Development and Characterization of a New Interpenetrating Phase Composite With an Architected Nitinol Core

Abstract

Architected smart materials have been gaining an increased interest for their light weight and versatile applications. Within this context, a recent trend involves leveraging various fabrication methods to form architected composites comprising multiple interpenetrating phases. These so-called interpenetrating phase composites (IPCs) have allowed an expanded design space enabled by the mixing of materials of different mechanical and functional properties. The present work focuses on the development of novel IPCs combining a shape memory nitinol phase with a second non-functional metal. This is carried out using two methods: the first involves additive manufacturing of triply periodic minimal surface nitinol scaffolds that are subsequently infiltrated with molten aluminum to form, upon solidification, dense IPCs; whereas the second utilizes spark plasma sintering (SPS) to consolidate nitinol powder surrounding additively fabricated architected aluminum cores. Both methods are found to yield functional IPCs, capable of some degree of shape recovery. Depending on the ratio of nitinol to the matrix material the IPC samples are shown to display various degrees of shape memory. The behavior of the samples is interpreted in light of microstructural and thermographic investigations including scanning electron microscopy, and differential scanning calorimetry. For IPC samples fabricated using SPS, the pressure and temperature used during the sintering process were found to dramatically influence shape recovery. For the highest pressure and temperature values, phase transformation peaks, indicative of phase transformation in the nitinol phase, were virtually eliminated. Moreover, the behavior of the nitinol core in samples obtained by casting infiltration of the aluminum phase was shown to greatly depend on its relative density. The present work establishes fabrication methods usable for manufacturing novel nitinol-based smart IPCs with demonstrated ability for shape recovery. It paves the way for utilizing these IPCs in various engineering applications, ranging from biomedical implants, to smart structures, and energy absorption solutions.

Date of Award	8 May 2025
Original language	American English
Supervisor	Wael Zaki (Supervisor)