Fabrication And Mechanical Properties Tailoring Of Heterogeneous Zr/Ti Materials

Zirconium(Zr)and its alloys are widely used in the nuclear industry because of their excellent corrosion resistance,radiation resistance,and small neutron absorption.Based on these superior properties,Zr alloys have important application potentiality in chemistry,biomedical materials and aerospace fields.However,the conventional zirconium alloys for nuclear power have low strength and cannot meet the mechanical properties requirements of many key structural parts.In addition,when the strength of the new Zr alloy developed based on the traditional strengthening method is increased,the plasticity is often significantly reduced,which cannot meet the requirements of plastic processing and service safety.In recent years,a large number of studies have shown that heterogeneous structures,for example laminated structure materials and gradient materials,etc,have good balance between the strength and the ductility.Based on Zr-Ti binary system,in which a complete solid solution can be achieved,pure Zr and pure Ti plate were used as raw materials in this work to fabrication heterogeneous Zr/Ti material.Pre-deformation and diffusion annealing method are used to fabricate the Zr/Ti heterogeneous materials,which combines layered structure and gradient structure.Microstructures and mechanical properties of the fabricated laminated gradient Zr/Ti(LG Zr/Ti)materials are further tailored by quenching at different temperatures,multi-stage heat treatmentw,and rolling-annealing treatments.The macro/microstructures of Zr/Ti laminated gradient materials in different processing states were characterized by SEM and EBSD,and their mechanical properties were tested by microhardness,compression,and tension.Results indicate that:(1)The microstructure of the Zr/Ti laminated gradient materials was composed of alternating Zr layers,Ti layers and Zr-Ti mutual diffusion layers(interface layers).The thickness of the interface layer increased with increasing annealing temperature and time.The average hardness and strength of the Zr/Ti laminated gradient materials increased with increasing annealing temperature and time,which can be higher than that of the constituent materials.(2)Quenching can introduce fine martensite structure in the interface layer.So,three sub-layers,quenched-sub-layer,Zr-enriched-layer,and Ti-enriched-layer,can be identified,and the thickness of the quenched sub-layer and the strength of the Zr/Ti laminated gradient material increase with the increasing quenching temperature.By multi-stage heat treatment,multiple sub-layers were introduced into the interface layer to form a multi-scale hierarchical structure,which has an additional strengthening effect on the Zr/Ti material.Cold rolling-annealing can achieve effective refinement for grains of Zr layers and Ti layers and improve the strength of the Zr / Ti laminated gradient material.Without changing the overall chemical composition,the yield strengths of the Zr/Ti laminated gradient materials could be tailored within a wide range(from 370 MPa to 840 MPa)and maintain good ductility by changing the layered and gradient microstructure.This lays the foundation for the wide application of Zr in different fields.