Effect of SiC particles on the friction and wear behavior of Ti3Si(Al)C2-based composites

The non-lubricated, sliding friction and wear behavior of Ti₃Si(Al)C₂ and SiC-reinforced Ti₃Si(Al)C₂ composites against AISI 52100 bearing steel ball were investigated using a ball-on-flat, reciprocating tribometer at room temperature. The contact load was varied from 5 to 20 N. For monolithic Ti₃Si(Al)C₂, high friction coefficients between 0.61 and 0.90 and wear rates between 1.79 × 10⁻³ and 2.68 × 10⁻³ mm³ (N m)⁻¹ were measured. With increasing SiC content in the composites, both the friction coefficients and the wear rates were significantly decreased. The friction coefficients reduced to a value between 0.38 and 0.50, and the wear rates to between 2.64 × 10⁻⁴ and 1.93 × 10⁻⁵ mm³ (N m)⁻¹ when the SiC content ranged from 10 to 30 vol.%. The enhanced wear resistance of Ti₃Si(Al)C₂ is mainly attributed to the facts that the hard SiC particles inhibit the plastic deformation and fracture of the soft matrix, the oxide debris lubricate the counterpair, and the wear mode converts from adhesive wear to abrasive wear during dry sliding.     

Wear characteristics of Cr3C2–NiCr and WC–Co coatings deposited by LPG fueled HVOF

Wear behavior of the HVOF deposited Cr₃C₂–NiCr and WC–Co coatings on Fe-base steels were evaluated by the pin-on-disc mechanism. The constant normal load applied to the pin was 49 N and sliding distance was 4500 m with velocity of 1 m/s, at ambient temperature and humidity. The specific wear rate of WC–Co coating was 3 mm³/N m and Cr₃C₂–NiCr coating was 5.3 mm³/N m. SEM/EDAX and XRD techniques were used to analyze the worn out surface and wear debris. The Fe₂O₃ was identified as the major phase in the wear debris. The wear mechanism is mild adhesive wear in nature.     

Tribological properties of Ni-17.5Si-29.3Cr alloy at room and elevated temperatures

The tribological properties of Ni-17.5Si-29.3Cr alloy against Si₃N₄ were studied on a ball-on-disc tribotester between room temperature and 1000 °C. The effects of temperature on the tribological properties of the alloy were investigated. The worn surfaces of the alloy were examined using scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The results indicated that the tribological behavior of the alloy expressed some differences with increase in testing temperature. At low and moderate temperatures (below 800 °C), the alloy showed excellent wear and oxidation resistances, and the wear rate of the alloy remained in the magnitude of 10^?5 mm³/Nm; but at elevated temperature (800–1000 °C), the wear and oxidation resistances decreased, and the wear rate of the alloy increased up to 10^?4 mm³/Nm. The friction coefficient decreased from 0.58 to 0.46 with the rising of testing temperature from 20 to 600 °C, and then remained nearly constant. The wear mechanism of the alloy was mainly fracture and delamination at low and moderate temperatures, and transformed to adhesive and oxidation at elevated temperatures.     

Wear of aligned silicon nitride under dry sliding conditions

The wear behaviour of textured silicon nitride (Si₃N₄) ceramics with aligned microstructures was analyzed under abrasive wear conditions. Dry reciprocating self-mated ball-on-flat wear tests were performed to study the influence of different microstructural plane/orientation combinations on the Si₃N₄ tribological behaviour. Textured materials showed superior wear resistance than non-textured reference Si₃N₄ for the whole range of loads and contact pressures, 5–50 N and 1.7–3.6 GPa, respectively, with an increase of about 70% for the maximum applied load. Within textured materials, the plane perpendicular to the extruding direction exhibited a 50% higher wear resistance (4 × 10^?5 mm³ N^?1 m^?1) than the parallel plane where the elongated grains were aligned. The severe wear process involved debonding, fracture and debris formation mechanisms. The progress of this sequence depended on the particular microstructure of each plane/orientation combination. A relationship between abrasive wear resistance and selected microstructural parameters has been established.     

