Structural and functional enhancement of Ni–Ti–Cu shape memory alloys via combined powder metallurgy techniques

Abstract This research aims to optimizing the synthesis of Ni–Ti–Cu alloys with shape memory effect (SME) through a combination of mechanosynthesis and spark plasma sintering (SPS). It has been established that the rotation speed (650/750 rpm) and the duration of mechanosynthesis (1–8 h) critically affect the phase composition and morphology of the powders. The speed of the formation of the intermetallic phase NiTi is limited at 650 rpm, whereas it intensifies defect accumulation and amorphization at 750 rpm. X-ray phase analysis and scanning electron microscopy confirmed that the optimal mechanosynthesis regime (8 h, 750 rpm) ensures: synthesis of target phases B2-NiTi and B19 ′ {}^{^{\prime} } -NiTi; minimal crystallite size ( ∼ 109 \sim 109 Å); high chemical homogeneity ( ∼ 46 \sim 46 at% Ni, ∼ 42 \sim 42 at% Ti, ∼ 10 \sim 10 at% Cu). Subsequent SPS at 850–900 ° C {}^{^\circ }{\rm{C}} and 49.2 MPa allowed for the production of dense samples. Sintering at 90 0 ° C 90{0}^{^\circ }{\rm{C}} after mechanosynthesis at 750 rpm ensured the predominance of the stable B2 austenitic phase, high microstructural homogeneity, and minimal porosity, which is critical for the reversibility of martensitic transformations. EDS analysis confirmed the chemical homogeneity ( ∼ 46 \sim 46 at% Ni, ∼ 42 \sim 42 at% Ti, ∼ 10 \sim 10 at% Cu) and the uniform distribution of elements. The results demonstrate the effectiveness of combining mechanosynthesis at an increased rotation speed and reduced duration with SPS for the formation of microstructures optimized for the requirements of shape memory alloy (SMA) materials.