The Multi-scale Deformation Mechanism Of Nanocrystalline Twined Materials

NC materials have attracted many investigations on their mechanical behavior dueto their superior properties such as high-strength. These superior mechanical propertiesare ascribed to their unique deformation mechanisms, which are different from those intheir coarse-grained (CG) counterparts. However, significant strengthening obtained inNC materials at the cost of its ductility. It has an adverse effects on the applications ofNC materials. In contrast with the traditional NC materials, twins in NC materialssubdivides the grains to increases the strength and also lead the growth of ductility, willhave a huge impact on other physical properties.There are many influence factors in deformation twinning process such as stackingfault energy, temperature and strain rate. It is widely knows that low temperature, hightemperature and low stacking fault energy can promote deformation twinning. In order toverify the temperature, strain rate couple effects on deformation twinning, we aim toestablished a constitutive model of Cu70-Zn30alloy：（1）The flow stress of materials is opposed by both short-range part andlong-range part. The short-range is a decreasing function of temperature T, and anincreasing function of strain rate. The long-range part increases with increasingaccumulated dislocation.（2）The deformation twins have strain hardening mechanism to the flow stress ofNC materials. The DTs structure refines grain size and leads to the improvement of thestrain hardening.（3）Use the constitutive model to analyze the couple effect of temperature andstrain rate.Through the study that concluded:（1）Low temperature can promote deformation twinning, twins spacing and twinlayer thickness decrease with the reduce of temperature. （2）High strain rate can also promote the growth of twins, the time of twinnucleation and growth are reduce with higher strain rate, therefore the thinner twin layerwill obtain.（3）It should be noted that the deformation twinning is more susceptible todeformation temperature than the strain rate according the result by theoreticalcalculation.