The lubrication of poly(etheretherketone) by an aqueous solution of nattokinase

Poly(etheretherketone) (PEEK) is a high strength and high temperature engineering polymer. However, its tribological performance is not very good in its pure form unless fillers or fibers are added to form composites. As polymers are often used for applications where traditional oil based lubrication may become an issue, water-based lubrication is desirable. This paper explores the lubrication performance of a natural fibrinolytic enzyme, nattokinase, found in fermented soybean (natto) in the aqueous solution. Pins of PEEK were slid against a steel disk in a pin-on-disk tester with the aqueous lubrication. The counterface disk material was a tool steel (R_a=0.37 μm). Tests were conducted at a rotational speed of 100 rpm and a normal load of 80 N. For comparison, tests were also conducted in NaCl solution. Nattokinase aqueous solution provides a coefficient of friction of 0.2 between PEEK and steel as compared to 0.3–0.35 for dry condition. The specific wear rates of PEEK for dry, deionized water, NaCl solution and aqueous nattokinase solution conditions were 10.5×10^?6, 51.6×10^?6, 228×10^?6 and 8.8×10^?6 mm³/N m, respectively. The fibrinolytic nattokinase enzyme provides lubricity with alkalinity reducing corrosion and eventually reducing wear.     

Study on tribological properties of UHMWPE irradiated by electron beam with TMPTMA and TPGDA as crosslinking agents

Trimethylolpropane trimethacrylate (TMPTMA) and tripropylene glycol diacrylate (TPGDA) used as crosslinking agents were blended with ultra-high molecular weight polyethylene (UHMWPE or UPE) in alcohol, respectively. Then UPE plates were made by compression molding and electron beam (EB) irradiation crosslinking methods. FTIR, Soxhlet extractor, DSC, Wear tester and SEM were used for the characterization of all specimens. FTIR analyses show that trans-vinylene (965 cm^?1) absorption increases in all specimens and the >C=C< stretching absorption decreases after irradiation. Soxhlet experiments reveal that gel fraction increases with the increasing dose. DSC results indicate that X_c of all the irradiated UPEs are higher than that of unirradiated UPEs because of the free radical and small molecular which can promote the crystallization. Wear rate of 100 kGy 1%TMPTMA/UPE and 1%TPGDA/UPE are 1.89×10^?7 mm³/(N m) and 4.28×10^?7 mm³/(N m), about 44.2% and 100% of that of 100 kGy UPE, respectively, illustrating that TMPTMA is beneficial to reduce the wear rate of UPE and TPGDA almost has no effect to reduce the wear rate of UPE before 100 kGy. SEMs of irradiated specimens are more smooth than that of unirradiated specimens. These can give some advice to improve tribological properties of UPE used in the friction field.     

Improved wear resistance in alumina-PTFE nanocomposites with irregular shaped nanoparticles

Past studies with PTFE nanocomposites showed up to 600× improvements in wear resistance over unfilled PTFE with the addition of Al₂O₃ nanoparticles. Irregular shaped nanoparticles are used in this study to increase the mechanical entanglement of PTFE fibrils with the filler. The tribological properties of 1, 2, 5 and 10 wt.% filled samples are evaluated under a normal pressure and sliding speed of 6.3 MPa and 50.8 mm/s, respectively. The wear resistance was found to improve 3000× over unfilled PTFE with the addition of 1 wt.% nanoparticles. The 5 wt.% sample had the lowest steady state wear rate of K = 1.3 × 10⁻⁷ mm³/N m and the lowest steady friction coefficient with μ = 0.21.     

