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The changes of thermal stability (crystallization temperature) and microstructure during annealing of amorphous Al-Ni-Ce-X(Cu, Zr) alloy ribbons have been studied by a combination of differential scanning calorimetry, transmission electron microscopy and X-ray diffractometry. In the case of Al_(88)Ni_8Ce₂Cu₂, 1st crystallization temperature decreased about 17℃ and 2nd crystallization temperature decreased about 22℃ compared to Al_(88)Ni_(10)Ce₂, Al particles were refined from 10 ㎚ to 5 ㎚. These changes are presumably due to an impairment of the amorphous formative ability by a decrease of constituent elements in the remaining amorphous phase resulting from the addition to Cu which is soluble in Al phase. In the case of Al_(88)Ni_(7.5)Ce₂Zr_(2.5), crystallization temperatures increased respectively about 9℃ and 17℃ and Al particle size was hardly changed. This improvement of thermal stability is presumably due to the suppress of crystallization by the addition of Zr which atomic radius is about 10% larger than that of Al and is nearly insoluble in Al and has low diffusivity. Consequently, Cu is concluded to be an effective element to refine Al particle and Zr is concluded to be an effective element to improve thermal stability. When Cu and Zr were added simultaneously in Al-Ni-Ce alloying system, in the case of Al_(87)Ni_8Ce₂Cu₂Zr₁, thermal stability increased and Al particle size decreased. In the case of Al_(85)Ni_8Ce₂Cu₂Zr₃, thermal stability and Al particle size is increased.

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Effect of Transtion Metal (TM = Ag, Ni, Zn), as a substitution for Cu, on the glass forming ability was examined in Mg_(65)Cu_(25-x)TM_xY_(10) (x = 0, 5, 10, 15, 20, 25) alloys by using thermal analysis and X-ray diffractometry. Partial substitution of Cu with less than 15 at% Ag and 5 at% Ni in Mg_(65)Cu_(25)Y_(10) alloy enhanced the glass-forming ability. Maximum diameter for single amorphous phase formation in Mg_(65)Cu_(15)Ag_(10)Y_(10) alloy by injection casting was 6 ㎜. Both amorphous alloys prepared by melt spinning and injection casting showed similar crystallization process during continuous heating in DSC. Also in this section as composition changes, co-relationship between variation of critical diameter for formation of an amorphous phase and that of parameters suggested to reflect glass-forming ability was examined.

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A new class of Co-base superalloy may be developed based on the ternary Co-Al-C system in which two phase alloys could be designed containing E2₁-type intermetallic compound Co₃AlC_x, known as κ-phase, being dispersed in the Co primary solid solution. Strength and ductility of the two phase alloys are evaluated at room to elevated temperatures. It is found that compressive 0.2% flow stress of the two phase alloys at room temperature seems to exhibit a maximum with 30 to 50% volume fraction of the intermetallic phase. Room temperature ductility of the two phase alloys is found to be 5 to 21% varying monotonously with increasing volume fraction of the intermetallic phase. At 1000℃, the 0.2% flow stress of the two phase alloys with κ-phase for more than 30% in volume are about 250 to 280 ㎫ under a strain rate of 1.4 ×10^(-4)s^(-1), which is comparable to that of commercial nickel base superalloy.

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The crystal structure of intermetallic compound Co₃AlC_x, κ-phase, is critically reinvestigated in the two phase alloys containing κ-phase in the Co primary solid solution matrix, α-Co, using conventional electron diffraction and convergent beam electron diffraction(CBED). Orientation relationship between κ-phase and α-Co and associated lattice misfit are also investigated. It is shown that the crystal structure of κ-phase is a derivative of E2₁ being a cubic structure composed of eight E2₁ sub-unit cells in half of which body center site is not occupied by carbon atom. Its space group is Fm3￣m and the chemical formula should be Co₃AlC_(0.5). Two types of anti-phase boundaries are predicted from the crystal structure of κ-phase and they are verified by experiment. Orient relationship between α-Co matrix and the κ-phase is found that three orthogonal axes of κ-phase are parallel to those of α-Co. Lattice misfit under this orientation relationship between the two phase is found to be about 2.5%.

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Using a method based on thickness extinction contour under week-beam condition in combination with g·b = 0 invisibility criterion the Burgers vector of slip dislocations of κ-phase in Co-Al-C system after deformation is determined. Results show that predominant slip dislocations are on {111} planes with a Burgers vector of $lt;110$gt; type. However, non-conservative $lt;110$gt; dislocations on the same {111} slip plane are also found. Dissociation of superlattice dislocations and further sub-dissociation of superpartials are observed. In α-Co alloy containing fine coherent κ-phase precipitates, deformation proceeds by cooperative movement of {a/6}$lt;211$gt; Schokley partial dislocations cutting through κ-phase particles, leaving behind a band of highly disordered region, which probably responsible for the low ductility of this alloy. The easy movement of dislocations in κ-phase and absence of localized deformation in α-Co matrix are believed to account for the relatively higher ductility of alloy consisting a large amount of κ-phase.

