Si3N4 Ball Research Articles

Fabrication and high-temperature tribological properties of self-lubricating NiCr–BaMoO4 composites

In the present work, NiCr–BaMoO4 self-lubricating composites have been fabricated by hot pressing to evaluate their tribological properties at elevated temperatures. Hydrothermal synthesis method has been used to prepare fine BaMoO4 spherical powders with a size of 500nm by adjusting different technological parameters. The synthesized BaMoO4 powders have a good thermal stability in air after calcining up to 1100°C for 5h. The friction and wear properties of NiCr–BaMoO4 composites were investigated by using a ball-on-disk friction and wear tester in sliding against Si3N4 ball up to 600°C. As contrasted with unmodified NiCr alloy, the composites incorporated with 10wt% or 20wt% BaMoO4 exhibit distinct improvements in effectively reducing friction and wear at elevated temperatures. NiCr–BaMoO4 composites have low friction coefficients of 0.26–0.30 and small wear rates in the order of magnitude of 10−5–10−6mm3/Nm at elevated temperatures. A dense oxidized surface layer is formed on the worn surface of NiCr matrix composites incorporated with BaMoO4. Tribo-oxidation reaction during high temperature wear tests is responsible for the formation of dense oxidized surface layer containing BaMoO4, NiCr2O4, NiO and Cr2O3. The coupled Si3N4 ball is covered with a transfer layer containing BaMoO4, which effectively reduces the friction and wear.

Effect of pH on wear and friction of silicon nitride sliding against alumina in water

The influence of the pH in water lubricated sliding contacts was evaluated in terms of friction and wear. The experiments were carried out using a ball-on-disc setup. Si3N4 balls and Al2O3 discs were tested at temperature of (22±2)°C, sliding speed of (1.00±0.03)m/s and normal load of (54.25±0.17)N. Eight types of water with pHs varying from 3 to 12 were used as lubricant. The running-in period, friction coefficient and wear-volume were shown to be nearly independent of the initial pH values within the DLVO range (4≤pH≤10), since at these range the water׳s pH tends to the same value (7.6±0.3) during the test. Superlubricity could be reached with negligible wear by properly setting the electrochemical properties and operating conditions of the tribosystem.

Effects of SiH4 flow rate on microstructure and mechanical properties of TiSiN nanocomposite coatings by cathodic arc ion plating

TiSiN nanocomposite coatings were deposited on Si and cemented carbide substrates by cathodic arc ion plating in SiH4 ambient. The effects of SiH4 flow rate on microstructure, mechanical and tribological properties of the coatings were investigated systemically. Transmission electron microscopy and X-ray diffraction were employed to probe the crystalline microstructure and X-ray photoelectron spectroscopy was used to investigate the chemical bonding states. Microhardness testers and tribometer were used to evaluate the mechanical and tribological properties of TiSiN nanocomposite coatings. The results showed that the structure of TiSiN coating changed from columnar grain to nanocrystalline with increasing SiH4 flow rate. The hardness increased up to 4100 HV0.025 at the SiH4 flow rate of 42 sccm (9.5 at.% Si in the coating), but it decreases with further addition of SiH4 gases. Friction coefficients of TiSiN composite coatings in the range of 0.6–0.7 were obtained when tested against Si3N4 balls.

Effect of counterparts on the tribological properties of TiCN coatings with low carbon concentration in water lubrication