Study of TiAlSiN coatings post-treated with N and C + N ion implantations. Part 2: The tribological analysis

Ion implantation has found to be an effective approach to modify surface properties of materials. The present research investigates the effect of (1) nitrogen (N), and (2) carbon subsequently with nitrogen (C + N) implantations on the mechanical and tribological properties of the titanium–aluminium–silicon–nitride (Ti–Al–Si–N) coatings. Superhard TiAlSiN coatings produced by magnetron sputtering, of approximately 2.5 μm thickness, were post-treated by implantations of N or C + N at an energy level of 50 keV. The dose range was between 5 × 10¹⁶ and 1 × 10¹⁸ ions cm^?2. After implantation, the tribological performance of the coatings was investigated by a ball-on-disk tribometer against WC–6 wt.%Co ball under dry condition in ambient air. The wear performance of the samples was examined by a variety of characterization techniques, such as secondary electron microscopy (SEM), 3D profilometry, atomic force microscopy (AFM), and micro-Raman. The results showed that the wear performance of the samples depended strongly on the implanted elements and doses. There was slight improvement on the samples implanted with N whereas significant improvement was found on the C + N implantations. Particularly, the friction coefficient of the sample with 5 × 10¹⁷ C⁺ cm^?2 and 5 × 10¹⁷ N⁺ cm^?2 could reach 0.1. In addition, the specific wear rate of the sample was extremely low (0.85 × 10^?7 mm³/Nm), which was nearly two orders of magnitude below that of the un-implanted coating. The speculation of the mechanical and tribological analyses of the samples indicates that the improvement of the N implanted and C + N implanted TiAlSiN samples could be due to a combined effect of improved hardness, plus enhanced adhesive and cohesive strength. In addition, the improved performance of the C + N implanted samples could be explained by the formation of lubricating implanted-layer, which existed mostly in sp² C–C and C–N forms. The formation of such implanted layer could lead to a change of wear mode from strong abrasive wear to mostly adhesive wear, and result in a drop of friction coefficient and wear rate.     

1-N-alkyl -3-methylimidazolium ionic liquids as neat lubricants and lubricant additives in steel–aluminium contacts

The influence of the alkyl chain length and of the anion on the lubricating ability has been studied for the room-temperature ionic liquids (IL) 1-n-alkyl-3-methylimidazolium X⁻ [X = PF₆; n = 6 (L-P106). X = BF₄; n = 2 (L102), 6 (L106), 8 (L108). X = CF₃SO₃; n = 2 (L-T102). X = (4-CH3C6H4SO3); n = 2 (L-To102)]. Neat IL have been used for AISI 52100 steel-ASTM 2011 aluminium contacts in pin-on-disk tests under variable sliding speed. While all IL give initial friction values lower than 0.15, real-time sharp friction increments related to tribochemical processes have been observed for L102 and L-P106, at room-temperature and at 100 °C. Electronic microscopy (SEM), energy dispersive (EDS) and X-ray photoelectron (XPS) spectroscopies show that wear scar surfaces are oxidized to Al₂O₃ and wear debris contain aluminium and iron (for L102) fluorides. For L-P106, the steel surface is covered with a P-containing tribolayer. A change of anion (L-T102; L-To102) reduces friction and wear, but the lowest values are obtained by increasing the alkyl chain length (L106; L108). When the more reactive L102 and L-P106 are used as 1 wt.% base oil additives at 25 °C, tribocorrosion processes are not observed and a friction reduction (69–75% for 1 wt.% L102) and a change from severe (10⁻³ mm³ m⁻¹) to mild wear (10⁻⁴ to 10⁻⁶ mm³ m⁻¹) is obtained with respect to the neat IL. 1 wt.% IL additives also show good lubricating performance at 100 °C.     

A comparative study on the wear properties of coarse-grained Al6061 alloy and nanostructured Al6061–Al2O3 composites

Wear behavior of nanostructured Al6061 alloy and Al6061–Al₂O₃ nanocomposites produced by milling and hot consolidation were investigated. The samples were characterized by hardness test, pin-on-disk wear test, X-ray diffraction (XRD), and scanning electron microscopy (SEM). Nanocomposites containing 3 vol% Al₂O₃ showed a maximum hardness of 235 HV and optimum wear rate of 4×10⁻³ mg/m. Increasing the amount of Al₂O₃ up to 5 vol% resulted in decrease in hardness values (∼112 HV) and a sharp rise in wear rate (∼18×10⁻³ mg/m).     

