An Investigation on Reasons Causing Inferiority in Unlubricated Sliding Wear Performance of 60NiTi as Compared to 440C Steel

60NiTi is gaining recognition as an alternative to 440C steel in ball bearing components due to its intrinsic corrosion resistance and unusually high static load capacity. 440C steel and 60NiTi exhibit comparable Rockwell hardness and would be expected to exhibit similar sliding wear behavior using hardness based models. However, results show that under unlubricated sliding conditions, 60NiTi shows inferior wear properties than 440C steel. In this study, a series of indentation and single pass scratching experiments are conducted to elucidate the reasons behind this unexpected observation. Moreover, sliding wear tests carried out under moderate and extreme tensile stress conditions were used to identify sliding conditions under which these materials exhibit similar and dissimilar behavior. The results show that 440C steel exhibits more microscopic plasticity than 60NiTi, halting the propagation of generated tensile microcracks. In contrast, the intrinsic brittleness of 60NiTi leads to the formation and growth of microcracks between the shear bands causing subsequent wear particle generation. These lead to the occurrence of wear through more aggressive abrasion processes in 60NiTi than 440C steel. These findings help explain why 60NiTi performs well when lubricated. 60NiTi is expected to tolerate ～912?MPa tensile stress before yielding. Under good lubricated conditions where a perfect lubricating film is formed, friction induced tensile stresses fall below the tensile strength of 60NiTi and wear is prevented. However, inadequate lubrication combined with high contact stress leads to damage and wear.     

Effect of Normal Load and Sliding Distance on the Wear Behavior of NiTi Alloy

Effect of normal load and sliding distance on the room temperature dry sliding wear behavior of a Ti-50.3 at% Ni alloy against a bearing steel was studied. The wear tests were conducted using a pin-on-disk tribometer under normal loads of 20, 40, 50, 60 and 80 N for sliding distances up to 1000 m. The wear results showed that the wear rate of NiTi alloy decreased as the normal load increased from 40 N to 60 N. Formation of iron rich tribological oxide layers under the higher loads could be the main reason of decrease in the wear of NiTi alloy. Increasing the sliding distance decreased the wear rate of NiTi alloy under normal loads of 60 N and 80 N, which was attributed to the formation of more stable iron rich tribological oxide layers on the worn surfaces of NiTi alloy.     

Tribological Effects of Vegetable Oil as Alternative Lubricant: A Pin-on-Disk Tribometer and Wear Study

The investigation of lubricated friction and wear is an extended study. The aim of this study is to investigate the friction and wear characteristics of double fractionated palm oil (DFPO) as a biolubricant using a pin-on-disk tribotester under loads of 50 and 100 N with rotating speeds of 1, 2, 3, 4, and 5 ms^?1 in a 1-h operation time. In this study, hydraulic oil and engine oil (SAE 40) were used as reference base lubricants. The experiment was conducted using aluminum pins and an SKD 11(alloy tool steel) disc lubricated with test lubricants. To investigate the wear and friction behavior, images of the worn surface were taken by optical microscopy. From the experimental results, the coefficient of friction (COF) rose when the sliding speed and load were high. In addition, the wear rate for a load of 100 N for all lubricants was almost always higher compared to lubricant with a load of 50 N. The results of this experiment reveal that the palm oil lubricant can be used as a lubricating oil, which would help to reduce the global demand for petroleum-based lubricants substantially.     

Wear of spheroidal graphite cast irons for tractor drive train components

This study was prompted by a desire to improve the wear resistance of power transmission components in rear axle drives on commercial farm tractors. Reciprocating wear tests were conducted under lubricated and non-lubricated conditions on three spheroidal cast irons which varied in strength and hardness (designated GGG450, GGG600, and GGG700). Hemispherically tipped steel pins (designated 42CrMoS4/41CrS4) were used as the sliders. Except for the selection of the test duration, test procedures were similar to those described in ASTM Standard Test Method G133 for linearly reciprocating sliding. Among the three cast irons tested, the harder and stronger the alloy, the lower was its wear rate. Wear factors were approximately four orders of magnitude lower for experiments lubricated with fresh, fully formulated oil. There was a linear relationship between the Brinell hardness of the alloys and the negative logarithm of the wear factors that were expressed in mm³/N-m. Wear of lubricated test pins was not measurable due to the presence of deposits; however under non-lubricated sliding, the ratio of the wear of the flat specimen to that of the pin decreased as the hardness of the flat specimens approached that of the pin specimen.     

