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Mccay, M. H.

Publications and source records attributed to Mccay, M. H..

11 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1993

The effects of shrinkage flow and gravity level on the onset of convection during vertical directional dendritic solidification of NH4Cl-H2O

A numerical investigation of the conditions influencing the onset of convection during Bridgman vertical directional solidification of NH4Cl- 72 wt percent H2O has been made using a linear stability model. The effects of shrinkage flow and gravity level on the transition from diffusion-dominated to convection-dominated solidification are shown to be significant. Both shrinkage flow opposite the direction of growth and increased gravity levels tend to decrease the stability limits defining the onset of convection for the solidifying NH4Cl-H2O system.

Hopkins, J. A.↗
NASA NTRS1993

Laser Welding Dissimilar Reflective Alloys

This project, jointly sponsored by Rocketdyne and CSTAR, involves the development of laser joining of materials which have heretofore been impractical to bond. Of particular interest are joints between stainless steel and copper and also aluminum 6061 to aluminum 2219. CSTAR has a unique opportunity in this area since both the process and development and diagnostics are of interest to industry. Initial results using the pulse tailored laser welding technique developed in CLA for joining crack sensitive materials have proven promising for the aluminum joints based upon metallurgical and electronic microprobe analysis. A declaration of success requires additional mechanical testing. A CW technique has been applied to the stainless-copper joining with some preliminary success. These joints are of significant interest for aeronautics and rocket propulsion applications and the project is expected to continue.

Mccay, M. H.↗
NASA NTRS1989

Surface tension measurements of aqueous ammonium chloride (NH4Cl) in air

Aqueous NH4Cl's solidification is often used to model metal alloy solidification processes. The present determinations of the magnitude of the variation of aqueous NH4Cl's surface tension as a function of both temperature and solutal concentration were conducted at 3, 24, and 40 C over the 72-100 wt pct water solutal range. In general, the surface tension increases 0.31 dyn/cm per percent decrease in wt pct of water, and decreases 0.13 dyn/cm for each increase in deg C. Attention is given to the experimental apparatus employed.

Lowry, S. A.↗
NASA NTRS1989

Effect Of Solidification Speed On Fatigue Properties

Fast solidification increases fatigue life, but failure distribution becomes less predictable. Report describes effects of rate of solidification on nickel-based super-alloy MAR-M246(Hf) used in turbine blades. Based on experiments in which specimens directionally solidified at 5 cm/h and 30 cm/h, then tested for high cycle fatigue. Specimens also inspected by energy-dispersive x-ray (EDX) analysis and optical and electron microscopy.

Mccay, M. H.↗
NASA NTRS1989

Measurements of diffusion limited solidification at varying gravity

The environment of the NASA KC-135 low gravity aircraft was employed to examine the effects of g-jitter on the growth of a solidification diffusion layer for 28 wt pct NH4Cl-H2O, a metal alloy model material. The hypothesis that jitter (vibrational) effects account for previously observed low gravity growth anomalies was investigated by comparing optical data (central dark ground method) for 10-squared g(e) (earth's gravity) KC-135 growth conditions and 1 g(e) laboratory conditions. Accelerometer data obtained during the flight program showed the KC-135 low gravity environment to have extreme levels of jitters.

Mccay, T. D.↗
NASA NTRS1988

Casting And Solidification Technology (CAST): Directional solidification phenomena in a metal model at reduced gravity

The Casting and Solidification Technology (CAST) experiment will study the phenomena that occur during directional solidification of an alloy, e.g., constitutional supercooling, freckling, and dendrite coarsening. The reduced gravity environment of space will permit the individual phenomena to be examined with minimum complication from buoyancy driven flows.

Mccay, M. H.↗
NASA NTRS1988

Convective effects on directional solidification of a simulated metal alloy

The first significant results of a ground-based experimental program which supports a low gravity space processing Spacelab experiment are reported. The phenomena which precipitate pluming and thus freckling in a metal alloy analog (ammonium chloride and water) are studied in detail and the sequential events leading to massive channeling and convection are optically documented. The pluming is shown to be other than a random burst of unstable fluid from a preferred channel but rather a natural occurrence resulting from a fundamental (Rayleigh-Benard) fluid dynamic instability at the density inversion interface. This extrapolates to critical size parameters appropriate to processing of actual metal alloys.

Mccay, T. D.↗
NASA NTRS1987

Experimental measurement of solutal and thermal layers in unidirectional solidification

An experimental study to evaluate and characterize the effects and causes of convection in the directional solidification of metal alloys is described. The temporal history of the inverted density layers in front of a dendritic interface for directionally solidified ammonium chloride-(72 wt pct) water is presented based on photographic data taken using a laser schlieren system. Data are given for both 1-g and low-g solidification runs, and the stability of the layer is discussed. The reduction of buoyancy effects is shown to be significant, and the possible impact of reducing gravity level on freckling in metal alloys is considered.

Mccay, M. H.↗
NASA NTRS1986

The effect of gravity level on the average primary dendritic spacing of a directionally solidified superalloy

The effect of alternating low (0.01 g) and high (1.8 g) gravity force on the primary spacings in the dendrite structure in a directionally solidified Ni-based superalloy (PWA 1480, containing 5 pct Co, 10 pct Cr, 4 pct W, 12 pct Ta, 5 pct Al, 1.5 pct Ti, and the balance Ni) was investigated using samples solidified in a directional solidification furnace aboard the NASA KC-135 aircraft that made a series of low-g parabolas. The cross-section slices for each growth rate were polished and etched with Kallings II, and the primary dendritic arm spacings were measured using the method of Jacobi and Schwerdtfeger (1976). The arm spacings were found to fluctuate with gravity force, increasing as the gravity level decreased, and growing finer as gravity increased.

Mccay, M. H.↗