Nearly equiatomic FePd (Fe-52at.%Pd) alloys have been deformed by cold-rolling to 60% thickness reduction. Ordering and disordering was studied during isochronal and isothermal annealing by residual resistometry (REST) in the deformed as well as in the recrystallized state. In both cases a first order phase transition with a broad thermal hysteresis is observed. Resistivity values corresponding to thermal equilibrium of LRO-states, however, result lower in the deformed case. This is interpreted as a consequence of internal stresses leading to a preference of one variant of ordered domains and consequently to a higher degree of LRO.

A detailed study by an isothermal small-step annealing treatment yields two counteracting exponential processes during order-order relaxation with an activation energy of 2.7eV and 2.4eV, respectively.

“Order-order” relaxations in γ-Ni3Al previously extensively studied by means of resistometry, are simulated within a model of vacancy mechanism of atomic migration in a superstructure implemented with Monte Carlo technique and the Glauber algorithm. The observed operation of two simultaneous relaxation processes showing different rates, as well as the theoretically predicted effect of vacancy ordering have been definitely reproduced and analysed in detail in terms of the dynamics of particular kinds of atomic jumps. The proposed model scenario for the creation and elimination of antisite atoms in the relaxing L12-type superstructure shows that the experimentally observed features of the “order-order” processes in Ni3Al follow from an interplay between two dominating and coupled modes of long- and short-range ordering: the creation/elimination of nn pairs of antisites (SRO) and the change of the “overall” number of antisites (LRO). High profile of the first process results in a high contribution of the fast component of LRO kinetics.

Recent Monte-Carlo simulations of order relaxations in L12-ordered Ni3Al reproduced the simultaneous action of two processes as experimentally observed by residual resistometry. It was shown that the fast process is related to the fast annihilation/creation of nearest neighbour antisite pairs. These findings are now strongly corroborated by a new supercell approach of ab initio quantum mechanical calculations describing the simultaneous displacement of Ni and Al atoms on their way to their respective antisite positions. Studies of single jumps suggest that such a cooperative migration of Ni and Al is necessary in order to prevent Al antisites from jumping back into their regular position. Relaxation of neighbouring atoms was taken into account. Thus, a minimum migration barrier of about 3 eV was derived which together with the calculated formation enthalpy of a Ni vacancy of 1.5 eV amounts to 4.5 eV, in remarkable agreement with the high activation enthalpy of 4.6 eV as observed experimentally.

Properties of point defects such as antisites and vacancies in Ni3A1 are studied by means of ab initio calculations for supercells. Temperature dependent quantitities such as defect formation energies are derived by means of a grandcanonical ensemble. Stimulated by experiments of residual resistivities suggesting an outstandingly large activation energy of 4.6 eV due to Al vacancies, several models for point like defects are treated in combination with calculated migration barriers for nearest neighbor jumps and also the six-jump model.

Changes in the degree of long-range order (LRO) have been investigated in B2-ordered intermetallicFe-44.8at%Al by electrical resistivity measurement (resistometry). Order variations were observed during isochronal annealing for different states of initial thermal treatment. A complicated behaviour of resistivity changes with temperature is observed when starting with a small degree of disorder. Very slight re-ordering is found already at about 470K and is surprisingly followed by a slight disordering above 530K. Only for very long annealing times the expected ordering tendency is observed in this temperature range. Above 710K re-ordering is continued and reversible equilibrium changes of order with temperature are observed above 830K.

Monte Carlo simulations of the isothermal long-range order (LRO) relaxation in A3B system with Ll2 superstructure have been performed within a model based on a vacancy jump mechanism between nearest neighbour lattice sites. The studies aimed at the explanation of the origin of two simultaneous LRO relaxation processes experimentally observed in Ni3Al. An effect of pair interaction energies and saddle-point energies (assigned to jumping atoms) was studied. The preference of vacancies for the A-sublattice (face centres), commonly postulated for Ni3Al, occurred only for a narrow range of pair-interaction energies within the domain corresponding to Ll2 ordering. It was found that the appearance of the fast relaxation process is definitely correlated with the efficiency of B-atom jumps, as well as with the values of the saddle-point energies. The results lead to a microscopic model of the “order-order” relaxation in Ll2 superstructure and yield new indications for the choice of pair-interaction energy parameters applied in Monte Carlo simulations of atomic migration in Ll2 intermetallic compounds.

Ordering in CuAu3 was investigated by residual resistivity and X-ray scattering. L12 longrange ordering (LRO) in this alloy is quite sluggish, therefore for low quenching temperatures and sufficiently short annealing times only effects of short-range order (SRO) are observed. With increasing quenching temperature and/or increasing annealing time evolution of LRO was observed by both residual resistometry and X-ray scattering. From the resistivity measurements information can be gained on the boundaries of the order-disorder two-phase field. An analysis of SRO-relaxation yields an ordering activation energy of 2.1±0.1 eV.

L12-long-range ordering (LRO) was studied by residual resistometry in Cu3Au. Variations of LRO-parameter were produced by isochronal and isothermal heat treatments for different initial states of order. By comparison of order-order and disorder-order relaxations, the contributions to ordering of atomic jumps within ordered domains and of antiphase boundaries were separated. Analysing isothermal annealings yielded ordering energies of vacancies involved.

Isothermal ‘order-order’ relaxations in Ll2-ordered N76Al24+0.19at.%B were studied by means of residual resistometry. This method made it possible to register very fine changes in the degree of LRO occurring about 1000K below the disordering temperature. The experimental results of two simultaneous processes being involved in these order-order relaxations with a high activation energy of 4.6eV are explained with an atomistic model of atomic jumps to nn vacancies. The parallel processes are connected with selected jumps of atoms to nn vacancies on different sublattices with a high activation energy of vacancy formation being involved.

The effect of heating and cooling on the long-range order transformation in stoichiometric CuAu is investigated by several complementary measuring methods. Measurements of heat flow, resistometry and acoustic emission are done dynamically by linear heating/cooling. It is shown that measuring dynamically yields the expected effect of undercooling, which decreases with decreasing cooling rate. The dependence of undercooling on cooling rate is compared with the concept of continuous cooling for glass forming. A small influence of heating rate on disordering temperature is reported (retro-effect).

Defect recovery and long-range ordering (LRO) in Ni76Al24+0.19at.%B (400 wt.ppm) were studied by means of residual resistometry, TEM methods and microhardness testing. The material was cold-rolled with intermediate annealings and the samples were prepared from sheets exhibiting effective thickness reductions of 8 and 14%, respectively, achieved in the final rolling step.

By TEM two recovery processes were observed. Firstly, superlattice intrinsic stacking faults (SISF) of large density recovered almost completely in the temperature regime between 443 and 700 K showing that they are bounded by dislocations of opposite sign. This indicates that most of the SISF are formed by pulling out dipoles and not by dislocation interactions as recently suggested. Secondly, the recovery of antiphase-boundary (APB) dissociated superlattice dislocations occurred by the annihilation of dipoles within the whole temperature regime leading finally to a loss of all dislocations at 1273 K.

Despite some excess disorder caused by cold-rolling, the mechanical deformation did not influence qualitatively the LRO processes.