Volume Loss Values Research Articles

Investigation of Tribological Properties of Inconel 601 under Environmentally Friendly MQL and Nano-Fluid MQL with Pack Boronizing

Friction and high temperatures greatly affect the hardness and processing efficiency of superalloys. Therefore, it is important to provide a coating on their surfaces with a hard layer. In this study, pack boronizing was applied on Inconel 601 to improve its microstructure and tribological properties. In this regard, tribological tests were performed under MQL, nano-MQL1 (MQL + CuO), and nano-MQL2 (MQL + TiO2) environments. The research results showed that the lowest wear depth, friction force, coefficient of friction (CoF), and volume loss values were obtained in pack-boronized Inconel 601 in a nano-MQL2 environment. In the nano-MQL2 environment, the wear depth decreased by 17.81% (from 57.922 µm to 47.605 µm) with package-boronized Inconel 601 compared to as-received Inconel 601 at a 45 N load. Pack-boronized Inconel 601 experienced an average reduction of 30.23%, 41.60%, and 52.32% in friction force when switching from dry to MQL, nano-MQL1, and nano-MQL2 environments, respectively. It was also observed that the coefficient of friction (CoF) and volume loss values decreased with pack boronizing in an MQL/nano-MQL environment. In a nano-MQL2 environment at 15 N load, volume losses for as-received and boron-coated Inconel 601 were determined as 0.288 mm3 and 0.249 mm3, respectively (13.54% decrease). The findings of this study demonstrate that pack boronizing and MQL and nano-MQL techniques enhance the tribological characteristics of Inconel 601 alloys.

A promising perspective in improving corrosion and wear resistance of plain steel through electrodeposition of thick Ni–Mo–W ternary alloy

In this study, thick Ni–Mo–W ternary alloy coatings (∼24 μm) with 13–27 wt% Mo and 4–11 wt% W were electrodeposited from an alkaline citrate-ammonia bath using direct current. The effect of current density (20–100 mA/cm2) on the composition, current efficiency, morphology, structure, surface topography, tribological behavior, and corrosion resistance of coatings was investigated. The findings revealed an advantageous induced co-deposition of Mo in an electrolyte containing equimolar Mo and W ions. While increasing the current density decreased the Mo content of the coatings, they always had more Mo than W. Increasing the current density, according to SEM and AFM observations, changed the smooth and nodular morphology of Ni–Mo–W coatings to a relatively rough and cauliflower shape. The microhardness of the produced nanocrystalline solid solution coatings was 3.8–4.9 times higher than that of the plain carbon steel substrate. While the hardest coating (793 Hv) deposited at 100 mA/cm2 had the best wear resistance with a volume loss value of 0.04 mm3, it had the worst corrosion resistance among the coatings with icorr = 4.4 μA/cm2. The least hard coating (607 Hv), deposited at 40 mA/cm2, with the highest wear volume loss value of 0.11 mm3, however, was the most corrosion resistant sample with icorr = 1.9 μA/cm2.

How Does Ethylenediaminetetraacetic Acid Irrigation Affect Biodentine? A Multimethod Ex Vivo Study.

The activity of biomaterials used during endodontic treatment can be affected by various factors. One of them is the chemical action of the irrigant that they are exposed to. The aim of this multimethod ex vivo study was to evaluate the influence of ethylenediaminetetraacetic acid (EDTA) on the surface appearance and chemical composition of Biodentine used in perforation repair. Twenty material specimens were prepared according to manufacturers' recommendations and divided into two setting-time-based groups, tested after 45 min (group A) and 24 h (group B) of setting. Material was irrigated with 17% EDTA solution with or without simultaneous ultrasonic activation. The surface characteristics and the chemical composition analysis of the Biodentine specimens were performed with the aid of a scanning electron microscope (SEM) and an energy dispersive spectroscopy (EDS) method, respectively. The volumetric loss of material was measured by dedicated digital software in an optical microscope. Statistical analysis was performed. The EDS study confirmed that after the rinsing protocol, the percentage content of elements differed between the groups. The EDTA rinse, whether ultrasonically activated or not, visibly affected the surface appearance and chemical composition of Biodentine. The specimens' surface subjected to irrigation was more irregular under SEM than in a control group. The US activation of the liquid amplified its impact on the tested material. The average volume loss in group A after 5 min irrigation was 3.98 µm3 for each µm2 of the chosen area and it increased up to 7.74 µm3/μm2 after the ultrasonic activation. In group B, indicated volume loss values were 6.30 and 11.70 µm3/μm2 for 5 min irrigation without and with US activation, respectively. Using a 20 min irrigation time and ultrasonic activation increased it up to 32.71 µm3/µm2. Each rinsing protocol involving irrigation with ethylenediaminetetraacetic acid modified the surface features and the chemical composition of the evaluated hydraulic tricalcium silicate cement. Further research is needed to indicate the possible impact of the observed changes on its long-term clinical performance.

