Effect of electric contact surface treatment on microstructure and wear behaviour of ductile iron

Abstract

A study of electric contact surface treatment to ductile iron has been carried out. This technology was based on the application of the contact resistance heating between the electrode and workpiece. For comparison, the experiments of induction hardening to ductile iron were studied. The microstructure, microhardness, surface residual stress and wear properties were investigated using optical microscope, scanning electron microscope, X-ray diffraction, Vickers microhardness and rolling contact wear tests. Electric contact surface treatment resulted in the formation of fine ledeburite (white bright layer) and martensite in the ductile iron surface, in which the hardness in these areas was higher than that of induction hardened surface. The wear test results showed that the ductile iron surface after electric contact surface treatment had better wear resistance owing to the fine microstructure, high hardness and residual compressive stress.     

Influence of annealing duration on the erosive wear behavior of polyphenylenesulphide composites

The influence of annealing duration on the erosive wear behavior of short glass fiber (40% w/w) and CaCO₃ mineral particulate (25% w/w)–short glass fiber (40% w/w) (total: 65% w/w) reinforced PPS composites has been characterized under various experimental conditions by differential scanning calorimetry (DSC) and erosion measurements. The erosive wear of the composites have been evaluated at different impingement angles (30, 45, 60, and 90°) and at four different annealing periods (30, 60, 90, and 120 min). Increase in the total crystallization causes an improvement in the erosive wear properties of the samples. Annealing time controls the morphology by influencing the degree of crystallinity in the matrix and in the fiber–matrix interface. This formation restricts fiber–matrix debonding. There is no linear proportionality between annealing time and relative degree of crystallization. The results indicate that PPS composites show maximum in wear versus impact angle relation at 60° confirming their semi-ductile failure behavior. The morphologies of eroded surface are examined by the scanning electron microscope.     

基于多尺度下塑性指数模型的结合面接触刚度计算方法EI北大核心CSCD

螺栓连接结合面的接触特性是影响机械系统动静态特性的关键。当结合面处于振动疲劳状态时,会导致阻尼增大和共振频率减小,因此建立精确的栓接结合面接触模型对研究整个机床的动态特性有着十分重要的意义。结合Greenwood和Williamson给出的塑性指数表达式、统计学的粗糙度参数和分形参数,建立了与微凸体频率序数相关的塑性指数模型,从而根据塑性指数得到微凸体弹性-弹塑性-塑性变形的临界频率序数,并基于赫兹接触理论,通过对不同频率区间内微凸体的积分得到整个结合面的接触载荷和接触刚度。最后,通过有限元仿真与试验相结合共同验证了理论模型的正确性,证明该理论模型具有较强的工程应用价值。     

Study on the variation of 3D topography of specific spot on sliding wear surface

The study of topography of wear surface is an effective method to determine the mechanism of material's wear. So, in this article, the process of materials' sliding wear at room temperature was simulated based on the pin-on-disk wear test. The change of three-dimensional surface topography of a specific spot on the sliding wear surface was studied. Then the wear mechanism was analyzed. The results indicated that friction coefficient can reflect the interfacial properties of the wear of materials in real-time. The change of three-dimensional surface topography of a specific spot can directly reflect the change of material's surface structure during the wear process, providing an important experimental evidence for the analysis of material's wear mechanism.     

Nanoscale characterisation of rolling contact wear surface of pearlitic steel

Abstract

Nanoscale characterisation of a rolling–sliding wear surface layer of pearlitic steel was performed with transmission electron microscopy and atom probe tomography to reveal microstructural changes in the pearlite structure. Plastically deformed fine pearlitic lamellae with interlamellar spacing of ～10 nm were observed just beneath the contact surface after the rolling–sliding wear test, where the hardness of the surface reached >800 HV, twice the initial bulk hardness of 400 HV. Lamellar cementite was slightly decomposed, but most lamellar cementite was retained as thinned lamellae in the deformed pearlitic structure. The large increment in hardness was mostly explained by the reduction in interlamellar spacing. The formation mechanism of the microstructure of the worn surface was compared with that of the white etching layer on the pearlitic rail surface.     