Fretting wear behavior of superelastic nickel titanium shape memory alloy

The fretting behavior of superelastic nickel titanium (NiTi) shape memory alloy was studied at various displacement amplitudes on a serve-hydraulic dynamic test machine. The results showed that the superelastic properties of the material played a key role in the observed excellent fretting behavior of NiTi alloy. Due to the low phase transition stress (only 1/4 the value of its plastic yield stress) and the large recoverable phase transition strain (5%) of NiTi, the friction force of NiTi/GCr15 stainless steel pair is smaller than the value of GCr15/GCr15 pair and at the same time the Rabinowicz wear coefficient of NiTi plate is about 1/9 the value of GCr15 plate under the same fretting conditions. For NiTi/GCr15 pair, even NiTi has a much lower hardness than GCr15, the superelastic NiTi alloy exhibits superior fretting wear property than GCr15 steel. It was found that the weak ploughing was the main wear mechanism of NiTi alloy in the partial slip regime. While in the mixed regime and gross slip regime, the wear of NiTi was mainly caused by the abrasive wear of the GCr15 debris in the three-body wear mode.     

Effect of surface treatment by ceramic conversion on the fretting behavior of NiTi shape memory alloy

Three types of surface-treated NiTi samples, M-1 (700 °C/0.5 h), M-2 (650 °C/1 h) and M-3 (400 °C/50 h), were prepared by ceramic conversion treatment under different conditions. The effect of the surface treatment on the fretting behavior of NiTi alloy was investigated in the Ringer’s solution by using a horizontal servo-hydraulic fretting apparatus. The experimental results indicated that the surface layer of the low temperature (400 °C) treated samples M-3 was dominated by a single TiO₂ layer, while the high temperature (650 and 700 °C) treated samples M-1 and M-2 consisted of surface TiO₂ layer followed by a TiNi₃ layer. These surface layers were found to have a strong effect on the fretting behavior of the NiTi alloy in terms of changes in the shape of the curves of the tangential force (F _t) versus displacement (d), the fretting regimes and the damage mechanisms involved. The stress-induced reorientation of martensite bands in the NiTi alloy could decrease the slope of the F _t–d curve and thus increase the elastic accommodation ability of the NiTi plate against 1Cr13 steel ball pair. However, since the surface-treated layers could suppress the martensite reorientation in the NiTi substrate and thus decrease the elastic accommodation ability of NiTi, the gross slip started at a smaller displacement amplitude for the surface-treated NiTi samples than for the untreated one. The main wear mechanism of the as-received NiTi alloy in slip regime was adhesion and delamination, while the major damage to the high temperature treated NiTi samples M-1 and M-2 was determined as the spallation of surface-treated layers. Due to the high bonding strength of the surface-treated layer with NiTi substrate, the low temperature treated NiTi samples M-3 showed the best fretting wear resistance in all samples tested.     

Effects of Contact Pressure and Sliding Speed on the Unlubricated Friction and Wear Properties of Zn-15Al-3Cu-1Si Alloy

The unlubricated friction and wear properties of Zn-15Al-3Cu-1Si alloy were studied over a range of contact pressure (1–5 MPa) and sliding speed (0.5–2.5 ms^?1) for a sliding distance of 2,500 m using a block-on-disc type test machine. It was observed that as the contact pressure increased, the friction coefficient of the alloy decreased but its working temperature, surface roughness, and wear volume increased. Sliding speed had no significant effect on the friction coefficient of the alloy but increased its working temperature, surface roughness, and wear volume. It was also observed that the formation of a hard and brittle surface layer had a great influence on the wear behavior of the experimental alloy. The hardness and thickness of this layer increased with increasing contact pressure and sliding speed. However, contact pressure was found to be much more effective on the hardness of the surface layer of this alloy. Both adhesion and abrasion were observed to be the dominant wear mechanisms for the alloy under the given sliding conditions. The results obtained from the friction and wear tests are discussed in terms of the test conditions and microstructural changes that take place during sliding.     

Tribological properties of AlCoCrFeNiCu high-entropy alloy in hydrogen peroxide solution and in oil lubricant

Pin-on-disc tests to investigate the tribological behavior of AlCoCrFeNiCu high-entropy alloy under lubrication conditions with 90% hydrogen peroxide solution and lubricant oil, respectively, were performed. The study demonstrates that the AlCoCrFeNiCu high-entropy alloy lubricated correspondingly with lubricant of 90% hydrogen peroxide solution (hereafter termed hydrogen peroxide lubricant) and lubricant oil significantly improves its friction and wear-resistance properties. Results showed that the friction coefficient, after a grinding stage, of the rubbing pair was lower than that with normal lubricant oil. The AlCoCrFeNiCu alloy in the lubricant with 90% hydrogen peroxide solution and lubricant oil exhibits a high resistance to wear. Analysis of the worn surface revealed that the AlCoCrFeNiCu high-entropy alloy lubricated with the hydrogen peroxide lubricant exhibited signs of inhomogeneous polishing oxidation and abrasive wear, with the wear mechanism changing with sliding distance, while the rubbing pair in normal lubricant oil is mainly dominated by abrasive wear.     

