The positron lifetime and coincidence Doppler broadening spectra have been measured in pure Al, Si, Ti, Cr, Nb elements and Ti50Al50, Ti50Al48Cr2, Ti50Al48Nb2 alloys. It has been found that the 3d electron signal and the electron density for binary TiAl alloy are relative low due to the Ti 3d-Al 3p interactions. The addition of Cr and Nb atoms to TiAl alloy leads to the increase of electron densities in the bulk and grain boundaries simultaneously as well as the enhancement of d-d electron interactions. The d electron signal in the spectrum of Ti50Al48Cr2 alloy is higher than that of Ti50Al48Nb2 alloy. The effects of Cr and Nb on the d electrons of TiAl alloys have been discussed