Effect of water absorption on erosive wear behaviour of polyamides

Two polyamides (PAs) viz. PA 6 and PA 12 were selected for investigating the influence of water absorption on some physical, mechanical and tribological properties. Erosive wear studies on water treated and untreated samples were carried out at two impact angles viz. 30° and 90°. Tests on tensile strength of untreated and treated polyamides revealed that the water treatment resulted in enhancement for PA12 and reduction for PA 6. Exactly similar trends were reflected in their erosive wear performance also. The water absorption deteriorated the wear performance of PA 6 at both the angles, whereas the erosion wear behaviour of PA 12 improved at both the angles due to water absorption. The improvement was more significant at the angle of 30° rather than 90°. Scanning electron microscopic (SEM) investigations were done to study the topography of worn surfaces and to understand the wear mechanisms.     

Influence of the ion incidence angle of alumina surface cleanness,roughness and topography

Polycrystalline ceramic specimens of 96% sintered alumina and mechanically polished 99.5% alumina were bombarded by Ar^ü ions at an applied voltage of 7 kV at various incident angles from 0 to 1.4 rad (0 to 80°) and at a beam current of about 70 A. The influence of the incidence angle on alumina surface cleanness, roughness and topography was investigated.     

Influence of stiffness and shape of contact surface on skull fractures and biomechanical metrics of the human head of different population underlateral impacts

The objective of this study was to determine the responses of 5th-percentile female, and 50th- and 95th-percentile male human heads during lateral impacts at different velocities and determine the role of the stiffness and shape of the impacting surface on peak forces and derived skull fracture metrics. A state-of-the-art validated finite element (FE) head model was used to study the influence of different population human heads on skull fracture for lateral impacts. The mass of the FE head model was altered to match the adult size dummies. Numerical simulations of lateral head impacts for 45 cases (15 experiments × 3 different population human heads) were performed at velocities ranging from 2.4 to 6.5 m/s and three impacting conditions (flat and cylindrical 90D; and flat 40D padding). The entire force-time signals from simulations were compared with experimental mean and upper/lower corridors at each velocity, stiffness (40 and 90 durometer) and shapes (flat and cylindrical) of the impacting surfaces. Average deviation of peak force from the 50th male to 95th male and 5th female were 6.4% and 10.6% considering impacts on the three impactors. These results indicate hierarchy of variables which can be used in injury mitigation efforts.     

The influence of surface chemistry and topography on the contact guidance of MG63 osteoblast cells

The purpose of the present study was to determine in vitro the effects of different surface topographies and chemistries of commercially pure titanium (cpTi) and diamond-like carbon (DLC) surfaces on osteoblast growth and attachment. Microgrooves (widths of 2, 4, 8 and 10 μm and a depth of 1.5–2 μm) were patterned onto silicon (Si) substrates using microlithography and reactive ion etching. The Si substrates were subsequently vapor coated with either cpTi or DLC coatings. All surfaces were characterized using atomic force microscopy (AFM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and contact angle measurements. Using the MG63 Osteoblast-Like cell line, we determined cell viability, adhesion, and morphology on different substrates over a 3 day culture period. The results showed cpTi surfaces to be significantly more hydrophilic than DLC for groove sizes larger than 2 μm. Cell contact guidance was observed for all grooved samples in comparison to the unpatterned controls. The cell viability tests indicated a significantly greater cell number for 8 and 10 μm grooves on cpTi surfaces compared to other groove sizes. The cell adhesion study showed that the smaller groove sizes, as well as the unpatterned control groups, displayed better cell adhesion to the substrate.     

