High-temperature sliding wear of metals

Temperature can have a considerable effect on the extent of wear damage to metallic components. During reciprocating sliding, under conditions where frictional heating has little impact on surface temperatures, there is generally a transition from severe wear to mild wear after a time of sliding that decreases with increase in ambient temperature. This is due to the generation and retention of oxide and partially-oxidized metal debris particles on the contacting load-bearing surfaces; these are compacted and agglomerated by the sliding action, giving protective layers on such surfaces. At low temperatures, from 20 to 200°C, the layers generally consist of loosely-compacted particles; at higher temperatures, there is an increase in the rates of generation and retention of particles while compaction, sintering and oxidation of the particles in the layers are facilitated, leading to development of hard, very protective oxide ‘glaze’ surfaces. This paper reviews some of the main findings of extensive research programmes into the development of such wear-protective layers, including a model that accounts closely for the observed effects of temperature on wear rates during like-on-like sliding.     

The role of triboparticulates in dry sliding wear

In this paper, wear processes and mechanisms for wear transitions with sliding time and temperature during sliding of a nickel-based alloy, N80A, in oxygen at temperatures to 250°C are discussed. Transitions in wear from high rates to low rates with sliding time were always observed at all the temperatures investigated. The transitions in wear were usually accompanied by transitions in contact resistance between the rubbing surfaces from nearly zero to positive high values. It was found that wear debris particles were heavily involved in the wear processes. The transitions in wear and contact resistance with sliding time mainly resulted from the development of wear-protective layers following the compaction of wear debris particles on the rubbing surfaces. The adhesion of triboparticulates to each other and to the rubbing surfaces played an important role in the rapid decrease in wear rate with sliding time and with increase in temperature. Processes involved in the development of the wear-protective particle layers and mechanisms for the wear transitions have been described on the basis of experimental observations. The importance of triboparticulates in wear and its implications for wear protection are discussed.     

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.     

Tribological characterization of electroless Ni–10% P coatings at elevated test temperature under dry conditions

An experimental study of wear characteristics of electroless Ni–10% P coating sliding against hard AISI 52100 steel pin is investigated. Experiments are carried out at room and 550°C temperatures. Heat treatment effects on tribological behavior of this coating are studied. The wear surface and the microstructure of the coatings are analyzed using optical microscopy, scanning electron microscopy, energy dispersion analysis X-ray, and microhardness testing equipment. It is observed that the forming of continuous oxide film on contacting surfaces of pin and disk improves wear resistance and decreases friction coefficient of the Ni–10% P coating. The results indicate that the wear resistance of electroless Ni–10% P coating has improved with heat treatment at room temperature wear test, but it reverses in the wear test at 550°C. In addition, specimens without heat treatment have the highest wear resistance and the lowest friction for wear tests at elevated temperatures.     

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     

Mild wear of a low alloy steel at temperatures up to 500°C

Wear behaviour of 52100 low alloy steel has been studied on a pin on disc wear machine at disc temperatures ranging from room temperature to 500°C. Transitions occur in the wear rate versus load curves at certain critical loads, the magnitude of which increase with temperature. These transitions were found to be associated with change in surface oxide, lower wear rates being recorded when the predominant oxide was the spinel Fe₃O₄ for all temperatures. At disc temperatures above 300°C out of contact oxidation appears to be the most important wear limiting factor. A surface model was developed enabling contact temperature, numbers and size of contacts and critical oxide film thickness to be deduced. Remarkable agreement was found between oxide thicknesses estimated from this model and measured values using a scanning electron microscope     

