Twinning, grain growth, shape memory …

April 23, 2011

[1] Effect of microelasticity on grain growth: Texture evolution and abnormal grain growth

D-U Kim et al

A phase field grain growth model including elastic anisotropy and inhomogeneity was developed to demonstrate the effect of microelasticity on the grain growth. The mechanical response against an external load was found to control grain growth and texture evolution. In contrast to previous macroelastic descriptions, these results showed that elastically soft grains with higher strain energy density can grow at the expense of the elastically hard grains to reduce the total strain energy.
Highlights

► We develop a phase field grain growth model combined with a micro-elasticity effect. ► The micro-elasticity turns out to play a key role in controlling grain growth and texture evolution. ► Strong localization of strain energy density and inhomogeneous distribution even inside grains are observed. ► An external load can cause abnormal grain growth in the system with high elastic anisotropy. ► Elastically soft grains with higher strain energy density grow at the expense of the elastically hard grains to reduce the total strain energy.

[2] Interface-facilitated deformation twinning in copper within submicron Ag–Cu multilayered composites

J Wang et al

Rolling of Ag–Cu layered eutectic composites with bilayer thicknesses in the submicron regime (not, vert, similar200–400 nm) activated deformation twinning in Cu. Using atomistic simulations and dislocation theory, we propose that the Ag–Cu interface facilitated deformation twinning in Cu by permitting the transmission of twinning partials from Ag to Cu. In this way, twins in Ag can provide an ample supply of twinning partials to Cu to support and sustain twin growth in Cu during deformation. Interface-driven twinning as revealed by this study suggests the exciting possibility of altering the roles of dislocation slip and twinning through the design of heterophase interface structure and properties.
Highlights

► Deformation twins in Cu are observed within submicron Ag–Cu multilayers. ► We propose that the Ag–Cu interface facilitated deformation twinning in Cu. ► We demonstrate the proposal using atomistic simulation and dislocation theory. ► Interface-driven twinning suggests the possibility of altering the roles of slip and twinning through the hetero-phase interface design.

[3] Twinning system selection in a metastable β-titanium alloy by Schmid factor analysis

E Bertrand et al

Electron backscattering diffraction and Schmid factor analysis were used to study the twinning variant selection in a Ti–25Ta–24Nb (mass%) metastable β-titanium alloy. The two twinning systems {1 1 2}left angle bracket1 1 1right-pointing angle bracket and {3 3 2}left angle bracket1 1 3right-pointing angle bracket were observed. For each system the Schmid factor was shown to be a relevant parameter to determine the activated variant. Moreover, selection between the two twinning systems depends on the crystallographic orientation of the grain with respect to the tensile direction.
Highlights

► A metastable beta Ti-25Ta-24Nb alloy was synthesized by cold crucible semi-leviation melting. ► Electron backscattering diffraction was used to characterize the deformation mechanisms. 2 twinning systems have been identified. ► The Schmid factor was used to determine the activated variant.

[4] The effects of grain size on the phase transformation properties of annealed (Ti/Ni/W) shape memory alloy multilayers

P J S Buenconjeso et al

(Ti/Ni/W)n multilayer films were annealed to form a two-phase (B2-TiNi and β-W) system. Grain sizes extracted from X-ray diffraction profiles of annealed films revealed that B2-TiNi decreases with increasing W, due to the immiscible W layers obstructing its grain growth. With decreasing B2-TiNi grain size the Rs (B2–R) transformation temperature is not affected but the Ms (R–B19′) transformation temperature decreases significantly. Thus the addition of W to Ti–Ni is effective to induce the B2–R single-step transformation due to grain size effects.
Research highlights

► Annealed Ti/Ni/W multilayer films forms two-phase B2-TiNi and β-W system. ► Grain size of B2-TiNi decreases with increasing W amount. ► Grain size effects explains the separation of Ms and Rs temperatures. ► W alloying is effective to induce B2–R transformation.

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