Production and caracterization of titanium hard-alpha phase via different techniques

Minute amounts of oxygen and nitrogen that may be present in the medium during melting or heat treating diffuses into the structure and forms a brittle and stable new phase named alpha-case or hard-alpha in titanium alloys. Since hard-alpha adversely affects fatigue resistance, impact strength, and ductility this phase, when forms on the surface, is normally removed via chemical milling or machining. The aim of this study is to produce hard-alpha phase to be employed as synthetic defects of known size, shape and location in Ti-6Al-4V material that is to be used as a reference block in ultrasonic inspection of aircraft engine parts.This study focused on establishing the optimum heat treatment for the formation of hard-alpha synthetic defect material, and the time, temperature and pressure parameters for vacuum-hot-pressing (VHP) as the method of incorporation of defects into the bulk materials. The hard-alpha phases produced by two methods were characterized using optical microscopy, Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM) Atomic Force Microscopy (AFM), Electron Probe Micro Analysis (EPMA), X-Ray Diffraction, Scratch Test and Confocal Raman Spectroscopy techniques. Finally, titanium blocks containing artificially introduced hard-alpha defects were subjected to ultrasonic inspection.Keywords: Hard-alpha, Vacuum Hot Press.