A structure analysis of Ti5Si3D0.9 has been carried out to determine the deuterium trap sites by neutron powder diffraction with the Rietveld profile analysis. It is revealed that the deuterium atoms are located at octahedral (2b) sites surrounded by six Ti atoms in the crystal structure of Ti5Si3D0.9, space group P63/mcm. Local vibration spectra of hydrogen in Ti5Si3H0.83 measured by neutron inelastic scattering support this result; the energy eigenvalue of the primary vibration mode is found at 7.53 kJ/mol (78 meV). The hole radius and the spring constant of the Ti-H(D) bond are discussed.
In order to make a quantitative description of the plastic deformation of polycrystalline alloys governed by the stress induced matensitic transformation (SIM), the condition of yield by SIM is formulated for multiaxial stress states. The relation between the plastic strain of a crystallite and the volume fractions of individual martensite variants formed in the crystallite is also given. Owing to its simplicity, the Taylor model is suitable for the present purpose to visualize the essential features of polycrystalline SIM. However, the volume change accompanying the martensitic transformation violates the basic hypothesis of the Taylor model; the homogeneity of strain. This problem is coped with by dealing only with the deviatric stress, deviatric strain and the plastic work done by them in terms of the Taylor model, and then by evaluating the effect of the hydrostatic stress and volume change. This scheme may be useful in predicting the deformation behavior of polycrystalline shape memory alloys, including the effect of their texture.
In connection with hot-shortness of tin-bronze, the ductility of a Cu-8 mass%Sn binary alloy and of the alloy containing B, Mg or P of about 0.1 mol% was investigated in detail at elevated temperatures up to 1073 K. All the alloys showed markedly a poor ductility near 673 K accompanied by intergranular fracture, i.e., intermediate temperature embrittlement. The ductility was improved to a greater extent at higher temperatures in B-bearing and Mg-bearing alloys, but to a lesser extent, in binary and P-bearing alloys. The improved ductility which was accompanied by transgranular fracture was commonly observed regardless of strain rate and grain size in the B-bearing alloy. This alloy showed an excellent ductility together with fine recrystallized structures due to dynamic recrystallization at higher temperatures. Recrystallization temperatures, however, were almost the same in the four sorts of alloys. In the binary and P-bearing alloys, intergranular fracture at higher temperatures was shown to start at the specimen surface. This fact suggested that the strength of the grain boundary of these alloys was reduced especially near the surface. Based on the result of oxidation experiment, the decrease in grain boundary strength was surmised to be caused by internal oxidation along grain boundaries.
The characteristic features of the structure factors for many liquid metals and alloys are known to be reproduced fairly well by the hard sphere model coupled with the Percus-Yevick equation, and then various properties of liquid metals and alloys have frequently been discussed in terms of the hard sphere approximation. With these facts in mind, the theoretical equation for the interaction parameters in multi-component metallic solutions has been presented in the framework of the hard sphere model. It was found from a series of test calculations by the present hard sphere model that the product of the difference in the hard sphere diameters between solute and solvent, (σ0−σ1) (σ0−σ2), where σi is the hard sphere diameter of i-component, plays a significant role in determining the sign and absolute values of the interaction parameters. This new equation for evaluating the interaction parameters from fundamental physical constants of the components in solution has been applied to 19 cases in Cu-base, Pb-case and Sn-base solutions, and the agreement between calculation and the experimental data appears to be at the reasonable level. Numerical calculations were also carried out in 60 cases in Fe-base solutions with the relevance to steelmaking, and the calculated values of εMnj, εCrj, εSij, εPj, εCj and εHj were found to be in reasonable agreement with the experimental data.
An experimental study had been made on the mechanism of mass-transfer between molten Cu-Si alloy and Li2O-SiO2-Al2O3-FeO slag at 1523 K. The explored reaction was the oxidation of silicon by FeO in slag taking place under the condition of rate-controlling by transport of silicon in the metal phase. By examining rate data influenced by the concentration of Si in the metal phase, a new concept on the reaction zone in metal-slag reactions has been proposed. It is presumed that the zone of reaction between Si and O is located within the metal-side boundary layer. The location of the zone is supposedly controlled by mass-tranfer fluxes of O from the slag-metal interface to the reaction zone and Si from the bulk metal to the zone. When the initial concentration of Si is high (≥0.08 mass%), the reaction zone is located in the vicinity of the slag-metal interface until Si concentration is lowered considerably. In this case, the apparent mass-transfer coefficient of Si (kSi′) is constant. When the initial concentration of Si is low (≤0.02 mass%), the reaction zone moves away from the interface during the reaction so that the distance through which Si is diffusing decreases, resulting in the increase in the mass transfer coefficient.
