Unworn Areas Research Articles

Dry sliding wear behaviour of ZrB2-based ceramics: Self-mated and cross coupling with alumina

Systematic dry sliding wear tests with monolithic ZrB2 and Al2O3 pins coupled to ZrB2, ZrB2-20 vol% SiC and Al2O3 discs were carried out in a disc-on-pin configuration. The steady state friction of ZrB2 self-mated or cross coupled with Al2O3 was about 1.1. Self-mated monolithic ZrB2 discs worn about three orders of magnitude more than self-mated Al2O3 discs. ZrB2 pin wear rate was almost double when coupled to ZrB2 or ZrB2-20 vol% SiC discs than when coupled to Al2O3 discs. The wear track of ZrB2-based materials showed an oxygen increment due to humidity-driven tribo-reaction. In all the systems, the main wear mechanisms observed were microfracture and abrasion. Numerical calculations and fracture models were employed to describe the wear mechanisms. By nanoindentation tests on worn and unworn areas, a significant lower hardness of the debris layer formed when ZrB2 materials were involved.

Tribocorrosion properties of AISI 1045 and AISI 2205 steels in seawater: Synergistic interactions of wear and corrosion

Tribocorrosion denotes an irreversible material degradation for several metallic components used in corrosive environments, and it arises from the interplay between chemical, mechanical, and electrochemical processes. In this study, some investigation has been performed to compare the tribocorrosion behavior of AISI 1045 steel and AISI 2205 duplex stainless steel sliding against an alumina pin in seawater. The lowering in the open circuit potential (OCP) of AISI 2205 during the tribocorrosion demonstrates that its protective passive film was damaged by wear and resulted in a wear-accelerated corrosion in the wear track. However, sliding was found to accelerate the corrosion of the unworn areas for AISI 1045, leading to an anodic shift of the OCP. Moreover, the total material loss increased with an increase in the applied potential for both materials. It was revealed that AISI 1045 was more sensitive to corrosion under sliding than AISI 2205. Therefore, pure corrosion loss and corrosion-induced wear constituted the primary reasons for the degradation of AISI 1045 at applied anodic potentials.

Research on Reverse Measuring Method of Screw Drill Rotor Based on Axis Section

The screw drilling tool is an important underground power tool in the oil fields. During the working process, the rotor will be damaged or unevenly worn. The repair and reuse of the damaged area of the rotor will greatly improve the utilization rate of the screw drilling tool and reduce the mining cost. To this end, based on the formation principle of the rotor surface of the five-head screw drill, the curve coordinates are described by the ray length and the rotation angle. The axis relationship equation is characterized by exploring the intrinsic relationship between the two coordinates, and the reverse model of a single screw drill rotor was constructed by point collection. At the same time, the experimental research was carried out to verify the feasibility of modeling the screw drilling tool according to the axial section. In order to provide an effective way to reverse the entire body based on the unworn area of the screw drilling tool, the inverse modeling theory of the spiral surface entity is greatly enriched.

Effect of Laser Shock Peening on the Wear–Corrosion Synergistic Behavior of an AZ31B Magnesium Alloy

AbstractLaser shock peening (LSP) is one of the widely used surface processing techniques for tailoring functional behavior of surfaces. LSP has been used to enhance friction, wear, and mechanical properties. However, understanding of LSP-treated surfaces involving tribological contacts in electrochemically active environments is limited because the mechanism of wear–corrosion interactions (tribocorrosion) for such surfaces is still unclear. In the present study, the effect of LSP on the wear–corrosion behavior of an AZ31B Mg alloy is investigated. A zero-resistance ammeter (ZRA) method is utilized to examine the evolution of open circuit potential (OCP) during wear–corrosion analysis. The study finds that the LSP processing can decrease the corrosion potential difference between worn and unworn regions of the surface, thereby mitigating the effect of wear-accelerated corrosion during sliding. The effect of wear-accelerated corrosion is evident from the change in average surface roughness (Sa) of the unworn areas. It is found that understanding the change in surface roughness due to wear–corrosion interactions is necessary to investigate the onset and propagation of galvanic corrosion. Based on these results, the study details the mechanism of wear–corrosion interactions during sliding.

