Strahlverschleiß von Stahl mit niedrigem Kohlenstoffgehalt: Untersuchungen zur Verschleißpartikelgeometrie

Erosion of low‐carbon steel by solid particle impingement: aspects of wear debris geometry Image analysis software was used to analyse the geometry of debris formed during the erosion of low‐carbon steel by impinging solid particles. Depending on the two‐dimensional aspect ratio (ratio between debris height and debris width), three different debris types could be distinguished. The most frequent type observed was a platelet‐type debris as suggested by the Bellman‐Levy (1981) model. This wear debris shape type covered about 60 % of all acquired debris. Plain micro‐machining according to Finnie’s (1959) suggestion played a negligible role only, but other processes, namely ploughing as suggested by Winter and Hutchings (1974), were more important. The statistically estimated mean debris size was about 14 μm. About 92 % of all wear debris had sizes smaller than the target material grain size. This result supports the figure that multi‐step removal modes – the formation and detachment of lip or platelet from crater rims ‐ were responsible for material removal.     

Quantitative analysis of the wear and wear debris from low and high carbon content cobalt chrome alloys used in metal on metal total hip replacements

The biological reactions to polyethylene wear debris have been shown to result in osteolysis and loosening of total hip arthroplasties. This has led to renewed interest in the use of metal on metal bearings in hip prostheses. This study employed uniaxial and biaxial multistation pin on plate reciprocators to assess how the carbon content of the cobalt chrome alloy and the types of motion affected the wear performance of the bearing surfaces and the morphology of the wear debris generated.The low carbon specimens demonstrated higher wear factors than both the mixed carbon pairings and the high carbon pairings. The biaxial motion decreased the wear rates of all specimens. Plate wear was significantly reduced by the biaxial motion, compared to pin wear. The metal wear particles isolated were an order of magnitude smaller than polyethylene particles, at 60–90 nm, and consequently, 100-fold more particles were produced per unit volume of wear compared to polyethylene. The low carbon specimens produced significantly larger particles than the other material combinations, although it is thought unlikely that the difference would be biologically significant in vivo.The volumetric wear rates were affected by the carbon content of the cobalt chrome alloy, the material combination used and type of motion applied. However, particle morphology was not affected by the carbon content of the alloy or the type of motion applied. ©©1999©Kluwer Academic Publishers     

Investigation of sliding wear surfaces in alumina using transmission electron microscopy

In this study, the subsurface microstructure of alumina wear surfaces and the microstructure of agglomerated debris generated from unlubricated sliding wear at room temperature have been investigated through transmission electron microscopy (TEM). Specimens were thinned through the use of a focused ion beam miller (FIB). TEM studies, including analysis of electron diffraction patterns from the agglomerated region of the specimen, revealed the presence of an aggregate of nano crystalline particles embedded in an amorphous phase, together with some larger alumina particles. These larger alumina particles appear at the base of pits in the alumina surface, whereas the finer material appears at the contact surface. The agglomerated debris was readily distinguished from the alumina substrate, which contained localised dislocation damage and microcracking. It is proposed that the wear process involves the removal of ‘large’ alumina particles from the surface by a combination of trans- and intergranular microcracking. These particles are then ground into very fine, nanometer-sized particles that react on the surface with moisture in the air to form an amorphous hydroxide film. These are then compacted to form a nanocrystalline structure within an amorphous matrix that may also be viewed as a grain boundary phase.     

Quantitative analysis of polyethylene wear debris, wear rate and head damage in retrieved Charnley hip prostheses

Submicrometer- and micrometer-sized ultra-high molecular weight polyethylene (UHMWPE) wear particles have been associated with osteolysis and failure of total artificial joints. Previous studies have isolated predominantly submicrometer-sized particles at the expense of larger particles (>10 m). This study aimed to isolate and characterize quantitatively all sizes of UHMWPE wear particles generated in 18 Charnley hip prostheses. In addition, to analyze the wear debris with respect to the total volumetric wear of the cup and damage to the femoral head. Particle size distributions ranged from 0.1 to ->1000 m. A significant proportion (3–82%) of the mass of the wear debris isolated was>10 m. The mode of the frequency distribution of the particles was in the range 0.1–0.5 m for all patients. However, analysis of the mass of wear debris as a function of its size allowed differentiation of the wear debris from different patients. Femoral head damage was associated with high volumetric wear and increased numbers of biologically active submicrometer-sized particles.     

