Abstract
This article describes the evaluation of high-speed superplastic forging and near-net-shape control in nanocrystalline titanium aluminide. The process analysis of isochronal forging at a constant displacement rate permits us to derive the strain rate sensitivity exponent (m) of approximately 0.4 on the basis of the constitutive equation of ε^m=Aδ(1/d)*exp(-Q/kT) for full density nanocrystalline (Ti_<50>Al_<50>)_<90>Fe_<10> with the average crystallite size of 20 nm. For the full density amorphous Ti_<50>Al_<50> sample, the isochronal forging under the constant load leads to a relatively high plastic strain rate of approximately 1×(10)^<-2>s_<-1> at 977K during Newtonian viscous flow that is given by a relation of η=η_0 exp(Q_v/kT) in a supercooled liquid. The apparent activation energy (Q) for nanocrystalline Ti_<50>Al_<50> is derived at 113 kJ・mol^<-1> that is a nearly quarter of the value (467 kJ・mol^<-1> ) of the amorphous alloy. The near-net-shape forging is successfully achieved for the amorphous and nanocrystalline TiAl by using a specially designed carbon plunger.
