| Freestanding metal nanowires have ultra-large elastic strain limit(4-7%)and ultra-high strength,however,their extraordinary mechanical properties are difficult to be exploited in bulk composites.Recently,based on the concept of the strain-matching between nanowire’s large elastic strain and the metal matrix lattice shear strain,our group successfully make Nb nanowires exhibit ultra-large elastic strain limit in the NiTi matrix deformed by stress-induced martensitic transformation(B2→B19’),.Thus the composite can exhibit extraordinary mechanical properties.In order to further prove the universality of this strain-matching design concept,we prepared an in-situ W nanoribbons/NiTi shape memory alloy composite using metal W with ultra-high Young’s Modulus instead of Nb,and studied the deformation behavior of the W nanoribbons in the phase transforming NiTi matrix.In addition,we investigated the deformation behavior of Nb nanowires in strain-induced martensitic transformation(first undergoing dislocation slip plastic deformation and followed by martensitic transformation deformation)in NiTi matrix,and the deformation behavior of Nb nanowires in NiTi matrix with different phase transition paths by in-situ high-energy X-ray diffraction technique.The main findings of this paper are as follows:An in-situ W nanoribbons/NiTi shape memory alloy composite was prepared by conventional metallurgical method.It was found that the W nanoribbons with high Young’s Modulus can exhibit a large elastic strain of 3% in the NiTi matrix deformed by stress-induced martensitic transformation,and the estimated phase strength is as high as 11.6 GPa.The martensitic transformation of the NiTi matrix is carried out in the Lüders-like style.About 20% volume fraction of the parent phase was remained in the matrix after the propagating of Lüders band,indicating that the martensitic transformation of the matrix is compressed by W nanoribbons.At the beginning of the unloading process,the NiTi matrix immediately undergoes inverse martensitic transformation,indicating that the presence of the W nanoribbons significantly reduce the hysteresis of matrix’s inverse martensitic transformation.It is found that there is a significant size effect between the elastic strain limit of the W nanorebbons in the NiTi matrix and its thickness,which can be characterized by the power-law relation.Nb nanowire/NiTi memory alloy in-situ composites were prepared by conventional metallurgical method.It was found that strain-induced martensitic transformation occurred in the matrix and it was carried out in the Luders-like style.In the end of the Lüders band,only about 10% volume fraction of parent phase undergoes strain-induced martensitic transformation.After the strain-induced martensitic transformation of the matrix,the tensile elastic strain of the Nb nanowires rapidly increased up to 4.2%;In addition,during the strain-induced phase transition carried out by about 10% volume fraction of the matrix,the remained parent phase matrix undergoes dislocation slip plastic deformation,accompanied with a sudden increased tensile elastic strain.The Nb nanowire/NiTi memory alloy composites were observed by in-situ temperature-variable high-energy X-ray diffraction technique.It was found that during the cooling process,the nanocrystalline NiTi matrix undergoes R phase transformation(B2→R),and its phase transition temperature range is up to 120°C(30 °C to-90 °C),the axial compressive stress of Nb nanowires gradually decreases,indicating that the axial compressive stress of Nb nanowires can be effectively released by the thermal-induced R phase transformation of NiTi matrix.In addition,it was found that Nb nanowires can exhibit large elastic strain(>3.6%)in the no matter stress-induced B2→B19’,B2→R→B19’,B2+R→B19’ or R→B19’ phase transition of the NiTi matrix.However,due to the different coupling behaviors between the matrix with different transition paths and nanowires,the Nb nanowires exhibit completely different deformation behaviors. |
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