Showing papers on "Microstructure published in 1972"

Ultrafine-grained microstructures and mechanical properties of alloy steels

Abstract: Ultrafine-grained microstructures can be developed in a variety of alloy steels by coldworking followed by annealing in theα +γ region. Because the annealing temperatures are relatively low and the recrystallized structure is two-phase, grain growth is restricted. Specimens with grain sizes in the range 0.3 to 1.1 μ.m (ASTM 20 to 16) were obtained in manganese and nickel steels by annealing 1 to 400 hr at temperatures between 450° and 650°C (840° to 1200°F). The expected improvement in yield strength through grain refinement was observed in almost all alloys. Other tensile properties depend on factors such as grain size, austenite stability, and specimen geometry, that determine which of three types of plastic behavior will occur. Transformation of austenite during straining improves the mechanical properties of ultrafine-grained specimens.

Synthesis and Mechanical Properties of Stoichiometric Aluminum Silicate (Mullite)

Abstract: Highly dense translucent polycrystalline bodies of stoichiometric aluminum silicate (mullite) were obtained by vacuum-hot-pressing of high-purity submicron mixed oxide powders. The powders were prepared by the hydrolytic decomposition of mixed metal alkoxides. X-ray diffraction and electron microscopy indicated that the initially amorphous needlelike fine particulates transform into highly crystalline orthorhombic mullite at ∼1200°C. Optimum hot-pressing conditions were 5 kpsi and 1500°C for 30 min. Densities within experimental error of the theoretical value of 3.19 g/cm3 were obtained. A typical microstructure consisted of fine interlocking needlelike grains arranged in an overall mosaic or “jigsaw” pattern. Microprobe traverses across the samples indicated homogeneous dispersion of SiO2 in the AlO3 matrix. Room-temperature mechanical properties were measured and correlated with the microstructure and crystal structure of the ceramic compact. A slightly higher melting temperature than has been previously reported was observed for the 3Al2O3·2SiO2 studied. All specimens exhibited a smooth surface finish and excellent thermal-shock resistance from 1200°C to room temperature.

Structure and Thermomechanical Properties of Partially Stabilized Zirconia in the CaO-ZrO2 System

Abstract: Partially stabilized zirconia (PSZ) ceramics in the system CaO-ZrO2 were characterized. The microstructure, as revealed by optical microscopy, consisted of grains of pure ZrO2 distributed in a matrix of fully stabilized material. Electron microscopy showed that the matrix grains have a complex substructure of 1000-A domains of cubic and monoclinic ZrO2. The grains appeared to fit Ubbelohde’s concept of a hybrid single crystal. Evidence obtained indicated that the substructure provides an effective stress-relieving mechanism during thermal shock. It is proposed that initiation of phase inversion in pure ZrO2 domains, even at subtransition temperatures (by thermal stresses), creates an extremely large microcrack density. On the basis of Hasselman’s thermal-shock criterion, only quasi-static crack propagation occurs during thermal shock of PSZ; evidence is presented to support this concept.

Cold‐Pressing and Low‐Temperature Sintering of Alkoxy‐Derived PLZT

Abstract: Multiorganometallic compounds were used to prepare high-purity submicron-size lead lanthanum zirconate-titanate (PLZT) powders which can be consolidated at low sintering temperatures to high-density piezoelectric and electrooptic ceramic bodies. Simultaneous hydrolytic decomposition of lead isoamyloxide, lanthanum isopropoxide, and zirconium and titanium tertiary amyloxides produced quaternary titanate powders with particle sizes of 75 to 300 A and analyzed purity of 99.92%; the major contaminant was Na from an intermediate reaction product. Homogeneity and stoichiometry of the powders before and after processing were demonstrated by electron microscopy and chemical analysis. High-temperature X-ray diffraction indicated an amorphous material up to ∼600°C, where the crystalline phase was first observed. Powders prepared in this manner sintered to high-density fine-grained transparent bodies with uniform microstructure. The experimental results suggest that less rigorous consolidation methods are required with high-purity homogeneous precursor materials with fine particle size.

The Effect of Substrate Temperature on the Structure of Titanium Carbide Deposited by Activated Reactive Evaporation

Abstract: A change in substrate temperature produces a marked change in the microstructure, preferred orientation, and microhardness of TiC deposits. At low temperatures (∼500 °C) the structure consists of tapered crystallites and changes to a structure consisting of columnar grains at the higher temperatures (∼1000 °C). The high temperature deposits exhibit very high microhardness values (∼4500–5000 kg/mm2 KHN).

