Tribological behaviors of B4C–SiC composites self-mated pairs in seawater and pure water

In this paper, the tribological behaviors of B₄C–SiC composites self-mated pairs in seawater and pure water were investigated, respectively. The results showed that the B₄C–SiC composite with the content of 20%SiC has good mechanical properties. For the B₄C–20%SiC self-mated pair in seawater, the abrasive wear is greatly weakened, and the tribo-chemical reactions between the composite surface and water molecules occurred. The tribo-chemical polishing causes very smooth wear surfaces, and the sliding pairs enter to the status of liquid lubrication. An extremely low friction coefficient (0.038) and wear rate (both below the order of magnitude 10⁻⁵ mm³/N m) were obtained in this study. Due to the lower viscosity of pure water, the load carrying capacity of the liquid film reduces. So, in pure water, the sliding pair shows slightly higher friction coefficient and wear rate than that in seawater.     

Effect of nanorelief structure formed in situ on tribological properties of ceramics in dry sliding

Nanorelief structure formed on the surface of B₄C–SiC ceramics by an in-situ method is reported. The nanorelief structure formed by the in-situ method, which differs from the relief structure produced by laser treatment, results from preferential wearing of SiC particles, which have lower hardness, by free diamond particles and mixed wear particles of B₄C and SiC during polishing and sliding, respectively. The effect of the nanorelief structure formed by the in-situ method on the sliding dry friction against a SiC ball is examined using a pin-on-disk tribometer. A comparison of dry sliding of the B₄C–SiC composite ceramics with nanorelief structure to that of SiC ceramics without nanorelief structure reveals that B₄C–SiC composite ceramics have a lower coefficient of friction and a significantly lower specific wear rate than the SiC ceramics. Worn surface analysis indicates that the nanorelief structure does not disappear after a dry sliding test. The depth of the nanorelief structure formed by the in-situ method ranges from 10 to 40 nm. The friction and wear results are associated with the nanorelief structure formed by the in-situ method.     

Evaluation of tribological behavior of B4C–hBN ceramic composites under water-lubricated condition

The aim of this study is to evaluate the influence of hexagonal boron nitride (hBN) addition on the tribological behavior of B₄C-based ceramic composites under distilled water lubrication. Water-lubricated sliding tests of hot-pressed B₄C–hBN ceramic composites with different hBN amounts against pure B₄C ceramic were carried out on a pin-disc type wear apparatus. It was found that the addition of hBN into B₄C ceramic matrix resulted in a severe decrease of the friction coefficient from 0.373 for B₄C/B₄C sliding pair to 0.005 for B₄C–20 wt% hBN/B₄C sliding pair. A B₂O₃ tribochemical film formed on the worn surface of the B₄C–hBN specimen protected both B₄C–hBN and B₄C and facilitated the frictional surfaces to smooth. Therefore, the tribological behaviors of the pairs were significantly improved. The formation process of the film and its antifriction mechanism are discussed.     

Tribological behaviour of TiB2-HfC ceramic tool material under dry sliding condition

In order to disclose friction and wear mechanism of TiB₂-HfC ceramic, tribological behaviour of TiB₂-HfC ceramic sliding against YG8, 316 stainless steel (316) and TA2 were investigated. Friction coefficients between TiB₂-HfC ceramics and these materials decreased not only with an increase of sliding speed but also with an increase of normal load, respectively. Wear rates of TiB₂-HfC ceramics sliding against these materials increased with an increase of sliding speed as well as with an increase of normal load, respectively. B₂O₃, TiO₂ and HfO₂ formed in TiB₂-HfC ceramics sliding against these materials. In addition, intergranular and transgranular microcracks and WO₃ appeared in the worn surface after the ceramic slid against YG8; lamellar structures like fish scale, areas of exposed grains, pits, Fe_xO_y and Cr₂O₃ existed in the worn surface after the ceramic slid against 316; ribbon-like structures, areas of exposed grains, wear particles and furrows existed in the worn surface after the ceramic slid against TA2. Besides oxidation wear, abrasive wear played an important role in TiB₂-HfC ceramic sliding against YG8, while adhesive wear and abrasive wear played a dominant role in TiB₂-HfC ceramic sliding against 316 or TA2.     

