The Breakdown of Fibrous Structures in Directionally Grown Monotectic Alloys
- PDF / 3,399,640 Bytes
- 6 Pages / 594 x 774 pts Page_size
- 34 Downloads / 197 Views
The Breakdown of Fibrous Structures in Directionally Grown Monotectic Alloys R.N. GRUGEL and A. HELLAWELL This communication concerns the monotectic reaction, Liquid (L~) ~ Solid (SI) + Liquid (L2) and relates particularly to the breakdown of aligned steady state growth products which have been described elsewhere. 1.2.3In addition to examples of metallic monotectic reaction products, the use of transparent analogues has already been illustrated 2,4 and is particularly useful to observe breakdown mechanisms which can only be inferred indirectly in opaque materials. The use of transparent analogue materials to metals and alloys is well established for the study of solidification pro~esses and has been used to observe dendrite growth, 5,6,7 eutectic growth, s macrocrystallization, and segregation in model castings. 9,1~ In what follows we offer more detailed illustrations of transparent materials to substantiate earlier conclusions made in Reference 3 about the monotectic reaction. Method: The structures were observed on a Zeiss Axiomat microscope using a temperature gradient stage of design R.N. GRUGEL is Postdoctoral Associate, l~cole F6d6rale Polytechnique, 1018 Lausanne, Switzerland. A. HELLAWELL is Professor, Department of Metallurgical Engineering, Michigan Technological University, Houghton, MI 49931. Manuscript submitted August 5, 1983. 1626--VOLUME 15A, AUGUST 1984
similar to that of other workers. 12 Cells were made of two 22 mm • 40 mm cover slides, thickness 0.14 mm which were pressed and sealed together by a cut frame of commercial plastic 'handi-wrap' (polyvinilidine chloride); this gave a cell gap which consistently lay between 10 to 20/xm, but thicker cells could be made with multiple layers of plastic. Such cells were then driven across hot and cold blocks made of stainless steel; the hot block was heated by a small resistance heater and the cold block cooled by chilled nitrogen and subject to block temperatures and separation; temperature gradients from 2 K mm -~ to 10 K mm -~ could easily be maintained. Block temperatures were recorded continuously and confirmation of gradients was also made by incorporating a fine (20/xm) thermocouple in a cell. The cells were pressed lightly against the hot/cold blocks by a teflon frame which was driven by a teflon washer on a fine thread (-~9 turns mm -~) and geared (500:1) servomotor--the assembly resembled a micro-lathe and traction rates from 0.1 /zm s ~to 28 /zm s -~ were possible. Choice of Systems: The considerations here concern (i) the relative temperatures of the monotectic horizontal, TM, to upper consolute temperature of the liquid miscibility gap, Tc, which through the relative liquid and solid surface energies appears to determine whether or not the reaction is capable of steady state growth, ~'2'~3 (ii) the growth characteristics of the solid--whether faceted or otherwise (e.g., Reference 6), and (iii) the relative wetting characteristics of parent and product phases with the glass cell walls. Succinnonitrile (CH2CN)2 is nonfaceted and has immisci
Data Loading...
