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The characteristics of fatigue crack propagation behavior under constant cyclic load and cyclic load including tensile overload have been compared in the thermomechanically treated Al 7039 alloy and the peak aged. Crack closure mechanism owing to surface roughness is found to be related with the higher fatigue resistance in the peak aged condition under constant load. During overload crack branching, in addition to residual stress induced crack closure, was observed to be an another important mechanism for the retardation of fatigue crack growth rate following overload. More significant crack branching observed in thermomechanically treated condition is intimately related with the higher retardation of fatigue crack growth. The primary mechanism of fatigue crack growth retardation due to overload varies with the loading condition and microstructures. Consecuently the retardation of fatigue crack growth becomes more obvious in lower stress intensity factor range and higher overload ratio.

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The effect of heat treatment on the surface precipitation of trace impurities and on the subsequent oxidation of an Invar alloy was investigated. An Fe-36% Ni Invar alloy with Mn, Cr, Si, S and C as impurities was heat-treated at 1100˚C in vacuum as well as in 60% N₂＋ 40% H₂gas. Surface analysis with AES, SEM and EPMA has revealed that BN compound and nonmetallic elements such as S, C and O precipitated on the surface of the Invar alloy after a heat treatment in vacuum, while metallic impurities like Mn, Al and Si precipitated as oxide particles especially along grain boundaries after a heat treatment in 60% N₂＋ 40% H₂gas. And it was found that the oxidation occured preferentially near the precipitated nonmetallic and metallic oxide particles. The oxide layers formed on vacuum heat-treated alloys showed the best adherence, while the oxide layers formed without any prior heat treatment spalled on the outer-inner oxide interface.

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Using the method of crystallite orientation distribution functions analysis, the main components of the transformation textures in the controlled rolled high strength 3.4Ni-1.5Cr-0.4Mo steel were studied. The transformation textures of Ni-Cr-Mo steel were compared with the experimentally determined transformation textures of austenitic Fe-27Ni-0.28C steel similarly processed and the deformation textures of the parent phase prior austenite were deduced from the deformation textures of the austenite in Fe-Ni-C steel. It has been found that the main omentations of transformation textures in Ni-Cr-Mo steel finish rolled below the dynamic recrystallized temperature of the austenite are {332} and a fibre texture running from {112} to {111} with a maximum at {223} and those rolled at the dynamic recrystallized temperature are {032} and {331}. Comparison with the transformation textures in Ni-Cr-Mo and Fe-Ni-C steel showed that the deformation texture for prior elongated austenite in Ni-Cr-Mo steel could be expressed as a {110} texture with components {123} and {112}.

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The Al₂O₃/STS304, Al₂O₃/Cu and Al₂O₃/Al₂O₃joints were vacuum-brazed with three types of Cu-Ag-Ti brazing alloy at 1193 K for 1.2 ks. The microstructure and microchemistry of reaction products formed at the Al₂O₃/braze alloy interface have been investigated by glancing x-ray diffractometer (G-XRD) and scanning electron microscope(SEM) equipped with energy-dispersive spectrometer (EDS). The reaction products of Al₂O₃/STS304 joint were a layered structure consisted of TiO (Monoclinic, ao=5.85Å, bo=9.34Å, co=4.14Å, Cu₂Ti₄O (Cubic, ao=11.49Å and Fe₂Ti₄O (Cubic, ao=11.297Å). For the Al₂O₃/Cu and Al₂O₃/Al₂O₃joints, reaction products were a layered structure consisted of TiO and Cu₂Ti₄O. For the Al₂O₃/STS304, Al₂O₃/Cu joints, the thickness of reaction product layer was in creased with Sn-addition and rapidly decreased with Al addition in Cu-Ag-Ti alloy. Type of reaction products was not varied with additional elements. The formation of TiO compound resulted from redox reaction between Al₂O₃and segregated Ti, but the Cu₂Ti₄O and Fe₂Ti₄O compounds was formed by solid-state reaction between TiO and Cu/Fe of brazing alloy and adhered metal respectively. The Cu₂Ti₄O and Fe₂Ti₄O compounds can be considered as (Cu, Fe)₂Ti₄O, because both of compounds have the nearly same crystal structure and lattice constant. That is, that compound seems to be formed as a result of the rearrangement of structure from monoclinic to cubic after the Cu and Fe atoms is diffused into the ordered vacant sites of pre-fomed titanium monoxide(TiO_(1±X), x=0.1). The formation of that compound means that the Cu and Fe atoms into TiO have the faster diffusion velocity than the other elements such as Ag, Al, Sn, Ni and Cr. Conclusively the thickness of reaction product layer depends on the diffusion velocity of metallic elements into the TiO layer and the additional elements in Cu-Ag-Ti brazing alloy effectuate the variation of that diffusion velocity.

