Mechanical and tribological properties of acrylonitrile–butadiene rubber filled with graphite and carbon black

In this work, acrylonitrile–butadiene rubber (NBR)/expanded graphite (EG)/carbon black (CB) micro- and nanocomposites were prepared by two different methods, and the resulting mechanical and tribological properties were compared with those of NBR/CB composites. Meanwhile, the effects of graphite dispersion and loading content, as well as the applied load and sliding velocity on the tribological behavior of the above composites under dry friction condition were also evaluated. The worn surfaces were analyzed by scanning electron microscopy (SEM) to disclose wear mechanism. As expected, the better the dispersion of graphite, the more remarkable enhancement on tensile and dynamic mechanical properties, and the greater reduction in the coefficient of friction (COF) and specific wear rate (W_s). It was found that a small amount of EG could effectively decrease COF and W_s of NBR/CB composites because of the formation of graphite lubricant films. The COF and W_s of NBR/CB/EG composites show a decreasing trend with a rise in applied load and sliding velocity. NBR/CB/EG nanocomposite always shows a stable wearing process with relatively low COF and W_s. It is thought that well-dispersed graphite nano-sheets were beneficial to the formation of a fine and durable lubricant film.     

Dry rolling and sliding friction and wear of organophilic layered silicate/hydrogenated nitrile rubber nanocomposite

Dry rolling and sliding tribological behaviors of hydrogenated nitrile rubber (HNBR) and its compound, containing 10 parts per hundred rubber (phr) organophilic layered silicates (OLS), were evaluated. As OLS modifier a quaternary amine with hydroxyl and double bonds was selected to support the intercalation/exfoliation by triggering possible interactions with HNBR. According to X-ray diffraction results the OLS was intercalated. Network-related parameters were deduced from dynamic-mechanical thermal analysis (DMTA). The tribological parameters, i.e., coefficient of friction (COF) and specific wear rate (W _s), were determined in various home-made test configurations. The OLS reinforcement of HNBR affected the COF and improved the resistance to rolling and sliding wear (except fretting) compared to the pure HNBR. The worn surfaces of the rubber compounds were inspected in scanning electron microscope (SEM) and the dominant wear mechanisms concluded.     

Processing and properties of bulk ultrafine-grained pure niobium

An ultrafine-grained (UFG) microstructure in electron beam-melted casts of commercial pure niobium (Nb) was produced in an equal-channel angular pressing die with a right angle, without roundings, at 12 passes, and by the B _c route. Additional microstructural improvements were made by hard cyclic viscoplastic deformation and the double-bounded microstructure was formed. The new nanoindentation technique was used to study the pure Nb micro-mechanical properties of the shear bands (SBs). The wear resistance of Nb was studied by a ball-on-plate tribometer with an alumina (Al₂O₃) counterface ball. The results showed that the nanohardness of pure Nb on boundaries of SBs was ~6 GPa, while inside of SBs, it was only ~3.5 GPa (measured under an indentation load of 10 mN). The corresponding elastic modules were ~150 and ~100 GPa, respectively. Such heterogeneity of the micromechanical properties has an influence on the coefficient of friction (COF) and the wear rate. The Nb with an UFG microstructure has an increased COF and a higher specific wear rate as compared to the as-cast sample. The COF depends on the direction of the wear test relative to the SBs’ orientation. As the boundaries of SBs have the highest hardness, compared to areas inside of SBs, the wear track surface has a high roughness, which leads to an increase in the COF of the double-banded ultrafine-rained pure Nb.     

Tungsten/tungsten nitride performance at elevated temperature

Abstract

Multilayer physical vapour deposition (PVD) coating of W/W₂N (tungsten/tungsten nitride) on Orvar Supreme steel was tested under the different conditions to investigate their friction and wear behaviour with their mechanical properties. Coatings were sputtered by reactive magnetron sputtering in a N₂/Ar atmosphere. Pin on disc test was performed on Orvar Supreme steel at room temperature to elevated temperature (800°C). Steel ball (100Cr6) and alumina ball are used to evaluate the frictional and wear properties. Scanning electron microscopy (SEM) and energy dispersive X-ray analyses were performed to obtain the microstructure and chemical composition of the material. Mechanical properties of coating were evaluated using nanoindentation and scratch test.     

