Microstructure Evolution During Thermal Processing of Ti-Al-4V ELI Alloy

The present work aims to analyze the microstructure and phases formed during heat treatments of Ti-6Al-4V ELI alloy used for healthcare application. The heat treatments involve one or two stages of solution treatments followed by water or air cooling and with or without aging treatment at 550oC. The heat treated samples were characterized for phases, phase morphology and texture by using X-Ray diffraction (XRD), optical microscopy (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The hardness measurements were performed using a Vickers microhardness machine. XRD patterns revealed primarily á/á' phases. The samples solution treated at 950oC followed by quenching and solution treated at 1050oC followed by aging at 550oC shows slightly basal plane texture along the longitudinal direction of the sample. Three morphologies of á phase were observed under transmission electron microscope: lamellar, martensitic (acicular) and equiaxed structure for various heat treated samples. The samples solution treated at 850oC followed by water or air cooling and subsequently with or without aging at 550oC showed equiaxed á grains with small amount of intergranular secondary á+â phases. The samples solution treated at 1050oC and 950oC exhibited lamellar and martensitic structure. The effect of aging treatment was investigated further with the help of TEM studies. The aged samples show higher hardness that the only solution treated samples expect the sample solution treated at 1050oC. Further work is underway on utilizing these diverse microstructural features in enhancing the fatigue properties of this alloy system.