High-translucent yttria-stabilized zirconia ceramics are wear-resistant and antagonist-friendly

ObjectivesTo evaluate two-body wear of three zirconia ceramics stabilized with 3, 4 and 5mol% yttria and to compare their wear behavior with that of a lithium-disilicate glass-ceramic. MethodsSixteen rectangular-shaped specimens made from three grades of zirconia ceramics and a lithium-disilicate glass-ceramic were polished and dynamically loaded in a chewing simulator (2kg vertical load, 2.1Hz) under water at 90°C for 1.2×106 cycles (about 7 days) in the ball-on-plate mode against steatite antagonists. Surface roughness was measured before and after wear testing. Wear tracks were scanned with a non-contact 3D profilometer and super-impositions were used to determine wear loss of the antagonists. Wear surfaces were imaged by SEM. XRD and micro-Raman spectroscopy were used to characterize phase transformation and stress status in the worn and unworn areas of the zirconia ceramics. ResultsIndependent of fracture toughness, strength and aging-susceptibility, the three zirconia ceramics showed a similar and limited amount of wear (∼10μm in depth) and were more wear-resistant than the lithium-disilicate glass-ceramic (∼880μm in depth). Abrasive wear without obvious cracks was observed for all investigated zirconias, whereas the glass-ceramic with a lower fatigue threshold and high susceptibility to surface dissolution exhibited significant abrasion, fatigue and corrosion wear. All three zirconia ceramics yielded a lower antagonist wear than the glass-ceramic and no significant differences were found between the zirconia ceramics. SignificanceIn the context of this study, high-translucent zirconia ceramics stabilized with a higher yttria content, recently introduced in the dental field, were as wear-resistant and antagonist-friendly as conventional high-strength zirconia and suitable for monolithic restorations.

Combined wear and ageing of ceramic-on-ceramic bearings in total hip replacement under edge loading conditions

Ceramic-on-ceramic bearings in total hip replacement have shown the potential to provide low wear solutions in hip replacement. Assessing the tribological performance of these materials is important to predict their long-term performance in patients. In this study, a methodology was devised to assess the tribological in vitro behaviour of composite ceramics under combined adverse edge loading conditions and accelerated ageing. Two commercial ceramic composites were considered, namely Alumina-Toughened Zirconia (ATZ, ceramys®) and Zirconia-Toughened Alumina (ZTA, symarec®). The bearing couples were studied using the Leeds Mark II hip joint simulator for a total of eight million cycles, the first two million under normal gait (no edge loading) and the following six million cycles with the addition of edge loading conditions driven by medial-lateral separation. The bearing couples underwent hydrothermal ageing using an accelerated protocol in autoclave every million cycles.The influence of edge loading combined with ageing was significant for ATZ bearings, resulting in a slower overall ageing kinetics over the wear stripe than on the control heads. During the autoclave ageing steps, the monoclinic fraction increased more over the wear stripe area than over the unworn area. Both results thus indicated that the monoclinic phase was removed during shocks induced by edge loading. The wear performance of the two materials were similar exhibiting relatively low wear rates and low level of microstructural damage for these clinically relevant adverse conditions.

Hip simulator testing of the taper-trunnion junction and bearing surfaces of contemporary metal-on-cross-linked-polyethylene hip prostheses.

Adverse reaction to metal debris released from the taper-trunnion junction of modular metal-on-polyethylene (MoP) total hip replacements (THRs) is an issue of contemporary concern. Therefore, a hip simulator was used to investigate material loss, if any, at both the articulating and taper-trunnion surfaces of five 32-mm metal-on-cross-linked-polyethylene THRs for 5 million cycles (Mc) with a sixth joint serving as a dynamically loaded soak control. Commercially available cobalt-chromium-molybdenum femoral heads articulating against cross-linked polyethylene (XLPE) acetabular liners were mounted on 12/14 titanium (Ti6Al4V) trunnions. Weight loss (mg) was measured gravimetrically and converted into volume loss (mm3 ) for heads, liners, and trunnions at regular intervals. Additionally, posttest volumetric wear measurements of the femoral tapers were obtained using a coordinate measuring machine (CMM). The surface roughness (Sa) of femoral tapers was measured posttest. After 5 Mc, the mean volumetric wear rate for XLPE liners was 2.74 ± 0.74 mm3 /Mc. The CMM measurements confirmed material loss from the femoral taper with the mean volumetric wear rate of 0.045 ± 0.024 mm3 /Mc. The Sa on the worn area of the femoral taper showed a significant increase (p < 0.001) compared with the unworn area. No other long-term hip simulator tests have investigated wear from the taper-trunnion junction of contemporary MoP THRs. © 2019 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 108B:156-166, 2020.

