Reciprocating Sliding Wear Behavior of 60NiTi As Compared to 440C Steel under Lubricated and Unlubricated Conditions

ABSTRACT

60NiTi is a hard (～60 HRC) and highly corrosion-resistant intermetallic with a relatively low elastic modulus (～100 GPa). In addition, this alloy exhibits a high compressive strength (～2,500 MPa) and a high elastic compressive strain of over 5%. These attributes make this alloy an attractive candidate to be employed in structural and mechanical component applications. However, sliding wear behavior of this intermetallic has not yet been studied in a systematic way. In this study, lubricated and unlubricated reciprocating sliding wear behavior of 60NiTi is compared to 440 C steel as a conventional bearing and wear-resistant alloy. Results of experiments carried out under different loads show that 60NiTi, despite having a higher hardness, exhibits a significantly inferior wear behavior under dry conditions in comparison to 440 C steel. These unexpected results indicate that 60NiTi does not follow conventional wear theories where the wear of materials has an inverse relationship to their hardness. On the other hand, under lubricated conditions with castor oil and a synthetic gear oil, 60NiTi exhibits low specific wear rates. These results exhibit the importance of proper lubrication in sliding mode applications where 60NiTi is exploited as a wear-resistant alloy.     

Reciprocating sliding wear of 9% Cr steel in carbon dioxide at elevated temperatures

Experiments were conducted on the initial stages of reciprocating sliding wear of a 9% chromium steel in an environment of carbon dioxide at temperatures in the range 200 to 550°C. At ambient temperatures of 290°C and above, an initial severe wear mode was followed by a transition to mild oxidational wear. At any given ambient temperature above 290°C, the distance of sliding required to reach such a transition was found to depend on load and mean sliding speed, although the dependency on speed was not simple. When a transition occurred, most of the surfaces were covered with a stable oxide film which consisted of an agglomerate layer of wear debris being mainly of oxide at the surface and mainly at the metal boundary. This film was supported by a work hardened layer extending for about 30 μm into the bulk of the metal. A surface model is proposed to explain the mechanism of formation of the supportive oxide layer; predictions of volume of material removed and final oxide coverage at the transition are in close agreement with experimental values     

Tribological Properties of Self-Lubricating Polymer–Steel Laminated Composites

Self-lubricating polymer–steel laminated composites (SLC) consisting of matrix zones and filled zones were fabricated by a laminating–bonding process. The matrix zones were silicon steel sheets and the filled zones were polymer matrix filled with MoS₂ and graphite, respectively. The control specimen was prepared by spraying a polymer composite coating on a GCr15 disc. The tribological properties of SLC were investigated using a ball-on-disc tribometer under different loads and frequencies. Compared to the control specimen, the friction coefficient and wear rate of SLC was reduced by 57% and threefold at 4 N and 6 Hz, respectively. In addition, the friction coefficient of SLC was low and stable under low reciprocating frequency, and it was high and fluctuating under high reciprocating frequency. In addition, the wear rate increased with increasing applied load and reciprocating frequency. Scanning electron microscopy (SEM) images show that the lubricating mechanism of SLC was that solid lubricants embedded in filled zones expanded and smeared a layer of transfer film on the sliding path to lubricate the surface. The thermal expansion of solid lubricants was simulated using ANSYS software with thermal-stress coupling. The simulation results showed the maximum temperature of the filled zones was 130°C, and the maximum normal displacement of solid lubricants was approximately 10 μm. This confirmed that the solid lubricants expanded effectively by the aid of frictional heat.     

Tribological Behavior of a 0.33% C Dual-Phase Steel with Pre I/C Hardening and Tempering Treatment under Abrasive Wear Condition

