Formation mechanism and characterization of nanostructured Ti6Al4V alloy prepared by mechanical alloying

Abstract

In recent years, researches on properties of nanocrystalline materials in comparison with coarse-grained materials have attracted a great deal of attention. The present investigation has been based on production of nanocrystalline Ti6Al4V powder from elemental powders by means of high energy mechanical milling. In this regard, Ti, Al and V powders were milled for up to 90h and heat treated at different temperatures. The structural and morphological changes of powders were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), differential thermal analysis (DTA) and microhardness measurements. The results demonstrated that Ti(Al) and Ti(Al, V) solid solutions with grain size of 95 and 20nm respectively form during mechanical alloying. In addition, an amorphous structure was obtained at longer milling times. The crystallization of amorphous phase upon annealing led to the formation of nanostructured Ti6Al4V phase with a grain size of 20–50nm. The as-milled Ti6Al4V powder with amorphous structure exhibited a high microhardness of ∼720Hv. Upon crystallization the hardness value reduced to ∼630Hv which is higher than those reported for Ti6Al4V alloys processed by conventional routes.