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An investigation has been carried out for the effects of Cu/Mg ratio of solute atom on precipitation behaviors in Al-3wt%(Cu＋Mg) alloy, by the observation of the transmission election microscopy and the detailed measurement of specific heat during ageing at 150˚and 200℃. The results obtained are summerized as follows. 1) The rate of formation and precipitation for the GPB zones and S` metastable phase is accelerated by the increasing of Cu/Mg solute atom ratio at the upper range of 1.0. From this result, it is considered that the Cu/Mg solute atom ratio of 1.0 for the GPB zones and S` metastable phase is almost the same as that for the specimen alloy which is in the dual phase regions of (α＋S). 2) θ` phase has been precipitated with S` phase in the alloy of solute atom ratio of Cu/Mg ≒ 2.4 and isomorphous T` phase has been also precipitated with S` phase in the alloy of solute atom ratio of Cu/Mg ≒ 0.2, after aged at 200℃. 3) The starting and finishing temperature for recovery of GPB zones in Al-3wt%(Cu＋Mg) alloy increased with decreasing of Cu/Mg solute atom ratio. This result means that the growth rate of GPB zones are accelerated by the increasing of Mg atoms.

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AISI 4140 Steel was austenitized in salt bath, oil quenched, then tempered to 650℃. Macroscopic residual stress and microscopic residual stress during repeated bending fatigue process of the steel were measured by shift of X-Ray diffraction Bragg Angle (2θ) of (211) plane; and broadening of integral breadth, respectively, using half value breadth method for the study on the possibility of fatigue life estimation of the steel. 1. Fatigue life estimation of the steel by measuring the variation of macroscopic residual stress during fatigue process is believed to be impossible. 2. Half value breadth ratio, B/Bo(B, Bo ; current, initial value of half value breadth, respectively.) of the steel during the fatigue process increased to a maximum point which is believed to be the fatigue initiation point, then began to decrease and decreased rapidly on the stage of fracture. Considering these facts, the useful life of AISI 4140 steel can be estimated roughly by X-Ray diffraction method.

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A study has been made of the mechanical properties of dual phase steels quenched from the austenite plus ferrite phase region to replace two kinds of initial structures (ferrite-pearlite and martensite) by ferrite-martensite structure. The distinct initial microstructures yielded different morphologies of martensite after annealing though the volume fraction of martensite remained almost the same. The volume fraction of martensite was varied from 15% to 80% by various annealing temperatures. The strength of dual phase steels was dependent on the volume fraction of martensite and independent of the morphology of martensite. However, the ductility of the dual phase steel having finer martensite particles resulted from 100% martensite initial structure was superior to that having coarser martensite particles resulted from ferrite-pearlite initial structure.

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Internal friction peaks associated with the presence of carbon in 18-8 type 304 stainless steel have been observed from measurements with a torsion pendulum. The temperature for maximum internal friction lies between 250℃ and 300℃ with a frequency of vibration. The height of the peak rises and the position of the peak shifts to a lower temperature with an increase of the carbon content. And a comparison of the activation energy and the diffusion coefficient determined by internal friction methods with those measured in conventional macro-diffusion experiments reveals that the diffusion data measured by internal friction method and the diffusion data measured by conventional method exist in the same line. It follows from the above fact that observed internal friction peak is associated with the stress-induced diffusion of carbon in face-centered cubic alloys.

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Fe-12% Mn alloy is chosen for this investigation due to its characteristic properties of high susceptibility of hydrogen embrittlement and of strain-induced phase transformation Specimens were heated at 1100℃ for 2 hours and either furnace cooled or water quenched. The results of the X-ray phase determination show that furnace cooled specimen (FC) is having ferrite phase (BCC) only while water quenched specimen (WQ) is observed to contain mostly unstable austenite phase (FCC). Hydrogen concentraton in the two specimens was same and linearly increased with charging time, however, above the concentration level of 15 ppm, WQ had more hydrogen than that of FC with same charging time. With same amount of hydrogen in the specimens, even though WQ showed strain-induced phase transformation, it was less embrittled by hydrogen than FC. When WQ had higher hydrogen concentration, the effect of hydrogen on the embrittlement was greater for WQ than for FC. Impact energy was also greatly reduced with hydrogen content for WQ while the impact property of FC was not influenced by hydrogen. All the experimental results strongly suggest that the phenomenon of hydrogen embrittlement of water quenched Fe-12% Mn alloy is associated with the strain-induced phase transformation along with the processes of the faster hydrogen diffusion in BCC and of forming moledular hydrogen gas pressure due to the excess hydrogen in the transformed BCC.

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The effect of melt temperatures on the thermal stability of amorphous Co_(75)B_(25) alloys was studied by DTA, tensile test, X-ray diffraction and electrical resistance measurement. The melt of Co_(75)B_(25) alloy were quenched from 1300, 1350, 1400 and 1500℃, respectively. The pre-existing crystallites were increased with increasing melt temperature. This can be explained by the increased superheating. The crystallization temperature of the first step reaction were increased as the melt temperature increase and the reaction of the first step is believed to be a peritectoid type reaction having the equation "amorphous +Co₂B- Co₃B". The transformation mechanism of Co_(75)B_(25) alloy can be explained by the diffusion controlled growth of discs of constant thickness. The apparent diffusion activation energy for amorphous Co_75B_25 alloy is found to be 59 ㎉/㏖for 1300℃, 61 ㎉/㏖ for 1350℃, 65 ㎉/㏖ for 1400℃, 72 ㎉/㏖ for 1500℃, respectively.

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