B4C Content Research Articles

Microstructures and mechanical properties of TiAl matrix composites with multi-precipitates quasi-continuous network reinforced structures

A novel quasi-continuous network reinforced structure that consists of borides and carbides in B4C/TiAl matrix composites was innovatively designed for the strengthening at high temperatures. Simultaneously, impacts of such reinforced structures on microstructures and mechanical properties of the composites have been unveiled. TiAl matrix units in B4C/TiAl composites are duplex microstructures which are composed of (α2+γ) colonies and γ grains. The ascent of B4C contents triggers off the formation of network reinforced structures in the layers of TiAl matrix units. With B4C contents increasing to 0.1 wt%, elasticity modulus and ultimate compressive strengths of B4C/TiAl composites are upgraded from 10.944 GPa and 723.10 MPa to 16.052 GPa and 774.611 MPa. As B4C contents reach at 5.0 wt%, elasticity modulus and ultimate compressive strengths further soar to 17.244 GPa and 799.19 MPa. Borides and carbides within the quasi-continuous network reinforced structures are unfolded as stripe and needle shaped TiB with B27 structure and Ti2AlC particles with MAX structure. Parts of Ti2AlC particles take TiB as cores to nucleate and grow. Moreover, TiC phases usually act as the cores for the nucleation of Ti2AlC particles. The orientation relationships of such reinforcements represent as [011]TiC//[010]TiB, (1–11)[011]TiC//(0006) [-2110]Ti2AlC, [100]TiB//[0001]Ti2AlC, [010]TiB//[-2110]Ti2AlC and [001]TiB//[01–10]Ti2AlC. The fractures of TiB are usually along or perpendicular to [010]TiB direction. Meanwhile, the fracture surfaces of TiB are always parallel to (100)TiB or (010)TiB planes. Additionally, dislocations slip through Ti2AlC particles and lead to separation and sliding of staking planes (0001)Ti2AlC within Ti2AlC lattices. TiB and Ti2AlC with alternative distribution can stabilize the network reinforced structures and upgrade properties of B4C/TiAl composites.

Microstructure and anti-ablation of laser cladding Ti-Zr-B-C coating on TC11 titanium alloy

To enhance the service life and application range of titanium alloys in the aerospace sector, Ti-Zr-B-C coatings with varying B4C contents (0–30 wt%) on TC11 titanium alloy was fabricated by laser cladding. The microstructure and anti-ablation were investigated in the present work. The results show that the whisker-like TiB phases and granular TiC and ZrC phases were observed in the coatings due to the in-situ reactions. With increasing the content of B4C, the number of reinforcing phases in the coating increased and distributed uniformly, resulting in the improvement of the microhardness up to 803.8HV. Furthermore, due to the formation of TiO2-ZrO2-B2O3 dense multiphase oxide layer on the surface during the ablation process, the coating with 20 wt% B4C exhibited the best anti-ablation at 1400ºC, the mass ablation rate (MAR) and linear ablation rate (LAR) were −2.62 mg/s and 3.67μm/s, respectively, which were just 62.8 % and 50.07 % in comparison with the substrate. This is mainly attributed to the formation of TiO2-ZrO2-B2O3 layer is beneficial to reduce the infiltration of O2 and the evaporation of liquid B2O3, leading to the excellent anti-ablation.

A Study on the Optimization of Nano-B4C Content for the Best Wear and Corrosion Properties of the Al-Based Hybrid Nanocomposites

This investigation is dedicated to producing hybrid nanocomposites based on AA2024, achieved through the utilization of powder metallurgy methods encompassing mechanical milling and hot pressing. The research focused on studying how changes in B4C content influence the mechanical, wear, and corrosion behavior of AA2024/h-BN/B4C hybrid nanocomposites. The findings revealed that as the B4C content increased, the relative density values decreased, and higher porosity values were observed in the hybrid nanocomposite samples. Among the tested samples, the hybrid nanocomposite with 4 wt% B4C exhibited the most favorable properties. It demonstrated significantly higher hardness and ultimate tensile strength compared to AA2024 matrix alloy, with values of 161 HB and 372 MPa, respectively. In contrast, the matrix alloy showed hardness and ultimate tensile strength values of 105 HB and 237 MPa, respectively. Furthermore, the wear resistance of hybrid nanocomposite with 4 wt% B4C displayed approximately 14 times greater wear resistance under 40 N load compared to the unreinforced AA2024 matrix alloy. The corrosion test results have revealed that the corrosion resistance of the hybrid nanocomposite reinforced with 4wt% B4C is nearly 47% higher compared to the corrosion resistance of the unreinforced AA2024 alloy. This nanocomposite exhibits the highest polarization resistance of 5.21 Ω.cm2.

