Creation of high strength and high ductility titanium materials by harmonic microstructure control

"Harmonic Microstructure" fabricated by combination of the Severe Plastic Deformation (SPD) process and the Powder Metallurgy (PM) process is one of a new tailored heterogeneous microstructure. A pure titanium powder and a Ti-6A1-4V alloy powder are subjected to mechanical milling (MM) process which is one of SPD processes. The MM process enables to produce a nano grain microstructure very easily and has been applied to many powder materials. Additionally, we can obtain a bimodal microstructure in the MM powders by controlling the MM conditions. Such a bimodal microstructure is composed of nano grains in the surface region and of micron sized (meso-scale) grains in the core region of the MM powders. The MM powders were used to fabricate compacts by HRS (Hot Roll Sintering) or HIP (Hot Isostatic Pressing) process. The sintered compacts show a network microstructure of nano grain structure ,as well as dispersed meso-scale grain structure. In other words, it demonstrates heterogeneous but well organized "Harmonic Microstructure". The titanium materials with "Harmonic Microstructure" lead to outstanding mechanical properties such as strength and elongation compared to the conventional materials.