Severe Metallic Wear Research Articles

High Temperature Tribology of A413/B4C Nanocomposites under Dry Sliding Contact

Abstract In this work, boron carbide (B4C) particulate (0.5, 1.0, 1.5, and 2.0 weight %) reinforced A413 alloy nanocomposites were fabricated by ultrasonic stir casting method. The prepared aluminum matrix nanocomposites were characterized using optical microscopy and field emission scanning electron microscopy to observe particle dispersion and quantify microstructural features. A high temperature pin-on-disk tribo-tester was employed to investigate the dry sliding tribological behavior of fabricated nanocomposites and unreinforced alloy at a constant speed (0.66 m/s) and different loads (20, 60 N) over the temperature range of 50°C–200°C. Specimens were slid against an AISI SAE 52100 counterface for the fixed duration of 10 minutes. Worn surfaces were examined under the scanning electron microscopy, and energy dispersive spectroscopy analysis was carried out to understand the wear mechanisms. It was revealed that the wear resistance of the alloy improved because of increasing B4C content. The wear rate of all specimens was found to increase with increased load and operating temperatures. A shift in the mild oxidative to severe metallic wear of an unreinforced alloy was seen increased by about 50°C–80°C because of particulate reinforcement. The mild abrasive wear mechanism of the base alloy at low temperature was changed to adhesion with heavy plastic deformation at elevated temperature. Increased thermal stability offered by boron carbide particles and oxides and a mechanically mixed transfer layer were key factors enhancing the wear resistance of the nanocomposites. Under the tested experimental conditions A413/B4C nanocomposite was found suitable and better than the base alloy for use in wear resistance applications.

Effect of Electromagnetic Stirring on the Reciprocating Wear Characteristics of A390 Alloy

Present study reports the effect of electromagnetic stirring (EMS) on reciprocating wear characteristics of A390 alloy. The microstructure features showed the refinement of eutectic silicon and reduction in size of primary silicon particles due to the effect of EMS. Hardness of the A390 alloy (100.28 BHN) prepared by EMS was higher than conventional A390 alloy (66.86 BHN). Reciprocating wear tests were carried out at different contact loads (15N to 90N) and speeds (0.2m/s to 1m/s) using pin-on-reciprocating plate tribometer for a constant sliding distance of 500m. As the reciprocating velocity increases from 0.2m/s to 1m/s, the wear loss of both EMS stirred and without stirred A390 alloys were found to decrease gradually up to the critical velocity 0.6m/s. It was noticed that above critical reciprocating velocity 0.6m/s, the wear loss was found to increase abruptly. Also, as the load increases from 15N to 90N, the wear loss of both the alloys were found to increase gradually up to 45N and thereafter abrupt increase in wear loss was noticed up to 90N. This clearly indicates a transition in the mode of wear from mild oxidative to severe metallic wear regime. Wear rate of without stirred A390 alloy in the region 45N to 90N showed predominant increase compared to EMS stirred A390 alloy. This trend suggests that EMS stirred A390 alloy is more coherent and stable under dry sliding wear conditions than without stirred A390 alloy.

Effect of Counter Surface Temperature and Load on the Transition from Mild to Severe Wear Behavior of Al-Si-SiC<sub>p</sub> Composites in Reciprocating Conditions

In the present paper, the effect of counter surface temperature and load on the transition from mild to severe wear of A319/15%SiCp, A336/15%SiCp, and A390/15%SiCp composites have been reported. Composites were produced through stir casting route. Adhesive wear behavior of composites was studied under dry reciprocating conditions using indigenously developed reciprocating friction wear test rig conforming to ASTM standard G133-05. It was found that increase in counter surface temperature increases wear rate and depending upon the load and type of composite mode of wear changes from mild oxidative to severe metallic wear noticed. At 120N load, the critical transition temperature for all the three Al-Si-SiCp composites was found to be 350°C. SEM study of wear surface and wear debris was conducted to analyze the mode of wear and operating wear mechanism. Severe wear was characterized by massive plastic deformation and gross material removal while the mild wear was found to be associated with delamination and scoring as main wear mechanisms responsible for material loss.

Influence of laser hardening on the tribological properties of forged steel for hot rolls

The influence of laser hardening on the tribological behaviour of a forged steel for hot profiled rolls is evaluated using a customary test rig which provides the rolling–sliding contact between the roll and a C40 plain carbon steel counterpart. Samples treated with different lasers and processing parameters were considered. Starting from a base value of 300 HV the surface hardness was increased up to 800 HV and the total case depth ranged from 1.2 to 2 mm. The benefits of the laser treatment could be clearly observed at low test temperature, due to the positive influence of a hard martensite microstructure in preventing severe metallic wear by adhesive fracture. The influence of laser hardening was less evident at high temperature, where the tendency of different microstructures towards the formation of wear protective oxide layers could result in a better or worse resistance compared to the base steel, respectively. The capability of the roll material to produce wear particles and their entrapment within the contact interface resulted of fundamental importance for the formation of oxide glazes.

