An Experimental Study On Strengthening Mechanism Of V-Zr Nano Crystalline Films

Nanocrystalline solid solution alloys have been the focus of intense research efforts and attractive application potential due to excellent mechanical behaviors and more stable structure in comparison with conventional coarse-grained materials and pure metals.As grain size reaches the tens of nanometer range,the traditional intragranular dislocation strengthening mechanisms based on coarse-grained materials are difficult to explain the novel deformation physics with an increasing volumn fraction of grain boundaries.Thus the strengthening mechanism of nanocrystalline alloys have been the subject of widespread research in recent years.It has recently been observed that isolating the effects and weight of various microstructural factors is vital to studying the strengthening mechanisms of nanocrystalline alloys.While it is rather difficult to separate each individual factor experimentally,limiting the study of strengthening mechanism for nanocrystalline alloys.In this paper,a series of V-Zr alloy films with different Zr content were synthesized by magnetron co-sputtering,with an aim to investigate the microstructure and mechanical properties.At the same time,we designed a structure of two-dimensional multilayered films to separate grain size,composition and other factors of nanocrystalline alloys.Through this method,this paper revealed the solid solution strengthening effect of various factors.The conclusions drawn from these studies are as follows:1.The results of V-Zr alloy films show that due to the high degree of non-equilibrium for film growth,the films with low Zr content form supersatuarated solid solution in which severe lattice distortion leads to a rapid nanocrystallization.With the increase of Zr content,the films form an amorphous structure of metals mixed with intermetallic compound V₂Zr and gradually become dominated by V₂Zr.Corresponding to the change of microstructure,the film hardness increases rapidly due to the nanocrystallization of supersaturated solid solution when Zr content is low.After the film forms an amorphous structure,the hardness increases slowly and keeps a high value due to the increase of V₂Zr with Zr content increasing.2.The results of V-Zr nano-multilayered films show that this paper realized the decoupling of grain size,composition and other microstructure factors and the independent change,using two-dimensional nano-multilayered films consisting of V-Zr alloy crystalline layers with low Zr content and amorphous layers with high Zr composition.The experimental results prove the existence of the inverse Hall-Petch phenomenon in nanocrystalline solid solution like pure metals.The critical grain sizes of inverse Hall-Petch phenomenon occurrence are about 30 nm and it is similar to nano-grained pure metals.And the solid solution strengthening effect of nanocrystalline alloys is independent of grain size not only as coarse-grained ones,but also,more importantly,when it becomes tens of nanometer.