Enhanced precipitate growth at reduced temperatures during chemical ordering in deformed red gold alloys

Abstract

Manufacturing of red gold components relies widely on controlling the formation of ordered precipitates during thermo-mechanical processing.The ordered phase hardens the material, makes it less workable and introduces residual stresses. We show that an industrial wire straightening process on chemically disordered wires enhances the formation of ordered precipitates in the near surface region during natural ageing. To address the role of plastic deformation during artificial ageing, in situ X-ray experiments are carried out on deformed and undeformed samples. It is shown that pre-deformation decreases the onset temperature for ordering and enhances precipitation growth at the early stages of the transformation.

Bragg coherent imaging of nanoprecipitates: role of superstructure reflections

“…2(b), a homogeneous tensile strain builds up during relaxation in the nanoprecipitate region (" 001 = 4.1%), associated with an increase in the c/a ratio from 0.92 to 0.96. The magnitude of this tensile strain is in reasonably good agreement with the experimental values measured by X-ray diffraction (Garcia-Gonzalez et al, 2019, where " 001 reaches a maximum value of 3.5% (Section S11). In the surrounding A1 matrix phase, alternating regions of compressive and tensile strain are observed.…”

Influence of thermo-mechanical history on the ordering kinetics in 18 carat Au alloys

“…It is, therefore, reasonable to assume that most precipitates are preserved during the deformation procedure. As expected, the widths of the fundamental peaks have increased significantly after the cold rolling process (see also [26] ). On the other hand, the widths of the superlattice reflections are hardly influenced.…”

“…The set-up was calibrated using a standard CeO2 powder yielding precise information on the beam centre, sample to detector distance and detector tilt. The samples are mounted in a custom-built heating chamber, which is described in details in Ref [26]. During the in situ experiment, the samples described in Table 1 were heated at a rate of 10°C/min up to 450°C while recording diffraction patterns with a frequency of 1Hz.…”

“…This allows to determine the TEChkl as the slope of a linear fit of the elastic lattice strain as a function of temperature. An example of such a fit can be found in reference [26].…”

“…It has been observed that the L10 domains align their c-axis with the stress field when ordering under the application of a stress-field [23][24][25]. Moreover, in-situ synchrotron x-ray studies in metastable FCC red gold show that predeformation with a 25% reduction cold rolling enhances ordering during isothermal annealing at 250°C [26]. However, the knowledge of how dislocations facilitate ordering and whether this phenomenon can happen at lower temperatures is still missing.…”