Reply to the Letter to the Editor: Five Hundred Fifty-five Retrieved Metal-on-metal Hip Replacements of a Single Design Show a Wide Range of Wear, Surface Features, and Histopathologic Reactions.

To the Editor, We appreciate the opportunity to reply to Dr. Langton’s recent letter to the editor regarding our study [13]. The primary question Dr. Langton raises is why we decided against reporting head-cup clearance (difference between head and cup diameters) for the 555 retrievals. Unfortunately, there is only so much information that can be included in one research article. As it stands, the study included 26 graphs and photos and two tables, occupying a total of 18 pages of the Journal. Reporting clearance data in isolation would not be sufficient. We have been analyzing several variables available in our ASR (DePuy Inc, Warsaw, IN, USA) cohort including clearance and will be presenting these results in upcoming submissions for publication in peer-reviewed journals. As an example, we have a study, currently in press [10], that focuses on 42 ball and cup pairs, which had the largest amounts of volumetric wear (> 100 mm3 combined ball and cup wear) in our ASR collection. The range of clearance values in these 42 pairs was comparable to the remaining pairs which had < 100 mm3 of volumetric wear, with no statistically significant differences. While the presentation of our complete findings regarding clearance is beyond the scope of a letter to the editor, suffice to say we found that there was no correlation of wear against clearance in this cohort. In addition, we did not observe any correlation between clearance and bone attachment to the cup in our large cohort. The revision rates of the ASR reported by major joint registries are well known [1, 12] but to date, there are no straightforward explanations to universally account for all or the majority of these revisions. We disagree with Dr. Langton’s proposed explanation, that is, extremely low clearance has led to cup deformation, high wear, or component loosening in these retrievals. This hypothesis is not supported by the data in the present study’s large cohort of retrieved ASR pairs [13]. Dr. Langton invites us to comment on the correspondence between himself and the London Implant Retrieval Center [4-7]. In reading the original correspondence, Dr. Langton asked Hothi and colleagues [6] whether they could confirm or refute evidence that a substantial number of ASR components were produced out of tolerance with respect to the bearing diameters, resulting in extremely low clearance values. In his letter to us, rather than discussing tolerances, Dr. Langton states that the UK retrieval center “chose not to report the dimensions of the components.” Some clarification of terminology is in order. In their article, Hothi and colleagues [5] reported wear depth maps and volumetric wear. These are the primary quantities of interest that virtually all retrieval studies of metal-on-metal implants that report wear volume provide, including Dr. Langton’s own studies [8, 9]. These quantities are obviously calculated using unworn surfaces to estimate the initial dimensions of the bearing surfaces. However, the question of whether a retrieved implant was initially manufactured out of tolerance is a different question. Analyzing this question requires comparing the estimated initial dimensions, including diameter, sphericity and clearance, to the manufacturer’s specified tolerances. The errors involved in arriving at these estimations must also be kept in mind. These include the measurement accuracy, quality and size (surface area) of the unworn surface on each component, the ability to accurately identify the unworn area, and, last but not least, the choice of numerical method to calculate the wear volume [3, 11]. Given the best of all possible conditions, the accuracy of the estimation of wear volume can be as low as 1 mm3. Finally, Dr. Langton states that our conclusion that decreased cup coverage angle of the ASR may have reduced the risk of impingement “is not accurate.” Our conclusion is based on the lack of observable evidence for impingement or dislocation in our large retrieval cohort, which includes 532 total hip replacement retrievals and 23 resurfacing implants. Dr. Langton’s statement, that the ASR’s reduced articular coverage angle does not confer a greater ROM [8], is apparently based on laboratory measurements of hip resurfacing bearing couples, which are shown to have less ROM than total hip replacements [2]. Be that as it may, our conclusion regarding impingement is based on the observations and analysis of 555 ASR retrievals but clearly, reasonable minds can disagree.

Origins of material loss in highly worn acetabular cups of metal-on-metal total hip replacements.