Metallurgical re-examination of wear modes I: erosive,electrical arcing and fretting

Solid particle erosion, electrical-arc-induced wear, fretting corrosion and fretting wear modes were studied. Scanning electron microscope examinations generally show significant differences in the different wear modes. Further scanning and transmission electron microscope examinations of the cross sections of worn samples show very little, if any, plastic deformation near the worn surfaces. Microhardness measurements on the cross section of arced samples show an increase of about 25% near the worn surface. Surface analysis of fretting and fretting corrosion wear samples show the existence of an adherent layer that is heavily oxidized in most cases. The source of the adherent layer can be either of the two mating surfaces. It was also found that the same surface may undergo both loss of the original surface layer and gain of an adherent layer. The metallurgical techniques described in this paper can be successfully used to diagnose the wear of solid surfaces.     

Effect of stress on abrasive and erosive wear of steels and sprayed coatings

The effect of stress on abrasive and erosive wear was studied for the hypoeutectoid steel, two hypereutectoid tool steels and flame sprayed coatings. In the experiment, the specially designed tester as well as SEM and contact profilometer were applied. Abrasion and erosion remove asperities protruding from the surface of coatings. The imposed stress increased erosive wear of coatings. Application of compressive stress to steels reduces roughness of the wear scar. Compressive stress caused distinct damage localization in abraded and eroded coatings, mean spacing of surface irregularities Rsm observed in erosion test was about 50% larger than in unstressed coatings. Results of fractal analysis confirm stress-induced change in surface topography.     

Carbon fabric reinforced polyetherimide composites: Influence of weave of fabric and processing parameters on performance properties and erosive wear

Woven carbon fabric reinforced (55 vol.%) polyetherimide (PEI) composites were fabricated using three types of weaves viz. plain (P), twill (T), and satin-4 H (S) by impregnation technique. Three more similar composites were fabricated with film technique to study the influence of both, weave of fabric and processing technique on the performance properties of the total seven composites including neat PEI. The composites were evaluated for physical and mechanical properties along with erosion wear behavior studied in identical conditions. In almost all properties viz. tensile strength (TS), modulus (TM), elongation to break (e), flexural strength and modulus, interlaminar shear strength (ILSS), etc., film technique proved far inferior to impregnation technique because of improper wetting of fiber strands, as evidenced by SEM studies. CF reinforcement enhanced all the properties of PEI manifold except elongation to break. None of the weaves proved best performer in all the mechanical properties. In case of erosive wear studies, plain weave composite proved slightly better than satin weave composite. Composite with twill weave proved poorest performer. In case of film technique, however, trends were different where plain weave composite proved poorest and satin proved best. Efforts were made to correlate various strength properties with wear resistance W_R. The factor (elongation × toughness) showed fairly good correlation with W_R. SEM studies were conducted to understand wear mechanisms.     

Flux rate effects in the erosive wear of elastomers

The variation of erosion rate with particle flux was studied for five elastomers (natural rubber and epoxidized natural rubber, both with and without antioxidant, and butyl rubber) whilst subject to erosion by 120m silica particles at 50 m sec^–1. Th.e erosion rate was found to increase at low particle fluxes, for the elastomers without antioxidant. Infrared spectroscopy showed that there was a considerable degree of oxygen incorporation into the elastomer surface during erosion. Studies with an intermittent erosion stream suggest that a transient reaction occurs on impact causing degradation of the elastomer surface, which can account for the variation of erosion rate with particle flux. Studies with a range of erodent particles (silica, alumina, silicon carbide and soda-lime glass beads) showed that the degradation is more pronounced for hydrophilic particles.     

Effect of post-sintering heat-treatments on the erosive wear behaviour of liquid-phase-sintered aluminas

The influence of microstructure on the indentation-strength and solidparticle erosive wear behaviour of a liquid-phase-sintered (LPS)alumina subjected to coarsening, quenching and crystallisationheat-treatments were investigated. Strength as a function of cracksize using Vickers indentations of varying loads was assessed. Theshort-crack toughness curves (T-curves) of the materials wereevaluated from indentation-strength data which is pertinent to wearproperties, since wear is governed by fracture characteristics atsmall flaw sizes. The effects of impact angle and particle velocityon erosive wear rates were also analysed. The relationship betweenshort-crack toughness behaviour and erosion resistance are discussedwith reference to the material microstructures and phase composition.     

