Effects of surface roughness on interfacial dynamic recrystallization and mechanical properties of Ti-6Al-3Nb-2Zr-1Mo alloy joints produced by hot-compression bonding

The influence of surface roughness on the interfacial dynamic recrystallization kinetics and mechanical properties of Ti-6 Al-3 Nb-2 Zr-1 Mo hot-compression bonding joints was systematically investigated.It is found that for the bonding interface of rough surfaces,elongated fine grains are formed at the bonding interface due to shear deformation of the interfacial area.As the surface roughness increases,the proportion of elongated grains drastically decreases as they further reorient to form equiaxed grains along the bonding interface of rougher surfaces resulting from severe incompatible deformation of the interface area.Meanwhile,high-density geometrically necessary dislocations accumulate around the interfacial recrystallization area to accommodate the incompatible strain and lattice rotation.A rotational dynamic recrystallization mechanism is thereby proposed to rationalize the formation of fine interfacial recrystallization grains during bonding of rough surfaces.In contrast to that of rough surfaces,bonding interface of polished surfaces exists in the form of straight interface grain boundaries without fine grains under the same deformation conditions.While with the increase of deformation strain,small grain nuclei form along the bonding interface,which is associated with discontinuous dynamic recrystallization assisted by strain-induced boundary migration of interface grain boundaries.Moreover,the bonding joints of rough surfaces show lower elongation compared with that of polished surfaces.This is because the formation of heterogeneous fine grains with low Schmid factor along the bonding interface of rough surfaces,leading to worse compatible deformation capability and thereby poor ductility of bonding joints.

Microstructure evolution of Mg-Zn-Zr magnesium alloy against soft steel core projectile

The study aimed to shed light on the post deformation and damage behavior of an extruded Mg-Zn-Zr alloy under a ballistic impact.The results revealed that the initial microstructure consisted of both{0001}basal and{1010}prismatic fiber texture.After impact,adiabatic shear bands,pronounce different twinning in big grains,,<c>,and<c+a>types of dislocations,and grain refinement through twinning induce recrystallization accommodated the strain,and absorbed∼65.7%of the energy during impact carried by a soft steel projectile.Interestingly,the deformation behavior at the top broad sides of the crater was entirely different.The weak basal texture was changed to a strong prismatic texture,which was further proved by typical sigmoidal compressive stress-strain curves.A revised model for the development of the ultra-fine grains adjacent to the crater has been proposed.The microhardness and yield strength was∼33%and∼40%higher and chiefly ascribed to strain hardening in ultra-fine grained near the surface of the perforation path.The exit of the perforation path was severely damaged and forms onion-shaped concentric rings which were comprised of melted zones,dimples,and cracks.Based on the all interesting findings,this study can be a clue for the development of the lightweight Mg alloy for military and aerospace applications.