Debris effect on the surface wear and damage evolution of counterpart materials subjected to contact sliding

This paper aims to explore the debris effect on surface wear and damage evolution of counterpart materials during contact sliding. A cylinder-on-flat testing configuration is used to investigate the wear behaviours of the contact pair. To explore the roles of wear debris, compressed air is applied to remove the debris in sliding zones. The comparative study demonstrates that the influence of debris removal is related to the surface properties of contact pairs. When substantial wear debris accumulates on the tool surface, debris removal can considerably alter surface damage evolution, resulting in different friction transitions, distinct surface morphology of contact pair, as well as different rates of material removal. It has been found that the surface damage evolution will not reach a stable stage unless the increase of wear particle number ceases or the average size of wear particles becomes lower than a specific threshold. However, the influence of debris removal reduces when the adhesion between the contact pair materials gets smaller.The full text can be downloaded at https://link.springer.com/article/10.1007/s40436-021-00377-8     

Corrosion behaviour and mechanical properties of functionally gradient materials developed for possible hard-tissue applications

Artificial hip joints have an average lifetime of 10 years due to aseptic loosening of the femoral stem attributed to polymeric wear debris; however, there is a steadily increasing demand from younger osteoarthritis patients aged between 15 and 40 year for a longer lasting joint of 25 years or more. Compliant layers incorporated into the acetabular cup generate elastohydrodynamic lubrication conditions between the bearing surfaces, reduce joint friction coefficients and wear debris production and could increase the average life of total hip replacements, and other human load-bearing joint replacements, i.e. total knee replacements. Poor adhesion between a fully dense substrate and the compliant layer has so far prevented any further exploitation. This work investigated the possibility of producing porous metallic, functionally gradient type acetabular cups using powder metallurgy techniques – where a porous surface was supported by a denser core – into which the compliant layers could be incorporated. The corrosion behaviour and mechanical properties of three biomedically approved alloys containing two levels of total porosity (>30% and <10%) were established, resulting in Ti–6Al–4V being identified as the most promising biocompatible functionally graded material, not only for this application but for other hard-tissue implants.     

The prediction of polyethylene wear rate and debris morphology produced by microscopic asperities on femoral heads

Counterface damage in the form of scratches, caused by bone cement, bone or metallic particles, has been cited as a cause of increased wear of ultra-high molecular weight polyethylene (UHMWPE) acetabular cups. It is known that high levels of particulate wear debris lead to osteolysis. Surface damage was characterized in a series of explanted Charnley femoral heads. The heads had a mean scratch height of 1 m with a mean aspect ratio (defined as height divided by half width) of 0.1. Wear discs were artificially scratched using these scratch geometries as a guide. In addition, the scratch geometries were incorporated into a finite element model of a stainless steel asperity repeatedly sliding over UHMWPE under conditions similar to those in an artificial hip joint. Wear tests showed a strong correlation between the average cross-sectional area of the scratch lip above the mean zero line and the measured wear factor. The finite element model predicted increases in the area of UHMWPE suffering plastic strain with increases in the cross-sectional area of the asperity above the mean line. Analysis of the wear debris showed the mode of the particle size was 0.01–0.5 m for all cases. The morphology of the particles varied with aspect ratio of the asperity, with an increased percentage mass of submicrometer-sized debris with increased scratch lip aspect ratio. The finite element results predicted that the maximum surface strains would increase with increasing asperity aspect ratio. Examination of the worn UHMWPE pin surfaces showed an association between increased surface damage, probably due to high surface strains, and increased aspect ratio. The large areas of surface plastic strain predicted for asperities with high cross-sectional areas above the mean line offer an explanation for the positive correlation between wear rate and the average cross-sectional area of the scratch lip material. The higher surface strains predicted for the higher aspect ratios may explain the increased percentage mass of biologically active submicrometer-sized wear particles found for scratch lips with higher aspect ratios. ©©2000 Kluwer Academic Publishers     