TiN and TiCN coatings have long been used for wear reduction in application like tooling, but there are other potential industrial applications in aqueous environments. Therefore, the current investigation explores the friction and wear compatibility of TiN and TiCN coatings against potential sliding partners in water. 316L discs coated with TiN and TiCN (containing 2.46 at% C) slid against fixed balls of Al2O3, SiC, Si3N4, and SUS440C in water. In terms of mean steady-state friction coefficient, the ranking from low to high was: SiC<Si3N4<Al2O3<SUS440C regardless of coating type. It is proposed that due to lubrication by silica gel, the friction coefficients and wear rates of TiCN coatings against SiC and Si3N4 balls were lower than those against Al2O3 and SUS440C balls. For the TiCN/SUS440C tribopairs, tribo-oxidation occurred easily for SUS440C ball, and the oxides on the wear track caused the highest friction coefficient and the roughest wear surfaces. But wear of the TiCN/Al2O3 tribopairs, which had the highest wear rate of the coatings, was dominated by abrasion. In terms of the friction and wear behavior under water-lubricated test conditions, SiC was the most suitable counterpart for TiCN-coated stainless steel.

Effect of surface reactions on steel, Al2O3 and Si3N4 counterparts on their tribological performance with polytetrafluoroethylene filled composites

The influence of surface reactions on the tribo-performance of steel, Al2O3 and Si3N4 balls sliding against polytetrafluoroethylene/SiO2/epoxy composites was investigated. Al2O3 ball were found to exhibit the best tribo-performance, namely a low coefficient of friction and the lowest wear rates of both the composites and the counterpart ball, when sliding against the PTFE filled composites. The difference in the tribo-performance of the Al2O3 ball and the Si3N4 ball can neither be attributed to the different morphology of the worn composite surfaces nor to the amount of PTFE transferred onto the wear surfaces. Instead we found that the friction is greatly reduced in the case of the Al2O3 ball because two fluoro-terminated surfaces are sliding over each other; in fact, the formation of AlF bonding was confirmed by X-ray photoelectron spectroscopy.

Tribological Properties of Si-Doped Graphite-Like Amorphous Carbon Film of PEEK Rubbing with Different Counterparts in SBF Medium

The present investigation has been conducted in order to evaluate the friction and wear behaviors of polyaryl-ether-ether-ketone coated with a Si/GLC film sliding against 100Cr6 steel, Al2O3 and Si3N4 balls in a biological medium of simulated body fluid, using the ball-on-disk tribological tests. The test results show that the wear volume loss of the rubbing pairs is two orders of magnitude greater than that determined for the tribo-pairs in SBF lubrication, coefficient of friction decreases by 50 % at least, as compared to that in dry conditions. The friction coefficient showed the same varied trend with Hertzian contact radius. The wear rate showed the inverse varied trend with the contact pressure. The interfacial tribochemically reacted with moisture available in SBF medium plays an effect role of the difference in the wear-resistant and lubricating behavior. Furthermore, some indexes including hardness ratio of pair and film were employed to predict the wear behavior of GLC composite films sliding against different counterparts. The Si/GLC nanocomposite films would be a new kind of promising materials applied to artificial heart valves and stents.

Friction and wear behaviors of polycrystalline diamond under vacuum conditions

In this work, the friction and wear behaviors of the polycrystalline diamond (PCD) sliding against Si3N4 ball were evaluated under both ambient air and vacuum by a ball-on-disk tribometer. The microstructures of the PCD were characterized by scanning electron microscopy, X-ray diffractometry, and Raman spectroscopy. The results showed that the friction coefficients obtained under vacuum are much higher than those under ambient air, and it mainly attributed to serious adhesion under vacuum because of the absence of the absorbed layer formed under ambient air. The high friction heat and the catalyzing of Co resulted in the graphitization of PCD under vacuum. The diamond grains shedding off from the PCD surface can be easily found under vacuum, whereas no observable abrasion was formed under ambient air. Both the strong adhesion between counter surfaces and the weak bonding strength among diamond grains contributed to the serious wear under vacuum.

