Computational Modeling and Experimental Study of the Deformation Behavior of γ-TiAl-Based Alloys

Abstract

We suggested how to obtain a high volume percentage of effective, stable and finely dispersed oxide particles. New dispersoids, created in the modeling process, consist of core and coat. The core is formed by internal oxidation of the soluble alloying element, whereas the oxide of the lower-solubility alloying element envelops the previously precipitated oxide and creates the coat with the appropriate particle/matrix interface.According to the proposed model the ternary alloying system Cu±Al±Zr was identified as one of the most promising candidates for the experimental confirmation of the proposed modeling process. It was confirmed that in rapidly solidified Cu±Al±Zr alloys internal oxidation proceeds with timeshifted precipitation of the oxides Al 2 O 3 and ZrO 2 at the internal oxidation front. The Al 2 O 3 oxide particles precipitate first from the solid solution and serve as seeds for heterogeneous precipitation of ZrO 2 oxide. Oxidation of zirconium starts with dissolution of Cu±Zr intermetallic particles ahead of the IO front, continues with diffusion of dissolved Zr atoms down the concentration gradient, and concludes with heterogeneous precipitation on the previously formed Al 2 O 3 oxide particles.

An energy approach to the formation of twins in TiAl

“…Marketz et al [15,16,18] and Schlögl and Fischer [17] have presented the most advanced formulation of twinning applied to both polysynthetically twinned single crystals and polycrystalline ␥(TiAl)-based alloys with a neargamma microstructure. They consider four twin systems (1/6 Ͻ 11 ]{111}) as a unilateral slip and a given amount of shear (␥ t ϭ /2) with the volume fraction of the twin system as an internal variable.…”

“…The formation of the twin is accompanied by a local strain jump (⌬ ij ) and a local stress jump (⌬ ij ). We assume fixed boundary displacements over ∂V during twinning, so that Green's theorem yields [16] We split ⌬ ij into ⌬⌺ ij and . As a direct consequence of Eq.…”

Acoustic Emission Technique to Study the Effect of Strain Rate on the Deformation Behaviour of TRIP Aided Steels with Different Matrix Microstructures

“…[17][18][19][20] This is generally believed to be due to the increase in source activation (i.e. number of AE events per unit time interval increases).…”

“…tests, intense activity is recorded in all three steels during yielding. But unlike the general AE behaviour observed in other materials, [17][18][19][20] AE activity persists in the post yielding stage as well.…”

“…[17][18][19][20][21][22][23][24] Possible sources of AE activity in these cases are believed to be deformation and fracture including crack initiation and growth; crack opening and closure; dislocation avalanche; twinning, in monolithic materials, and fibre breakage and fibre-matrix debonding in composites. It has been observed further that twinning, micro yielding and crack growth are typical sources of burst type of AE signals whereas dislocation motion generates continuous AE signals.…”