The activities of indium in liquid In-Pb and In-Tl alloys were measured by the E.M.F. method over the temperature range 1023-1273 K and 1023-1223 K, respectively. From these activities and their dependence on temperature, the partial and integral molar free energies, the entropies and the enthalpies were calculated for these systems. The cells used were as follows: (This article is not displayable. Please see full text pdf.) From the present experimental results the following conclusion is obtained: (1) The activities of indium and lead in the liquid In-Pb alloys show slightly positive deviations from Raoult’s law. The activity of indium is in agreement with the result by Terpilowski et al. and the activity of lead is located between the result by Sommer et al. and that by Shiu et al. The heat of mixing almost agrees with the result of calorimetric method by Wittig et al. The properties of this system appear to be similar to those of regular solution. (2) The activities of indium and thallium in the liquid In-Tl alloys show very slightly positive deviations from Raoult’s law. The activity values are smaller than those reported by Kundys et al. The heat of mixing in the In-Tl system is close to the result by Wittig et al. The entropy is closer to that of ideal solution than that of the In-Pb system, but the lnγIn vs. NTl2 relation is not linear.
The rate of CrO reduction from silicate slag containing low concentrations of CrO, melted in a graphite crucible has been investigated by thermogravimetry under argon atmosphere. The first-order-type rate equation was found to be applicable to the CrO reduction. The rate is markedly affected by the wettability of the slag to the graphite crucible. In case of the immersional wetting, the rate constant varied from 3.5×10−3 to 3.6×10−2 kg/m2·s at 1873 K, whereas in the adhesional wetting, it was 1 to 2 orders of magnitude lower than in the former case. The reduction of CrO depended strongly on the phases present in the CaO-SiO2-Cr2O3 system. The reduction from the slag with two liquids phase proceeded significantly faster than that from the slag with other phases. The apparent activation energy for CrO reduction was about 300 kJ/mol. It is considered that the reduction rate of CrO would be under a mixed controle of the interfacial reaction and the mass transfer in the slag.
The interdiffusion coefficients in the wustite solid solutions containing CaO, BaO, MgO and Na2O were measured by means of a diffusion couple method at temperatures between 1073 and 1473 K in a controlled atmosphere of PCO⁄PCO2=1 The following interdiffusion coefficients were obtained. (This article is not displayable. Please see full text pdf.) \
oindentFurther, \ ildeDNa at 1173 K coincides approximately with \ ildeDCa at 1173 K.
The pitting potential of titanium is very high in NaCl-HCl solutions, and hence the pitting corrosion is not responsible for the initiation of corrosion in the crevice region. Crevice corrosion of titanium takes place, when the pH within the crevice decreases so as to induce active dissolution of titanium. Measurement of buffer capacity of NaCl-HCl solutions suggests that concentrated Cl− solutions give rise to a large decrease in pH with a small addition of H+, and that the Cl− concentration in the crevice leads readily to a decrease in pH within the crevice to about 1-2. Once titanium is activated, corrosion propagates rapidly. During propagation of crevice corrosion, the potential of creviced specimen is about −0.6 V (vs.S.C.E).
In order to investigate the t→m transformation of ZrO2 and the retention of tetragonal-ZrO2 in Mo-ZrO2 composites, the composites containing ∼50 vol%ZrO2 were fabricated by the powder metallurgical process. The t→m transformation temperature (Ms point) was measured by the dilatometric method, and the retention of tetragonal-ZrO2(t-ZrO2) was determined by X-ray diffraction analysis as functions of variables such as powder mixing time, sintered density and zirconia content. The results are as follows: (1) The powder mixing time had a significant influence on Ms point and t-ZrO2. Appropriate mixing time made it possible to retain the t-ZrO2 comparable to that of Al2O3-ZrO2 composite. (2) Although the sintered density did not affect so much, the zirconia content had a great influence, especially in the range from 10 to 15 vol%ZrO2 there was a steep decrease in the t-ZrO2 content with increasing zirconia content. This decrease is due to the growth of zirconia particles. (3) The Ms point and t-ZrO2 content depended on the size of zirconia, and the critical size below which t-ZrO2 was stable lay between 0.4 μm and 0.6 μm. The reason why this size effect occurred could not be explained from the results of this study.
The improvement of the fracture toughness at room temperature of Mo-sintered material, which is heat-resisting, is strongly required in service. One of improving methods is fabrication of a composite material with dispersion strengthening secondary particles. Therefore, we pointed out previously that ZrO2, as these secondary particles, was excellent from a standpoint of the utilization as a heat-resisting material and the effect of sintering characteristics and t→m phase transformation on toughness. The aim of this investigation is to study experimentally the mechanical properties of Mo-ZrO2 sintered composites, i.e. Young’s modulus, bending strength and fracture toughness, and to understand the effect of ZrO2 on the mechanical properties of this material. \
oindentThe results are summarized as follows: (1) Young’s modulus of Mo-ZrO2 composite material decreases with increase in the volume fraction of ZrO2 and agrees well with the results of theoretical prediction based on the self-consistent method, as far as the ZrO2 content does not exceed 20 vol%. (2) The size of transformation zone of ZrO2 in the vicinity of fracture surface is about 3.0-4.0 μm in maximum, and this maximum size depends on the volume fraction of ZrO2. (3) The volume fraction of ZrO2 has a great influence on the bending strength and fracture toughness. That is, the former reaches a maximum value in case of specimens containing 12.5-15.0 vol% ZrO2 and decreases with increase of ZrO2 content. (4) The increment of toughness may be explained by the contribution of the effect of t→m stress induced phase transformation of ZrO2.