The effect of boron carbide doping content on the mechanical properties of polyethylene

ABSTRACT This paper presents Martin Buber‘s unpublished manuscript ‘Fragen und Antworten. Die jüdische Besiedlung Palästinas’ in the original German with English translation and contextualizes it within the main stations of Buber‘s Zionist thinking: cultural Zionism, religious Zionism, and Zionism of realization. It problematizes Buber‘s reflection on Jewish settlements in Palestine with reference to the significance of Zionism for humanity as well as the possibility of reconciliation between Jews and Arabs in the Middle East. It also addresses the problem of Jewish terror, framing it in correlation with the restrictions on Jewish migration to Palestine and the catastrophe of the Shoah.

A novel B4C/Al-316 L neutron absorbing clad plate prepared by cold spraying: Microstructure and mechanical properties

Due to the excellent mechanical properties and neutron shielding properties, B4C/Al composites have become the most commonly used neutron absorbers. However, there is a problem of mutual restriction between the B4C content and mechanical properties (at high temperature) in B4C/Al composites. Therefore, for a B4C/Al-316 L clad plate prepared by cold spraying and subsequent annealing, it was proposed that the 316 L substrate will bear the mechanical properties at the high temperature required by the material, while B4C/Al composites will be used for neutron absorption. The neutron shielding performance of the B4C/Al composites was evaluated by Monte Carlo approach. EBSD tests were performed to characterize the microstructure, and a series of tensile and shearing tests were carried out to characterize the mechanical properties of the B4C/Al-316 L clad plates. The results revealed that the B4C/Al-316 L clad plates have good neutron absorbing qualities and excellent mechanical properties at room temperature and high temperature. In addition, the fracture mechanism of B4C/Al composites on B4C/Al-316 L clad plates was analyzed.

Study on the friction drilling behaviors and tribological properties of aluminum matrix composites

This study investigates Al 6063 matrix composites reinforced with different weight percentages of B4C (5%, 10%, 15%, and 20%) produced through powder metallurgy and hot extrusion. The resulting specimens were subjected to a comprehensive investigation to elucidate the effect of B4C reinforcement on the density, tensile strength, transverse rupture strength (TRS), hardness, tribological characteristics, and friction drilling behavior. The pin-on-disk wear tests were conducted in a dry environment, while the friction drilling experiments were performed under constant spindle speed and feed rate conditions, both in dry and minimum quantity lubrication (MQL) environments. The findings revealed a uniform B4C particle dispersion and strong interface bonding in the matrix and that the hardness, tensile strength, TRS, and wear resistance of the specimens increased as the weight fraction of the reinforcement increased. The 15 wt% and 20 wt% B4C composites showed the highest wear resistance, improving by 62.78% compared to Al6063. Higher B4C content reduced specific wear rates and reduced friction coefficients. Among the specimens under investigation, the Al6063 composite reinforced with 15 wt% B4C indicated the highest tensile, transverse rupture, whereas the Al6063 composite with 10 wt% B4C exhibited the best thread-pull-out strength (TPS). The friction-drilled 10 wt% B4C composites showed the highest thread-pull-out strength reaching 373.44 N/mm² in MQL and 329.74 N/mm² in dry conditions.

Effect of BN or B4C content on physical and tribological properties of copper‐clad laminates reinforced with carbon fiber and epoxy resin

AbstractPlasma treatment was used to improve the surface roughness of copper foil. The copper‐clad laminates reinforced with carbon fiber, boron nitride (BN), or boron carbide (B4C), and epoxy resin were prepared by hot pressing. The effect of BN or B4C content on the physical properties and tribological properties of copper‐clad laminates reinforced with carbon fiber and epoxy resin were studied. The resulting copper‐clad laminate exhibited desirable properties, such as dielectric constant, peel strength, oxygen index, and arc resistance, which were influenced by the concentration of BN or B4C particles. Additionally, the wear and friction properties of the laminate were evaluated, revealing the effects of load, sliding speed, and particle content on weight loss, specific wear rate, and coefficient of friction. SEM analysis of worn surfaces provided insight into the stages of wear, highlighting the importance of an oxide layer in reducing wear and protecting the copper surface.