The present study investigates the effect of prior hardening and tempering treatment on the microstructure, mechanical properties, and high-stress abrasive wear response of 0.33% carbon dual-phase (DP) steel. For this purpose, two different DP steels were produced by subjecting the as-received steel to hardening (DP-H) and hardening + tempering (DP-HT) treatments prior to the intercritical (I/C) annealing treatment. These steels along with the as-received steel were subsequently characterized by optical and scanning electron microscopy (SEM) metallography. Furthermore, tensile properties were evaluated along with microhardness measurements. The fracture surfaces of the failed tensile specimens were studied under SEM. Prior hardening and tempering treatment resulted in the formation of a nearly spherical martensite (aspect ratio = 1.2 ± 0.13) phase along with fine iron carbides in DP-HT steel. These fine iron carbides and spherical martensite act as the void nucleation sites in DP-HT steel. Therefore, DP-HT steel exhibits good ductility along with reasonable strength. On contrary, DP-H steel exhibits the presence of a fine elongated martensite (aspect ratio = 6.1 ± 3) phase, which causes poor ductility. Furthermore, abrasion tests were carried out at varying sliding distances at three different applied loads. Dual-phase treatment results in improved overall wear response. Moreover, tempering of prior hardened steel leads to improvement in wear resistance in DP-HT steel under all conditions studied in comparison with DP-H steel. This is attributed to higher strain hardening and greater resistance to particle scooping in DP-HT steel.     

Oil-Lubricated Fretting Behaviors of 304 Stainless Steels under Different Fretting Strokes and Normal Loads

The influence of oil lubrication on the fretting wear behaviors of 304 stainless steel flat specimens under different fretting strokes and normal loads has been investigated. The results proved that fretting regimes and fretting wear behaviors of 304 stainless steels were closely related to the fretting conditions. In general, the increase in normal load could increase wear damage during sliding wear. However, according to the results, a significant reduction in wear volume and increase in friction coefficient was observed when the normal load was increased to critical values of 40 and 50 N at a fretting stroke of 50 μm due to the transformation of the fretting regime from a gross slip regime to partial slip regime. Only when the fretting stroke further increased to a higher value of 70 μm at 50 N, fretting could enter the gross slip regime. There was low wear volume and a high friction coefficient when fretting was in the partial slip regime, because oil penetration was poor. The wear mechanisms were fatigue damage and plastic deformation. There was high wear volume and low friction coefficient when fretting was in the gross slip regime, because the oil could penetrate into the contact surfaces. Unlike the wear mechanisms in the partial slip regime, fretting damage of 304 stainless steels was mainly caused by abrasive wear in the gross slip regime.     

Study on transition between fretting and reciprocating sliding wear

An experimental investigation was conducted to find the associated changes in characteristics of wear before and after the transition between fretting and reciprocating sliding wear. A set of experiments were carried out using a AISI 52100 steel ball rubbing against a plate specimen made from the same steel under dry condition. Wear coefficient, wear volume, coefficient of friction, profile of the scars and wear debris were analyzed. The results displayed that there were significant differences in wear coefficient, wear volume, profile of the wear scars and wear debris before and after the transition. Wear coefficient and wear volume at a constant sliding distance were found to be the most appropriate for identifying the transition amplitude between fretting and reciprocating sliding 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.     

Friction and Wear Behavior of Irradiated Polyethylene Sliding Against a Rough Steel Surface

The aim of this study was to evaluate the tribological behavior of polyethylene crosslinked by gamma radiation sliding against a steel surface. Two high-density polyethylenes were irradiated to a total dose in the range of 2?20 Mrad under vacuum and at room temperature. After irradiation, the materials were annealed at 423 K and then cooled slowly to room temperature. The same thermal treatment was applied to the non-irradiated polymer. The wear behavior of the polymers was determined under controlled ambient temperature of 298 and 333 K using a homemade tribometer. Sheet-shaped specimens were loaded against the surface of a steel disc with different normal loads to generate nominal contact pressures in the range of 0.25–1.5 MPa. The tests were performed under dry conditions using a disc rotation to produce an average sliding speed of 0.6 m/s and during a period of time to provide an average sliding distance of 1,080 m. The wear rate was obtained as the mass loss by the sample divided by the sliding distance, and the friction coefficient was determined by measuring the friction force. The results indicate that the wear rate increases with load in the case of non-irradiated polyethylene and low-dose irradiated polymers, while the wear rate reaches a maximum value with the load in the case of the irradiated samples with high doses. The samples irradiated with a dose of 10 Mrad showed the lowest wear. The coefficient of friction (COF) increases slightly with the load in all the cases. Most irradiated polymers show higher COF than the non-irradiated material when compared at a given load. The results show that the irradiation dose applied to the polyethylenes produced no noticeable effect on the COF values when a comparison was made at a given applied load.     

