Hardness measurements, and optical and transmission electron microscopic observations were made on Al-8%Mg alloy specimens subjected to two kinds of thermomechanical treatments: either cold-worked in a large range up to 75% just after quenching and then aged (Process I), or else pre-aged for various times after quenching, cold-worked and finally aged (Process II). After Process I, the hardness increased with increasing cold reduction, although the precipitate density in the cold-worked specimens was lower than that in the specimen without cold-work: the precipitate density initially decreased markedly and then gradually increased with increasing cold reduction. This variation was attributed to the loss in the precipitation that required quenched-in excess vacancies and to the gain in the preferential precipitation on deformation bands revealed by TEM observations. The pre-aging treatment before cold-working in Process II resulted in a greater increase in hardness than in Process I owing to dislocation hardening without any loss in precipitate density.
The change in the grain size distribution during grain growth has been investigated for a commercially-pure titanium. The one- and two-dimensional distributions were measured experimentally. Further, the grain diameter distribution, which is one of the three-dimensional grain size distributions corresponding directly to grain growth, was estimated by the method suggested in the previous paper using the values obtained from the one-dimensional distribution. This method was based on an assumption of the log-normal distribution of the grain diameter (the equivalent volume diameter) D; the distribution of this grain diameter was clearly defined by the geometric mean grain diameter Dg and the standard deviation of lnD or lnσg. The three-dimensional analysis revealed that the change of the grain diameter distribution of titanium during grain growth was similar to that of its one- or two-dimensional distribution, which is in contrast to the previous result of aluminum. This implies that the increase in Dg with annealing time is analogous to that in the one- or two-dimensional mean grain size; such a tendency was definitly supported by the fact that the standard deviation of logarithm of the grain diameter, lnσg, was almost constant.
The purpose of the present study is to clarify effects of hydrogen diffusion on hydrogen embrittlement of 18%Ni maraging steel. Thin plate specimens were machined after being solution-treated under recrystallizing and unrecrystallizing conditions for austenite. An electrochemical transportation method was carried out in order to measure hydrogen diffusion coefficient D of structure-controlled specimens. The values of D decreased with prior-austenite grain size for the specimens solution-treated under recrystallizing condition for austenite. On the other hand, for the specimens solution-treated under unrecrystallizing condition for austenite, there was almost no influence of the grain sizes on the D values and besides these values were smaller than the recrystallized specimens. The above results were quite consistent with the effects of the prior-austenite grain sizes on the crack growth rate in the stage II region. Consequently it was elucidated that the hydrogen diffusion predominantly controlled the crack growth rate of the hydrogen embrittlement for the maraging steel.
Dissolution of manganese and cobalt and their deposition on Type 304 stainless steel in liquid sodium at 833 K for 3.6×103 ks were examined using a liquid sodium pot. Manganese was easily dissolved in sodium from the iron-manganese alloy specimen and deposited on the steel to form two kind of deposition particles, α-phase (body-centered cubic) composed of iron and γ-phase (face-centered cubic) composed of iron and manganese, respectively. Cobalt which was less easily dissolved than manganese also deposited on the Type 304 stainless steel, giving an iron-cobalt alloy. These three deposition particles corresponded to the precipitation lines of iron-manganese and iron-cobalt phase diagrams at 833 K, respectively. Therefore, the deposition process of manganese or cobalt in sodium was explained as a precipitation process of iron-manganese or iron-cobalt in the solid region of the binary phase diagram. A sodium chromite (NaCrO2) layer was formed on the steel surface.
The standard Gibbs free energy of formation of NiMo2B2 has been determined in the temperature range from 1183 to 1423 K by measuring electromotive forces of a galvanic cell having a solid oxide electrolyte. Also, the standard Gibbs free energy of formation of MoO2 and the Gibbs free energy of mixing of the Ni-Mo binary system, which are necessary to determine the standard Gibbs free energy of formation of NiMo2B2, have been determined in the temperature range from 1183 to 1423 K, The results obtained are as follows: (1) ΔGf°(NiMo2B2)=−250000+19.7T±1000 J/mol (1183∼1423 K). (2) ΔGf°(MoO2)=−567700+160.0T±200 J/mol (1183∼1423 K). (3) The standard Gibbs free energy of formation of the intermediate phase, NiMo, which exists in the Ni-Mo binary system is: (This article is not displayable. Please see full text pdf.)