Microstructural and sliding wear behaviour of a heat-treated zinc-based alloy

The effect of heat treatment on microstructure, hardness, tensile properties, fracture mode and wear behaviour during lubricated and dry sliding of the zinc-based alloy with 25 wt.%Al was studied. Microstructural investigation and chemical analysis of as-cast and heat-treated specimens, the fracture and worn surfaces, as well as wear debris were performed by scanning electron microscopy and energy dispersive spectroscopy. Wear tests were carried out using a disc-on block-type wear machine. By a relatively simple heat treating consisting of a short-term annealing in the single-phase region followed by water-quenching, the elongation has been markedly improved, while the strength was maintained high. The results indicate that the wear rate strongly depends on the microstructure, applied load and sliding conditions. The wear rate increases with load, and under dry sliding conditions the wear rate is approximately two orders of a magnitude higher than under lubricated conditions. During dry sliding the best wear behaviour was displayed by the water-quenched specimens, whereas slowly cooled specimens showed the higher wear rate. Lubrication strongly affects the wear behaviour. Contrary to dry sliding, slowly cooled specimens exhibit the best wear properties under lubricated conditions. The wear mechanisms were proposed for dry and lubricated sliding. An erratum to this article can be found at     

Effects of Aging Treatments on the High-Temperature Wear Behavior of 60Nitinol Alloy

This study was undertaken to investigate the effect of heat treatments on the high-temperature wear behavior of 60Nitinol. The samples were hot-worked, aged at two temperatures of 400 and 700°C for 1 h and then water quenched. The microstructure of the alloys was investigated by scanning electron microscopy and X-ray diffraction. Sliding wear tests were performed at two temperatures of 25 and 200°C using three types of 60Nitinol disks: hot-worked, aged at 400°C, and aged at 700°C. All wear tests were performed at a speed of 0.3 m/s under a normal load of 60 N for a total sliding distance of 1,000 m using WC-Co pins sliding against 60Nitinol disks. The worn surfaces and microstructure of the subsurfaces were studied by scanning electron microscopy. Compression and hardness tests were also performed to characterize the mechanical properties of the alloys. The highest fracture strain and lowest hardness were obtained for the sample aged at 700°C that contained Ni₃Ti₂ precipitants. This sample also showed the maximum wear resistance at a wear testing temperature of 200°C. This was attributed to the formation of a more compact and stable tribological layer on the worn surface of the softer sample.     

Abrasive wear resistance of textured steel rings

The fundamental aim of the present research is to study the effect of dimple shape and area density on abrasive wear in lubricated sliding. The other aims are to recommend a method of obtaining the local linear wear of a textured ring on the basis of profilometric measurement and to analyse the changes in the surface topography of this ring with selection of parameters that could monitor the “zero-wear” process.The experiments were conducted on a block-on ring tester. The stationary block made from cast iron of 50 HRC hardness was ground. The rotated ground ring was made from 42CrMO4 steel of 32 HRC hardness. The rings were modified by a burnishing technique in order to obtain surfaces with oil pockets. Oil pockets of spherical and of drop shape were tested. The pit-area ratios were in the range: 7.5–20%. The tested assembly was lubricated by oil L-AN 46. Because of the great hardness of the co-acting parts the wear resistance test was carried out under artificially increased dustiness conditions. The dust consists mainly of SiO₂ and Al₂O₃ particles. Measurement of local microscopic ring wear was made using a three-dimensional scanning instrument. The tendencies of ring surface topography changes during wear were analysed. Various methods of obtaining the local wear value during a low wear process were proposed and compared. We found that a spherical shape of dimples was superior to a drop shape with regard to wear resistance of steel rings.     

Experimental Investigations of the Superelastic Impact Performance of Nitinol 60

Nitinol 60 (NiTi60) is a nickel–titanium alloy that has a unique combination of properties such as high hardness, low elastic modulus, and superelasticity. Recent studies of static indentation tests on prestressed samples demonstrated a considerable load capacity increase, which led to the current experimental work. The coefficient of restitution (COR) is measured for two NiTi60 spheres of different diameters (0.635 and 1.270 cm). This work shows that mechanically stressing NiTi60 spheres enables them to achieve a normal COR greater than 0.9 when colliding with NiTi60 landing. This is one of the highest ever reported COR values for self-mated crystalline metal alloys at moderate impact velocities. Consequently, it is believed that this material may be a potential candidate for use in applications requiring highly resilient and wear-resistant metallic materials. A well-known analytical formulation for the coefficient of restitution is used to gain insight and to elucidate some of the COR results presented.     