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The effects of P/M processing methods on the mechanical properties of Ni₃Al-0.5 B intermetallic compound were studied. The major gases evolved during the degassing were water vapor and hydrogen. The density of experimental alloy was improved by hot isostatic pressing (HIP) following either reactive sintering (RS) or vacuum hot pressing (VHP); a full density was obtained by hot extruding (HE) elemental powder compacts. The ambient tensile yield strength, 840 MPa and elongation, 41% of hot extruded experimental alloys with 7㎛ grain sizes were superior to those of cast alloys found in the literature. However, the peak temperatures (T_P=400∼500℃) corresponding to the maximum yield strength of experimental alloys were lower than those (T_P=600℃ ) of cast alloys. The tensile characteristics of the experimental alloys were explained in terms of grain refinement, formation of γ＋γ` duplex structure and a distribution of oxides.

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As the magnetic properties of the Fe_(73.5)Si_(13.5)B_9Cu₁Nb₃alloy depend on the microstructure of the alloy, annealing condition - annealing temperature and annealing time - affects the magnetic properties of the alloy. The aim of this study is to investigate the effect of annealing condition on the magnetic properties of the Fe_(73.5)Si_(13.5)B_9Cu₁Nb₃alloy, and find the fittest annealing condition. For this investigation, annealing experiments have been performed in two ways. Firstly, Fe_(73.5)Si_(13.5)B_9Cu₁Nb₃amorphous alloy ribbons have been annealed isochronally at various temperatures for 1hr. Secondly, they have been annealed isothermally at 500, 560, 580, 600℃ respectively. The magnetic permeability(μ) was measured for each ribbon, and the microstructure was investigated using Transmission Electron Microscopy(T.E.M.).

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Precipitation process, microstructural and hardness changes in 2090 and Cl alloy were investigated by optical observation, hardness test, transmission electron microscopy and STEM energy dispersive X-ray spectra mode. Hardness in Cl alloy was remarkably higher than that of an 2090 alloy. As result of TEM observation, δ`, α`, θ`/δ`, β`/δ` and T₁phases were precipitated on aging conditions in 2090 alloy, but GP zone, β`, θ`, S`, T and T₁phases were formed on aging conditions in the Cl alloy. And, θ` and T₁phases in the Cl alloy were finer than thoes of an 2090 alloy. This fine precipitates contributed to the increase in hardness. The precipitation process in Cl alloy was as follows: α`_(sss)＋β`→α`_(sss)＋β`＋GP zone→α``_(sss)＋β`＋θ`→α```_(sss)＋β`＋θ＋T₁＋S`＋T

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This study was perfomed as fundamental studies on the solid state sintering. The ordinary process of Rene 95 forming is canning of powders followed by HIPP`ing. In this study, the effects of pre -heat treatment, at 1150℃ for 30min after canning of powders, on the microstructure of the HIPP`ed Rene 95 were studied as compared with the ordinary HIPP`ing. The prior particle boundaries(PPB`s) are well known to impair significantly the mechanical properties at service conditions. The PPB`s are observed after 60 min ordinary HIPP`ing at 1150℃, 100MPa, In case of pre-heat treated powders the PPB`s couldn`t be found after 5 min HIPP`ing. The PPB`s were appeared to be related to the precipitation of γ` phase in Rene 95. The pre-heat treatment of powders also assist the recrystallization during HIPP`ing. The grain size variations during HIPP`ing were caused by nuclation of recrystallization, grain growth and subsequent recrystallization(dynamic recrystallization). The microstructure of 30 min HIPP`ed sample of pre-heat treated powders was comparable with the sample HIPP`ed by ordinary process for 180 min at the same condition.

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A thermodynamic evaluation of the Fe-Cr-Ni system has been made by using thermodynamic models for the gibbs energy of individual phases. An optimized set of thermodynamic parameters was obtained taking into consideration relevant experimental information. The thermodynamic parameters of the Fe-Cr-Ni systems and comparisons between calculation and experimental data are presented.

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The grain size dependence on mechanical properties of Ni₃Al-0.5 B alloys hot extruded from elemental powders was studied. Yield strength of the Ni₃Al-0.5 B decreased with increasing grain size produced by annealing at 1000℃, but weakened at higher temperatures. The reduced grain size also diminished the extent of anomalous yielding. For the range of grain size from 6 to 103㎛, the yield strength of the alloys was given by the Hall-Petch relationship, σ_y=σ_o＋ k_y·d^(-1), where n = 0.85±0.05, σ_o=420±8 MPa and k_y=2041±168 MPa·㎛^(0.85±0.05). The deviation of the relationship from n=-0.5 was explained in terms of work hardening within Lu¨ders bands and oxide dispersion hardening. Tensile elongation of the test specimens showed insignificant variation for small grain sizes but decreased moderately for the grain size larger than about 70㎛. Regardless of the grain size, all the test specimens showed predominantly ductile transgranular fracture at room temperature.

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