Dry sliding wear behavior of cast SiC-reinforced Al MMCs

Dry sliding block-on-ring wear tests were performed on a squeeze cast A390 Al alloy, a high pressure die cast 20%SiC–Al MMC, and a newly developed as-cast 50%SiC–Al MMC. The testing conditions spanned the transition that control the mild to severe wear for all materials. The results show that the sliding wear resistance increases as SiC particle volume fraction increases. The critical transition temperature, at which wear rates transit from mild to severe, also increases with increasing SiC content. Examination of the wear surfaces, the subsurface characteristics, and the wear debris indicate that a hard ‘mechanically alloyed’ layer, high in SiC content, forms on the sliding surface of the 50%SiC composite. This layer prevents the surface adhesion wear mechanisms active in the A390 alloy, and it inhibits delamination wear mechanisms that control the mild wear of the 20%SiC composite. As a result, mild wear of the 50%SiC composite occurs by an oxidation process. In the 20%SiC material, severe wear occurs as a consequence of material removal by a flow-related extrusion-like process. In contrast, the high SiC content prevents plasticity in the 50%SiC composite, which eventually is susceptible to severe wear at very high temperatures (≈450 °C) due to a near-brittle cracking processes.     

Studies on the development of aluminium alloy–mild steel reinforced composite

With a view to developing a new metal–metal cast composite material as a possible substitute for ferrous materials in wear resistant applications, Al alloy (LM11) is reinforced with mild steel (ms) wires and it is heat treated to get ‘reaction interface’ (RI). Microhardness, tensile properties and wear characteristics of the matrix, as-cast and heat treated composites have been determined. While microhardness of the composite showed variation from 150 to 45 VHN across the interface in the as-cast composite, annealed (500–525°C) composite showed a microhardness of 350–420 VHN at the interface indicating the effectiveness of the heat treatment. It is seen that the % improvement in wear resistance increased with increase in number of wires when embedded in the aluminium alloy matrix. Further imrpovement of about 30% was observed when heat treated at 500°C for 15 h. These results have been discussed in terms of wetting between ms wires and the matrix, particularly the increase of hardness and tensile strength to the formation of ‘reaction interface’ due to annealing. The width of the interface increased with annealing time and temperature and the kinetics of reaction followed logarithmic and parabolic growth rate. The activation energy for the formation of intermetallics constituting the reaction interface is found to be 20.7 KJ mol⁻¹. From the measured hardness and ultimate tensile strength of the constituents and composites an empirical relation was deduced.     

Carbon–carbon composite bearing materials in hip arthroplasty: analysis of wear and biological response to wear debris

Ultra-high molecular weight polyethylene wear particles have been implicated as the major cause of osteolysis, implant loosening and late aseptic failure in total hip arthroplasties in vivo. This study initially screened 22 carbon-carbon composite materials as alternatives for UHMWPE in joint bearings. New bearing materials should satisfy certain criteria--they should have good wear properties that at least match UHMWPE, and produce wear particles with low levels of cytotoxic and osteolytic activity. Initial screening was based on wear resistance determined in short-term tribological pin-on-plate tests. Three materials (HMU-PP(s), HMU-RC-P(s), and SMS-RC-P(s)) which had superior wear resistance were selected for long-term testing. All materials had very low wear factors and SMS-RC-P(s), which had a wear factor of 0.08 +/- 0.56 x 10(-7) mm3/Nm, was selected for the subsequent biological testing and particle size analysis. SMS-RC-P(s) showed good biocompatibility in bulk material form and also the wear particles had low cytotoxicity for L929 fibroblasts in culture compared to metal wear particles. Wear debris size analysis by transmission electron microscopy showed that the particles were very small, with the vast majority being under 100 nm in size, similar to metal wear particles. The potential osteolytic effect of SMS-RC-P(s) wear particles was investigated by culturing particles with human peripheral blood mononuclear cells and measuring TNFalpha production. SMS-RC-P(s) did not significantly stimulate TNFalpha production at a particle volume to cell number ratio of 80:1, indicating that the debris had a low osteolytic potential. The results of this study suggest that carbon-carbon composites, particularly those composed of PAN-based fibers may be important biomaterials in the development of next generation bearing surfaces for use in total joint replacements that have very low wear rates and reduced osteolytic and cytotoxic potential.     

