Cu bicrystals with various  symmetric tilt boundaries doped with Bi were tensile tested at several temperatures. The fracture behavior depended strongly on the misorientation angle, Bi doping time, aging conditions and testing temperature. Grain boundaries were more embrittled with increase in the Bi doping time and by the aging treatment depending on misorientation. As the testing temperature increases, the difference in the degree of embrittlement among different grain boundaries became more significant. These observations could be understood reasonably by considering the grain-boundary energy. The grain boundaries are more brittle and fracture more easily at lower tensile stresses with increasing grain-boundary energy.
A method for predicting the type of defect structures in a binary intermetallic compound is proposed based on the comparison of internal energies of a crystalline solid having a certain defect structure at the pseudo-ground state, i.e. at near 0 K. These defects are structurally introduced with deviation from stoichiometry. The internal energy can be estimated by taking only the nearest neighbor atoms into account. This simple method can be applied to Kurnakov and Daltnide type compounds as well as of Berthollide type. The predicted results are in good agreement with the experimental data in literatures.
The dependence of mechanical properties and erosion resistance on the chemical composition of various high Cr-Ni-Mo cast stainless steels was investigated. In accordance with these results, the relationship between these properties and martensitic transformation of austenite was discussed. The results are summarized as follows. (1) Tensile properties and Charpy impact values have a mutual relation to Hirayama’s Ni equivalent. The tensile strength/0.2% proof stress, elongation and Charpy impact value have a maximum value at 19∼21% of Hirayama’s Ni equivalent. (2) The chemical composition of the cast stainless steels having superior erosion resistance corresponds to 19∼21% of Hirayama’s Ni equivalent. After erosion test, it is found that above 90% of the residual austenite transformed to martensite and a remarkable increase of hardness occurred with the test specimens having these chemical compositions. Judging from the present results, the reason why high strength 18%Cr cast stainless steel has superior mechanical properties and erosion resistance is summarized as follows. Chemical composition of this cast steel corresponds to 19∼21% of Hirayama’s Ni equivalent and in regard to this composition, the stress-induced martensite easily forms. During the tensile or erosion test, the stress-induced martensitic transformation of the residual austenite causes a large increase in tensile strength and hardness.
The relationship between the dislocation structures and the surface orientations was investigated by TEM on the formation of recrystallized grains in the surface layers normal and parallel to edge dislocations of the primary slip system in aluminum single crystals with Schmid factor 0.5, which were deformed in tension to a strain of 0.3. The dislocation structures inside deformation bands existing in the surface layers normal to the edge dislocations show the cell structures with rectangle shapes and are thermally stable, while those parallel to them form the cell structures with wavy shapes and are thermally unstable. The mean growth rate of recrystallized grains in the surface layers parallel to the edge dislocations is larger than that normal to them, because on the former surface edge dislocations are annihilated easily on account of their climbing. However, the number of nucleation site in the former is smaller than that normal to the latter.
The influence of deformation temperature on the Bauschinger effect (BE) of a high-strength TRIP-aided dual-phase (TDP) steel containing retained austenite particles of 10 vol% was investigated in a temperature range between 27 and 200°C. The BE of the TDP steel depended significantly on the deformation temperature, although such a temperature dependence did not appear in a conventional ferrite-martensite dual-phase (DP) steel. Large BE, i.e., remarkable transitional-softening and subsequent permanent-softening proposed by Orowan, appeared at 100 and 200°C, at which the retained austenite particles are more resistant to the strain-induced α′ transformation (SIT) than those at 27°C. The Bauschinger stress obtained at 200°C was as high as that of the DP steel. The retained austenite particles as a hard phase increased the Bauschinger stress. The SIT, however, was expected to lower the Bauschinger stress by the following reason. An expansion and shear deformation resulting from the SIT reduce both internal stresses in retained austenite islands and in the ferrite matrix.
