LONG-RANGE ORDERING KINETICS AND ORDERING ENERGY IN NI3AL-BASED GAMMA'-ALLOYS

Chemical long-range order kinetics were studied for the Ll2-ordered ga mma'-phase domains of the quasi-binary systems Ni75AL25-xMx (M=Fe, Mn, Cr, 0 less-than-or-equal-to x less-than-or-equal-to 25), where the ga mma'-phase stability (ordering energy) rapidly decreases with increasi ng M-component concentration x. The sample gamma' homogeneity was test ed by means of transmission electron microscopy. The 'order-order' rel axations measured by means of in-situ resistometry indicated that an i ncrease in x caused a systematic decrease in the activation energy, E( A), of homogeneous long-range order kinetics. Discussing a possible in fluence of various parameters, it was concluded that the observed decr ease in E(A) was predominantly due to an effect of the ordering energy on the bulk vacancy diffusion in these Ll2-ordered compounds.