Origin and evolution of false brinelling and fretting corrosion under rolling conditions

Rolling bearings working in oscillating applications often suffer from false brinelling and fretting corrosion that limit their service life.At present,the study of oscillation-induced failures is primarily dominated by a large number of sliding and bench tests.However,most of the previous work are not able to fully describe the two closely related but different failure mechanisms.In this study,the origin and evolution of the two failures are thoroughly investigated under strictly controlled oscillating rolling conditions.The results show that failure evolves from false brinelling to fretting corrosion under dry friction conditions regardless of the oscillation amplitude.This process is accompanied by a large area peeling and serious oxidation,and the oxygen content increases from 2.50 wt%to 21.22 wt%.Oxidation is a crucial factor in the evolution of false brinelling into fretting corrosion.However,the distribution of microwear and oxygen content depend on the oscillation amplitude.Under lubrication conditions,the friction coefficient(COF)is smaller in the initial stage and led to local slip or transient instability of rolling elements.Therefore,the size of the wear marks and COF increased and appeared to be larger than those under a dry friction condition.However,grease can separate the contact surfaces,only surface deformation owing to false brinelling and slight damage at the roughness level occurred.The evolution of false brinelling and fretting corrosion is also closely related to residual stress.False brinelling often occurrs with residual stress accomulation,meanwhile,the residual stress increases from 120 to 300 MPa.When peeling occurs,residual stress is released.The failure pattern transformed from false brinelling to fretting corrosion and is accompanied by oxidation.So far,none of investigation is able to show satisfactory evolution of oscillating-induced failures,this study may contribute to more scientific understanding of rolling bearings against long-run reciprocating oscillating wear.

Self tempering effect of near eutectic Al-Si casting with different wall thickness solidified and cooled in permanent die

In order to study the self tempering effect on the solidification of Al-Si alloy, a setup was designed to conduct experiments. The characters of β phases in different thicknesses of Al-Si samples were investigated. The results show that the size distributions of β phases obey the logarithmic normal distribution. The Brinell hardness tests were also carried out. The tested hardness results show that the hardness distribution of the casting cooled in water is evener than that cooled in air, and its averaged value is higher than that cooled in air.

Effects of Sc, Zr and Tion the microstructure and properties of Al alloys with high Mg content

The effects of trace Sc, Zr, and Ti on the microstructure and hardness of A1 alloys with high Mg content （Al-6Mg, Al-8Mg, and Al-10Mg） were studied by optical microscope, scanning electron microscopy （SEM）, transmission electron microscopy （TEM）, and Brinell hardness. The grain size of the as-cast alloys was refined by the addition of Sc and Zr, and it was further refined by the addition of Ti. With the same contents of Sc, Zr, and Ti, an increase in Mg content was beneficial to the refinement due to the solution of Mg into α-Al. The refined microstructures of the as-cast alloys were favorable for Brinell hardness. Addition of Sc, Zr, and Ti to the Al-10Mg alloy results in the improvement of peak hardness and it is about 45% higher than that of the Al-10Mg alloy, which is due to fine precipitations of Al3（SC1-xZrx）, Al3（Sc1-xTix）, and Al3（Sc1-x-yZrxTiy）.

Preparation &Characterization of Al-5083 Alloy Composites

This paper reports the dry sliding wear behavior & Brinell hardness test of AA 5083 aluminium reinforced with SiC particles fabricated by stir casting technique. Different volume fraction of SiC particles (3, 5 and 7 wt%) were used for synthesis. The wear test has been conducted on pin-on-disc testing machine to examine the wear behaviour of the aluminium alloy and its composites. An attempt has been made to study the influence of wear parameters like applied load, sliding speed, sliding distance and percentage of reinforcement on the dry sliding wear of metal matrix composites (MMCs). A plan of experiments, based on the techniques of Taguchi, was performed to acquire data in controlled way. An orthogonal array of L9 (34) and signal to noise ratios as smaller the better was selected. Analysis of variance (ANOVA) was employed to investigate the influence of wear parameter on pin of aluminium MMCs. The correlation was obtained by multiple general regressions model. Finally, conformation tests were done to make a comparison between the experimental results foreseen from the mentioned correlation.

Mechanical and Electrical Properties of the Ternary Ag-Sb-Zn System

This paper presents comparative review of experimental and thermodynamic assessment of ternary Ag-Sb-Zn system. Isothermal section of the Ag-Sb-Zn system at 300 ~C has been calculated by CALPHAD method using ther- modynamic parameters from literature. Microstructural analysis of a number of alloys was carried out by scanning electron microscopy and optical microscopy, whereas chemical composition of observed phases was analyzed using energy- dispersive X-ray spectroscopy. Hardness of selected alloys from four vertical sections was determined using Brinell hardness test and additionally by micro Vickers hardness test. Electrical conductivity of a number of alloys in the ternary Ag-Sb-Zn system was experimentally determined. Good overall agreement between experimental and calculated values was obtained.