Effect of Aging on Precipitation Behavior and Mechanical Properties of Ag-Added Ti–2Cr–9Sn Biomedical Shape Memory Alloy

The effects of Ag addition and aging treatment on the phase stability, microstructure, element partitioning, and mechanical properties of Ti–2Cr–9Sn–1.7Ag (mol%) alloy were systematically investigated. Ag addition promoted β phase stability in the solution-treated condition and suppressed α′′-martensite formation at room temperature. Aging treatment of the Ti–2Cr–9Sn–1.7Ag alloy induced distinct precipitation behavior depending on aging temperature, including the formation of fine α precipitates at lower temperatures and Sn-rich α2 (Ti3Sn) precipitates at higher temperatures. The formation of fine α precipitates caused severe embrittlement, while high-temperature aging restored superelasticity. A clear correlation was established between precipitation behavior, solute redistribution in the β matrix, and deformation mode. Under optimized aging conditions, a maximum recoverable strain of 2.5% was achieved, demonstrating that appropriate aging treatment can effectively induce superelasticity even in alloy compositions that exhibit predominantly plastic deformation in the solution-treated condition.