Taguchi optimized wear and self-lubricating properties of Al-alloy composite reinforced with hybrid B4C–MoS2 particulates

We investigated self-lubricating Al–Mg–Si hybrid metal matrix composites (HMMCs) embedded with MoS2–B4C particulates, for use in automotive engine components. Composites with different B4C content (x = 3.5, 7.0, 10.5, 14.0, and 17 wt%) were prepared, with the MoS2 content of 3.0 wt%. The metal matrix composites were processed using the powder metallurgy route comprising milling for 2 h and cold pressing and consolidation at a sintering temperature of 560 °C. Their dry sliding wear behavior was examined at applied loads (20–50 N) and sliding distances (1–3 km), and the wear variables were optimized using the Taguchi model (L9). Microstructural analysis was performed using a scanning electron microscope equipped with an energy dispersive spectrometer. A homogeneous particle distribution was observed in the HMMCs, without any appreciable instance of agglomerates. The wear resistance and friction coefficient (COF) improved when MoS2 was incorporated into the HMMCs, compared with a matrix alloy under the same operating conditions. In particular, the COF fluctuated up to a sliding distance of 250 m and was constant for larger values. The wear rate depends on not only the maximum hardness but also the appreciation of self-lubricant MoS2. The Taguchi findings showed that the fraction of hybrid reinforcement had the strongest effect on the wear resistance, and it was followed by the applied load, sliding distance, and track diameter. Apart from providing self-lubrication, the MoS2 particles reduced the wear rate.

Wear and corrosion properties of in-situ TiC–TiB2 modified Ni-based composite coatings with different B/C ratios prepared by laser cladding

The ever-evolving service conditions of high-end equipment continue to bring new challenges to the surface coating of the key components. Thus, modified nickel-based composite coatings with enhanced service performance must be further explored. The work aimed to improve the wear resistance and corrosion resistance of Ni-based coating by in-situ synthesis of TiC–TiB2 composite ceramic phase using TA0, B4C, and nickel (Ni)-coated graphite. First, coatings with different contents of B4C (from 3 wt% to 6 wt%) and Ni-coated graphite (from 0 wt% to 8 wt%) were prepared by laser cladding. The microstructure, phase composition, microhardness, wear properties, and electrochemical properties of the coatings were examined. The increase in the C/Ti ratio after adding Ni-coated graphite led to a decrease in the nucleation rate of the ceramic phase in the molten pool. Ultimately, the size of the ceramic phase gradually increased. The coatings with 3 wt% B4C and 8 wt% Ni-coated graphite showed the best wear resistance, with a 26.47 % reduction in wear volume compared with those of Ni-based alloy coatings. The variation in wear properties was due to the change in wear form caused by the increase in the size of the ceramic phase within the coating. The corrosion potential of the coating added with in-situ TiC–TiB2 increased by 39 % at best, and the corrosion current density was reduced by more than an order of magnitude. This finding was because the ceramic particles distributed throughout the grain boundaries increased the impedance of the coating and blocked the corrosion channels. This study provided theoretical guidance on the preparation of modified Ni-based coatings with excellent wear resistance and corrosion resistance.

Effect of B4C on microstructure evolution and high-temperature mechanical properties of TiAl matrix composites

This study synthesized and characterized the Ti-48Al-2Cr-2 Nb-based composite reinforced by B4C addition, which was produced by spark plasma sintering. The grain size of composites decreased significantly from 225 ± 5 µm to 51 ± 5 µm with the increase of B4C content, mainly due to the pinning effect of in-situ generated TiB2 and Ti2AlC particles at grain boundaries, which limited the rapid grain growth of the matrix. With the addition of B4C, the volume fraction of Ti2AlC increased from 3.0% to 7.4%, with an average size of approximately 5 µm. The ultimate tensile strength and total fracture elongation of the Ti-48Al-2Cr-2 Nb alloy were 482.9 MPa and 10.2% at 800 ℃, correspondingly. With 0.3 wt% addition of B4C, B4C/Ti-48Al-2Cr-2 Nb composite exhibited superior strength (579.5 MPa) and ductility (12.6%) at the same tensile temperature. The reinforced strength of the composite was mainly attributed to the grain refinement and precipitation strengthening.

