The influence of alloying and heat treatment on structure and properties of TiAl alloys was studied by means of Optical Micrograph, Electron Probe Microanalysis, Transmission Electron Microscope, Scanning Electron Microscope and compression tests. The existing of α→α+γ phase transformation of TiAl alloys has been found, and the transformation temperature of α→α+γ of ternery alloys Ti_(50)Al_(48)M_2(M = V,Cr,Mn,Cu,Ga,Zr,Nb and Ag) have been precisely determined and local sections of ternary phase diagrams of Ti_(50)Al_(48)M_2(M = Cr and Mn) have been drawn. All of these results provide a reliable basis for adjusting the microstructure of TiAl alloys. TEM observation revealed that there existed on parallel arranged α_2lamellae and γ lamallae, the former is thinner than the latter, in the lamellar zone, which was formed through eutectic transformation. The lamellae became thinner as increasing the solid solution temperature in α+γ phase one, and the lamellae became thicker when Cr or Mn was added in alloys. The compression results shown that the compresibility of Ti_(50)Al_(48)M_2(M = Cr,Mn) alloys decreased and the yield strength increased with increasing solid solution temperature. The fracture strength increased with increasing primary bulk of γ phase volume percentage, and reached a maximum at the vicinity of 50% primary bulk γ phase volume percentage, then it droped with the continuing increase of γ content. the fracture mode of the TiAl alloys treated by solid solution at high temperature mainly was along lamellae, but the fracture of the alloys treated at low temperature mainly was transgranular and cleavage in the primary bulk of γ phase.
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