The existence of critical stresses for SCC initiation, σth and KISCC, is often confirmed in several kinds of chloride solutions. The σth was reported to depend on yield point of materials. On the other hand, the existence of KISCC shows that the passive film can repair on plastic deformed crack tip because of the stress and strain diverging to infinity. This contradiction could not be explained with static mechanics. In this paper, supposing that SCC initiation would occur by dynamic mechanics such as dynamic strain, even in a dead weight condition, the relation between the mechanisms for SCC initiation in smooth and cracked specimens were investigated. As the result, a sort of plastic strain induced by corrosion was detected with mechanochemical methods. This phenomenon seemed to resemble the Rehbinder’s effect. The relation between σth and KISCC was explained with this corrosion induced strain concept.
Ni-Ti alloys which have large recovery strains and recovery stresses, are used as a functional material. In this study the shape memory effect of clamped Ni-Ti alloys (50.20 and 50.85 at%Ni) has been investigated by tensile tests with heating. Then simulation with a finite element method (FEM) have been carried out to estimate the behavior of the alloys. The results obtained are summarized as follows: (1) Dislocation would be generated by slip when a clamped specimen is heated, then it induces internal stress. As a result, on the first heating recovery stress appeared unstable, while on the second heating it became stable and could exceed the first one relatively. (2) The generation of recovery stress played an important role in obtaining a high apparent Young’s modulus. (3) FEM analysis proved that the apparent Young’s modulus and the stress generated inside the structure could be controlled by the recovery stress.
The polycrystalline disks of BeS, MgS, CaS and SrS in group IIa and Sc2S3 and Y2S3 in group IIIa were carefully prepared to avoid contamination. The electrical conductivities of the disks have been measured under the atmosphere of the various sulfur pressures by the two wire AC method (1 KHz). All sulfides of IIa metals showed ionic conduction The apparent activation energies for the ionic conduction were compared with those of other alkaline-earth oxides and sulfides, and the charge carriers of the sulfides predominant in ionic conduction are estimated as metal cations. A p-type electronic conduction linearly dependent on PS21⁄6 is observed for MgS and BeS in the high sulfur partial pressure range. The observed sulfur pressure dependence is attributed to the predominance of fully ionized magnesium and beryllium vacancies. An n-type conduction is observed for Sc2S3 and Y2S3 with partly proportional to PS2−3⁄16. The sulfur pressure dependence is attributed to the predominance of ionized scandium and yttrium interstitial ions. The electrical conductivity of Y2S3 showed PS23⁄16 dependence in the PS2 range indicator p-type conduction. This dependence is attributed to the fully ionized yttrium vacancies.
For the analysis of steels by glow discharge mass spectrometry (GDMS), the relative sensitivity factors (RSFs) of alloying elements, C, Si, V, Cr, Mn, Co, Ni, Cu, Mo and W, and trace impurities, P, S and N, have been determined using 30 samples selected from 5 kinds of the Japanese Standards of Iron and Steel (JSS) certified reference materials. The measurement was made by using a VG 9000 type GDMS instrument. Preliminary discharge was conducted for about 60 min after a disk sample was mounted in the discharge cell (Mega flat cell) cooled with liquid nitrogen. RSF-values were calculated individually for the Faraday collector and for the Daly collector. Analytical values of a heat-resisting superalloy JSS CRM 680-3 were obtained by using a newly designed correction program RSFATOM, and the values were in good agreement with the certified values. Relative standard deviations (RSDs) for the alloying elements were within 1%.
