The origin of thermal stability and crystallization process of Zr50Cu40Al10 metallic glass have been investigated by means of differential scanning calorimetry (DSC), x-ray diffraction (XRD) and resonant ultrasound spectroscopy (RUS) techniques, by comparing to Zr70Cu20Al10 and Zr70Cu30 glassy alloys. The thermal stability of Zr50Cu40Al10 is significantly higher than those of the others. The x-ray diffraction analysis indicates that constituent atoms in Zr50Cu40Al10 are closely packed in a glassy state. It was found from DSC that Zr50Cu40Al10 glass shows a complicated crystallization process when it is heated at usual heating rates, but when it is rapidly heated, the ordered B2-type ZrCu (equilibrium phase higher than 984K) is formed as a primary phase. This behavior is discussed in terms of the long-range-diffusion of atoms.
Elastic constants Cij of Pd40Ni40P20 and Zr55Al10Ni5Cu30 bulk metallic glasses (BMGs) has been investigated by MHz frequency range electromagnetic acoustic resonance (EMAR) from ambient temperature to their glass transition point Tg. With increasing in temperature the BMGs show elastically plateau region in Cij(T) curves which is due to two competitive processes; elastic softening by anharmonicity and stiffening by structural relaxation. Significant elastic softening in Cij(T) curves was confirmed around Tg without any precursor phenomena. Our theoretical analysis revealed that elastic inhomogeneity can explain the characteristic elastic behaviors around Tg.
Change in microstructure and mechanical properties by friction stir processing (FSP) is investigated in Zr-Cu-Al-Ni bulk metallic glass. The microstructure exhibits an amorphous band-like structure with widths of 10∼45nm and nanoscale crystalline particles of 5∼20nm. The contrast in amorphous band-like structure arises as the result of the difference of the thickness, which should be introduced by the difference of the density. The hardness increases by FSP. In compression tests, the increment of stress with strain decreases by FSP. Since the increment of hardness by FSP is larger than that by crystallization by annealing and the density seems to be different in amorphous band-like structure, the change in mechanical properties must be originated from the change in local structure such as free volume by FSP.
Crack propagation tests on a bulk metallic glass, Zr55Cu30Ni5Al10, were conducted either in aqueous sodium chloride (NaCl) solutions or high purity water under sinusoidal cyclic loading or sustained loading. Although the crack growth rate in high purity water was almost identical to that in air, the rate in NaCl solution was much higher than that in air even in a very low concentration of NaCl such as 0.01%. In 3.5% NaCl solution, the time-based crack propagation rate during cyclic loading, da/dt, was determined by the maximum stress intensity factor, Kmax, but was almost independent of the loading frequency and the stress ratio, and the rate was close to that of environment-assisted cracking under a sustained load.
Intermediate temperature embrittlement and its restraint were studied about Ni-Cu-Al alloy ingot for single layer warm damper of superconducting generator. Cracking of Ni-Cu-Al alloy ingot occurred when the ingot was given homogenization heat treatment. It is supposed that the cracking has close relationship to intermediate temperature embrittlement of the Ni-Cu-Al alloy ingot. It was found that increase of Cu, Al, Ti or C promotes the intermediate temperature embrittlement and reduces elongation at 625°C in Ni-Cu-Al alloy ingot. However addition of Zr or B restrains the intermediate temperature embrittlement and increases elongation at 625°C in Ni-Cu-Al alloy ingot. Electro-slag remelted ingot of Ni-12.2%Cu-4.15%Al-0.36%Ti-0.15%C alloy which is added 0.039%Zr weighed 21 tons and it was given homogenization heat treatment, however cracking of the ingot did not occur.
