NiTi基体中增强相的变形行为研究进展

Research Progress on Deformation Behavior of Metal Nanowires in NiTi Matrix

现代社会的发展对材料的性能提出新的要求,传统的单质金属或合金已不能满足需求。复合材料因其质量轻、强度高、耐腐蚀等优点具有广泛应用前景,因而对新型复合材料的开发非常重要。在近些年的研究中,学者们发现通过NiTi合金与金属纳米线复合,复合材料中的金属纳米线可以表现出超大弹性变形现象,可以达到或超过独立纳米线的弹性应变极限,这种现象主要源于NiTi形状记忆合金中应力诱发马氏体相变与纳米线弹性变形的应变匹配效应(lattice strain matching effect)。金属纳米线在NiTi基体中表现出的超大弹性变形现象对研究如何在复合材料中保留纳米线的超高强度具有重要意义。目前研究的NiTi/纳米线复合材料主要有NiTiNb,NiTiW,NiTiV等,纳米线主要为Nb纳米线和V纳米线,这些纳米线在NiTi基体的相互作用下表现出了独特的性能,本文主要介绍了NiTi基体中不同种类的纳米线的变形行为,并简述纳米线对NiTi基体马氏体相变的影响。

The tendency of modern industrial manufacturing was miniaturization,lightweight and intelligent so that composite materials had a very wide application prospect.Composite materials had been widely studied since it was discovered because of its light weight,high strength and other excellent performance.Nanomaterials,the most promising reinforcement materials,were also used in the research and development of composite materials.However,the researchers found that the strength of the nanostructure composite materials were unsatisfactory,this was mainly due to the deformation mechanisms of common metal matrix was dislocation slip.In the process of deformation,the tremendous internal stress concentration at the interface led the nanowires plastic deform and fracture.As a result,the elastic deformation of the nanowires embedded in the matrix was lower than that of the independent nanowires.NiTi shape memory alloy was the most widely used shape memory material due to the advantages of high damping,super elasticity,good shape memory effect,etc.The unique shape memory effect and the martensitic transformation could be used to develop new intelligent composite materials.In recent years,scholars found that the inherent characteristics of NiTi alloy in composites could combine well with other materials and the nanowires embedded in NiTi shape memory alloy matrix could exhibit ultra-large elastic deformation,which provided a new idea for us to transfer the high strength of nanowires into composite materials.The metal nanowire with large elastic deformation by using the lattice strain matching effect between NiTi shape memory alloy and metal nanowire could be obtained.It was very important to enlarge its application scope and ensures the fast transfer of load.Although the better performance of composite material than common metal matrix with this method could be got,composite material was not the simple superposition between different materials.The interaction between them was the root of excellent performance,for a multi-constituent composite,the mechanical response to an external load was related not only to the intrinsic properties of each of the components,but also to the interactions between them.Moreover,NiTi shape memory alloy had huge restorable strain,and the internal phase transformation process was very complex during the tensile recovery process.Therefore,the interaction mechanism between metal nanowires and NiTi matrix composites needed to be further studied.At present,the main NiTi matrix composites included NiTiNb,NiTiW,NiTiV,etc,the deformation behavior of nanowires through these composite materials could be studied.Due to the mismatch in recoverable strains of NiTi matrix and Nb nanowires,internal stresses coupling was created between the nanowire and the matrix after tensile deformation.The internal stress-affected zone in the matrix was limited to within a small range around the nanowires.These stresses affected the stress-induced martensitic transformation behavior of NiTi in the zones.It was found that such a phenomenon in bulk metallic materials in spite of elastic strain in bulk metallic materials was usually limited to only a mass fraction of 1%.Developing bulk metallic materials showing large linear elasticity and high strength had proven to be difficult.Here,based on the synergistic effect between nanowires and orientated martensite NiTi shape memory alloy,an in-situ Nb nanowires orientated martensitic NiTi matrix composite showing an ultra-large linear elastic strain of 4%could be developed.It was demonstrated that the synergistic effect allowed the exceptional mechanical properties of nanowires to be harvested at macroscale and the mechanical properties of matrix to be greatly improved,resulting in these superior properties.This study provided new avenues for developing advanced composites with superior properties by using effective synergistic effect between components.In addition,other behaviors of NiTi matrix were observed in W/NiTi composites.The deformation incompatibility between W layers and NiTi layers caused some microcracks at the interface,which could release stress concentration.However,the bridging effect of NiTi matrix and the crack deflection at interfacial made the composites exhibit a high damage tolerance.This result provided a new way to design new W-based composites with good strength,ductility and damage tolerance.The scholars found that different types,morphologies and quantities of the second phase would affect the overall properties of the composites through the research of V nanowires.Theoretically,we could design specific composite materials based on these characteristics,and obtain materials with the same excellent performance while reducing the volume and weight to meet the needs of the manufacturing field.Finally,we should make more extensive use of the excellent performance of NiTi shape memory alloy in combined with other materials to develop new high-performance composite materials.The focus of future research was to apply such intelligent composite materials to practical applications,we could use them firstly to military,aerospace and other cutting-edge fields,and then gradually to civil fields after cost reduction.In this paper,the deformation behavior of different kinds of nanowires in NiTi matrix were introduced,and the effect of nanowires on martensitic transformation of NiTi matrix were described briefly.