Effect of particle volume fraction on wear behavior in Al–SiC MMC coated on DIN AlZnMgCu1.5 alloy

Abstract In this study, DIN AlZnMgCu1.5 alloy surface (Al + SiC) was coated with metal matrix composite (MMC) by using hot press sintering method (HPSM). Al was used as matrix material and SiC powders were used as reinforcing material in the coating process on DIN AlZnMgCu1.5 alloy surface. Al/SiC MMC coating was produced at 600 °C under 120 MPa pressure and with varying SiC content (5, 10 and 15 vol.%). Optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD) were used to examine the microstructure, elemental analysis and phase structure of both the coating zone and the transition zone between the substrate and the coating. The hardness was measured and a dry sliding linear reciprocating wear test was run to determine the mechanical properties of the coating layer. Consequently, the coefficient of friction (COF) and wear volume were determined. OM and SEM images showed a homogeneous distribution of SiC particles and a less porous structure. The hardness of the MMC coating increased with increasing SiC content. Also, the numerical analysis of the wear test simulation was done based on Archard’s law. The results of both wear tests showed that the volume loss values were consistent with each other and the amount of wear significantly reduced by increasing the rate of SiC reinforcement.

Er,Cr:YSGG and 980nm diode lasers influence dentin surface volume after cariogenic challenge: in vitro study.

This study aimed to evaluate the influence of the Er,Cr:YSGG irradiation and 980-nm diode lasers on the surface roughness (SR) and volume loss (VL) of dentin subjected to cariogenic challenge. Subsequently, 130 specimens of bovine dentin were divided into the following 13 groups: NT: no treatment; FG: fluoride gel; FV: fluoride varnish; Di: 980-nm diode; Di + FG; Di + FV; FG + D; FV + Di; Er: Er,Cr:YSGG; Er + FG; Er + FV; FG + Er and FV + Er. Er,Cr:YSGG laser parameters were as follows: 0.25 W; 5.0 Hz; 4.46 J/cm2 without water and 55% air. Furthermore, the 980-nm diode laser parameters were 2.0 W; 2.0 Hz; 21.41 J/cm2. The samples from each group were subjected to pH cycling. A confocal laser scanning microscope was used to evaluate SR and VL. Difference between the volume of the reference and treated areas + DES/RE was used to determine SR and VL. The mean values of the different groups were subjected to analysis of variance and Tukey's post-hoc test. The VL values were analyzed using the Kruskal-Wallis and Dunn post-hoc test (p < 0.05). The SR of the reference area did not show a statistically significant 1807-3107-bor-38-e025treatment and cariogenic challenge (p > 0.05). Moreover, VL in the FV + Di and FV + Er groups showed a statistically significant difference compared with areas submitted to different types of treatment and cariogenic challenge (p > 0.05). Er,Cr:YSGG and 980-nm diode lasers associated with fluoride varnishes decreased dentin VL in bovine teeth submitted to cariogenic challenge.

