H. Soda

Microstructure and mechanical properties of Fe–Cr–C eutectic composites

Abstract In the present investigation, an Fe–Cr–C eutectic alloy was prepared from industry-grade materials and subjected to unidirectional solidification (UDS), through which new types of fibre reinforced composites, eutectic composites, were generated. The composites obtained were examined using X-ray diffraction (XRD), electron microprobe and field emission scanning electron microscopy (FESEM). According to XRD, the composites consist of three phases, i.e. γ, M 7 C 3 and trace amounts of M 23 C 6 . While the compositions of γ and M 7 C 3 were determined by electron microprobe analysis, M 23 C 6 was not detected due to the limited amount present. Fibre morphology was studied as a function of solidification rate ( R ) using FESEM. Fibre diameter, spacing and regularity decreased with increasing solidification rate; however, the volume fraction of fibres remained essentially constant at around 32%. Mechanical testing was carried out on both eutectic composites and as cast alloys. The tensile strength of Fe–Cr–C eutectic composites varied parabolically with solidification rate. When R was 58 mm h −1 , a maximum strength of 2300 MPa was reached, which is about seven times as strong as that of conventional high chromium cast iron of similar composition. Two other alloys with hyper- and hypo-eutectic compositions were included in the present investigation for comparison purposes. It was found that the presence of primary phases significantly diminished fibre regularity and, therefore, the material strength.

Pilot-scale casting of single-crystal copper wires by the Ohno continuous casting process

Single-crystal copper wires, 4 mm in diameter, have been produced using the horizontal Ohno continuous casting (OCC) process and a casting regime for the production of single crystals has been established. It was found that at lower casting speeds (< 50 mm min−1), single-crystal wires with no visible substructures were produced. However, at casting speeds above 50 mm min−1, the wire contained unidirectional subtexture and occasional stray crystals. The orientation of crystals parallel to the casting direction tended to be ť001〉 at higher casting speeds (∼ 120 mm min−1); at lower casting speeds, the orientation appeared to be random. It was also found that the solidifying wire recrystallized as it emerged from the mould if local strains were inflicted upon the cast surface by mould-strand friction.

Microstructure and properties of a bismuth-indium-tin eutectic alloy

A ternary eutectic alloy with a composition of 57.2%Bi, 24.8%In and 18%Sn was continuously cast into wire of 2 mm diameter with casting speeds of 14 and 79 mm min−1 using the Ohno continuous casting process. The microstructures and mechanical properties of the wires were compared with those of statically cast specimens. Extensive segregation of massive bismuth crystals, bismuth complex structures, and tin rich dendrites was found in specimens which were statically cast. The bismuth complex-regular structures, which are a ternary eutectic constituent, existed along the boundaries of the BiIn dendrite cells forming a double binary eutectic. In the continuously cast wires, primary tin dendrites coupled with a fine bismuth phase were uniformly distributed within the Bi-In alloy matrix. With this novel, net-shape, casting process, the formation of massive bismuth crystals, bismuth complex-regular structures and BiIn eutectic dendrite cells was prevented, resulting in a more uniform microstructure which was in contrast to the heavily segregated structures of the statically cast specimens. These differences in structure significantly affected the mechanical properties. The continuously cast wires exhibited considerable ductility in contrast with the statically cast specimens which had lower toughness and exhibited cleavage fracture with little or no elongation at higher strain rates.

The characteristics of single crystal bismuth wires produced by the Ohno continuous casting process

Bismuth wires approximately 2 mm in diameter were produced by the heated mould Ohno Continuous Casting process and their mechanical characteristics evaluated. It was found that cast wires produced under all speed conditions from 30 to 170 mm min−1 were single crystals. Cast wires with an angle between the cleavage plane and wire axis of less than about 40° were significantly more ductile than those with an angle of over 57°. The former could be bent repeatedly before fracture occurred whereas the latter fractured after only a single bend. It was also found that the bismuth wires with a cleavage angle of less than 45°, exhibited tensile elongations up to about 130%.

Development of net-shape cast aluminium-yttrium alloy wires and their solidification structures

Cast-aluminium-1.5–7 wt% yttrium alloy wires were produced by the heated mould (Ohno Continuous Casting) process with a typical casting speed of 1.1 m min-1. Using a 2 mm diameter channel bore and positioning the solidification front outside the mould, it was possible to cast wires of 1.6–1.9 mm diameter with uniform chemical composition along the length of the wire. Cast wires contained directionally solidified cells or dendrites of α-aluminium with metastable Al4Y and β-Al3Y phases in intercellular or interdendritic regions. At higher casting speeds (>1.1 m min-1), the predominant metastable phase was found to be Al4Y.

Studies of the solid–liquid interface location during heated mould continuous casting of metals and alloys

Abstract With the industrial implementation of the Ohno continuous casting (OCC) process, many investigations have been carried out on both the fundamental and practical aspects of the process. This paper reviews some of the research, focusing on crucial processing conditions that influence the location of the solidification front in the horizontal Ohno continuous casting system. The effects of the solid–liquid interface position with respect to pure metals, and the liquid + solid (mushy) zone in the case of alloys, on the quality of the cast products have been studied.

SiC particulate-reinforced, aluminium-matrix composite rods and wires produced by a new continuous casting route

Abstract The feasibility of applying the Ohno continuous casting (OCC) process for fabricating net-shape MMC welding rods and wires has been examined using Al-Si and Al-Cu-Si alloys containing 8–11 vol% SiC particles. It was confirmed that MMC rods 4 mm in diameter and wires 2 mm in diameter could in fact be produced by the OCC process. For both rods and wires, it was found that the distribution of SiC particles was relatively uniform. It was also found that an angle-entry channel must be used to avoid clogging of the channel inlet. Furthermore, faster casting speeds assisted particle incorporation into the wire. Casting speeds employed were between 0.2 and 1.1 m min −1 .

Al-CuAl2 eutectic structure in unidirectionally solidified rods by the Ohno continuous casting process

Abstracts are not published in this journal

A new method for continuous casting of particulate reinforced metal matrix composite wires

Abstract The horizontal Ohno continuous casting (OCC) process has been used to examine the possibility of casting net-shape metal matrix composite (MMC) wires, ∼2 mm in diameter. The foundry alloy, Al-7%Si-0.4%Mg (A356) containing ∼ 11 vol.%SiC particles was used for this study. It was confirmed for the first time that net-shape MMC wires with relatively uniform particle distribution could in fact be produced by the OCC process. At lower casting speeds (0.15-0.2 m min −1 ), an external force, induced by impeller stirring in the mould cavity, was necessary in order to assist particle flow into the narrow mould channel and thus ensure incorporation of particles within the wires. At higher casting speeds of about 1 m min −1 , particles were incorporated without external force. It was observed that the distribution of particles within the matrix was independent of the refinement of the microstructure when the dendrite arm spacing was smaller than the particle size.

Thick-aluminum-coated optical fibers: fabrication and sensor application

A continuous casting method has been used to produce thick aluminum coatings on optical fibers, allowing the production of fibers with coating thicknesses between 0.5 and 1.5 mm and lengths of 1 - 3 m. The thickness is determined by the mold channel diameter and the length is chosen arbitrarily. Such thick metallic coatings with unidirectional grain structures improve the mechanical strength of glass optical fibers and allow fibers to be embedded successfully in concrete without additional attention. A polarimetric type of optical fiber sensor implemented with a strand of thick-aluminum-coated birefringent optical fiber to sense dynamic load is described and a new method for evaluating the polarimetric sensor response is presented.