Electrophoretic deposition of Al2O3 insulation films on tungsten coils was studied by using an in-situ observation technique of the deposition process. Morphological changes of the gel-like hydroxide deposits that were formed on tungsten coils were studied in relation to the electrolyte content of the water-ethanol suspension medium. Tungsten surfaces were covered with gel-like deposits containing Al2O3 particles immediately when the current was passed between tungsten cathode and pure aluminum anode in the water-ethanol suspension medium containing Al3+ and Mg2+ ions. The gel-like deposits were hydroxides of Al and Mg. The shape of gel-like deposits covering tungsten coils changed with the content of Al3+ and Mg2+ ions. The thickness of the deposit decreased with increasing Al3+ ion content and increased with increasing Mg2+ ion content of the suspension.
The values of emf of the following cells involving solid and fused salt electrolytes have been measured in order to obtain the standard free energy of formation of In2O3 in the temperature range from 875 to 1275 K and the thermodynamic data on the liquid Bi-In system for NIn=0.16-0.89 and NIn=0.09-0.87, in the temperature ranges from 877 to 1269 and from 950 to 1200 K, respectively: (This article is not displayable. Please see full text pdf.) The standard free energy of formation of In2O3 was determined as the following equation: (This article is not displayable. Please see full text pdf.) Activities of indium and bismuth by both galvanic cell methods show negative deviations from Raoult’s law over the whole concentration range and the aIn values agree well with the data measured by Niwa et al. and Terpilowski. The activities of both components for the Sb-In system exhibit more negative deviations than those for the Bi-In system, suggesting the larger affinity of indium for antimony than that for bismuth. The peak values of the heat of mixing by emf method using zirconia solid electrolytes is −2.08 kJ/mol at about NIn=0.56.
The rolling workability of sintered chromium, which is very brittle at room temperature was examined as a function of temperature. The present sintered chromium of 99.9% purity was produced by CIP (cold isostatic press) and HIP (hot isostatic press). The specimen could be successfully rolled in a limited temperature range from 673 to 1073 K. This formability characteristic is different from the experimental results found in the upset and the tensile tests in which no upper limit of temperature was found for workability and ductility. The deterioration in rolling at temperatures above 1173 K was caused by rapid cooling of the specimen by the rolls. The temperature of the specimen during rolling decreased greatly in the roll-contact region, while the inner part of the workpiece retained its starting temperature. Hence, the large tensile stress in the rolling direction occurred near the roll-contace material because of a large difference in the flow stress between the roll-contact region and the inner part of the workpiece. The tensile stress was responsible for cracking on the surface of the specimen heated at temperatures above 1173 K. The steel/chromium/steel sandwich plate could be successfully rolled to a large reduction even at temperatures above 1173 K without occurrence of the surface cracks because the steel skins prevented the temperature decrease of the specimen during rolling.
For the purpose of developing a structural steel having a good combination of cold forgeability and machinability, cold upsetting and drilling tests have been carried out for a series of the hypo-eutectoid graphitic steels composed of ferrite matrices and graphite nodules. The upsetting limit of cylindrical specimens with longitudinal notch decreased with increasing amount of graphite up to the volume fraction of 1.4×10−2, and then became almost insensitive to the amount of graphite. The drillability was improved remarkably with increasing amount of graphite, and no difference in drillability was found before and after the cold upsetting. In the steels with less amounts of graphite, the good cold forgeability corresponded to the poor machinability as is usually observed. On the other hand, in the steels with a volume fraction of graphite greater than 1.4×10−2, the machinability could be improved without any deterioration of the cold forgeability.
An investigation is made on the homogenization of microstructure and the improvement of elevated temperature tensile properties in the Ni-base superalloy containing 6.74%Co, 11.15%Cr, 3,12%Mo, 3.25%W, 3.98%Al, 2.74%Ti, 3.93%Nb and Bal.Ni by rheocasting with the rotation of a stirrer at a speed in the range of 20 to 70 rev/s. The results are follows: (1) The torque value remains almost unchanged during the solidification of the alloy with the rotational stirring except its initial stage. The level of torque values increases with the increase in stirrer speed. (2) When the alloy is agitated at 70 s−1 from the start of solidification to above the volume fraction of solid of 0.42, the columnar dendrites are broken up and equiaxed grain structures are formed. However, when the rotational stirring of the alloy at 10 or 70 s−1 is interrupted at the fraction of solid of 0.19, equiaxed dendrites will grow from the primary solid particles in the subsequent process of solidification. (3) When the fraction of solid at the end of the rotational stirring is increased from 0.42 to 0.95, the average primary solid particle size is slightly decreased. (4) The primary solid particle sizes in the alloys agitated from the start of solidification to the fraction of solid of 0.95 at the stirrer speeds of 20, 30, 40, 50, 60, 65 and 70 s−1 are 87±21, 80±16, 75±18, 73±15, 76±14, 72±13 and 66±14 μm, respectively. (5) The elongation values are 91% for the strain rate of 1.67×10−4 s−1 at 1373 K and 70% for the strain rate of 0.83×10−4 s−1 at 1323 K in the alloy agitated at the speed of 70−1 from the start of solidification to the fraction of solid of 0.42 and subsequently solidified without stirring.
