Study On The Thermal Stability Of Ti/Zr Metallic Layered Composite Processed By Accumulative Roll Bonding

Metallic layered composites are a new type of layered material prepared by using compound technology to make two or more dissimilar metals achieve strong metallurgical bonding at the interface.It can integrate the advantages of each component,complement each other in performance,and produce a synergetic effect,while introducing heterogeneous interlayer interfaces with different intrinsic properties and different structures.Among them,heterogeneous metallic multilayered composites,consisting of alternating ultrafine scale layers,shows many excellent properties due to their unique layered structure and the high-density heterogeneous interface,so it has a broad application prospect in various fields.However,thermal stability severely restricts the application and development of metallic multilayered composites under extreme service conditions.Therefore,studying the thermal stability of metallic multilayered composites has important theoretical guiding significance for their design and development under extreme service conditions.In this study,pure titanium and pure zirconium sheet were chosen as the initial objects.The Ti/Zr metallic layered composites with component layer thicknesses ranging from micrometers to submicrometers(333 ?m-0.19 ?m)were successfully prepared by accumulative roll bonding(ARB).The mechanical properties and thermal stability of Ti/Zr metallic layered composites with different unit layer thickness were studied by using scanning electron microscope(SEM),X-ray diffraction(XRD),energy dispersive spectrum analysis(EDS),tensile test and Vickers microhardness test.The test results of mechanical properties show that there is a significant size effect on the mechanical properties of Ti/Zr metallic layered composites.With the increasing number of ARB cycles,the thickness of the unit layer decreases,the strength of the material continues to increase.After eight cycles of rolling,Ti/Zr metallic layered composite has a yield strength of 654 MPa and tensile strength of 844 MPa.Its tensile strength is 1.6 times that of annealed pure zirconium and 2.3 times that of annealed pure titanium.Although the plastic loss is serious,the fracture elongation still be maintained at 9.3%.The morphology analysis of tensile fracture shows that the fracture mode of Ti/Zr metallic layered composite is plastic fracture dominated by dimples.XRD results show that no intermetallic compounds are formed during the accumulative roll bonding process.Studies on the thermal stability of layered composites have shown that the Ti/Zr metallic layered composite that has undergone one,three,and six cycles rolling can maintain its strength unchanged after annealing at 400? for 1h,showing good thermal stability.As the annealing temperature increases,the relationship between the strength of the three groups is shown in three stages,that is,stage I:the strength gradually decreases to the minimum as the annealing temperature increases;stage II:the strength increases sharply with the increase of annealing temperature;stage III:the strength reahes saturation as the annealing temperature increases.This is because as the annealing temperature increases,the thickness of the diffusion layer continues to increase.When the diffusion layer reaches a certain thickness,the diffusion layer plays a leading role in improving strength.At this time,the Ti and Zr atoms in the diffusion layer sharply increase the strength of the composite due to the solid solution strengthening effect.After annealing at a higher temperature,the Ti and Zr atoms gradually diffuse completely,and the composite even transitioned into a solid solution alloy so that the strength value reached saturation.The thermal stability of the Ti/Zr metallic layered composite also has a significant size effect.As the thickness of the unit layer decreases,the thermal stability gradually increases.After one,three and six cycles rolling of metallic layered composite,the strength decreased to minimum at 700?,600? and 500?,respectively.The six cycles layered composite has the lowest strength loss,followed by three cycles,and one cycle has the largest strength loss.