Plane contact problem of wear

We solve a two-dimensional contact problem of wear of an elastic half space by a rigid punch. The punch moves with constant velocity, crushes inhomogeneities of the surfaces, and rubs out the half space. Outside the punch the surface of the half space is unloaded. The solution of the problem of the theory of elasticity is constructed by using Fourier integral transformations. Contact stresses are sought in the form of a Fourier series whose coefficients satisfy dual integral equations which can be reduced to a system of nonlinear algebraic equations for unknown coefficients. We also analyze the dependences of contact stresses, wear, and abrasion on time.Franko L'viv State University, L'viv. Translated from Fiziko-Khimicheskaya Mekhanika Materialov, Vol. 31, No. 4, pp. 55–60, July – August, 1995.     

The influence of surface topography on wear debris generation at the cement/bone interface under cyclic loading

The long-term success of a total joint replacement can be undermined by loosening of the implant, generation of wear debris or a combination of both factors. In the present study the influence of the surface morphologies of the bone and cement mantle on loosening of cemented total joint replacements (THJRs) and development of wear debris were studied. Model cemented THJR specimens were prepared in which the femoral canal was textured using specific cutting tools. The specimens were subjected to cyclic loads inducing pure shear fatigue of the cement/bone interface. Changes in both the femoral canal and cement mantle resulting from fatigue were quantified in terms of the surface topography and the volume of wear debris. Loosening occurred with cyclic loading due to degradation of the cement and bone and resulted in the development of cement and bone particles. There was no correlation between the fatigue strength of the interfaces and the volume of wear debris. In general, the change in surface topography of the cement mantle with fatigue decreased with increasing volume of cement interdigitation. Femoral canal surfaces with symmetric profile height distribution (i.e., Gaussian surfaces) resulted in the lowest volume of generated debris.     

Nano-indentation at the surface contact level: applying a harmonic frequency for measuring contact stiffness of self-assembled monolayers adsorbed on Au

In this study, the well-ordered alkanethiolate self-assembled monolayers (SAMs) of varied chain lengths and tail groups were employed as examples for nano-characterization on their mechanical properties. A novel nano-indentation technique with a constant harmonic frequency was applied on SAMs chemically adsorbed on Au to explore their contact mechanics, and furthermore to interpret how SAM molecules respond to an infinitesimal oscillation force without pressing them. Experimental results demonstrated that the harmonic contact stiffness along with the measured displacement of SAMs/Au was distinguishable using a dynamic contact modulus with the distinct feature of phase angles. Phase angles resulted from the relaxing continuation of an applied harmonic frequency and mostly influenced by the outermost tail group of SAM molecules. The harmonic contact stiffness of SAM molecules obviously increased with the densely packed alkyl chains and relatively intense agglomeration of the head group at the anchoring site. As a consequence, the result of this work is relevant to contact mechanics at the surface contact level for the distinction of molecular substances attached on a solid surface. Furthermore it is particularly anticipated to identify biological molecules of variable qualities under a fluid-like micro-environment.     

Influence of deep-cryogenic treatment on wear resistance of vacuum heat-treated HSS

In this paper we compare the wear behaviour of a vacuum heat-treated ESR AISI M2 high-speed steel and the same steel that was vacuum heat treated in conjunction with a deep-cryogenic treatment at −196 °C. Four different tempering temperatures for the specimens austenized at the same austenitizing temperature were carefully selected to obtain various in-advance-determined combinations of the Rockwell-C hardness and the fracture toughness K_Ic. Each of the eight specimens was therefore characterised by these two resulting material properties. The wear behaviours were then compared and discussed in terms of these two properties and the related microstructures. The differences in the wear resistance obtained in our investigation were as high as an order of magnitude. However, the beneficial effects are not a direct result of the type of the treatment, but relate to a proper combination of the resulting fracture toughness and the hardness. The more uniform and moderate (but sufficiently high) values, which tend to be obtained with a deep-cryogenic treatment, are beneficial to the high wear resistance of the selected high-speed steel.