Surface hardening of a FeCrNiAl alloy by the ion nitriding method has been investigated. This alloy was originally developed for applications as cutting tools and its surface is hardened by the alumina layer produced by heat-treatment at a high temperature between 1373 and 1573 K. This heat-treatment, however, tends to cause deformation of the alloy. Thus has been explored the surface hardening of the FeCrNiAl alloy by the ion nitriding method which is thought to be suitable for hardening the alloy surface at a lower temperature avoiding deformation of the alloy. The obtained results are as follows: (1) CrN, ε-Fe2∼3N, Fe4N and AlN are formed near the surface of the FeCrNiAl alloy resulting in the increase of the surface hardness. (2) Vickers hardness of the nitrided layer ranges from 12.0 GPa to 13.5 GPa as the result of ion nitriding at various temperatures from 773 to 873 K. (3) Thickness of the nitrided layer changes with nitriding duration and temperature. The thickness of the nitrided layer is roughly proportional to the square of the nitriding duration. (4) Corrosion resistance after the nitriding treatment is lower than that before the nitriding treatment.
Rapidly solidified Fe-30Cr-5Al alloy powders produced by the rotating-water-atomization-process were sheath-rolled. Three kinds of sheath-rolling which are hot sheath-rolling, cold sheath-rolling after hot sheath-rolling and sintering after cold sheath-rolling were carried out. Microstructures and mechanical properties of the sheath-rolled samples were examined. Sintering after cold sheath-rolling was not effective in the breakage of Al2O3 oxide films of the powder particle surface. By hot sheath-rolling, Al2O3 oxide films were broken or divided to small pieces and the shape of Al2O3 was changed from plate to granular form. By hot sheath-rolling, the mean diameter of Al2O3 was 2.5 μm for the reduction in cross-sectional area of 80%. Cold sheath-rolling after hot sheath-rolling were very effective in fine dispersion of Al2O3 oxides. By cold sheath-rolling after hot sheath-rolling, the mean diameter of Al2O3 was 1.2 μm and the tensile strength was 1060 MPa for the reduction in cross-sectional area of 79%. The tensile strength and elongation increased drastically with decreasing mean diameter of Al2O3 oxides to less than 2 μm.
In order to obtain useful information about the improvement of mechanical properties of Fe-30 mass%Cr-5 mass%Al alloys with decrement carbon content, on Fe-30Cr-5Al alloy whose carbon content decreased to 3.0×10−3 mass% was produced. Some examinations were made on this alloy, as-cast and as-rolled, using various techniques such as the tensile test, hardness test, optical microscopy and electron prove microanalysis. The results are summarized as follows: (1) The precipitation amount of Cr23C6 decreases and mechanical properties are improved with decrement of carbon content. By decreasing carbon content to 3.0×10−3 mass%, the tensile strength and elongation of this as-cast alloy are 400 MPa and 2∼3%, respectively. (2) The grain size of this alloy decreased with increasing reduction in cold-rolling. However, the grain size less than 350 μm does not affect the mechanical properties of this alloy. (3) The tensile strength and elongation of this as-hot-rolled alloy are 750 MPa and 30%, respectively. (4) Critical reduction per 1 pass without cracking increases with decrement in carbon content.
In order to make infiltration mechanism clear, pressure change and ram speed were measured when SiC whiskers reinforced aluminum composites were fabricated by squeeze casting. Preforms were deformed due to compression stress during infiltration by aluminum. To analyze the correlation between applied pressure and infiltration front in the preform, the distribution of hardness along infiltration direction in the composite was measured and distribution of volume fraction was calculated by the hardness. The volume fraction increased along the infiltration direction after starting point of compression. Infiltration of preforms by aluminum finished in the course of pressure rise up to 100 MPa. A theoretical expression is derived to describe fluid flow in the preform during the infiltration, on the condition that the pressure on the preform surface starts to rise from zero and when the applied pressure exceeds the compression strength of preform, deformation starts. The starting point of deformation, distribution of volume fraction in the composites can be calculated by the theory in good agreement with experiments. This theory is valid in every cases of the fabrication of composites by squeeze casting.