Deposition and tribological behaviors of ternary BCN coatings at elevated temperatures

In this work we studied the mechanical properties, thermal stability and tribological properties of ternary boron carbon nitride (BCN) coatings with controlled boron content. BCN coatings with different boron contents (B=0, 1, 5, 20at.%) were deposited by ion beam assisted deposition (IBAD). The thermal stability and oxidation resistance were investigated by the weight loss method in ambient air. The structure and composition were evaluated by Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS). The hardness was measured by a nano-indenter. The tribological properties at room temperature and 300°C were investigated by a designed high temperature ball-on-disk tribo-meter. The results show that the hardness and residual stress increased with the boron content. At room temperature, the friction coefficient was in the range of 0.2–0.3 and did not change a lot with the boron content. At 300°C, the B0.05CNx coating shows the lowest friction coefficient (~0.1) among the four coatings, because the graphitized carbon transfer layer forms on the Si3N4 ball.

Precision Shaping Experiment of Ceramic Ball Blank with Oscillating-Plate Lapping Method

An oscillating-plane lapping method, by which pre-sintered ceramic ball blanks are shaped before full sintering, was proposed to improve the precision of the ceramic ball blanks. For good sphercity and diameter consistency of ceramic ball blanks obtained after this shaping process, much less workmaterial is needed to be removed in the following lapping process of the full sintered ceramic ball blanks. Shaping experiments were carried out on a newly developed oscillating-plane lapping device. Results show that material removal rate of the pre-sintered Si3N4 ball blanks with nominal diameter Ø13mm reaches 0.92mm/h in average. The sphericity error is reduced from 0.07-0.196mm to 0.002-0.006mm, and the consistency error of diameter is reduced from 0.309 to 0.019mm after 45min's shaping. Compared with the processing time of the unshaped full-sintered blanks in the following lapping process, it takes just a half time for the shaped full-sintered blanks to be semi-finished in this study. It indicates that the oscillating-plane lapping is a promising high efficient method to improve the precision and consistency of the ceramic ball blanks, and the efficiency of the followed lapping process can be improved notably.

Rippling on Wear Scar Surfaces of Nanocrystalline Diamond Films After Reciprocating Sliding Against Ceramic Balls

The formation of nanoscopic ripple patterns on top of material surfaces has been reported for different materials and processes, such as sliding against polymers, high-force scanning in atomic force microscopy (AFM), and surface treatment by ion beam sputtering. In this work, we show that such periodic ripples can also be obtained in prolonged reciprocating sliding against nanocrystalline diamond (NCD) films. NCD films with a thickness of 0.8 µm were grown on top of silicon wafer substrates by hot-filament chemical vapor deposition using a mixture of methane and hydrogen. The chemical structure, surface morphology, and surface wear were characterized by Raman spectroscopy, scanning electron microscopy (SEM), and AFM. The tribological properties of the NCD films were evaluated by reciprocating sliding tests against Al2O3, Si3N4, and ZrO2 counter balls. Independent of the counter body material, clear ripple patterns with typical heights of about 30 nm induced during the sliding test are observed by means of AFM and SEM on the NCD wear scar surfaces. Although the underlying mechanisms of ripple formation are not yet fully understood, these surface corrugations could be attributed to the different wear phenomena, including a stress-induced micro-fracture and plastic deformation, a surface smoothening, and a surface rehybridization from diamond bonding to an sp2 configuration. The similarity between ripples observed in the present study and ripples reported after repeated AFM tip scanning indicates that ripple formation is a rather universal phenomenon occurring in moving tribological contacts of different materials.

