Master sintering curves of nickel-titanium and nickel-titanium open-cell foams fabricated by spark plasma sintering

Abstract

Master sintering curves (MSCs) were developed for monolithic nickel-titanium (NiTi) and composite NiTi-copper specimens densified by spark plasma sintering (SPS) to efficiently establish the density–process parameter relationship. NiTi-copper specimens simulated the porogen (a.k.a. space holder) replication technique used to fabricate NiTi open-cell foams. The effect of copper porogens on the densification behavior of NiTi powder was examined through the comparison of the generated MSCs. Several additional monolithic NiTi specimens and a NiTi open-cell foam specimen were sintered isothermally to verify the accuracy of the generated MSCs. The experimental data indicated the copper porogens had little-to-no effect on the densification behavior of NiTi powder. Using an apparent activation energy of 201 kJ mol-1, both MSCs were able to predict the final density of the validation specimens within 1.2%. The current study demonstrated the successful application of the MSC concept to the SPS of monolithic NiTi and composite NiTi-copper specimens enabling accurate predictions of final specimen density based on any arbitrary time–temperature sintering profile. This efficient mapping of the density–process parameter space has eliminated the trial-and-error methodology typically used and has resulted in significant savings of time, energy, and raw materials.