The crack and pore formation mechanism of Ti–47Al–2Cr–2Nb alloy fabricated by selective laser melting

Abstract

In this study, a broad range of parameter combinations (laser power: 100–400 W; scanning speed: 10–90 mm/s) were used to fabricate Ti-47Al-2Cr-2Nb alloy at the layer thickness of 100 μm by selective laser melting (SLM). The preparation of the TiAl-single track by SLM was prone not only to balling and irregularity but also to cracking. Although the optimized process parameters were used to fabricate TiAl specimens, many pores and cracks still existed and a low density was achieved. To understand the mechanism for the crack and pore formation, the connections among the cracks, pores, and the process parameters were investigated in addition to the variation in the crack propagation with an increase in the number of deposition layers. The results indicated that the cracks originated in the third layer, because of the accumulation of residual stresses and the changes in the composition of Ti-47Al-2Cr-2Nb deposition layers. Additionally, the frequency of cracks constantly increased with an increase in the number of deposition layers. Preheating the substrate to 200 °C improved the degree of cracking to a certain extent, as the initiation layer for the cracks increased from the third layer to the fifth layer. Despite the achieved improvement, it was not possible to produce crack-free specimens on the SLM machine used for this study. Finally, there was a good metallurgical bond between the Ti-6Al-4 V substrate and the Ti-47Al-2Cr-2Nb deposition layers that was free of pore and crack defects. These findings suggest that using SLM to fabricate Ti-6Al-4 V/TiAl intermetallic laminate composites may potentially eliminate cracking and improve the properties of TiAl alloys.