Study on microstructure and wear characteristics of carburized steel at different carburizing times using catalyst strombus turturella shell waste powders

The feasibility of strombus turturella or dog conch shell powder (DCSP) as a catalyst of the carburizing process was investigated. The microstructure and wear characteristics of carburized specimens at various carburizing times were determined and compared. The microstructures and chemical compositions of the carburized specimen were observed by Scanning Electron Microscopy (SEM) machine with a detector energy dispersive spectroscopy (EDS). The wear characteristics were detected by a Pin-on-disk wear testing machine. While the worn surface morphology of carburized specimens was examined by Scanning Electron Microscopy (SEM) machine. The number of martensite structures of carburized specimens increased by increasing the carburization time from 3 to 12 hours. From the results, it is found that the volume loss value of 0.1 mm3, and wear depths value of 0.18 mm were obtained from carburized specimens prepared with 40% DCSP and carburizing time of 12 hours. This result is much better than that obtained by carburizing times of 6, and 3 hours, respectively. Moreover, the worn surface morphology results depicted that the carburized specimens for carburization times of 3, and 6 hours exhibit more severe spalling, wear debris, and extensive adhesion wear and grooves than that achieved of carburized specimens with a carburizing time of 12 hours. The results clearly showed that the wear characteristics of carburized specimens improved with increasing carburizing time.

Investigation of Mechanical Properties of Grey Cast Irons Reinforced with Carbon Titanium Nitride (TiNC)

In this study, grey cast iron (GG25) was produced via reinforcement with carbon titanium nitride (TiNC) in different amounts (0%, 0.153%, 0.204% and 0.255%). Samples were made from this material according to the standards for hardness, compression and wear, and then experiments were conducted. The test conditions applied for the TiNC-reinforced samples were similarly applied to unreinforced samples. The TiNC-reinforced and unreinforced samples were compared regarding their compression, hardness, and wear properties. The results of the hardness tests showed the highest average hardness value of 215 HB for sample A (0% TiNC). For TiNC-reinforced specimens, the hardness values of the reinforced specimens increased with increasing reinforcement. Sample B (0.153% TiNC) had an average hardness value of 193 HB. For sample C (0.204% TiNC), an average hardness value of 200 HB was measured. For sample D (0.255% TiNC), an average hardness value of 204 HB was determined. Sample A’s highest compression strength value was 780 MPA (0% TiNC). Similar to the hardness test values, the compression strength of the reinforced samples increased with the increasing reinforcement rate. The compression test value was found to be 747 MPa for sample B (0.153% TiNC), 765 MPa for sample C (0.204% TiNC) and 778 MPa for sample D (0.255% TiNC). Wear tests were performed on all samples to examine changes in the wear volume loss, wear rate and friction coefficients. Scanning electron microscopy (SEM) was used to determine the wear mechanisms on the worn surfaces of the samples. When examining the wear condition of the samples with the same hardness value as a function of increasing load values, increases in the wear volume loss values were observed as the load value increased.

Influence of Different Surface Finishing Protocols on the Wear Behavior of Lithium Disilicate Glass-Ceramics.

To evaluate the effect of different finishing protocols on the wear behavior of lithium disilicate glass-ceramics (LD). Specimens were produced from LD prefabricated CAD/CAM blocks and divided into three groups according to the surface treatment (n = 8): control, polishing, and glaze. Ceramic specimens were subjected to wear testing using a dual-axis chewing simulator. A 49-N load was applied in the axial direction combined with a lateral movement (1-mm path) using an LD spherical piston for a total of 106 cycles. Qualitative analysis of the wear surface was performed using an optical microscope. Quantitative analysis of surface roughness and volume loss was performed using a confocal microscope and a 3D-image editing software, respectively. Surface roughness and volume loss data were analyzed using Friedman's nonparametric statistical test for repeated measures and the Student-Newman-Keuls test (α = .050). There were statistical differences for surface roughness and volume loss of LD specimens in the different experimental conditions (P < .001). The control and polishing groups showed similar surface roughness and volume loss values for all testing times. The glaze group had greater wear volume after 103, 104, and 105 cycles. After 106 cycles, surface roughness and volume loss were similar in all groups. For the piston, surface roughness was similar over time and among groups. A distinct wear behavior was found for glazed glass-ceramic specimens compared to control and polished specimens. At the end of the simulation, the surface roughness and volume loss was similar for the groups.

Abrasive Wear Resistance of Ultrafine Ausferritic Ductile Iron Intended for the Manufacture of Gears for Mining Machinery.

