Microstructure, phase transformation, and deformation behavior of CuZr martensite

CuZr alloys are promising candidates for advanced structural applications due to their unique martensitic transformations. However, fundamental questions regarding the twinning systems that govern their deformation behavior remain unresolved. Here, through an integrated study of a levitation-melted equiatomic CuZr alloy, we report transformative findings that challenge prior understanding. We present the first experimental evidence of (001) twinning in the primitive B19′ (P2$_1$/m) martensite and discover a new, high-shear (111) twin system in the superstructured (Cm) martensite. These results, revealed via transmission electron microscopy and X-ray diffraction, fundamentally expand the known deformation mechanisms in this system. We correlate these specific twin systems directly to the material's macroscopic behavior: reversible (001) and (021) twins facilitate limited plastic strain, while the high-shear (111) twins underpin the observed irreversible deformation and pronounced serrated flow (>1370 MPa) during compression. Furthermore, rapid cooling is shown to kinetically suppress eutectoid decomposition, leading to a higher martensite start temperature (423 K). ... mehrThese insights into twin diversity and phase stability provide a crucial foundation for the rational design of CuZr-based shape memory alloys with tailored mechanical properties.