Environmental hydrogen embrittlement of an α-β titanium alloy: Effect of microstructure

Abstract: Study of environmental hydrogen embrittlement of a Ti-6 Al-4 alloy as a function of test displacement rate and of variations in alpha-beta microstructure Embrittlement in low-pressure (about 1 atm) gaseous hydrogen was inversely dependent on test displacement rate and strongly dependent on microstructure At a given displacement rate, microstructures having a continuous alpha-phase matrix were less severely embrittled than those having a continuous beta-phase matrix Further, brittle fracture occurred in the former microstructures by transgranular cleavage and in the latter microstructures by intergranular separation These observations are consistent with previous studies made on slow strain-rate embrittlement of hydrogen-charged titanium alloys and are explained in terms of relative hydrogen transport rates within the alpha-phase and beta-phase titanium

Preswitching electrical properties, ‘forming’, and switching in amorphous chalcogenide alloy threshold and memory devices

Abstract: Results are presented on the preswitching current-voltage characteristics, the ‘forming’ or ‘firstfire’ process on virgin devices, and the switching operation of two chalcogenide alloys. The properties are given as a function of film thickness, temperature of operation, and preswitching heat treatment. Electron diffraction micrographs are used to illustrate the anneal phenomena and to emphasise that the microstructure so produced should be included in any model of switching in these materials.

Influence of microstructure on the mechanical

Abstract: The significance of matrix and grain boundary microstructural characteristics on the mechanical properties and stress corrosion susceptibility of 7075 aluminum alloy has been evaluated. Maximum strength was found to be associated with a Guinier-Preston zone matrix. The precipitate-free-zone adjacent to high angle grain boundaries had only a slight effect on yield and tensile strength but a greater influence on hardness. Stress corrosion susceptibility was studied in an aqueous chloride environment over a 0.7–3.5 pH range. For material of highest strength, grain boundary precipitate spacing was found to be of primary importance to susceptibility. The effect of grain boundary precipitate spacing is most significant to the crack propagation stage of stress corrosion. These results indicate that improved properties for Al-Mg-Zn type alloys could be attained by a desirable combination of matrix and grain boundary structure.

Thermal stability of thin PtSi films on silicon substrates

Abstract: The thermal stability of PtSi is an important parameter in large‐scale integration processing schemes which involve postmetallization high‐temperature operations. For this reason, the effect of annealing on various properties of PtSi has been studied over the temperature range 800–900°C, for 200‐ and 900‐A‐thick PtSi films on single‐crystal silicon substrates. The as‐prepared films, produced by backsputter cleaning of Si surface followed by sputtering of Pt, in situ sintering at 700°C for 10 min, and etching to dissolve any unreacted Pt, were found to be single‐phase PtSi. The 200‐A‐thick PtSi films on (111) Si possess a strong degree of preferred orientation with grains which are triply positioned with (100) PtSi ∥ (111) Si and [010] PtSi ∥ 〈110〉 Si; the orientation remains unchanged upon further annealing. On going to higher thickness (900 A), the preferred orientation of PtSi changes to (010) type and then to a partial (111) type on annealing at 900°C. Rapid grain growth is observed on annealing in the range 800–900°C; the grain size increases from 0.01–0.25 μ in the as‐deposited film to several μ at 850°C. The grain growth is followed at 900°C by agglomeration, i.e., a changeover from continuous film to island‐type microstructure. The final stage of agglomeration, which has been observed in 200‐A PtSi at 900°C, is associated with a drastic increase in resistivity. The resistivity of as‐prepared PtSi films is estimated to be 15 (±5) μΩ cm. Partial agglomeration of 900‐A PtSi occurs at 900°C; it produces only a 10% increase in resistivity. It is concluded that for PtSi films 200–900 A thick, 800°C is a safe upper‐limit (and 850°C, absolute‐limit) temperature below which there is no agglomeration, no change in crystallographic orientation, and grain growth is not excessive.

Microstructure of Melt Blended Polymer Systems

Abstract: Two thermodynamically incompatible polymers were melt blended. The resulting microstructure and, consequently, the physical properties were dependent on the blending conditions and the rheological properties of the components. In this study the blending conditions were held constant while the rheological properties were varied and correlated with dispersion characteristics of the phases and the physical properties of the composite. A series of five atactic polystyrenes (weight average molecular weight from 75,000 to 400,000) and five linear polyethylenes (weight average molecular weight from 43,000 to 347,000) were used. The blending was done over a range of composition ratios in a normal stress extruder. Viscosity and normal stress of each pure component were measured in torsional flow. The mixed extrudates were examined by light interference microscopy, scanning electron microscopy, and solvent leaching. The nature and the fineness of the microstructure were interpreted in terms of the composition ratio...

