Papers by Keyword: Submicrocrystalline Materials

Abstract: The structure of submicrocrystalline Mo, obtained by high pressure torsion, its thermal stability and the state of grain boundaries have been studied by transmission electron microscopy and emission Mössbauer spectroscopy.

Abstract: Light weight nano/submicrocrystalline materials are promising group of constructional materials combining low density with high mechanical properties. However, their potential application requires extensive testing of functional properties, e.g. tribological ones, which may be significant and determine their practical use. Available information on abrasive wear and friction coefficients in nano/submicrocrystalline materials is rather poor. Therefore the aim of this paper is to fill the gap in the literature in this field. The AlSi12Fe5Cu3Mg alloy (RS422) produced by rapid solidification and plastic consolidation with grain size of basic phase components in the range from 50 nm to 300 nm was examined. Microstructure and mechanical properties of the materials were determined. Abrasive wear tests, static and kinematics friction coefficients measurement were carried out under the surface condition including dry, wet and oil lubricant. The results have been compared to the values of similar quantities determined in the same conditions for conventionally produced alloy AlSi11FeCuMn (AK11). Substantial increase of friction coefficients for RS442 comparing to AlSi11FeCuMn material was found, however, abrasive wear for nano/submicron grained materials were low in comparison to conventional one. Considerable increase of abrasive wear at water presence and very weak attrition at oil lubrication was observed. Relationship between structure and mechanical properties of tested materials was analyzed.

Abstract: Ultrafine grained low carbon steel processed by high pressure torsion (HPT) has been investigated. Depending on initial state (ferritic-pearlitic state after normalization at 950°C, or martensitic ones after quenching from 950°C and 1180°C), the evolution of the microstructure and the mechanical properties was investigated after HPT and annealing at 400-600°C using transmission electron microscopy and X-ray analysis. It has been shown that HPT of martensitic low carbon steel provides a finer structure then that for ferritic-pearlitic initial state, and the initial martensitic morphology and phase composition is strongly dependent on the temperature of quenching. The initial structure was refined by HPT to 95nm in ferritic-pearlitic state and up to 65 and 50 nm in martensitic ones (after quenching from 950°C and 1180°C, respectively). Such ultrafine grained structures demonstrate substantial mechanical properties and possess a high thermal stability up to 500°C in all investigated states. Annealing for 1 h at 500°C results in grain growth up to 860nm for ferritic-pearlitic initial state and 150-450 nm for martensitic ones.

Abstract: The paper is devoted to the problem of thermal stability of ultra-fine grained (submicrocrystalline) materials prepared by severe plastic deformation. A basis of the paper lies in a fact that there is practically no grain growth in submicrocrystalline materials when annealing temperature is less than 0.35Tm. Reasons of high thermal stability of submicrocrystalline materials at low temperatures are widely discussed in literature. One of them is the affect of triple junction drag on grain boundaries motion. During annealing at a low temperature triple junction drag controls microstructure evolution in submicrocrystalline materials, and this phenomenon can be used to improve their thermal stability at high temperatures. The aim of this paper is to investigate grain growth kinetics in a two-step regime, low temperature and high temperature annealing. The experiments on grain growth were performed in submicrocrystalline Armco-iron fabricated by high pressure torsion. It is established that long-time low temperature pre-annealing reduces the grain growth rate in following high temperature annealing by a factor greater than two.