Wear Reduction of Borosilicate Glass Microballs Using Vapor-Phase Lubrication With n-Pentanol

The effect of n-pentanol vapor-phase lubrication on the wear mechanism of borosilicate glass was investigated. Glass microballs with a diameter of ～60 μm were slid against a silicon wafer under a normal load of 100 μN up to a sliding distance of ～210 km. It was shown that wear volume of the microball could be reduced by ～18 times using n-pentanol vapor-phase lubrication. The wear mechanism was assessed using 3D laser microscopy and scanning electron microscopy. Abrasion was identified as the main mechanism of wear for the borosilicate glass under n-pentanol vapor-phase lubrication condition. In addition, despite the fact that lubrication was supplied to the sliding interface as a vapor, it was sufficient to prevent agglomeration of wear debris, which aided in decreasing abrasion.     

Effect of 10 wt% VC on the Friction and Sliding Wear of Spark Plasma–Sintered WC–12 wt% Co Cemented Carbides

The effect of 10 wt% VC addition on the friction and sliding wear response of WC–12 wt% Co cemented carbides produced by spark plasma sintering (SPS) was studied. The SPS of WC–12 wt% Co alloys with and without 10 wt% VC, at 1100 and 1130°C, respectively, yielded dense materials with minimal porosity. No eta phase was found in any of the alloys. The WC–12 wt% Co–10 wt% VC alloy showed the formation of a hard WV₄C₅ phase, which improved the alloy's hardness. Friction and dry sliding wear tests were done using a ball-on-disk configuration under an applied load of 10 N and sliding speed of 0.26 m.s^?1, and a 100Cr-steel ball was used as the counterface. A significant improvement in the sliding wear response of the harder and more fracture tough WC–12 wt% Co–10 wt% VC alloy compared to the WC–12 wt% Co alloy was found. Analysis of the worn surfaces by scanning electron microscopy showed that the wear mechanisms included plastic deformation, preferential binder removal, adhesion, and carbide grain cracking and fragmentation.     

The Role of Reversible Martensitic Transformation in the Wear Process of TiNi Shape Memory Alloy

It has been established that the superelastic effect of TiNi alloy is related to a reversible martensitic transformation; that is, stress-induced transformation. The high elastic recovery of TiNi alloy has made it a potential candidate for high wear resistance applications. In the present study the tribological behavior of superelastic TiNi alloy was studied and compared to Ni, Ti, and AISI 304 stainless steel using dry sliding wear and friction tests. The effect of normal load and testing temperature on superelasticity has been investigated. It has been found that although AISI 304 stainless steel and superelastic TiNi alloy have similar hardness, TiNi exhibits superior wear resistance. The wear rate of AISI 304 stainless steel is over four times higher than TiNi. The superior wear resistance of TiNi and the effect of load and temperature on wear were discussed and related to the reversible martensitic phase transformation, as well as self-accommodation and stabilization of martensite.     

Tribological Characterisation of Graphene Oxide as Lubricant Additive on Hypereutectic Al-25Si/Steel Tribopair

The performance of a lubricant greatly depends on the additives it involves. However, recently used additives produce severe pollution when they are burned and exhausted. Therefore, it is necessary to develop a new generation of green additives. Graphene oxide (GO) is considered to be environmentally friendly. The scope of this study is to explore the fundamental tribological behavior of graphene, the first existing 2D material, and evaluate its performance as a lubricant additive. The friction and wear behavior of 0.5 wt% concentrations of GO particles in ethanol and SAE20W50 engine oil on a hypereutectic Al-25Si alloy disc against steel ball was studied at 5 N load. GO as an additive reduced the wear coefficient by 60–80% with 30 Hz frequency for 120 m sliding distance. The minimum value of the coefficient of friction (0.057) was found with SAE20W50 + 0.5 wt% GO. A possible explanation for these results is that the graphene layers act as a 2D nanomaterial and form a conformal protective film on the sliding contact interfaces and easily shear off due to weak Van der Waal's forces and drastically reduce the wear. Scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and Raman spectroscopy were used for characterization of GO and wear scars.     

