Unravelling Role of the Microwave Sintering Effects on Microstructure, Density, and Corrosion Behavior of porous Ti-13.3at.% Nb Shape Memory Alloys

Abstract This study investigates the impact of microwave sintering on the microstructure, density, and corrosion behaviour of porous Ti-13.3at.% Nb shape memory alloys (SMAs). The alloys were subjected to microwave sintering at 800°C and 1100°C for 20 and 40 minutes, focusing on understanding the structural changes and corrosion resistance. Microstructural characterization, including scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), and electron backscatter diffraction (EBSD), were performed. The results revealed the formation of two distinct needle-like morphologies: straight and cross-linked needles (βSC) and irregular lines or spaghetti-like needles (βS). The area fraction of these needle structures increased with prolonged sintering duration and elevated sintering temperature, indicating enhanced diffusion between Ti and Nb elements. Density measurements showed a range of 73-75.5%, with the highest density (75.5%) achieved for samples sintered at 800°C for 40 minutes. However, a lower density (73%) was observed for samples sintered at 1100°C for 20 minutes, attributed to the rapid heating rate of microwave sintering. Corrosion characteristics were evaluated using potentiodynamic polarization (PDP) and electrochemical impedance spectra (EIS) in simulated body fluid (SBF). The corrosion behaviour was significantly influenced by sintering temperature rather than sintering duration. Samples sintered at 1100°C exhibited larger capacitive loops on their Nyquist plots compared to those sintered at 800°C, indicating improved corrosion resistance. With the 800°C sintering temperature, the sintering duration had a less pronounced impact on corrosion behaviour. The EBSD analysis revealed that Ti-Nb diffusion predominantly occurred at grain boundaries, with reduced diffusion in areas further from the grain boundaries. In conclusion, this study elucidates the profound influence of microwave sintering parameters on the microstructure and corrosion behaviour of porous Ti-13.3at.% Nb SMAs. The findings provide valuable insights into optimizing the sintering process for enhanced material properties, offering potential applications in biocompatible and corrosion-resistant engineering components.