The lowest sintering temperature (Tsc) for complete densification of Fe, Co, Ni and Cu ultrafine metal powders (average particle size, 0.02-0.05 μm; oxygen content, 6-15 mass%) was investigated under the pressure up to 400 MPa in H2 gas, and the crystal grain size and hardness of the dense sintered compacts were measured. Under 400 MPa, Tsc for Fe, Co, Ni and Cu powders were about 620, 670, 470 and 470 K, respectively, which were 350∼600 K lower than those under 0 MPa. The minimum average crystal grain sizes of Fe, Co, Ni and Cu dense sintered compacts were as small as about 0.08, 0.21, 0.12 and 0.40 μm, respectively. The highest values of hardness (HV) of the sintered compacts were abut 600, 550, 550 and 130, which were extremely high compared with usual coarsegrained metals. The Hall-petch linear relationship between HV and the inverse of square root of grain size hold for each element.
The effect of cold working on the logarithmic decrement δ and the mechanical properties were investigated for Al-Co alloys containing 0.2 to 10.0%Co. δ and the rigidity modulus G were measured at room temperatures with an inverted torsion pendulum, and the tensile strength σt with an Instron-type tensile testing machine. The heat-treated alloys showed a slight increase in δ by the Co addition, but the value of δ remained as low as 9×10−3. At the same Co concentration the value of δ after furnace cooling was somewhat higher than that after water quenching. By cold working after heat-treatments, the value of δ considerably increased with increasing reduction in cross-sectional area, RA, for all alloys. With the increase in Co concentration, the value of δ after cold working steeply increased at first and above 1%Co, δ showed saturation for small RA or tended to decrease for large RA. Moreover, the alloys cold-worked after furnace cooling were higher in δ than those cold-worked after water quenching. The increment in δ by cold working was considered to be due to a remarkable increase in dislocation density. With increasing Co concentration, both G and σt of the heat-treated specimens increased but σt became almost constant above 2%Co. Cold working after heat-treatments gave a decrease in G and an increase in σt.
The electrical insulating effects of interlayer coating in thin tape wound magnetic cores have been investigated for grain-oriented 50 Permalloy and Supermalloy, treated with different coatings of MgO type ceramics, e.g., MgO, MgCO3 and Mg(OH)2, by a cataphoresis method. Among the various coatings, Mg(OH)2 coatings result in superior qualities in both uniformity and adhesiveness, such that the coatings maintain the interlayer insulation satisfactorily even after annealing in H2 atmosphere at a high temperature such as 1473 K and hinder secondary recrystallization in the cubic texture. The tape wound magnetic cores of grain-oriented 50 Permalloy subjected to the interlayer insulation by Mg(OH)2 coatings to the thickness of about 2 μm exhibit excellent rectangular hysteresis loop characteristics with low coercivity, and those of Supermalloy are high in effective permeability and low in core loss at a high frequency field.
In this work, the formation of Al thin film on the surface of the carbon fiber with chemical vapor deposition of tri-isobutyl aluminum (TIBA) was studied. Experiments were conducted to clarify the effects of TIBA evaporation temperature, argon flow as carrier gas, reaction pressure and temperature on aluminum precipitation rate to the surface of pitch type carbon fiber. The results obtained indicated that the aluminum precipitation rate is accelerated (1) as the rate of argon flow increases under the condition of constant reaction pressure, (2) as the reaction pressure increases under the conditions of the constant argon flow, and (3) as the reaction temperature rises. This implies that the precipitation rate of aluminum depends on the gas velocity, the soluble gas concentration and the reaction temperature. The relatively high pressure makes the film structure rough, while the relatively low pressure makes it smooth.
Magnetic properties of Fe-Cu-M-Si-B (M: Nb, Mo, Ta, W, etc.) alloys prepared by annealing amorphous alloys were investigated for development of new Fe based soft magnetic alloys. In the case of annealing the alloys above the crystallization temperature, excellent soft magnebc properties which correspond to those of Co based amorphous alloys were obtained. Especially, the alloys containing Cu and Nb were superior to the alloys containing other elements. These new alloys were composed of ultrafine grain structure. The alloys were about 10 nm in grain diameter and the main phase of them was presumed to be a bcc Fe solid solution which contains Si and B. This might be attributed to the effect of the bcc Fe solid solution nucleation by Cu and the suppression of the grain growth by Nb. The newly developed alloys are suitable for many kinds of magnetic components such as saturable reactors, choke coiles and transformers because of their excellent soft magnetic properties and high saturation flux density.