Low frictions of self-mated CNx coatings in dry and humid inert gas environments

The friction behavior of CNx coated Si3N4 disk sliding against CNx coated Si3N4 ball (denoted as CNx/CNx) in dry and humid inert gas environments (i.e. nitrogen, argon, and helium) is investigated in this study. The sliding contact of self-mated CNx coatings has been realized thanks to the promising two-step ball-on-disk friction test, where the rubbed Si3N4 ball in the running-in stage (step 1) is replaced by a new CNx coated Si3N4 ball in the subsequent stage (step 2). As a result, friction coefficients of less than 0.05 are obtained for self-mated CNx coatings in all three dry inert gas environments with relative humidity under 5%RH. Moreover, friction coefficients of less than 0.10 are obtained for the sliding contact of CNx/CNx in inert gas environments with relative humidity of larger than 35%RH. Especially, the lowest friction coefficient of 0.020 is achieved in the nitrogen gas environment with relative humidity of 37%RH. Furthermore, the sliding contact of self-mated CNx coatings survives after friction tests in humid nitrogen and argon gas environments. The low frictional performance and low sensitivity of friction to water vapor for the self-mated CNx coatings in inert gas environments are mainly attributed to the formation of a sp2 rich carbon tribo-layer on the mating surface. The pronounced frictional performance of self-mated CNx coatings has made them good candidates for the demanding industrial applications.

Sliding wear resistance of sintered SiC-fiber bonded ceramics

Advanced SiC-based ceramics and fiber reinforced composites are interesting materials for a wide variety of applications involving sliding wear conditions because of their excellent thermomechanical properties. The microstructure and wear resistance of sintered SiC fiber bonded ceramics (SA Tyrannohex) were studied. The material is composed of SiC-fibers in two orientations, with polygonal cross sections and cores having higher carbon content than their surroundings, as observed with SEM. A thin layer of C exists between the fibers. This layer has been found to be a turbostratic-layered structure oriented parallel to the fiber surface. XRD shows that the material is highly crystalline and composed mostly of β-SiC. Unlubricated wear behavior of the SA-Tyrannohex material when sliding against a Si3N4 ball in air at room temperature was evaluated. Experiments were performed using a pin on disk apparatus, under different normal loads of 2, 5 and 10N at sliding speeds of 25, 50, 100mm/s. A decrease of the friction coefficient with load was found due to the presence of the turbostratic carbon layer between the fibers. Wear rates of the order of 100mm3/MJ were obtained, independently of sliding speed. Microfracture of the fibers is the main wear mechanism.

Sliding wear resistance of biomorphic SiC ceramics

Biomorphic SiC ceramics were fabricated from four different wood precursors and their Knoop hardness and sliding wear resistance when sliding against a Si3N4 ball in air were studied. Tribological experiments were performed using a pin on disk apparatus, under normal loads of 2 and 5N, at a sliding speed of 100mm/s. The effects of specimen porosity and microstructure on measured wear were evaluated. A commercial sintered silicon carbide ceramic was also tested for comparison. Small differences in friction coefficient comparable to monolithic SiC ceramics were obtained. Several concurrent wear mechanisms are taking place: microfracture, plastic deformation in the Si phase and oxidation of the Si and/or SiC phase. The presence of an oxide tribolayer was assessed using fluorescence microscopy. Wear rates were found to scale with SiC content and depend on residual porosity in the composite.

Structural transformation and friction behavior in turbostratic graphite sliding against Si3N4, SiC and Al2O3 balls

Friction behavior of turbostratic graphite was investigated in ambient atmospheric condition while sliding against Si3N4, SiC and Al2O3 spherical balls. Low friction coefficients of ~0.02 and ~0.1 were measured for tests with Si3N4 and SiC balls, respectively. In contrast, a high friction coefficient of 0.22 was observed in same graphite sample when Al2O3 ball was used for sliding counterbody. In all the three wear tracks formed by Si3N4, SiC and Al2O3 balls, structural transformation of 2D turbostratic to 3D graphite was observed. This transformation is driven by kinetic energy released during sliding. Structural transformation was quite similar in all the three wear tracks of turbostratic graphite. However, the value of friction coefficient differs greatly from each other. Therefore, friction behavior cannot be explained through structural transformation alone. In the light of above facts, carbon transferlayer and chemical interaction between the sliding interfaces were considered to explain friction mechanism. Absence of carbon transferlayer on Si3N4 ball scar leads to less dangling bonds, which are efficiently passivated by the oxygen molecules and water vapor present in the ambient atmosphere. Such surface passivation results in ultra-low-friction coefficient. In contrast, the high friction coefficient in Al2O3 ball against graphite is due to the formation of graphitic transferlayer on the ball scar. Transferlayer assists formation of C-C strong bond between the sliding members leading to chemical locking.

