Directional solidification of binary eutectic alloys and investigation of mechanical properties

Ill DIRECTIONAL SOLIDIFICATION OF BINARY EUTECTIC ALLOYS AND INVESTIGATION OF MECHANICAL PROPERTIES (PhD Thesis) Hasan KAYA GAZİ UNIVERSITY INSTITUTE OF SCIENCE AND TECHNOLOGY Fabruary 2001 ABSTRACT The purpose of this work is to investigate the variation of microstructural parameter, A,E, (the lamellar spacing) and the microhardness, Hv, as a function of the solidification parameters, such as temperature gradient G, growth rate V and cooling rate GV, and also is to determine the dependency of Hv on XE. Therefore, ten samples have been prepared from each of the different binary eutectic alloy systems (Pb-Cd, Sn-Zn, Bi-Cd and Al-Si). The eutectic samples were prepared by melting weighed quantities of metals. (>99 %) high purity in a graphite crucible within a vacuum melting furnace. After the molten alloy was poured into graphite crucibles (200 mm length, 4 mm ID and 6,35 mm OD), which were they placed in the hot filling furnace and then directional solidified. The solidified samples were taken from the filling furnace and each one of the samples was positioned in a Bridgman type directional solidification furnace respectively. Five samples were solidified with a constant V, but different G (16-78 °C/cm) and five samples wereIV solidified with a constant G, but different V (8-500). 10"4 cm/s for each eutectic system. In order to appear the microstructure of the sample, metalographic processes have been carried out on the prepared samples. After this process, the photographs of samples have been taken by means of optic microscope and SEM (Scanning Electron Microscopy) in order to find the values of A,E,The values of XE have been found by means of the photographes by applying linear intercept method. Microhardness values of the samples, Hv's have been measured by means of Vickers type hardness measuring test device. The variations of both A,E and Hv with respect to G, V, and GV and dependency of Hv on A,E have determined by using the linear regression analysis method. According to these results, it has been found that XE decreases with the increasing values of G, V, and GV, and that Hv increases with the increasing values of G, V, and GV, but it increases with the decreasing values of XE. Finally, the results obtained in this study have been compared with theoretical models and the previous experimental results and it has been observed that they were in quite good agreement. Science code : 404.05.01 Key words : Binary eutectic alloys, solidification, microstructure, microhardness Pages number : 172 Advisor : Prof. Dr. Atilla ÖZMEN, Prof. Dr. Mehmet GÜNDÜZ