Sponsored by: MDMD Solidification and SCAMP Committees
Program Organizers: E.F. Matthys, Mechanical Engineering Department, University of California, Santa Barbara, CA 93106; W.G. Truckner, Technical Director--Product Development, Alcoa Technical Center, Alcoa Center, PA 15069
Tuesday, PM Room: B3
February 6, 1996 Location: Anaheim Convention Center
Session Chairperson: E.F. Matthys, University of California, Mech Engrg Dept., Santa Barbara, CA 93106
2:15 pm
EXPERIMENTAL INVESTIGATION ON THE SPACING OF DENDRITE ARRAYS: Q. Han, X. Wan, and J.D. Hunt, Department of Materials, University of Oxford, Parks Road, Oxford OX1 3PH, United Kingdom
Experiments have been carried out to measure the arm spacing of dendrite arrays and the spacing distribution. The results show that there is a minimum spacing under which overgrowth takes place and a maximum spacing above which arm splitting occurs. The minimum spacing agrees well with recent predictions. Primary dendrite arm spacing lies between the minimum and the maximum spacings, but the spacing distribution varies randomly as the freezing front advances. When a dimensionless velocity exceeds a critical value, the dendrite array becomes irregular. The critical value is investigated both experimentally and theoretically.
2:40 pm
EFFECT OF GRAIN SIZE UPON OXIDATION RESISTANCE IN RAPIDLY SOLIDIFIED Fe-20Cr-5Al-0.05La ALLOYS: K.S. Lee, Y.C. Shin, K.H. Oh, H.Y. Ra, Department of Metallurgical Engineering, Seoul National University, 56-1 Shilim-dong, Kwanak-ku, Seoul 151-742, Korea
The strip of Fe-20Cr-5Al-0.05La alloys was produced by Planar Flow Casting. Microstructures evolved pure ferritic phase and grain size was less than 10um. Preferred orientation of strip was (110) texture. The effect of the preferred orientation and grain size on oxidation resistance were studied comparing with the conventionally rolled alloys, which has grain size of about 20 ~ 600um and (200) texture. Oxidation resistance was remarkably improved in melt spun strip. This improvement is related with good adherence of oxide scale, the purpose of this study is to find the effect of grain size and crystal orientation on the adherence of oxide scale. Addition of La element was favorite to the supression of grain growth at high temperature and showed good oxidation resistance. Effect of crystal orientation seemed to be related with recrystallization and regarded to growth of (200) orientation at high temperature.
3:05 pm
MELT SPINNING OF A SHAPE MEMORY ALLOY: A.A Tseng, S.Y. Yang, Department of Mechanical Engineering and Mechanics, Drexel University, Philadelphia, PA 19104; C.L. Lin, J.S. Chen, Materials Research Center, Temple University, Philadelphia, PA 19122; M.V. Nathal, Advanced Metallics Branch, NASA-Lewis Research Center, Cleveland, OH 44135
Rapidly solidified TiNi ribbons for shape memory applications have been produced by melt spinning under an argon atmosphere. The effects of rapid solidification with different processing conditions on the structure and transformation characteristics of the alloy have been investigated. The martensitic transformation characteristics of melt-spun specimens are described in relation to the fine-grained structure and the ordered state of the material. The paper details the melting of the master alloys, production of rapidly solidified ribbons, and processing of the ribbon to sheet by hot pressing and hot rolling.
3:30 pm BREAK
3:50 pm
MICROSTRUCTURAL DEFECTS IN THIN SHEET TWIN-ROLL CAST ALUMINUM ALLOYS: Ming Yun, S.A. Lockyer, J.D. Hunt, Department of Materials, University of Oxford, Parks Road, Oxford, United Kingdom
Twin-roll casting has been used to produce thin sheet (1-4 mm thick) in aluminum alloys. The microstructural defects found in thin sheet twin-roll cast material have been investigated. The defects include surface bleeds, channel segregates, deformation segregates and inhomogeneity in grain structure. This paper describes an experimental observation and metallographical examination of the defects and anlyzes the relationship to the operating parameters. Various generalization can be made for occurrence of the defects in different alloys and mechanisms are proposed for their formation. The defects are illustrated in a number of commercial alloys cast at different gauges and with very different loads.
4:15 pm
MICROSTRUCTURE EVOLUTION OF AISI 430 STAINLESS STEEL PRODUCED BY TWIN ROLL STRIP CASTER: J.T. Choi, Y.H. Kim, K.H. Oh, H.Y.Ra, Department of Metallurgical Engineering, Seoul National University, 56-1 Shilim-dong, Kwanak-ku, Seoul 151-742, Korea
AISI 430 stainless steel strip was fabricated by twin roll strip caster and the thickness of as cast strip was 0.6 ~ 2.0 mm. The microstructure of as cast strip consists of ferritic matrix, carbides and martensite at grain boundary, observed in the transmission electron microscopy. Martensite was transformed from retained austenite at grain boundary because austenite to ferrite transformation was suppressed due to rapid cooling of strip casting. The thinner thickness of strip, the larger volume fraction of martensite. The texture evolution of the strip was investigated by the analysis of pole figure and orientation distribution function. In as cast strip, strong component of g fibre, {111} // rolling plane, was observed and typical soidification texture component, <100> texture, was rarely observed. Crystallographic rotation of surface texture component was observed, which showed the asymmetry of pole figure and development of rolling texture. This rotation is due to shear and plane strain deformation near the kissing point during strip casting.
4:40 pm
A METHOD FOR SOLUTION OF THE LAMELLAR EUTECTICS GROWTH PROBLEM: Ljubomir Andreev Anestiev, Institute for Metal Science, 1574-Sofia, Bulgaria
A model for the explicit solution of the steady state growth problem of lamellar eutectics has been developed. The proposed model takes into account the complex form of the old-new phases interface, the capillarity effects and the influence of the growth velocity on the solute redistribution between the phases. The obtained results compare favorably with the ones obtained with other models.
5:05 pm
OPEN FORUM/VIDEO PRESENTATIONS
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