Wear Behavior of Magnesium Alloy AZ91 Hybrid Composite Materials

The influence of hybrid reinforcements including silicon carbide and graphite particles with a size 37–50 μm on the wear characteristics of AZ91 magnesium alloy was studied. The dry sliding wear test was conducted using a pin-on-disc wear testing machine in the load range of 20 to 80 N at different sliding velocities in the range of 1.047 to 2.618 m/s. The results show that the wear resistance of composites was much better than that of the base matrix material under the test conditions. At a speed of 1.047 m/s and load of 40 N, the wear rate (mm³/km) of the unreinforced alloy was 6.3, which reduced to 3.8 in the case of 3% reinforced composite. The antiwear ability of magnesium alloy composite was found to improve substantially with the increase in silicon carbide and graphite content from 1 to 3% by weight and the wear rate was found to decrease considerably. At a speed of 1.047 m/s and load of 80 N, the wear rate (mm³/km) reduced from 11.8 to 9.1 when the reinforcement content increased from 1 to 3%. However in both the unreinforced alloy and reinforced composite, the wear rate increased with the increase in load and sliding velocity. An increase in the applied load increases the wear severity by changing the wear mechanism from abrasion to particle cracking-induced delamination. The worn surface morphologies of the composite containing 3% reinforcement by weight for the sliding velocity of 1.047 m/s were examined using scanning electron microscopy. Different wear mechanisms, namely, abrasion, oxidation, and delamination, have been observed.     

Formation of a Metallic Amorphous Layer During the Sliding Wear of Ti/TiN Nanolaminates

This paper describes experimental studies of metallic/ceramic nanolaminate performance under sliding contact and identifies the formation of an amorphous layer between the nanolaminate and counterface. Nanolaminates used for this study had either 20- or 100-nm-thick alternating layers of Ti and TiN, resulting in a total thickness of ~1-μm films. The structure of the Ti and TiN layers was confirmed using X-ray diffraction [(111)_TiN and (002)_Ti], and compositions were determined using electron energy loss spectroscopy (EELS)—Ti and TiN_0.7. Variation of the individual layer thicknesses within Ti/TiN nanolaminates was shown to influence both the deformation observed through the nanolaminate thickness and also the friction coefficient between the nanolaminate and 440C steel counterface during linear reciprocating wear. During sliding, the 100-nm-layered nanolaminate had a lower coefficient of friction (0.25 ± 0.01) than the 20-nm-layered nanolaminate (0.56 ± 0.06). An amorphous titanium layer developed during sliding at the interface between the 100-nm nanolaminate and steel counterface. EELS confirmed that this layer did not contain any nitrogen and recrystallization occurred near the in-contact surface. While phase changes under compressive loading have been reported for other systems, this is the first report to indicate this response within a titanium layer.     

Stick–Slip Friction of Stainless Steel in Sodium Dodecyl Sulfate Aqueous Solution in the Boundary Lubrication Regime

The service life of a diesel fuel injector is highly affected by the tribological properties of the fuel. This study aims to investigate the friction and wear behaviors of emulsified bio-oil (EBO), which is a very promising alternative fuel for engines. Sliding wear tests were performed with a ball-on-disk tribometer using a GCr15 steel ball and a flat specimen as a counterpart. In these tests, the total sliding distance was 500 m, the load ranged from 10 to 20 N, and the oscillation frequency ranged from 30 to 50 Hz. Experimental results showed that EBO had better tribological properties than diesel oil and crude bio-oil. Contact load and oscillation frequency significantly influenced friction coefficient, wear volume, and wear damage pattern. The friction coefficient decreased with an increase in load and increased with an increase in oscillation frequency. Furthermore, the wear volume slightly increased with an increase in load or oscillation frequency. The damage mechanism is attributed to adhesive wear under low load and to abrasive wear under high load. The transition in the wear mechanism is related to the adsorption of the molecules in the EBO, the microstructural contact surface, and the mechanical actions.     

Friction and Wear Behavior of Steels under Different Reciprocating Sliding Conditions

The friction and wear behavior of ISO 100Cr6 steel ball sliding against conventionally hardened carbon and low-alloy steels was studied. The effect of hardness, hardening capacity, normal load, and sliding speed on the coefficient of friction and friction energy was investigated. Friction tests were carried out, without lubrication and under ambient conditions, on a reciprocating friction tester in which a ball-on-flat contact configuration was adopted. The results showed that there is a relative tendency for the friction properties to decrease with increased hardening capacity and decreased hardness. The results showed that increasing normal load decreases the coefficient of friction for the two steel nuances. However, increasing sliding speed increases the coefficient of friction of low-alloy steel and decreases the coefficient of friction of carbon steel. The oxidation of wear debris influences the wear mechanisms and friction behavior.     

