Solidification behaviour of eutectic and near eutectic aluminum-copper alloys

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Metallurgy, 1963.Includes bibliographical references (leaves 101-103).by Pradeep Rohatgi.M.S

Directional solidification of aluminum-nickel eutectic alloys using electroslag remelting

Attempts were made to produce directionally solidified, specifically grain aligned Al-6 wt pct Ni eutectic alloy using a laboratory scale ESR unit. For this purpose sand cast alloy electrodes were electroslag remelted under different mold conditions. The grain structure of the ingots obtained from these meltings showed that insulated silica molds gave the best vertical alignment of grains along the length of the ingot. The NiAl3 fibers within the grains tended to fan out and there was only a preferred alignment of fibers along the growth direction under the conditions of our experiments. The ESR parameters most suitable for vertical alignment of eutectic grains have been identified. In some electroslag remelting trials ingots were grown on a seed ingot. This resulted in a fewer vertical grains compared to the case when no seed ingot was used. The sand cast specimen of the eutectic exhibited a maximum tensile strength of around 88.2 MN/m2 (9.0 kg/mm2) whereas conventional ESR using water cooled mold gave strength value of 98.0 MN/m2 (10 kg/mm2). The directionally solidified ESR material showed longitudinal tensile strength as high as 213.7 MN/m2 (21.8 kg/mm2) which could be further increased to 220.6 MN/m2 (22.5 kg/mm2) by using the seed ingot. The average growth rate was varied between 5 to 25 mm/min during electroslag remelting in this study. The flow stresses, tangent modulus and ultimate tensile strength of directionally solidified eutectic increased with increasing growth rates

Dendritic solidification of aqueous solutions.

Massachusetts Institute of Technology. Dept. of Metallurgy. Thesis. 1964. Sc.D.Sc.D

Development of Lead-Free Copper Alloy Graphite Castings. Annual Report for the Period January Through December 1996

Centrifugal casting of Copper alloys containing graphite particles established the feasibility of making hollow cylindrical castings. In theses castings, the graphite particles are segregated to the inner periphery making them well suited for bearing applications because of the lubricity of the graphite particles. The recovery of graphite is found to be around 90%. Chemical analysis shows that the average concentration of graphite particles near the inner periphery is 13 vol.% (3.5 wt.%) and 16.3 vol.% (4.54 wt.%) for castings made from melts originally containing 7 vol.% (2 wt.%) and 13 vol.% (3.5 wt. %) graphite particles, respectively. Hardness tests show that as the volume fraction of graphite particles increases, the hardness values in the graphite rich zone is found to be widely scattered. The results indicate that it is feasible to centrifugally cast copper alloys containing dispersed graphite particles to produce cylindrical components with graphite rich inner periphery for bearing and plumbing applications

A study of dermatoglyphics in club foot

Background:Development of dermatoglyphics pattern is under genetic control and it is established that aetiology of club foot is partly environmental and partly genetic. So study of dermatoglyphics pattern in club foot patient may become a diagnostic tool to know the development & inheritance of this clinical disorder.  Methods:A total of 42 male child aged b/w 1-8 year were included, for obtaining the palmar and finger tip print standard ink method suggested by Kilgariff was used, and each palmar and finger print were examined for important parameters like loops, whorls, arches, a-t-d angle, a-b ridge count and TFRC count. Then results were tabulated and analysed statistically.Results:Frequency of whorls increase in both hands significantly, frequency of arches and ulnar loops decrease significantly, frequency of radial loops increase in right hand and decrease in left hand but difference was not significant. TFRC count was reduced significantly and no significant difference was found in a-t-d angle and a-b ridge count.Conclusion: Dermatoglyphics is a genetically determined reliable marker for detecting the incidence of club foot. Merely by identifying the dermatoglyphics pattern of couples with family history of club foot may be at risk of having their offspring affected, and they can be diagnosed early and preventive measures can be taken.

Life support systems analysis and technical trades for a lunar outpost

The NASA/JPL life support systems analysis (LISSA) software tool was used to perform life support system analysis and technology trades for a Lunar Outpost. The life support system was modeled using a chemical process simulation program on a steady-state, one-person, daily basis. Inputs to the LiSSA model include metabolic balance load data, hygiene load data, technology selection, process operational assumptions and mission parameter assumptions. A baseline set of technologies has been used against which comparisons have been made by running twenty-two cases with technology substitutions. System, subsystem, and technology weights and powers are compared for a crew of 4 and missions of 90 and 600 days. By assigning a weight value to power, equivalent system weights are compared. Several less-developed technologies show potential advantages over the baseline. Solid waste treatment technologies show weight and power disadvantages but one could have benefits associated with the reduction of hazardous wastes and very long missions. Technology development towards reducing the weight of resupplies and lighter materials of construction was recommended. It was also recommended that as technologies are funded for development, contractors should be required to generate and report data useful for quantitative technology comparisons

