G.J.L. van der Wegen

Superlattice dislocations in the L12 ordered structure of Cu2NiZn

Abstract Dissociation criteria for superlattice dislocations on {111} planes have been applied to the ordering alloy Cu2NiZn. The calculations showed that the splitting of a superlattice dislocation into two superlattice Shockley partials, with Burgers vector of type 1/3a 0⟨211⟩, bounding a superlattice intrinsic stacking fault. (SISF), is energetically less favourable than the splitting inta two unit dislocations, with Burgers vector of type 1/2a 0⟨110⟩, separated by an antiphase boundary (APB). This theoretical prediction is in agreement with the type of superlattice dislocation observed in the electron microscope. It is rather difficult to predict a priori whether each unit dislocation is split into two Shockley partials separated by a complex stacking fault (CRF) because the cut-off parameters for the dislocation cores are not known with sufficient accuracy. The splitting into two Shockley partials could not be resolved in the electron microscope, which means that either the separation between the Sho...

Mechanical Properties of the Ordering Alloy Cu2NiZn

Abstract The mechanical properties characterizing the true stress-true strain curve of Cu 2 NiZn are investigated as a function of the deformation temperature between 77 and 343 K and as a function of the quench temperature in compression as well as in tension. The behaviour of the yield stress could be explained in terms of the stress necessary to operate an initially edge-oriented Frank-Read source, consisting of a superlattice dislocation with a length of 1.45 μm and to destroy the short-range order across the slip plane. The behaviour of the strain hardening coefficient could be accounted for by the superposition of the strengthening due to interacting and non-interacting forest dislocations, formation of jogs and APB-tubes and long-range stresses. The stress σ III at the onset of stage III behaves according to the {111} cross-slip model for the disordered alloy. Its behaviour for the ordered alloy can be explained by movement of single dislocations, leaving sheets of APB in its wake. The mechanical properties of the ordered L1 0 and L1 2 structures behave about the same, whereas the behaviour of the disordered alloy is quite different. The same behaviour holds for the dislocation microstructure as observed by transmission electron microscopy.

Order-strengthening in the ternary alloy Cu2NiZn

Abstract The order-strengthening mechanism in Cu 2 NiZn was studied by comparing stress-strain curves and electron micrographs of corresponding dislocation structures in disordered, partly ordered and ordered samples. At the low strain level superdipoles were frequently observed showing a whole range of interdislocation distances, which were compared with the calculated equilibrium distance between the dislocations based on a zero force consideration.

On the determination of the stacking fault energy from extended nodes in Cu2NiZn

Stacking fault energies can be determined from the dimensions of extended dislocation nodes. Different theoretical treatments of the node problem have been published. The aim of the present paper is to compare the results obtained using the theories of Brown and Thöléen, Siems and Jøssanget al and to provide quantitative information about the dependence of the stacking fault energy for Cu2NiZn on the model used. Extended nodes in networks with mesh size larger than the outer radius of the node (R) can be used for the determination of the stacking fault energy. Isolated nodes as well as network nodes are used to obtain the stacking fault energy in Cu2NiZn, which appeared to be 33 ± 9 mJ/m2.

Temperature Anomaly of Work Hardening in Cu2NiZn

ABSTRACT Cu2NiZn shows an anomalous temperature dependence of the workhardening due to severe (100) cross-slip. A maximum occurs near 375 K. The samples with cube-type domains do exhibit this effect more exclusively than the samples with a more isotropic type of domain structure. In this respect Cu2NiZn behaves more like Cu3Au with a similar peak near 350 K than like Ni3Fe or Ni3Mn, two alloys which do not show such an anomaly at all.

Deformation Behaviour of the Ordering Alloy Cu2NiZn

ABSTRACT The deformation behaviour of the ordering alloy Cu2NiZn was studied by investigating the stress-strain curves as a function of the deformation temperature between 77 K and 343 K and as a function of the quench temperature in compression as well as in tension. The mechanical properties of the ordered L1Q and L12 structures are about the same whereas that of the disordered one is quite different. The behaviour of the yield stress has been discussed quantitatively in terms of Ashby-Moines formulae for Frank-Read sources. It could be explained in terms of the stress necessary to operate an initially edge-oriented Frank-Read source, consisting of a superlattice dislocation with a length of 1.45 μm, and to destroy the short-range order across the slip plane. Electron microscopic observations show that even in disordered alloy when short range order exists, superlattice dislocations were created by Frank-Read sources rather than the generation of single dislocations.