Enhancing tribological performance of Ti-6Al-4V by sliding process

The exceptional combination of mechanical, physical and anti-corrosive properties of Titanium alloy Ti-6Al-4?V (Ti64) makes it idle material for the applications like aerospace, automobile, chemical, medical etc. However, Ti64 exhibits poor tribological (friction and wear) properties, which limits its implementation in the intended applications. The tribological performance of the Ti64 can be enhanced by developing a protective layer or coating on its surface. It has been reported in literatures that through rubbing process the oxide layers can be achieved at much lower temperature compared to external heating process. Therefore, an endeavour is made in the present work to achieve a tribo-oxide protective layer on the surface of Ti64 through rubbing process. For this, at first the tribological behaviour of tribo pair: Ti64 pin-alumina disc is studied under dry ambient condition for diverse loading and sliding speed conditions, using pin on disc experimental set-up. The obtained results are compared with literatures. The tribological performance is quantified in terms of coefficient of friction (COF) and wear rate. To investigate the tribological mechanism and behaviour, in-situ analysis was performed on the pin’s surface using (i) scanning electron microscopy, and (ii) energy dispersive analysis of X-ray. The mechanical properties like nano-hardness and elastic modulus of the pins surface were also determined. It was envisaged that the tribological behaviour were extremely transient and depend greatly on what the surface has precisely experienced Based on the experimental observations, the experimental conditions providing (i) Case1: deprived tribological properties and (ii) Case 2: higher oxide layer is selected. Now, to enhance the tribological behaviour of Case 1, the pin with high oxide layer, i.e. Case 2 is used. For this experiment is performed initially for Case 2 conditions for the sliding distance of 1000 m (for developing oxide layer) and the experiment is continued for next 1000 m for Case 1 condition. The experimental results in terms of COF and wear rate are presented and corresponding enhancement in their values are discussed.     

Estimation of Surface Temperature of a Pin Wearing on a Disk

The surface bulk temperature of a titanium alloy pin sliding on an alumina flat disk surface is estimated semi-empirically by measuring the temperature at two points along the pin axis away from the sliding interface and assuming a realistic flow field of air around the pin. The predicted temperatures are found to be better estimates than those given by ab initio calculations.     

Abrasive wear behavior of high speed steel and hard metal coated with TiAlN and TiCN

The wear behavior of M2 high speed HSS steel and WC hard metal coated with TiAlN and TiCN were investigated and compared, using the pin on disk standard test with different loads. The coating PVD process has been done by two different suppliers, using an industrial equipment unit with optimized conditions. The coated layers were measured and characterized. The load, sliding distance and velocity of 0.5 m/s were kept constant during the abrasion test in order to control these variables. The counterface disks used were electric steel sheets from three different suppliers. The lost volume and temperature at the pin end have been measured during the wear test. Comparisons of tribological performance for the coated HSS and hard metal were done, using a plot of lost volume versus sliding distance for substrates and coatings. The pin worn surfaces were observed using a scanning electron microscope. A significant increase in the wear resistance of M2 steel and WC hard metal when coated with TiAlN and TiCN was observed. Quality of these coatings depended upon the supplier. Excessive porosity has diminished the TiAlN counting wear resistance from one supplier. However, in general the performance of TiAlN is superior to TiCN. The pin wear rate depended on the disk microstructure.     

Wear of Unlubricated Steel Surfaces in Sliding Contact

Observations have been made of the wear from an SAE 1113 steel pin specimen rubbing on a SAE 113 steel disk in a normal laboratory atmosphere in relation to normal load (0.5–10.4 lbf), slidinq speed (21–188 ft/sec), sliding distance and track history. As a function of sliding distance, three regions are observed; (i) initial severe wear, (ii) mild wear resultinq from the formation of oxide layers on both the pin specimen and transferred particles adhering to the track, (iii) a milder wear, due to the attainment of a uniform track condition. The wear rate measured in (ii) is observed to be proportional to normal load for constant (normal load)^1/2 × (sliding speed) provided that the magnitude of this parameter is insufficient to cause periodic removal of the surface film. This conclusion is shown to be compatible with earlier theoretical predictions when the presence of an oxide layer was pre-supposed. Unlike the coefficient of friction which is primarily determined by the pin surface condition only, the pin wear rate depends on the conditions of both the pin and track surface.     

