Showing papers on "Equiaxed crystals published in 1975"

Separation of second phase particles in spheroidized 1045 steel, Cu-0.6pct Cr alloy, and maraging steel in plastic straining

Abstract: Experiments were performed on spheroidized 1045 steel, Cu-06 pct Cr alloy, and maraging steel containing respectively Fe3C, Cu-Cr, and TiC particles of nearly equiaxed shape The local interfacial stresses for separation of these particles during plastic deformation were evaluated by the methods described in the two preceding papers The results show that the interfacial strengths for these particles in their respective matrices are 242, 144, and 264 ksi In the spheroidized steel the average diam of the separated particles is distinctly larger than the average diam of the whole population This is quantitatively explained by the enhanced interfacial stresses developed in regions of above average volume fraction of second phase which frequently occur in very dense populations of particles No such effect was observed in the other two systems which is consistent with their much lower volume fraction of second phase Some tension experiments have also been performed with the spheroidized 1045 steel at elevated temperature, giving results qualitatively similar to those at room temperature

Crystallographic Properties of LaB 6 Formed in Molten Aluminium

Abstract: By cooling slowly a homogeneous solution of La, B and Al from about 1200°C, single crystals of lanthanum hexaboride (LaB6) were precipitated, and their lattice constant, purity and growh-orientations were investigated. The products are needle-like crystals with a rectangular cross section, thin plate-like crystals and cubical crystals. The LaB6 crystal has the lattice constant 4.1564A and contains impurities of less than 0.01 wt%. More needle-like crystals with [110] growth direction tend to be formed than any crystals with other shapes. For the typical needle-like crystals, the crystal thickness depends on the cooling rate. The average size is 0.1 to 0.5 mm square in cross section and about 5 mm in length.

Hot‐Working of Aluminum Oxide: II, Optical Properties

Abstract: Polycrystalline Al2O3 fabricated into plates or shapes by hot-working techniques exhibits high in-line transmittance from 0.4 to 5.5 μm. Examination of the product by an inverse pole figure technique demonstrated a strong {0001} texture normal to the pressing direction for both equiaxed and textured microstructures. The crystallographic texture was attributed to the dominance of basal slip in deformation. A comparison of transmissivity in the 2 principal directions of a forged plate strongly suggested that a reduction of birefringence resulting from the crystallographic texture was partially responsible for the high transmissivity. The absorption coefficient at 4.5 μm was 0.15 mm-1, ∼ that for sintered Al2O3 and 5 times that for sapphire

Dense sintered boron carbide containing beryllium carbide

Abstract: A polycrystalline boron carbide sintered body containing beryllium carbide with a density ranging from 85% to 96% of the theoretical density of boron carbide and having a uniform microstructure of equiaxed grains.

The Mechanical Behavior of Rapidly Solidified Al-Al2Cu and Al-Al3Ni Eutectics at Elevated Temperatures

Abstract: The mechanical behavior of semi-continuously cast Al-Al2 Cu and Al-Al3 Ni eutectics has been studied in tension at temperatures between 350–500 deg C (Al-Al2 Cu) and 500–625 deg C (Al-Al3 Ni). The microstructures of both eutectics were found to be relatively unstable at elevated temperatures, even in the absence of deformation, as a result of their fine, imperfect microstructures in the as-cast condition. During deformation spheroidization occurred rapidly, so that the fibrous/lamellar reinforcement was largely eliminated. During hot deformation of the Al-Al2 Cu eutectic, the “degenerate” lamellar structure was gradually replaced by an equiaxed microduplex structure via polygonization of both phases. This structure subsequently demonstrated superplastic flow, with an increase in the strain-rate sensitivity index from about 0.3 to about 0.5. Final failure resulted from nucleation of cavities at Al2 Cu - Al2 Cu - Al triple junctions with cavity growth along Al2 Cu-Al2 Cu grain boundaries. The Al-Al3 Ni eutectic did not exhibit superplastic flow probably due to the lower volume fraction of the Al3 Ni phase, which “spheroidized” during deformation. A process for fabricating wire by a continuous process from the melt is outlined.

