Preparation,Microstructure And Mechanical Properties Of Strengthened And Toughened Tialalloy Composite

Due to its low density,high specific strength and superior elevated temperature property,Titanium Aluminum alloy are regarded as excellent succedaneum,and was used widely in aerospace industry.However,bad ductility in room temperature,low fracture toughness property become a vital factor to limit TiAl alloy's further development.Thus,strengthening and toughening TiAl alloy become an important field in TiAl field.By adding?phase stabilizer to gain?phase,which have more slip system,could improve room temperature ductility and fracture toughness property.This method has become a basic way to strengthen and toughen TiAl alloy.In this?stabilizing elements,add Nb become a vital orientation because the good high temperature strength and creep resistance in high Nb TiAl alloys.But the high content of Nb inevitably increase the density of TiAl alloys.Meanwhile,technologies such as hot pressed sintering and high temperature pack rolling raise the cost a lot.In this research,we plan to fabricate fibers/whiskers reinforced TiAl alloy composite by foundry technique,strengthen and toughen TiAl alloys with little increasement in density.Carbon fiber/graphene reinforced TiAl alloy composite and SiC whiskers reinforced TiAl alloy composite were fabricated by several steps.Carbon fiber/graphene reinforced TiAl alloy composite was fabricated by power metallurgy,melt spun and two times vacuum suspension melting.The composite exhibits a grain size in about 60?m.Compared with pure TiAl alloys,the Vickers hardness was improved from 502HV to 626HV,compressive strength was improved from 1801MPa to2301MPa,fracture strain was improved from 17.02%to 26.27%in the room temperature compression test.Microstructure and phases of this composite were analysed.And the improvement in its mechanical properties is due to refined crystalline strengthening,Second Phase Strengthening and fiber toughening.SiC whiskers reinforced TiAl alloy composite was fabricated by vacuum suspension melting.Commercial pure Titanium and Aluminum and Nb/Fe was used as raw materials to fabricate Ti-46Al-2Nb-2Fe master alloy.Then SiC whikers were introducing into this alloy to improve the properties of TiAl alloys.By using SiC in different volume fraction,the result shows that SiC whiskers in 0.5 at.%reinforced TiAl alloy composite exhibits the greatest mechanical properties.This composite gets a grain size smaller than 50?m,a compressive strength of 2700MPa and a fracture strain in 17.35%.By using scanning electron microscope and transmission electron microscope,the interface between the in-situ Nb₄C₃ phase and matrix was studied.Nanotwins of?0002?_?2-Ti3Al2-Ti3Al were found in the phase interface.