The purpose of this study was to experimentally determine the abrasion wear properties of ausferritic ductile iron austempered at 250 °C in order to obtain cast iron of class EN-GJS-1400-1. It has been found that such a cast iron grade makes it possible to create structures for material conveyors used for short-distance transport purposes, required to perform in terms of abrasion resistance under extreme conditions. The wear tests addressed in the paper were conducted at a ring-on-ring type of test rig. The test samples were examined under the conditions of slide mating, where the main destructive process was surface microcutting via loose corundum grains. The mass loss of the examined samples was measured as a parameter characteristic of the wear. The volume loss values thus obtained were plotted as a function of initial hardness. Based on these results, it has been found that prolonged heat treatment (of more than 6 h) causes only an insignificant increase in the resistance to abrasive wear.

Toothpaste Abrasion and Abrasive Particle Content: Correlating High-Resolution Profilometric Analysis with Relative Dentin Abrasivity (RDA).

In this in vitro study, the influence of the concentration of abrasive particles on the abrasivity of toothpastes was investigated using laser scan profilometry on polymethyl methacrylate (PMMA) surfaces with the aim of providing an alternative method to developers for screening of new toothpaste formulations. PMMA plates were tested in a toothbrush simulator with distilled water and four model toothpastes with increasing content of hydrated silica (2.5, 5.0, 7.5, 10.0 wt%). The viscosity of the model toothpaste formulations was kept constant by means of varying the content of sodium carboxymethyl cellulose and water. The brushed surfaces were evaluated using laser scan profilometry at micrometer-scale resolutions, and the total volume of the introduced scratches was calculated along with the roughness parameters Ra, Rz and Rv. RDA measurements commissioned for the same toothpaste formulations were used to analyze the correlation between results obtained with the different methods. The same experimental procedure was applied to five commercially available toothpastes, and the results were evaluated against our model system. In addition, we characterize abrasive hydrated silica and discuss their effects on PMMA-sample surfaces. The results show that the abrasiveness of a model toothpaste increases with the weight percentage of hydrated silica. Increasing roughness parameter and volume loss values show good correlation with the likewise increasing corresponding RDA values for all model toothpastes, as well as commercial toothpastes without ingredients that can damage the used substrate PMMA. From our results, we deduce an abrasion classification that corresponds to the RDA classification established for marketed toothpastes.

A comparative analysis of the effect of laser surface treatment on the dry sliding wear behavior of ductile cast irons with different microstructures

In this study, the wear behavior of ferritic (GJS 400) and pearlitic (GJS 700) ductile cast iron (DCI) specimens after laser surface hardening were investigated comparatively. In general, multi-pass laser applications are inevitable in a laser surface treatment (LST) applied for surface hardening because the laser spot diameter is quite small compared to the applied surface area. This situation may cause a decrease in wear resistance due to residual stress formation because of the thermal gradient and softening effect due to the overlap ratio. In this study, a single-pass laser surface hardening (LSH) process with a laser pulse area of 20 × 5 mm2 compatible with the laser energy density (6.28 J/mm3) used in the literature, was applied to overcome these limitations. Thus, it is aimed to make it possible to evaluate the comparative analysis more reliably. After LSH processes, hardness values of DCI samples increased approximately 4.3 times compared to untreated ones due to the transformation hardening effect. In the microstructure of the laser-treated pearlitic DCI samples, martensite was present as the dominant phase in addition to a small amount of residual austenite. As for the ferritic DCI samples, the ledeburite and martensite phases were detected. Dry sliding wear tests were performed using different loads (5 N, 10 N) and sliding speeds (10 mm/s, 20 mm/s, 30 mm/s). As a result, the wear volume loss values of laser-treated ferritic and pearlitic DCI samples could be reduced by approximately 26.6% and 30.7%, respectively, compared to untreated ones. The COF values of the untreated samples increased with increasing load, while those of LSHed decreased. Severe plastic deformation and delamination were observed for untreated samples, while mild plastic deformation and micro-grooves were observed for samples with LSHed.

