The Effect Of Fe On The Microstructure And Mechanical Properties Of Ti46A16Nb Based Alloys

TiAl based alloys are potential high-temperature structural materials with lowdensity, high specific strength, excellent creep resistance and oxidation resistance atelevated temperature, while the poor room ductility and toughness greatly restrict theircomprehensive applications in aero-engine fabrication and automotive filed. Alloying isan easy and efficient way to improve the room ductility with significant achievement. Itis known that Nb as one kind of refractory metals can obviously improve the tensilestrength and compression stress; V can enhance the ductility availably and Cr mayimprove the fracture toughness remarkably; Fe is good for the castability by increasingthe mobility of TiAl based alloy. However, the studies about the comprehensive effectof various elements on the TiAl alloys with high Nb are necessary to be furtherresearched.The experimental alloys with a nominal composition of Ti46Al6Nb-xFe,Ti46Al6Nb1.0Cr-xFe, Ti46Al6Nb2.5V-xFe (x=0,0.3,0.5,0.8,1.0) at.%are prepared bythe non-consumable vacuum arc melting furnace. This research mainly studies the effectof Fe with different addition on the macrostructure, microstructure, phase compositionand microsegregation by SEM, EDS and XRD analysis. Room compression testsand three-point bending tests are conducted to figure out the effect of Fe on thecompression stress, compression strain and fracture toughness of Ti46Al6Nb basedalloy. Fracture morphology is also researched by secondary electron images in SEM.The composition with the superior performance is finally obtained by assessing themechanical properties comprehensively.Experimental results show that a nearly fully lamellar microstructure is obtained atroom temperature. When the Fe content is less than0.5at.%, the microstructure consistsof parallel dendrites and the diameter of dendrite is refined as the Fe content increaseswithout changing the morphology of dendrites; when Fe is added more than0.5at.%,there are large amounts of fine dendrites with different growth direction and fine grainssimilar to equiaxed grains with1.0at%Fe. EDS analysis indicates that Fe will be richbetween the dendrites and accelerate the segregation of Nb, Cr and V. Roomtemperature compression tests show Fe promotes the compression stress of TiAl based alloy by the combined effect of grain refinement, solid solution strengthening andprecipitation strengthening. Certain content of Fe can improve the fracture toughness ofTi46Al6Nb based alloys, mainly through influencing the grain size, microstructuremorphology, shape and distribution of the second phase, such as B2. Although Fe canimprove the mechanical properties, brittle fracture is the main character of TiAl alloywith Fe addition. In conclusion, Ti46Al6Nb1.0Fe, Ti46Al6Nb1.0Cr0.5Fe andTi46Al6Nb2.5V0.3Fe alloys exhibit the excellent performance.