Effect of cryogenic treatment on the tribological behaviour of H11 hot die steel dry sliding against D3 steel

The tribological behaviour, hardness and microstructural characteristics of vacuum and cryogenically treated AISI H11 steel at varied soaking temperature (?154 and ?184 °C) for specific time period (6, 21 and 36 h) have been examined in this research work. The influence of selected parameters on the tribological behaviour have been studied at five levels of varying sliding velocities (0.628–1.885 m/s) and normal loads (60–140 N) through block–on–ring dry sliding wear test against hardened and tempered AISI D3 tool steel (counter face). The experiments are designed based on full factorial response surface methodology. The responses (wear rate, average coefficient of friction and maximum contact temperature) are analyzed based on plotted graphs. The results reveal that 21 h at ?184 °C for H11steel is the optimal soak time to have the lowest wear rate. The sliding speed influences the wear rate more in comparison to load. Wear debris have shape of metallic plate. Carbide particles appeared to delaminate from the sample surface due to subsurface cracks and plastic deformation. The augmentation of apparent and bulk hardness number and wear resistance ascribed to the increase in number of fine globular secondary carbide and improved morphology of matrix microstructure of cryogenic-treated sample. It is also observed that cryogenic treatment reduces the retained austenite content to near zero.     

Lubrication of Steel/Steel Contacts by Choline Chloride Ionic Liquids

There is a growing interest in the use of ionic liquids to provide lubrication for challenging contacts. This study is an initial assessment of the application of two ionic liquids based on choline chloride cations to be used as ionic liquid lubricants for engineering contacts, in this case steel on steel. These ionic liquids, termed ethaline and reline, have anions of ethylene glycol and urea, respectively, and are available at relatively low costs and in high quantities. In order to assess the lubrication performance of the ionic liquids, lubricated reciprocating sliding wear tests were conducted between M2 tool steel samples and a steel stylus. Initial tests conducted at a sliding speed of 0.005 m s^?1 and 30 N showed that ionic liquids could provide low friction lubrication, comparable to that of SAE 5W30 friction modifier free engine oil under the same test conditions; however, lubrication was lost after short sliding distances. Further testing with higher sliding speed/lower load and varying sample surface textures showed that ionic liquid lubrication could be better maintained in high-speed/low-load testing and by increasing the roughness and therefore surface area of the sample. It was also observed that the choline chloride/urea ionic liquid formed a residual film when tested on iron silicate peened samples, and that this film may promote lubrication.     

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.     

The friction and sliding wear of unlubricated 316 stainless steel in air at room temperature in the load range 0.5–90 N

The reciprocating self-wear of 316 stainless steel in air and at room temperature has been investigated in the load range 0.5–90 N. Above approximately 40 N the debris was metallic, indicating a severe wear mode. The wear volume was a linear function of the sliding distance and the specific wear rate was independent of load.Below the 40 N load, after an initial severe stage, a transition occurred with a decrease in wear rate by up to an order of magnitude. The specific wear rate in both wear stages decreased with decreasing load, showing no indication of saturating at low loads. The load dependence of the wear volume V per unit sliding distance was of the form V = kLⁿ where n ≈ 1.8 for both pre- and post-transition stages.The transition and the decreasing specific wear rates with decreasing load are thought to be associated with an increasing proportion of asperity interactions' being elastic rather than involving plastic deformation. It is proposed that wear occurs by a multistage mechanism of metal transfer to form prows, prow oxidation in the post-transition stage and prow breakdown. The transition is associated with a change in the rate-limiting step. This is believed to be the metal transfer step in the pre-transitional stage and the prow breakdown step in the post-transitional stage. Only a tentative correlation could be made between the onset of a wear transition and changes either in the friction behaviour or in the appearance of oxide in the wear debris. The friction data suggest that wear in the post-transition stage is a cyclic process of prow breakdown, prow re-formation by further metallic transfer, prow embrittlement by oxidation leading once again to breakdown and the formation of oxide-containing wear debris.     

