Nanoindentation responses of NiCoFe medium-entropy alloys from cryogenic to elevated temperatures

NiCoFe alloy,a medium-entropy alloy,shows potential for applications in extreme environments.However,there is a theoretical barrier concerning the unclear understanding of its high-temperature dislocation motion mechanism.The load response exhibits distinct signatures relevant to thermal activation,most notably a decrease in critical force(i.e,softening)from cryogenic to elevated temperatures,e.g.,from 200 to 1000 K.The onset of plasticity is characterized by the nucleation of stacking faults and prismatic loops at low temperatures,whereas the surface nucleation of Shockley partial dislocations dominates plasticity at elevated temperatures.We show that thermal effects lead to non-uniform atom pile-ups and control the rate of phase transformation with increasing indentation depth.The findings in this work extend the understanding of the mechanical response of NiCoFe alloys under indentation at different temperatures,shedding light on the underlying dislocation motion mechanisms and surface deformation characteristics.The observed transformation-induced plasticity mechanism has implications for the properties of medium-entropy alloys and their potential applications in extreme environments.

Learning local,quenched disorder in plasticity and other crackling noise phenomena

When far from equilibrium,many-body systems display behavior that strongly depends on the initial conditions.A characteristic such example is the phenomenon of plasticity of crystalline and amorphous materials that strongly depends on the material history.In plasticity modeling,the history is captured by a quenched,local and disordered flow stress distribution.While it is this disorder that causes avalanches that are commonly observed during nanoscale plastic deformation,the functional form and scaling properties have remained elusive.In this paper,a generic formalism is developed for deriving local disorder distributions from fieldresponse(e.g.,stress/strain)timeseries in models of crackling noise.We demonstrate the efficiency of the method in the hysteretic random-field Ising model and also,models of elastic interface depinning that have been used to model crystalline and amorphous plasticity.We show that the capacity to resolve the quenched disorder distribution improves with the temporal resolution and number of samples.