Thermally induced reaction and transient hardening of miscible spinodoid alloys

Spinodoid alloys prepared by dealloying and deposition exhibit a bicontinuous dual-phase nanostructure with (semi-)coherent interfaces, resembling some features of the structure formed in spinodal decompostion. Composition fluctuation in such material and its spinodal-like hardening may then be tuned via thermally induced interdiffusion, even in undecomposable alloys. This paper studied the annealing behavior of miscible Cu/Au and Ag/Au spinodoid alloys with semi-coherent and coherent interfaces respectively. While the interdiffusion-dominated interfacial mixing occurs in both alloys, this process is interrupted in the Cu/Au alloys by a recrystallization-like reaction due to the large lattice mismatch between Cu and Au. We also found that interdiffusion does not monotonically soften these materials; instead, hardening can be observed in both alloys at the early stage of annealing, though further annealing eventually leads to softening. Thermally induced transient hardening is attributed to the formation of a diffuse Cu/Au or Ag/Au interface whose barrier strength to dislocation transmission is enhanced comparing to the sharp interface before annealing. Localized solid solution hardening and the dissociation of misfit dislocations within the diffuse interface might have led to the increase of interfacial barrier strength.