Effect of mono and hybrid ceramic reinforcement particles on the tribological behavior of the AZ31 matrix surface composites developed by friction stir processing

The effects of the size and morphology of the reinforcement particles on hardness and tribological behaviors of the AZ31 Mg alloy matrix composites were studied. Different ceramic compounds, including boron carbide (B₄C), tungsten carbide (WC), and Zirconia (ZrO₂) were selected as the reinforcement materials for developing mono composites. The average sizes of the B₄C, WC, and ZrO₂ particles were about 150 μm, 5 μm, and 35 nm, respectively. Besides, hybrid reinforcements composed of the B₄C + ZrO₂ and WC + ZrO₂ powders were employed to develop hybrid composites. All the composite were fabricated using the friction stir processing (FSP) technique. Investigating the microstructure of the composites by secondary electron microscopy (SEM) analysis showed a homogenous distribution of the reinforcement particles in the AZ31 Mg alloy matrix. Microhardness measurements revealed that the hardness of AZ31/ZrO₂ nanocomposite is about 120% higher than that of AZ31 base metal. According to the results of the dry sliding wear tests, the AZ31/B₄C and AZ31/ZrO₂ composites had a maximum wear resistance and a minimum friction coefficient average, respectively. Combining the B₄C and WC reinforcements with the ZrO₂ nanoparticles caused an improvement in wear resistance and friction performances of the hybrid composites. SEM observations of the worn surfaces and debris resulted from wearing of the samples after 500 m sliding distance under the normal load of 10 N, revealed that the severe and mild abrasive mechanisms are dominant.     

Effect of load on the friction and wear characteristics of Si3N4-hBN ceramic composites sliding against steels

The tribological behaviors of Si₃N₄-hBN ceramic composites sliding against steels (austenitic stainless steel (ASS) and 45 steel) under dry friction conditions at different loads were investigated by using an MMW-1 type vertical universal friction and wear tester. The experimental results showed that the friction coefficients and wear rates first showed a decrease and then an increase with an increase in the load under dry friction conditions. The better tribological performance was exhibited by the SN10/ASS sliding pair under a load of 20 N (the friction coefficient was as low as 0.27 and the wear rates of both pin and disc had a magnitude of 10⁻⁶ mm³ N⁻¹ m⁻¹). This may be attributed to the formation of a black surface film (consisting of B₂O₃, SiO₂, and Fe₂O₃). For the same sliding pair, when the load was 10 N, the dominating wear mechanism was abrasive wear. Hence, the friction coefficient was higher (0.7). When the load increased to 30 and 50 N, the wear mechanism of the SN10/ASS sliding pair was a combination of abrasive and adhesive wears, and higher friction coefficients (0.48 and 0.72 under loads of 30 and 50 N, respectively) were obtained. On the other hand, the contents of hBN also showed a significant impact on the tribological behaviors of the Si₃N₄-hBN/ASS sliding pairs. When the hBN content was less than 10%, the friction coefficients of the Si₃N₄-hBN/ASS sliding pairs decreased with an increase in the hBN content. On the other hand, at hBN contents of 10% or more, the friction coefficients of the sliding pairs increased with an increase in the hBN content. Under the same experimental conditions, the Si₃N₄-hBN/45 steel pairs showed poor tribological properties as compared with the Si₃N₄-hBN/ASS pairs.     

Friction and wear characteristics of ceramic particle filled polytetrafluoroethylene composites under oil-lubricated conditions