Excessive wear has been one of the major failure modes of metal-on-metal hip implants. From a collection of 541 retrieved ASR metal-on-metal implants, we selected those head-cup pairs with combined wear >100 mm3 , (N = 42) to assess the distributions of wear volume on cups, and non-conformance in the worn areas at the head-cup interfaces. All 42 had severe cup edge wear (average maximum wear depth 500 μm). On average, 58% of wear volume of cups occurred at the edge areas, whereas 42% occurred well inside the socket, indicating that substantial wear volume of cups was generated well inside the socket. Particularly, in eight cups, more than half of the wear volume occurred well inside the socket. The head-cup conformance in the worn areas was deteriorated. On average, in worn areas, head-cup clearance was approximately eight times greater than in unworn areas, and the sphericity of heads and cups was approximately 36 times and 84 times higher, respectively, than in unworn areas. The radius of curvature of the worn surfaces of heads and cups varied widely, with an average variation of 3 mm (0.6-7 mm) and 11 mm (2-47 mm) for heads and cups, respectively. The severely deteriorated conformance at the edge areas and the areas well inside the socket, due to edge contact, could be the major factor for excessive wear of these 42 pairs. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res.

Characterisation of wear areas on UHMWPE total knee replacement prostheses through study of their areal surface topographical parameters

Total knee replacement is one of the most common elective surgeries in the world, and presents a number of challenges related to the wear of ultra-high molecular weight polyethylene (UHMWPE). This paper presents an analysis of the surface topographical properties of the worn and unworn condylar surfaces on a small cohort of both wear simulated and retrieved prostheses of varying designs. A number of measurement points were taken on each prostheses in a mixture of worn and unworn areas through the use of focus-variation microscopy (FVM), a non-contact method of surface measurement. Surface areal parameters were extracted from this data to analyse and search for patterns within the data. It was found that in general, worn implant surfaces appear to show smoother, less peak dominated surfaces than unworn area. It was also found that wear simulated and retrieved implants display similar characteristics of surface topography. In addition, variation was noted between different designs of TKR device, with posterior stabilised designs found to be peak dominated and cruciate retaining type implants being valley dominated.

Influence of temperature on the corrosion and tribocorrosion behaviour of High-Strength Low-Alloy steels used in offshore applications

Abstract Tribocorrosion is an important failure cause of High-Strength Low-Alloy steel (HSLA) components in offshore applications due to the synergistic effect of wear and the corrosiveness of seawater. In this work, the effect of temperature on the tribocorrosion behaviour of two steel grades has been investigated by performing tribocorrosion tests under reciprocating sliding at two electrolyte temperatures. The total material loss due to corrosion in the unworn surface and due to tribocorrosion in the wear track was quantified. Sliding was found to accelerate the corrosion in the unworn area. Furthermore, temperature was confirmed to have an important effect on the tribocorrosion behaviour of the steels, in terms of higher material losses due to corrosion at higher test temperature.

Zirconia phase transformation in retrieved, wear simulated, and artificially aged ceramic femoral heads.

ABSTRACTZirconia in Zirconia toughened alumina ceramic hip replacements exists in an unstable state and can transform in response to stress giving the material improved fracture toughness. Phase transformation also occurs under hydrothermal conditions such as exist in vivo. To predict the hydrothermal aging that will occur in vivo accelerated aging procedures have been used, but validation of these models requires the study of retrieved hip joints. Here 26 retrievals are analysed to determine the degree of phase transformation in vivo. These were compared with virgin heads, heads that had undergone the accelerated aging process and heads wear tested to 5 million cycles in a hip simulator. Monoclinic content and surface roughness were measured using Raman spectroscopy and white light interferometry respectively. The monoclinic content for retrieved heads was 28.5% ± 7.8, greater than twice that in virgin, aged, or wear tested heads and did not have a significant correlation with time, contrary to the predictions of the hydrothermal aging model. The surface roughness for retrieved heads in the unworn area was not significantly different to that in virgin, aged, or unworn areas of wear tested heads. However in worn areas of the retrieved heads, the surface roughness was higher than observed in wear simulator testing. These results indicate that current testing methodologies do not fully capture the operational conditions of the material and the real performance of future new materials may not be adequately predicted by current pre‐clinical testing methods. © 2017 The Authors. Journal of Orthopaedic Research Published by Wiley Periodicals, Inc. on behalf of Orthopaedic Research Society 35:2781–2789, 2017.

