Showing papers on "Equiaxed crystals published in 1982"

Comparison of the quench rates attained in gas-atomized powders and melt-spun ribbons of Co- and Ni-base superalloys: influence on resulting microstructures

Abstract: The cooling rates of gas-atomized Stellite 6 powders range from 103 to 106 K sec−1 for 400 to 10μm diameter powder particles, respectively. The microstructures vary from the equiaxed type in the coarser particles to dendritic and finally microcrystalline in the finer particles. In the melt-spun ribbons, the microstructure along a cross-section of the ribbon changes from microcrystalline at cooling rates higher than 107 K sec−1 to columnar dendritic at cooling rates of the order of 106 K sec−1.

Solidification Microstructure of Ingots and Continuously Cast Slabs Treated with Rare Earth Metal

Abstract: Investigation has been made to evaluate the effect of REM addition on the solidification macrostructure of commercial ingots and continuously cast slabs. The results are as follows:(1) REM addition brings about diminution of macro-segregation, enlargement of equiaxed zone, and reduction of loose structure.(2) Also, the starting position of the formation of the inverse V-segregation moves toward the center of ingot and the segregated area expands. The length of segregation line and the segregation ratio are reduced.(3) Autoradiographic observation does not show large differences in macrosolidification rate. However, mushy zone at the bottom of an ingot is formed earlier.(4) REM-oxides, sulphides, and oxysulphides are mainly precipitated in dendrite arms. The constituents of inclusions are varied depending on the methods of REM addition.Non-metallic inclusions formed by REM addition seem to act as nucleation catalyst and thus improve not only the microstructure but also the macrostructure of the casts.

Superplastic Behavior of the Sn-Pb Eutectic in the As-Worked State

Abstract: Superplastic behavior of the Sn-Pb eutectic was studied in the as-worked state by mechanically working the cast material to varying degrees. The flow behavior was explored in the temperature range of 298 to 443 K and metallographic observations of longitudinal and transverse sections were made. The microstructure was inhomogeneous for low degrees of working, while at high reductions the grains were nonequiaxed. There was strain softening or hardening up to some strain depending on the test conditions. The grains became more equiaxed and coarser in size with increasing deformation. Due to these changes in microstructure and the nonunique stress-strain rate relation, the as-worked material is not suitable from the viewpoint of assessing the mechanisms of superplastic flow based on steady state. Strain dependency of flow stress was also observed in specimens specially processed to obtain equiaxed grains in the as-worked state.

Characterization of Fine-Grained Superplastic Aluminum Alloys

Abstract: This paper summarizes the results of some recent research on a thermomechanical method of refining the grain size in precipitation hardenable aluminum alloys and illustrates the infuence of grain refinement on several material properties. Grain refinement is achieved by deliberately introducing a large number of nucleation sites for recrystallization and by controlling grain growth after recrystallization. Recrystallization to a relatively small and equiaxed grain size has been achieved in a number of commercial aluminum alloys using these concepts. The influence of the fine recrystallized grain size on such properties as superplastic deformation, room temperature tensile properties, fatigue life, and exfoliation corrosion resistance is discussed. The results show that refinement to a grain size of 8–14 µm is sufficient to develop extensive superplasticity and to yield a small increase in tensile properties in alloys such as 7075 and 7475.

Copper base spinodal alloy strip and process for its preparation

Abstract: Copper base spinodal alloy strip of good strength and ductility is provided, the alloy containing 5 to 35 percent nickel, 7 to 13 percent tin, balance essentially copper, and having an unaged microstructure characterized by an equiaxed grain structure of substantially all alpha, face-centered-cubic phase with a substantially uniform dispersed concentration of tin and a substantial absence of tin segregation. The strip is prepared from copper alloy powder of the indicated composition by a process comprising the steps of compaction, sintering, cooling, rolling and annealing. The strip after aging may contain up to about 50 percent alpha plus gamma phase.

The structure of rapidly solidified Al- Fe- Cr alloys

Abstract: Four aluminum alloys, designed for use at elevated temperatures, were studied. The alloys were supersaturated with iron and chromium, and one of them contained small amounts of Ti, V, and Zr. The starting materials were alloy powders made by the RSR (Rapid Solidification Rate) centrifugal atomization process. Extrusion bars were made from the four powders. The as-extruded microstructure and the microstructure of the alloys after annealing at 482 °C were investigated by optical and transmission electron microscopy and by X-ray diffraction. The microstructure consists of equiaxed grains of aluminum matrix and two types of precipitates, namely, Al3(Fe ,Cr) and a metastable phase, Al6(Fe,Cr). The precipitates were different in their shape, size, distribution, and location within the grains.

Fracture in Equiaxed Two Phase Alloys: Part I. Fracture in Alloys with Isolated Elastic Particles

Abstract: Fracture in equiaxed two phase alloys containing isolated elastic particles has been analyzed from the viewpoint of a recently proposed model for fracture initiation and propagation in such materials. This model predicts fracture toughness parameters in terms of the microstructural geometry, relative phase volume fractions, and tensile properties of the materials. Predictions of the model are tested experimentally for two phase Co-CoAl alloys over a wide range of compositions, and the results indicate good agreement between predicted and observed fracture toughnesses.

Method of producing superplastic aluminum sheet

Abstract: The use of a sequentially applied warm working/cold working procedure in the conventional steps of preparing heat treatable superplastic alloys yields material which demonstrates substantially equiaxed fine grain structure and improved superplastic forming characteristics.

