Authors: Mahyar Sojoodi | Alireza Behvar | Hari C. Bajaj | Shiva Mohajerani | Saeedeh Vanaei | Nasrin Taheri Andani | Anwar Algamal | Fatemeh Ghasemibojd | Mohammad Taghi Khorasani | Ahu Çelebi | Mohammad Elahinia
Source: Shape Memory and Superelasticity (review, 2025-10-28)
Field: Materials Science — Materials Chemistry

Integration of Circular Economy into Metal Additive Manufacturing: A Review of Ultrasonic Plasma Atomization for Producing Virgin and Recycled NiTi Powder Abstract Integration of circular economy principles into additive manufacturing (AM) has emerged as a critical strategy for addressing economic and environmental challenges associated with the high-cost, resource-intensive production of NiTi shape memory alloys (SMAs). This review presents a comprehensive analysis of the ultrasonic plasma atomization (UPA) technique as an advanced recycling approach for converting NiTi AM waste into high-quality feedstock. Furthermore, UPA demonstrates significant potential as a dual-function method, enabling both alloying and fine powder production within a single integrated process. AM processes, such as powder bed fusion-laser beam (PBF-LB), binder jetting, and direct energy deposition (DED), often result in substantial material losses, exacerbated by powder degradation phenomena including oxidation, particle morphology changes, and loss of flowability. While conventional atomization techniques, such as gas and plasma atomization, offer partial solutions for powder production, they are limited by significant energy inefficiencies, high capital investment requirements, and increased risks of contamination. Moreover, powders produced via gas atomization typically exhibit inferior quality compared to those generated by UPA, including lower sphericity and a higher prevalence of surface satellites. In contrast, the UPA system, a hybrid technique combining high-frequency ultrasonic vibrations and plasma melting, offers precise control over droplet formation through acoustic cavitation, Faraday wave instabilities, and rapid solidification, enabling the production of highly spherical, homogeneous, and contamination-minimized NiTi powders. Drawing on thermofluidic principles, vibrational mechanics, and metallurgical kinetics, this review systematically deconstructs the UPA mechanism, highlighting key phenomena such as resonance-induced cavitation dynamics, ultrasonic capillary wave collapse, and non-equilibrium solidification. Furthermore, it investigates contamination pathways specific to UPA and proposes strategies for impurity mitigation, including sonotrode design optimization, inert atmosphere refinement, and post-atomization conditioning. Experimental findings are analyzed to demonstrate the feasibility of achieving high sphericity (&gt; 0.9), compositionally stable, and thermally responsive NiTi powders from recycled feedstock. Finally, the review outlines a roadmap for industrial-scale deployment, advocating the integration of machine learning and closed-loop recycling models to enhance process predictability, quality control, and resource efficiency. The insights presented herein position UPA as a transformative solution for enabling sustainable, high-performance NiTi powder regeneration within AM workflows, advancing the circular economy in advanced manufacturing. Nickel titanium ; Ultrasonic sensor ; Particle (ecology) ; Deposition (geology) ; Circular economy ; Metal powder Shape Memory Alloy Transformations ; Additive Manufacturing Materials and Processes ; Additive Manufacturing and 3D Printing Technologies