A series of Fe-Cr alloy thin films having various Cr contents (11-34 mass%) and thicknesses (60-550 nm) were prepared by ion-beam-sputter (IBS) deposition. The structure of the films was examined by transmission electron microscopy (TEM), electron diffraction (ED), glancing angle incidence X-ray diffraction (GIXRD), and atomic force microscopy (AFM). The anodic polarization curves of IBS-Fe-Cr alloy films were measured in 1 kmol·m−3 Na2SO4(pH 3.0), 1 kmol·m−3 HCl(pH 0.0) and 1 kmol·m−3 NaCl(pH 5.8) at 298 K, and then compared with those of vacuum-induction-melted (VIM) Fe-Cr alloys containing 10-25 mass%Cr. TEM images and ED patterns of IBS-Fe-Cr alloy films indicated that the films consist of equiaxial bcc microcrystals with an average grain size of approximately 30 nm. The root-mean-square roughness value estimated from AFM images of IBS-Fe-Cr alloy films increases from 0.36 nm for a film 60 nm thick to 0.77 nm for a film 550 nm thick with increasing film thickness. This suggests that the surface microroughness becomes large as the film thickness increases. The critical passivation current density, icrit, of IBS-Fe-Cr alloy films in 1 kmol·m−3 Na2SO4(pH 3.0) is lower than that of VIM-Fe-Cr alloys: the value of icrit for an IBS-Fe-12Cr alloy film 140 nm thick is less than that for a VIM-Fe-14Cr alloy by a factor of about 100. The value of icrit for IBS-Fe-18Cr alloy films increases with increasing film thickness in the range of 60-550 nm, while it never exceeds that for a VIM-Fe-18Cr alloy. The IBS-Fe-21Cr alloy film 90 nm thick covered with a native oxide film does not show spontaneous activation in 1 kmol·m−3 HCl under the open circuit condition. The alloy film never develops pitting under the subsequent anodic polarization in 1 kmol·m−3 HCl and 1 kmol·m−3 NaCl.
The aluminum alloy (JIS-A1070: 99.7%Al) plate showing a large grain patterns is used as an interior material. We investigated the relationship between the optical properties to surface morphology and crystal orientations of this type of aluminum plate. The annealed sample having coarsened grains (5-20 mm diameter) was etched with a mixture of sulfuric acid and hydrochloric acid. The crystals are classified into two types from the reflective properties by the measurement of regular reflectance for each crystal: one is the crystal which has smooth surface and shows high regular reflectance. The other one is the crystal which has ∼2 μm high jagged surfaces such as a wavy pattern: the regular reflectance is less than a few % on the surface of the crystal. (The main reflective face of this type of crystal should be the oblique plane of jag.) The former type of crystal is named “type A” and the latter is “type B” provisionally. Some of these types of crystals were cut out and their crystal orientations were measured by using an Xray diffractometer having the 3-axis goniometer. As a result, type A crystals have the (310) or (100) plane and all of type B have the (110) plane, which are parallel or inclined less than 10 degrees to the plate surface. Furthermore, the longish direction of wavy jag is virtually parallel to the 〈100〉 direction of type B crystal. Since the incident light on type B crystal should be mainly reflected on the oblique plane, the brilliancy of each type B crystal depends on the direction of the wavy pattern, namely on the 〈100〉 direction. From these results, it is important for a interior material to have a properly dispersed direction of 〈100〉 with a view to showing a multiform reflection. Accordingly, the materials composed of strongly oriented crystals are found to be unsuitable for interior materials.
Production of Al matrix/Al3Ti composite materials has been performed by the Low Pressure Casting-Combustion Synthesis Process(LCCS process). The formation of Al3Ti in the composites produced by the LCCS process was accelerated drastically at the temperatures higher than 1193 K. At the particle size between 25∼125 μm, the volume fraction of Al3Ti in the composites increased with decreasing particle size. When the Al-Ti mixed powder was kept in liquid Al at 1193 K for 15 s, the microstructure of the composites produced was homogeneous up to the length of 90 mm from the liquid Al entrance. With increasing Ti content in the mixed powder, decreasing particle size of the mixed powder and increasing immersion time of the mixed powder in liquid Al, the tensile strength of the composite increased but its elongation decreased. On the fracture surfaces of the composites, transgranuler cracks were observed in the Al3Ti particles due to the good bonding between Al matrix and Al3Ti particles.
