Processing of nano-grained materials

Sintering and deformation were studied in nano-grained (n-)TiO₂ and n-TiAl as part of a program to develop materials for near-net shaping and superplasticity applications. An important concern for processing nano-grained materials is the control of grain growth during both densification and deformation. In this study, the effectiveness of doping n-TiO₂ with yttrium for controlling grain growth during isothermal annealing was examined. In addition, an empirical constitutive law for the densification of n-TiO₂ was determined. Comparison of sinter-forming in n-TiO₂ with larger grained oxide ceramics shows many similar features. The studies on TiAl examined the hardness as a function of grain size, indentation time and temperature. At large grain sizes, the hardness obeys the Hall-Petch relation, but below a critical grain size, approximately 30 nm, the hardness decreases with decreasing grain size. Finally, the potential for synthesizing metallic glasses with nanoscale amorphous particles is discussed.