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IMI834 was developed to be used for the compressor parts of gas turbine engines. Compressor parts of gas turbine engine are subjected to cyclic and static loading simultaneously at high temperature and can be degraded by creep-fatigue interaction. The effects of microstructure and various superimposed hold times on high temperature low cycle fatigue behavior of IMI834, near-α titanium alloy, were investigated and the damage process under these conditions was also discussed. In both lamellar and bi-modal microstructures, it was found that fatigue lives for 10 to 30 min tensile hold were lower than those in continuous cycle fatigue due to additional creep resulting from stress relaxation during the tensile hold. This can be explained by the gradual change of the damage mechanism from fatigue dominant crack propagation to creep dominant grain boundary failure. It was also observed that in bi-modal structure of IMI834, low primary α volume fraction in the order of 10% leads to better creep-fatigue resistance at 600℃. Apparent activation energy for creep deformation of about 510-580 kJ/㏖ was obtained from the stress relaxation curve and was consistent with results of other near-α titanium alloys. This means that creep deformation during hold time must be controlled by a mechanism different from that in diffusion-controlled behavior.

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To assess the fatigue crack growth behavior of reactor pressure vessel at the nuclear reactor operating condition, the fatigue test was performed under water environments of high temperature and pressure. Test parameters were loading frequency, dissolved oxygen(DO) content and temperature. The results at low DO condition were similar to that in air environment. At high DO condition (8000 ppb), the crack growth rate was increased with the decrease of loading frequency. Fractographic study and surface analysis indicated that the enhancement of crack growth rate was due to environmentally assisted cracks near sulfur inclusions. For the case of 0.05 ㎐ test, crack path was the lath boundaries at low ΔK, while at high ΔK there was brittle facets around carbides. These features were coincident to hydrogen embrittlement. And it is understood crack growth rate depended on the quantities of absorbed hydrogen and also on the number of trapping sites at the plastic flow zone of crack. Especially, the dependence of crack growth rate on ΔK was particularly high in the case of 0.05 ㎐ condition, this may be enhanced by the dynamic strain aging which increases hydrogen trapping sites.

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The steady-static creep behavior of Cu-45Ni alloy has been investigated over the temperature range of 673-703K (0.43-0.44Tm) and the stress levels of 40-45 ㎏/㎟. Constant stress creep tests were carried out in the experiment. Measured stress exponents, n, of the alloy obtained during the creep deformation under the given conditions were 5.54, 5.28, 5.14, and 4.96 at the temperatures of 673, 683, 693 and 703K, respectively. The activation energy, Qc, was measured to be 44.93, 43.78, 43.31 and 42.74 ㎉/mole through the stress ranges of 40.0, 42.0, 43.5 and 45 ㎏/㎟, respectively. Lason-Miller parameter(P) determined from the crept specimen of Cu-45Ni solid solution alloy could be described as (T + 460)(21 + log t_r), where T is absolute temperature and t_r is fracture time. Empirically determined static creep rate was investigated. Cu-Ni system was classified as group II solid solution and dominated by intergranular type fracture with dimples.

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The present study was investigated the effect of rolling finishing temperature, slab reheating temperature and manufacturing process on the high temperature strength characteristic of 0.1%C-1%Mn 0.5%Mo steel containing Ti and B respectively. In the specimen containing Ti was obtained a little bainite in matrix of ferrite and pearlite phase, while, the specimen containing B was obtained boride and martensite phase. With increase of rolling finished temperature, in the A specimen containing Ti, bainite phase was increased and in the B specimen containing B, martensite lath was coarsened. In the two specimens treated by air cooling or quenching and tempering after rolling, with increasing of test temperature, yield strength and yield strength ratio decrease slowly, and rapidly decreased at over 600℃, but Y.S ratio at 600℃ appears higher value than 70%. In the B specimen, yield and tensile strength, Y.S ratio of specimens tempered after air cooling appears higher than quenching and tempered, but lower than air cooling specimens. With increase of rolling finished temperature, Y.S ratio of A and B specimens increased at RT and 600℃, but, when rolling finished temperature become over 900℃, Y.S and T.S of B specimens are decreased and A specimens are rapidely increased, while, with increased of slab reheating temperature, Y.S and T.S of A specimens was unchanged, but B specimens were decreased and Y.S ratio of A and B specimens increased. In the A specimen, Y.S ratio is strongly controlled by the volume fraction of secondary phase, but strength is affected by other factors except the volume fraction of secondary phase.

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In authors` previous study using the synthetic HAZ specimens, it was found that, like other structural steels, there were local brittle zones (LBZs) in the weld heat-affected zones (HAZs) of QLT (quenching, lamellarizing and tempering) - treated 9% Ni steels which are used for inner walls of domestic LNG (liquefied natural gas) storage tanks. In the continuing line of research, this study was performed to evaluate the influence of the LBZs on the brittle fracture resistance of the actual weldment of the steel. Crack tip opening displacement (CTOD) tests and compact crack arrest (CCA) tests were conducted to measure the crack initiation toughness and the crack arrest toughness respectively, and the results from both tests were compared each other. The results indicated that unlike CTOD test which showed the toughness decrease as approaching to fusion line, the crack arrest toughness values of the regions near fusion line, i.e., the regions containing LBZs, were higher than those of the other regions. It was due to the fact that the arrest toughness was ruled by the large fraction of fine-grained HAZs surrounding LBZs instead of LBZs themselves. Conclusively, by the comparison of the brittle crack arrest toughness, K_a, with brittle crack initiation toughness, K_c, calculated from CTOD test results, it was suggested that the LBZ was not a main risk factor affecting the fracture mechanical safety of the actual 9% Ni steel weldments.

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