Refining of Solidification Structures of Continuously Cast Type 430 Stainless Steel Slabs by Electromagnetic Stirring

Abstract: Refining of the solidification structure of Type 430 stainless steel by the electromagnetic stirring was studied. By the preliminary tests for small ingots, it was made clear that the following conditions must be satisfied for a preferably equiaxed solidification:1) the formation of sufficient fragments of solidified steel which act as nuclei, and2) the stability of nuclei in the molten pool.A pair of linear-motor type stirrers was set in the slab machine and Type 430 steels were treated by the electromagnetic stirring under various conditions of stirring powers, stirring modes and superheats of liquid steels. By controlling these conditions, the formation of equiaxed structure having the thickness more than 50% of slab was realized and the ridging of cold sheet was improved.

The isothermal austenite-ferrite transformation in some deformed vanadium steels

Abstract: The effect of vanadium on the isothermal austenite-ferrite transformation, between 725 °C and 775 °C, of a hot-deformed microalloyed steel has been studied by examination of the microstructure and measurement of the volume fraction of ferrite in specimens quenched from the reaction temperature. The accompanying precipitation was studied by transmission electron microscopy of thin foils and carbon extraction replicas and by electron energy-loss spectroscopy. Very early in the transformation a continuous band of fine-grained ferrite forms at austenite grain boundaries. After some time some of these grains coarsen to form large equiaxed ferrite grains. It is found that vanadium has no effect on the time to the start of coarsening but thereafter accelerates the rate of formation of ferrite. Interphase precipitation of VN occurs throughout the transformation in the vanadium steels and this is thought to influence the rate at which the ferrite coarsens at the lower temperatures (750 ° and 725 °C) in the range studied.

Superplastic behaviour during compression of as-cast Al–Cu eutectic alloy

Abstract: This work investigates the superplastic behaviour of as-cast Al-Cu eutectic alloy. Compression tests were carried out at different strain rates and it is shown by measurements of the strain-rate-sensitivity index that the material becomes superplastic after about 25% engineering strain. Metallographic examinations of the deformed samples show that this superplasticity is achieved by the transformation of the initial lamellar structure to an equiaxed one. The same behaviour is observed during tensile tests with, however, a high degree of heterogeneity of the deformation. Similarly, during the compression tests, the specimen does not deform homogeneously, but through the development of shear bands with an equiaxed structure, which gradually extend over the whole volume of the sample. By deforming the specimens at different strain rates, it is shown that the homogeneity of deformation increases with increasing strain rate. The effect of a predeformation at high velocity under non-superplastic condit...

Dynamic Recrystallization of Copper Observed by SEM Channeling Contrast

Abstract: Oxygen-free copper was deformed in torsion between 3.7 and 11.1 s–1 at 800 and 950°C (0.8–0.9 TM) to a true strain of 30. Specimens were quenched just before the end of deformation in order to retain the as-worked microstructure whereas others were quenched within 3 seconds to preserve the statically recrystallized grains without grain growth. Optical microscopy of the as-deformed metal revealed equiaxed grains with evidence of substructure and a low twin density. SEM channeling contrast showed the presence of a distorted structure within the grains at 800°C and of subgrains at 950°C, which was confirmed by TEM. Both SEM and TEM revealed the presence of dynamic nuclei of low dislocation density. In the optical microscope, the 3-s-quench specimens displayed classical recrystallization; SEM confirmed this but also showed regions not-yet-recrystallized. Additional clarifications of the mechanism of dynamic recrystallization are discussed.

Super fine grain ferrite steel

Abstract: PURPOSE: To obtain the super fine grain ferrite steel consisting of metallographical structure including many equiaxed ferrite grain surrounded with great inclination grain boundary, by working, in a hot state, low alloy steel by regulating C content without alloying any special element. CONSTITUTION: The steel slab containing not more than 0.3% C, alloy content excepting C of not more than 3%, and not practically containing Nb, Ta, Mo and W, is rolled within a range of temperature practically consisting of austenite range near the transformation point Ar 3 with continuous rolling, etc. When processed in this hot rolling, the transformation and recrystallization of austenite are promoted and the grain size is reduced. The super fine grain ferrite steel of metallographical structure including not less than 70% of equiaxed ferrite crystal surrounded with great inclination grain boundary of not more than 4μm in average particle size can be provided as rolled in a hot state thereby. This steel member is excellent in characteristics such as tensile strength, yield stress, etc. and has sufficient ductility and workability as practical steel. COPYRIGHT: (C)1983,JPO&Japio

High Temperature Fatigue of an Austenitic Stainless Steel

Abstract: Solution heat treated austenitic stainless steel containing boron (Sandvik 12R72HV) was cycled in fully reversed push-pull tests performed at 800°C with a total strain range of 2.0%, and frequencies of 1 Hz and 0.001 Hz. Extensive scanning and transmission electron microscopy were performed on selected specimens to determine the mode of failure and the substructure produced during cyclic straining. strain rate cycling produced cells (approximately 1.4 μm in size) along the grain boundaries and especially at triple junctions. The fracture path was intercrystalline. By contrast, high strain rate cycling produced a uniform equiaxed cell structure (0.7 μm) and the fracture was transgranular.

EFFECTS OF TiA16V4 METALLURGICAL STRUCTURES ON FATIGUE PROPERTIES

Abstract: There are many investigations on the influence of microstructure on the fatigue strength of TiA16V4 which have shown that large grain size material with Widmannstatten structure has a much lower fatigue strength than fine grain size material with an equiaxed structure. By aging processes the fatigue strength can be increased but the ratio between tensile strength and fatigue strength is in most cases decreased (1) – (7).