Comparison of self-mated hardmetal coatings under dry sliding conditions up to 600 °C

Hardmetal coatings prepared by high velocity oxy-fuel (HVOF) spraying represent an advanced solution for surface protection against wear. In the current systematic study the high-temperature oxidation and unidirectional sliding wear in dry and lubricated conditions were studied. Results for a series of experiments on self-mated pairs in dry conditions as part of that work are described in this paper. Coatings with nominal compositions WC-10%Co4%Cr, WC-(W,Cr)₂C-7%Ni, Cr₃C₂-25%NiCr, (Ti,Mo)(C,N)-29%Ni and (Ti,Mo)(C,N)-29%Co were prepared with an ethylene-fuelled DJH 2700 HVOF spray gun. Electrolytic hard chromium (EHC) coatings and bulk (Ti,Mo)(C,N)-15%NiMo (TM10) hardmetal specimens were studied for comparison. The wear behaviour was investigated at room temperature, 400 and 600 °C. For the coatings sliding speeds were varied in the range 0.1–1 m/s for a wear distance of 5000 m and a normal force of 10 N. In some cases the WC- and (Ti,Mo)(C,N)-based coatings showed total wear rates (sum of wear rates of the rotating and stationary samples) of less than 10^?6 mm³/Nm, i.e., comparable to values typically measured under mixed/boundary conditions. Coefficients of friction above 0.4 were found for all test conditions. The P × V values as an engineering parameter for coating application are discussed. The microstructures and the sliding wear behaviour of the (Ti,Mo)(C,N)-based coatings and the (Ti,Mo)(C,N)-15%NiMo hardmetal are compared.     

Synthesis of multiple degrees-of-freedom spatial-motion compliant parallel mechanisms with desired stiffness and dynamics characteristics

This paper presents a new design method to synthesize multiple degrees-of-freedom (DOF) spatial-motion compliant parallel mechanisms (CPMs). Termed as the beam-based structural optimization approach, a novel curved-and-twisted (C-T) beam configuration is used as the basic design module to optimize the design parameters of the CPMs so as to achieve the targeted stiffness and dynamic characteristics. To derive well-defined fitness (objective) functions for the optimization algorithm, a new analytical approach is introduced to normalize the differences in the units, e.g., N/m or N m/rad, etc., for every component within the stiffness matrix. To evaluate the effectiveness of this design method, it was used to synthesize a 3-DOF spatial-motion (θ_x − θ_y − Z) CPM that delivers an optimized stiffness characteristics with a desired natural frequency of 100 Hz. A working prototype was developed and the experimental investigations show that the synthesized 3-DOF CPM can achieved a large workspace of 8°×8°×5.5 mm, high stiffness ratios, i.e., >200 for non-actuating over actuating stiffness, and a measured natural frequency of 84.4 Hz.     

Microstructure and wear resistance of low temperature hot pressed TiB2

Fine-grained TiB₂ compacts have been hot pressed to 98–99% theoretical density at 1400 °C. The compacts were consolidated from sub-micron powders prepared by a high-energy ball milling technique. Titanium diboride (TiB₂) powders were obtained from the milling of commercially synthesized TiB₂ and also from the mechanical alloying (MA) of Ti and B precursors. The formation of TiB₂ from Ti and B powders by mechanical alloying was found to reach completion after 3 h, and wear debris from steel mill vials and media introduced 0.8 to 1.5 wt% Fe in the sintered compacts. The dry erosion resistance of the highest density compacts was examined using an ASTM standard test with an abrasive jet of Al₂O₃ impinging at a normal angle of incidence. Steady-state erosion rates of 0.5 mm³/kg of erodent compare favorably with the measured value of 9 mm³/kg for commercial, fine-grained WC–Co cermets under identical conditions. Microstructures, fracture surfaces, and erosion craters were also examined by electron microscopy.     