Characterization and microstructural modifications of a pressure die cast eutectic aluminum-silicon alloy-graphite composite

The present investigation was carried out to see if intricate shaped castings can be made from a eutectic Al-Si (BS LM13) alloy dispersed with 5.5 mass% graphite particles by pressure die casting technique. A bushing spring guide (BSG) component used for electrical applications was selected for the purpose. The study involved the characterization of a few properties e.g. hardness, density and electrical resistivity of the pressure die cast (PDC) composite and their comparison with that of the gravity die cast (GDC) one. The influence of heat treatment on the microstructure of the PDC composite has also been studied. Visual examinations revealed that the components were perfect in shape and pore free indicating that the technique could be a promising route to synthesize graphitic aluminium alloys into intricate shapes. Machined sections of the PDC components indicated reasonably uniform distribution of graphite particles in various regions of the former. This was also confirmed by the quantitative analysis of the graphite content recovered from the dissolved specimens. The variation in hardness, density and electrical resistivity of the composite was quite less agreeing well with better uniformity of distribution of graphite particles in the matrix. The matrix microstructure of the PDC composite was considerably refined over the one processed by GDC technique, although the morphology of the microstructural constituents remained unchanged. The higher rate of solidification in this case was found to be responsible for the improvement in the uniformity of graphite distribution in the matrix and the microstructural refinement. Reduced secondary dendritic arm spacing (DAS) further confirmed a higher rate of solidification as a result of applying the pressure. Improvement in the graphite/matrix interfacial bonding was found to be one of the interesting features of pressure application. This was attributed to the increased solubility of the dissolved gases in the matrix and squeezing out of the entrapped gases from the latter under the conditions of applied pressure during solidification. The graphite particles were found to have fractured in this case probably due to the possible application of a combination of impact, shear and compressive stresses under the influence of the applied injection pressure. Heat treatment of the PDC composite was found to have brought about significant and useful modifications in the matrix microstructure at the little loss in properties like hardness, density and electrical resistivity

Improving Interferometric Null Depth Measurements using Statistical Distributions: Theory and First Results with the Palomar Fiber Nuller

A new "self-calibrated" statistical analysis method has been developed for the reduction of nulling interferometry data. The idea is to use the statistical distributions of the fluctuating null depth and beam intensities to retrieve the astrophysical null depth (or equivalently the object's visibility) in the presence of fast atmospheric fluctuations. The approach yields an accuracy much better (about an order of magnitude) than is presently possible with standard data reduction methods, because the astrophysical null depth accuracy is no longer limited by the magnitude of the instrumental phase and intensity errors but by uncertainties on their probability distributions. This approach was tested on the sky with the two-aperture fiber nulling instrument mounted on the Palomar Hale telescope. Using our new data analysis approach alone-and no observations of calibrators-we find that error bars on the astrophysical null depth as low as a few 10-4 can be obtained in the near-infrared, which means that null depths lower than 10-3 can be reliably measured. This statistical analysis is not specific to our instrument and may be applicable to other interferometers

Propagation of AC magnetic field through high-T<SUB>c</SUB> coatings

Studies on the propagation of AC magnetic field through plasma-sprayed superconducting Y1Ba2Cu3O7-x coatings show that complete shielding is achieved up to a certain critical magnetic field strength H0. Increase in the thickness or Jc of the specimen increases the H0 value. Flux-trapping occurs in the specimen at high frequencies and the frequency at which it occurs increases with increase in specimen Jc

Eutectic Colony Formation: A Stability Analysis

Experiments have widely shown that a steady-state lamellar eutectic solidification front is destabilized on a scale much larger than the lamellar spacing by the rejection of a dilute ternary impurity and forms two-phase cells commonly referred to as `eutectic colonies'. We extend the stability analysis of Datye and Langer for a binary eutectic to include the effect of a ternary impurity. We find that the expressions for the critical onset velocity and morphological instability wavelength are analogous to those for the classic Mullins-Sekerka instability of a monophase planar interface, albeit with an effective surface tension that depends on the geometry of the lamellar interface and, non-trivially, on interlamellar diffusion. A qualitatively new aspect of this instability is the occurence of oscillatory modes due to the interplay between the destabilizing effect of the ternary impurity and the dynamical feedback of the local change in lamellar spacing on the front motion. In a transient regime, these modes lead to the formation of large scale oscillatory microstructures for which there is recent experimental evidence in a transparent organic system. Moreover, it is shown that the eutectic front dynamics on a scale larger than the lamellar spacing can be formulated as an effective monophase interface free boundary problem with a modified Gibbs-Thomson condition that is coupled to a slow evolution equation for the lamellar spacing. This formulation provides additional physical insights into the nature of the instability and a simple means to calculate an approximate stability spectrum. Finally, we investigate the influence of the ternary impurity on a short wavelength oscillatory instability that is already present at off-eutectic compositions in binary eutectics.Comment: 26 pages RevTex, 14 figures (28 EPS files); some minor changes; references adde