Microstructural evolution and electrochemical corrosion characteristics of Ti–Ni matrix composite in NaCl and HCl solutions

Ti–Ni matrix composites were produced using spark plasma sintering (SPS), a powder metallurgy technique. The influence of Ni-xTiB₂ additions on the titanium matrix microstructure, hardness, and electrochemical properties was investigated. Scanning electron microscopy, hardness analysis incorporating regression analysis, potentiodynamic polarization, and electrochemical impedance spectroscopy tests were used to characterize the titanium matrix composites. The titanium matrix induced microstructural changes, leading to the coexistence of α and β phases along grain boundaries. A more substantial equiaxed α phase was observed in the Ti+5Ni+20TiB₂ composite. The X-ray diffraction analysis showed that the crystal structures of the composites were altered and that the grains were refined. The microhardness increased with the TiB₂ content. The potentiodynamic polarization analysis indicated that the corrosion resistance of the composites improved with the addition of Ni and TiB₂, with the Ti+5Ni+20TiB₂ composite exhibiting the highest corrosion resistance. The electrochemical impedance spectroscopy revealed that the Ti+5Ni+20TiB₂ composite had enhanced diffusion properties and a stable passive layer, further confirming its exceptional corrosion resistance. Additionally, the composites exhibited a distinct capacitive behavior, indicative of strong corrosion resistance. This is characterized by phase angle values close to −90° and high impedance values (10⁹ Ω cm²) at low and medium frequencies. This is due to the formation of a very stable film on the composites in the test solutions (NaCl and HCl).