Influence of annealing treatment on the microstructure, mechanical performance and magnetic susceptibility of low magnetic Zr–1Mo parts manufactured via laser additive manufacturing

In recent years, a low magnetic and fully dense Zr–1Mo (wt%) part was successfully manufactured via the laser powder bed fusion (L-PBF) process, which shows the great potential as metallic biomaterials under the magnetic resonance imaging (MRI) environment. However, due to the high cooling rate after laser incident during the L-PBF process, the as-fabricated Zr–1Mo part consists of a non-equilibrium α′ phase, which contributed to high strength (UTS: 1107 MPa) but insufficient ductility (elongation: 4.3%) for biomedical applications. In order to enhance the mechanical performance of as-fabricated Zr–1Mo parts, various annealing processes that have been recognized as an efficient post-treatment to adjust the mechanical performance of additive manufactured products were executed. After the annealing process, acicular martensite α’ microstructure in as-fabricated Zr–1Mo parts changed to stress relieved/partial relieved acicular α microstructure, basketweave α + β microstructure, lamellar α + β microstructure or retain α+ lamellar α + β microstructure depending on different annealing conditions. In the meantime, elongation increased with increasing holding temperature and residence time, but the tensile strength exhibits a converse trend. The specimens annealed at 873 K, 803 K for 2 h and at 773 K for 8 h possessed UTS of 779 MPa, 964 MPa and 981 MPa as well as elongation of 14.3%, 11.0% and 9.6%, respectively. These annealing conditions could contributed to adequate strength and sufficient ductility, and should be the appropriate annealing conditions for Zr–1Mo parts produced by the L-PBF technology. By comparison with other conventional metallic biomaterials, annealed Zr–1Mo alloy could be applied for the medical devices under MRI environments.