Sliding wear response of zinc based alloy as affected by suspended solid lubricant particles in oil lubricant

Abstract

Wear behaviour of a zinc based alloy has been studied in partially lubricated condition. The test environment comprised a mixture of oil plus graphite/talc particles. The composition of the lubricant mixture was varied by changing the concentration of the solid lubricant particles suspended in the oil lubricant. Wear response of the alloy was noted to improve in terms of decreased wear rate, frictional heating and friction coefficient initially with the increasing concentration of the solid lubricant particles suspended in the oil lubricant. A critical content of the solid lubricant led to the best wear performance of the samples. This was followed by a reversal in the trend at concentrations of the solid lubricant particles in the lubricant mixture that were greater than the critical one. Wear behaviour of the alloy has been substantiated through the characteristics of wear surfaces, subsurface regions and debris particles.     

Influence of load and speed on wear characteristics of grey cast iron in dry sliding — selection for minimum wear

The wear of grey cast iron in dry sliding conditions has been studied with the aims of (1) finding the influence of working conditions on the wear rate, and (2) determining the region of speed and load where low wear is accomplished. Grey cast iron with flake and nodular graphite was submitted to investigation using a pin-on-disc machine. The results indicate that the flake graphite cast iron is more suitable for applications at speeds greater than 4 m s⁻¹ and lower loads, while nodular cast iron has greater wear resistance at lower speeds in the range of loads investigated - from 50 N cm⁻² to 200 N cm⁻²     

Effect of phosphide and matrix microstructures on the dry sliding wear of grey cast iron

The effect of a continuous phosphide network in matrices of pearlite, ferrite, martensite, and tempered martensite has been investigated on the dry wear of a grey iron, sliding at a speed of 1.5 m s⁻¹ with stresses of 0.5 and 2.0 MPa against cast iron. A running-in period was observed with a 0.2% P iron, whereas no running-in was observed with the 1.0% P irons. The presence of a continuous phosphide network reduced the wear rate of the pearlite iron by a factor of 0.25. In the weaker matrices (pearlite, ferrite, and tempered martensite) the phosphide network stiffened the matrix, fractured, and formed a particulate composite of phosphide in the deformed surface which resisted deformation. The wear rates and wear mechanisms of the irons are presented and discussed.     

Sliding wear response of a cast iron under varying test environments and traversal speed and pressure conditions

This study pertains to the examination of sliding wear behaviour of a gray cast iron over a range of sliding speeds and applied pressures in dry and (oil and oil plus graphite) lubricated conditions. Wear properties characterized were wear rate and frictional heating. The cast iron revealed various forms and sizes of graphite particles in a matrix of pearlite and limited quantity of free ferrite. Different solidification patterns, as controlled by the chemical composition and/or carbon equivalent of the alloy and rate of cooling, were thought to be responsible for the varying morphology of the graphite phase formed in the material matrix. Occasional decohesion of graphite at ferrite/graphite interfacial regions was also observed.The wear rate of the cast iron increased with the speed and pressure of sliding due to increasing severity of wear condition. The specimens tended to lose proper contact with the disc at larger pressures when slid dry. This was attributed to severe cracking tendency of the material. On the contrary, specimen seizure was noticed in the oil and oil plus graphite lubricated conditions; the seizure resistance (pressure) decreased with sliding speed in presence of the lubricants. The wear rate versus pressure plots attained different slopes, i.e. the rate of increase in wear rate with pressure, depending on the test environment. One slope and inappreciable effect of pressure on wear rate were noticed due to substantial cracking tendency of the cast iron when tested in dry condition. In the oil lubricated condition also, virtually one slope was observed but it was higher than that in dry condition indicating greater sensitivity of wear rate towards the applied pressure. Also, the samples attained lower wear rate in oil than in dry condition in view of suppressed cracking tendency causing more stable lubricating film formation in presence of the oil lubricant. Addition of graphite particles to the oil lubricant caused a further reduction in wear rate because of the enhanced possibility of a more stable lubricant film formation due to smearing of the graphite particles. In this case, the slope of the wear rate versus pressure plots was the least in the intermediate range of pressures irrespective of the sliding speed owing to more stable lubricating film formation.A higher rate of temperature increase with test duration (intermediate sliding distance) in the beginning was attributed to the abrasive action of the hard debris generated through the fragmentation of the initially contacting asperities. A subsequently observed lower rate of increase at longer durations could be owing to the occurrence of mild wear condition in view of less stressing of the contacting asperities and increased stability of the lubricant film formed. Increase in the rate of frictional heating at still longer durations resulted from destabilization of the lubricating film.Frictional heating increased with applied pressure and sliding speed in view of increasing severity of wear condition. The rate of increase in frictional heating was low initially up to a specific pressure followed by a higher rate of increase at still larger pressures when the tests were conducted in oil plus graphite at both the sliding speeds and in the oil lubricant at the lower speed. A constant (high) rate of increase in frictional heating with pressure was noticed in the dry condition at both the sliding speeds and in the oil lubricant at the higher speed. Low rate of frictional heating with pressure was attributed to the occurrence of mild wear condition while a higher rate of frictional heating with pressure resulted from the occurrence of severe wear condition. As far as the influence of test environment on frictional heating is concerned, least frictional heat was generated in the oil plus graphite lubricant mixture while the maximum was noticed in dry condition, intermediate response of the samples being observed in oil. Formation of more stable lubricating film was thought to be responsible for lower frictional heating in the lubricated conditions; the presence of graphite in the oil lubricant increased the extent of lubricating film formation and stability of the film so formed.The wear response of the samples has been explained in terms of cracking tendency and lubricating effects of graphite, predominance of the counteracting effects of the two parameters over each other, and lubricating film formation by the external oil (plus graphite) lubricant on the sliding surfaces in specific test conditions. Characterization of wear surfaces, subsurface regions and debris particles of the material enabled to further substantiate the observed wear performance of the samples.     

The friction and wear of automotive grey cast iron under dry sliding conditions Part 1-relationships between wear loss and testing parameters

The material investigated in this study is automotive grey cast iron (SAE G-3500) used for the manufacture of cylinder liners in a range of diesel engines. A comprehensive model for the understanding of wear and friction of this type of materials is presented here for the first time. This model takes into account the cumulative contribution of various mechanisms of wear and friction (truncation, adhesion, delamination and ploughing) to the overall phenomenon of wear loss. Quantitative aspects and statistical modelling were employed to develop a mathematical relationship between measurements of friction and wear under varying conditions of load, number of cycles and velocity (rev min⁻¹).     

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.     

Corrosion and wear resistance characteristics of NiCr coating by laser alloying with powder feeding on grey iron liner

To reduce the mixed fuel induced excessive wear of the cast iron engine cylinder liners, research on laser alloying of NiCr alloy with powder feeding was performed to locally change both the composition and the microstructure of the liner. The research indicated that laser alloying of 75Ni25Cr on grey cast iron liner demonstrates sound alloying layers free of cracks and porosities. The microstructure of the alloyed layer is composed of pre-eutectic austenite and ledeburite. The alloying element Ni is mainly located in the austenite, while Cr is mainly in cementite. The average hardness is HV_0.2500. The corrosion resistance of the alloyed layers in diluted H₂SO₄ solution and NaOH solution is dramatically improved compared to the grey cast iron. The relative wear resistance of the laser-alloyed 75Ni25Cr layer is 4.34 times of that of the grey cast iron. The improvements on the corrosion and wear resistance of the cast iron are attributed to the composition and microstructure change by laser alloying of 75Ni25Cr. Laser alloying can be a good solution to improve wear and corrosion resistance of the grey iron liners in mixed fuel environment.