Matvienko L. Mechanisms of influence of impurities on the substructure and mechanical properties of single crystals of molybdenum and tungsten

The influence of alloying on structure and mechanical properties of Mo and W single crystals was studied. It was shown that the perfection of single crystals of Mo (0 3.5 at.% Ru) system with <100> growth direction was characterized by two minima of subgrain disorientation depending on Ru content. These minima were caused by the interaction of interstitial impurity (carbon) and substitution impurity (Ru) as well as by inhibiting the dislocation movement by cellular structure. Crystallographic anisotropy of Mo and W single crystal growth depending on the impurities is caused by the anisotropy of crystal-melt interphase energy and by the ability of different planes to reduce concentration supercooling. Increase in perfection of single crystals of these metals in the <100> -> <110> -> <111> directions with the optimum content of impurities is due to plastic properties of BCC structures, the behavior of dislocations and low-angle grain boundaries. Mechanical properties of Mo-1.5 at.% Ir single crystals depend not only on the content of impurities, but also on the crystal structure: either microhomogeneous or cellular. High temperature creep rate of single crystals having cellular structure is greater with lower concentration inhomogeneity and with formation of superequilibrium vacancies that accelerates creep. Microhardness and creep of W-7.8 at.% Ta crystals at high temperatures demonstrates a significant advantage over non-alloyed sample. In particular, creep rate of alloyed single crystal at 1800oC and load of 12 MPa is two orders of magnitude smaller than that for unalloyed one