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Structural changes in pyrolytic graphite accompanying deformation produced by applying stress parallel to substrate examined by electron microscopy and X-ray diffraction
An investigation was conducted to determine the thermomechanical and thermochemical behavior of a high temperature, oxidation resistant, hafnium-20 percent tantalum alloy. The elastic and shear moduli of this alloy were determined in air up to 1000 C and in vacuum up to 2000 C using a mechanical resonance technique. The internal friction of the alloy was measured up to temperatures greater than 1400 C. Room temperature stress-strain behavior of the oxidized and unoxidized alloy was established. The effect of annealing on the elastic and shear moduli of the extruded rod material was investigated. The martensitic-type phase transformation occurring in the alloy was studied using hot stage metallography and electron microscopy. Static oxidation tests were conducted on the alloy at temperatures from 1000 C to 1700 C with weight gain measurements made as a function of time and temperatures. Surface morphology studies were conducted on the oxide coatings formed at the different temperatures using scanning electron microscopy and X-ray diffraction techniques.
Methods for analyzing atmospheric aerosols and particulate contaminants from natural and industrial sources are briefly described. Their development was spurred by interest in cosmic dust investigations. These methods make it possible to analyze individual particles ranging in size from 0.01 to 1000 microns for elemental and mineralogical content. The described methods include transmission electron microscopy, scanning electron microscopy, electron probe microanalysis, X-ray diffraction, optical mineralogy, and density measurement.
The major scientific accomplishments through 1971 are reported for the particle track studies of lunar samples. Results are discussed of nuclear track measurements by optical and electron microscopy, thermoluminescence, X-ray diffraction, and differential thermal analysis.
Titanate phase relations at liquidus temperatures are determined for the CaAl2Si2O8-Fe2TiO4-FeTi2O5 system in contact with metallic iron by reflected- and transmitted-light microscopy, electron microprobe, and X-ray diffraction analyses. Results of critical equilibration runs are presented, various primary phase areas and liquidus isotherms are illustrated, and the geometry of the system is described. Three piercing points are determined, and it is noted that the compositional interrelations among coexisting crystalline and liquid phases as well as the sequence of the various titanate phases are indicative of the significant effects of the various cations on the relative stability of these phases. It is found that Al2O3 exerts a strong stabilizing effect on the phase assemblage of ulvospinel plus ferropseudobrookite relative to ilemite.
An initial investigation of worn surfaces in friction pads and steel rotors used in current aircraft brakes was carried out using electron microprobe and X-ray diffraction analysis. It consists of the topographical study and the analysis of chemical element distribution. Based upon this initial examination, two approaches, microscopic and macroscopic have been conducted to interpret and formulate the wear mechanism of the aircraft brake materials. Microscopically, the wear particles were examined. The initiation and growth of surface cracks and the oxidation were emphasized in this investigation. Macroscopically, it has been found that, for the current copper based brake material sliding against 17-22 AS steel in a caliper brake, the surface temperature raised due to frictional heat is nonlinearly proportional to the load applied and slide time with speed at 1750 rpm. The wear of brake materials is then proportional to this temperature and is also a function of the melting temperature for copper.
Optical microscopy, electron microscopy, and X-ray diffraction were utilized to characterize silicon ribbon structure. Complex twin formation was observed in nearly all ribbons examined. Twins formed in the 110-plane 112-line ribbon orientation appear stable, and this orientation may be preferable when the ribbon is utilized for solar cells. In addition to twinning, grain boundaries and other structural defects were observed in the ribbon material. Hall effect, resistivity, spreading resistance, surface photovoltage, and solar cell electrical/optical measurements were performed on ribbon samples and correlated with structural and ribbon growth characteristics. Only those ribbon samples with either single-crystal structure or with 'parallel' twin formations were capable of solar-cell performance approaching that of Czochralski material.
Various forms of potassium titanate were found to have almost complete resistance to chemical attack in 45 wt % KOH at 150 C (423 K) for up to 9600 hours. Electron microscopy and X-ray diffraction disclosed important differences with respect to fibricity and stability. The octatitanate appeared to possess the best combination of properties. It was concluded that potassium titanate could be produced in a more asbestos-like form. Fiber dispersion is important in matrix manufacture.
The effects of simulated reentry heating on the emittance of TD-NiCr were investigated. Groups of specimens with three different preconditioning treatments were exposed to 6, 24, and 30 half-hour simulated reentry exposure cycles in a supersonic arc tunnel at each of three conditions intended to produce surface temperatures of 1255, 1365, and 1475 K. Emittance was determined at 1300 K on specimens which were preconditioned only and specimens after completion of reentry simulation exposure. Oxide morphology and chemistry were studied by scanning electron microscopy and X-ray diffraction analysis. A consistent relationship was established between oxide morphology and total normal emittance. Specimens with coarser textured oxides tended to have lower emittances than specimens with finer textured oxides.
Metallography, electron microscopy, and X-ray diffraction techniques were employed to study a fragment of the Tishomingo iron meteorite. The results suggest the following thermal-mechanical history: The fragment was originally a large crystal of taenite (gamma). Cooling through the alpha + gamma phase boundary did not result in accompanying precipitation of kamacite (alpha). Transformation to a martensitic structure initiated between -25 and -65 C. Transformation continued as the temperature fell to -75 to -115 C, resulting in approx 80% martensite (alpha-prime). Subsequent shock deformation and thermal aging processes substantially modified the taenite and martensite microstructures. Twins in the retained taenite phase are attributed to shock deformation at a pressure estimated for a single event at about 170 kbar. The existing complex altered martensite structure containing both taenite and kamacite (3-15% Ni) particles was apparently the product of both shock deformation and thermal aging processes. The maximum temperature reached during thermal aging is estimated to be less than 400 C and perhaps below 310 C.