Deposition rate and substrate temperature effects on the structure and properties of bulk-sputtered OFHC Cu and Cu--O.15 Zr

Abstract: Bulk-sputtered OFHC Cu and Cu-0.15 Zr used as inner walls of advanced regeneratively cooled thrust chambers are evaluated as to microstructure, surface topography, and fractography. It is found that under conditions of low substrate temperature, crystallite size and openness of the structure increase with increasing deposition rate for both materials. At elevated temperatures, an equiaxed ductile structure of OFHC Cu is produced only at low deposition rates; at higher deposition rate, open structures are observed with recrystallized equiaxed grains within large poorly bonded crystallites. The Cu-0.15 Zr alloy sputtered from the hollow cathode using a diode discharge shows open-type structures for all conditions evaluated. The use of a triode discharge in generating a dense non-voided structure of Cu-0.15 Zr is discussed.

The effect of thermal exposure on the mechanical properties of the directionally solidified superalloy TRW-NASA VIA

Abstract: The nickel-base superalloy TRW-NASA VIA was studied in the directionally solidified (DS) condition utilizing metallographic and residue analysis techniques in conjunction with mechanical property tests to determine the effect of thermal exposure on the microstructure and mechanical properties. Exposure conditions of 1000 h at temperatures from 1500 to 1900°F (816 to 1038°C) were investigated. Four minor phases (two varieties of MC, MgC and M3B2) plus gamma-prime were identified in the gamma matrix of the DS material. Significant variations were observed to occur in the mechanical properties with thermal exposure. Microstructural evaluation indicated that as in the equiaxed condition these variations were due principally to gamma-prime agglomeration or ripening. Comparison of the findings from the DS and the equiaxed process conditions indicated several factors which contributed to the property enhancement observed in the DS condition. These included the virtual elimination of the transverse grain boundaries by the DS process which improved the 1400 (760°C) and 1800°F (982°C) properties, the heterogeneous distribution of the blocky and the spherical-like gamma-prime which primarily improved the room temperature and the 1400°F (760°C) strength properties, the generally larger gamma-prime size as well as the intragranular columnar form which improved the ductility properties and the longitudinal grain boundaries containing the stabilized Hf enriched MC and the MgC carbides which in conjunction with the intergranular gamma-prime formation also improved the ductility properties.

Microbands in 80% Drawn Copper Single Crystals With and Starting Orientations

Abstract: Copper single crystals with the starting orientations and were drawn 80%. In the core region of the rods the orientations and the microstructures were investigated. The stable crystal had a structure consisting of equiaxed cells and microbands which were formed parallel to the {111} planes with the exception of the {111} plane in the cross section of the rod. The orientation was not entirely stable; the beginning of some orientational changes was observed at a high degree of deformation. In the parts with stable orientation a cylindrical cell structure was found with the long axes parallel to the drawing direction. Single microbands formed locally. Dislocation tangles around them finally developed, which lead to a change of the orientation.

Growth of single crystals of aluminum nitride

Abstract: The growth mechanism and the growth condition of single crystals of aluminum nitride (AlN) prepared by the sublimation method are studied in relation with their morphology. The whiskers of AlN, whose growth directions are perpendicular to the (10-10) plane (a-type whiskers), the (10-11) plane (b-type whiskers) and the (0001) plane (c-type whiskers) grow through the VLS mechanism, iron acting as liquid-forming agent in the mechanism. The growth directions of whiskers depend on the growth temperature; the c-type whiskers grow above 1550°C, the a-type above 1700°C and the b-type above 1850°C. Blade-shaped crystals with large (0001) faces (a-type crystals) grow from lateral surfaces of the a-type whiskers.Prismatic crystals with large prismatic (10-10) faces (P-type crystals) and tabular crystals with large (0001) faces (T-type crystals) grow above 1900°C in the atmosphere free from iron. The P-type crystals grow in the circumstance of high purity. The T-type crystals grow in the atmosphere comprising carbon mono-oxide.Growth spirals are observed on the (0001) face of the T-type crystals. The growth steps parallel to the c-axis and a-axis observed on the (10-10) face of the P-type crystals.

