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Title: An Auger electron spectroscopic study of surface segregation on Fe-Cr, Fe-C and Fe-Cr-C alloys
Author: Jones, Keith Roger
ISNI:       0000 0001 3592 4332
Awarding Body: University of Warwick
Current Institution: University of Warwick
Date of Award: 1982
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This thesis reports an Auger Electron Spectroscopic study of the surface behaviour of a high-carbon-chrome (HCC) steel, and of its pure binary and ternary analogues, with particular reference to the kinetics of surface segregation. In all, four pure alloys were studied: iron - 0.65wt% carbon, iron - 0.8?wt% carton, iron - 1.50wt% chromium and iron - 1.46wt% chromium - 0.91wt% carbon. The temperature range of the experiments was limited at its lower end to 550°C by the slow rate of segregation, and at its upper end to 850°C by evaporation of the segregation from the surface. Two types of surface behaviour were observed on the pure alloys: segregation and precipitation. The discussion considers each in turn, followed by a consideration of the results from the commercial HCC alloy. Surface segregation occurred on all the alloys studied) surface precipitation was restricted to the plain-carbon alloys. Sulphur was the dominant segregation on the pure alloys, but segregations of phosphorus, nitrogen, chromium and possibly carbon were also observed. On the plain-carbon alloys, segregation occurred in competition with graphite precipitation. An analysis of the sulphur segregation kinetics permitted the calculation of reasonable values of the lattice diffusion coefficient. Some previously unreported features of its segregation kinetics were explained in terms of interference by labile sulphide particles at or near the surface. The average sizes and spacing’s of these particles were estimated from the kinetic experiments. When sulphur was depleted at the surface, segregation of the other elements became important. A limited analysis of the phosphorus segregation kinetics permitted the calculation of reasonable values of the lattice diffusion coefficient. On the commercial HCC alloy, the presence of manganese was found to largely suppress sulphur segregation. Where segregation of sulphur did occur it was thought to be due to surface effects such as manganese evaporation. Phosphorus segregation was the most important feature on HCC. An Auger calibration for monolayer graphite upon iron was deduced from the precipitation results. With the aid of this calibration, the graphite growth processes were elucidated. The mechanism of graphite precipitation at a sulphur-covered surface was found to be different to the reported precipitation mechanism at a clean surface. It was found possible to measure the attenuation of Auger electrons in graphite, and the values obtained were in good agreement with a theoretical analysis.
Supervisor: Not available Sponsor: Engineering and Physical Sciences Research Council
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: QC Physics