Twins, grain boundaries, dislocations, precipitates

September 23, 2011

[1] Dislocation interactions and low-angle grain boundary strengthening

B liu et al

The transmission of an incoming dislocation through a symmetrical low-angle tilt grain boundary (GB) is studied for {1 1 0}〈1 1 1〉 slip systems in body-centered cubic metals using discrete dislocation dynamics (DD) simulations. The transmission resistance is quantified in terms of the different types of interactions between the incoming and GB dislocations. Five different dislocation interaction types are considered: collinear, mixed-symmetrical junction, mixed-asymmetrical junction, edge junction, and coplanar. Mixed-symmetrical junction formation events are found not only to cause a strong resistance against the incident dislocation penetration, but also to transform the symmetrical low-angle tilt GB into a hexagonal network (a general low-angle GB). The interactions between the incident dislocation and the GB dislocations can form an array of 〈1 0 0〉 dislocations (binary junctions) in non-coplanar interactions, or a single 〈1 0 0〉 dislocation in coplanar interaction. We study how the transmission resistance depends on the mobility of 〈1 0 0〉 dislocations. 〈1 0 0〉 dislocations have usually been treated as immobile in DD simulations. In this work, we discuss and implement the mobility law for 〈1 0 0〉 dislocations. As an example, we report how the mobility of 〈1 0 0〉 dislocations affects the equilibrium configuration of a ternary dislocation interaction.

[2] Nucleation and growth of the γ′(AlAg2) precipitate in Al–Ag(–Cu) alloys

J M Rosalie et al

Precipitation of the γ′(AlAg2) phase was investigated in Al–Ag(–Cu) alloys using high-resolution transmission electron microscopy and scanning transmission electron microscopy. Precipitation commenced with segregation of Ag to stacking faults, followed by thickening in steps corresponding to single unit cell height ledges. In conjunction with gradual segregation of Ag and Al into ordered layers, this yielded γ′ phase platelets with a thickness of either 2 or 3 × the AlAg2c-lattice parameter. Plates with a thickness of 2c(AlAg2) could not achieve self-accommodation of the shape strain for transformation. Further thickening of the precipitates was slow, despite considerable Ag segregation around the precipitates. Growth by the addition of single unit cell height ledges is expected to lead to an additional shear strain energy barrier to ledge nucleation and this may contribute to a process of nucleation-limited growth.

[3] Bulk eutectic Cu-Ag alloys with abundant twin boundaries

Y Z Tian and Z F Zhang

Abundant growth twin boundaries are found and characterized in two bulk eutectic Cu-Ag alloys which can be obtained conveniently. The statistical electron backscattering diffraction (EBSD) results show that both hetero-twin and cube-on-cube orientation relationships coexist in the eutectic Cu-Ag alloy. The tensile strength of the eutectic alloy increases with decreasing the layer thickness of the Cu/Ag phase. This study provides a potential way to produce bulk eutectic Cu-Ag alloy with abundant twin boundaries for achieving high strength and high ductility.

[4] Effect of Cu addition on the mechanical behavior of austenitic twinning-induced plasticity steel

S Lee et al

The effect of copper additions on the mechanical behavior of a Fe-12%Mn-0.7%C-1.0%Al twinning-induced plasticity steel was investigated by analysis of the mechanical properties obtained in uniaxial tensile tests by means of a physically-based constitutive model. The addition of copper was found to retard the kinetics of twin formation and influenced the type of the serrations on the stress-strain curve. The copper additions also resulted in a remarkable increase in the total elongation without a loss of strength.


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