Understanding the roles of interdendritic bridging on hot tearing formation during alloy solidification

Abstract

Dendritic bridging plays a key role in hot tearing formation and crack propagation, but it has yet to be clearly understood. This article describes the formation process of interdendritic bridging and its effect on the propagation of hot tearing. Two types of interdendritic bridging are proposed: mechanical bridging where dendrites are in contact with each other but are connected only by the surface tension of liquid film and metallurgical bridging where dendrites are metallurgically bonded at their contact points. Mechanical bridging cannot effectively impede crack propagation, thus exhibiting a brittle fracture characteristic, while metallurgical bridging can hinder crack propagation, resulting in a ductile fracture characteristic. Experiments on a high manganese steel were carried out to provide evidence of these two types of bridging and illustrate unique features on fractured surface that are associated with these two types of bridging. In this paper, the process of dendritic bridge formation is clearly described and its effect on hot tearing propagation is discussed.