Meso And Microscope Behavior And Mechanisms In Plastic Deformation Bonding Of Dissimilar Titanium Alloys

The plastic deformation bonding is one of the key technologies to manufacture the high performance components and achieve light-weighting,in which using dissimilar titanium alloys with different initial structure makes full use of the excellent properties of dissimilar titanium alloys in order to meet the property requirements.The interfacial voids and micro/nano-structural features in the bonding interface are the two key factors affecting the mechanical property of dissimilar titanium bonds.The present work focused on the fundamental issues in the interfacial voids and micro/nanostructure evolution in the bonding interface of TC4 with equiaxed structure and TC17 with different structures,and the main results and conclusions were as follows:The interfacial micro/nanostructure in the bonding interface of TC4 with equiaxed structure and TC17 with different structures was investigated via the electron backscattered diffraction(EBSD)and transmission electron microscope(TEM)techniques,in which the main mechanisms responsible for the interfacial recrystallization,gradient structure evolution and interface migration were discussed.The results showed that the original bond line(BL)during the plastic deformation bonding of TC4 with equiaxed structure and TC17 with different structures mainly transformed into the?(TC4)/?(TC17)interfacial phase boundary(IPB).The interfacial recrystallized?grains as a result of continuous dynamic recrystallization(CDRX)occurred during bonding of TC4 with equiaxed structure and TC17 with lamellar and equiaxed structures,and the recrystallized?grains in the primary?(?_p)grains of TC4 side as a result of discontinuous dynamic recrystallization(DDRX)occurred during bonding of TC4 with equiaxed structure and TC17 with equiaxed structure and nanocrystalline surface layer,which was mainly due to the plastic flow in the bonding interface.During bonding of TC4 with equiaxed structure and TC17with nanocrystalline surface layer,the gradient structure disappeared and the local texture intensity for?phase in TC17 side decreased with the increasing of bonding temperature,which was due to the grain growth in TC17 side of bonding interface.The plastic flow in the bonding interface promoted the interpenetration between TC4with equiaxed structure and TC17 with lamellar structure,resulting in the interface migration.During the bonding of TC4 with equiaxed structure and TC17 with equiaxed structure,the recrystallization in the?_p grains of TC4 side of bonding interface promoted the interface migration.Following bonding at 840?,30 MPa and30 min,the original BL in the bonding interface of TC4 with equiaxed structure and TC17 with equiaxed and lamellar structures disappeared.The interfacial voids morphology and size in the bonding interface of TC4 with equiaxed structure and TC17 with different structures were investigated via scanning electron microscope(SEM),in which the mechanism governing the interfacial void evolution was discussed.The results showed that during bonding of TC4 with equiaxed structure and TC17 with different structures,the large-sized interfacial voids transformed into small round voids with the increasing of bonding pressure,bonding temperature and bonding time,in which these small round voids generally occurred on TC4 side or on the?(TC4)/?(TC17)interface grain boundary(IGB)as a result of faster material flow from the?phase to the interfacial voids than that from the?phase.Compared to the interfacial void shrinkage rate in the bonding interface of TC4with equiaxed structure and TC17 with lamellar structure,the interfacial void shrinkage rate in the bonding interface of TC4 with equiaxed structure and TC17 with equiaxed structure was faster under the same bonding condition since the temperature increase in the bonding interface was higher.During the bonding of TC4 with equiaxed structure and TC17 with nanocrystalline surface layer,the large-sized interfacial voids transformed into small round voids with the increasing of bonding temperature,and these small round voids generally occurred in TC4 side of bonding interface.The shear strength of bonds of TC4 with equiaxed structure and TC17 with different structures was investigated via shear strength test,in which effect of the bonding parameters on the shear strength of bond was discussed.The results showed that for the bonds of TC4 with equiaxed structure and TC17 with lamellar structure at30 MPa and 30min,the shear strength increased up to that of the as-received TC4with the increasing of bonding temperature from 780?to 820?due to the disappearance of large-sized interfacial voids,and the shear strength further increased to 756 MPa with the increasing bonding temperature up to 840?due to the disappearance of original BL.For the bonds of TC4 with equiaxed structure and TC17with nanocrystalline surface layer,the shear strength at a bonding temperature of 780?was 672 MPa due to the large-sized interfacial voids,and the shear strength increased to 789 MPa with the increasing bonding temperature up to 820?,which was due to the synergistic effect of disappearance of large-sized interfacial voids and original BL.