Ductile Ribbons Research Articles

Slice-push, formation of grooves and the scale effect in cutting.

Three separate aspects of cutting are investigated which complement other papers on the mechanics of separation processes presented at this interdisciplinary Theo Murphy meeting. They apply in all types of cutting whether blades are sharp or blunt, and whether the material being cut is 'hard, stiff and strong' or 'soft, compliant and weak'. The first topic discusses why it is easier to cut when there is motion along (parallel to) the blade as well motion across (perpendicular to) the cutting edge, and the analysis is applied to optimization of blade geometries to produce minimum cutting forces and hence minimum damage to cut surfaces. The second topic concerns cutting with more than one edge with particular application to the formation of grooves in surfaces by hard pointed tools. The mechanics are investigated and applied to the topic of abrasive wear by hard particles. Traditional analyses say that abrasive wear resistance increases monotonically with the hardness of the workpiece, but we show that the fracture toughness of the surface material is also important, and that behaviour is determined by the toughness-to-hardness ratio rather than hardness alone. Scaling forms the third subject. As cutting is a branch of elasto-plastic fracture mechanics, cube-square energy scaling applies in which the important length scale is (ER/k (2)), where E is Young's modulus, R is the fracture toughness and k is the shear yield strength. Whether, in cutting, material is removed as ductile ribbons, as semi-ductile discontinuous chips, or by brittle 'knocking lumps out' is shown to depend on the depth of cut relative to this characteristic length parameter. Scaling in biology is called allometry and its relationship with engineering scaling is discussed. Some speculative predictions are made in relation to the action of teeth on food.

Secondary recrystallization in Fe–6.5 wt% Si alloys by internal friction

Samples, Fe–6.5 wt% Si, were obtained by quenching from the liquid using the single roller method. Under these conditions, ductile ribbons (20×1×0.05) mm 3 were obtained. The initial structure of the as-cast alloy, characterized by X-ray diffraction, was mainly a disordered bcc α phase. Under suitable thermal treatments, annealing at 1373 K during 1 h, the second recrystallization took place. The annealed sample contained precipitates of the ordered B2 Fe–Si phase with a (1 0 0)–(1 1 0) double texture that changed the magnetic properties of the alloy. To analyze the microstructural processes associated with the recrystallization texture, internal friction (IF) spectra were obtained employing an inverted torsion pendulum at frequencies around 1 Hz. The spectra, obtained as a function of the heating temperature, were analysed for the initial as-cast and thermally treated samples. The results show that the recrystallization process is dominated by two grain boundary contributions: a low temperature (∼800 K) peak associated with the free movement of grain boundaries and a peak at around 1000 K where the grain boundary mobility is determined by the interaction with Si solute atoms.

Effect of impurities on amorphous ribbon forming and crystallization characteristics in the Fe-B-Si system

The effect of manganese and carbon impurities on ribbon forming characteristics and crystallization behavior in Fe 80.8− x Mn x B 13.6Si 5.6− y C y , has been studied. The source of these impurities was carbothermic ferroboron, iron powder or steel. Alloy 1 ( x = 0.1, y = 0.2) gave good quality ductile ribbons of 35 ± 2 μm thickness, but Alloy 2 ( x = 0.5, y = 2), with higher manganese, gave brittle ribbons. Differential scanning calorimetric studies on amorphous ribbons at different heating rates showed two step crystallization for both alloys, i.e first α-Fe crystallizes, followed by tetragonal Fe 3B at higher temperature. These phases were confirmed by X-ray diffraction and transmission electron microscopy. The effect of manganese content on peak temperatures was studied. Higher manganese content (0.5 a/o) increased the peak temperatures for the crystallization of α-Fe at all heating rates. This trend was not observed for the second peak at heating rates of 0–20 K/min. However, heating rates exceeding 20 K/min caused the same effect as observed in α-Fe. The activation energies for α-Fe crystallization were not affected by a higher manganese content. For the crystallization of Fe 3B the activation energy was 299 kJ/mol for Alloy 1, which is lower than for 2605 SC or Alloy 2. The average and local Avrami exponents determined by isothermal annealing experiments were the same (≈2.5) in both alloys for the first-stage crystallization. The average Avrami exponent was the same for the second stage of crystallization. The local Avrami exponent, which showed nonuniformity, indicates that multiple mechanisms for crystallization are operational.

Preparation of ductile AlGe soldering foils by PFC technique

Ductile ribbons in the thickness range of 28–40 μm can be produced with the PFC process and subsequent annealing. The solder of composition Al 77Ge 23 shows optimum properties relating to manufacturing and soldering at 450°C. The soldering experiments with silicon-chips and metallic supporting substrates show that the soldering joints are equivalent to those produced with gold or AuSi solders. Soldering demands neither soldering flux nor inert gas. The economy of the solder follows from the substitution of gold as well as from the low density of AlGe (one fifth that of gold) which enables many times more soldering joints to be produced with the same mass of solder.

Production of metal powder from rapidly solidified ductile ribbons

Ductile metallic ribbons have been reduced into small particles by a blade cutter mill designed to cut and slash the ribbons. The resulting powders are suitable for subsequent P/M processing. This batch process and the results obtained with a Zn-20.5Al-0.7Cu alloy are described.

Some novel melt-spun superconducting materials (abstract)

A new class of Fe-, Co-, Ni-, Cu-, and Ge-based ductile ribbons in which an amorphous matrix containing less than 12 vol. % of a fine dispersion of 0.1–3-μm size particles of immiscible elements M=Pb, Bi, Sn, or In have been produced by a modified melt-quenching technique. The Fe- and Co-based alloys containing Bi and Pb are found to be ferromagnetic above room temperature and also superconducting at temperatures in a range 7–9 K depending on the alloy. The saturation magnetization in these usual alloys range from 92 emu/gm for Co-Si-B-Pb-Bi to 15 emu/g for Fe-P-Pb-Bi at 77 K. At the superconducting transition the resistivity typically is found to drop by 2–3 orders of magnitude with a transition width ∼0.5 K before the ‘‘zero’’ resistance value is reached. In all the alloys studied the T dependence of the resistivity shows a typical metallic behavior despite its high magnitude (a few thousand μΩ cm in some cases). Extremely high values are found for the upper critical fields (1.6–1.72 T at 4.2 K) with critical current densities typically around 1.3×107 A m−2 at 4.2 K. For Ge-Pb-Bi-Sn Hc2 values of 5 T are obtained at 3 K. Along with detailed studies of magnetic and superconducting properties, extensive TEM, and x-ray characterization data will also be presented. Attempts to explain the above described behavior in terms of proximity, percolation, and surface properties at the dispersed Pb, Bi particles are found to be unsatisfactory. As far as we know there exists no theory that can explain the co-existence of ferromagnetism and superconductivity of the type described above. Time permitting, we will also discuss our recent work on high Tc oxide materials produced by melt-quenching techniques. Thus amorphous composite materials exhibiting unique and useful characteristics which cannot be achieved for homogeneous amorphous alloys can be produced by melt quenching. These materials are of importance both for scientific and engineering points of view.

Effect of melt spinning on the structure and superconducting transition temperature of “Nb 3Si” alloys

Melt spinning with a sample suspension device was used to rapidly solidify Nb-Si alloys ranging from 18 to 24 at% Si. Amorphous ductile ribbons were obtained for all of the above compositions; the superconducting transition temperatures T c were 4.0 to 4.4 K. Furthermore, by accurate control of the quenching rates, metastable A-15 crystallites embedded in an amorphous matrix were obtained; the ribbons were semi-ductile and T c onset of the A-15 phase was 5.6 K.