Alloys in and near the ε single phase region found by Morral In the iron-aluminum-carbon system were prepared and their ferromagnetic and structural properties determined„ The ε phase has been described as chiefly Fe₃Al plus 15 atomic percent carbon with the possibility of varying the Fe:Al ratio from approximately 2 to 3.5. The face-centred cubic ε phase was found to be highly ordered with iron at the face centre positions, aluminum at the cube corners and carbon in the body-centred position. The lattice parameter varies with carbon content from 3.73 to 3.76 A°. Keeping the amount of carbon constant at 14.6 atomic percent the alloys with the Fe:Al ratio less than 3 have their saturation magnetization increasing with increasing iron by an amount corresponding to the estimated increase of 5.4 Bohr magnetons per iron atom. However, for values of the ratio greater than 3 the magnetization is decreased with increasing iron. The amount of this decrease is not certain but it is thought to be of the order of 8 Bohr magnetons per iron atom in excess of that required to give Fe:Al equal to 3. Increasing the carbon content with the Fe:Al ratio kept at 2.9 ± .1 also decreases the magnetization by an amount corresponding to an estimated 8.5 Bohr magnetons per carbon atom. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

A magnetic balance for the measurement of the saturation magnetization of alloys has been designed and built. The magnet develops a field strength of 21,000 oersteds in a gap approximately seven-eighths inch long and two inches in diameter, when consuming a power of 4.5 kilowatts. This field is sufficient to saturate solid metal samples of random shape. Specially shaped pole caps are used which produce a gradient in the direction of the axis of the gap which is constant to within two percent, within a volume cube three-sixteenths of an inch on edge. The ratio of saturation magnetizations of iron and nickel at room temperature agree closely with the accepted values. A new magnetic phase has been discovered in the manganese carbon system. It has been identified as ferromagnetic, but its composition and crystal structure remain unknown. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The investigation of ferromagnetic phases in the manganese indium, manganese antimony carbon and the manganese magnesium alloy systems was conducted mainly by means of x-ray diffraction methods and where ever permissible by metal1ographic examination. The manganese indium and the manganese antimony carbon alloys were prepared in the vacuum melting furnace in an argon atmosphere, while the manganese magnesium alloys were prepared by sinter-compact techniques. Heat treatments were carried out in tube furnaces in an argon atmosphere. Ferromagnetic phases were not found in either the manganese indium or the manganese magnesium systems. The presence of the compound Mn₃In in the manganese indium system was established. The compound has a gamma brass structure with a lattice parameter a₀ = 9.413 A°. In the manganese magnesium system only solid solutions of manganese and magnesium were found to exist. The manganese solid solution was not magnetic suggesting that the addition of magnesium atoms did not give the degree of separation of manganese atoms for favourable ferromagnetic conditions. It was concluded also that the manganese atoms in the compound Mn₃In were not sufficiently separated for favourable ferromagnetic conditions. The ferromagnetic phase found in the manganese antimony carbon alloys was attributed to the compound Mn₂Sb. This suggested that elements in Group Vb which are strongly electronegative to manganese and form stable binary compounds, do not tend to form ternary compounds containing carbon. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

Binary alloys of manganese and boron and ternary alloys of manganese and boron with aluminum, zinc, tin and indium were prepared. Their structures were determined from x-ray powder photographs, and their ferromagnetic properties were measured with a Sucksmith rinf balance, using a powerful electromagnet. The orthorhombic phase MnB had a ferromagnetic Bohr magneton number of 1.73 per molecule and a Curie point of 309°C. Most of the ternary alloys were slightly ferromagnetic, but no strongly ferromagnetic single phase regions were found. Paramagnetic measurements on Heusler alloys showed that they followed the Curie-Weiss law for the restricted range of temperature in which measurements could be made. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