Si3N4和52100钢对磨副材料对CrN薄膜干摩擦学行为的影响

利用阴极电弧离子镀技术在316L不锈钢基体上制备了CrN薄膜。采用扫描电子显微镜(SEM)、X射线衍射仪(XRD)、纳米压痕仪对CrN薄膜的形貌、成分和力学性能进行了表征。为了研究Si_3N_4和52100钢对磨副材料对CrN薄膜和316L不锈钢干摩擦行为的影响,在2N、5N、8N三种载荷下,将CrN薄膜和316L不锈钢基体与Si_3N_4陶瓷球和52100钢球分别进行了往复式滑动干摩擦实验。采用扫描电子显微镜观察了磨痕的微观形貌,并对CrN薄膜和316L不锈钢基体的磨损机制进行了分析。结果表明:CrN薄膜表面平整,缺陷较少;CrN薄膜的纳米硬度约为28GPa,弹性模量约为350GPa;与Si_3N_4陶瓷球相比,CrN薄膜与52100钢球摩擦时摩擦因数相对较小(保持在0.7左右)且更加稳定;316L不锈钢的摩擦因数远大于CrN薄膜且波动较大;对磨球为Si_3N_4陶瓷球时,CrN薄膜的主要磨损机制为磨粒磨损,伴有少量的氧化和黏着磨损,316L不锈钢的磨损机制主要为磨粒磨损和塑性变形,伴有少量的氧化和黏着磨损;对磨球为52100钢球时,CrN薄膜的主要磨损机制为黏着磨损,伴有少量的氧化,316L不锈钢的磨损机制主要为黏着磨损,伴有少量的氧化和磨粒磨损。CrN薄膜与两种对磨球的磨损量均小于316L不锈钢基体的磨损量,说明CrN薄膜有效提高了基体的耐磨性。     

Tungsten oxide with different oxygen contents: Sliding properties

In this study, tungsten oxide coatings with 13 and 75 at% of oxygen were prepared by DC reactive magnetron sputtering from a pure W target in an Ar+O₂ atmosphere. The coating hardness (H) decreased with increasing oxygen content from 25 to 7.7 GPa. The values of H/E ratio were 0.08 and 0.07 for W₈₇O₁₃ and W₂₅O₇₅, respectively.The tribological measurements were carried out on a pin-on-disc tribometer at room temperature, with a load of 5 N and steel 100Cr6, ceramic Si₃N₄ and Al₂O₃ balls as sliding partners. The wear track and wear debris were visualised by scanning electron microscopy and the chemical composition of the later was estimated by energy-dispersive X-ray analysis. The friction coefficient was rather high in case of the W₈₇O₁₃ coating reaching values in the range from 0.7 to 0.75 for both counterpart materials, and slightly lower for W₂₅O₇₅ (∼0.50). The coating wear rate decreased with increasing oxygen content with the Al₂O₃ ball, while using Si₃N₄ ball as a counterpart showed an opposite trend. The coating with low oxygen content was more resistant to abrasive wear.     

Wear behaviour and rolling contact fatigue life of Ti/TiN/DLC multilayer films fabricated on bearing steel by PIIID

