Session: 01-03 Shape Memory Alloys 2

Paper Number: 168618

168618 - Optimizing Wire-Ded Processing and Heat Treatment for High-Performance Niti Shape Memory Alloys 

NiTi shape memory alloys (SMAs) are widely recognized for their unique superelastic and shape memory properties, making them highly desirable for a range of engineering and biomedical applications. These alloys undergo a reversible phase transformation between martensite and austenite phases when exposed to temperature changes or mechanical stress, allowing them to exhibit distinct mechanical properties, including high recoverable strain and functional fatigue resistance. Despite the promising characteristics of NiTi SMAs, fabricating high-quality components with consistent microstructure and functional properties remains a significant challenge, especially when using additive manufacturing (AM) methods like Direct Energy Deposition (DED). In this study, the optimization of the Wire-DED process was explored to fabricate NiTi components with enhanced functional performance, targeting minimal defects and optimized phase transformation characteristics.

The research first focuses on refining the Wire-DED printing parameters to achieve an optimized microstructure. Through careful control of processing parameters such as laser power, feed rate, and travel speed, a defect-free and homogeneous microstructure was achieved, reducing porosity and ensuring improved phase stability. The optimized process was then subjected to a systematic heat treatment study, aimed at enhancing the superelasticity and transformation behavior of the printed NiTi parts. Solutionizing and aging treatments were applied to evaluate their effects on critical material properties, including thermal hysteresis, martensite-to-austenite transformation temperatures, and cyclic stress hysteresis under compression loading.

Differential Scanning Calorimetry (DSC) was used to closely monitor phase transformations and assess thermal behavior, while scanning electron microscopy (SEM) was employed to analyze the microstructural evolution. Cyclic compression testing was performed to evaluate the superelastic behavior and cyclic stability of the heat-treated samples under mechanical loading. The results revealed that a solutionizing treatment at 950°C for 5.5 hours, followed by aging at 350°C for 10 hours, led to a significant shift in the austenite finish (Af) temperature, from -20°C to 50°C. This shift in transformation temperatures enhances the material’s functional properties and improves its responsiveness under thermal and mechanical loading conditions.

The heat treatment strategy also resulted in the refinement of the NiTi microstructure, leading to increased phase stability and enhanced superelasticity. The processed NiTi components exhibited reduced stress hysteresis, improved recoverable strain, and superior cyclic stability under mechanical loading, demonstrating the potential for improved functional performance and durability in real-world applications.

This study provides a comprehensive framework for optimizing both the additive manufacturing process and post-processing conditions of Wire-DED NiTi SMAs. By systematically refining these parameters, this work paves the way for the broader use of Wire-DED in fabricating advanced NiTi components for structural, aerospace, and biomedical applications, where precise control of phase transformation and superelastic behavior is critical. The results provide valuable insights into the relationship between heat treatment, phase transformation behavior, and mechanical response, highlighting the potential for additively manufactured NiTi alloys in high-performance applications.

Presenting Author: Nasrin Taheri Andani university of toledo

Presenting Author Biography: Nasrin Taheri is a Ph.D. student in mechanical engineering at the University of Toledo, working under the supervision of Dr. Mohammad Elahinia. Her research focuses on understanding the relationship between the structure, process, and properties of superelastic nickel-titanium (NiTi) alloys produced through laser powder bed fusion and laser direct energy deposition techniques. Specifically, she investigates how scan strategy parameters, particularly rotation angles, affect the microstructural characteristics and superelastic behavior of these alloys. This work aims to facilitate the design of functional materials with predictable and tailored properties, advancing the field of material science and expanding the applications of NiTi alloys across various industries