Dry sliding tribological behavior of AZ31 magnesium alloy irradiated by high-intensity pulsed ion beam

The dry sliding tribological behavior of AZ31 magnesium alloy irradiated by high-intensity pulsed ion beam (HIPIB) at energy density of 3.4 J/cm 2 with 10 shots is investigated by dry sliding wear tests in order to explore the effect of HIPIB irradiation on tribological property of magnesium alloy. Surface morphologies, composition and structure of the irradiated AZ31 magnesium alloys are examined by electron probe microanalysis (EPMA) and X-ray diffraction (XRD). The results indicated that HIPIB irradiation led to the increase in surface microhardness and the reduction in friction coefficient and wear rate. Wear rate for both the original and the irradiated samples increased with increasing sliding load from 0.1 to 0.5 N. The transition from severe metallic wear to mild oxidative wear induced by HIPIB irradiation was observed by a combined analysis in surface morphology and chemical composition of wear tracks, mechanically mixed materials and wear debris, which is mainly attributed to the significant increase in microhardness resulting from grain refinement on the irradiated surface. In addition, defects induced by HIPIB irradiation promoted the diffusion of oxygen during sliding wear and therefore led to the formation of compact mixed materials and protective films on the wear tracks surface, which also contributes to the transition in wear mechanism of AZ31 magnesium alloy induced by HIPIB irradiation.

Effect of load and reciprocating velocity on the transition from mild to severe wear behavior of Al–Si–SiC p composites in reciprocating conditions

In the present paper, the effect of normal load and reciprocating velocity on transition from mild to severe wear of A319/15%SiC p, A336/15%SiC p, and A390/15%SiC p composites have been reported. Composites were produced through liquid metal metallurgy route. Adhesive wear behavior of composites was studied under dry reciprocating conditions using indigenously developed reciprocating friction wear test rig conforming to ASTM Standard G133-05. It was found that increase in normal load increases wear rate and depending upon the reciprocating velocity and type of composites, mode of wear changes from mild oxidative to severe metallic wear was noticed. The load corresponding to the transition from mild to severe wear usually termed as transition load was found to decrease with increase in reciprocating velocity and reduction in silicon content in the alloys used for the development of Al–Si–SiC p composites. At 1 m/s reciprocating velocity, the transition load for A319/15%SiC p, A336/15%SiC p and A390/15%SiC p composites were found to be in the range of 60–90 N, 60–105 N and 60–120 N respectively. Scanning electron microscope (SEM) study of wear surface and wear debris were conducted to analyze the mode of wear and operating wear mechanism. Severe wear was characterized by massive plastic deformation and gross material removal while the mild wear was found to be associated with delamination and scoring as main wear mechanisms responsible for material loss. Wear mechanism maps for different Al–(6–18)%Si–15%SiC p composites were proposed in reciprocating contacts.

Wear mechanism of AZ31 magnesium alloy irradiated by high-intensity pulsed ion beam

The wear resistance and wear mechanism of AZ31 magnesium alloy irradiated by high-intensity pulsed ion beam (HIPIB) at an ion current density of 100 A/cm 2 with shot number from one to ten are investigated by dry sliding wear tests. The cross-sectional microstructure and surface microhardness of the irradiated AZ31 magnesium alloys are examined by optical microscopy (OM) and Vickers tester, respectively. It is found that surface hardness increased with increasing shot number, from an original value of 570 MPa to a maximal value of 820 MPa with ten shots, and the wear rate of the samples irradiated with five and ten shots was about one order of magnitude less than that of the original sample. The transition from severe metallic wear to mild oxidative wear induced by HIPIB irradiation was identified through a combined analysis in surface morphology and chemical composition of wear tracks, mechanically mixed materials, wear debris and wear scars of counterface steel ball by using scanning electron microscopy (SEM) and electron probe microanalysis (EPMA), which is mainly attributed to the significant increase in microhardness resulting from grain refinement on the irradiated surface.