In this study, EBSP (electron backscatter diffraction pattern) method was applied to evaluate changes in misorientation during creep deformation. The tested material was a solid solution strengthened Ni base superalloy, Hastelloy X, and creep tests were conducted at 1123K under the stress of 49MPa. It was confirmed that Kernel Average Misorientation (KAM), which indicates the degree of misorientation in grains, increased with creep on the later period of creep life. And KAM showed a good correlation with creep strain at the strain of larger than about 5%. Analyses of grain size dependence showed smaller grains had larger KAM than larger grains. As the investigation of crystal orientation dependence, KAM changes in grains with <001>, <011> and <111> toward the stress axis were analyzed and compared. The starting point of increase of KAM in <001> grains was the latest among the three directions. KAM was thought to be an effective parameter for the evaluation of local damages on high temperature components such as turbine blades and pressure tubes.
Extruded magnesium alloy shows a mechanical anisotropy caused by the particular deformation characteristics of the hexagonal crystal structure. Cyclic deformation behavior and fatigue life of the extruded AZ61 and AZ80 alloys were investigated in the total strain controlled low-cycle fatigue test in ambient atmosphere at room temperature. The low-cycle fatigue lifetime of the two alloys extruded was almost same, but AZ80 alloy treated by an artificial aging after the extrusion had shorter lifetime compared with the extruded alloy, even though higher static mechanical properties with the aging. The hysteresis loop in experiments showed asymmetric behavior in tension and in compression and differed from the hysteresis of steels et al. The particular shape of the hysteresis was caused by the difference of the yield stress between tension and compression, and pseudoelastic behavior during reloading in the opposite direction, which tends to be more pronounced in compression than in tension. The pseudoelastic strain of the aged specimen was smaller than that of the extruded specimen. It was suggested that the asymmetric phenomenon was revealed by the reversal of twins upon unloading and the fatigue fracture was affected by the formation of the twin.
Physical parameters of wurtzite Zn1-xMgxO (0 ≤ x ≤ 1) were analyzed using first-principles calculations. A plane-wave pseudopotential method was employed to a density functional theory, then the effect of Mg incorporation on its lattice parameters and spontaneous polarization in the c-axis direction was studied as a function of the Mg content x. Calculations showed only a little difference in the bond length while a considerable change in the bond angle by the replacement of the Zn atoms in Zn1-xMgxO with Mg atoms. Due to the atomic replacement, a linear decrease and increase with increasing x were brought about the c-axis and a-axis lengths, respectively, deducing an increase of the spontaneous polarization in the –c-axis direction. Cohesive energies of wurtzite and rocksalt Zn1-xMgxO were also calculated to compare the structural stability, and the former structure was shown to be more stable till the Mg content at around x = 0.5.
The thermal degradation and the combustion tests of epoxy resins (prepolymer) whose molecular weights are from 1,650 to 50,000 have been conducted. From the result of the vertical firing experiments of epoxy resins with different molecular weight, it was found that there is a molecular weight region where combustion do not continued because volatile gas components are hardly generated by burning. In the thermo-gravimetric analyses, it was observed that the degradation behaviors did not change for the difference of the molecular weight. In the relation between the molecular weight and combustibility, it was observed that the molecular weight distribution did not change in the samples that did not burn. On the other hand, it was seen that molecular weight lowered in the burned sample. These results suggest that there is a possibility that the combustibility can be controlled by adjusting the molecular weight.
This paper describes a molecular-dynamics study on the relationship between lattice mismatch and adhesion strength of interfaces between organic materials and metals. Aromatic resins with benzene-ring connected structures are used as examples of organic materials. A lattice constant of the aromatic resins is defined as the distance between the second nearest neighbors of a benzene ring. The value of the lattice constant of a wholly aromatic polyester resin is about 0.24 nm. On the other hand, a lattice constant of face-centered-cubic structured metals is defined as the distance between the nearest neighbors. The lattice constants of copper and silver are about 0.255 nm and 0.29 nm, respectively. The adhesion of aromatic polyester resin with copper is stronger than that with silver because the lattice mismatch of the resin with copper is smaller than that with silver. Reducing the lattice mismatch is found to be effective in strengthening the adhesion.