Comprehensive Study on the Microstructural Characterization and Strengthening Mechanism of (α + β) Based Ti-6Al-7Nb Alloy Processed Via Mechanical Alloying and Spark Plasma Sintering

This study investigates the severe plastic deformation of Ti–6Al–7Nb alloy synthesized through mechanical alloying (MA, 0–120 h) and subsequently processed via spark plasma sintering (SPS, 50 MPa, 1050 °C, 6 min). Advanced characterization techniques such as XRD, optical microscopy, HRSEM, HRTEM, EDAX, and EBSD analysis were employed to analyze the powder and consolidated specimens, focusing on the grain microstructure and formation mechanisms during MA and SPS. Mechanical properties were evaluated through micro-hardness, nano-indentation, and compression tests. The SPS 120 h sample exhibited a fine-grained microstructure dominated by the α-Ti phase, with needle-shaped minor β-Ti phases, while the SPS blended sample (0 h) displayed coarse-grained phases. Processing via MA and SPS significantly influenced the material, rendering it suitable for medical and dental applications. It is confirmed that the 120 h milled nanocrystallite sample demonstrated higher strength, with a micro-hardness of 760 VHN and compressive strength of 905 MPa, compared to the initial blended sample (0 h) with a coarse grain, which exhibited a micro-hardness of 120 VHN and compressive strength of 874 MPa. The influence of various strengthening mechanisms, such as grain boundary strengthening, solid solution strengthening, and dislocation strengthening, were elucidated and correlated with the total strength of the material.