Constitution and microstructure of rapidly solidified aluminium-germanium alloys

Abstract: X-ray and electron metallographic techniques, electron microscope micro-analysis and differential thermal analysis have been used to study splat-cooled aluminium-germanium alloys containing between 15 and 50 at. % germanium. The observed microstructure and constitution have been correlated with the solidification process at cooling rates in the range 102–109 K/sec. At very high cooling rates the retention of almost all the germanium in f.c.c. solid solution has been shown possible. At slightly lower cooling rates two metastable intermediate compounds were produced; δ1, which was tetragonal with α=6.59 A and c=12.01 A with the possible stoichiometric composition Al5,Go3, and S2, also tetragonal, with a=6.25 A and c=9.44 A, and having a composition AlGe or AlGe2. On thermal decomposition the two compounds yielded a further metastable compound δ3, which was hexagonal with a=2.88 A and c=4.58 A. On further heating, this compound decomposed to the equilibrium aluminium and germanium solid solutions. D...

Correlation between cleared channels and surface slip steps in neutron irradiated copper crystals

Abstract: A technique utilizing electroplating is described for the preparation of specimens for transmission electron microscopy, which show the relation between surface detail and internal structure. The cleared channels in deformed neutron irradiated copper crystals have been correlated with surface slip steps indicating that the surface slip bands are a true representation of the bulk deformation behaviour. The slip steps show a uniform distribution of shear within the central region of the cleared channel, with a decreasing shear strain near the edges. The channel is, however, cleared of irradiation produced defects for approximately the full width of the slip step, indicating that the removal mechanism is relatively efficient. This and other features of the slip process are discussed in terms of the observations.

The role of hafnium in modifying the microstructure of cast nickel-base superalloys

Abstract: The effects of hafnium additions on the microstructure of ALLOY 713-LC have been investigated using electron microscopy and by a radiographic technique which reveals the grain boundary structure. It is shown that the Chinese script MC carbides in ALLOY 713-LC are altered to a particulate morphology in alloy MM-004 (hafnium-modified ALLOY 713-LC). Unlike the script carbides, the discrete MC particles do not provide any easy path for rapid crack propagation and hence, ductility is enhanced. In the hafnium-bearing alloy, the morphology of γ’ phase is also modified. Colonies of ((γ + γ′) with a rosette morphology are formed and individual γ’ platelets exhibit dendritic growth. It is shown that this morphology of γ’ causes grain boundaries to be distorted from planar equilibrium interfaces to a convoluted interlocking configuration. It is suggested that the interlocking boundaries retard grain boundary sliding and separation during creep and result in higher stress-rupture life for hafnium-modified alloys.

Materials useful for prosthetic devices and the like

Abstract: A material useful as a biomaterial for the manufacture of prosthetic devices and the like is provided by a synthetic material characterized by having the microstructure corresponding to the microstructure of porous carbonate skeletal material of marine life, such as marine invertebrate skeletal material, e.g. echinoid spine calcite and Porites skeletal aragonite. Such synthetic materials are prepared by producing a replicate in negative or positive form of the microstructure of the aforesaid porous carbonate skeletal material.

Cu-Zr and Cu-Zr-Cr alloys produced from rapidly quenched powders

Abstract: The production of alloys by means of ingot technology leads to micro-and macrosegregation, separation of phases and impurities, often into large, brittle particles, and coarse grain size. Alloy development is frequently restricted because of the coarseness of the structure and the resultant imposed limitations on hot and cold plasticity. One ready means of avoiding these problems is to produce the alloy in powder or pellet form; this permits attainment of high cooling rates in the liquid and solid, minimizes segregation, alters phase separation and distribution advantageously, and results in significantly finer structures. The powders utilized to produce wrought shapes may be much coarser than press-and-sinter powders, leading to important processing economies without sacrifice of structure refinement. The alloy systems Cu-Zr and Cu-Zr-Cr were selected for the present study; these are high conductivity, high strength alloys of commercial interest. Cooling rates for these specific powders using nitrogen atomization varied from about 103 to 104°CJsec. Powders were cleaned, canned, and hot extruded to produce bar stock; mechanical testing was performed on both as-extruded and thermomechanically-worked samples, with highly beneficial improvements in strength, ductility, and high-temperature structural stability.

