The wettability of Mg0 by liquid iron was studied using the sessile drop technique in vacuo at 1550°C. Specimens of vacuum-cast iron were melted on single crystals of optical-grade magnesium oxide. Tests were limited to two minutes because of iron volatilization. Chemical reaction at the liquid-vapor interface caused the contact angle to decrease from 117° to 65° during the first minute. Reaction between the iron and oxygen provided through the dissociation of Mg0 resulted in formation of an Fe0 layer over the drop surface. The Fe0 was drawn to the base of the drop where it accumulated as an annular Interfacial deposit. After solidification, the Fe0 decomposed to magnetite with separation of iron. Within the peripheral annulus the interface showed no sign of chemical attack. This effect was related to formation of a protective interfacial monolayer from electropositive impurities initially present in the iron. The major constituent of the monolayer appeared to be silicon although positive identification was not achieved. Chemical reaction occurred in each case where alloying additions to the iron of Ti, V, Cr, Nb, Ta, and Zr were made. Variation of contact angle with concentration was studied. Both V and Cr improved the wettability. The effect of Zr, Ti, Nb, and Ta on the wettability was not determined because oxide deposits around the basal periphery of the drops restricted expansion. Complete interfacial attack was observed with additions of Zr, Ti, and V whereas additions of Nb, Ta, and Cr resulted in an annular interfacial deposit around the drop perimeter similar to the pure Fe-Mg0 specimens. This phenomena supported the existence of an interfacial monolayer. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

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The morphology and crystallography of the martensite transformation in pure iron and low alloy Fe-C, Fe-Mn, Fe-Mn-Si, Fe-Ni steels which contain no retained austenite was studied. Single surface trace analyses by transmission electron microscopy on directions parallel and normal to the martensite substructure were found to be consistent with the martensite crystals having the form of plates rather than needles. The directions normal to the martensite substructure plates were consistent with a {145}M habit plane. Optical studies of the martensite surface shears within prior austenite grains revealed that 4 shear variants generally occur. However grains containing 5 or more shear variants could be found which appears to suggest an austenite habit plan close to but different from {111}A. A single surface trace analysis of the martensite surface shears using the austenite annealing twin vestiges to orient the grain was consistent with an austenite habit plant ~ 7° from {111}A. Two inhomogeneous shear systems were found to predict the experimental results when applied to the Wecheler, Lieberman, Read theory of martensite transformations. They are (100)A[010]A and (111)A[112]A. The (111)A[112]A system is to be generally preferred as its predicted habit planes ( 7.12° from {111}A and 5.03° from {145}M are more consistent with the trace analyses. Preliminary work included an investigation of the maraging properties of the Fe-Mn-Si system. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

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