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Survey work has resolved certain reported anomalies in this system. In particular, TiNi was found to undergo two displacive phase transformations at temperatures near room temperature. Below 50°C the pseudo body-centered cubic compound undergoes a gradual distortion in an unusual second order phase transformation producing the "transition phase”, the existence of which is terminated by a typical martensitic burst transform nation at 20°C which produces the "martensitic phase”. The crystal structures of the parent phase and transformation products, and the transformation characteristics have been studied with X-ray and electron diffraction, electron microscopy, electrical resistance and density measurements. / Thesis / Master of Science (MS)

This thesis describes a study of the portion of the iron- manganese-sulphur constitution diagram important in steel solidification and ingot soaking (1300°C). Attempts were made to determine a ternary isotherm at 1300°G by microanalysis of samples comprising Mn and FeS contained in and equilibrated with iron pots. A levitation melting technique was used to equilibrate Fe-Mn sulphide and Fe at 1535°C· Diffusion couples between solid Fe - 3.16% Mn and liquid FeS wore reacted at l300°C, quenched and then microanalyzed to determine the stages by which manganese in the iron diffuses to the sulphide phase to produce the BMnS inclusions found in many stools. / Thesis / Master of Engineering (ME)

Thesis: Sc. D., Massachusetts Institute of Technology, Department of Metallurgy, 1945 / Vita. / Bibliography: leaves 134-140. / Sc. D. / Sc. D. Massachusetts Institute of Technology, Department of Metallurgy

<p>A thermodynamically self consistent phase diagram together with T₀ line for iron-rich Fe-Mn system has been evaluated using the experimental tie-line information from this study and other sources and thermodynamic data from the literature.</p> <p>The competing morphologies resulting from the decomposition of Fe-Mn austenite due to variation in composition and cooling rate are equiaxed, ragged ferrite and lath morphology. The former two may result via a massive mode, whereas the last one may be due to a martensitic reaction. The massive mode of decomposition has been observed in the two phase field of this system.</p> <p>The solute drag theory for massive transformation due to Hillert and Sundman has been further developed for the low velocity branch. Our theory predicts a C-shaped TTT curve and an optimum in the rate of entropy production with respect to a structure parameter related to defect density.</p> <p>Isothermal transformation tests have yielded a C-shaped TTT curve for Fe-3.1%Mn alloy. The transformation behaviour has been explained as controlled by trace interstitial impurities (C and N) diffusion above the nose and by the massive mode at lower temperatures.</p> / Doctor of Philosophy (PhD)

<p>The phase equilibria in the Fe-C-Cr system, essential for the understanding of the pearlite reaction in low chromium steels, has been calculated from the thermodynamic data. The experimentally determined tie-lines are in good agreement with the calculated phase diagrams.</p> <p>The pearlite growth rates and interlamellar spacings in a series of low chromium Fe-C-Cr alloys have been experimentally determined. The growth rates in these alloys are explained in terms of chromium partitioning and chromium phase boundary diffusion control at low supersaturations and in terms of the local equilibrium no-partition mechanism and carbon volume diffusion control at high supersaturations.</p> <p>The relative effect of Cr, Mn, and Ni on the pearlite reaction is qualitatively discussed in terms of the above mechanisms, established for the chromium steels. The results have an application to the hardenability problem in steels.</p> / Doctor of Philosophy (PhD)

Master of Science (MSc)

Doctor of Philosophy (PhD)