Wednesday, PM Room: B3
February 7, 1996 Location: Anaheim Convention Center
Session Chairperson: TBA
THERMAL EXPANSION AND SOLIFICATION BEHAVIOR OF Mo-V ALLOYS: J.J. Stephens, B. K. Damkroger, S. L. Monroe, R. H. Moore, Sandia National Laboratories, Albuquerque, NM 87185-0340
Molybdenum-vanadium alloys are interesting for application in conductive cermet composites because of 94% alumina ceramic combines with hydrogen atmosphere compatibility. We have recently investigated thermal expansion of five compositions of Mo-V alloys, ranging (in wt.%) from Mo-11V up to Mo-31V, and have found that compositions slightly above 31 wt.% are needed to precisely match the CTE of 94% alumina between room temperature and 1000°C. Arc-cast ingots of these alloys exhibit significant coring which we have characterized in detail for selected compositions. Results of hydrogen compatibility tests for these alloys will also be presented.
MICROSTRUCTURES OF SENSITIZED ALLOY 600 SURFACE-MELTED BY C02 LASER: Joung Soo Kim, Jeong Hun Suh, Yun Soo Lim, Il Hyun Kuk, Korea Atomic Energy Research Institute, P. 0. Box 105, Yusung, Taejun, Korea
Microstructures of sensitized Alloy 600 the surface of which had been melted by a C02 laser was examined under transmission electron microscope(TEM) and analyzed using EDX attached to the TEM. The molten metal solidified epitaxially from the boundary between the melted and unmeted(matrix) regions. The cells formed in the grains during rapid solidification were observed to have different orientations depending on the orientation of each grain. The boundatries of the cell and the grains formed during the rapid solidification were with higher density of dislocations than that in the cells, and very fine precipitates (less than 50 nm) were often observed to form along the boundaries. Also, it was interestingly observed that the concentration of Cr along the boundaries of the cells and the grains was higher than that in the cells. From these observations, it can be concluded that the prevention of IGSCC in sensitized and subsequently laser-melted Alloy 600 might be attributed to the desensitization and the segregation of Cr along the boundaries of the cells and the grains occurred during the rapid melting and solidification processes.
MICROSTRUCTURAL STUDY OF THE BEAM WELDS ACROSS DISSIMILAR TI-AL ALLOYS: O. Umezawa, S. Tsukamoto, National Research Institute for Metals, 1-2-1 Sengen, Tsukuba, Ibaraki 305, Japan
The microstructures of Ti-Al alloys produced by electron beam or laser re-melting on Ti3Al (OC2) and -TiAl substrates have been investigated in the equiatomic range. The substrate was overlaid with samples (Ti-43, 49, 53, 55 at.%Al) 0.5 mm thick. Lap weldings were then carried out to allow the rapid solidification from the bottom of partial penetration beam welds. The beam penetration into the substrate was minimized just below the dissimilar alloy interface. Phases observed are in agreement with those produced by other rapid solidification methods. An optically featureless, planar zone was observed at an interface between the solidified zone and the substrate; the zone gave way to a dendritic structure away from the interface. Effects of the substrate on the microstructures have been also examined. Epitaxial growth from the -TiAl substrate into the melt was not detected. This work was done under auspices of the AADC project, a collaboration between University of Cambridge and the Research and Development Corporation of Japan.
ROLE OF THE MICRO/MACRO STRUCTURE OF WELDS IN CRACK NUCLEATION AND PROPAGATION IN AL-LI ALLOYS: G. E. Talia, Wichita State University, Department of Mechanical Engineering, Wichita, KS 67208; A. C. Nunes, NASA, Marshall Space Flight Center, Huntsville, AL 35812
A model relating the micro/macrostructure of welds of aluminum alloys with the fracture event and fracture criterion capable of predicting the mechanical behavior of these welds are sought. A study was therefore conducted on the microstructure aspects of crack nucleation and propagation in welds of 2195 Al-Li Alloy. These welds were produced by the Variable Polarity Plasma Arc (VPPA) process. The critical role of grain boundaries, phases, and other features of the microstructure were identified and compared with the crack propagation paths. Analysis of weld fusion zone revealed instances of intergranular porosity and the segregation of a Cu-rich second phase. Optical and electron micrograph of deformed specimens displayed a ductile grain material and a Cu-rich phase brittle in nature. The fracture strengths appear to be controlled by planes of weakness dominated by the second phase material.
3:20 pm BREAK
ANALYSIS OF AGING HARDENING IN Ni-Cr-All ALLOYS: Liu Guilan, Liu Wei, Zhu Liming, Northeastern University, Shenyang, China
In the present work, the microstructure morphologies and the micro-zoned composition in the wire specimen with a diameter of 0.3 mm of Ni-Cr-3%Al-0.2%Ce alloy, aged at 500-600°C, have been examined by Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM) and Programmed Image Analysis as well as Quantitative Extraction Technique (QET) etc. It has shown that precipitated phase with a fcc superstructure is a primary strengthening one which is separated in a coherent pattern with respect to (100) planes of the matrix and assumes granular form. A great quantity of supersaturated Cr(a)-rich phase, it may be termed combination strengthening.
EFFECT OF POST-SOLUTION TREATMENT ON THE MICROSTRUCTURE OF Zn-22%Al: Kimberly Duong, Souping Yan, Farghalli A. Mohamed, Materials Science and Engineering, Dept. of Chemical and Biochemical Engineering, University of California, Irvine, CA 92717
An examination of the microstructure of Zn-22%Al after quenching from the single phase region has revealed that groups of fine and -phases are surrounded by traces of former boundaries. During superplastic deformation, the former boundaries behave as independent domains. The presence and density of these former boundaries have been investigated as a function of impurity level and annealing conditions.
STRUCTURE-PROPERTY RELATIONS IN A HTGH-STRENGTH CUPRONICKEL ALLOY: R. J.Grylls, M. H. Loretto, I.R.C. inMaterials, The University of Birmingham, Edgbaston, Birmingham, B15 2TT, England; C. D. S. Tuck, Langley Alloys Ltd., Alloys House, Cordwallis Park, Maidenhead, Berkshire, SL6 7BU, England
Marinel is the latest alloy in a series of age-hardening, wrought cupronickels. It combines high strength with excellent resistance to corrosion and hydrogen embrittlement, and is designed for use in critical applications such as subsea bolting. Strengthening is provided by additions of Mn, Al, Fe, Nb and Cr. The aim of the present work is to understand the nature of the alloy's microstructure and hardening mechanisms such that mechanical properties can be optimised. The phases present in Marinel have been identified using electron microdiffraction and analytical electron microscopy. The microstructure of the alloy has been studied after various heat-treatments, which has led to a detailed understanding of the strengthening mechanisms. Production of trial ingots with differing compositions has established the relationships between alloying additions, microstructure and mechanical properties. This paper will describe the initial results of this alloy development program, indicating the routes whereby mechanical property enhancement has been achieved.
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