In order to improve the friction and wear behaviours and rolling contact fatigue (RCF) life of bearing steel materials, Ti/TiN/DLC (diamond-like carbon) multilayer hard films were fabricated onto AISI52100 bearing steel surface by plasma immersion ion implantation and deposition (PIIID) technique. The micro-Raman spectroscopy analysis confirms that the surface film layer possess the characteristic of diamond-like carbon, and it is composed of a mixture of amorphous and crystalline phases, with a variable ratio of sp²/sp³ carbon bonds. Atomic force microscope (AFM) reveals that the multilayer films have extremely smooth area, excellent adhesion, high uniformity and efficiency of space filling over large areas. The nanohardness (H) and elastic modulus (E) measurement indicates that the H and E of DLC multilayer films is about 32 GPa and 410 GPa, increases by 190.9% and 86.4%. The friction and wear behaviours and RCF life of DLC multilayer films specimen have also been investigated by ball-on-disc and three-ball-rod fatigue testers. Results show that the friction coefficient against AISI52100 steel ball decreases from 0.92 to 0.25, the longest wear life increases nearly by 22 times. In addition, wear tracks of the PIIID samples as well as wear tracks of the sliding steel ball were analyzed with the help of optical microscopy and scanning electron microscopy (SEM). The L₁₀, L₅₀, L_a and mean RCF life L of treated bearing samples, in 90% confidence level, increases by 10.1, 4.2, 3.5 and 3.4 times, respectively. Compared with the bearing steel substrate, the RCF life scatter extent of Ti/TiN/DLC multilayer films sample is improved obviously.     

Effect of expanded graphite and modified graphite flakes on the physical and thermo-mechanical properties of styrene butadiene rubber/polybutadiene rubber (SBR/BR) blends

The aim of the present research work is to develop expanded graphite (EG) and isocyanate modified graphite nanoplatelets (i-MG) filled SBR/BR blends, which can substitute natural rubber (NR) in some application areas. The present study investigated the effect of i-MG on the physical, mechanical and thermo-mechanical properties of polybutadiene rubber (BR), styrene butadiene rubber (SBR) and SBR/BR blends in the presence of carbon black (CB). Graphite sheets were modified to enhance its dispersion in the rubber matrices, which resulting in an improvement in the overall physical and mechanical properties of the rubber vulcanizates. Compounds based on 50:50 of BR and SBR with ∼3 wt% nanofillers with CB were fabricated by melt mixing. The morphology of the filled rubber blends was investigated by wide angle X-ray diffraction (WAXD) and high resolution transmission electron microscopic (HR-TEM) analyses. The intercalated and delaminated structures of the nanofiller loaded rubber blends were observed. Scanning electron microscopic (SEM) analysis of the cryo-fractured surfaces of the rubber compounds showed more rough and tortuous pathway of the fractured surfaces compared to the fractured surfaces of the only CB loaded rubber composites. Filled rubber compounds exhibit increase in the ΔS (torque difference) value, reduced scorch and cure time compared to their respective controls. Dynamic mechanical thermal analysis (DMTA) of the filled rubber compounds shows an increase in the storage modulus compared to the controls. Isocyanate modified graphite nanoplatelets (i-MG) containing rubber compounds in the presence of CB showed an increase in the mechanical, dynamic mechanical, hardness, abrasion resistance and thermal properties compared to the alone CB filled rubber vulcanizates.     

Particle effects on friction and wear of aluminium matrix composites

Particle effects on friction and wear of 6061 aluminium (6061 Al) reinforced with silicon carbide (SiC) and alumina (Al₂O₃) particles were investigated by means of Vickers microhardness measurements and scratch tests. Unreinforced 6061 Al matrix alloy was also studied for comparison. To explore the effect of heat treatment, materials subjected to three different heat treatment conditions, i.e. under-aged, over-aged and T6, were used. Multiplescratch tests using a diamond and a steel indentor were also carried out to simulate real abrasive wear processes. Vickers microhardness measurements indicated that T6 heattreated composites had the highest hardness. Single-scratch tests showed that the variation of friction coefficient was similar to that of Vickers hardness and the peak-aged composites exhibited the best wear resistance. The wear rate of fine particle-reinforced composites was mainly affected by hardness. However, the wear rate of large particle-reinforced composites was influenced by both the hardness and fracture of the particles.     

Differences in dry sliding wear behavior between HVAF-sprayed amorphous steel and crystalline stainless steel coatings

Dry sliding wear behavior of amorphous steel coating(ASC) and crystalline stainless steel coating(SSC)manufactured by high-velocity-air-fuel-spraying was investigated. With increasing normal load, coefficient of friction(COF) of ASC decreases slightly from 0.78 to 0.69. COF of SSC presents a minor difference under various normal loads but increases with sliding time accompanied by relatively large fluctuation.Such a difference in friction behavior between such two coatings can be understood based upon the roles of shear stress and flash temperature. Wear rate of SSC is much higher than that of ASC, suggesting better wear resistance of ASC. The enhanced wear resistance is correlated with high hardness(H), reduced Young's modulus(E_r), and ratios of H/Erand H~3/E_r~2. Detailed analyses on worn surfaces and sub-surfaces indicate that the wear mechanisms for ASC include delamination, abrasive and oxidation wear, whereas those for SSC are delamination and oxidation.     

