In-phase (IP) and out-of-phase (OP) thermo-mechanical fatigue (TMF) experiments were undertaken on 6061 aluminum alloy reinforced with 15% volume fraction whiskers. Both TMF tests were conducted under mechanical strain range control with temperature cycling between 150∼300°C. The mechanical behavior and fatigue resistance of both TMF fatigue was investigated and discussed. The result shows that the two kinds of TMF cycling exhibited continuous cyclic softening, out-of-phase TMF loading gave rise to tensile mean stress, whereas in-phase TMF cycling led to compressive mean stress. It is also illustrated that at small strain range, the in-phase TMF life was longer than that of the out-of-phase TMF; on the contrary, out-of-phase TMF showed longer life at large strain range. This is tentatively explained by the various damage mechanisms with the help of SEM, which were predominantly operative under different strain ranges and different phasing conditions.

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This work investigates the characteristics of vibration fatigue under a resonant state for different aging conditions, and the microstructural variation of Pb–Sn solder alloys. The major experimental parameters include natural aging time and Pb–Sn composition. Examination of crack initiation and major crack formation behavior during a resonant vibration test shows that cracks initiated at different sites of the Sn–Pb and Sn–Sn phase boundary on the specimen’s surface, and that some cracks then linked up with each other to form a major crack that grew into the specimen. It is worth noticing that a stratum-type deformation occurred in the Pb-rich phase during the vibration deformation process because of the high frequency fatigue deformation of Pb–Sn eutectic alloys. In addition, coarsening was found to develop with natural aging time, and a decrease in deflection amplitude occurred during vibration tests. The investigation used heat treatment to provide further insight into the coarsening effect on the resonant fracture resistance of Pb–Sn alloys. In addition, as greater Sn content increased the fraction of the Sn-rich phase, it definitely improved vibration fracture resistance.

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The annealing textures were analyzed by means of an ODF software in an Fe–27Mn–6Si–5Cr alloy wire annealed at various temperatures from 873∼1223 K. At the same time, the shape-recoverable degrees of the wire specimens were measured by tensile strain at room temperature followed by recovery heating. A nearly unique ⟨001⟩ texture appears in the wire specimen annealed at 973 K, in which the highest shape recovery ratio is obtained. A synthesis orientation factor S has been definded as a parameter for estimating the tendency for polycrystalline materials to stress-induced martensitic transformation. The reason for the influence of texture on the shape memory effect is discussed.

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Various phase diagrams including an icosahedral (i-) phase in Al–Cu–Fe alloy system were examined in order to reveal the composition of the liquid in equilibrium with the Al₆₄Cu₂₃Fe₁₃ i-phase. The i-phase was formed through the peritectic reaction between the liquid and the primary λ₂-crystal. Prevention of the peritectic reaction was necessary to produce a single quasicrystal, however, there was a little compositional area of the molten alloy, which can crystallize the i-phase as a primary crystal. In the conventional solidification of Al₆₀Cu₃₇Fe₃ alloy, almost primary crystalline particles were classified as i-phase, and the rests were λ₂-phase. The λ₂-particles acted as the inhomogeneous crystallization sites of an i-quasicrystal growth. So, several metallurgical treatments were tried to prevent the λ₂-crystallization. Consequently, we found out an Al₅₉Cu₃₇Fe₃Si₁ molten alloy, which can crystallize the Al₆₄Cu₂₃Fe₁₃ i-phase as a primary crystal at 978 K. The Al₅₉Cu₃₇Fe₃Si₁ molten alloy should be treated the preliminary cyclic melting process to prevent the λ₂-crystallization. And we succeeded to grow up the large grained Al₆₄Cu₂₃Fe₁₃ i-quasicrystal directly from the molten alloy.

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The fatigue strength and the fatigue crack propagation of Zr₅₅Cu₃₀Al₁₀Ni₅ bulk glassy alloys were examined using fully glassy plate shape samples produced by metallic mold casting. Fatigue testing was done under a tensile-tensile stress condition with a stress ratio R(σ_max⁄σ_min)=0.5. As the results, we could confirm that the Wöhler curve is different from those of ordinary crystalline structural alloys in that the fatigue strength decrease significantly from N=10³ to 10⁴. Besides, the crack propagation rate of the samples were examined with macroscopic mechanical testing and microscopic fracture surface observation, and the both methods lead to the same result that the forced factor is about 2 with a power-law.