Effect of B4C particle size and TiB2 content on the mechanical properties of B4C composites and their dynamic mechanical properties

AbstractB4C–MAS and B4C–TiB2–MAS ceramic composites were prepared by hot pressed sintering. The effects of particle size of B4C and TiB2 content on the microstructure and general mechanical properties of the ceramic composites were investigated by using X‐ray diffractometer, scanning electron microscope, and universal testing machine. The strengthening and toughening mechanism of ceramic composites is mainly attributed to the addition of magnesium–aluminosilicate (MAS) and thermal mismatch effect of TiB2. When the TiB2 content was 20 wt.%, the bending strength, fracture toughness, and Vickers hardness of B4C–TiB2–MAS ceramic composites were 375 MPa, 4.42 MPa·m1/2, and 23.9 GPa, respectively, and its relative density could reach 99.7%. The dynamic mechanical properties of B4C–TiB2–MAS ceramic composites were investigated at strain rates of 2000–6000 s−1 using a Separate Hopkinson Pressure Bar (SHPB) device. The results showed that the B4C–TiB2–MAS ceramic composites exhibited significant strain rate sensitivity. The dynamic compressive strength of the ceramic composites increased from 4634 to 5734 MPa with increasing strain rate in the tested strain rate range.

Study of the influence of ZrB2 content and thermal shock on the elastic modulus of spark plasma sintered ZrB2-B4C composites using a non-destructive ultrasonic technique

Non-destructive ultrasound phase spectroscopy (UPS) was used to study the influence of thermal shock on the longitudinal elastic constant (C11) of ZrB2-B4C composites. C11 of the composites was measured in the as-fabricated condition and after different numbers of thermal shock cycles. The relative change in C11 was used as the thermal shock resistance parameter. Composites with 70 and 50 vol% ZrB2 were subjected to three thermal shock temperature differences (ΔT) of 600 °C, 800 °C, and 1000 °C, respectively. The rate of drop in C11 increased significantly with an increase in ΔT and B4C content. The mechanism of thermal shock damage has been discussed considering the influence of processing-induced thermal residual stresses and the average stress state in both phases during thermal shock. It was shown that the powder particle arrangement plays a major role in the damage mechanism and B4C-B4C particle contacts provide easy paths for crack propagation.

Mechanical and Structural Characterization of Laser-Cladded Medium-Entropy FeNiCr-B4C Coatings.

Equiatomic medium-entropy alloy (MEA) FeNiCr-B4C (0, 1, and 3 wt.% B4C) coatings were deposited onto an AISI 1040 steel substrate using pulsed laser cladding. Based on an SEM microstructural analysis, it was found that the cross-sections of all the obtained specimens were characterized by an average coating thickness of 400 ± 20 μm, a sufficiently narrow (100 ± 20 μm) "coating-substrate" transition zone, and the presence of a small number of defects, including cracks and pores. An XRD analysis showed that the formed coatings consisted of a single face-centered cubic (FCC) γ-phase and the space group Fm-3m, regardless of the B4C content. However, additional TEM analysis of the FeNiCr coating with 3 wt.% B4C revealed a two-phase FCC structure consisting of grains (FCC-1 phase, Fm-3m) up to 1 µm in size and banded interlayers (FCC-2 phase, Fm-3m) between the grains. The grains were clean with a low density of dislocations. Raman spectroscopy confirmed the presence of B4C carbides inside the FeNiCr (1 and 3 wt.% B4C) coatings, as evidenced by detected peaks corresponding to amorphous carbon and peaks indicating the stretching of C-B-C chains. The mechanical characterization of the FeNiCr-B4C coatings specified that additions of 1 and 3 wt.% B4C resulted in a notable increase in microhardness of 16% and 38%, respectively, with a slight decrease in ductility of 4% and 10%, respectively, compared to the B4C-free FeNiCr coating. Thus, the B4C addition can be considered a promising method for strengthening laser-cladded MEA FeNiCr-B4C coatings.