Tribocorrosion studies of metallic biomaterials: The effect of plasma nitriding and DLC surface modifications

The medical grade pure titanium, stainless steel and CoCrMo alloy have been utilized as biomaterials for load-bearing orthopedic prosthesis. The conventional surgery metals suffer from a combined effect of wear and corrosion once they are implanted, which may significantly accelerate the material degradation process. In this work, the tribocorrosion performance of the metallic biomaterials with different surface modifications was studied in the simulated body fluid for the purpose of investigating the effect of the surface treatments on the tribocorrosion performance and eventually finding the most suitable implantation materials. The metals were subjected to surface modifications by plasma nitriding in different treatment temperatures or physical vapor deposition (PVD) to produce diamond-like carbon (DLC) coating, respectively. The dry wear and tribocorrosion properties of the samples were evaluated by using a reciprocating ball-on-disc tribometer equipped with an electrochemical cell. Prior to the tribocorrosion tests, their electrochemical behavior was measured by the potentiodynamic polarization in phosphate buffer saline (PBS) solution at room temperature. Both stainless steel and CoCrMo after low temperature nitriding kept their passive nature by forming an expanded austenite phase. The DLC coated samples presented the low anodic corrosion current due to the chemical inertness of the carbon layer. During the tribocorrosion tests at open circuit potential, the untreated and low temperature nitrided samples exhibited significant potential drop towards the cathodic direction, which was a result of the worn out of the passive film. Galvanic coupling was established between the depassivated (worn) area and the still passive (unworn) area, making the materials suffered from wear-accelerated corrosion. The DLC coating performed as a solid lubricant in both dry wear and tribocorrosion tests, and the resulting wear after the tests was almost negligible.

Tribocorrosion behaviour of mooring high strength low alloy steels in synthetic seawater

Offshore components of High-Strength Low-Alloy Steel (HSLA) are frequently exposed to tribological and corrosion effects during their working life. In the present work, several experiments have been performed to study the tribocorrosion behaviour of two steel grades, under unidirectional sliding in synthetic seawater. Sliding wear tests were performed under potentiodynamic and potentiostatic conditions at different applied potentials. The wear tracks were analysed by means of optical microscope and profilometry. The wear-corrosion synergism was quantified according to the ASTM G119 standard. Sliding promotes the wear accelerated corrosion of the unworn area in both alloys. Furthermore, the coefficient of friction of the steels is strongly influenced by the corrosion products and the applied potential.

Assessing the tribocorrosion performance of Ti–6Al–4V, 316 stainless steel and Monel K500 alloys in artificial seawater

AbstractThe electrochemical and tribocorrosion behaviors of Ti–6Al–4V, 316 stainless steel and Monel K500 alloys sliding against Al2O3 in artificial seawater are investigated in this paper. It can be observed that the open circuit potential drops down to more negative values due to the removal of passive film. And a rapid dissolution occurs in the wear track compared with the unworn area. The wear loss polarized in cathodic potential is lower than that in anodic potential and open circuit potential conditions, because the material deterioration is enhanced by corrosive attack. The wear volumes of 316 stainless steel are much higher than the ones measured for Ti–6Al–4V and Monel K500 alloys. Friction coefficients are significant large in cathodic polarization compared with anodic polarization for all alloys. Moreover, the 316 stainless steel exhibits large friction coefficients compared with Ti–6Al–4V and Monel K500 alloys.

Raman characterisation of conventional and cross‐linked polyethylene in acetabular cups run on a hip joint simulator

AbstractFive sets of differently sterilised conventional ultra‐high molecular weight polyethylene (UHMWPE) and cross‐linked polyethylene (XLPE) acetabular cups were run for 5 million cycles on a hip joint simulator in order to evaluate their wear behaviour in relation to material properties (PE grade, conventional or cross‐linked) and sterilisation method (ethylene oxide (EtO) treatment or γ‐irradiation). Gravimetric measurements revealed that conventional UHMWPE wore significantly more than XLPE. The differences in wear behaviour could be partly related to the orthorhombic contents obtained by Raman spectroscopy in the unworn areas of the cups: XLPE cups showed a significantly higher crystallinity degree than the UHMWPE specimens. Raman analysis showed that wear testing did not significantly modify the orthorhombic content of any of the tested acetabular cups. However, the set of cups that showed the highest weight loss, i.e. γ‐sterilised PE GUR1020, appeared the most homogeneously polished upon wear testing; from a molecular point of view, only this set of cups showed a significant increase of the I1130/I1060 intensity ratio, suggesting the occurrence of chain orientation. On the other hand, XLPE cups, despite the lowest weight loss undergone, showed a decrease in the amorphous content upon wear testing as well as a limited orthorhombic → monoclinic transformation, which did not appear detrimental. Copyright © 2011 John Wiley &amp; Sons, Ltd.

