Portevin-Le Chatelier effect in a Ni-Cr-Mo alloy containing ordered phase with Pt₂Mo-type structure at room temperature

Serrated flow behavior or the Portevin-Le Chatelier (PLC) effect in a Ni-Cr-Mo alloy containing ordered phase was investigated at uniaxial tensile and nanoindentation tests at room temperature. Results demonstrate that the periodic arrangement of atoms for nano-sized ordered phase with Pt₂Mo-type structure obtained by ageing treatment at 600°C, induces the appearance of an embedded serration (a small serration is embedded in two adjacent large serrations) in the alloy during uniaxial tensile tests at room temperature with strain rates of 10^-3 and 10^-4s^-1. The behavior characteristic of small serration is almost independent on strain rate, but that of large serration is significantly dependent on strain rate. Both the stress drop (δσ) of the large serration and the interval (t_w) between adjacent large serrations increase with decreasing strain rate from 10^-3 to 10^-4s^-1. Moreover, a single serration also appears in load-displacement curve of aged sample at loading rate of 10^-3s^-1. Both formation of order-disorder transformation-induced twins and twinning of ordered phase itself are responsible for the occurrence of the embedded serrations.