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A thermodynamic study of the Ti–O system at 1573 K has been conducted using a combination of thermogravimetric and emf techniques. The results indicate that the variation of oxygen potential with the nonstoichiometric parameter δ in stability domain of TiO_2−δ with rutile structure can be represented by the relation, Δμ_O2=−6RTlnδ−711970(±1600) J/mol. The corresponding relation between non-stoichiometric parameter δ and partial pressure of oxygen across the whole stability range of TiO_2−δ at 1573 K is δ ∝ P_O2^−1⁄6. It is therefore evident that the oxygen deficient behavior of nonstoichiometric TiO_2−δ is dominated by the presence of doubly charged oxygen vacancies and free electrons. The high-precision measurements enabled the resolution of oxygen potential steps corresponding to the different Magneli phases (Ti_nO_2n−1) up to n=15. Beyond this value of n, the oxygen potential steps were too small to be resolved. Based on composition of the Magneli phase in equilibrium with TiO_2−δ, the maximum value of n is estimated to be 28. The chemical potential of titanium was derived as a function of composition using the Gibbs-Duhem relation. Gibbs energies of formation of the Magneli phases were derived from the chemical potentials of oxygen and titanium. The values of −2441.8(±5.8) kJ/mol for Ti₄O₇ and −1775.4(±4.3) kJ/mol for Ti₃O₅ obtained in this study refine values of −2436.2(±26.1) kJ/mol and −1771.3(±6.9) kJ/mol, respectively, given in the JANAF thermochemical tables.

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Effects of cold rolling on the aging kinetics in an Al–Mg–Si alloy have been examined mainly by means of differential scanning calorimetry and transmission electron microscopy. The first exothermic reaction detected at temperatures around 350 K in the cold rolled specimen is probably due to the migration of quenched-in vacancies to the dislocations introduced by cold rolling and the molar heat for this reaction is decreased by cold rolling. The subsequent diffuse exothermic reaction may arise from the segregation of solute atoms to the dislocations, Cottrell’s atmospheres being formed. The needlelike precipitates formed in the non-recrystallized matrix of the cold-rolled specimens, and this reaction was displaced to lower temperature side by cold rolling. The molar heat and the activation energy for the needle formation did not vary with reduction, but the activation entropy increased.

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The thermal stability, crystallized structure and mag netic properties of rapidly solidified Fe–Co–Nd–B amorphous alloys with Dy addition have been investigated. The supercooled liquid region (ΔT_x) of an amorphous Fe_66.5Co₁₀Nd_3.5B₂₀ alloy increases from 40 to 45 K by the addition of 0.5 at%Dy. Both the amorphous alloys with and without Dy addition after optimum annealing are composed mainly of Fe₃B, Nd₂Fe₁₄B and α-(Fe, Co) phases. By the addition of the small amount of Dy, the coercivity (_iH_c) and maximum energy product (BH)_max are greatly enhanced, though the remanence (B_r) slightly decreases. The B_r, _iH_c and (BH)_max after optimum annealing are 1.27 T, 187 kA/m and 86 kJ/m³, respectively, for the Fe_66.5Co₁₀Nd_3.5B₂₀ alloy and 1.24 T, 263 kA/m and 92 kJ/m³, respectively, for the Fe_66.5Co_9.5Nd_3.5Dy_0.5B₂₀ alloy.

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Interface debonding and its effect on crack stability in a single-edge-notched PMMA/glass bi-material have been studied. Direct observation of crack growth behavior is carried out and crack tip stress intensity factor during crack growth process is obtained by a laser Caustics method. Interface stress distribution at the onset of interface debonding is obtained by FEA with experimentally obtained stress/strain conditions. The interface debonding ahead of a growing crack tip occurs before the crack reaches the interface. A transition from slow to rapid crack growth is predicted by the event of an interface debonding ahead of a growing crack tip. This debonding is caused by an interface tensile stress. The maximum interface tensile stress obtained by FEA with experimental boundary condition, σ_d, and the distance between the crack tip and interface at the onset of interface debonding, x₀, follows the relation, σ_d=A_d⁄\sqrtx₀. This relation provides the condition for the interface tensile debonding. The condition suggests that the interface tensile debonding has a probabilistic nature.

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The effects of Fe content on the microstructure (intermetallic compounds, available copper and strengthening precipitates) and mechanical properties of A206 alloy have been investigated. The network of CuAl₂ and needle-like (or platelet-like) Cu₂FeAl₇ compounds, which coexist in the α-Al inter-dendrites, characterize the typical solidification structures of A206 alloys. The volume fraction and number of Cu₂FeAl₇ needles, determined by image analysis, are proportional to the Fe content. The available copper and the supersaturated copper atoms in matrix in richer Fe alloys will decrease after the solution treatment. In DSC analysis, the smaller heat effect and the increase in peak temperature for precipitation θ′ phase suggest that the amount and kinetics of precipitation are lowered in higher Fe content alloys. The relation between the mechanical properties and microstructure has been examined quantitatively. The tensile strength and hardness are mainly dominated by the volume fraction of θ′ phase, and the elongation by the Cu₂FeAl₇ compound. All of these properties, especially the elongation, decrease when the Fe content increases because of reduced quantity of θ′ phase and increased amount of Cu₂FeAl₇ compounds. The tensile strength decreases linearly with increasing Fe content.

