Shinzo Kobayashi

Microscopic deformations in KC1 single crystals by indentation and scratching with steel ball and pyramidal indenters

Abstract The subject of sliding friction is of great technological importance and has been studied extensively on an engineering basis. However, many of the underlying microscopic factors that control friction and wear remain obscure. The present study is part of an effort to relate sliding deformation to the crystal structures of the contacting surfaces. The methods used are to indent a steel ball or a diamond quadrangular pyramid and to scratch these indenters on the accurately finished {100} crystal face of KC1 single crystals. Two scratch directions, 〈100〉 and 〈110〉, were chosen in the scratch tests. The study was made to examine the appearance of the dislocation structure and the mechanism of microscopic deformation and to elucidate the topographical deformations and strain hardening due to indentations and scratches. The width of the scratched track, the distribution pattern of etch pits and the dislocation density around the indent or track were examined in detail. The width of the scratched track is wider in the 〈100〉 scratch than in the 〈110〉 scratch, whereas the plastic deformation range is greater in the 〈110〉 scratch. The plastic deformation produced by scratching is formed with a continuous series of deformations due to indentation. Dislocation motions with the slip system {110}90〈110〉 are mainly observed on the scratched surface, while {110}45〈110〉 dislocations are observed on the cross-section perpendicular to the scratched surface.

Deformation mechanism in αCu-Al single crystals and bicrystals under scratching with pyramidal indentor

In order to elucidate the deformation mechanism of materials in abrasive wear process, scratching tests were carried out on the (111) face of Cu-14.7 at % Al single crystals and Σ13 b bicrystals with pyramidal indentor. In the scratching on the single crystals three kinds of scratching directions, [11 ¯2], [¯1¯12] and [¯110], were chosen. In the case of bicrystals, the [1 ¯21] and [1¯10] directions were adopted. After scratching the dislocation structure, slip trace patterns and surface profiles across the scratched track were examined. In addition, the dislocation distributions inside the crystals were revealed by successively removing thin layers and developing etch pits on the exposed surface.The slip traces on either side of the scratched track are produced more extensively than those around the indented point. These slip traces are observed only in the surface of about 100 μm deep, and are not observed in the deeper area. It is found that the microscopic deformations produced due to the scratching consist of three kinds of deformation: formed by indentation, formed by both normal and frictional stresses in the surface layer and formed by stress which is caused in certain limited depth.The swells of the material were produced in the front of the indentor due to the slips on the {111} crystal faces which are arranged so as to be diverging into the inside. The azimuths of formation of the swells are [11¯2] and [¯211] in the [11¯2] and [¯110] scratching respectively and [1¯21], [¯211] in the [¯1¯12] scratching.In the scratching of the bicrystal, the propagation of dislocation in the surface layer of the one side crystal is obstructed by the grain boundary. The microscopic deformation range on the dislocation order is affected by the distribution density of the grain boundaries.

Deformation mechanism in α-Cu-Al single crystals with a spherical indentor

The subject of sliding friction is of great technological importance and has been studied extensively on an engineering basis, but many of the underlying microscopic factors that control friction or wear remain obscure. The present study is part of an effort to relate sliding deformation to the crystal structure of the contacting surfaces. The method was to scratch a steel ball in various crystal directions on an accurately finished surface of Cu-Al single crystals. For a scratch on the (1 1 1) face, the scratched track width and the width of the slipped area were found to be wider in the [¯2 1 1] direction than in the [2 ¯1 ¯1]. The mechanism of the active slip produced by the scratch can be explained in terms of stress patterns and interactions among the dislocations produced in the subsurface region. The distributions of dislocation density on the cross-section perpendicular to the (1 1 1) face were elucidated.

Pitting failure of annealed carbon steel under rolling contact

Abstract The mechanism of pitting failure observed during rolling contact wear tests of carbon steel ring specimens is reported. Microscope observations of the specimens were made to obtain detailed fundamental information on the occurrence and growth of surface cracks and pits. The pitted area, wear loss and hardness of the contact surface of each specimen were measured at regular intervals during testing. The results gave useful information regarding the processes of pit formation and rate of pit growth under rolling contact. An equation was derived to determine the rate of pit growth and was found to give good results for rolling contact conditions.

An equation for the centre-line average roughness of material slid against abrasive paper

Abstract An analysis was made to determine the magnitude of the surface roughness of a material abraded with an abrasive paper. The theory used in the analysis includes a simple theory of plasticity based on wedge penetration into a soft material. Experimental abrasion test results show that the analysis is useful for the derivation of the centre-line average roughness of material slid against abrasive papers.