Pressureless-sintered (PLS) SiC was bonded to SiC using V foils by solid state bonding at 1373∼1673 K for 1.8∼64.8 ks and 30 MPa in vacuum. The interfacial reaction layers and microstructure were investigated by electron probe microanalysis and X-ray diffractometry. At 1573 K for 7.2 ks, granular V2C and V3Si layer zone were formed on the V and SiC side, respectively. A hexagonal V5Si3Cx phase was formed at the interface between V3Si and SiC at 1573 K for 7.2-14.4 ks, and the interface structure of the joint became SiC/V5Si3Cx/V3Si/V2C+V/V. With the further bonding at 1573 K, V was completely consumed, and the interface structure of the joint became SiC/V5Si3Cx/V3Si/V2C. The fracture shear strength of the SiC/V/SiC couples bonded at 1573 K for 14.4 ks, comprized a thin layer of V5Si3Cx adjacent to SiC and showed a maximum of 130 MPa at room temperature and exhibited stable strength at the temperatures up to 1073 K.
Quaternary interdiffusion experiments of Al-rich α Al-Zn-Mg-Cu alloys have been performed in the temperature range from 755 to 833 K. The concentration profiles indicate that the diffusion distance of Cu is shorter than those of Zn and Mg in the solid solutions. The direct interdiffusion coefficients \ ildeDZnZn4, \ ildeDMgMg4 and \ ildeDCuCu4 are positive, and indirect coefficients are negative. The impurity diffusion coefficients of Zn (or Cu) in Al-Cu(or Zn)-Mg alloys can be expressed by the follwing equations. (This article is not displayable. Please see full text pdf.) \
oindentFrom the ratio values of indirect coefficient to direct one, it is expected that attractive interactions of Zn-Mg, Zn-Cu and Cu-Mg atoms exist in the Al-Zn-Mg-Cu alloys.
The mechanical properties of the ordered intermetallic Ni-Fe-Al β phase alloys with and without boron has been studied as a function of composition and temperature by compression testing. The alloys without boron where Al is kept constant at 45 and 40 mol%, whereas that with boron where Al is kept constant at 45 mol% and addition of 0.05 mass% boron. The present work indicated that (1) the temperature dependence of strength behavior of (Ni, Fe)Al; (45 mol%Al) alloys is similar to bcc metals and binary NiAl alloys, characterized by three different stages. The alloys of stoichiometry in binary NiAl, FeAl and near the second stoichiometry in ternary (Ni, Fe)Al; (45 mol%Al) show plateaus distinctly and have a wide plateau temperature range, which becomes narrower and less distinct when the composition of the alloy is off stoichiometry. (2) Consisting with the hardness, the ternary alloys of near the second stoichiometry that with the β phase in the Ni-Fe-Al system show the lowest 0.2% flow stress, and an increase in iron content largely enhances the solid solution strength. (3) The boron improved the strength of (Ni, Fe)Al; (45 mol%Al) alloys, especially at low temperature, and with increasing temperature, the effect becomes weaker and disappears beyond 1250 K. (4) The brittle-ductile transition temperatures (BDTT) of (Ni, Fe)Al; (45 mol%Al) alloys were also largely decreased by a small amount of boron addition in comparison to the unalloyed (Ni, Fe)Al; (45 mol%Al) alloys, indicating a better high-temperature mechanical properties with a favorable of strength and fracture toughness.
Fatigue crack propagation has been studied to identify the effect of graphite and matrix structure in spheroidal graphite cast irons mainly by in-situ observation within a scanning electron microscope (SEM). Two types of ductile cast irons, i.e. a ferritic ductile cast iron (FDI) widely known as bull’s eye and an austempered ductile cast iron (ADI) with a bainitic matrix were investigated. Fatigue crack propagation tests were carried out in a wide ΔK range under load control by using the fatigue machine combined with the scanning electron microscope. Little graphites affect the fatigue crack propagation. Holes surrounding these graphites initiate microcracks independent of the main crack propagation, which delay the fatigue crack propagation. From this result, the graphite may behave as the hole for the fatigue crack propagation. The fatigue crack propagation rate of the FDI material decreases in the low ΔK region due to the main crack deflection and increases in the high ΔK region because of the cleavage crack initiation, compared with the ADI material.
