High-temperature X-ray diffraction and TEM studies were conducted on nickel-rich boron-doped Ni3Al in order to confirm our earlier observations on the existence of a structural transformation in these alloys. The results obtained are discussed through a model proposed. The L1(2) structure appears to transform to another L1(2) or to a DO22 structure during heating. Such a transformation starts at around 700 degrees C and seems to complete around 1100 degrees C and appears to be of a continuous type. In the temperature range 700-1100 degrees C both phases coexist, which causes a tetragonal distortion of the L1(2) lattice giving rise to a tweed morphology in TEM observations. The transformation mechanism involves a periodic modulation of lattice constant. The calculated values for this periodicity (expressed as a number of unit cells in the [1 0 0] direction) obtained from X-ray diffraction (L = 62, 70, 74) matched well with that (L = 65) obtained using TEM.