| TiAl alloys have great prospects for the application of lightweight high temperature structural materials in the field of aerospace,due to its low density,high specific strength and good oxidation resistance.However,TiAl alloys,which are intermetallic compounds,have the characteristics of brittleness,low ductility and low fracture toughness at room temperature,which limit the wide application of TiAl alloys.Pure Tiand Ti-6Al-4V alloys have good ductility and toughness at room temperature.The introduction of pure Tiand Ti-6Al-4V alloy in TiAl alloy is expected to enhance the room temperature toughness of TiAl alloy.In this paper,Ti-43Al-9Y-Ti/Tiand Ti-43Al-9Y-Ti/Ti-6Al-4V laminated composite sheets were fabricated by the method of vacuum hot pressing using Ti-43Al-9V-0.3Y alloy sheets,pure Tisheets and Ti-6Al-4V alloy sheets.Ti-43Al-9V-0.3Y/Ti-6Al-4V laminated composite sheets after heat treatment were processed by multi-step heat treatment.The phase composition,microstructure and interface microstructure of the laminated composite sheets were analyzed,and the mechanical properties of the laminated composite sheets were discussed.Ti-43Al-9V-0.3Y/Tiand Ti-43Al-9V-0.3Y/Ti-6Al-4V laminated composite sheets were fabricated by vacuum hot pressing under(1000?-1100?)/30MPa/3h.It was found that there are a clear distinction of laminated composite sheets with good interface bonding,no holes and cracks,high density.The microstructures of the interfacial layer of composite sheets were studied.Due to the interdiffusion of atoms,the thickness of the interface layer of Ti-43Al-9V-0.3Y/Tilayered composite fabricated by vacuum hot pressing at 1000? and 1100? is about20?m and 193?m respectively,the thickness of the interface layer of Ti-43Al-9V-0.3Y/Ti-6Al-4V layered composite fabricated by vacuum hot pressing at1000? is about 33?m;The interface layer of Ti-43Al-9V-0.3Y/Tiand Ti-43Al-9V-0.3Y/Ti-6Al-4V laminated composite is mainly composed of two parts.The interface area near the TiAl alloy is consisted of a large amount of ?/?0 phase and the interface area near the pure Tior Ti-6Al-4V alloy is consisted of a large number of ?/?2phase.The microhardness of the interfacial area of the laminated composite indicated that where contains the most ?/?0 phase,microhardness is highest,where contains the highest ?/?2 Phase,microhardness is lowest.The results of the three-point bending test at room temperature showed that the specimens tested are not broken due to the addition of pure Tiand Ti-6Al-4V alloy sheets with good ductility and toughness,and the bending strength of layered composites in the direction parallel to the hot pressing is higher than that of in thedirection perpendicular to the hot pressing.Ti-43Al-9V-0.3Y/Tilaminated composites under hot pressing at 1000? have higher bending strength and deflection than the laminated composites under hot pressing at 1100?.The bending strength of Ti-43Al-9V-0.3Y/Tithree layers composite under hot pressing at 1000? in the direction parallel to the hot pressing is the highest,which is 1062.92 MPa.The bending strength of Ti-43Al-9V-0.3Y/Ti-6Al-4V five layers composite under hot pressing at1000? in the direction parallel to the hot pressing is the highest,which is 1215.07 MPa.The room temperature tensile test results showed that the tensile strength and tensile strain of Ti-43Al-9V-0.3Y/Tifive layers composite under hot pressing at 1000? is the highest,which is 513.63 MPa and 0.90% respectively,which is higher than that of under hot pressing at 1100?.The tensile strength and tensile strain of Ti-43Al-9V-0.3Y/Ti-6Al-4V three layers laminated composite is the highest,which is692.63 MPa and 0.82% respectively.The fracture toughness test at room temperature results showed that the laminated composites have higher fracture toughness in parallel to the hot pressing direction than that of in the direction perpendicular to the hot pressing.The reason is that pure Tiand titanium alloy sheets with good ductility and toughness are added.When the crack was extended from the brittle TiAl alloy layer to the pure Tior Tialloy layer,the crack cracked in the interlayer,crack deflection,crack bridge and so on,thus consumed the energy of crack propagation to achieve the purpose of toughening.The fracture toughness of Ti-43Al-9V-0.3Y/Tithree layers composite under hot pressing at 1000?and 1100? in the direction parallel to the hot pressing is the highest,which is18.20MPa·m1/2 and 19.17MPa·m1/2 respectively.The fracture toughness of Ti-43Al-9V-0.3Y/Ti-6Al-4V five layers composite in parallel to the hot pressing direction is the highest,which is 31.37MPa·m1/2,which is about 90% higher than that of TiAl alloy.The microstructure and mechanical properties of Ti-43Al-9V-0.3Y/Ti-6Al-4V layered composite sheet after heat treatment were studied.When the multi-step heat treatment process is 1230?/30min/FC+960?/1h/AC+500?/4h/AC and1270?/30min/FC+960?/1h/AC+500?/4h/AC,the thickness of the interface layer of Ti-43Al-9V-0.3Y/Ti-6Al-4V laminated composite is about 440?m and 550?m respectively.The microstructures of TiAl and Ti-6Al-4V alloy in laminated composite are duplex.The fracture toughness of Ti-43Al-9V-0.3Y/Ti-6Al-4V five layers composite after heat treatment at 1270?/30min/FC+960?/1h/AC+500?/4h/AC is the highest,which is 39.19MPa·m1/2,which is about 25% higher than the Ti-43Al-9V-0.3Y/Ti-6Al-4V laminated composites before the heat treatment,which is about 137% higher than that of TiAl alloy.The bending strength of TiAl/Ti-6Al-4V fivelayers composite after heat treatment in parallel to the hot pressing direction is the highest,which is 1237.77 MPa and 1101.70 MPa respectively. |
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