The relation between the martensitic transformation temperature and long range order in the β phase of an Ag-Zn-Al alloy was investigated mainly by means of electrical resistivity measurements. In this alloy, the disordered state (of the bcc structure) can be brought about down to room temperature by quenching from a temperature a little above the critical temperature (about 340 K). By aging at a temperature around or below room temperature, ordering of atomic arrangements proceeds to result in the C11b structure. It was observed that the resistivity of specimens lowers in accordance with this ordering. It was also found that the martensitic transformation temperature, at which the crystallographic structure changes to the 9R-type structure, lowers markedly with ordering. This indicates that ordering affects the relative stability between the matrix phase and the martensitic phase. A good linear relation was obtained between the decrease in transformation temperature (ΔT) and the change in resistivity. By making use of the maximum value of resistivity change as a reference, the resistivity change was related to the degree of long range order (φ). Then, the relation ΔT=−1100φ2 [K], was obtained. A themodynamical consideration, based on the Bragg-Williams-Gorsky approximation, has been given for the effect of ordering on the transformation. The theoretical results agree fairly well with the experimental relation.
The mechanism of second-harmonic generation (SHG) was investigated for the thermal poled fused quartz and synthesized silica glasses. The current was measured for silica glasses during the thermal poling process. As a result, fused quartz with a relatively higher current generated SHG. We discussed the relationship between crystallization from glass to crystal and second-order nonlinearity, based on a continuous-heating transformation (C-H-T) diagram and the sample temperature, which was calculated from the Joule’s heat of the poling process. It was observed that grain size of the α-quartz and α-cristobalite crystal was about 20 nm at the depth at 5 μm from the anodic surface in the poled fused quartz (553 K, 4 kV, 103.56 s), by a field emission scanning electron microscope (FE-SEM) and X-ray diffraction (XRD) analysis. The distribution of intensity of the second-harmonic (SH) signal was measured in a layer of SHG near the anodic surface. As a result the mechanism of SHG was deemed due to crystallization from silica glass to the orientated α-quartz possessing second-order nonlinearity under a high electric field and Joule’s heat in the thermal poling condition. It was considered that the intensity of SH signal was higher with increasing quantity of orientated nano-crystals, but was lower with decreasing orientation of the nano-crystals, but was lower with decreasing orientation of the nano-crystals, along with decreasing electric field.
The present study was conducted in order to analyze the microstructure and corrosion resistance of Ti-M (M=Ru, Rh, Pd, Ir, Pt) alloy prepared from titanium and M powders using spark plasma sintering (SPS). The microstructure of SPS’s specimens were observed by scanning electron microscope and X-ray diffraction. Corrosion resistance was determined by measuring the potentiodynamic polarization at a scanning speed of 0.124 V/min using a 5 mass%HCl solution open to air at 25°C. For this measurement, each specimen was scanned beginning at a potential of −1.0 to +2.0 V (SCE), and potential approached noble. The microstructure observed that the SPS alloys were the particle dispersion type, with added element phases dispersed in the Ti matrix. Most of the added elements (Ru, Rh, Pd, Pt) formed Ti-M intermetallic compounds on the border between the Ti matrix and added element phase. Low dispersion of the added element phase reduces the current density in the cathodic area of the SPS alloy polarization curves, and the current density may also decrease if several compounds are generated. Compared to other Ti-M alloys, the current density of Ti-Ir is low because the dispersion is low and that of Ti-Pt is low because several compounds are generated. Since the active area of the Ti-M (Ru, Rh, Pd, Pt) compound phase is 0 to 1 V (SCE), the compounds increase the current density in the anode area. In the Ti-Pd and Ti-Pt alloys, corrosion marks were observed where the TiPd and TiPt phases were eluded. The Ti-Ir alloy generates no compounds and its current density in the anode area is smaller than those of other Ti-M alloys. Consideration about Ti-M alloys prepared using SPS is that added element phases are dispersed in the Ti matrix as smaller particles and, moreover, no Ti-M compounds are generated. If Ti-M intermetallic compounds are generated, raising the SPS temperature disperses the compounds into the Ti matrix and reduces the related active area, reducing the corrosion resistance.
Phase transformation behaviors of Ti-Al mechanically alloyed (MA) powders during heating were investigated with analytical TEM, DSC and XRD. Elemental Ti and Al powders with overall compositions of 33, 41 and 46 mol%Al were blended for mechanical alloying. N-heptane was used as a process control agent for the mechanical alloying. Irregular shaped and dislocation free Al supersaturated α-Ti nanocrystals were formed in the MA powders after 720 ks of milling. The mean grain size is about 25 nm. An hcp→fcc→hcp→DO19 transformation in the Ti rich MA powders and an hcp→fcc→L10 transformation in the Al rich MA powders were observed during heating. The morphological features are as follows: (1) an fcc/hcp thin layered structure, (2) a composition invariant, (3) a large number of defects, and (4) rapid grain growth. They strongly suggest that the grains are formed by shear mechanism as well as short range diffusion, i.e., a massive transformation during heating. The fcc phase formation can be explained by an hcp→fcc structure change by the motion of a a⁄3[1\bar100] type Shockley partial dislocation on every second plane of the basal plane of the hcp crystal. Since an hcp structure is stable in Ti rich MA powders, the fcc phase, which in turn transforms to the hcp phase by the motion of a a⁄6[11\bar2] type partial dislocation. Finally, the DO19 (α2) or L10 (γ) phases form from the hcp or fcc phases by the short range diffusion.