Damage and Wear: An Important Distinction in Rotating Platform Knee Bearings

Abstract Rotating platform mobile bearing knees are an appealing approach to the problems of tibial loosening and rotational malignment in fixed bearing knees. A potential disadvantage is the additional large articular surface that accommodates tibio-femoral rotation. Accurately assessing the tribological performance of this additional articular surface is important to understanding how mobile bearings perform in terms of generating polyethylene wear debris and associated osteolysis. A series of 76 retrieved Sigma Rotating Platform bearings were assessed for damage rating according to conventional protocol and through-thickness wear measurements were taken. The results show that the rotation surface of these bearings is very commonly subject to moderate and severe damage and that damage can occur early following implantation. The decrease of the through-thickness dimension is strongly correlated with time in vivo. The rotation surface damage rating shows a weak though statistically significant correlation to through-thickness wear. Three dimensional surface profilometry on the bearings illuminates phenomena that can explain the paradoxical observations that severely damaged bearings may not be worn and worn bearing areas are smoother and show less damage than unworn areas. This study finds that bearing damage is distinct from bearing wear and the two terms are not interchangeable in the context of assessing material loss from artificial knee bearings. While both processes are important in the tribology of knee devices, it is not accurate to use damage on ultrahigh molecular weight polyethylene as a proxy for wear.

Comparison of Biotribology of Swine Compact Bone Against UHMWPE

Abstract A pin-on-disk tribometer was used, in a comparative test to observe the tribological behavior of the swine femoral bone against UHMWPE with dry friction, physiological water and human plasma lubrication. The wear mechanisms of swine bones and UHMWPE were investigated by SEM. The experimental results of these wear tests demonstrated that both the friction coefficient and wear rate of UHMWPE were the lowest when human plasma lubrication was used. The wear mechanism of the compact bone was mainly fatigue wear with dry friction, corrosive wear under physiological water lubrication and abrasive wear with human plasma lubrication. For UHMWPE, the wear mechanism was adhesive wear and plastic deformation with dry friction, serious ploughing and fatigue fracture wear under physiological water lubrication, fine ploughing and plastic deformation with human plasma lubrication. An analysis of nitrogen elements on the wear surface of UHMWPE indicated that the content of nitrogen in worn areas was 16 times higher than that in unworn areas, which proved that serum protein deposition occurred on worn areas.

Backside Wear of Polyethylene Tibial Inserts

Wear of the underside of modular tibial inserts (backside wear) in total knee replacements has been reported by several authors. Although, for some implant designs, this phenomenon seems to contribute to osteolysis, the actual volume of material lost through wear of the backside surface has not been quantified. This study describes the results of computerized measurements of tibial inserts of one design known to be associated with a high prevalence of backside wear in situ. A series of retrieved total knee components of one design were examined. The duration of implantation of the retrieved components ranged from thirty-six to 146 months. Laser surface profilometry and computer-aided design software were used to develop individual three-dimensional models of each worn, retrieved tibial insert to compare with scanned unused inserts. Volumetric subtraction of both models revealed the material lost because of backside wear. Worn and unworn areas on the backside surface were easily identified by stereomicroscopy and laser profilometry. The computer reconstructions showed that, in all retrievals, all unworn surfaces on the nonarticulating surface lay in one plane. The average volume (and standard deviation) of the material lost because of backside wear was 925 +/- 637 mm(3) (range, 197 to 2720 mm(3)). On the basis of the time in situ for each implant, the average volumetric wear rate was 138 +/- 95 mm(3)/yr. The predicted volume of material removed because of backside wear is substantial and may be sufficient to induce osteolysis. Our results suggest that peg-like protrusions are not generated by the extrusion of polyethylene into screw-holes within the base-plate but by abrasion of the underside of the bearing insert, leaving the protruding pegs as the only remnants of the original surface.

Friction and head and disk interface durability in contact recording

The role of ambient air, nitrogen and water on the frictional behavior of a micro-contact recording head against an amorphous nitrogenated carbon (a-C:N) overcoat disk was investigated. Water was found to play a major role in the time evolution of the friction between the disk and diamond-like carbon wear pads. No substantial differences between friction with and without oxygen in the system were noted. A long-term fixed track friction test in an extremely dry atmosphere showed friction force build-up over time and resulted in magnetically recorded side-band frequency increases due to similar beam vibration. Atomic force microscopy on a track in continuous sliding contact for 910 h revealed that the track summits became smooth over time. Lateral force microscopy of these summit areas showed high friction relative to unworn areas.