Slotted electrodes for the improvement of machining performances in EDM drilling

In electrical discharge machining (EDM), poor debris removal may occur under certain conditions. This leads to debris accumulation and degrades machining efficiency. In this study, the rotation and retracting movements of slotted electrodes were coordinated during EDM to realize a pumping effect for expelling debris in the gap between the electrodes and workpieces. The study compared the performance of different slotted electrodes with that of a regular cylindrical (RC) electrode. Moreover, a computational fluid dynamics module was adopted to simulate the effects of the RC and slotted electrodes on debris removal capability in EDM under different conditions. The experimental results demonstrated that among all slotted electrodes, the deep slotted electrode engendered the most-favorable debris removal capability. The deep slotted electrode saved machining time by shortening the electrode jump time or even obviating electrode jumping. This increased the material removal rates by 120%–153% during EDM drilling.     

Effects of thermo-mechanical processing parameters on the special boundary configurations of commercially pure nickel

The roles of plastic strain, annealing temperature, and annealing time in affecting the fraction of special boundaries (Fsp), and twin densities of thermo-mechanically processed commercially pure nickel are examined. Different strain levels were achieved by cold rolling the material at different amounts. One-step low strain-recovery processing with strain levels in the range of 3.0–7.5% and annealing temperatures in the range 800–1000 °C were conducted in order to ensure that recrystallization did not occur. From orientation image microscopy analysis it was found that the fraction of special boundaries increased from about 30% for the as-received material to almost 80% for plastically deformed and annealed material. This showed that material strained in the range from 3.0% to 7.5% and annealed at 800 °C for different times all reached Fsp values in the range 75–80%, a considerable increase over the as-received material. Various multi-processing cycle treatments did not increase the fraction of special boundaries to above the value of 80% achieved in single processing cycles.TEM observations indicated dislocation tangles/cells occurred near grain boundaries in material strained at 6%. The density of these dislocation tangles decreased with annealing time at 800 °C and was reduced considerably after 20 min.Experimental results for the variation of twin density with grain size showed that the twin density decreased with increase in grain size. However, there was a tendency for the twin density to decrease more slowly with increase in grain size in the more highly strained samples. The experimental data for twin density were compared with values calculated from the equation suggested by Pande et al. [1]. With appropriate choice of the two variable parameters in the equation, a good “average” fit for all the data was obtained. However, the effect of plastic strain on the twin density could not be accommodated in the model.The experimental twin density–grain size relationship was also compared to values calculated from the formulation developed by Gleiter [2] modified to accommodate the effects of prior plastic train on the twin densities of annealed samples. Calculations from the modified model followed the observed trend that twin densities for the more highly deformed samples decreased more slowly with grain size than those for lesser strained samples. Good quantitative agreement between the experimental values of twin density and those calculated from the modified Gleiter formulation was achieved.     

A Methodology for Determining the Proper Point Size for Display Type on Packaging by Means of the Package's Proportions

The point size of display text on a package was evaluated relative to package proportion with the use of a preference test. This test involved 150 participants examining packaging images showing the product name in various point sizes and being asked their preference. A cascading presentation method modelled after the binary search algorithm was used to determine the exact point size preference for each participant. Participants also completed a survey intended to gather information regarding their motives for their choice. This study was developed to determine the optimal display type size of a package on the basis of its relationship with the package's proportions. It was hypothesized that this proportion would be related to the golden ratio (a ratio of about two‐thirds) that has been suggested to be a particularly aesthetic proportion throughout nature and human history. The results of the study showed that the preferred ratio was actually greater than the golden ratio, equaling 10/12 of the package's width. These results were found to be further influenced by the participant's gender and the packaging structure on which the display type is applied. Although the results are not generalizable to all demographics and products, the methodology used is easily extensible to arbitrary product types. We propose that this methodology for evaluating type size on packages be used by designers as part of the package creation process. Copyright © 2014 John Wiley & Sons, Ltd.     

