Study of microplastic deformation of W-Ni-Fe tungsten alloys during compression tests

The widespread use of heavy tungsten alloys (HTAs) in power engineering and mechanical engineering stimulates the development of new methods of synthesis, powder processing and sintering, including additive technologies. At the same time, the mechanisms of HTAs microplastic deformation and their relationship with interphase boundaries remain poorly understood. The paper presents the results of a study of the features of microplastic deformation in coarse-grained HTAs with different strength levels. HTAs with different initial grain sizes were studied. The samples were tested in the initial state and after annealing in a vacuum at 1400°C, the melting point of the γ-phase. Microplastic tests were carried out using the standard technique of relaxation tests of flat microspecimens for compression. The microstructure of the samples was analyzed after loading (at stresses less than and greater than the yield strength). It is shown that the deformation of pure tungsten at stresses close to the yield strength leads to the formation of dislocation «steps» in the volume of grains and the appearance of grain-boundary microcracks. In coarse-grained strain-hardened HTAs, the formation of dislocation «steps» begins in the region of microplastic deformation at stresses below the yield point. With increasing stress, the size and number of traces of dislocations emerging on the grain surface increase. Deformed HTAs have a high Hall-Petch coefficient due to the increased dislocation density in the interphase boundaries. Annealing of deformed HTAs leads to a decrease in the density of deformation-induced defects and an increase in the concentration of atoms in the interphase boundaries. During deformation of fine-grained HTAs, the formation of dislocation «steps» is not observed, which indicates a significant contribution of plastic interphase boundaries to the deformation process. The results obtained can be used in the manufacture of HTAs for use in the nuclear and aerospace industries.