Effect of Abrasive Grain Size on the Abrasion Volume Loss of Subfossil and Recent Oak Wood in Three Characteristic Sections

Subfossil wood is a valuable and rare material often used for production of expensive furniture and decorative artistic items of unique beauty. Its mechanical and tribological properties are still being studied and are considered specific due to the particular conditions of its long-lasting formation in aqueous sediment sludge. Various elements that have been impregnated into the wood tissue over many years make the machining and grinding of this type of wood rather difficult compared to normal recent wood. The main objective of this study was to determine the influence of the abrasive grain size of sandpaper on the abrasion volume loss of recent and two subfossil oak samples in three characteristic sections (cross, radial, and tangential). The results showed that the average size of abrasive grains and the orientation of the wood structure have an influence on the abrasion volume loss of all three samples. The phenomenon of the critical size of abrasive grains was observed in all samples and on all sections. As the size of abrasive grains increased to the critical size, the abrasive volume loss of the sample increased simultaneously. The lowest abrasion volume loss was observed on recent oak. In all samples, the lowest volume loss was measured on the cross sections, and the tangential and radial sections had mutually equal values. It was also found that the increase in the size of abrasive grains to a critical value resulted in the increasing value of the absolute difference between the abrasion volume loss of the cross, radial, and tangential section samples, while the relative relations between the abrasive volume loss values of three different sections (C/R, C/T, R/T) within the same grit of sandpaper remained quite similar.

Microstructure, hardness and high temperature wear characteristics of boronized Monel 400

Boronizing processes were carried out at 900 °C, 950 °C and 1000 °C for 2, 4 and 6 h to improve the wear performance of Monel 400 alloy. According to microstructure analyses and nanoindentation tests, Ni2B, FeNiB and FeB phases were detected as dominant phases in the boronized layer. Apart from this, it was observed that the amount of Cu deposits in the boronized layers increased depending on the increasing boronizing temperature. After the boronizing process, the boride layer thickness and hardness values were found to be in the range of 32–272 μm and 12.76–17.83 GPa, respectively. From the results of dry sliding wear test, the wear volume loss values of the boronized Monel 400 alloy decreased by approximately 25 times compared to the untreated samples. The lowest volume loss value among all test samples was observed in the boronized sample at 950 °C for 4 h. In addition to the hardness value, it was determined that the morphology and mechanical properties of the boronized layer were also effective on the wear results. Plastic deformation, delamination and oxidation type wear mechanisms were observed as the dominant wear mechanisms in the room and high temperature tests of boronized samples.

The corrosion of carbon steel under delaminating repair coatings after long‐term marine splash zone exposure

AbstractOrganic repair coatings are applied to repair areas of previously coated low‐carbon steel samples, and the samples are exposed to the splash zone in an offshore environment (Helgoland, North Sea) for 57 months. The volume loss of the steel underneath the delaminated coating is estimated with a three‐dimensional optical stripe line projection. The samples show a small variation in the degree of delamination (22%) only. The steel volume loss values, in contrast, range between 164 × 109 and 320 × 109 µm³, which is a variation of 196%. The degree of delamination of the scribed coatings does not mirror the corrosion of the steel underneath the delaminated sections. The coating with the widest degree of delamination exhibits the lowest steel volume loss due to corrosion. A good scribe performance of a coating is, therefore, no guarantee for a low corrosion loss nor for a low local corrosion depth in the steels to be protected.

Wear behavior of current computer-aided design and computer-aided manufacturing composites and reinforced high performance polymers: An in vitro study.

To analyze the wear rate of computer-aided design and computer-aided manufacturing (CAD/CAM) composites, polyetheretherketones and glass ceramics. Our study groups were prepared from two different resin-based composites (Brillant Crios, Cerasmart), a glass ceramic (IPS Emax CAD) and reinforced polyetheretherketone (BioHPP) material (n=10). Premolar teeth were used as antagonists. The specimens, which were subjected to two body wear tests (240,000 cycles, 1.2Hz, 50N) in the chewing simulator, were scanned with a 3D laser scanner both before and after the wear test. Volume loss and wear depth were determined by means of the obtained images software program. The wear pattern was examined by scanning electron microscopy. Kruskal Wallis test served for analyzing. The least volume loss and wear depth were seen in the polyetheretherketone material (0.06 ± 0.04 mm3 , 0.02 ± 0.01 mm), while the maximum volume loss was seen in the groups containing resin-based composite. (p=0.05). The volume loss value in glass ceramics is between CAD/CAM composites and polyetheretherketone. The behavior of polyetheretherketone against enamel was different from glass ceramics and composite materials in terms of the amount of wear. Polyetheretheketone can be considered as an alternative to other chairside materials in terms of wear resistance.