Five kinds of polytetrafluoroethylene (PTFE)-based composites were prepared: PTFE, PTFE + 30 vol % SiC, PTFE + 30 vol % Si₃N₄, PTFE + 30 vol % BN, and PTFE + 30 vol % B₂O₃. The friction and wear properties of these ceramic particle filled PTFE composites sliding against GCr15 bearing steel under both dry and liquid paraffin lubricated conditions were studied by using an MHK-500 ring-block wear tester. The worn surfaces and the transfer films formed on the surface of the GCr15 bearing steel of these PTFE composites were investigated by using a scanning electron microscope (SEM)and an optical microscope, respectively. The experimental results show that the ceramic particles of SiC, Si₃N₄, BN, and B₂O₃ can greatly reduce the wear of the PTFE composites; the wear-reducing action of Si₃N₄ is the most effective, that of SiC is the next most effective, then the BN, and that of B₂O₃ is the worst. We found that B₂O₃ reduces the friction coefficient of the PTFE composite but SiC, Si₃N₄, and BN increase the friction coefficients of the PTFE composites. However, the friction and wear properties of the ceramic particle filled PTFE composites can be greatly improved by lubrication with liquid paraffin, and the friction coefficients of the PTFE composites can be decreased by 1 order of magnitude. Under lubrication of liquid paraffin the friction coefficients of these ceramic particle filled PTFE composites decrease with an increase of load, but the wear of the PTFE composites increases with a load increase. The variations of the friction coefficients with load for these ceramic particle filled PTFE composites under lubrication of liquid paraffin can be properly described by the relationship between the friction coefficient (μ) and the simplified Sommerfeld variable N/P as given here. The investigations of the frictional surfaces show that the ceramic particles SiC, Si₃N₄, BN, and B₂O₃ enhance the adhesion of the transfer films of the PTFE composites to the surface of GCr15 bearing steel, so they greatly reduce the wear of the PTFE composites. However, the transfer of the PTFE composites onto the surface of the GCr15 bearing steel can be greatly reduced by lubrication with liquid paraffin, but the transfer still takes place. Meanwhile, the interactions between the liquid paraffin and the PTFE composites, especially the absorption of liquid paraffin into the surface layers of the PTFE composites, create some cracks on the worn surfaces of the ceramic particle filled PTFE composites; the creation and development of these cracks reduces the load-supporting capacity of the PTFE composites. This leads to the deterioration of the friction and wear properties of the PTFE composites under higher loads in liquid paraffin lubrication. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 2611–2619, 1999     

Two-step strategy for improving the tribological performance of Si3N4 ceramics: Controlled addition of SiC nanoparticles and graphene-based nanostructures

The tribological behaviour of silicon nitride (Si₃N₄) ceramics is investigated using a two-step strategy. A set of ceramic composites containing silicon carbide nanoparticles (SiC_n) is developed and, subsequently, graphene-based fillers are added to the Si₃N₄/SiC composite with the best tribological performance. The friction coefficient and the wear rate of Si₃N₄ are reduced up to 22 % and 40 %, respectively, when a 10 vol.% of SiC_n is incorporated into the ceramic matrix due to its improved mechanical response. Si₃N₄/SiC composites containing 11 vol.% of graphene nanoplatelets (GNPs) or reduced graphene oxide sheets (rGOs) are analysed under isooctane lubrication and dry testing. rGOs composite leads to an important decrease of the friction coefficient (50 %) under lubricated conditions, and an enhancement of the wear resistance (44 %) under dry sliding tests, as compared to the reference Si₃N₄/SiC. The best performance of rGOs composite is due to the nature of the lubricating tribofilm and its excellent toughness.     

Mechanical properties and microstructure evolution of pressureless-sintered B4C–SiC ceramic composite with CeO2 additive

Boron carbide ceramic composites (B₄C)-silicon carbide (SiC) with the cerium oxide (CeO₂) additive, which was varied from 0 wt% to 9 wt%, were prepared by pressureless sintering at 2150 °C for 60 min. The effect of CeO₂ additive content on the microstructure and mechanical properties of the B₄C–SiC ceramic composites was investigated in detail. In-situ synthesised cerium hexaboride (CeB₆) was identified in the B₄C–SiC ceramic composites. B-rich transition zones (such as B_38.22C₆, B_51.02C_1.82) were formed between the B₄C and CeB₆ grains, which introduced local lattice distortion to increase the sintering driving force. The thermal conductivity coefficient of CeB₆ was higher than that of B₄C, which benefited the delivery of heat quantity and helped achieve a highly dense and uniform sintered body. When the CeO₂ additive was excessively increased (more than 5 wt%), the CeB₆ grains had a large grain size and exhibited an increase in the amount of generated carbon monoxide (CO) gas, which led to an increase in the porosity of the B₄C–SiC ceramic composites and decrease in the mechanical properties. The optimum values of the relative density, Vickers hardness, flexural strength, and fracture toughness of the B₄C–SiC ceramic composite with 5 wt% CeO₂ additive were 96.42%, 32.21 GPa, 380 MPa, and 4.32 MPa m^1/2, respectively.     