The influence of third-body particles on wear rate in unicondylar knee arthroplasty: a wear simulator study with bone and cement debris

The reduced intraoperative visibility of minimally invasive implanted unicondylar knee arthroplasty makes it difficult to remove bone and cement debris, which have been reported on the surface of damaged and retrieved bearings. Therefore, the aim of this study was to analyze the influence of bone and cement particles on the wear rate of unicompartmental knee prostheses in vitro. Fixed bearing unicompartmental knee prostheses were tested using a knee-wear-simulator according to the ISO standard 14243-1:2002(E) for 5.0 million cycles. Afterwards bone debris (particle size 671 ± 262 μm) were added to the test fluid in a concentration of 5 g/l for 1.5 million cycles, followed by 1.5 million cycles blended with cement debris (particle size 644 ± 186 μm) in the same concentration. Wear rate, knee-kinematics and wear-pattern were analyzed. The wear rate reached 12.5 ± 1.0 mm³/million cycles in the running-in and decreased during the steady state phase to 4.4 ± 0.91 mm³/million cycles. Bone particles resulted in a wear rate of 3.0 ± 1.27 mm³/million cycles with no influence on the wear rate compared to the steady state phase. Cement particles, however, lead to a significantly higher wear rate (25.0 ± 16.93 mm³/million cycles) compared to the steady state phase. The careful removal of extruded cement debris during implantation may help in reducing wear rate. Bone debris are suggested to have less critical influence on the prostheses wear rate.     

Effect of load and reciprocating velocity on the transition from mild to severe wear behavior of Al–Si–SiCp composites in reciprocating conditions

In the present paper, the effect of normal load and reciprocating velocity on transition from mild to severe wear of A319/15%SiC_p, A336/15%SiC_p, and A390/15%SiC_p composites have been reported. Composites were produced through liquid metal metallurgy route. Adhesive wear behavior of composites was studied under dry reciprocating conditions using indigenously developed reciprocating friction wear test rig conforming to ASTM Standard G133-05. It was found that increase in normal load increases wear rate and depending upon the reciprocating velocity and type of composites, mode of wear changes from mild oxidative to severe metallic wear was noticed. The load corresponding to the transition from mild to severe wear usually termed as transition load was found to decrease with increase in reciprocating velocity and reduction in silicon content in the alloys used for the development of Al–Si–SiC_p composites. At 1 m/s reciprocating velocity, the transition load for A319/15%SiC_p, A336/15%SiC_p and A390/15%SiC_p composites were found to be in the range of 60–90 N, 60–105 N and 60–120 N respectively. Scanning electron microscope (SEM) study of wear surface and wear debris were conducted to analyze the mode of wear and operating wear mechanism. Severe wear was characterized by massive plastic deformation and gross material removal while the mild wear was found to be associated with delamination and scoring as main wear mechanisms responsible for material loss. Wear mechanism maps for different Al–(6–18)%Si–15%SiC_p composites were proposed in reciprocating contacts.     

Effect of the SiC particle size on the dry sliding wear behavior of SiC and SiC–Gr-reinforced Al6061 composites

The effect of size of silicon carbide particles on the dry sliding wear properties of composites with three different sized SiC particles (19, 93, and 146 μm) has been studied. Wear behavior of Al6061/10 vol% SiC and Al6061/10 vol% SiC/5 vol% graphite composites processed by in situ powder metallurgy technique has been investigated using a pin-on-disk wear tester. The debris and wear surfaces of samples were identified using SEM. It was found that the porosity content and hardness of Al/10SiC composites decreased by 5 vol% graphite addition. The increased SiC particle size reduced the porosity, hardness, volume loss, and coefficient of friction of both types of composites. Moreover, the hybrid composites exhibited lower coefficient of friction and wear rates. The wear mechanism changed from mostly adhesive and micro-cutting in the Al/10SiC composite containing fine SiC particles to the prominently abrasive and delamination wear by increasing of SiC particle size. While the main wear mechanism for the unreinforced alloy was adhesive wear, all the hybrid composites were worn mainly by abrasion and delamination mechanisms.     