Microstructure and tribological properties of Fe–Cr matrix self-lubricating composites against Si3N4 at high temperature

A series of Fe–Cr matrix high temperature self-lubricating composites were prepared by powder metallurgy technique (PM). The tribological properties of composites sliding against ceramic Si3N4 ball were studied by using a ball-on-disc high-temperature tribometer at 10N and 0.19m/s for 20min from room temperature to 800°C. Mo element showed an obvious solid solution strengthening effect on the matrix, and formed the high temperature solid lubricant BaMoO4. The obtained results showed that the tribological properties of specimens greatly depended on the additives. Generally speaking, the specimen containing 8.0wt.% BaF2, 10.0wt.% Ag and 8.5wt.% Mo kept the lowest friction coefficient (0.4) and specific wear rate (1.8–3.7×10−4mm3N−1m−1) from room temperature to 800°C. The high-temperature tribological properties of Fe–Cr based alloy were improved due to the addition of additives. The excellent tribological behavior of specimen was attributed to the synergetic action of solid lubricants and high hardness. The wear mechanism of specimen FM is ploughing and slightly delamination at room temperature and 400°C. At 800°C, the specimen FM shows the micro-ploughing characteristics.

Microstructure and thermoelectric properties of Y x Al y B14 samples fabricated through the spark plasma sintering

Excellent control in p- and n-type transport characteristics was previously obtained for the thermoelectric Y x Al y B14 compounds through Al flux method. In this study, new attempts were made to reduce their grain sizes to obtain dense samples and to possibly lower the thermal conductivity. Introducing the reduction of grain sizes into Y x Al y B14 samples was attempted by two methods; one was through mechanical grinding, and the other was by synthesizing Y x Al y B14 via Y0.56B14 (denoted as “vYB-YAlB14”). Mechanical grinding using ball milling with Si3N4 pots and balls was found not to be an efficient way to decrease the grain size because of contamination of Si3N4. In contrast, vYB-YAlB14 samples were successfully synthesized. Through the synthesis of Y0.56B14, the boron network structure was first formed. Afterward, Y x Al y B14 was obtained by adding Al in the boron network structure through a heat treatment. Due to shorter heating time at lower temperature, the grain sizes were discovered to be smaller than that of Al flux method. The decrease of grain size was found to be beneficial for the densification of Y x Al y B14 and the decrease of its thermal conductivity.

Micro-scale abrasive wear behavior of medical implant material Ti–25Nb–3Mo–3Zr–2Sn alloy on various friction pairs

The micro-scale abrasion behaviors of surgical implant materials have often been reported in the literature. However, little work has been reported on the micro-scale abrasive wear behavior of Ti–25Nb–3Mo–3Zr–2Sn (TLM) titanium alloy in simulated body fluids, especially with respect to friction pairs. Therefore, a TE66 Micro-Scale Abrasion Tester was used to study the micro-scale abrasive wear behavior of the TLM alloy. This study covers the friction coefficient and wear loss of the TLM alloy induced by various friction pairs. Different friction pairs comprised of ZrO2, Si3N4 and Al2O3 ceramic balls with 25.4mm diameters were employed. The micro-scale abrasive wear mechanisms and synergistic effect between corrosion and micro-abrasion of the TLM alloy were investigated under various wear-corrosion conditions employing an abrasive, comprised of SiC (3.5±0.5μm), in two test solutions, Hanks' solution and distilled water. Before the test, the specimens were heat treated at 760°C/1.0/AC+550°C/6.0/AC. It was discovered that the friction coefficient values of the TLM alloy are larger than those in distilled water regardless of friction pairs used, because of the corrosive Hanks' solution. It was also found that the value of the friction coefficient was volatile at the beginning of wear testing, and it became more stable with further experiments. Because the ceramic balls have different properties, especially with respect to the Vickers hardness (Hv), the wear loss of the TLM alloy increased as the ball hardness increased. In addition, the wear loss of the TLM alloy in Hanks' solution was greater than that in distilled water, and this was due to the synergistic effect of micro-abrasion and corrosion, and this micro-abrasion played a leading role in the wear process. The micro-scale abrasive wear mechanism of the TLM alloy gradually changed from two-body to mixed abrasion and then to three-body abrasion as the Vickers hardness of the balls increased.