Investigation on thermal stability and tribological properties of ZrB2 particles filling cyanate ester resin composites by experiments and numerical simulation

The thermal stability and tribological properties of cyanate ester (CE) composites filled with Zirconium boride (ZrB₂) particles were investigated by experimental and numerical simulation. The results of thermogravimetric analysis and differential scanning calorimetry showed that the thermal stability of composites was improved by introduction of ZrB₂ particles. The tribological properties of composites including friction coefficient and wear rate measured by pin‐on‐disk friction and wear tester were enhanced. Friction coefficient and wear rate of composites were decreased significantly with an increase of ZrB₂ particles content under dry and oil sliding conditions. The 5 wt% ZrB₂ particles reinforced CE resin composite presented optimal thermal stability and tribological performance due to good dispersion of ZrB₂ particles. The worn surfaces of composites were observed by scanning electron microscopy to explore wear mechanism, indicating that the dominant wear mechanism of composites was transformed from adhesive wear to abrasive wear after incorporation of ZrB₂ particles. Finite element model was established to study the distribution of friction stress. The results revealed that filling ZrB₂ particles in the friction process of composites could bear more friction stress than CE resin matrix, which further illustrated that abrasive wear is main wear mechanism of ZrB₂/CE resin composites. POLYM. ENG. SCI., 59:602–607, 2019. © 2018 Society of Plastics Engineers     

Degradation mechanisms of a self-healing SiC(f)/BN(i)/[SiC-B4C](m) composite at high temperature under different oxidizing atmospheres

Chemical vapor-infiltrated self-healing SiC_(f)/BN_(i)/[SiC-B₄C]_(m) composite specimens were exposed at 1300?°C for 300?h at atmospheric pressure under two different oxidizing atmospheres (i.e., wet (12%H₂O:8%O₂:80%Ar) and dry (0.01%O₂:99.99%Ar)) representative of rich and poor oxidizing conditions, respectively. Mechanical testing, microstructural observations, and element analyses were performed on the treated specimens. The flexural strength retentions of the specimens were 47.9 and 39.4% under wet and dry oxygen conditions, respectively. The SiC and B₄C matrices were severely oxidized under wet oxygen conditions, whereas the BN interphase remained intact. The BN interphase and the B₄C layered phase were both partially oxidized under dry oxygen conditions. Thus, the SiC_(f)/BN_(i)/[SiC-B₄C]_(m) composites exhibited improved oxidation resistance under wet oxygen atmospheres as compared to dry oxygen conditions as a result of the formation of borosilicate glasses. In addition, two different degradation mechanisms for the composites during the oxidation process were discussed.     

Effect of oxide and carbide nanoparticles on tribological properties of phenolic-based nanocomposites

The phenolic-based composites and components are widely used because of their excellent thermal, tribological and mechanical behaviors. In the present study, phenolic resin composed of hexamine, novalac, furfural, and furfuryl alcohol has been used. The effects of two carbide nanoparticles (SiC and TiC) and two oxide nanoparticles (TiO₂ and ZrO₂) on the tribological properties of phenolic resin were experimentally investigated. This paper intends to identify the effects of different fillers, fraction of particles and normal load on wear rate and coefficient of friction in dry sliding wear of phenolic-based nanocomposites against hard metal. The proportions of fillers were 0.5, 1 and 2?vol% and experiments were carried out under 40, 50, 60 and 70?N loads and at 0.2?m/s speed. The fillers were mixed with phenolic resin and molded in the form of a cylinder (8.5?mm diameter?×?25?mm height). The samples were cured at 135?°C with a special heating cycle. The wear tests were performed on pin-on-disk testing apparatus at ambient temperature. The composite pins were tested in dry sliding against carbon steel disk. The worn surfaces of samples have been investigated by SEM and the effects of nanometer particles showed different wear mechanisms. Observations showed that carbide particles have better enhancing effect on tribological properties of phenolic resin as compared to the oxide particles. Nanocomposites with SiC particles showed the best tribological properties among the investigated samples. The optimal content of SiC nanoparticles were 1?vol%.     

