Michiaki Hagiwara

Mechanical properties of Fe-Si-B amorphous wires produced by in-rotating-water spinning method

Amorphous wires with high strength and good ductility have been produced in Fe-Si-B alloy system by the modified melt-spinning technique in which a melt stream is ejected into a rotating water layer. These wires have a circular cross section and smooth peripheral surface. The diameter is in the range of about 0.07 to 0.27 mm. Their Vickers hardness (Hv) and tensile strength (σf) increase with silicon and boron content and reach 1100 DPN and 3920 MPa, respectively, for Fe70Si10B20, exceeding the values of heavily cold-drawn steel wires. Fracture elongation(εf), including elastic elongation, is about 2.1 to 2.8 pct. An appropriate cold drawing results in the increase of σf and εf by about eight and 65 pct, respectively. This increase is interpreted to result from an interaction among crossing deformation bands introduced by cold drawing. The undrawn and drawn amorphous wires are so ductile that no cracks are observed, even after closely contacted bending. Further, it is demonstrated that the σf of the Fe75Si10Bl5 amorphous wire increases by the replacement of iron with a small amount of tantalum, niobium, tungsten, molybdenum, or chromium without detriment to the formation tendency of an amorphous wire. Such iron-based amorphous wires are attractive as fine gauge, high strength materials because of their uniform shape and superior mechanical qualities.

The critical thickness for the formation of Ni-Si-B amorphous alloys

In order to estimate the critical sample thickness for the formation of an amorphous phase, a new melt-spinning type quenching apparatus has been constructed which enables the roller revolving at high speeds, such as 5000 rpm, to stop in a very short time of 1 to 2 s. A long ribbon of Ni-Si-B alloy with a continuous variation in thickness in the range of about 30 to 300 μm has been produced in one ejective operation using this modified quenching apparatus. The critical thickness, taken as that thickness where we just observed a crystalline particle by optical microscopy at the magnification of 100 times, is the largest (225 μm) for Ni75Si8B17, decreases with increasing or decreasing silicon and boron contents and is about 30 to 40 μm near the boundary between amorphous and crystalline phases. Further, the effect of ribbon thickness on crystallization temperature, the heat of crystallization, the activation energy for crystallization, hardness and ductility has been examined and it has been demonstrated that the disordered state differs with cooling rate even in an amorphous alloy with the same alloy composition.

Preparation, mechanical strengths, and thermal

Ni-based amorphous wires with good bending ductility have been prepared for Ni75Si8B17 and Ni78P12B10 alloys containing 1 to 2 at. pct Al or Zr by melt spinning in rotating water. The enhancement of the wire-formation tendency by the addition of Al has been clarified to be due to the increase in the stability of the melt jet through the formation of a thin A12O3 film on the outer surface. The maximum wire diameter is about 190 to 200 μm for the Ni-Si (or P)-B-Al alloys and increases to about 250 μm for the Ni-Si-B-Al-Cr alloys containing 4 to 6 at. pct Cr. The tensile fracture strength and fracture elongation are 2730 MPa and 2.9 pct for (Ni0.75Si0.08B0.1799Al1) wire and 2170 MPa and 2.4 pct for (Ni0.78P0.12B0.1)99Al1 wire. These wires exhibit a fatigue limit under dynamic bending strain in air with a relative humidity of 65 pct; this limit is 0.50 pct for a Ni-Si-B-Al wire, which is higher by 0.15 pct than that of a Fe75Si10B15 amorphous wire. Furthermore, the Ni-base wires do not fracture during a 180-deg bending even for a sample annealed at temperatures just below the crystallization temperature, in sharp contrast to high embrittlement tendency for Fe-base amorphous alloys. Thus, the Ni-based amorphous wires have been shown to be an attractive material similar to Fe- and Co-based amorphous wires because of its high static and dynamic strength, high ductility, high stability to thermal embrittlement, and good corrosion resistance.

The structural relaxation behavior of Pd48Ni32P20, Fe75Si10B15 and Co72.5Si12.5B15 amorphous alloy wire and ribbon

Abstract The structural relaxation behavior of Pd48Ni32P20, Fe75Si10B15 and Co72.5−Si12.5B15 amorphous alloys of different shapes, wire and ribbon, was examined with a differential scanning calorimetry measurement to assess the difference in the quenched-in structure between the wire and ribbon samples produced by different quenching methods. Despite the fact that the diameter of the wire is larger by about 3–5 times than the thickness of the ribbon, the integrated heat release associated with structural relaxation (ΔH) was considerably larger for the wires ( ⋍100 μ m diameter ) than for the ribbons (about 20–30 μm thickness) mainly due to the larger heat evolution at lower temperatures for the former. This unexpected result was interpreted to originate from the inherent differences in the solidification process of the ejected melt as well as the manner of cooling after solidification. The extremely good ductility of the wire samples found in the previous experiment was interpreted as due to the high degree of frozen-in disorder in the amorphous wire. As it may be expected, either an increase in the wire diameter or in the ribbon thickness results in a significant decrease in the heat of structural relaxation and a rise of the onset temperature of the structural relaxation.