The effects of load and substrate hardness on the development and maintenance of wear-protective layers during sliding at elevated temperatures

Transitions to low wear rates often occur during sliding between contacting metal surfaces, due to the establishment of high-resistance load-bearing layers. Such layers are developed from compaction of wear debris particles, with adhesion between the particles being an important factor in determining whether the layers are maintained, leading to wear protection, or break down, leading to abrasive wear. They are formed more easily and retained more effectively at higher temperatures, due to increased sintering and adhesion between the debris particles and to enhanced oxidation of these particles. This paper presents the results of a study of the reciprocating sliding wear and friction of dissimilar combinations of pin and disc steel specimens (high-speed steel and high-chrome steel pins and carbon steel discs) at temperatures of 500–600°C, with emphasis on the influence of load and substrate hardness on the development and maintenance of such wear-protective particulate layers. Complex relationships occur between the effects of increased load in producing larger debris particles, in decreasing the critical particle size for establishing the layers and in decreasing the separation between the sliding surfaces, and the effects of hardness of the substrates on the sizes and amounts of wear particles and on the topographies of the wear scars. The relationships are complicated further by oxidation and sintering of debris particles, leading to development of oxide or oxide-containing ‘glaze’ surfaces, and subsequent breakdown of the layers during sliding.     

Dry Sliding Friction and Wear Characteristics of Cu-Sn Alloy Containing Molybdenum Disulfide

The wear and sliding friction response of a hybrid copper metal matrix composite reinforced with 10 wt% of tin (Sn) and soft solid lubricant (1, 5, and 7 wt% of MoS₂) fabricated by a powder metallurgy route was investigated. The influence of the percentages of reinforcement, load, sliding speed, and sliding distance on both the wear and friction coefficient were studied. The wear test with an experimental plan of six loads (5–30 N) and five sliding speeds (0.5–2.5 m/s) was conducted on a pin-on-disc machine to record loss in mass due to wear for two total sliding distances of 1,000 and 2,000 m. The results showed that the specific wear rate of the composites increased at room temperature with sliding distance and decreased with load. The wear resistance of the hybrid composite containing 7 wt% MoS₂ was superior to that of the other composites. It was also observed that the specific wear rates of the composites decreased with the addition of MoS₂. The 7 wt% MoS₂ composites exhibited a very low coefficient of friction of 0.35. The hardness of the composite increased as the weight percentage of MoS₂ increased. The wear and friction coefficient were mainly influenced by both the percentage of reinforcement and the load applied. Wear morphology was also studied using scanning electron microscopy and energy-dispersive X-ray analysis.     

Influence of Sliding Speed on the Tribological Characteristics of Si3N4-hBN Ceramic Materials

The influence of sliding speed on the unlubricated tribological behaviors of silicon nitride–boron nitride (Si₃N₄-hBN) composites was investigated with two modes in air by a pin-on-disc tribometer. Using the upper disc–on–bottom pin test mode, as the sliding speed increased, the friction coefficient of the sliding pairs showed an upward trend; for example, from 0.18 at the sliding speed of 0.40 m/s to 0.54 at the sliding speed of 1.31 m/s for the Si₃N₄/Si₃N₄–20% hBN pair. The surface analysis indicated that a tribochemical film consisting of SiO₂ and H₃BO₃ formed on the wear surfaces of the Si3N4/Si3N4–20% hBN sliding pair at sliding speeds of 0.40 and 0.66 m/s. Moreover, the formation of this film lubricated the wear surfaces. At the sliding speed of 1.31 m/s, no tribochemical film formed on the wear surfaces, most likely due to the increase in surface temperature. In the upper pin–on–bottom disc test mode, the wear mechanism was dominated by abrasive wear, and no tribochemical products could be detected on the wear surfaces. The increase in sliding speed weakened the degree of abrasive wear, leading to a decrease in the friction coefficients.     

An experimental study of wear of ferrous metals

An experimental study of tracks generated by point contact sliding surfaces under different loads has been carried out on a Bowden-Laben machine. The damage to mild steel, cast iron and carburized steel under repeated rubbing was studied by microhardness testing and microscope examination.The microhardness value at various depths below the track can be an indication of severe wear by sliding action. A critical value for a combination of materials was determined. The mechanism of wear and its gradual change at the contact surface with increased load and cycles of reciprocating sliding motion are discussed.