A physical model is proposed for the solid/liquid interfacial drag in both globular and dendritic equiaxed solidification. By accounting for the presence of multiple particles and the nonsphericity and porosity of the individual equiaxed crystals, a drag correlation is developed, which is valid over the full range of solid volume fractions. It is shown that neither the solid liquid interfacial area concentration nor the grain size alone is adequate to characterize the interfacial drag for equiaxed dendritic crystals in both the free particle and packed bed regimes; thus, the present model is based on a multiple length scale approach. The model predictions are compared to previous analytical and numerical results as well as to experimental data available in the literature, and favorable agreement is achieved.
The mechanical properties of six highly conductive copper alloys, GRCop-84, AMZIRC, GlidCop Al-15, Cu-1Cr-0.1Zr, Cu-0.9Cr, and NARloy-Z were compared. Tests were done on as-received hard drawn material, and after a heat treatment designed to simulate a brazing operation at 935 °C. In the as-received condition AMZIRC, GlidCop Al-15, Cu1Cr-0.1Zr and Cu-0.9Cr had excellent strengths at temperatures below 500 °C. However, the brazing heat treatment substantially decreased the mechanical properties of AMZIRC, Cu-1Cr-0.1Zr, Cu-0.9Cr, and NARloy-Z. The properties of GlidCop Al-15 and GRCop-84 were not significantly affected by the heat treatment. Thus there appear to be advantages to GRCop-84 over AMZIRC, Cu-1Cr-0.1Zr, Cu-0.9Cr, and NARloy-Z if use or processing temperatures greater than 500 °C are expected. Ductility was lowest in GlidCop Al-15 and Cu-0.9Cr; reduction in area was particularly low in GlidCop Al-15 above 500 °C, and as-received Cu-0.9Cr was brittle between 500 and 650 °C. Tensile creep tests were done at 500 and 650 °C; the creep properties of GRCop-84 were superior to those of brazed AMZIRC, Cu-1Cr-0.1Zr, Cu-0.9Cr, and NARloy-Z. In the brazed condition, GRCop-84 was superior to the other alloys due to its greater strength and creep resistance (compared to AMZIRC, Cu-1Cr-0.1Zr, Cu-0.9Cr, and NARloy-Z) and ductility (compared to GlidCop Al-15).Keywords GRCop-84, AMZIRC, GlidCop Al-15, Cu-Cr-Zr, Cu-Cr, NARloy-Z, Copper, compression, tension, creep, mechanical properties IntroductionGRCop-84 (Cu-8 at%Cr-4 at% Nb) is a newly-developed copper alloy with an attractive balance of high temperature strength, creep resistance, low cycle fatigue life, and thermal conductivity. Our goal is to compare GRCop-84 to similar commercial copper alloys in a consistent manner. Data on alloys such as NARloy-Z, AMZIRC, GlidCop Al-15 low oxygen grade, Cu-0.9Cr, and Cu-1Cr-0.1Zr can be found in the literature. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] However, the test conditions are rarely matching for "apples-to-apples" comparisons. Most literature also deals only with as-received material. The alloys being considered in this work are used in high temperature applications where high thermal conductivity, high strength, and resistance to creep and low cycle fatigue are required. Such applications include high performance metal gaskets, rocket engine combustion chambers, nozzle liners, and various Reusable Launch Vehicle (RLV) technologies. [1] In regeneratively cooled combustion chamber applications, such as nozzle liners, these alloys are subjected to the combustion gas temperatures on the hot side and are cooled by cryogenic hydrogen flow on the back side. The tensile, creep, low cycle fatigue, and compressive strength of GRCop-84 will be compared to those of the existing commercially available alloys shown in Table 1. To compare the properties these alloys would actually have during use, they were tested in the as-received condition and after a heat treatment designed to simulate a typical high temperature brazing...
A combined experimental and numerical study of the horizontal Bridgman growth of pure succinonitrile (SCN) has been performed. The effect of convection on interface propagation and shape is quantified and discussed. Measurements were obtained both under conditions of nogrowth and for a 40 µm/s growth rate. The quantities measured include interface shape and location, melt velocities, and temperature boundary conditions on the ampoule exterior. The melt velocities were measured using a new technique that employed digital cameras to image the locations of seed particles in the melt. The growth front was stable and non-dendritic, but was significantly distorted by the influence of convection in the melt and, for the growth case, by the moving temperature boundary conditions along the ampoule. Both two-and three-dimensional numerical simulations of the growth process were performed. Temperatures throughout the phase change material and ampoule as well as melt velocities were obtained from the simulations. The predicted interface shapes and melt velocities agree well with experimental results. Two different numerical algorithms were used; the utility of each for simulating phase-change problems is discussed. This combined experimental and numerical study provides a database for the validation of phase-change numerical models, in addition to furnishing detailed information about the influence of convection on the Bridgman growth process. In ongoing work, the computer models presented in this study are being used to simulate alloy solidification problems.
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