Effects of temperature and sliding distance on the wear behavior of austenitic Fe-Cr-C-Si hardfacing alloy

The effects of temperature and sliding distance on the metal-to-metal wear behavior of austenitic Fe-20Cr-1.7C-1Si hardfacing alloy were investigated in air in the temperature range from 25 to 450 °C. The applied contact stress was 55 MPa and the maximum sliding distance was 18 m. In the temperature range from 25 to 200 °C, the weight loss increased linearly with increasing sliding distance. The weight loss increased parabolically with increasing sliding distance up to 18 m at 300 °C, but at 450 °C, the weight loss drastically increased from the beginning of the wear test and became almost saturated above a sliding distance of 3.6 m. The initial friction coefficient was not changed with temperature up to 300 °C. However, at 450 °C, the initial friction coefficient increased abruptly. It was thought to be due to the increasing tendency of adhesive bonding to occur between the two self-mating specimens. At temperatures below 200 °C, the steady state friction coefficient did not change significantly. Above 300 °C, the steady state friction coefficient decreased due to the oxide layers that formed on the worn surfaces during wear.     

铜基粉末冶金载流摩擦磨损微观形貌分析

对铜基粉末冶金材料进行载流摩擦磨损实验,对磨损后的微观组织进行了观察与分析.结果表明,铜基粉末冶金材料在载流条件下,销试样表面不断发生氧化,电流为40和60 A时,摩擦表面覆盖着一层Fe的氧化物;电流为80和100 A时试样由于表面温度更高,形成Cu的氧化物.产生氧化物的不同,电弧产生烧损的严重程度不同,是导致不同电流下磨损机制不同、磨损率相差大的原因.电流较大时电烧蚀严重,加快了磨损进程.     

Influence of Combined Addition of Boron and Strontium on High-Temperature Wear Behavior of A356 Alloy

In the present study, the effect of the combined addition of boron (B) and strontium (Sr) on the high-temperature dry sliding wear behavior of A356 alloy has been investigated using a pin-on-disc wear testing machine attached with a furnace. During wear studies, the effect of alloy composition, normal pressure, sliding speed, and sliding distance on A356 alloy at four temperatures, namely, room temperature and 100, 200, and 300°C, have been investigated. Further, the cast alloys and worn surfaces of A356 alloy with and without B and Sr were characterized by scanning electron microscopy (SEM)/energy-dispersive spectroscopy (EDS) microanalysis. Results indicate that the combined addition of B and Sr to A356 alloy has led to improvements in wear properties. This is due to a change in microstructure, improvement in mechanical properties, and the formation of an oxide layer between the mating surfaces during the sliding wear process.     

A study on wear and worn surfaces of grey cast iron affected by a novel silicate additive

A novel aluminium silicate hydroxide additive has shown excellent anti‐wear effect in practical applications and has been mainly studied on steels in laboratory conditions. In this paper, the pin‐on‐disk sliding wear tests were carried out to investigate the wear and worn surfaces of grey cast iron with additives in different concentration. It was found that the silicate additive showed an obvious anti‐wear effect and a reliable duration, reduced the number of pits and cracks on the worn surfaces and improved the nanohardness of the worn surfaces of grey cast iron disks by 72%. Furthermore, Raman spectroscopy displayed that the carbon structure of the worn surface of grey cast iron disks with the additive had an obvious transformation from nanocrystalline graphite to amorphous carbon. Copyright © 2015 John Wiley & Sons, Ltd.     

The effect of temperature on the unlubricated sliding wear of 5 CrNiMo steel against 40 MnB steel in the range 400–600°C

5 CrNiMo steel is used traditionally as hot forging die material in China. High temperature wear is a common failure mode of the steel. This paper deals with the sliding wear behavior of the steel in the temperature range 400°C to 600°C. The composition and features of the worn surface were analyzed using SEM, EDS and XRD. The oxidation of 5 CrNiMo steel under sliding wear condition at elevated temperature indicated that the oxide transfer layer formed on the sliding surface consisted of Fe₃O₄ and Fe₂O₃. The wear mechanism changed with the test temperature and the oxide transfer layer played an important part in the change in wear mechanism. At lower temperatures, wear was due to abrasive wear. From 500°C to 550°C, the oxide transfer layer presented a relatively compact morphology and the oxidational wear was the principal wear mechanism resulting in low wear rate at 500°C. When the test temperature was at 600°C, adhesive wear was predominant, and the wear rate increased greatly.     