Oriented single crystals of niobium and dilute alloys with molybdenum and tantalum were deformed in tension between 77°K and 500°K, and the macroflow and slip parameters established. At high temperatures the main effect of alloying was to increase the flow stress, considerably more with molybdenum than with tantalum. The observed yield drop and subsequent plastic flow were explained in terms of a stability theory relating changes in yield and work hardening parameters with temperature and addition of solute. A technique was developed for measuring small plastic strains in the microflow region, and for recording the dynamic transition to macroflow. From studies on pure niobium between 77°K and 295°K, the nature of dislocation motion at small strains was established; microflow was explained in terms of a transition from edge dislocation motion to screw dislocation motion at the macroflow stress. Interstitial effects were found to be particularly significant during microflow, and are probably important in determining the low temperature flow stress in: even the highest purity bcc metals. A further low temperature contribution comes from a directional component of the internal stress field which depends on the distribution of dislocations rather than on their density. Microflow curves were obtained for niobium alloy crystals, land the interaction of dislocations with substitutional solute atoms established. In contradiction to previous suggestions, substitutional solute was found to restrict the mobility rather than the multiplication of dislocations. The elastic contribution of solute atoms to the internal stress field was confirmed, although a quantitative theory for bcc alloys does not yet exist. Peierls stress considerations alone were found to be incapable of explaining either the temperature sensitivity of flow or the low temperature solution softening; the short range interaction of interstitials with the dislocation core was considered to be more significant. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

Pure Nickel, 80% Ni-20% Cr, 98% Ni-2% ThO₂ and 78% Ni-20% Cr-2% ThO₂ have been studied to compare the mechanisms of dispersion strengthening in the latter two materials. All four materials were subjected to a wide range of thermo-mechanical treatments including cold rolling reductions up to 90% and annealing treatments which in the case of the materials containing ThO₂ were at temperatures up to 0.97Tm (1400°C). In each condition the materials were examined by an x-ray line profile technique to determine the distribution of non-uniform lattice strain, the coherent crystallite domain size and the twin and stacking fault probabilities. The x-ray data were also interpreted in terms of dislocation configurations. Supporting transmission electron microscopy was carried out on each material. Tensile tests were done at room temperature and at an elevated temperature on all materials to determine the strength properties and initial work hardening rate. It was concluded that the room temperature strength and the high temperature strength of all materials were determined by the presence of a fine domain or cell size and that the high temperature strength was also determined by the degree of polygonization of the fine substructure boundaries. In the case of the dispersion strengthened alloys the substructure boundaries were stabilized by the presence of ThO₂. It was observed that the Ni-Cr-ThO₂ material developed a different lattice strain distribution during cold rolling than did the Ni-ThO₂. This was characterized by a very small domain size and a high level of lattice strain averaged over short distances. It is proposed that this strain distribution favours recrystallization and grain growth and leads to the inferior structural stability in cold rolled Ni-Cr-Th0₂ at elevated temperatures compared to Ni-ThO₂. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

The effect of Li additions to Mg on the texture and mechanical properties in both the hot and cold rolled condition has been examined. It was found that using the texture goniometer (Schulz technique) only the surface texture is obtained. As a result average textures were prepared for each alloy. Lithium additions to Mg causes a loss in sharpness of the (0001) texture. No indication of a <1120> directional texture was found. The change in texture was explained successfully on the basis of deformation systems active during rolling. Cold rolling of the alloys caused a loss in sharpness of the (0001) texture for low Li alloys. In the high Li alloys (6 at. % and 12.4 at. %) a pronounced split occurred. A definite <1120> directional texture was observed on the surface of the cold-rolled low Li alloys but this disappeared in the "average" pole figure. Again the change in texture was explained on the basis of deformation systems active during rolling. Tensile tests of hot-rolled Mg-Li alloys agreed completely with those of Yoshinaga & Horiuchi (9) but showed some variance with those of Hauser, Landon, and Dorn (8). Tensile tests of cold-rolled Mg-Li alloys showed appreciable strain hardening and a loss of ductility due to the cold work. The higher the Li content the higher the rate of strain hardening observed for large increments of strain. The ratio of the transverse to longitudinal tensile properties decreased with increasing Li content. A qualitative explanation of the above was made on the basis of active deformation systems. Limited success was obtained in attempts to correlate mechanical properties and texture in low Li alloys. No attempt was made for high Li alloys. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