Production of Al matrix/TiAl3 dispersion composite materials by an in-situ infiltration-combustion synthesis has been proposed. According to Semlak and Rhines’ formula for infiltration, the present infiltration-combustion synthesis has been found to consist of two different stages; the initial infiltration and the subsequent enhanced infiltration accompanied by combustion synthesis. The microstructural observation has shown that the present synthesis process consists of the infiltration of Al melt into the green compact, the combustion synthesis reaction and the formation of the porous TiAl3 skeleton, the second infiltration of Al melt into the porous TiAl3 skeleton, which accompanies rearrangement shrinkage of the infiltrated region, and the reinfiltration of Al melt into the non-infiltrated green region. The initial infiltration and the secondary infiltration as analyzed by the Semlak-Rhines equation correspond with the infiltration of the Al melt into the Ti green and the later mixed infiltration process, respectively. The larger particle size of Ti powder (in the present case larger than 100 μm) has been found to discontinuously enhance the second infiltration rate, due to the larger pore space formation, i. e., the larger capillary channel size.
Ti-(30∼38 mass%)Al-(0∼1 mass%)N alloys prepared by a precision casting method were investigated. The addition of nitrogen was found to be effective in refining TiAl/Ti3Al lamellar grains. Two-phase nitride particles composed of TiN as a core and Ti2AlN as an outer shell, together with fine precipitates of Ti3AlN, were identified in the present alloys containing nitrogen. The room-temperature ductility and strength increased with increasing nitrigen content up to about 0.3 mass%N, while they were decreased by further addition of nitrogen. The improvement in the room-temperature mechanical properties is mainly caused by grain refining and precipitation hardening.
Structure and magnetic properties of rapidly solidified 6.5 mass%Si-Fe alloy ribbons were studied by controlling the atmosphere during heat treatment. The ribbons were annealed in three kinds of atmosphere listed as below. (1) in the vacuum atmosphere for 3.6 ks at 1448 K (2) in the sulfur atmosphere for 3.6 ks at 1448 K (3) in the vacuum atmosphere for 180 s at 1373 K and the sulfur atmosphere for 3.6 ks at 1448 K The structure of ribbon, which were showed random structure at as prepared state, was developed into (110) texture by the heat treatment (1). On the contrary, the structure was developed into (100) texture by the heat treatment (2). In the case of the heat treatment (3), the structure of ribbon was also developed into (100) texture and the grain size was large such as 2.5-5 mm, as compared with heat treatment (1) and (2). The coercive force decreased to 2-4 A/m remarkably.
The crystallization processes of amorphous Sb-Se thin films were studied in detail mainly by calorimetry and mean time for crystallization at room temperature was estimated. Amorphous Sb100−x-Sex thin films (X=20∼65 at%) were deposited on glass plates and Polymethyl-Methacrylate (PMMA) substrate using two-point electron beam deposition and RF magnetron sputtering techniques. The crystallization process of amorphous Sb-Se thin films have been investigated by X-ray diffraction (XRD), differential scanning calorimetry (DSC) and transmission electron microscopy (TEM). An activation energy for the crystallization is estimated by Kissinger’s plot and Johnson-Mehl-Avrami (J.M.A) equation. The crystallization temperatures were found to be proportional to the Se concentration (Se≤60 at%) and those of Sb40Se60(Sb2Se3) and Sb67Se33(Sb2Se) films were estimated to be 220°C and 195°C respectively by DSC measurements (heated at a scanning rate of 10°C/min). An activation energy for the crystallization in an Sb67Se33(Sb2Se) film is estimated to be (2.85±0.02)×105 J/mol by Kissinger’s plot (from the analysis of the DSC data on the continuous heating) and (2.78±0.02)×105 J/mol by J.M.A equation (from the analysis of the DSC data on the isothermal annealing), and its reaction order is n=5∼6 and the frequency factor is ν=1.61×1029 (s−1). It was concluded that the amorphous Sb67Se33(Sb2Se) thin film is sufficiently stable at room temperature for practical use. The mean time for 10% crystallization was estimated to be about 100 years at 100°C. The structure of the crystalline Sb67Se33(Sb2Se) transformed from the amorphous phase was found to be monoclinic, which does not correspond to any known compounds in the Sb-Se system.