Effect of iron (Wt.%) on adhesive wear response of Al-12Si-1Cu-0.1Mg alloy in dry sliding conditions

The presence of iron leads to different types of intermetallics in Al-Si alloys, among them needle shaped β-phase (Al5FeSi) can lead to variations in hardness of the Al-Si alloy which ultimately can affect the wear resistance of the alloy. In this paper, the effect of iron on wear behavior of cast Al-Si alloys has been reported. Sliding wear behavior of eutectic alloy Al-12Si-1Cu-0.1Mg was investigated in dry sliding conditions by using pin-on-disk test configuration against heat treated EN31 steel counter-surface at room temperature. Sliding wear behavior has been evaluated at four normal loads of 5, 20, 50 and 70 N and two sliding speeds, 2 m/s and 4 m/s. Worn pin surfaces were examined by scanning electron microscopy (SEM) for analyzing wear mechanisms. The wear mechanism has been found to be mild oxidative type at lower sliding speed of 2m/s for entire range of loads used in the study. Transition to severe metallic wear occurs at higher sliding speed of 4 m/s at normal load of 5 N. Hardness of the alloy increased with increase in iron addition primarily due to presence of needle shaped Fe-rich intermetallics but it leads to an increased wear rate.

Sliding Friction and Wear Behavior of Pack-Boronized AISI 1050, 4140, and 8620 Steels

This paper describes the dry sliding friction and wear performance of boronized AISI 1050, 4140, and 8620 steels with the Fe 2 B phase coating on the surface. The studies were carried out using a pin-on-disc arrangement. The disc material was made of carburized AISI 1020 steel. For the normalized (untreated) steels, two basic wear regimes were observed; namely, oxidative and severe metallic wear. In the oxidative regime, a low wear rate of 1E-5 mm 3 /Nm was found. The worn surfaces of the pins and discs were smooth and covered with patchy oxides. In severe wear, the wear rate was very high (1 E-3 mm 3 /Nm). The worn specimens were characterized by rough surfaces, plastic deformation, and metallic wear debris. Boronizing changed the wear mechanisms of steels. The test results showed that the boronized steels underwent oxidative fatigue wear with very low wear rate of 2 E-6 mm 3 /Nm. In addition, boronized steels exhibited lower friction coefficient than normalized steels at a sliding speed of 2 m/s.

Surface properties of laser processed ductile iron

On laser melt treatment, Sliding Wear of pearlitic ductile iron reduced from severe metallic wear to oxidative mild wear by nearly two orders of magnitude at $7.5 ms^{-1}$ over a load range of $14-31 kg cm^{-2}$; resistance to Cavitation Erosion improved by a factor of seven in corrosive media and surface hardness increased from 20-22 to 40-58 $HR_c$. Laser melting could effectively reduce Corrosion rates in dilute acids by nearly 40%. These improvements were caused by the ultrafine microstructure $(1-4 \mu, DAS)$, microhardness $(700-900, HV_{0,1})$ and the consequent high resistance to plastic flow and subsurface crack initiation. In this investigation, pin-on-disc adhesive wear, ultrasonic vibratory cavitation erosion and potentiodynamic corrosion in synthetic sea water and 0.01 $NH_2SO_4$, were assessed after laser surface melting or transformation hardening of hyper-eutectic ductile iron, typically employed in automotive and marine engine components by using $CO_2$ CW or Nd-YAG pulsed high power laser. Also the processing parameters viz, beam power (P), scan rate (U), and specific energy intensity $(P/UD_b^2)$ for threshold and specific depth of transformation hardening or melting have been determined.

Microstructural effects on the sliding wear resistance of a cobalt-based alloy

The influence of the microstructure on the dry sliding wear resistance of a hypo-eutectic Stellite 6 alloy was investigated under conditions leading to severe metallic wear of the hardfacing alloy. Conventional chill casting as well as laser surface cladding were used to produce a wide range of solidification microstructures. The hardness of the alloy was strongly dependent on the microstructure and in particular on the size of the dendrites. Under the sliding conditions investigated, severe delamination wear of the Stellite occurred. High coefficients of friction were measured and the structure in the subsurface was completely destroyed by the resulting stress cycles. During the stationary wear regime, no dependence of the wear rate on the as-solidified microstructure could therefore be determined. However, a strong influence on the wear resistance of alloying elements which affect the matrix properties was observed. Suggestions are made for the improvement of the wear resistance of such alloys under similar sliding conditions.

Microstructure, corrosion and tribological behaviour of plasma immersion ion-implanted austenitic stainless steel

The surface modification of AISI 316 stainless steel by plasma immersion ion implantation (PI3) has been investigated over a range of treatment temperatures. Below 250°C the results are similar to those obtained by conventional ion beam implantation of nitrogen, but the depth of nitrogen penetration increases dramatically with temperature. Up to 450 °C a nitrogen-expanded austenite phase is formed which is shown to have improved corrosion performance over the untreated material. At 520 °C chromium nitride is precipated and the expanded austenite transforms to martensite, leading to a reduction in corrosion resistance. Pin-on-disc testing indicates improved wear resistance at all temperatures, with reduction in the wear volume by factors of several hundred at high loads. This can be attributed to the formation of an oxide layer which prevents the initiation of severe metallic wear.