Mechanical properties and sliding wear behaviour of Al2O3-SiC nanocomposites with 3–20 vol% SiC

Al₂O₃/SiC composites containing different volume fractions (3, 5, 10, 15, and 20 vol%) of SiC particles were produced by conventional mixing of alumina and silicon carbide powders, followed by hot pressing at 1740 °C for 1 h under the pressure of 30 MPa in the atmosphere of Ar. The influence of the volume fraction and size of SiC particles (two different powders with the mean size of SiC particles 40 and 200 nm were used), and final microstructure on mechanical properties and dry sliding wear behaviour in ball-on-disc arrangement were evaluated. The properties of the composites were related to a monolithic Al₂O₃ reference. Microstructure of the composites was significantly affected by the volume fraction of added SiC, with the mean size of alumina matrix grains decreasing with increasing content of SiC particles. The addition of SiC moderately improved the Vickers hardness. Fracture toughness was lower with respect to monolithic Al₂O₃, irrespective of the volume fraction and size of SiC particles. Al₂O₃/SiC nanocomposites conferred significant benefits in terms of wear behaviour under the conditions of mild dry sliding wear. Wear resistance of the alumina reference was poor, especially at the applied load of 50 N. The wear rates of composites markedly decreased with increasing volume fraction of SiC. Wear of the composites was also influenced by the material of counterparts, especially their hardness, with softer counterparts resulting in lower wear rates. All composites wore by a combination of grain pull-out with plastic deformation associated with grooving and small contribution of mechanical wear (micro-fracture). No influence of SiC particle size on wear rate or mechanism of wear was observed in the materials with identical volume fractions of SiC.     

Effect of self-developed graphene lubricant on tribological behaviour of silicon carbide/silicon nitride interface

The research presented in this paper aims to investigate the effectiveness of different surface roughness and lubrication conditions on the interfacial tribological properties between silicon carbide (SiC) and silicon nitride (Si₃N₄) ceramics, particularly for providing insight into the mechanisms of how graphene reduces the friction and wear rate. The worn groove topography and surface composition were characterised in detail with 3D laser measuring microscopy and X-ray photoelectron spectroscopy. The tribological test results on the UMT-TriboLab show that a smooth initial surface is more likely to obtain a low friction coefficient and wear rate under water lubrication. The proper initial surface roughness for SiC and Si₃N₄ ceramics is approximately Ra 10?nm, and it will be lower in an alcohol or graphene aqueous solution. A large load does not worsen the tribological behaviour of a Si₃N₄ ball sliding against a SiC disk, and it reduces the friction coefficient and wear rate. Among the five lubrication states of dry friction, dry graphene lubrication, water lubrication, graphene solution lubrication, and self-developed graphene lubrication, the self-developed graphene lubricant can exhibit an ultra-low friction coefficient of 0.009 and ultra-low wear rate of 1.69?×?10^?7?mm³/N·m. The excellent tribological property of the graphene-coated ceramic surface helps the prepared lubricant to decrease the friction coefficient effectively. Furthermore, the graphene film can protect the SiC from being oxidised by water under the tribo-activated action, and therefore, lead to ultra-low wear rate under low friction condition. Alcohol improves the tribological property of the self-developed graphene lubricant, mainly because of the good wettability between graphene and ethanol. The self-developed graphene lubricant can be applied in water-lubricated ceramic bearings and motorised precision spindles.     

Comparative study on wear behavior of plasma sprayed Al2O3 coatings sliding against different counterparts

Although the friction and wear behavior of plasma sprayed aluminum matrix ceramic coatings have been extensively discussed in the last decades, only few researches have been carried out the wear mechanisms sliding against different pairs. The tribological behaviors of plasma sprayed Al₂O₃ coating sliding against ZrO₂, Si₃N₄, Al₂O₃ and stainless steel balls in air were comparatively investigated in this study. It was showed that Al₂O₃ coating sliding against different counterparts exhibited diverse tribological behaviors, which could be mainly ascribed to the different mechanical properties of counterparts. Meanwhile, the tribochemical reactions influenced the friction performances significantly. Moreover, the transform of γ-Al₂O₃ to α-Al₂O₃ occurred during the friction, which was closely related to the coefficient of friction and thermal conductivities of counterparts. The main wear of Al₂O₃ coating sliding against ceramic materials resulted from the brittle fracture and abrasive wear. While it was dominated by adhesive wear when sliding against stainless steel, and accompanied with abrasive wear.     

