Shigeteru Isa

Preparation of iron-nickel based metal-metalloid amorphous powders by mechanical alloying

Abstract Powders of crystalline, elemental iron and nickel metals and metal-metalloid systems such as Feue5f8B, Feue5f8P, and Feue5f8Si alloys were mechanically alloyed to obtain the alloys of compositions Fe40Ni40 P14B6 and Fe39Ni39Si10B12 (at. pct) by high energy ball milling. X-ray diffraction traces of both the powders of Fe4)Ni40P14B6 and Fe39Ni39Si10B12 synthesized by mechanical alloying for 700 ks or so showed halo-patterns typical of amorphous materials. The crystallization enthalpy of the former powder thus produced, measured by differential scanning calorimetry, was also almost the same as those of the liquid-quenched sample of the same composition. This suggests that amorphization in metal-metalloid systems, i.e. ductile-brittle systems, like Fe40Ni40P14B6 is fully achieved by ball milling alone using high milling energy and metalloid elements as their alloys with metals.

Preparation of Fe–Ni-Based Metal-Metalloid Amorphous Alloys by Mechanical Alloying and Mechanical Grinding Methods

Using a high energy ball mill, alloys of Fe40Ni40P14B6 and Fe40Ni40B20 were synthesized from crystalline, elemental iron and nickel metals and iron-metalloid alloys such as Fe-B and Fe-P by mechanical alloying (MA). Powders of the Fe40Ni40P14B6 alloy were also prepared from the cast ingot products by mechanical grinding (MG). Each of the MA and MG powder products showed a halo pattern typical of amorphous materials in the X-ray diffraction trace, and the crystallization enthalpy of the Fe40Ni40P14B6 MA powder, measured by differential scanning calorimetry, was almost the same as that of the melt-quenched sample of the same composition.

Activation energies for crystallization of amorphous FeNiPB alloys

Abstract A method of calculating the thermal activation free energy (thermodynamic barrier) and diffusion activation free energy for crystallization of an amorphous alloy is proposed. In the calculation the solid-liquid surface free energies given in the present study are employed. An example of its application is made to the amorphous Fe80−xNixP14B6 alloy and it is quantitatively shown that the crystallization of this alloy system is a diffusion-controlled process.

Estimation of free energies of crystallization of amorphous alloys

Abstract A new method of calculating the Gibbs free energy change Δ G c on crystallization of an amorphous alloy is proposed and discussed. Data used here are the thermal properties such as the heat of crystallization of the amorphous alloy, easily obtained with ordinary experimental equipment for thermal analysis, and the ones, such as the heat of fusion and heat capacity of the alloy calculated additively from the thermodynamic data of the components. It is shown that the values of Δ G c calculated by the present method give excellent estimates from results of statistical analyses of errors included in them and from those of the application of the method to the amorphous Au 81.4 Si 18.6 alloy in which the Δ G c value is available.

Warm consolidation of spray-quenched amorphous NiFe-based alloy powders

Abstract Spray-quenched amorphous powders of the alloy Ni49Fe29P14B6Al2 were consolidated by uniaxial warm die pressing into disc samples at different temperatures T below the crystallization temperature Tx under a compacting pressure σ of 0.98 GPa. The homogeneous-to-inhomogeneous transition temperature Tx of deformation of the powders was determined from analysis for the ln e vs. 1/T plot (where e is the strain rate of the powders during compaction). Densification of compacts of the present alloy has been found to proceed markedly as the compacting temperature exceeds the temperature Tp, from observations of the cross-sections of compacts; there were only a few voids in the compacts produced from amorphous powders below 46 μm in size at a temperature approximately 30 K above Tp. These results suggest that densification of the compact of an amorphous alloy powder by warm consolidation is achieved even at temperatures several tens of kelvins above Tp, i.e. well below Tp, if, in particular, the size and shape of the powder used and the compacting pressure and time are appropriate.

Some considerations on wetting behaviour in liquid-alloy-substrate-metal systems

Abstract A study on the wetting behaviour in liquid nickel-based-alloy(L)-substrate-solid-metal(S) systems has been performed by means of a spray-quenching technique using various substrate metals such as copper, nickel and aluminium. An expression calculating the interchange energy ω, corresponding to the interaction energies between solid and liquid metal atoms arising from the formation of the Sue5f8L interface, with the aid of the heat of mixing of the binary solution composed of the solid and liquid component metals is proposed. The values of ω evaluated by using the expression for the respective substrate metals clearly correlated with those of the specific surface Sw and thickness tf of sprayquenched flaky powders; when the ω value decreased (namely, the atomic bonding force in the Sue5f8L interface increased), the value of Sw increased and, in contrast, that of tf decreased. Therefore, the value of ω evaluated in this work may be employed as a criterion for selecting a substrate metal in accordance with desirable characteristics of the quenched products.

FREE ENERGY CHANGES ON CRYSTALLIZATION OF AMORPHOUS (Fel-xNix)80Pl4B6 ALLOYS

The Gibbs free energy change λGC on crystallization of an amorphous (Fel-xNix)80P14B6 alloy. 0–10 ≤ x ≤ 0.90, is calculated by a method, previously proposed by the present authors, using the thermal analysis data of the amorphous alloy and the thermodynamic data of the components. An anomalous behavior in x = 0.20 − 0.50 seen in the |λGC| versus × relation is explained on the assumption that the structure of crystallized products transfers from bcc to fee phase in such a composition range as in case of amorphous (Fel-xNix)83B17 alloys indicated in the literature. It is also shown that the |λGC| versus × relation with two minima near x = 0.15 and 0.50–0.60, substantially agrees with the composition dependence of the glass-formability and the thermal stability in amorphous state of the present alloy.

SURFACE-SMOOTHING AND DENSIFICATION OF SPRAY-QUENCHED AMORPHOUS ALLOY SHEETS BY WARM-ROLLING

An experimental study of surface-smoothing and densification of amorphous alloy sheets fabricated by spray-quenching and warm-rolling has been performed on an iron-nickel based alloy. The rolling system consists basically of a two-high mill and an electric furnace containing the mill. Amorphous sheets of the alloy were prepared by using the spray-quenching equipment previously reported by the present authors. Amorphous sheets thus obtained were rolled with the aid of the rolling system at temperatures up to the crystallization temperature. From surface – roughness measurements and metallographic examinations of rolled sheets, it is shown that surface-smoothing and densification of the sheets was successfully achieved.