Chilled Layer Research Articles

Effect of Microstructure on Mechanical Properties and Fracture Toughness of Aluminum Alloy Die Castings.

The effect of microstructure, especially DAS II (Secondary Dendrite Arm Spacing) and chill layer in ADC10 aluminum alloy die castings on the tensile properties, the fracture toughness and the crack propergation is examined by preparing the die castings which have different DAS II and different thickness of chill layer cast under several casting conditions by cold chamber die casting machine. The results are as follows. (1) The tensile strength increases with the decrease in DAS II and there is the Hall-Petch relation between DAS II and 0.2% proof stress. While DAS II doesn't affect the fracture strain. (2) As a crack propagates through the boundary between α-phase and eutectic Si crystal, the increase in DAS II makes the fracture surface be rougher and it causes the increase in the fracture toughness. (3) The tensile strength and the surface hardness of chill layer are higher than substrate. It is possible for the reason to be not only relaxation of stress concentration due to small DAS II but also strengthening by solid solution due to the larger amount of occluded copper and magnesium.

熱膨張抑制埋没材を用いたチタン鋳造 第２報 練和液が表面反応層に与える影響

We discussed the relation between the behavior of the reaction layer and the concentration of the colloidal silica solution as the mixing liquid, on the surface layer of the pure titanium crowns that was produced by using the phosphate-bonded thermal expansion inhibited, investment, and compared it with the phosphate-bonded investments on the market as well.The results were as follows:1.There was a hardened layer in the surface layer of cast crowns, and the hardness showed the greatest value in the condition of 40% colloidal silica concentration.2.In the surface layers of metallic textures, there were chill layer and columnar structure layer in that order from surface.3.There was a poor Tilayer on the surface. The thickness of the layer increased accordingly to the increase in colloidal silica concentration.4.In the poor Ti layer, there were O, Si and P.5.Si and P were observed correspondingly in the cellular boundary in a string form.6.Not only the refractory material but also the concentration of colloidal silica solution as the mixing liquid influenced the behavior of the reaction layer.

The microstructure of plasma arc cold-hearth melted Ti-48Al-2Mn-2Nb

The purpose of this paper is to show the results of some work at the IRC in Materials for High Performance Applications at the University of Birmingham into the effect of processing and process parameters on the microstructure, macrostructure and chemistry of 100 mm diameter single plasma-melted ingots of a gamma-based titanium aluminide (Ti-48at%Al-2at%Nb). The microstructure of the asmelted bars is almost completely lamellar and consists of a chill layer of fine prior alpha grains at the surface and larger columnar grains growing into the centre ofthe bar. These microstructural features show little variation with processing conditions. The orientations of the alpha grains have been used to determine the effect of plasma torch current and ingot withdrawal rate on melt pool shape under a variety of operating condtions and it has been established that, at typical operating conditions, the ingot withdrawal rate has a more significant effect on melt pool depth than the plasma torch currrent, especially at faster withdrawal rates. Chemical analyses has shown that there is negligible net loss of any of the major alloying elements, although the degree of as-cast chemical homogeneity needs to be increased in the light of the extreme microstructural sensitivity. Further investigation has shown that one major cause of inhomogeneity is macrosegregation is macrosegregation induced by short-term variations in melt pool shape. The implications of these results for the processing of titanium aluminides are then discussed

Solidification Structure and Segregation in Cast Ingots of Titanium Alloy Produced by Vacuum Arc Consumable Electrode Method.

The solidification structures and segregation of the VAR cast ingots of alpha+beta titanium alloys were investigated by using a new etching technique and CMA analysis.Main results were summarized as follows:(1) The fine structures of the solidification were revealed by immersing the specimens in an advanced hydrofluoric acid etchant.(2) The metallographic structure consist of the chilled layer, the columnar grain structure in its inner zone and the equi-axis grain structure in the central zone.(3) The etch pit and shrinkage cavity lines intersect perpendicularly to the growing directions of the columnar grains. And these lines correspond to the interface of solid-liquid phases under solidification. This parallel lines show intermitted solidification.(4) In Ti-6Al-6V-2Sn alloy with 0.7% Fe and 0.7% Cu, the segregation of these elements was observed in the final solidification zone, which is referred to so called beta flecks.(5) To prevent segregation, the authors proposed a melting method in which faster solidification is maintained by making the edge diameter of the consumable electrodes smaller, as the hot-topping of VAR.

Transient infrared transmission spectroscopy

Transient infrared transmission spectroscopy is a new method that can acquire analytically useful transmission spectra from moving, optically thick solids. No sample preparation is required. The spectra are of sufficient quality for accurate quantitative compositional analysis. The method works by the creation of a thin, short-lived, chilled layer at the sample surface. Blackbody-like thermal emission from the bulk of the sample is selectively absorbed as it passes through the chilled layer, so the transmission spectrum of the layer is superimposed on the observed thermal emission. Spectra of polycarbonate, beeswax, and copolymers of methyl and butyl methacrylate are presented. Compositional analysis of the methacrylate copolymers with a standard error of prediction of only 0.87 mol % is demonstrated.

