Strong and ductile niobium-based refractory alloy via deformable zirconia nanoparticles

Abstract

The use of dispersed precipitates is an effective method for strengthening metals, but it typically results in a reduction in ductility. A potential way to overcome this strength-ductility trade-off is through the incorporation of coherent nanoscale deformable precipitates. Here, we present an approach of designing and fabricating a niobium-based (Nb-5W-2Mo-1Zr, Nb521) alloy with copiously and semi-coherently dispersed nanoscale zirconia (ZrO2) precipitates through laser powder bed fusion followed by heat treating. The intergranular ZrO2 precipitates at grain boundaries underwent tetragonal-to-monoclinic martensitic phase transformation and deformation twinning, while the intragranular ZrO2 precipitates within the matrix experienced deformation twinning and substantial plastic deformation during tension. The combination of transformation induced plasticity (TRIP) and twinning induced plasticity (TWIP) from the nanoscale ZrO2 precipitates provides sufficient capacity to accommodate strain and relieve stress concentration. Additionally, the intragranular ZrO2 precipitates effectively piled up incoming dislocations from the Nb matrix to form high-density dislocation networks during tension, which interacted with each other via the Orowan mechanism and finally resulted in its significant plastic deformation. These mechanisms contribute to the exceptional tensile properties of the Nb521 alloy, including an ultimate strength of 628.7 ± 2.3 MPa and a ductility of 17.8 ± 0.6% with a superior work-hardening capacity (∼230 MPa), achieving a record of strength and ductility combination for the Nb521 alloys fabricated by additive manufacturing to date. This strategy represents a promising approach for designing dispersion-strengthened refractory alloys with excellent synergy of strength and ductility.