A study on the improvement of wear and corrosion properties of ZA40/Graphene/B4C hybrid nanocomposites

The objective of the study was to investigate the production and evaluation of ZA40/Graphene/B4C hybrid nanocomposite (HNC). To fabricate the HNC powders (HNPs) involved the combination of graphene nanoplatelets and B4C micro-particles with ZA40 powders through mechanical milling. The graphene content remained constant 1 wt%, while the B4C content varied at 1 wt%, 2 wt%, and 3 wt%. After an 8-hour milling process, the HNPs were subjected to hot-pressing to create bulk HNC samples. Various tests, including microstructural analysis, hardness, tensile strength, wear resistance, and corrosion resistance, were conducted on the consolidated samples. The results indicated that the HNC sample containing 3 wt% B4C (S3) exhibited the most favorable properties. This sample displayed a hardness value of 181 HB, significantly higher than the ZA40 matrix alloy's hardness of 133 HB. Moreover, its ultimate tensile strength measured at 243 MPa, which was much higher than the ZA40 matrix alloy (157 MPa). The wear resistance of HNCs increased significantly with an increase in B4C content. The sample containing 3 wt% B4C demonstrated approximately 3.5 times greater corrosion resistance than the unreinforced ZA40 matrix alloy.

A theoretical focus on nanoparticle attenuation capabilities for potential utilizations in radiation protect: TiO2-SiO2-Fe3O4-B4C-Al2O3

Radiation shielding materials are essential for various applications in space exploration, nuclear power plants, and medical devices. In this study, we present a theoretical design of radiation shielding nanocomposites based on a combination of TiO2-SiO2-Fe3O4-B4C-Al2O3 materials. Using the Phy-X/PSD, EpiXS, and XMuDAT programs, we calculated the radiation shielding properties, including mass attenuation coefficient, mean free path, and effective atomic number, of a series of nanocomposite structures with different Fe3O4 and B4C contents. Our results show that the addition of Fe3O4 and B4C to nanocomposites enhances the radiation shielding efficiency and the maximum shielding is observed in the nanocomposite with the highest density. The theoretical calculations also reveal that the proposed nanocomposites have excellent radiation shielding properties compared to conventional shielding materials, such as lead and concrete. This work demonstrates the potential of using a computational approach to design novel radiation shielding nanocomposites with improved performance, which could have significant implications for a wide range of applications.

ELECTROCHEMICAL POLARIZATION STUDIES ON SPARK PLASMA SINTERED SS316-B4C COMPOSITE

The corrosion behavior of 316 stainless steel with 10[Formula: see text]wt.% B4C composites has been investigated using electrochemical measurements and electron backscattered diffraction (EBSD) and scanning electron microscopy (SEM) analyzes are performed. Spark plasma sintering (SPS) is used to achieve various heat treatments, which are performed at the temperatures of 800∘C, 900∘C, and 1000∘C. It significantly affects the materials’ ability to resist corrosion. The increase in grain size improves corrosion resistance, except at 900∘C when recrystallization is imperfect. However, grain homogeneity should be taken into consideration. The corrosion behavior of the composites is assessed using Tafel plots. The corrosion rate of the sample at 900∘C (0.2945[Formula: see text]mm/yr) is significantly lower than the rates of the samples at 800∘C and 1000∘C, respectively, as per the corrosion process of composites of 3.5[Formula: see text]wt.% NaCl solution. The B4C contents have a significant impact on the particle size reduction, low-density average crystallite size, mechanical, hardness, corrosion resistance, and thermal stability of composite powder. It is primarily utilized in nuclear applications as a neutron radiation absorbent. The research has revealed that the sample at 900∘C has fewer grain boundaries and the finest passivation film quality and superior corrosion resistance are found in intermediate grain size.

Microstructural evolution and wear properties of in-situ (TiB + TiC)-reinforced Ti6Al4V matrix composite coating by laser melting deposition

