Phase Transformation and Morphology Evolution of Ti₅₀Cu₂₅Ni₂₀Sn₅ during Mechanical Milling

Nanocrystalline/amorphous powder was produced by ball milling of Ti₅₀Cu₂₅Ni₂₀Sn₅ (at.%) master alloy. Both laser diffraction particle size analyzer and scanning electron microscope (SEM) were used to monitor the changes in the particle size as well as in the shape of particles as a function of milling time. During ball milling, the average particle size decreased with milling time from >320 µm to ~38 µm after 180 min of milling. The deformation-induced hardening and phase transformation caused the hardness value to increase from 506 to 779 HV. X-ray diffraction (XRD) analysis was used to observe the changes in the phases/amorphous content as a function of milling time. The amount of amorphous fraction increased continuously until 120 min milling (36 wt % amorphous content). The interval of crystallite size was between 1 and 10 nm after 180 min of milling with 25 wt % amorphous fractions. Cubic Cu(Ni,Cu)Ti₂ structure was transformed into the orthorhombic structure owing to the shear/stress, dislocations, and Cu substitution during the milling process.