Sliding Friction and Wear Behavior of GCr15 Bearing Steel at Different Temperatures

The effects of temperature on the friction and wear properties of GCr15 were studied by using a RETC multifunctional friction and wear testing machine. The microstructure characterization of the worn surface of the experimental steel was studied by means of metallographic microscope (OM), white light interferometer, secondary electron image (SEI) and back scattered electron image (BEI).The results show that the wear resistance of GCr15 bearing steel at room temperature is better than that at 100°C, 150°C and 200°C. At room temperature, the main wear forms of GCr15 are adhesion wear and fatigue wear. However, at 100°C, 150°C, 200°C, the friction coefficient and oxidation degree in the wear zone first increase and then decrease with the increase of temperature, and the wear form is mainly oxidized wear, accompanied by abrasive wear.

Method and Implementation of High-Performance Diagnostics of Form of Electron Probe of Raster Electron Microscope

An important unit of an electron microscope is the system controlling the electron beam, responsible for raster forming on the specimen and the electron probe focusing, which provides an achievement of minimum of aberrations and the maximum of resolving capacity of formed electron image. During using electron microscope the image quality gradually deteriorates, manifesting the resolving capacity reduction and the astigmatism appearance. An attachment developed for the raster electron microscope, permitting to perform the highly effective diagnostics of the configuration of the scanning electron beam, controlled by a precision magneto-optical system, has been offered. It has been shown that the direct visual observing the scanning electron probe, in particular the evaluation of the ellipticity of its cross-section using the WEB camera matrix, combined with the sample plane, as a result, provides more efficient tuning and repair of the scanning electron microscope.

The failure process of mortars during sulfate attack

External sulfate attacks on concrete structures may cause serious damage and it has attracted a wide range of attention from numerous researchers over the past decades. However, many studies have been concentrated on the sample which has been already destroyed. This paper investigated the entire deterioration process of mortars that were immersed in Na2SO4 solution containing 3 gSO4 2-/L and 33.8g SO4 2-/l at 20 o C up to 600 days. The study on time-varying regularity of expansion, cracks, compressive strength and mineral phases was investigated. Back scattered electron image was used to further examine the evolution of microstructures of the mortars during the attack process. The results showed that damage process of mortars can be described as induction stage, surface damage, bulk damage and then completely damage stage. Fine ettringites that were formed in restricted spaces, approximately 2-5 μm, result in surface damage. At the bulk damage stage, cracking was the main characteristic of mortar which leads to obvious expansion. In this stage, some large ettringite crystals (>20μm) were just deposited in the formed cracks. At the later stage, gypsum can be easily formed at interfacial transition zones as the consumption of calcium hydroxide, which mainly contributed to completely strength failure rather than expansion.