COMPUTER CONTROLLED CONTAINERLESS PROCESSING OF HIGH TEMPERATURE INTERMETALLIC COMPOUNDS

A containerless automated system for processing high temperature reactive intermetallic compounds from the liquid state has been developed. Single crystals 2.5 cm in diameter have been processed in various atmospheres from nearly turbulent liquids. The liquid is electromagnetically contained in such a fashion as to permit the propagation of the solidification interface to control the resulting dimensions and structure. The operating temperature reaches nearly 2000°C depending upon the material and the resulting diameter control is within ± 0.08 mm

Several operational characteristics that mandate the need for a dedicated computer control and data acquisition system are its fast response to changes in inputs, sensitivity to changes in inputs, highly interactive nature, inherent transient behavior and small parameter region of stable operation. The computer control system is built around a DEC 11/23⁺computer and an interfaced image camera. The control system is contactless as all measurements are from on-line image analysis and remote sensors. Two control configurations, both of which employ three control loops are used to control three process outputs by manipulating two process inputs. In order to do this two controllers are cascaded. One control configuration is based totally on image analysis. The controllers are standard PI or I mode controllers. Several ingots processed using the flexible computer control system are shown. Samples are presented of processed specimens that show the degree of dimensional control possible. The systems TiAI, TiAI × X, and Ni₃AI are discussed as examples of the control of structure and properties that are attainable utilizing the processing techniques described.