Reciprocating Wear Performance and Interfacial Microstructure of a TiC–Ni2AlTi Cermet

Wear performance of a near equi-volume TiC–Ni2AlTi cermet with minor NiAl was evaluated by reciprocal sliding against Si3N4 balls. Both coefficient of friction (COF) and specific wear rate (SWR) decrease with the applied load in the range from 5 to 20 N, reaching minimums of 0.34 and 2.2 × 10−6 mm3/Nm, respectively, at 20 N. To understand the novel wear resistance, interfacial microstructure was investigated. As indicated by high resolution transmission electron microscopy observations, the interfaces are either coherent (TiC/NiAl and Ni2AlTi/NiAl) or semi-coherent (TiC/Ni2AlTi). Depending on the grain size of Ni2AlTi, two types of TiC/Ni2AlTi interface were observed. For the micrometer or sub-micrometer sized Ni2AlTi grains, the orientation relationship (OR) is (111) TiC ∥ (220) Ni2AlTi, [1 $$\bar{1}$$ 0] TiC ∥ [1 $$\bar{1}$$ 0] Ni2AlTi, while for the Ni2AlTi grains in tens of nanometers, the OR is (020) TiC ∥ (002) Ni2AlTi, [101] TiC ∥ [010] Ni2AlTi. The strongly bonded coherent and semi-coherent interfaces impede the failure of the heterophase boundaries, which accounts for the excellent wear resistance of the newly prepared cermet.

Tribological behavior of tetrahedral amorphous carbon (ta-C) coatings at elevated temperatures

In this study, tribological behavior of tetrahedral amorphous carbon (ta-C) coatings was investigated at elevated temperatures, from which it was found that it could be broadly defined by three distinct temperature regions: Region I at 23 and 100°C; Region II at 200, 300, and 400°C; and Region III at 500°C. A qualitative analysis of the toughness and adhesion of the ta-C coatings within each of these regions was conducted by scratch testing. The formation of a transfer layer on Si3N4 balls in Region II was determined as the cause of a reduced friction and higher wear rate when compared with Region I. In Region III, the generation and propagation of cracks in the ta-C coating resulted in severe delamination.

Friction and wear properties of α-AlB12- and SiB6-based ceramics in water

In this study, α-AlB12- and SiB6-based ceramic disk specimens were prepared by spark plasma sintering, and their X-ray diffraction patterns, microstructure, microvickers hardness were examined. Also, the friction and wear properties of the α-AlB12- and SiB6-based ceramic disk specimens were investigated when they were slid against Si3N4, Al2O3 and SiC ball specimens in water. Additionally, the friction and wear properties of the Si3N4–Si3N4 and Al2O3–Al2O3 tribopairs were investigated in water as references. Both the α-AlB12- and SiB6-based ceramic disk specimens exhibited friction coefficients lower than 0.2 when they were slid against the Si3N4, Al2O3 and SiC ball specimens. On the other hand, the Si3N4–Si3N4 and Al2O3–Al2O3 tribopairs exhibited friction coefficients as low as 0.6. The α-AlB12- and SiB6-based ceramic disk specimens and their paired Si3N4, Al2O3 and SiC ball specimens exhibited much lower specific wear rates than the Si3N4–Si3N4 and Al2O3–Al2O3 tribopairs.