Preparation and characterization of splat-cooled R-Co compounds

Abstract: Rapidly quenched alloys of Sm‐Co, Pr‐Co and MM‐Co of the approximate composition RCo5 were prepared by splat cooling droplets of the alloys in a modified arc furnace. X‐ray diffraction analysis indicated a fine grained structure and also the possibility of some texture in the splat‐cooled samples. Microscopic examination of the alloys in a light microscope revealed an equiaxed fine grained structure with a grain size of 2 to 5 μm.Magnetic measurements were performed on a vibrating sample magnetometer. Coercive force values were 5000 Oe for SmCo5, 1500 Oe for PrCo5 and 1250 Oe for MMCo5. Thermomagnetic curves were obtained on the splat‐cooled alloys by plotting magnetization versus temperature up to 900C. The data indicated that all the alloys were single phase with Curie points in fair agreement with published values for these compounds. Splat‐cooled PrCo5 was found to be unstable near its Curie temperature.Rapidly quenched alloys of Sm‐Co, Pr‐Co and MM‐Co of the approximate composition RCo5 were prepared by splat cooling droplets of the alloys in a modified arc furnace. X‐ray diffraction analysis indicated a fine grained structure and also the possibility of some texture in the splat‐cooled samples. Microscopic examination of the alloys in a light microscope revealed an equiaxed fine grained structure with a grain size of 2 to 5 μm.Magnetic measurements were performed on a vibrating sample magnetometer. Coercive force values were 5000 Oe for SmCo5, 1500 Oe for PrCo5 and 1250 Oe for MMCo5. Thermomagnetic curves were obtained on the splat‐cooled alloys by plotting magnetization versus temperature up to 900C. The data indicated that all the alloys were single phase with Curie points in fair agreement with published values for these compounds. Splat‐cooled PrCo5 was found to be unstable near its Curie temperature.

Effect of Additions of Coarse Grains and Fibers on the Densification of a Sinterable Sic

Abstract: This note reports the effects on densification of independent additions of coarse equiaxed SiC grains and fibrous SiC that were mixed with fine beta-SiC to develop a duplex microstructure with improved toughness. The fine-matrix SiC did not contain excess boron and carbon. The equiaxed CVD beta-SiC was introduced in the fine beta-SiC matrix material in amounts of 5 and 10 wt%. Results indicate that the CVD beta-SiC, which is quite coarse, exhibits little indication of sinterability. The effect of these coarse-grained and fibrous additions on the sinterability of fine beta-SiC may result from a geometric type of interaction. This interpretation is reinforced by X-ray diffraction of the powders and sintered pellets via monochromatic CuK-alpha radiation; the diffraction patterns of the sintered composite structures are virtually a combination of those of the components. The addition of nonsinterable SiC to the sinterable material slightly reduces sinterability, the larger particles interacting geometrically with the fine matrix material to prevent complete densification.

Skylab M551 metals melting experiment

Abstract: The objectives of the M551 Metals Melting Experiment were to: (1) study behavior of molten metal, (2) characterize metals melted and solidified in the low gravity space environment compared to one-gravity of earth, and (3) determine feasibility of joining metals in space. The experiment used the electron beam (EB) and chamber of the M512 apparatus to make a dwell puddle and a melt in a rotating disc of varying thickness. Hence, the EB performed cut-through, full and partial penetration melts, in addition to a resolidified button. The three disc materials were aluminum 2219-T87, 304 stainless steel, and pure tantalum to provide a wide range of density and melting conditions. Observations to date include the proof that EB welding, cutting, and melting can be done successfully in low gravity. Earlier, some welding authorities had postulated that without gravity the EB would force the molten puddle out of contact. However, the experiment proved that surface tension forces predominate. From the viewpoint of cast-solidification, small, equiaxed grains in Skylab specimens compared to large, elongated grains in ground based specimens were observed. The former are thought to be associated with constitutional supercooling and nucleation where the latter are associated with dendritic solidification. In further support of the more equiaxed grain growth in Skylab, symmetric subgrain patterns were frequently observed where there was much less symmetry in ground based specimens.