Understanding Crack Formation Mechanisms of Ti–48Al–2Cr–2Nb Single Tracks During Laser Powder Bed Fusion

The crack formation mechanisms of Ti–48Al–2Cr–2Nb single tracks processed by laser powder bed fusion were extensively investigated in a wide range of laser powers and scan speeds. The crack patterns were categorized by their directionalities, which were parallel (longitudinal crack) and/or perpendicular (transverse crack) to the scan direction. For the representative process conditions of the keyhole, transition, and conduction modes, cracking behaviors were characterized by combining the fractography and the microstructural analysis. Further, thermal-mechanical finite element method simulations were performed to predict the distribution of temperatures and thermal stresses during the melt pool formation. On the basis of the combined results, the cracks formed in keyhole, transition, and conduction modes were clarified as a solidification crack and/or a thermal crack. In addition, the formation of these cracks was thoroughly understood in terms of thermal stresses and microstructural factors that affect the crack susceptibility. Finally, comprehensive mechanisms responsible for cracking of Ti–48Al–2Cr–2Nb single tracks under laser powder bed fusion were proposed for different process conditions (the keyhole, transition and conduction modes). Graphic Abstract