The microstructure of Class I lodestones was investigated by X-ray diffraction and by optical and transmission electron microscopy, and the behavior of lodestone magnetization was studied at temperatures of 4 to 825 K. It was found that intense magnetization is associated with the gamma Fe2O3-Fe3O4 intergrowth. Thermal demagnetization of the lodestone studied was nearly complete at 300 C. The loss of natural remanence was found to be associated with transformation of gamma Fe2O3 to alpha Fe2O3.
A study was undertaken to identify the mechanisms of mechanical property degradation in a Borsic (silicon-carbide coated boron) fiber reinforced Ti-3Al-2.5V composite exposed to elevated temperature. Samples containing 0.45 volume fraction of fibers were exposed, in vacuum, to temperatures from 700 K to 1255 K for times up to 240 hours. Room temperature tensile properties of unidirectional material were determined in both the longitudinal and transverse directions, before and after high-temperature exposure. Electron micro-probe analysis, scanning electron microscopy, and X-ray diffraction were used to determine the compounds formed and the extent of interaction between the boron, SiC coating, and matrix materials.
The sulfation of plasma sprayed calcium silicate in flowing SO2/air mixtures at 900 and 1000 C was investigated thermogravimetrically. Reaction products were analyzed using electron microprobe and X-ray diffraction analysis techniques, and results were compared with thermodynamic predictions. The percentage, by volume, of SO2 in air was varied between 0.036 and 10 percent. At 10 percent SO2 the weight gain curve displays a concave downward shoulder early in the sulfation process. An analytical model was developed which treats the initial process as one which decays exponentially with increasing time and the subsequent process as one which decays exponentially with increasing weight gain. At lower SO2 levels the initial rate is controlled by the reactant flow rate. At 1100 C and 0.036 percent SO2 there is no reaction, in agreement with thermodynamic predictions.
A description is presented of a television detector system which has been designed to accommodate a wide range of applications. It is currently being developed for use in X-ray diffraction, X-ray astrophysics, and electron microscopy, but it is also well suited for astronomical observations. The image can be integrated in a large, high-speed memory system, in the memory of a computer system, or the target of the TV tube or CCD array. The detector system consists of a continuously scanned, intensified SIT vidicon with scan and processing electronics which generate a digital image that is integrated in the detector memory. Attention is given to details regarding the camera system, scan control and image processing electronics, the memory system, and aspects of detector performance.
New interior samples of four Yamato polymict eucrites (Y74159, Y74450, Y75011, and Y75015) have been studied by electron microprobe, transmission electron microscope, and X-ray diffraction techniques, and compared with several samples of the Victoria Land polymict eucrites. These same samples have been analysed using Rb-Sr and Nd-Sm isotopic systematics. Several grains of inverted pigeonite, with blebby augite similar to those in Binda and Moama, have been identified in all four Yamato eucrites. Coarse-grained meso-stasis-rich subophitic basalts, which contain Mg-rich pigeonite (with Fe-rich olivine veinlets) zoned outward to a subcalcic ferroaugite rims, have also been found. These unique clasts were not found in ALH76005, 77302, 78040, 7858, and 78165 and EET eucrites. The tight grouping of Rb/Sr and Sm/Nd ratos, and similar modal compositions of the Yamato group indicate that they are most likely to be pieces from a single fall, and distinct from the ALH and EET groups. However, the Yamato, Allan Hills, and Elephant Moraine groups may sample a few distinct magmas or similar but different source regions on the same parent body.
Lunar sample 77135, an impact melt breccia full of vesicles, has been reinvestigated by electron microprobe and X-ray diffraction techniques and compared with a vesicular melt LL chondrite, Yamato 790964, in an attempt to understand their impact heating processes and subsequent cooling history. Notable similarities between the lunar and chondritic melt breccias include: abundant vesicles, similar pyroxene chemical zoning trends, the presence of variable amounts of clastic material, and similar chemical compositions except for K and Na contents of glass and mesostasis. Some constraints on the cooling history are estimated from Mg-Fe diffusion profiles in olivine and pyroxene. The burial depth of lunar sample 77135 during cooling was 0.2-100 m; the depth for the chondrite was probably smaller. Impact melts were probably produced and a layer of regolith retained on the parent body sufficiently thick to allow the olivines to homogenize during slow cooling.
The yttrium-rich compositions in the Y-Ba-Cu-O system were mapped out in a systematic manner to quantify their magnetic properties and to correlate them with the microstructure and phase composition as determined by scanning electron microscopy and X-ray diffraction analysis. It is found that the microstructure of Y-Ba-Cu-O compositions is a sensitive function of both their composition and processing conditions. Measurements of magnetic susceptibility and maximum (low-field) and remanent magnetization for the system Y:Ba:Cu = x:2:3 show highest values for x = 2. The corresponding structures involve numerous small crystals of Y2BaCuO5 (211) embedded in highly ordered assemblages of continous YBa2Cu3O(7-y) (123) layers.
Mechanical alloying is being investigated as a processing route for the production of aluminide intermetallics. This program involves powder production and characterization, consolidation and thermal treatments and determination of microstructure-property relationships. An attritor mill is being used to produce powder in lots up to 1000 grams and the processing parameters are being systematically varied to establish the optimum milling conditions. The mill is being instrumented to generate data related to the processing to provide a basis for theoretical modeling. Powder is being characterized using thermal analysis, optical and electron microscopy and X-ray diffraction. Particle size distributions and powder density are being determined. Consolidation of the powder is being approached in several different ways including, cold isostatic pressing, sintering, extrusion and hot pressing. The results of the program so far will be presented and future directions discussed.