Reduction of the grain size to the nanometric range is well known to produce dramatic improvements in the mechanical properties of metals. The increase in strength, however, is often accompanied by a reduction in ductility and toughness, reducing drastically the possibility of practical application for these materials.
An effecttive approach for addressing this limitation is represented by the use of complex microstructures, presenting bi- or multimodal grain size distributions. In this approach materials presenting a combination of coarse and nanometric grain size are produced. The basic idea is that the coarse fraction should retain the toughness of the regular material, while the nanometric fraction should increase its hardness and wear resistance.
This approach appear particularly interesting in the case of commercialy pure titanium (CP-Ti). The vast majority of titanium applications, in fact, involve the use of Ti alloys,as the pure metal presents relatively low strength. On the other hand, CP-Ti presents higher biocompatibility and higher corrosion resistance and is particularly suited for biomedical implants and for applications in extreme corrosive environments.
Investigations on the synthesis of bi- multi- modal titanium, however, have been quite limited, due to some technical difficulties, mostly associated to the availability of nano Ti and to its extreme reactivity. Most of the available studies were based on the use of cryomilled Ti nanopowders. Recently, however, commercial nanopowders became available at a reasonable cost. The use of these nanopowders coupled with FAST/SPS sintering offer the opportunity to develop multi-modal materials with interesting mechanical properties.
Related publications:
U.Anselmi-Tamburini, I.G.Tredici, T.B.Holland…. , “An affordable approach towards the synthesis of multimodal CP-Ti based on commercial nanopowders and SPS densification”, in preparation.