The martensitic transformation behavior and shape memory effect of laser powder bed fusion NiTi alloys influenced by rare earth addition

Additively manufactured (AM) has attracted extensive research due to its ability to precisely form NiTi alloys with complex structures compared to conventional fabrication processes. However, the strong-plastic mismatch, poor shape memory effect (SME) and functional properties severely limit the wide application of AM-NiTi alloys. Rare earth oxides are common additives to improve the mechanical properties of alloys. This paper is the first to report the effect of different additions of CeO2 (0.03% CeO2, 0.3% CeO2 and 3% CeO2) on the properties of NiTi alloys prepared by laser powder bed fusion (LPBF) technology. The results showed that different amounts of CeO2 seriously affect the transition temperatures (TTs), SME and mechanical strength of LPBF-NiTi alloys. The change of TTs is mainly related to the precipitates formed after the addition of CeO2. The formation of NiCe reduces the Ni content in the matrix and thus increases the TTs, while the generation of CeTi2O6 reduces the content of Ti in the matrix, resulting in a decrease in TTs. The improvement of mechanical properties is mainly attributed to the grain refinement strengthening, precipitate-dislocation interaction and solid solution strengthening after rare earth addition. More significantly, the addition of an appropriate amount of CeO2 (0.03% CeO2) promoted the grain order of LPBF-NiTi alloys and improved the yield strength and SME.