Origin of strong solid solution strengthening in the CrCoNi-W medium entropy alloy

Solid solution strengthening is one of the most conventional strategies for optimizing alloys strength, while the corresponding mechanisms can be more complicated than we traditionally thought specifically as heterogeneity of microstructure is involved. In this work, by comparing the change of chemical distribution, dislocation behaviors and mechanical properties after doping equivalent amount of tungsten (W) atoms in CrCoNi alloy and pure Ni, respectively, it is found that the alloying element W in CrCoNi alloy resulted in much stronger strengthening effect due to the significant increase of heterogeneity in chemical distribution after doping trace amount of W. The large atomic scale concentration fluctuation of all elements in CrCoNi-3W causes dislocation motion via strong nanoscale segment detrapping and severe dislocation pile up which is not the case in Ni-3W. The results revealed the high sensitivity of elements distribution in multi-principle element alloys to composition and the significant consequent influence in tuning the mechanical properties, giving insight for complex alloy design.