The mechanism of formation of wear particles of polytetrafluoroethylene

To obtain information about the basic processes involved in the formation of wear particles of polytetrafluoroethylene (PTFE), the rubbing surface of a PTFE pin was observed through a glass disk.In the initial stages of rubbing, small PTFE fragments transferred to the glass disk from the PTFE pin but did not necessarily adhere strongly to the glass disk. Some wear fragments were observed moving against the PTFE pin at a speed lower than the sliding speed of the glass disk. The fragments at higher travelling speeds combined with the fragments at lower travelling speeds and increased in size. The fragments also increased in size by scratching the surface of the PTFE pin.In steady state rubbing, large and small fragments were observed and the enlarged fragments were successively detached from the glass disk. The variation in the volume and the travelling speed of the fragments with rubbing was also examined. The total increase in the volume of transferred fragments in a definite sliding distance was found to be similar to the volume of removed fragments.     

Origins and development of oxidational wear at low ambient temperatures

The origins and the development of the oxidational theory of mild wear under conditions where the ambient temperatures are sufficiently low that no significant oxidation can occur outside the instantaneous real areas of contact between two sliding surfaces are reviewed in this paper. Emphasis is placed on the importance of heat flow analysis for calculating surface temperatures and the division of heat at the sliding interface, especially in so far as it is used for checking the surface model used for explaining the wear rates obtained in some pin-on-disc experiments with low alloy steels. It is shown that it is possible to deduce values for the oxidation constants during wear that are different from those obtained from static oxidation tests and which are relevant to a range of low alloy steels. The implications of some of the computed values of the number N of asperities beneath the pin at any given time, the temperature T_c within the real areas of contact and the critical oxide film thickness ξ are discussed.     

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.     

Modelling sliding wear: From dry to wet environments

Corrosive species in various forms exist widely in the environment and can significantly affect wear behaviour of materials, usually accelerating wear. Under conditions where the environments are seemingly non-deleterious in terms of corrosivity, some species from the environment can still affect the tribological behaviour of materials. It is thus extremely important to recognise the roles of reactive species in affecting the tribological processes and to understand the processes of tribo-corrosion interactions. In this paper, the mechanisms of wear debris generation and the roles of reactive species in the generation of wear debris during sliding wear in gaseous or aqueous environments are discussed. The effect of environment on the development of wear-protective layers is described. Based on the proposed mechanisms, mathematical models for sliding wear in both dry and aqueous environments are outlined, and the validity of the models is assessed against experimental data in sliding conditions.     

Tribofilm formation and mild wear by tribo-sintering of nanometer-sized oxide particles on rubbing steel surfaces

The present study is the first to show that the supply of nanometer-sized particles of Fe₂O₃, SnO₂, CuO, or Bi₂O₃ oxide on rubbing steel surfaces induces transition to mild wear with sliding distance, and that the wear transition behavior depends on the type of supplied oxide. The mild wear is due to formation of the wear-protective tribofilm on the rubbing surfaces, and observations confirm that the tribofilms are produced by tribo-sintering of the supplied oxide particles. The mild wear transition behavior is explained by the sintering rate of the supplied oxide particles, which is related to the oxygen diffusion coefficient in the oxide and the particle diameter. When the supplied oxide is of high diffusivity, the tribofilm formation rate is high, owing to the high sintering rate of the oxide particles, and the mild wear transition occurs at a short sliding distance. In the case of Fe₂O₃ oxide, the sliding distance of the transition from severe to mild wear is decreased when finer particles are supplied, suggesting that fine particles are easily sintered on the wear surface.