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 ′ -NiTi; minimal crystallite size ( ∼ 109 Å); high chemical homogeneity ( ∼ 46 at% Ni, ∼ 42 at% Ti, ∼ 10 at% Cu). Subsequent SPS at 850–900 ° C and 49.2 MPa allowed for the production of dense samples. Sintering at 90 0 ° 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 at% Ni, ∼ 42 at% Ti, ∼ 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.

This study investigates the control of the phase-structural state in Ni–45Ti–xCu (x = 5, 7 at.%) shape memory alloys fabricated via a shortened powder metallurgy route: mechanical activation → spark plasma sintering (SPS) → heat treatment. Compact samples were produced from mechanically alloyed powders (650–750 rpm, up to 5 h) and sintered at 900 °C. The structure and microstructure were characterized using X-ray diffraction (to identify B2/B19′/Ni₄Ti₃ phases and assess ordering) and SEM–BSE/EDS (to analyze morphology, porosity, and Ni-rich precipitates). Two post-processing treatments were applied: single-stage annealing (500 °C, 2 h) and a three-stage treatment (900 °C/30 min → water quenching → 300 °C/20 min). Mechanical alloying transformed the initial elemental powder mixture (fcc-Ni, hcp-Ti, fcc-Cu) into a supersaturated fcc-(Ni, Cu, Ti) solid solution with emerging NiTi phases, with a minimum particle size achieved after ~300 min at 750 rpm. SPS compaction yielded a high-density matrix consisting predominantly of the B2 phase. Single-stage annealing preserved B19′ martensite and Ni₄Ti₃ precipitates, particularly in the 5 at.% Cu alloy. In contrast, the three-stage treatment dissolved the Ni₄Ti₃ precipitates, suppressed the formation of B19′ and R phases, and stabilized a highly ordered B2 matrix. Increasing the Cu content from 5 to 7 at.% significantly enhanced the B2 phase fraction, reduced secondary nickel-rich phases, and improved structural homogeneity, evidenced by a continuous neck network and closed porosity. The optimized condition—7 at.% Cu combined with the three-stage annealing—produced a microstructure with >95% B2 phase, <1% Ni₄Ti₃, and ~98% relative density. This forms the prerequisite microstructural state for a narrow transformation hysteresis and high functional cyclic stability.