In this study, a laser melting deposition (LDM) process was employed to deposit titanium matrix composite (TMC) coatings on a titanium alloy substrate by adding 1–5 wt% nanosized B4C particles, which were annealed at 900 °C. The microstructure and dry sliding friction behavior of TMC coatings were studied before and after the annealing treatment. The experimental results show that the TiB + TiC hybrid reinforced phase formed by the in-situ reaction of B4C and Ti matrix mainly precipitated at the grain boundary, providing the grain boundary and second-phase strengthening. Specific orientation relationships of TiB and TiC phases with the matrix phase were revealed, which had an essential effect on the microhardness distribution along the coatings. The annealing treatment promoted the diffusion of hybrid reinforcement into the matrix, strengthening their interface bonding, and has an significant impact on the wear properties of TMC coating. The room temperature friction coefficient (COF) of all the coatings remained relatively constant at 0.3–0.6. With increasing B4C content, the wear loss of the as-deposited coatings continually increased from 0.024 mm3 to 0.054 mm3, while the wear loss of the annealed TMC coatings are much lower than before, from 0.032 mm3 (TMC1) to 0.020 mm3 (TMC2) and then rise to 0.023 mm3 (TMC3). Scanning electron microscopy (SEM) morphologies determined that annealing reduced the abrasive and adhesive wear of TMC composite coating and improved its wear resistance.

Microstructural evaluation and wear behavior of B4C particle reinforced TiO2-SiO2-ZnO compound by hot-pressing method

In this study, different wt% of B4C material added to TiO2, ZnO, and SiO2 materials known with distinguished properties by hot-pressing method to produce new materials. Characterization of the materials was performed by using XRD, SEM and EDS. The micro-hardness of the materials was measured and the wear characteristics of B4C-added materials were determined by subjecting them to wear loads of 5 N, 10 N and 15 N. In XRD, it was observed that the intensity of the peak was decreased depending on the increase in B4C content. In SEM, it was determined that there was a two-phase structure with complex boundaries and indefinite grain boundary formation. Besides, it was determined that elements in the EDS and the compounds in the XRD supported each other. In wear analyses, it was seen that as the wear load increased, the depth and width of the wear track in all materials increased. Furthermore, as the weight ratio of B4C material in the composition was increased, the weight loss at different wear loads was decreased and the lowest weight loss was found in Ti45Si15Zn20B20 material. Moreover, it was observed that the wear track and its depth were inversely proportional to the increasing B4C content in the compound. Friction coefficients of the materials under 5 N wear load varied between 0.15–0.43, whereas under 10 N and 15 N wear load, it varied between 0.09–0.28 and 0.06–0.29, respectively. While the hardness value of B4C-free Ti60Si20Zn20 was 260 HV, the highest hardness value was seen in Ti45Si15Zn20B20 material as 1010 HV.

Investigation on the impact of B4C content in AA5052 based metal matrix composites on the mechanical properties of welded joints

In this research, the tungsten inert gas welding was used to join together metal matrix composites (MMCs) reinforced in different percentages with B4C. The welding settings were maintained at a constant value for all specimen situations. Thermal ageing was used to achieve maximum age-hardening in the welded composites. Misorientation and energy storage are the microscopic features of aged composites that distinguish them from composites that have not been aged. Tensile strength and hardness both increased with increasing B4C concentration, but at opposite rates, suggesting that hardness resulted from energy storage while tensile strength resulted from misorientation. Age hardening as measured by electron backscatter diffraction (EBSD) occurs due to a active recovery of the weld metal (WM) region following a reorganization in displacement structures caused by the precipitation of magnesium silicate or an increase in boron carbide content. The healing process is primarily driven by the action of precipitation strengthening, rather than the impact of obliteration of displacements, as evidenced by the correlation between tensile strength and reduction in misorientation. Adding B4C to aluminium metal matrix composites before welding causes the structural changes that need to be characterized. The welding process's structural changes are analysed, and connections are made to the welded junctions' mechanical behaviour. The study's findings suggest that the microstructure's misorientation distribution is as crucial as the average amount of misorientation in determining a material's strength.

Influences of powder ratios on the mechanical properties of in-situ synthetic NbC coatings

NbC-enhanced Ni-based coatings were prepared by laser cladding to explore the effect law of B4C with different proportions on the coating microstructures and mechanical properties. Results showed that the coating was mainly composed of the reinforced phase (NbC, Cr5B3) and the matrix (Fe-Cr solid solution), and the changed powder ratio did not affect the phase composition of coatings. Meanwhile, increased B4C improved coating hardness. The highest coating hardness was 1794.1 HV1.0, which was 1.56 times that of the matrix. The wear resistance of coatings first increased and then decreased with increased B4C content. Wear resistance was optimal when the ratio was 1:1.3. The main wear mechanism of the coating was abrasive wear, accompanied by a small amount of adhesive wear.