An accurate measuring system of electrical resistivity has been designed and constructed, and has been applied to determination of transition temperatures in quenched γ-phase Mn–Ni alloys containing 16.5 to 20.5 at%Ni. The Néel temperature as well as the fcc to fct (c/a>1) structure transformation temperature is detectable, and a small change in electrical resistivity due to an orthorhombic distortion is also detected. The magnetic and crystallographic phase diagram for the Mn–Ni alloy system was found to be well confirmed.
The free decay of flexural vibration in (Mn1−XCoX)Cu0.05 metalstable alloys was examined with a frequency of 210–310 Hz and the maximum strain of 1×10−5 as a function of temperature (125 K–370 K) and lattice structure. Only a small peak (SDC\simeq0.1%) near 240 K was found in the damping capacity of fcc alloys, while fct (both with c⁄a<1 and c⁄a>1) and fco alloys showed a high (SDC\simeq12%) but broad peak between 250 K and 280 K as well as a relatively large increase of damping capacity (SDC\simeq2% at 125 K) with decreasing temperature below 180 K. Young’s modulus showed either a broad maximum or a minimum in this temperature range, depending on the alloy concentration. No anomalies were, however, observed in both the damping capacity and Young’s modulus at fcc/fct or fct/fco transition temperatures. As compared with results of other γ-Mn alloys previously reported, these characteristics have been concluded to be essentially common to the γ-Mn alloys. Effects of cold rolling on these properties were further examined. But clarification of the detailed mechanisms of the damping process have not been aimed at.
The fatigue properties of the soluted and the sensitized type 304 stainless steel were investigated in high pressure hydrogen up to 4.0 MPa at room temperature. It is found that both the number of cycles to failure and the fatigue limits of the soluted and the sensitized steel decreased with increasing hydrogen pressure. Typical fatigue fracture modes were observed on a main fatigue crack growth area of the fracture surface, that is, the striations in argon and the transgranular fracture in hydrogen, respectively. It is concluded that the fatigue crack growth is promoted by hydrogen along the boundary surface between the martensite and the austenite.
Grain boundary fracture in molybdenum was investigated by the four-point bending test at 77 K as a function of misorientation angle, by using bicrystals with various 〈110〉 twist boundaries. Main results obtained are as follows: (1) Fracture always occurs at the grain boundary. (2) The fracture strength and strain to fracture markedly depend on the misorientation angle, i.e., the bicrystals of misorientation up to 20° and those of around 70° (Σ3) have much higher fracture strength than the others, and some appreciable plastic strain is observed only for these strong bicrystals. (3) Broadness of the peak in strength plotted against misorientation angle agrees with the predicted value from the Brandon’s equation. (4) There are no peaks in strength around Σ9 and Σ11 coincidence boundaries.
In order to investigate the grain boundary fracture in molybdenum with 〈110〉 symmetric tilt boundaries, the four-point bending test was conducted at 77 K by using bicrystals with various misorientations from 0° to 90°. A stress-strain curve to fracture was measured as a function of misorientation angle φ. Two classes of specimens were used to clarify the impurity effect on the grain boundary fracture: One was as-grown specimens which contained carbide precipitates at grain boundaries and the other was purified specimens in which no precipitates were observed. A marked misorientation dependence of fracture stress and plastic strain to fracture, was observed for the purified specimen; the stress and strain were both much higher for φ=0°–10° (Σ1), around 70° (Σ3, (112) twin boundary) and around 87°(Σ17, (223) twin boundary) than for the other boundaries. The dependence observed for the as-grown specimen was qualitatively similar to, but quantitatively much less than, that for the purified specimen. The misorientation dependence of grain boundary energy (cohesion) and the effect of carbon impurity on this cohesion were discussed.
Emf measurements of the following galvanic cells with beta-alumina (β- and β″-alumina) solid electrolyte were carried out to determine the Na2O activities in the (α+β)- and (β+β″)-alumina: Pt, Au+Au2Na(s)/β- or β″-alumina/(α+β)-alumina, Air, Pt and Pt, Au+Au2Na(s)/β″-alumina/(β+β″)-alumina, Air, Pt. Temperature dependence of the Na2O activity in the beta-alumina was represented by the following equations: logaNa2O=−0.40–12140(K⁄T)(±0.05), (874–1054 K) for (α+β)-alumina and logaNa2O=0.85–11380(K⁄T)(±0.09), (823–1075 K) for (β+β″)-alumina. High temperature stability of the beta-alumina in the SOx (x=2, 3) and CO2 atmospheres were investigated using these activity data. Equilibrium sodium vapor pressure over the beta-alumina was represented by the following equations: log(PNa⁄P\ominus)=−22050(K⁄T)+7.68–1⁄4log(PO2⁄P\ominus), (P\ominus=101325 Pa) for (α+β)-alumina and log(PNa⁄P\ominus)=−21670(K⁄T)+8.31–1⁄4log(PO2⁄P\ominus) for (β+β″)-alumina.
The present authors have previously reported the permanent magnet properties of iron-rich Fe–Pt alloys and a new magnet alloy (Fe-38.5 at%Pt) with a high energy product of 159 kJ·m−3, which was named as Platiron Magnet. In this paper are further studied the effects of additions of Ti, V, Rh, Pd, Ir, Au, Al, Ga and Ge on the magnetic properties of the magnet alloy. The permanent magnet poperties of Fe–Pt alloys can be improved by addition of a small amount of Ti or V. Especially, the alloy containing 60 at% iron, 39 at% platinum and 1 at% titanium shows the highest maximum energy product of 165 kJ·m−3, a coercive force of 360 kA·m−1 and a residual flux density of 1.0 T when aged at 823 K for 1.8 Ms after water-quenching. Further, the alloy containing 60.5 at% iron, 38.5 at% platinum and 1 at% vanadium shows the highest coercive force of 410 kA·m−1, a maximum energy product of 160 kJ·m−3 and a residual flux density of 1.04 T when aged at 773 K for 252 ks after water-quenching. In the case of addition of each of the other elements, however, the permanent magnet properties are remarkably deteriorated. It is presumed that the excellent permanent magnet properties of the Platiron Magnet alloys are related to the existence of the γ1 ordered phase of the Llo-type having high magneto-crystalline anisotropy.
The phase transformation from a sintered eutectic alloy of ε-FeSi and α-Fe2Si5 to β-FeSi2, has been studied by metallographic observations and X-ray quantitative analysis, and by measurements of the resistivity and thermoelectric power. The resistivity increases with increasing amount of β-FeSi2, and two maximum values occur at 1123 and 1133 K in the relationship between the resistivity and the annealing temperature. A drastic decrease in the resistivity is found between the temperatures 1123 and 1133 K. Two different reactions separately occur in the regions below 1123 K and above 1133 K. Below 1123 K β-FeSi2 is formed mainly by the decomposition reaction, α→β+Si, and followed by the subsidiary reaction, Si+ε→β; above 1133 K β-FeSi2, is produced by the peritectoid reaction, ε+α→β. In the former reaction, the complete β-FeSi2 is obtained by an effective annealing at 1113 K for 3.6×104 s.