Thermo-Physical Characteristics of Glaciers — Toward a Rational Classification

Thermo-Physical Characteristics of Glaciers — Toward a Rational Classification

Thermo-Physical Characteristics of Glaciers — Toward a Rational Classification

Thermo-Physical Characteristics of Glaciers — Toward a Rational Classification

鋳鉄の共晶集団発生におよぼす諸元素の影響

In chilled cast iron, the depth of the ledeburite layer, that of mottled structure and its coarseness of it, depend on the number of eutectic cells formed at different distances from the chill end. In the present investigation, the number of eutectic cells was counted on vertical sections of wedge castings of various compositions. It is shown that the number of eutectic cells increases as the cooling rate increases till ledeburite begins to form. The cell number is far larger in the hyper-eutectic alloys than in hypo-eutectic ones. Phosphorus to 0.4% increases the number but more phosphorus decreases it. Silicon increases the number. Manganese and chromium decrease the number and widen the mottled part and coarsen the mottled structure making the size of flake graphite uniform. Sulfur, tellurium and oxygen remove the maximum point of cell number more slowly cooled part and increase the number, accordingly increase the chilled layer without widening the mottled part and refine the structure, and change the flake graphite to fine undercooled graphite. When manganese and sulphur coexist, the effects of both the elements appear in proportion to their balance. Titanium decreases the cell number and refine the graphite structure, but the structure is peculiar because the ledeburite containing titanium decomposes rather quickly after solidification.

ダイカストにおける離型剤の挙動について

The behavior of die lubricant during casting in a diecasting process has not been fully investigated. Small amounts of HCl solution of radioactive H/sub 3/PO/sub 4/ were added to the die lubricant mechanically, and the radiographs of the surface and the inner part of the casting were taken after solidification. Comparatively large amounts of radioactive lubricant were applied. Zinc alloy ZAC No. 1 was cast in the dies. The results obtained were as follows: (1) The lubricant travelled with the flow front of the molten metal through the die cavity and accumulated at the place where the movement of molten metal came to end or remarkable turbulent motion occurred. (2) A large amount of lubricant was entrapped in the casting and distributed comparatively uniformly. (3) The chilled layer of casting occluded hardly any particles of the lubricant. (4) The entrapping of lubri cant increased with the rise of casting temperature and with the increase of gate area. (auth)

Fundamental studies on semi-continuous casting of aluminium alloys

Using the continuos casting apparatus, alumiminium-copper 4% slabs were made under various conditions, and the author investigated the segregation that appeared in the slabs obtained. The results are as follows: The degree of segregation is very low when the conditions of casting-casting speed, casting temperature, descending speed and cooling speed-are suitable. The stsucture of the slabs is shown in photo. 3, in which fine granular structure can be seen just as was expected from the diagram of the 1st Report, Fig. 27.Phenomenon of periodic segregation, appeared in the surface of continuous casting slabs, has attracted our attention since the same problem was reported by G. Siebel in 1953. And the author studied the periodic segregation of 2S aluminium ingots, which was cast by the apparatus shower in Fig. 4. The effect of casting temperature, decending speed, sump height, cooling speed, mould materials and impurities (Fe, Si) of 2S aluminium on the periodicity of the segregate band are determined, and it is found that the shorter the periodicity of the segregate bandies, the smoother is the surface of the ingot. Furthermore, macro and micro structure and chemical analysis of ingots are examined.From these results, the mechanisum of the periodic segregation can be explained by using our schematic diagram of the segregation (Fig. 27.). When the ingot is cooled from the mould wall, chill layer appears on the surface of the ingot and the 1st, and 2nd, inverse segregation occurs. By this time, the periodically segregated band does not appear on the surface of the ingot. As the ingot shrinks and leaves the mould wall, the cooling speed of the ingot decreases. Then columnar layer appears on the surface of the ingot and only the 2nd. inverse segregation occurs and sweat appears. Periodically segregated band seems to be the same thing as this sweat.

