Grade Silicon Carbide Research Articles

Abrasion groove sizes and shapes in relation to the mechanism of abrasion

Average abrasion profiles for polymer and metal surfaces abraded with emery cloth grades of 00, 320, 180, 100 and 40 have been obtained using a frictional method. Profiles using 180 grade silicon carbide abrasive are compared with those obtained using 180 emery abrasive. There is a simple relation between the slope β of a groove profile and the slope θ of the contact area-load curve of the form β = a − bθ where a and b are constants. As the abrasive grain size increases there is evidence of a sharp change in average groove profile at a particular grain size which depends on the abraded material. This appears to be due to a transition from ploughing to cutting. Secondary microroughness along the grooves produces a significant and surprisingly uniform influence on the results which appears to be largely independent of both the abrasive and the abraded material. The results are of interest in relation to the mechanism of wear.

Analysis of oxidized layers on pyrite surfaces by X-ray emission spectroscopy and cyclic voltammetry

X-Ray emission spectroscopic analysis of the surface of the iron sulphide mineral, pyrite, has demonstrated the presence of an oxygen- containing layer. Differences between the quantity of oxygen detected after grinding the pyrite on 600 grade silicon carbide paper and polishing it to the 10 μm or 0.25 μm diamond stage are considered to be due to differences in surface roughness. Triangular potential sweep voltammograms display current peaks which have been identified with the oxidation and reduction of the oxide layer between iron(II) and iron(III) valence states. The quantities of oxide on the surface determined from the charge passed on a potential sweep correlate with the X-ray emission measurements for the three surface preparations.

A simple thinning technique for transmission electron microscopy observation of an AlCu alloy

During the course of a study of the age-hardening characteristics of AI-4 wt.% Cu alloy under stress the need for thinning this alloy for transmission electron microscopy became apparent. Although ~me microscopic ~vestigation of A1-Cu alloys has been reported in the literature [1, 2], no standard procedure for preparing thin foils was to be found. In the following we describe in detail a quick and effective method of preparing t,hin foils of this al~ioy. First, a specimen (approximately ~ in. square and 0.01 in. thick) is cut from the age-hardened single crystal using ~n A1203 cut-off wheel (0.015 in. thick). While mounted on a small metal bloct: ~vith wax the specimen is very slowly wet-ground (using only 400 and 600 grade silicon carbide paper on polishing wheels) to a thickness of approximately 0.005 in. Exl~re.rne caution is r.ecessary in order to prevent introducing any deformation iin the specimen. The specimen is then mounted in a holder ctevised by Goodell [3], as :shown in Fig. 1. The specimen holder is simpb a long (approx. 9 in.) stainless steel rod ~ 'J in. diam) with a housing at one end to hold two round stainless steel inserts. The specimen is held betweei~ these two inserts. The above assembiy is lacquered with a paint (trade name Microstop) to prevent it from being attacked by the electrolyte (see Fig. 1). Important to note here is that the central portion of the inserts is left unlacquered. This ensures a free flow zone around that area of the specimen which is to be ~hinned [4]. As a result, the electrolyte action usually produces a fairly large thinned region around the central hole, thus providing a large overall

Transient temperatures produced by abrasion of aragonite

The transformation of aragonite to calcite has been used to provide an indication of the thermal history of debris and the surface of aragonite during abrasion on 320 grade silicon carbide papers. The temperature rise of debris was estimated to be 500°–600°C whereas the specimen surface temperature was considerably lower. This supports the view that the mechanism of material removal during the abrasion of non metallic materials is essentially similar to that occurring in metals.

Hertzian Stress Cracks in Beryllia and Glass

The effect of Hertzian stresses resulting from loads acting at the points of contact of beryllia spheres was determined. As‐drawn glass and glass ground with various grades of silicon carbide were indented with beryllia spheres, 1 in. in diameter. Also, pairs of these beryllia spheres were pressed together. Circular cracks due to Hertzian stresses were produced; an optical technique was developed for detecting them in a beryllia surface. The outer crack radius was proportional to the cube root of the maximum applied load. Average values obtained for the respective inner crack radii were used to determine average values of the minimum load to fracture these materials. The average minimum load to fracture 1 in. diameter beryllia spheres in air at room temperature under dynamic loading was 235 1b. The crack radius in glass and beryllia was about 20% greater than the radius of the contact surface. This was not significantly affected (in glass) by flaw density. It is considered that the Hertz analysis does not give the correct location and value of the maximum tensile stress when finite displacements of material occur.