The substructure of pure aluminum and over-aged Al-4Cu has been varied by mechanical and thermal treatments. The nature of this substructure and its resistance to annealing has been studied, together with the effect of the substructure on tensile strength at ambient and elevated temperatures. It has been found that in at least some respects the response of the strength of the over-aged Al-4Cu to mechanical and thermal processing is very comparable to that of oxide-dispersion-strengthened alloys such as S.A.P. and Ni-ThO₂. The over-aged Al-4Cu is strengthened appreciably by cold work. Much of this incremental room-temperature strengthening can be removed by annealing at relatively low temperatures; i.e. temperatures at which the strength of cold worked pure aluminum is not lowered. In common with oxide-dispersion hardened alloys, the yield strength of cold-worked Al-4Cu at elevated temperatures (300°C or 0.62 Tm) is actually improved by a static anneal at 300°C before testing. This benefit increases with increasing amounts of prior cold work. Similar studies have been carried out with an S.A.P. extruded alloy (10 wt. % A1₂O₃) and comparable results have been obtained. Pure aluminum, Al-4Cu and S.A.P. materials have been examined by X-ray line profile analysis to determine the distribution of nonuniform lattice strain and the coherently-diffracting crystallite domain size. The X-ray data have been interpreted in terms of dislocation densities and configurations, and compared with direct observations made by transmission electron microscopy. An attempt has been made to account semiquantitatively for the strength of the deformed and annealed materials at ordinary and elevated temperatures in terms of available strengthening mechanisms. The 0.2 pet yield strengths of simple aged Al-4Cu alloys (no substructure) was found to be consistent with the Orowan model of dispersion-strengthening both at R.T. and at 300°C. The room temperature yield strength (ϭ0.2) of cold worked and annealed pure aluminum and A1-4Cu alloys was related to the subgrain diameter [symbol omitted] by the Hall-Petch equation: °0 2 = ϭ₀ + kg⁻½ where and k are constants. In such cases it was not believed that there was a contribution to strength from the Orowan mechanism. Similarly the 20°C yield strength of the S.A.P. alloy was associated with the fine dislocation substructure produced by thermo-mechanical treatments. The high temperature yield strength of Al-4Cu and S.A.P. was related to the polygonized substructure produced by static annealing, which was much finer and more stable in the case of the oxide dispersion-strengthened alloy. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

A study has been made of super-elasticity and the strain-memory effect in Cu-Al-Ni alloys in the composition range 14 wt. % Al and 2 to 6 wt. % Ni. These alloys have a bcc structure on quenching and show a low temperature transformation to a body-centered orthorhombic martensitic structure. It is this transformation that is responsible for the super-elastic and strain-memory effects. Tests on both single and polycrystalline specimens showed that the maximum super-elasticity occurred close to As. At higher temperatures the effect gradually decreased, whilst at lower temperatures it decreased very quickly. The magnitude of the effect was large in single crystal specimens (> 6%), but small in polycrystal specimens (< 1.5%). The super-elastic effect was caused by stress-induced martensite (SIM). Two types of SIM were observed: thin plates of thermoelastic martensite which was always reversible, and wide plates of burst-type martensite. This burst-type martensite was responsible for the major portion of SIM, and whether it was reversible or not on removal of the stress controlled the amount of super-elasticity observed. The strain-memory effect occurred on deformation either in the martensitic state (temperature <Mf) or in the temperature range where the martensite once formed was stable (temperatures close to Ms). Deformation caused reorientation of the martensite plates and when the specimen was heated, the martensite disappeared and the specimen reverted back to its original shape. This effect was explained on the basis of development of martensite plates of favorable orientation on stressing. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

A qualitative investigation of interdendritic liquid flow was carried out on pre-cast Pb-20Sn ingots at temperatures where the casting was partially liquid. The liquid flow was found to be preferential in nature, and strongly dependent on surface tension effects. Castings of Cu-8Ag and Al-30Ag were made in which the chill was removed during solidification to cause exudation of solute rich liquid. Nacrosegregation was detected using radioactive tracer elements. The castings were characterized by a solute enriched exuded zone and a solute depleted region adjacent to the chill. Models based on the simple back-flow of residual liquid to feed exudation were developed to explain the composition profiles adjacent to the chill. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate