Surface modification strategies for Ni–Ti-based thermosensitive shape memory alloys: a review of techniques, trade-offs, and performance

Recent advancements in material fabrication technologies have led to the creation of dual-property materials, characterized by distinct core and surface properties tailored to meet specific functional requirements. Surface modification is crucial for enhancing the functionality of Ni–Ti-based thermosensitive shape memory alloys (SMAs). This enhancement is important for various applications, including corrosion resistance, wear resistance, biocompatibility, and thermal stability. This review presents a novel process-based framework that categorizes surface modification strategies into five distinct classes: bulk alloying, thermochemical, thermophysical, hybrid, and direct surface coatings. It systematically evaluates their performance trade-offs, thermal compatibility issues, and failure mechanisms. By incorporating a meta-analysis of failure susceptibility and offering application-driven selection guidelines, this work provides a structured decision-support tool for researchers and engineers involved in the design of surface-modified Ni–Ti SMAs for biomedical, aerospace, and civil applications.