Features of the Firn on Upper Seward Glacier St. Elias Mountains, Canada

Particular attention is devoted to diagenetic changes within firn, leading to an increase in density and producing structures such as ice layers, lenses, and glands. Density increases irregularly downward in the Seward firn, with layers of exceptionally low density underlying impermeable horizontal ice masses. The mean rate of density increase with depth in the first 50 feet is 0.0054 per foot, being more rapid-0.01 per foot-in the first 20 than in the last 30 feet, where it is 0.0023 per foot. The rate of density increase in time varies with depth and with the season. Mean density of the 1948-1949 firn layer increased by 0.10 in ten weeks during the summer of 1949, but mean density of the 1946-1947 layer at a depth of 15-18 feet increased only 0.021 in a year. On the upper Seward, a geo-physically temperate glacier, the increase of firn density is caused about 25 per cent by meltwater freezing and about 75 per cent by compaction-settling within the zone of annual chilling, the upper 40-50 feet. Horizontal layers and lenses of ice in firn are formed by freezing of meltwater that has percolated downward and collected above or moved laterally along impermeable horizons. An estimated 20-25 per cent of the Seward firn is converted to solid ice by this process before passing beyond the depth of annual chilling. Ice glands-crude vertical columns of ice within the firn-are likewise attributed to the freezing of meltwater that has been concentrated along channels extending downward into the firn. The process is pictured as occurring in two stages: first the development of a water-rich condition without much freezing, followed by freezing of the entire mass as a unit, rather than as a process of incremental growth produced by alternate meltwater invasions and repeated freezings along a single channel. As ice layers and lenses are thickest and most numerous near ice glands and extend horizontally from them, a common origin is indicated. These bodies of ice form within the firn during spring when the winter's chilled layer is being ameliorated by the heat given up through freezing of the meltwater that has percolated downward from the surface.

Thermal Regimen of Firn on Upper Seward Glacier, Yukon Territory, Canada

Abstract Temperatures were measured within the firn and ice of the upper reaches of the Seward Glacier (referred to in this paper as the “upper Seward Glacier”) to a depth of 204 ft. (62.2 m.) by means of thermohms and a Wheatstone bridge. Thermal boring proved a feasible means of penetrating this glacier. The winter’s chilled layer here develops a thickness of 40–50 ft. (12.2–15.2 m.) and attains temperatures of at least −13° C. Deterioration of the chilled Iayer is rapid and irregular in the final phase and is attributed largely to freezing of percolating melt water. Melt water exerts such a powerful influence on thermal regimen that bodies of firn in environments with mean annual temperatures below freezing may, nonetheless, be geophyaically temperate because of extensive warming by melt water in summer. In both 1948 and 1949, the annual chilled layer on the upper Seward Glacier disappeared within the first 10 days of July. The slow development and rapid deterioration of diurnal crusts on firn and the lag effects at depth reproduce in miniature the behavior of the annual chilled layer. On the basis of its thermal regimen the upper Seward Glacier is geophysically temperate.

Thermal Regimen of Firn on Upper Seward Glacier, Yukon Territory, Canada

AbstractTemperatures were measured within the firn and ice of the upper reaches of the Seward Glacier (referred to in this paper as the “upper Seward Glacier”) to a depth of 204 ft. (62.2 m.) by means of thermohms and a Wheatstone bridge. Thermal boring proved a feasible means of penetrating this glacier. The winter’s chilled layer here develops a thickness of 40–50 ft. (12.2–15.2 m.) and attains temperatures of at least −13° C. Deterioration of the chilled Iayer is rapid and irregular in the final phase and is attributed largely to freezing of percolating melt water. Melt water exerts such a powerful influence on thermal regimen that bodies of firn in environments with mean annual temperatures below freezing may, nonetheless, be geophyaically temperate because of extensive warming by melt water in summer. In both 1948 and 1949, the annual chilled layer on the upper Seward Glacier disappeared within the first 10 days of July. The slow development and rapid deterioration of diurnal crusts on firn and the lag effects at depth reproduce in miniature the behavior of the annual chilled layer. On the basis of its thermal regimen the upper Seward Glacier is geophysically temperate.

CAUSE OF PINHOLES AND SOME RELATED DEFECTS IN ENAMEL COATINGS ON CAST IRON*

The confusion in identifying hydrogen as the predominating cause of certain defects in enamel on cast iron has been due largely to the close association of carbon and hydrogen in cast iron and steel. The principal relation of carbide and graphite to enameling defects is the release of hydrogen from the carbon during enamel firing. The much-discussed “chill layer” therefore is important chiefly because this layer often contains hydrogen that is bound to the carbon in the cementite. Experiments show that when hydrogen is absent, regardless of the depth or nature of the surface chill, no pinholing or blistering results during firing at 725°C. Sources of the hydrogen that causes the defacement are found chiefly in melting and in casting. The low oxygen pressure of molten cast iron favors hydrogen absorption. Moisture in the atmosphere, in the charge, or chemically combined in the rust on scrap provides the greatest quantities of the gas, and moisture and organic materials in the mold are also prolific sources of hydrogen for absorption by the iron. At ordinary temperatures, rusting is often harmful. Flushing the melt with a dry, hydrogen-free gas, such as nitrogen, removes the dissolved hydrogen, and defects during subsequent enameling will not occur unless hydrogen is obtained later from other sources. Chipping phenomena probably are caused chiefly by hydrogen effusion, just as are analogous defects in sheet-steel enameling.