The effects of Cephalaria syriaca flour on physical, rheological and textural properties of sunn pest (Eurygaster integriceps) damaged wheat dough and bread

The aim of this study was to investigate the effects of Cephalaria syriaca flour (CSF; 0.5, 1.0 and 1.5%) on the physical, textural and rheological characteristics of dough and bread obtained from sunn pest-damaged wheat (SPDW; 5, 10 and 15%). An increased CSF level significantly decreased the stickiness and volume loss values of dough and the firmness and chewiness values of bread for all SPDW levels. The dough stickiness and bread firmness values were considerably increased by the addition of SPDW at the 15% level (1.05 N and 29.76 N), whereas these values were reduced by the addition of 1.5% CSF (0.6439 N and 22.56 N). In general, the stress relaxation, gas retention and gluten extensibility parameters of dough; and the specific volume, colour, cohesiveness, springiness and resilience values of bread significantly increased depending on the increasing level of CSF. Especially, the 1.5% CSF level significantly improved the quality of the dough and breads. The results of the present study revealed that CSF addition to SPDW flour positively affected the stickiness, gas retention and stress relaxation of dough and the specific volume and instrumental textural properties of bread.

Effect of dentifrice slurry abrasivity and erosive challenge on simulated non-carious cervical lesions development in vitro.

To investigate the effect of slurry abrasive levels and acidic challenges on the development of non-carious cervical lesions. Ninety-six extracted upper premolars were affixed in pairs to acrylic blocks and had their root surfaces covered by acrylic resin except for 2 mm from the cemento-enamel junction. The specimens were distributed into six groups (n = 8 pairs) based on two experimental factors: (1) slurry abrasivity level [low/medium/high] and (2) citric acid challenge [yes/no]. Specimens were brushed for 5,000, 15,000, 35,000, and 65,000 strokes. Volume loss (VL) was determined based on optical profilometry scans of specimens impressions at the baseline and at subsequent brushing levels. Data were analyzed using repeated measures analysis of variance and Bonferroni pairwise comparison (α = 0.05). Higher VL values were associated with high-abrasivity slurries relative to low- and medium-abrasivity slurries (P < 0.001). Increasing the slurry abrasivity level increased the VL regardless of the acidic challenge, which did not have a significant effect (P = 0.184). After 65,000 strokes, significant VL was recorded in all groups relative to preceding brushing levels (P < 0.001). Higher values of time-dependent surface loss were associated with increased dentifrice slurry abrasivity, regardless of the citric acid challenge.

Analysis of Tribological Properties in Disks of AA-5754 and AA-5083 Aluminium Alloys Previously Processed by Equal Channel Angular Pressing and Isothermally Forged

In the present study, the wear behaviour of two aluminium alloys (AA-5754 and AA-5083) is analysed where these have been previously processed by severe plastic deformation (SPD) with equal channel angular pressing (ECAP). In order to achieve the objectives of this study, several disks made of these alloys are manufactured by isothermal forging from different initial states. The microstructures of the initial materials analysed in this study have different accumulated deformation levels. In order to compare the properties of the nanostructured materials with those which have not been ECAP-processed, several disks with a height of 6 mm and a diameter of 35 mm are manufactured from both aluminium alloys (that is, AA-5754 and AA-5083) isothermally forged at temperatures of 150 and 200 °C, respectively. These thus-manufactured disks are tested under a load of 0.6 kN, which is equivalent to a stress mean value of 18 MPa, and at a rotational speed of 200 rpm. In order to determine the wear values, the disks are weighed at the beginning, at 10,000 revolutions, at 50,000 revolutions and at 100,000 revolutions, and then the volume-loss values are calculated. This study was carried out using specific equipment, which may be considered to have a block-on-ring configuration, developed for testing in-service wear behaviour of mechanical components. From this, the wear coefficients for the two materials at different initial states are obtained. In addition, a comparison is made between the behaviour of the previously ECAP-processed aluminium alloys and those that are non-ECAP-processed. A methodology is proposed to determine wear coefficients for the aluminium alloys under consideration, which may be used to predict the wear behaviour. It is demonstrated that AA-5754 and AA-5083 aluminium alloys improve wear behaviour after the ECAP process compared to that obtained in non-ECAP-processed materials.

