Deformation Mechanism Of Nanocale Single Crystal Tantalum

The plasticity of nanomaterial is one of the important mechanical properties,especially to the body centered cubic(BCC),which has high hardness and high strength.The excellent plasticity is the precondition for preventing brittle fracture and safe application.Although there are plenty of studies focusing on the plastic deformation of BCC bulk materials,few results have been reported on small-sized BCC materials.At present,BCC materials such as W,Mo,Nb etc.have been intensively investigated.However,not so much work has been concentrated on BCC Ta,which is widely used in aerospace engines and capacitors.Correspondingly,the plastic deformation of small sized Ta is still an unsettled question.In this work,in-situ tensile tests of single crystal tantalum(Ta)nanoplates(thickness:100 nm)were conducted inside a transmission electron microscope(TEM)by using our home-made device.The main points that we obtained are as follows:(1)an unusual ultra-large elongation(63%)of Ta nanoplates at ambient temperature(below~60?)is observed,which is more than twice of the amount uniform deformation comparing with bulk tantalum;(2)in-situ observations revealed that the continuous and homogeneous dislocation nucleation and fast dislocation escape are responsible for the ultra-large elongation in BCC Ta nanoplates,followed by the decrease of dislocation density;(3)in-situ observations of deformation and cracking showed that a large amount of curved or hook-liked dislocations nucleate and slip towards curved part.With the further loading,the long straight parts of dislocation become longer and pile up.The HRTEM images show that there are large amounts of mixed dislocations with b=1/2?111?at crack tip and inside of sample.This investigation proves that the mixed dislocations contribute to the plastic deformation of nano-scaled BCC Ta.It also gives the direct evidence of dislocation pile up in the BCC Ta nanomaterial.