Wear behavior of SiC particulate reinforced aluminum composites sliding against steel balls under dry and lubricated conditions

Wear behavior of Al–Si alloys reinforced with SiC particulate has been investigated under dry and lubricated reciprocating sliding conditions using a ball-on-block wear test method. It was shown that in the dry sliding wear of the composite/steel ball system, the wear mechanism of the composite was predominantly adhesive. With further sliding motion, delamination and abrasive wear occurred as a result of fracture and debonding of the SiC particles. Under lubricated conditions, the wear rate of the composite was drastically reduced due to the presence of the lubricant, and a boundary lubrication condition existed and dominated the normal wear process. The debonding of the SiC particles from the matrix of the composite was a predominant factor in determining the wear loss of the composite in the boundary lubrication sliding process. This revised version was published online in July 2006 with corrections to the Cover Date.     

Relation Between Tribolayers and Wear Behavior During Dry Sliding of Fe-Al Hot-Dipped Coating

An Fe-Al coating consisting of FeAl and Fe₃Al was prepared on AISI 1045 steel by hot-dip aluminizing and subsequent high-temperature diffusion. Dry sliding wear tests were performed for Fe-Al coating against AISI 52100 steel under various sliding speeds and loads. During sliding, thin tribolayers formed on the worn surfaces of the Fe-Al coating. After wear, they were observed to be a nonoxidized mechanically mixed layer (MML) at 0.5 m/s, an oxide-containing MML at 0.75–2.68 m/s, and an in situ oxide layer at 4 m/s. The tribolayers presented a close relation with the wear behavior. Because of their different ingredients, structures, and types, the tribolayers resulted in significant changes in the wear behavior. At 0.75–2.68 m/s (except for 2.68 m/s, 40 N), the compact tribooxide layers exerted a protective function for Fe-Al coating to reduce the wear rate. However, for the tribolayers containing no or trace tribooxides at 0.5 m/s or the unstable ones formed at 2.68 m/s, 40 N and 4 m/s, no protection was presented. In these cases, the Fe-Al coating would be partly or totally ground off, thus presenting poor wear resistance at high wear rates.     

Sliding wear behavior of planar random zinc-alloy matrix composites

The friction and wear behavior of planar random zinc-alloy matrix composites reinforced by discontinuous carbon fibres under dry sliding and lubricated sliding conditions has been investigated using a block-on-ring apparatus. The effects of fibre volume fractions and loads on the sliding wear resistance of the zinc-alloy matrix composites were studied. Experiments were performed within a load range of 50–300 N at a constant sliding velocity of 0.8 m s⁻¹. The composites with different volume fractions of carbon fibres (0–30%) were used as the block specimens, and a medium-carbon steel used as the ring specimen. Increasing the carbon fibre volume fraction significantly decreased the coefficient of friction and wear rates of both the composites and the medium-carbon steel under dry sliding conditions. Under lubricated sliding conditions, however, increasing the carbon fibre volume fraction substantially increased the coefficient of friction, and slightly increased the wear of the medium-carbon steel, while reducing the wear of the composite.Under dry sliding conditions, an increasing load increased not only the wear rates of both the composite and the unreinforced zinc alloy, but also those of their corresponding steel rings. However, the rate of increase of wear with increasing load for both the composite and its corresponding steel ring was much smaller than for the unreinforced zinc alloy and its corresponding steel ring. The coefficient of friction under dry sliding conditions appeared to be constant as load increased within a load range of 50–150 N for both the composite and the unreinforced zinc alloy, but increased at the higher loads. Under any load the coefficient of friction of the composite was lower than half that of the unreinforced zinc alloy under dry sliding conditions.     

Experimental investigation of oil pockets effect on abrasive wear resistance

The experiments were carried out using a block-on-ring tester. The stationary blocks were modified by a burnishing technique in order to obtain surfaces with oil pockets of spherical shape. The area density of oil pockets varied in order to explore their effect on wear resistance and wear intensity. Specimen surfaces had dimples with depths 45-60 μm and diameters 1-1.2 mm. The area density of oil pockets S_p was in the range 4-20%. The block samples were made from bronze B101 (CuSn10P) of 138 HB hardness. The rotated rings were made from 42CrMo4 steel, hardness of 40 HRC obtained after heat treatment. The tested assembly was lubricated by mineral oil L-AN 46. The experiment was carried out under artificially increased dustiness conditions. The dust added to oil consists mainly of SiO₂ (74%) and Al₂O₃ (15%) particles. During the test friction force and temperature of block sample were registered. The tendencies of block surface topography changes during wear were analysed. It was found that sliding pairs with textured specimens were not superior to a system with a turned block with regard to abrasive wear resistance.