Severe wear of rolling/sliding contacts

The wear of wheel flanges against the sides of rails is shown to be caused by rolling/sliding contacts sustaining high cyclic stresses at low slide/roll ratios. When these conditions are reproduced in the laboratory severe metallic wear is initiated when the resultant shear stress, which is dependent on both normal (pressure) and tangential (friction) forces, exceeds a critical value. The results are discussed in terms of Johnson's shakedown limit and the material's stress/strain characteristics. It is concluded that the severe wear of contacts at low slide/roll ratios is caused by high resolved cyclic stresses that result in continual plastic deformation of the surface layers.

Failure criteria in thin film lubrication — the irg program

Cooperative efforts of the IRG have led in recent years to highly reproducible results in the study of failure criteria of lubricated steel contacts. It is shown that during running-in several transitions from EHD to boundary lubrication and to severe metallic wear occur. They are now predictable for certain well-defined tribo-systems. At intersections of such transitions in the load/speed diagram, scuffing is a stochastic process. It is suggested that the nomenclature and the experimental approach proposed by the IRG could be applied in the analysis of many related tribo-systems.

A model junction study of severe metallic wear

Model junction experiments simulating severe metallic wear are described. A dual shear mode of junction failure, which gives rise to a detached particle is demonstrated. Division of the particle volume by the distance traversed during particle formation gives a simulated wear rate. A linear relationship is found to exist when wear rate vs. simulated load area is plotted for a series of models of equivalent geometry. A probability factor K, calculated from the results suggests that all junctions of the type investigated will give rise to a particle.

The formation of surface films at the transition between mild and severe metallic wear : J. K. Lancaster, Proc. Roy. Soc., A 273 (1963) 466–483; 14 figs., 9 refs.

An electrochemical approach for the preparation of Mg-Li-Ce alloys by co-reduction of Mg, Li and Ce on a molybdenum electrode in KCl-LiCl-MgCl2-CeCl3 melts at 873 K was investigated. Cyclic voltammograms (CVs) and square wave voltammograms indicated that the underpotential deposition (UPD) of cerium on pre-deposited magnesium led to the formation of Mg-Ce alloys at electrode potentials around −1.87 V. The order of electrode reactions was as follows: discharge of Mg(II) to Mg-metal, UPD of Ce on the surface of pre-deposited Mg with formation of Mg-Ce alloys, discharge of Ce(III) to Ce-metal and after that the discharge of Li+ with the deposition of Mg-Li-Ce alloys, which was investigated by CVs, chronoamperometry, chronopotentiometry and open circuit chronopotentiometry. X-ray diffraction (XRD) illuminated that Mg-Li-Ce alloys with different phases were obtained via galvanostatic electrolysis by different current densities. The microstructures of Mg-Li-Ce alloys were characterized by optical microscopy (OM) and scanning electron microscopy (SEM), respectively. The analysis of energy dispersive spectrometry (EDS) showed that Ce existed at grain boundaries to restrain the grain growth. The compositions and the average grain sizes of Mg-Li-Ce alloys could be obtained controllably corresponding with the phase structures of the XRD patterns.

The formation of surface films at the transition between mild and severe metallic wear

The conditions of sliding have been found in which a transition occurs between the régimes of mild and severe wear for a leaded brass (60/40 brass containing 2% lead) sliding on hardened steel without lubrication. At light loads, low speeds, and low temperatures, mild wear begins when sufficient time is available to establish a protective surface film by oxidation; in addition, mild wear also occurs at heavy loads, high speeds and high temperatures because of an increase in the rate of oxidation. The topography and composition of the films generated on the brass during mild wear have been examined by reflexion electron microscopy and X-ray micro-analysis. The presence of a relatively large proportion of iron oxide in the surface layers, originating from the steel, increases their hardness and, in turn, causes wear of the steel itself. The variation of the rates of mild wear with load and speed is complex and, in contrast to the severe wear process, there is no unique mechanism of wear. It is concluded that mild wear of brass results from the combined effects of intermittent metal-to-metal contact, abrasion by oxide particles, and flaking of the oxide layers from the surface.

The stages in a process of severe metallic wear

In order to provide information about the basic processes involved in the wear of metals, a detailed study has been made of a severe type of wear. The particular system chosen was the wear of brass against a harder material under conditions in which the debris produced is metallic. Using radioactivity methods, transfer of metal between the rubbing surfaces was determined concurrently with measurements of the total wear. In experiments at various loads, the relationship between the rates of transfer and wear was studied. Particle-size distributions of the wear debris were obtained and compared with size distributions of the transferred fragments. It is concluded that wear occurs via a layer of transferred metal and that there is no direct production of loose wear particles. The wear process has at least two distinct stages; namely, the removal of metal from the wearing surface by transfer, and the formation of wear debris from the transferred layer on the opposing member. The magnitude of the applied load determines primarily the scale of the phenomena rather than the rate at which they occur.