Influence of laser dispersed treatment on rolling contact wear and fatigue behavior of railway wheel steel

The aim of this paper is to improve the rolling contact wear and fatigue resistance of ferrite–pearlite railway wheel steel by laser dispersed treatment. Such treatment creates isolated glazed regions on the surface layer of railway wheel steel, which are composed of fine martensite and retained austenite and have an average hardness of 762HV_0.3. The wear rate and rolling contact fatigue life of treated and untreated railway wheel steel were evaluated and compared by Amsler twin-disc testing machines in dry and lubricated condition, respectively. The test results show that laser dispersed treatment improves the rolling contact wear and fatigue resistance of railway wheel steel. The stable wear rate of the laser treated railway wheel steel is about 0.3 times that of untreated railway wheel steel and the average rolling contact life of treated railway wheel steel is about double that of the untreated steel. Further investigations show that the glazed regions suppress the plastic deformation of railway wheel steel. This inhibits the treated railway wheel steel from delamination wear and delays the formation of fatigue crack initiation.     

Tribological Studies of a Zr‐Based Glass‐Forming Alloy with Different States

The tribological characteristics of a glass‐forming alloy, Zr_52.5Cu_17.9Ni_14.6Al_10.0Ti_5.0, in atomic percent (at.%, Vit 105), with different microstructural states have been investigated. Friction and wear studies were conducted using a ball‐on‐flat reciprocating sliding apparatus against an AISI E52100 bearing steel under dry condition. The observed wear resistance in an ascending order is: the deformed, creep‐tested, and as‐cast states. Wear analyses suggested that the wear processes of glass‐forming alloys involved abrasion, adhesion, and oxidation. The differences in hardness, free volume, and brittleness in different states significantly affected the friction and wear behaviors of the glass‐forming alloys.     

Friction and wear properties of Cr:(Wx,N0.1) coatings deposited by magnetron sputtering

This paper discusses the friction and wear properties of Cr:(W_x,N_0.1) coatings with different tungsten contents. The Cr:(W_x,N_0.1) coatings with x being in the range of 0-0.16 were deposited using unbalanced magnetron sputtering technology. The microstructures and mechanical properties of Cr:(W_x,N_0.1) coatings have been characterized by SEM, TEM, X-ray diffraction (XRD), nanoindentation and adhesion techniques. The tribological properties of the coatings were investigated using an oscillating friction and wear tester under dry conditions. Indexable inserts with Cr:(W_x,N_0.1) coatings were applied to turning AISI 1045 steel material by a lathe. Micron-drills with Cr:(W_x,N_0.1) coatings were adopted in the ultra high speed (10⁵ rpm) PCB through-hole drilling test. Experimental results indicate that the coating microstructure, mechanical properties and wear resistance vary according to the tungsten content. All the coatings crystallize in the BCC phase. Cr:(W_0.06,N_0.1)-coated tools showed the best wear resistance in 1045 steel turning and PCB through-hole drilling tests. The service life of Cr:(W_0.06,N_0.1)-coated tool is three times greater than that of an uncoated tool in PCB through-hole drilling test.     