Effect of counterbody on the dry sliding wear performance of plasma sprayed calcia-stabilized zirconia coating

In this study, the effect of counterbody on the dry sliding wear behavior of plasma sprayed calcia-stabilized zirconia coating was investigated. The commercial ZrO2-5CaO coating powder (Metco 201NS, −53 + 11 μm) was deposited onto the surface of AISI 316L substrate using Atmospheric Plasma Spray method. Dry sliding wear tests were performed with Al2O3 and WC-Co counterbody balls at different loads (5 N, 10 N and 15 N) and sliding speeds (10 mm/s, 20 mm/s and 30 mm/s) using a ball-on-disc device. From the test results, the COF values obtained from the Al2O3 ball were recorded to be lower than that of the WC-Co ball especially at 20 N and 30 N loads. The sliding speed did not cause a remarkable change in the COF values of the wear tests performed with both counterbody balls. However, in the case of WC-Co ball, COF values also increased especially with increasing the load from 5 N to 10 N at the 20 mm/s of sliding speed. In general, increasing load and sliding speed led to an increase in the wear volume loss values for all the tests. When using Al2O3 ball, under the 5 N load, lots of pitting and spalling zones were observed, whereas for 10 N and 15 N loads, plastically deformed worn areas which had lots of wear debris and deep cracks were determined. As for the WC-Co ball, the plastic deformation was observed as the predominant wear mechanism as well as the swelling-induced spallation and delamination. In addition, the wear mechanisms identified as a result of this study were explained by associating them with the Hertzian contact theory.

Age-dependent cut-offs for pathological deep gray matter and thalamic volume loss using Jacobian integration

IntroductionSeveral recent studies indicate that deep gray matter or thalamic volume loss (VL) might be promising surrogate markers of disease activity in multiple sclerosis (MS) patients. To allow applying these markers to individual MS patients in clinical routine, age-dependent cut-offs distinguishing physiological from pathological VL and an estimation of the measurement error, which provides the confidence of the result, are to be defined. MethodsLongitudinal MRI scans of the following cohorts were analyzed in this study: 189 healthy controls (HC) (mean age 54 years, 22% female), 98 MS patients from Zurich university hospital (mean age 34 years, 62% female), 33 MS patients from Dresden university hospital (mean age 38 years, 60% female), and publicly available reliability data sets consisting of 162 short-term MRI scan-rescan pairs with scan intervals of days or few weeks. Percentage annualized whole brain volume loss (BVL), gray matter (GM) volume loss (GMVL), deep gray matter volume loss (deep GMVL), and thalamic volume loss (ThalaVL) were computed deploying the Jacobian integration (JI) method. BVL was additionally computed using Siena, an established method used in many Phase III drug trials. A linear mixed effect model was used to estimate the measurement error as the standard deviation (SD) of model residuals of all 162 scan-rescan pairs For estimation of age-dependent cut-offs, a quadratic regression function between age and the corresponding annualized VL values of the HC was computed. The 5th percentile was defined as the threshold for pathological VL per year since 95% of HC subjects exhibit a less pronounced VL for a given age. For the MS patients BVL, GMVL, deep GMVL, and ThalaVL were mutually compared and a paired t-test was used to test whether there are systematic differences in VL between these brain regions. ResultsSiena and JI showed a high agreement for BVL measures, with a median absolute difference of 0.1% and a correlation coefficient of r = 0.78. Siena and GMVL showed a similar standard deviation (SD) of the scan-rescan error of 0.28% and 0.29%, respectively. For deep GMVL, ThalaVL the SD of the scan-rescan error was slightly higher (0.43% and 0.5%, respectively). Among the HC the thalamus showed the highest mean VL (−0.16%, −0.39%, and −0.59% at ages 35, 55, and 75, respectively). Corresponding cut-offs for a pathological VL/year were −0.68%, −0.91%, and −1.11%. The MS cohorts did not differ in BVL and GMVL. However, both MS cohorts showed a significantly (p = 0.05) stronger deep GMVL than BVL per year. ConclusionIt might be methodologically feasible to assess deep GMVL using JI in individual MS patients. However, age and the measurement error need to be taken into account. Furthermore, deep GMVL may be used as a complementary marker to BVL since MS patients exhibit a significantly stronger deep GMVL than BVL.