Thermo-mechanical analysis of the ingot-crucible contact during multi-crystalline silicon ingot casting
The purpose of the present work is to present a thermo-mechanical model of the multi-crystalline ingot casting and its application to a laboratory-scale directional crystallisation furnace. In thermo-mechanical modelling, stresses and deformations in the ingot are the results of combined effects of thermal contractions and mechanical loads induced by the ingot-crucible contact. The model takes into account plastic relaxation at high temperature and is, therefore, capable of predicting the final residual stress and strain fields in the ingot. The contact between the ingot and the crucible is modelled using a variable stiffness model and simple coating fracture model. The model is applied to analyse the crystallisation and cooling process during directional crystallisation of small silicon ingots in a silica crucible. Several situations are studied to illustrate ingot-crucible interactions (air gap formation, sticking and loss of contact due fracture of the coating layer) and their consequences on the residual stress and strain fields. The simulation results show that the residual stress and strain fields due to sticking of the ingot to the crucible can be significantly higher than those due to the sole effect of thermally induced deformations.