Triboactive materials for dry reciprocating sliding motion at ultra-high frequency

High-power piezo-electric motors with power densities of 1.4 kW/kg display a potential for substituting hydraulic actuators. For this application, two novel tribometers of the same type have been designed using commercially available components for sliding motion at 40 kHz with amplitudes between 2.5 μm and 5 μm. The tribometers are equipped with means to measure amplitude, frequency, power required to keep the samples in motion and load applied. The effective motion between the two contacting bodies is monitored in each of the tribometers. These data are used to evaluate the coefficient of friction. The wear rate was determined after the tests. The set-ups were tested using well-known 100Cr6H (AISI 52100) samples before investigating novel, non-commercial substrates such as AlFeCrTi-alloys and tungsten carbide-based coatings as well as Magnéli-type coatings (Ti_n?2Cr₂O_2n?1 and Ti_nO_2n?1). This paper presents the principle of the ultra-high frequency tribometers and first tribological quantities of materials and coatings tested up to and above 10¹¹ cycles. Very low wear rates in the range 10^?8 mm³/Nm down to 10^?10 mm³/Nm were determined under dry oscillation in air.     

Tribological Property of Ni<Subscript>3</Subscript>Al Matrix Composites with Addition of BaMoO<Subscript>4</Subscript>

The Ni₃Al matrix composites with addition of 10, 15, and 20 wt% BaMoO₄ were fabricated by powder metallurgy technique, and the tribological behaviors were studied from room temperature to 800 °C. It was found that BaAl₂O₄ formed during the fabrication process. The Ni₃Al composites showed poor tribological property below 400 °C, with high friction coefficients (above 0.6) and wear rates (above 10⁻⁴ mm³/Nm). However, the composites exhibited excellent self-lubricating and anti-wear properties at higher temperatures, and the composite with addition of 15 wt% BaMoO₄ had the lowest wear rate (1.10 × 10⁻⁵ mm³/Nm) and friction coefficient (0.26). In addition, the results also indicated that BaAl₂O₄ for the Ni₃Al composites did not exhibit lubricating property from room temperature to 800 °C.     

Non-contact temperature measurement of silicon wafers based on the combined use of transmittance and radiance

We propose a non-contact temperature measurement method that combines the temperature dependence of transmittance below 600 °C and radiation thermometry above 600 °C. The combined method uses a polarization technique and the Brewster angle between air and a dielectric film such as SiO₂ or Si₃N₄ grown on silicon wafers. A prominent feature of this method is that both measurements of transmittance and radiance are performed with the same geometrical arrangement.For a semitransparent wafer, the measurement of p-polarized transmittance at the wavelengths of 1.1, 1.2 and 1.3 μm enables temperature measurement in the range from room temperature to 600 °C. For an opaque wafer above 600 °C, the p-polarized radiation thermometry at the wavelength of 4.5 μm allows the temperature measurement without the emissivity problem. The combined method with the use of transmittance and radiance is valid in the entire temperature range irrespective of variations of film thickness and resistivity.     

Mechanical and tribological properties of NiCr–Al2O3 composites at elevated temperatures

The effect of Al₂O₃ content on the mechanical and tribological properties of Ni–Cr alloy was investigated from room temperature to 1000 °C. The results indicated that NiCr–40 wt% Al₂O₃ composite exhibited good wear resistance and its compressive strength remained 540 MPa even at 1000 °C. The values obtained for flexural strength and fracture toughness at room temperature were 771 MPa, 15.2 MPa m^1/2, respectively. Between 800 °C and 1000 °C, the adhesive and plastic oxide layer on the worn surface of the composite was claimed to be responsible for low friction coefficient and wear rate.     