The effect of microstructure on fatigue strength, small fatigue crack initiation and propagation characteristics in biomedical Ti-6Al-7Nb and Ti-6Al-4V ELI alloys were investigated. In the Widmanstätten α structure, the tensile strength of Ti-6Al-7Nb is slightly lower than that of Ti-6Al-4V ELI. In equiaxed α structure, the tensile strength of Ti-6Al-7Nb is apparently lower than that of Ti-6Al-4V ELI. The elongation of both alloys with same structure is nearly the same in each microstructure. The fatigue strength of Ti-6Al-7Nb alloy nearly equals that of Ti-6Al-4V ELI alloy with the Widmanstätten α structure. While the fatigue strength of Ti-6Al-7Nb alloy is lower than that of Ti-6Al-4V ELI in equiaxed α structure, in particular, in the high-cycle fatigue region. The fatigue crack initiation in each titanium alloy with equiaxed α (volume fraction of primary α : 50%) and Widmanstätten α structures mainly occurs at the primary α grain boundary while in the colony and prior β grain which are about 45 degree inclined to the stress axis direction in WidmanstWidmanstätten α structure. The fatigue life increases when the small fatigue crack propagation resistance increases with the volume fraction of primary α. When the cooling rate after solutionizing is increased, the fatigue strength of Ti-6Al-7Nb approaches that of Ti-6Al-4V ELI.
The research of adsorption water on metal surfaces has been conducted mainly with FT-IR and QCM (Quartz Crystal Micro-balance). Among these methods, QCM has the high reliability as a research technique of adsorption water because of its relatively easy experiment. However, there has been no report on the direct observation of growth of water droplet or a water film on QCM surface. At present, therefore, it is difficult to understand the growth mechanism of water droplets or water film. In this study, the QCM measurement of adsorption water was carried out using a gold-coated quartz crystal. Moreover, for comparison with the QCM results, the non-contact mode AFM measurement was made by using an environmental cell that can control the relative humidity, and the nucleation and disappearance of water droplets were directly observed. As the results, the change in weight as a function of relative humidity by the QCM measurement was small when the gold surface of QCM was clean and few water droplets were present on the surface. It has been confirmed that the increase and decrease in weight depending on the relative humidity are due to the growth and shrink of adsorbed water droplets.
The occurrence of dynamic recrystallization in ferritic iron, which is a typical dynamic recovery-type material, was confirmed in the present study using a Ti-added interstitial-free (IF) steel. The specimens were hot-compressed at various strain rates at various temperatures within the ferritic region and quenched immediately after compression. Equiaxed grains surrounded by clearly-etched boundaries appeared preferentially near the initial grain boundaries in the small Zener-Hollomon parameter (Z) deformations. Microtextural analysis by Kikuchi-line measurements in TEM or EBSP in SEM clearly showed that these equiaxed grains are dynamically recrystallized with both the high angle grain boundaries and the dislocation substructures inside. The fraction and the size of the dynamically recrystallized grains increased with decreasing strain rates or increasing deformation temperature, i.e., decreasing Z. Consequently, the condition where dynamic recrystallization of ferrite occurred was expressed as, Z≤1011 s−1 in the present material. Nevertheless, despite the occurrence of dynamic recrystallization, a large stress drop in stress-strain curves was not observed. The size of the dynamically recrystallized grains was much larger than that of the subgrains formed under the same deformation condition, which suggests that the dynamically recrystallized grains grew immediately after they obtained mobile boundaries. The characteristics of the dynamic recrystallization of ferrite were the inhomogeneity of recrystallization as well as the small drop in stress. Some of the initial grains were hardly recrystallized even in the small-Z deformation, which is presumably due to the initial orientation dependence of recrystallization in ferrite. The nucleation of dynamic recrystallization in ferrite was explained on the basis of the introduction of inhomogeneous deformation microstructure with large local misorientations.