Some microstructural features of the welds in butt-welded polyethylene and polybutene-1 pipes

Abstract: Microstructural features characterizing butt welds in polyethylene and polybutene-1 pipes have been studied using scanning electron and transmission optical microscopy. The microstructures are explained on the basis of temperature gradients measured in the region of the welds and the flow of molten material during welding.

Magnetic Behavior and Microstructure of Vanadium Phosphate Glasses

Abstract: The magnetic properties and microstructures of the vanadium phosphate glass system over the composition range 60 to 90 mol% V2O5 were investigated to study magnetic ordering in the glass and the effect of microstructure on its magnetic properties. Direct antiferromagnetic coupling between V4+ ions in the glassy matrix exists, and a transition temperature near - 70°C was observed. As-cast glasses with high V2O5 concentrations separated into two glassy phases; this separation increased the ESR line width as a result of inhomogeneity broadening. The separation, which concentrated the vanadium ions in a vanadium-rich phase, caused a hysteresis in the plot of ESR line intensity vs temperature at the transition temperature. Reduction of the vanadium ions by dextrose added to the melt enhanced phase separation and resulted in weak antiferromagnetic transitions at +70° and -120°C, the Neel temperatures of VO2 and V2O3, respectively.

A Study of the Precipitation of Copper from α-Iron in the Pre-Peak to Peak Hardness Range of Ageing

Abstract: The microstructure of an Fe–I.7 wt.-% Cu alloy has been studied in the pre-peak to peak hardness range of ageing, when a fine-scale distribution of copper-rich precipitates occurs. These precipitates are not visible in the electron microscope below ∼ 6 nm in dia.; field-ion microscopy has thus been employed to elucidate the microstructure. Precipitation was confirmed to occur randomly in the matrix, on line defects, and preferentially at grain boundaries where there was enhanced growth. The mean size of particles was found to be approximately constant until the volume fraction of precipitates exceeded 1%, while the number density of precipitates increased initially until particle coarsening began to take place. The maximum hardness state corresponded to a mean precipitate size of ∼ 3 nm, when the maximum number density of particles occurred.

Preparation, Microstructure, and High‐Field Superconducting Properties of Nb3 Sn Doped with Group‐III, ‐IV, ‐V, and ‐VI Elements

Abstract: The influence of incorporating elements from groups III, IV, V, and VI into vapor‐deposited Nb3Sn superconducting ribbon on the critical current density in magnetic fields up to 190 kOe has been examined, and the mechanism of the enhancement of Jc by carbon‐containing gases has been investigated. It had been found previously that CO2, CO, and N2, but not O2 or CH4 are effective in increasing Jc. We have now established that the less stable C2H6 and C3H8 are as effective as CO2, and that BCl3 increases Jc to a lesser extent. However, H2S, NH3, and NO decrease Jc compared with an undoped Nb3Sn sample. By optimizing the CO2 concentration in the gas phase, the Jc increase can be as much as a factor of 5; this optimum concentration corresponds to about 2000 ppm carbon in the Nb3Sn vapor‐grown layer, as determined by radioactive tracer and mass spectrographic analyses. Since the solid solubility limit of carbon in Nb3Sn is less than 200 ppm, carbon or carbide in excess of this amount is distributed as a second ...

Microstructure and phase relations for Ti-Mo-Al alloys

Abstract: The influence of aluminum additions to a Ti-7 at. pet Mo alloy on the phase equilibria was investigated. The microstructures of the alloys, Ti-7 pct Mo-7 pct Al and Ti-7 pct Mo-16 pct Al, were determined by light and electron microscopy. It was found that with increasing aluminum concentration the formation of the metastable w phase was suppressed. In the Ti-7 pct Mo-16 pct Al alloy the β phase decomposed upon quenching by precipitating coherent, ordered particles having a B2 type of crystal structure (β2). At low temperatures the equilibrium phases for this alloy were β + α+ β2, whereas at high temperature (850° to 950°C) the Ti3Al phase was in two-phase equilibrium with the β phase. The four-phase equilibrium which exists at a temperature of about 550°C involves the reaction β + Ti3Al ⇌ α + β2.

Laser Welding of Gold Alloys

Abstract: A neodymium glass laser was used to produce weld joints between test pieces of four different casting gold alloys. The mechanical properties of the welds were determined and their microstructures were evaluated. The results of this study indicate that laser welding of dental casting gold alloys is metallurgically feasible.