Effects of grain boundary on deformation due to scratching in α CuAl bicrystals having symmetrical 〈111〉-tilt boundary

Abstract The effects of grain boundary on the microscopic deformation of materials subjected to scratching were investigated. Scratch tests were carried out with a pyramidal indentor on the crystal face of bicrystals possessing various misfit angles. Four types of bicrystal which have a symmetrical 〈111〉-tilt grain boundary were used. Five types of applied load given to an indentor during scratching were adopted. The indentor was moved in the direction at right angles to a boundary. Scratch hardness was calculated using the width of a scratch track, and the relationship between the scratch hardness at the boundary and the misfit angle of two adjacent grains was discussed. The results obtained are as follows. (1) Anisotropy in the width of scratch track formed by the pyramidal indentor on the (111) face of α CuAl single crystal is hardly affected by load. (2) The variation ratio of width and depth of scratch track and scratch hardness are also hardly affected by load. (3) The scratch hardness is affected by load. The scratch hardness is greater under comparatively lower load. (4) The greater the misfit angle, the greater the increase in scratch hardness at the grain boundary.

Deformation Mechanism of KCl Single Crystal by Spherical Indentor. I. Indentation with Steel Ball.

The indentation test is probably the simplest method of estimating the strength of material under the frictional condition that the asperity tips are pressed into other body and that wear debris are scratched between two bodies. With the advancement of techniques of revealing dislocations in crystals, it has been thought possible to obtain a right understanding of the deformation in the material with a single crystalline structure caused by indentation.In the present study, KCl single crystal was indented with a steel ball to examine the dislocation structures associated with indentation at various loads. The slip systems and the range of deformed area were investigated in detail on the indented surface and on its cross section by using a dislocation etching technique.The results obtained are as follows:(1) The deformed area on the indented surface consists of a circular high dislocation density area and the area of comparatively low dislocation density shaped like wings and extended in the ‹110› and ‹100› directions.(2) Dislocation patterns on the indented surface and on its cross section consist of etch pit rows that belong to the {110}90 and {110}45 planes, respectively.(3) The plastic deformation range is affected by the diameter of indentor under comparatively high loads, but not under exceedingly low loads.

Deformation of KCl Single Crystal by Spherical and Pyramidal Indentors.

In order to elucidate the mechnism of friction and wear, it is necessary to have a knowledge on deformation in materials produced by invasion of sharp projections or wear particles.In this study, the cleaved faces of KCl single crystal were indented with a steel ball or a Vickers diamond indentor. The deformation and hardness around the indentation were examined from macroscopic viewpoints, and the dislocation patterns were observed from microscopic one. The results obtained are as follows:(1) The indents formed on the indented surfaces with a ball or a pyramid were not perfectly circular nor square in shape due to the crystal anisotropy.(2) The appearances of the pile-up and sink-in around indents were clarified.(3) The strain hardening around the indent was more active in the ‹110› direction than in the ‹100›.(4) The deformed area on {100} face with a ball or pyramidal indentor consisted of a high dislocation density range and a wing shaped area of comparatively low density extended along the ‹110› and ‹100› directions.(5) The hardness and the dislocation density were related each other.(6) The etch pit patterns in the cleaved cross section were observed on {110}45 faces.

Mechanism of deformation in .ALPHA. Cu-Al single crystals by spherical indentor. II. Scratch with steel ball.

αCu-Al single crystals were scratched with a steel ball in various directions in order to clarify the mechanism of the deformation observed in abrasive wear of the finished surface. Microscopic observations of the slip traces and of the scratched track were made on the (111) face scratched in the [211], [211] and [011] directions.After the (111) face had been scratched, the face was electropolished to remove a thin layer of suitable thickness in order to observe the distribution of the etch pits and slip traces on the exposed surface. This in turn permitted the determination of the distribution of the dislocation density on the cross-section perpendicular to the (111) crystal face.The conclusions are summarized as follows:(1) The slip width and slip depth increase in proportion to the load.(2) The scratched track width and the slip depth are wider for scratches in the [211] direction than for scratches in the [211] direction.(3) The active slip systems in the scratch can be explained by taking into consideration the stresses produced in the material.(4) Beyond a certain depth, the effect of the frictional stress produced by the scratch disappears, and only the effect of the normal stress remains.

Prediction of life to pitting failure under conditions of multiple stress

Abstract Wear under service conditions is a complicated but important problem. The study of wear under periodical multiple stresses is one approach to the problem. Rolling wear tests were performed on annealed carbon steel under two-stress and multistress conditions and a method of predicting life to pitting failure was derived. It was confirmed that the concept of cumulative damage is applicable to the prediction of the life to pitting failure under multiple stresses.