Abrasive wear of refractory composite ceramic SiC–Si-material

Results are provided for a study of the effect of the action of abrasive media on the wear resistance of refractory ceramic SiC–Si-material prepared by reaction sintering. The abrasive media used are boron and silicon carbides (B₄C, SiC) and standard electrocorundum (Al₂O₃).     

Fabrication of dense B4C-preceramic polymer derived SiC composite

B₄C-SiC composites were fabricated via the preceramic polymer (PCP) route combined with pressure-assisted sintering. Fully dense bodies were achieved by controlling surface oxide on B₄C powder and pyrolysis conditions for PCP coated powder. We elucidate i) the microstructure and phase developments observed in the process of fabricating dense B₄C-PCP derived SiC composites and ii) the mechanical properties and crack deflection behavior of dense bodies. The incorporation of PCP derived SiC to B₄C decreases hardness due to the lower hardness value of SiC compared to B₄C and the residual carbon accompanied by SiC formation. Instead, the PCP derived SiC improved indentation fracture toughness. The main toughening mechanism supposed is a combination of crack impeding by SiC grains and crack deflection within SiC grains, likely due to the presence of subgrains or layered microstructure in the PCP derived SiC grains.     

Effects of SiC on the microstructures and mechanical properties of B4C–SiC–rGO composites prepared using spark plasma sintering

In this study, B₄C–SiC–rGO composites with different SiC contents were prepared by spark plasma sintering at 1800 °C for 5 min under a uniaxial pressure of 50 MPa. The effects of SiC on the microstructures and mechanical properties of the B₄C–SiC–rGO composites were investigated. The optimal values for flexural strength (545.25 ± 23 MPa) and fracture toughness (5.72 ± 0.13 MPa·m^1/2) were obtained simultaneously when 15 wt.% SiC was added to 5 wt.%–GO reinforced B₄C composites (BS15G5). It was found that SiC and rGO inhibited the grain growth of B₄C and improved the mechanical properties of the B₄C–SiC–rGO composites. The clear and narrow grain boundaries of rGO–B₄C and rGO–SiC, as well as the semi-coherent B₄C–SiC interface, indicated strong interface compatibility. The twin structures of SiC and B₄C observed in the composites improved their fracture toughness. Crack deflection and crack bridging caused by the SiC grains as well as rGO bridging and rGO pull-out were observed on the crack propagation path.     

Erosion behaviour of B4C-based ceramic composites

In this paper, TiO₂ was introduced into boron carbide and B₄C-based ceramic composites were obtained by uniaxial hot pressing. The mechanical properties, relative density and erosion behaviour of B₄C-based ceramic composites were investigated. X-ray analysis showed that the fabricated composites were composed of B₄C, TiB₂ and C phases. SEM technique was employed to observe the original polished surfaces and the eroded surfaces of B₄C-based ceramic composites. The effect of impingement angle, impact velocity of SiC erodent particle, relative density and phase ratio on the erosion rate of B₄C-based ceramic composites was determined. It was found that the erosion rate of B₄C-based ceramic composites increased with increasing of impingement angle and erodent particle velocity. The relative density and phase ratio influenced the erosion rate of B₄C-based ceramic composites significantly by influencing their mechanical properties.     

Evaluation of tribological behavior of silicon carbide and silicon nitride ceramics under different conditions

A comparative analysis of the tribological behavior of commercially available sintered silicon carbide (SiC) and three different types of silicon nitride (Si₃N₄) ceramics have been carried out using the ball-on-disk method in dry and lubrication (deionized [DI] water and ethanol) environment. Scanning electron microscopy (SEM) was used to understand the morphology and chemical composition of the tribo-surfaces. Sintered SiC (Hexoloy-SA) had the highest friction coefficient during dry sliding with an average of ∼0.34. Deionized water showed a minor improvement in friction (∼0.27) while ethanol reduced the friction greatly to ∼0.18 compared to dry sliding. During dry sliding, the presence of an abrasive third body was responsible for the high wear rates (WRs) in these compositions. Hexoloy-SA showed a lower WR during ethanol and DI water lubrication due to the formation of stable tribofilms as well as higher hardness which resisted the formation of third bodies. In comparison, Si₃N₄ samples showed a lower WR in DI water and ethanol. The samples also showed composition-dependent behavior which indicates that grain structure and grain boundary chemistry are playing a vital role in the tribological process.