Severe surface deformation and boronizing of CP-Ti: microstructure and properties study

Abstract

Commercially pure titanium (CP-Ti Grade 2) is widely used in biomedical, aerospace, and chemical industries because of its excellent corrosion resistance, biocompatibility, and high strength-ta-weight ratio. However, its relatively low surface hardness and poor tribological properties significantly limit its performance in wear-intensive applications. The present work focuses on improving the surface properties of CP-Ti through Surface Mechanical Attrition Treatment (SMAT), annealing, and low-temperature pack boronizing. SMAT was carried out using hardened steel balls under different impact velocities to produce severe plastic deformation on the titanium surface. The repeated high velocity impacts generated a gradient nanostructured surface layer with refined grains, high dislocation density, and deformation twins. The influence of SMA T processing parameters on microstructural refinement, crystallite size, microstrain, and hardness evolution was systematically investigated. X-ray diffraction analysis confirmed peak broadening due to grain refinement and induced lattice strain, while SEM observations revealed the formation of a highly deformed surface layer. Annealing of the SMATed samples was further performed to study the thermal stability and recovery behaviour of the nanostructured surface. The study al so investigated the boronizing behaviour of both untreated and SMATed CP-Ti samples using different pack mixtures and geometric setup configurations. Low-temperature pack boronizing was successfully achieved on SMA Ted CP-Ti due to the enhanced boron diffusivity provided by the high density of grain boundaries and defects generated during SMA T. Different pack compositions and setup arrangements were designed to study their influence on boride layer formation, oxidation behaviour, and Kirkendall porosity.