Abstract: The displacive phase transformation in an appoximately equiatomic Ti-Ni alloy and Fe-Ni-V-C alloy has been studied by TEM. The results show that the stress has strong effects on the lattice instability. A tensile stress promotes soft modes which relate to the nucleation of the R-phase and the Martensite phase. It has been identified that the diffuse streaks in the electron diffraction arise from the softening of phonons which <111>olarization vectors which results from the softening of C_off<111>. The R-phase nucleus formed on the plate of Ti₁₁Ni₁₄ where a tensile stress field was good to R-transfor-mation. The regular shape of the R-phase is the comprehensive effect of strain energy and interface energy. The special dislocation constitution has been observed in Fe-Ni-V-C alloy. An array of shorter dislocation which b =1/2 011_fcc piled up within long envelope dislocation with b = 1/2110_fcc. It provide necessary atomic displacement (in double-shear) and can transform into butterfly martensite.