The Formation And Effects On Deformation Behavior Of Heterogeneous Structures In Laminated Metal Composites

With the growing shortage of energy,laminated metal composites(LMCs)have attracted much interest due to their good comprehensive mechanical properties.Most research of architectural materials including LMCs focuses on macro mechanical properties and simulation of deformation behavior based on mechanics.However,as heterogeneous structures are introduced in the materials,the effects of heterogenous microstructures on mechanical properties and deformation behavior still need to be further studied.The objective of this study is to explore the strengthening and toughening theories of LMCs from an angle of materials science through investigating the effects of heterogeneous structures on annealing and deformation behavior of laminated Ni Al and Ti-Al composites.For laminated Ni Al system,the laminated Ni Al composites have been synthesized by in situ reaction annealing at 1200?C.The laminated Ni Al shows a heterogeneity of grain size difference and chemical composition gradient and the heterogeneity weakens with increasing annealing time.Based on electron microscopy,the orientation inheritance in laminated Ni Al has been studied.It has been found that there is a K-S orientation relationship between a Ni Al layer with high density defects formed by solid-state diffusion and a parent Ni layer via a Ni3 Al interfacial layer.Moreover,dislocations form at the interfaces due to heterogeneity effects including atomic spacing mismatch,difference of elastic modules and thermal expansion coefficients between interfacial phases,and mechanical/thermal residual stresses.In addition,the effects of heterogeneous structures on mechanical and deformation behavior of laminated Ni Al have been studied through room/high temperature mechanical tests and corresponding deformed microstructural analysis,and both strengthening and toughening effects have been found.Based on electron microscopy,it has been found that there are differences of deformed microstructures between coarse and fine grains including internal sub-microstructures,average misorientation,dislocation structures and interface effects.Furthermore,the crack length of laminated Ni Al has been simulated and it turns out to be prolonged 20% compared with bulk Ni Al.For laminated Ti-Al system,the laminated Ti-Al composites with different structural parameters have been fabricated through hot pressing followed by multi-pass hot rolling at 500?C.Based on electron microscopy,the microstructures of component layers and interfaces have been studied.It has been found that the interfaces are rough with protrusions and retrusions with the formation of nanoscale Ti Al3 interfacial layers.Recovery and recrystallization prefer these protrusions and retrusions and expand to the middle of layers with increasing annealing time.Moreover,the softening behavior of component layers has been studied through hardness tests for different annealing conditions and corresponding microstructures.In addition,the effects of heterogeneous structures on mechanical and deformation behavior of the laminated Ti-Al composites have been studied through analysis of mechanical properties and deformed microstructures.It shows that the laminated Ti-Al composites show extra strengthening in elastic-plastic stage compared to the rule of mixture and this strengthening effect increases with decreasing Al layer thickness.Furthermore,the deformed microstructure of Al shows gradient and it has been proved to be related to interfacial constraint effect by quantitative electron microscopy characterization and applying the theory of strength.It has been found that the elongation of laminated Ti-Al composites shows optimum with specific Al layer thickness by analysing crack distribution during deformation.Comparing with the mechanical properties of individual component layers,it has been found that the strengthening effect of submicrostructure is stronger than that of layer scale for Al,and local strain relaxation increases the elongation of Ti by inhibiting its {10-11}<10-12> compression twinning.Moreover,the deformed microstructures of Al layer show orientation dependence but difference with bulk Al.As strong constraint effect of interface plays significant role in laminated structure,it is too hard to form geometrically necessary boundaries due to multi slip systems activation.