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The equilibrium between liquid III group metal and B₂O₃ flux was investigated thermodynamically as a fundamental study on impurity control in single crystal growth of III–V group compound semiconductors. The oxygen distribution ratio between gallium melt and B₂O₃ flux and the activity of Ga₂O₃ in B₂O₃ flux were clarified at 1373 and 1273 K by measuring oxygen contents in gallium melt and Ga₂O₃ contents in B₂O₃ flux. The standard free energies of formation of GaBO₃ and InBO₃ were determined by measuring oxygen content of liquid III group metal (gallium or indium) equilibrated with B₂O₃ flux and GaBO₃ or InBO₃:
ΔG_GaBO3°=−1.14×10⁶+251T (J) (T: 1123∼1173 K)
ΔG_InBO3°=−1.02×10⁶+220T (J) (T: 1223∼1373 K)

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Nb_ss/Nb₅Si₃ in-situ composites (Nb–16 mol%Si) for high-temperature structural applications were synthesized by reactive spark plasma sintering (RSPS), mechanically milled (MM) Nb–Si powders. Microstructures were characterized by OM, SEM, XRD and EPMA, and the mechanical properties of the composites were investigated by microhardness and compression tests. This consolidation process can produce the compacts of Nb_ss/Nb₅Si₃ in-situ composites having equiaxed grain microstructures and a nearly full density when RSPS is carried out above the melting point of silicon. The RSPS in-situ composites exhibit large compressive ductility at room temperature and considerably high strength at elevated temperatures.

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The stress distribution and strain energy have been calculated for two shapes of inclusions, i.e., an oblate spheroid and a hexagonal plate bearing identical uniform transformation strains associated with γ(fcc) → ε(hcp) martensitic transformation in a high Mn ferrous alloy. The stress distribution within the inclusion is constant for the spheroid but shows a maximum near the interface and decreases gradually with a distance from the interface for the hexagonal plate. The stress concentration behavior at the tip of the inclusion is different from each other for these two shapes. The influences of the plate thickness on the stress distribution and strain energy are computed and the results suggest that the hexagonal plate is more realistic in order to discuss the improvement of shape memory effect by alloying or training treatment.

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Sintering of elemental powders and conventional arc-melting were used to form ternary L1₂ intermetallic compounds in the Al–Ti–Fe system. The L1₂ phase field and phase equilibria surrounding the L1₂ phase in the temperature range of interest were established. Two isothermal sections at 1423 and 1273 K were determined from metallography, X-ray diffraction and electron probe microanalyses. The compositions of L1₂ phase field, the center compositions of oval-shaped region, were about 28Ti–8Fe–64Al and 27Ti–9Fe–64Al compositions at 1423 and 1273 K, respectively. Thus the L1₂ phases had less ternary and more titanium than those reported in the other Al–Ti–X (X=Mn, Cr) systems. Besides the L1₂ phase, the pertinent second phases were TiAl (L1₀-type), TiAl₂ (HfGa₂-type), Ti₂Al₅ (28 atoms/unit cell-type), Al₃Ti (D0₂₂-type), C14 (Laves phase, MgZn₂-type), and D8_a (cubic, Mn₂₃Th₆-type). The solubility of iron in TiAl₂ phase was about 2 and 3 mol% at 1423 and 1273 K, respectively. The TiAl₂ phase is more stable at 1273 K and can coexist with L1₂, TiAl, C14, and D8_a phases in separate phase fields. Thus in the isothermal section at 1273 K, no two-phase equilibrium between the TiAl and L1₂ phases exists. This impedes the development of bonding between TiAl and L1₂ alloys in coating applications.

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Aluminum ion implantation into near equi-atomic titanium-nickel (Ti–Ni) alloy was carried out to clarify the effect of the surface characteristics on the shape memory properties associated with cyclic deformation. Obvious changes in deformation behavior were observed in the ion implanted specimens. At a low implantation dose, the required stress was lower for R phase accommodation followed by martensite phase deformation compared with the non-implanted alloy. On the other hand, the stress-strain curves of the specimens associated with a high implantation dose revealed characteristics of a mixed structure consisting of the R phase, the martensite phase and the austenite phase. In the latter case, the shape memory properties degraded and almost disappeared after several cyclic deformations. Two factors were considered to explain these results. First, the residual stress field induced by implanted aluminum ions at the surface assisted the stress accommodation of both R phase and martensite phase. Second, there was a shift in transformation temperatures due to preferential sputtering of titanium atoms at the surface followed by a composition change. When the implantation dose was low, the first factor seemed to play a major role. When the implantation dose exceeded a critical value, the second factor was more important. Thus, we assumed that the mechanism involves deformation of the surface region which, in turn, triggers transmission of the deformation toward the interior of the specimen.

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