Effect of step-wise change in processing pressure on isolated pore growth during controlled directional solidification in small channels

Directional solidification experiments were performed using succinonitrile saturated with nitrogen gas to examine the effects of in situ processing pressure changes on the formation, growth, and evolution of an isolated, cylindrical gaseous pore. A novel solidification facility capable of processing small cylindrical samples (I.D. <= 1.0 mm), under controlled pressure conditions, was developed for the experiments. A new experimental method for growing the isolated pore from a seed bubble is introduced. The experimental results indicate that a step-wise processing pressure change will result in either a transient change in pore diameter or a complete termination of pore growth, demonstrating that pressure changes can be used as a control parameter to influence bubble growth. During steady-state growth, however, pore size shows no dependence on processing pressure. A simple analytical model has been introduced to explain the experimental observations. (C) 2008 Elsevier B.V. All rights reserved.