In order to study a posibility of hot working of TiAl, tensile and compressive tests of arc melted Ti-37 mass%Al have been conducted at high temperatures up to 1473 K and various strain rates. On tensile testing, this material shows ductile behaviour above 1200 K and brittle fracture below this temperature. The critical brittle fracture stress was found to be constant and was about 320 MPa. Elongation increases remarkably above 1300 K. The flow stress of this material at low strain rates coincides well with the hyperbolic relations proposed by Sellars et al. The flow stress at high srain rates estimated from this relation exceeds the brittle fracture stress, which means that a usual working process will not be applicable. For the successful hot working of this material, high hydrostatic compressive stress components have to be applied or the temperature and strain rate have to be adjusted so that the flow stress may become less than 320 MPa. Fine recrystallized grains of average size 18 μm in diameter were obtained for the material strained to a true strain of 1.6 at 1300 K.
Carburizing behavior is clarified by investigating the effects of carburizing conditions, i.e., temperature, time and methane pressure, on case depth, surface carbon content and rate of flow of carbon into the steel, namely, the flux of carbon. A steel, SNCM 815, was carburized at temperatures from 1193 to 1313 K for times up to 14.4 ks under methane pressures from 13.3 to 80.0 kPa. Carbon concentration-distance curves were determined by a succession of grindings and emission spectrochemical analyses of the ground surfaces. The chemical reaction controll brings about a constant flux of carbon until the surface carbon content reaches the solubility limit of carbon. The carburizing is thereafter controlled by carbon diffusion within the steel. A mathematical model is presented for describing the behavior mentioned above. Comparisons between the calculated and the experimental carbon concentration-distance curve reveal that the concentration dependence of diffusion coefficient of carbon plays an important role in the carburizing behavior.
Fracture behavior of a newly developed metal-ceramic composite has been studied. Especially the effect of impact loading has been mainly studied and fracture mechanics analysis has been carried out. The dynamic fracture toughness at room temperature of a metal-ceramic composite has been evaluated by the absorbed energy method and by the impact load obtained from an instrumented Charpy type impact test which can easily evaluate the dynamic fracture toughness of materials. The fracture strength of brittle material is generally apt to have values widely varied, and therefore, the value of the fracture toughness of this material should be defined statistically. Thus, its dynamic fracture toughness has been analyzed by Weibull distribution which is popularly used for the statistical analysis of the fracture strength. As a result, KIdyn value evaluated from Kalthoff’s formula has been found to be most reliable. Moreover, the critical flaw size has been estimated in the unnotched specimen. As a result, the flaw size has corresponded to the acicular ceramic particle size.
The magnetic property, electrical resistivity and hardness were measured on Ni-Fe-Cu-V alloys consisting of 60-90%Ni, 5-25%Fe, 3-30%Cu and 0.5-10%V, Ni-Fe-Cu-Nb alloys consisting of 55-85%Ni, 5-25%Fe, 3-30%Cu and 1-12%Nb as well as Ni-Fe-Cu-Ta alloys consisting of 50-85%Ni, 5-25%Fe, 3-30%Cu and 2-18%Ta. These alloys were first heated in hydrogen atmosphere at temperatures between 1173 and 1573 K and then cooled at various rates from a temperature above the order-disorder transformation point. In the Ni-Fe-Cu-V system, the highest initial permeability μi of 74.9 mH·m−1 and the highest maximum permeability μm of 392 mH·m−1 was obtained for the alloy of 74%Ni, 14%Fe, 10%Cu and 2%V when cooled at a rate of 2.78×10−2 K·s−1 after annealing at 1473 K for 18 ks. This alloy exhibited the electrical resistivity ρ of 0.475 μΩ·m and vickers hardness Hv of 140. In the Ni-Fe-Cu-Nb system, the highest μi of 78.0 mH·m−1 was shown for the alloy of 69.5%Ni, 11.5%Fe, 15%Cu and 4%Nb when cooled at a rate of 2.78×10−2 K·s−1 and the highest μm of 608 mH·m−1 for the alloy of 76%Ni, 12%Fe, 5%Cu and 7%Nb when cooled at a rate of 16.67×10−2 K·s−1 after annealing at 1473 K for 18 ks. The alloy with the highest μi showed ρ of 0.580 μΩ·m and Hv of 185. In the Ni-Fe-Cu-Ta system, the highest μi of 74.5 mH·m−1 and the highest μm of 463 mH·m−1 were obtained for the alloy of 66.5%Ni, 11.5%Fe, 15%Cu and 7%Ta when cooled at a rate of 2.78×10−2 K·s−1 after annealing at 1473 K for 18 ks. The alloy exhibited ρ of 0.555 μΩ·m and Hv of 180. Further it was confirmed that those high permeability alloys containing Va group elements showed low magnetostriction.