Quantitative mapping of surface elastic moduli in silica-reinforced rubbers and rubber blends across the length scales by AFM

The surface elastic moduli of silica-reinforced rubbers and rubber blends were investigated by atomic force microscopy (AFM)-based HarmoniX material mapping. Styrene–butadiene rubbers (SBR) and ethylene–propylene–diene rubbers (EPDM) and SBR/EPDM rubber blends with varying concentrations of silica nanoparticles (0, 5, 10, 20, 50 parts per hundred rubber, phr) were prepared to investigate the effect of different composition on the resulting morphology, filler distribution and elastic moduli of a specific rubber or rubber blend sample. For SBR, the elastic modulus values varied from 0.5 MPa for unfilled SBR to 5 MPa for 50 phr reinforced SBR with the increase in the concentration of filler. For EPDM, the corresponding values increased from 1.4 MPa for unfilled EPDM to 4.5 MPa for 50 phr reinforced EPDM. Local stiff and soft domains in silica-reinforced SBR and EPDM rubbers and rubber blends were identified by HarmoniX AFM imaging. While the stiff silica particles show modulus values as high as 2 GPa, the rubber matrix reveals modulus values in the range of ca. 30 MPa for the rubber blends to ca. 300 MPa for the unfilled rubbers. The lower value of elastic modulus of the EPDM phase in the blend, compared to the blank EPDM compound can be attributed to the presence of Sunpar oil in the compound which has a very good affinity with EPDM and decreases the rubber modulus. The elastic moduli maps revealed an increase of the areal fraction of silica particles showing an intrinsic surface modulus value with rising silica content in the compound preparation mixture. HarmoniX AFM measurements revealed the formation of larger silica aggregates in EPDM in contrast to SBR where isolated silica particles were observed. For silica-reinforced rubber blends a phase separation into a soft (ca. 40 MPa) and a significantly harder phase could be observed (ca. 500 MPa–1.5 GPa) indicating the incorporation of silica particles in the SBR phase. Using HarmoniX AFM imaging significantly higher surface elastic moduli were observed compared to those obtained by bulk tensile testing. Possible reasons for the observed differences between bulk modulus values and those measured by AFM are discussed in detail, including the aspect of different averaging procedures like inherent to surface probing by AFM versus bulk tensile testing, different filler distributions in SBR and EPDM and the AFM modulus calibration procedures.     

Tribological behavior of poly (phenyl p-hydroxybenzoate)/polytetrafluoroethylene composites filled with hexagonal boron nitride under dry sliding condition

The sliding friction and wear behavior of polytetrafluoroethylene (PTFE) composites filled with poly (phenyl p-hydroxybenzoate) (PHBA) and hexagonal boron nitride (h-BN) was investigated with a pin-on-disc tester. The tensile properties, ball indentation hardness, impact strength and thermal diffusivity were measured. The test results in this paper indicate that the tensile strength, elongation at break, and impact strength decreased, however, the ball indentation hardness and thermal diffusivity were increased when the content of h-BN was increased. PTFE composites filled with 20 wt% PHBA and 20 wt% h-BN exhibited a comparative friction coefficient to pure PTFE. Meantime, the wear rate of the composite decreased about 15 times compared to pure PTFE. The synergistic effect of h-BN with low friction and PHBA with high bearing ability promoted the low friction coefficient and wear rate of h-BN/PHBA/PTFE composites.     

Influence of bias voltages on the structure and wear properties of TiSiN coating synthesized by cathodic arc plasma evaporation

Nanocomposite TiSiN films have been deposited on M2 tool steel substrates using TiSi alloy as target by a dual cathodic arc plasma deposition (CAPD) system. The influences of bias voltages on the microstructure, mechanical and tribological properties of the films were investigated. Scanning electron microscopy, transmission electron microscopy, X-ray diffraction techniques were employed to analyse the microstructure, grain size and residual stress. Nano-indentation and tribometer testers were used to measure the mechanical and tribological properties of nanocomposite TiSiN thin films. The results showed that the hardness of the films ranged from 25 to 37 GPa, which were higher than that of TiN (21 GPa). The coefficient of friction of the TiSiN thin films was more stable but was higher than that of TiN when wear against both Cr steel and WC-Co ball, respectively. When encountered with both Cr steel and WC-Co ball of the counter ball, the tribological mechanisms of TiSiN thin films are adhesive and abrasion wears, respectively. It has been found that the microstructure, mechanical and wear properties of the films were correlated to bias voltage, grain size, and amorphous Si₃N₄ nanocomposite formed in film structure, resulting in a superhard TiSiN coating.     