Characterization of Properties of Cryogenically Treated Al-SiC Composites Fabricated by Powder Metallurgy

The basis of this research was an exploration of the fundamental phenomena that determine the response of silicon carbide-reinforced aluminium composite material to thermal cycling between cryogenic and ambient temperatures. This analysis began with a phenomenological approach that investigated the role of the production, processing, and machining of composite materials, and led to study of their mechanical behavior at cryogenic temperatures. Electric discharge machining was done on the composite specimens and mathematical models were developed for predicting the machining parameters such as metal removal rate, tool wear rate, and surface roughness. A five-level factorial design was chosen for experimentation and mathematical models were developed using the software DOE-PC IV. An analysis of variance technique was used to calculate the regression coefficients and to check the significance of the models developed. This approach provided an understanding of how temperature and vol.% of SiC influence composite machining behavior. The hardness, wear resistance, and tensile property are high for cryo-treated specimens and these properties reduce with increase in temperature. The properties also increase with increasing % of SiC reinforcements. The microstructures of the wear specimens show worn-out layers and grooves formed in the debris. The cryo-treated and the higher reinforced specimens exhibit less material removal and tool wear rate and this increases with increase in temperature. There is a relatively higher surface roughness when there is greater material removal.     

Factors controlling dry sliding wear behaviour of a leaded tin bronze

The sliding wear behaviour of a leaded tin bearing bronze was investigated over a range of applied pressures and sliding speeds with respect to the influence of microconstituents such as lead on the wear response. Significantly high wear rates were found at the minimum sliding speed due to extensive microcracking. This was evinced by the formation of coarse debris and considerable subsurface/wear surface cracking. The (micro) cracking tendency of the alloy prohibited the occurrence of subsurface deformation. The absence of a lead film was primarily due to the lead particles being engulfed in the coarse debris. Higher sliding speeds led to increased frictional heating making the alloy matrix viscoplastic. This in turn greatly suppressed the tendency of the alloy to exhibit microcracking, thereby facilitating interaction between the materials of the mating surfaces through wear induced plastic deformation. As a result, a stable transfer layer formed on the specimen surface. Interestingly, the formation of a lead film on the wear surface was also observed under these conditions. The above factors were mainly responsible for the improved wear behaviour of the alloy at higher speeds. Finer debris formation, less surface and subsurface damage, and the presence of both a deformed and stable transfer layer and a lead film strongly supported these observations. Material removal mechanisms involved delamination of the undeformed subsurface region causing chipping off at the minimum sliding speed. Higher speeds, however, caused delamination of the transfer layer. In addition to adhesion, three body abrasion was found to contribute considerably towards material removal. The formation and stability of a transfer layer and the presence of a lead film are at least two major factors which control the wear behaviour of leaded tin bronzes. It is found that the above phenomena which provide improved wear characteristics occur only under specific sliding conditions.

MST/3218     

Synthesis,characterization and structural refinement of polycrystalline uranium substituted zirconolite

Ceramic precursors of Zirconolite (CaZrTi₂O₇) family have a remarkable property of substitution on Zr^{4 +} cationic sites. This makes them potential material for nuclear waste management in ‘synroc’ technology. In order to simulate the mechanism of partial substitution of zirconium by tetravalent actinides, a solid phase of composition CaZr_0.95U_0.05Ti₂O₇ has been synthesized through ceramic route by taking calculated quantities of oxides of Ca, Ti and nitrates of uranium and zirconium respectively. Solid state synthesis has been carried out by repeated pelletizing and sintering the finely powdered oxide mixture in a muffle furnace at 1050°C. The polycrystalline solid phase has been characterized by its typical powder diffraction pattern. Step analysis data has been used for ab initio calculation of structural parameters. The SEM and EDAX analysis also confirm that zirconolite acts as a host material for uranium. The powder diffraction data of 3500 points between 2θ = 10–80° has been analysed by GSAS (general structure analysis system) software to obtain the best fit of the observed data points. The uranium substituted zirconolite crystallizes in monoclinic symmetry with space group C2/c (#15). The following unit cell parameters have been calculated: a = 12.4883(15), b = 7.2448(5), c = 11.3973(10) and β = 100.615(9)°. The calculated and observed values of the intensities, lattice parameters and density measurement shows good agreement. The Rietveld analysis and GSAS based calculations for bond distance Ti—O, Ca—O, Zr—O, and O—M—O bond angles have been made. The structure was refined to satisfactory completion.The and Rp and Rwp are found to be 7.48 and 9.74 % respectively.