Fabrication And Mechanical Properties Of Ti-Al Laminated Composites Based On Ultrasonic Consolidation

In recent years,ultrasonic additive manufacturing has been developed on the basis of metal ultrasonic consolidation?UC?technique,which has drawn considerable attention.The intelligent manufacture and integrated consolidation can be realized by combining ultrasonic consolidation and computer numerical control?CNC?milling process.Using the new UC machine developed in China,this thesis dealt with the Al/Al laminated structures?LS?,Ti/Al laminated structures?LS?and fiber reinforced Al/Al and Ti/Al tapes,which were made of A1 1100 foil and TA1 foil.The effects of processing parameters on the microstructure,peeling and tensile properties of Al/Al and Ti/Al LS and their fracture mechanisms were systemically studied using metallographic microscope,scanning electron microscope,X-ray diffractometer and INSTRON universal testing machine.Finally,Ti/Al₃Ti metal-intermetallic laminate?MIL?composites were fabricated by hot pressing sintering using the ultrasonically consolidated Ti/Al LS and Ti/Al tapes containing C fibers and SiC fibers.The reaction kinetics of synthesized Ti/Al₃Ti using Ti/Al LS was also investigated.Moreover,the microstructure,mechanical properties and fracture mechanisms of Ti/Al₃Ti MIL composites were comprehensively characterized and evaluated.The results indicated that the optimal parameters to fabricate Al/Al LS with superior performance are:normal force 1177-1373N,vibration amplitude 20?32?m,welding speed 20-28mm/s.After the peeling tests,two fracture models are observed,including partial and complete peeling phenomenon.After tensile tests,the main fracture mode of Al/Al LS is ductile fracture in that considerable dimples are observed,along with some brittle fracture features in some near interface regions.The continuous SiC fibers can be dispersed evenly as individual ones in the Al/Al LS in large scale when the normal force,vibration amplitude and welding speed are 1236N,30?m and 25mm/s,respectively.And the tensile strength of SiC f-Al/Al tape is 1.06 times than that of Al/Al LS but with approximately equivalent elongation.The results indicated that the optimal parameters to fabricate Ti/Al LS with superior performance are:vibration amplitude 34-36?m,normal force 2059-2206N,welding speed 20?23mm/s.The XRD and EDS results indicated that no obvious new phase forms and the atoms only diffuse within several microns in the metallurgical bonding zones.The microstructure analysis of Ti/Al LS peeling fracture surface indicated that three regions occur along the Ti/Al LS interfaces,including mechanical bonding region,hybrid bonding region and metallurgical bonding region.After tensile tests,conspicuous yield stage is found in Ti/Al LS.In addition,inter layer of the Ti/Al LS mainly presents brittle fracture,while the inner layer mainly manifests ductile fracture.The continuous fibers?C fibers or SiC fibers?can be dispersed evenly as individual ones in the Ti/Al LS in large scale when the normal force,vibration amplitude and welding speed are 2001N,32?m and 25mm/s,respectively.And the tensile strength of the fiber reinforced Ti/Al tapes are slightly lower than that of Ti/Al LS but with approximately equivalent elongation.Al₃Ti is the only newly formed phase when the Ti/Al tapes are annealed between 660 ?and 700?,and after hot pressing sintering process the interfaces of Ti/Al₃Ti exhibit wave shape.And during hot pressing sintering process,the growth of Al₃Ti is consistent with the exponential growth law and the kinetic index is 2.38 in 660 ?.The quasi-static compressive test results indicated that when the load is perpendicular to layer,the compressive strength of Ti/Al3i MIL and failure strain are 582MPa and 0.047,respectively;and when the load is parallel to layer,the compressive strength and failure strain of Ti/Al₃TiMIL are 865MPa and 0.017,respectively.Additionally,the tensile test results showed that the quasi-static tensile strength and failure strain of Ti/Al₃Ti MIL are 174MPa and 0.049,respectively.After hot pressing sintering process of Cf-Ti/Al and SiCf-Ti/Al tapes,the continuous C fibers and SiC fibers are also dispersed as individual ones in the Al₃Ti center line.And a small atom diffusion region formed within a scale of microns,indicating metallurgical bonding took place in the interfaces of fiber/Al₃Ti.The fibers introduced to the Ti/Al₃Ti MIL can improve the tensile strength,elongation as well as the compression strength when the load is perpendicular to layer.It is found that the compression strength of the fiber reinforced Ti/Al₃Ti MIL reduces slightly when load is parallel to layer.The fracture mechanisms results indicated that Ti alloy shows a typical ductile fracture characteristic with a lot of dimples,and Al₃Ti presents typical brittle fracture with the mixed transgranular and intergranular features.In the tensile fracture surface of Ti/Al₃Ti MIL,transition boundary of Ti alloy and Al₃Ti exhibits the mixed fracture of flutes and cleavage.