Influence of compositional variables and testing temperature on the wear of hydrogenated nitrile rubber

The influence of the nature and level of the curing system, the loading of carbon black and the resin content on the abrasion loss,V, dynamic coefficient of friction, , and frictional force,F, of hydrogenated nitrile rubber (HNBR) against silicone carbide abrader, is reported at different temperatures.V, , andF decrease with cross-link density. At equal cross-link density, these parameters are the same for both peroxide and sulphur-curing systems. Incorporation of resin decreasesV, , andF progressively.V decreases, but and Fincrease with loading of carbon black at any particular testing temperature, and the opposite trend is observed with increasing temperature. Experimental results on natural rubber (NR) and styrene-butadiene rubber (SBR) are also compared with those of HNBR. The abrasion loss of HNBR is much lower than that of NR and SBR. The abraded surface of NR and SBR is tar-like and ridges are found at all temperatures. In the case of HNBR compounds no ridge, except plough marks in the direction of abrasion, is observed at 25°C. However, at high temperature (> 50°C) the abrasion mechanism changes, and ridge formation takes place. The ridge spacing,R _s, reduces with carbon black loading and decreasing temperature.R _s is related to dynamic shear modulus,G, byR _s=const. (1/G)^1.55.V increases linearly withR _s. The abradability, A, is related to reciprocal of breaking energy,E _b, byA-itC/E _b, where C is a constant having a value of the order of 10^–12 m³.     

Reinforcements affect mechanical properties and wear behaviors of WC clad layer by gas tungsten arc welding

This work deals with the surface analysis, mechanical properties and wear performances of the clad layer, which is made from tungsten carbide (WC) powders on SKD61 die steel by the gas tungsten arc welding method. According to the experimental results, due to the high hardness and elastic modulus reinforcements (Fe₃W₃C and M₇C₃) existing in the WC clad layer, the WC clad specimen has excellent wear performance at different sliding speeds.According to the wear analysis, wear behaviors of the WC clad layer are two-body abrasion and oxidation wear. In addition, oxidation wear dominates the wear behaviors of the SKD61 die steel specimen at different sliding speeds.     

Wear behaviors of Fe-based amorphous composite coatings reinforced by Al2O3 particles in air and in NaCl solution

In this paper, the influence of the addition of Al₂O₃ particles on the microstructure and wear properties of Fe-based amorphous coatings prepared by high velocity oxygen fuel (HVOF) has been studied. The wear behaviors of the composite coatings were evaluated against Si₃N₄ in a pin-on-disk mode in air and in 3.5 wt.% NaCl solution. It was found that the Al₂O₃ particles were homogenously distributed in the amorphous matrix and the composite coatings exhibited improved wear resistance and reduced coefficient of friction (COF) in both air and wet conditions as compared to the monolithic amorphous coating. The composite coating reinforced with 20 wt.% Al₂O₃ particles exhibit the best wear performance, which, for example, has extremely low COF (< 0.2) and high wear resistance (2–3 times higher than monolithic amorphous coating). Detailed analysis on the worn surface indicated that the wear mechanism for the amorphous and composite coatings is similar and is dominated by oxidative delamination in air and by corrosion wear in 3.5% NaCl solution. The enhanced wear resistance is mainly attributed to the addition of Al₂O₃ particles which exhibit high hardness, good corrosion resistance and excellent chemical and thermal stability.     

Failure analysis of a ceramic ball race bearing made of Y-TZP zirconia

Full ceramic ball bearings have some advantages compared to conventional steel bearings. They have for instance higher stiffness and hardness, lower density and reduced friction. Because they need less lubrication than steel bearings and owing to their wear and corrosion resistance they are generally materials of choice for pharmaceutical and food industries.In this work a full ceramic bearing that was used in a small mixer in the pharmaceutical industry is investigated. The bearing, consisting of two ZrO₂ rings and silicon nitride balls in between, was damaged during service because of premature wear. A failure analysis is performed by fractography and Raman spectroscopy, and it is shown that a stress induced phase transition from the tetragonal to the monoclinic phase was the reason behind the failure of the ZrO₂-rings.