Tribological properties of nitrogen ion implanted steel

Nitrogen ions (N⁺) with three different doses were implanted on the AISI 304 LN steel samples under high vacuum at room temperature. Dose dependent morphological and structural changes were observed in the specimen. Structural changes were triggered by formation of nitrides; irradiation induced surface segregation of carbon and deposition of amorphous carbon (a-C) by the cracking of hydrocarbons during implantation from oil diffusion pump. Morphological and structural changes were found to influence nano-mechanical and tribological properties of ion implanted surfaces. The nano-indentation hardness was found to increase to 10.26 GPa with highest N⁺ ion dose due to formation of surface nitrides and amorphous carbon. Frictional force was found to decrease with increase in N⁺ ion dose and a minimum value of 0.078 N was obtained at higher dose presumably due to the formation of amorphous graphite like phase. In addition, amorphous diamond like carbon on the implanted surface can be contributing facts for high hardness. At higher dose, both deformation induced damage and wear rate (2.4 × 10^?7 mm³/Nm) were found to be minimum.     

Effect of bovine serum constituents on the surface of the tribological pair alumina/alumina nanocomposites for total hip replacement

Alumina has been widely used in the fabrication of hip joint replacement due to its excellent properties. But one of its drawbacks is the low fracture toughness, which can be enhanced with the addition of a second ceramic phase of nanometer size. Another property to be improved is its wear resistance under severe rubbing conditions. In this work Yttria Tetragonal Zirconia Polycrystal, Y-TZP (TZ-8YS, 100 nm), TiO₂ (PS-25, 50 nm) and Co (Nilaco, 28 nm) were added to Al₂O₃ (AKP 50, 300 nm). These starting powders were mixed and hot pressed, in order to fabricate alumina nanocomposites. Mechanical properties of the nanocomposites were estimated using the indentation method. Wear tests were carried out using a ball-on-plate tribometer, with a frequency of 1 Hz, at a load of 49 N, for 1 h. Alumina balls were used as the counterface. Distilled water and fetal bovine serum solution (FBSS) were the environments. The specific wear rate was within 10^?8 to 10^?7 mm³/N m and the coefficient of friction was around 0.3–0.7. Keeping in mind that wear is a process that starts on the surface and it is related to the physical chemistry of the surfaces, techniques such as scanning electron microscopy (SEM), and X-ray photoelectron spectrometry (XPS) were used to elucidate the role played by the proteins and phospholipids present in the fetal bovine serum solution and the new chemical specie formed on the surface.     

Specific energy and surface roughness of minimum quantity lubrication grinding Ni-based alloy with mixed vegetable oil-based nanofluids

Vegetable oil is a low toxic, excellent biodegradable and renewable energy source used as an ideal lubricating base oil in machining. Castor oil exhibits good lubrication performance but poor mobility, which limits its application especially in precision grinding. The main objective of the work presented to obtain optimal mixed vegetable based-oil and optimal nanoparticles adding concentration in grinding Ni-based alloy with minimum quantity lubrication. An experimental investigation is carried out first to study the different vegetable oils with excellent mobility mixed with castor oil. The lubrication property of the oil was evaluated in terms of grinding force, force ratio, specific grinding energy, and surface roughness. Based on the test conditions, it is found that soybean/castor mixed oil obtained the optimal results (μ= 0.379, U = 83.27 J/mm³ and Ra = 0.325 μm) and lubricating effect compared with castor oil and other mixed base oils. To further explore the lubricating capability of soybean/castor mixed oil, MoS₂ nanoparticles which have excellent lubricating property were added into the soybean/castor mixed oil to prepare different concentrations nanofluids. From the present study, it can be concluded that 8% mass fraction of the oil mixture should be added to obtain the optimal machining results, with the lowest force ratio (0.329), specific energy (58.60 J/mm³), and average grinding temperature (182.6 °C). Meanwhile, better surface microtopography of ground parts and grinding debris morphologies were also observed for the machining conditions.