and feed rate. The maps also demonstrate that the benefits of TiN coatings on HSS tools may be easily realized over a wide range of machining conditions.     

The relevance of wear-mechanism maps to mild-oxidational wear

The presence of oxygen in the environment in which a steel sliding system operates will promote a mild form of wear with wear debris consisting mainly of iron oxides. Of the oxidation-dominated mechanisms, mild-oxidational wear (the prefix describes the extent of oxidation and not the wear rate) has been most extensively investigated. In this paper, examples will be used to show that the wear-mechanism map for the unlubricated sliding of steels can adequately predict the occurrence of mild-oxidational wear and the trend of wear rates as well as describe the resultant features on the worn surfaces. It is also shown that this map is relevant to delamination wear and to test geometries other than the pin-on-disk configuration. It is suggested that the more-recently constructed wear maps for aluminium and magnesium alloys could similarly be used to predict the wear characteristics of these alloys during sliding.     

Microwear Mechanisms of Silicon Sliding Against Diamond in Water Vapor

Microwear mechanisms of single-crystal silicon (111) in water vapor have been investigated. A diamond pin with a radius of 10 μm was used as a pin specimen. All tests were carried out in the chamber of environmental scanning electron microscopy (ESEM), with which contact point could be observed simultaneously during the sliding test. The water vapor pressure was changed from 40 Pa (0.3 Torr) to 2667 Pa (20 Torr). Three different wear modes were observed in the tests and consolidated as wear mode diagram according to initial maximum Hertzian contact pressure and friction coefficient. These wear modes are

A No removal of material

B Microcutting of feather-like wear particles

C Fracture

Corresponding to these wear modes, the friction coefficients are 0.07 ～ 0.13 in Wear Mode A, 0.19 ～ 0.23 in Wear Mode B and 0.16 ～ 0.18 in Wear Mode C. Transitions of wear mode are not influenced by water vapor in the range of 40 ～ 2667 Pa. Friction coefficient changes by the change of water vapor pressure in Range A but does not change in Ranges B and C.     

硅油润滑对莫来石基陶瓷摩擦磨损性能的影响研究

莫来石基陶瓷具有一系列优异的性能,其在摩擦学领域中的应用越来越广泛。本文研究了硅油润滑对该类陶瓷摩擦磨损性能的影响规律。研究结果表明,硅油可明显地降低莫来石基陶瓷的摩擦系数和磨损率,但却使摩擦系数在稳定阶段的波动幅度增加。硅油润滑条件下,莫来石基陶瓷的磨损机理主要是微观断裂和磨料磨损。     

Coating thickness effects on initial wear of nitrogen-doped amorphous carbon in nano-scale sliding contact: Part I—in situ examination

This paper, the first of a two-part series, presents the empirical data obtained from in situ examination on the generation of wear particles on carbon nitride coatings by a spherical diamond counter-face during repeated sliding contacts. In particular, the effect of coating thickness, varying from 1 to 500 nm, on the generation of wear particles was examined.Based on the in situ examination, the shape transition maps for generated wear particles were obtained for carbon nitride coatings of various thickness. The results show that the critical number of friction cycles, Nc, for the transition from “no observable wear particles” to “wear particle generation” generally increased with increasing coating thickness. It was noted that up to 20 friction cycles, the maximum Hertzian contact pressure, P_max, for “no observable wear particles” regime can be increased from 1.39Y to 1.53Y if silicon was coated with carbon nitride coating thicker than 10 nm, where Y is defined as the yield strength of silicon.     

磨粒分形识别及发展

相互作用表面间必然会产生磨粒,磨粒含有大量的有关材料摩擦磨损的信息。磨粒形态分析是确定磨损方式和磨损程度的有益手段。磨粒并非是欧氏几何体,而是展示出了分形性质。基于分形几何理论,可获得尺度不变的分形参数,用这类参数可对磨粒形态进行客观、全面的表征。本文综合评述了磨粒分形表征以及磨粒形态与磨损方式、磨损程度间的定量耦合关系等的研究进展,对将来磨粒分形研究的趋势和注意的问题进行了探讨。     

Abrasive erosive wear of powder steels and cermets

Composite materials produced by powder metallurgy provide solutions to many engineering applications that require materials with high abrasive wear resistance. The actual wear behaviour of a material is associated with many external factors (abrasive particle size, velocity and angularity) and intrinsic material properties of wear (hardness, toughness, Young modulus, etc.). Hardness and toughness properties of wear resistant materials are highly dependent on the content of the reinforcing phase, its size and on the mechanical properties of the constituent phase. This study is focused on the analysis of the (AEW) abrasive erosive wear (solid particle erosion) using different wear devices and abrasives. Powder materials (steels, cermets and hardmetals) were studied. Wear resistance of materials and wear mechanisms were studied and compared with those of commercial steels. Based on the results of wear studies, surface degradation mechanisms are proposed. The following parameters characterizing the materials were found necessary in materials creation and selection: hardness (preferably in scale comparable with impact), type of structure (preferably hardmetal type) and wear parameters characterizing material removal at plastic deformation.     

Dry reciprocating wear of Al-Si-SiCp composites: A statistical analysis

In this paper, effect of various wear test and material related parameters (applied load, sliding distance, reciprocating velocity, counter surface temperature and weight percentage of silicon) on dry wear behavior of two Al-Si-SiC_p composites under reciprocating conditions was studied using fractional factorial design. Developed mathematical model showed that Al-Si-SiC_p with high silicon content composite is subjected to a lower wear compared to that of low silicon composite. The applied load, sliding distance, reciprocating velocity and percentage silicon weight in composite are the four important and controlling factors; counter surface temperature has a minor effect on the wear of the composite specimens in dry condition.