The mechanisms of high-speed sintering of tungsten and W+5wt%Ni nanopowders obtained by high-energy ball milling (HEBM) have been studied. The phase composition, microstructure parameters, hardness and fracture resistance of the obtained samples were investigated. It is shown that the samples have high relative density, small grain size and increased hardness. It is established that the formation of strong intermetallic phases MexWyCz and MexWy, as well as MeO oxides occurs at SPS of mechanically activated nanopowders. The simultaneous increase in the content of intermetallic phases and reduction of the grain size leads to a non-monotone character of the dependence of the SPS activation energy on the HEBM time. It is shown that the main mechanism of SPS of tungsten W+5wt%Ni nanopowders is Coble creep.

The mechanisms of high-speed sintering of tungsten and W+5wt

Методами прямого осаждения из кислых растворов получены фосфаты со структурой минерала монацита – NdPO 4 , GdPO 4 , твердый раствор La 0.3 Nd 0.5 Sm 0.1 Eu 0.1 PO 4 , моделирующий состав фракции РАО, и YbPO 4 , кристаллизующийся в структуре ксенотима. В гидротермальных условиях получены кристаллогидраты NdPO 4 ·0.67Н 2 О со структурой минерала рабдофана и YbPO 4 со структурой ксенотима. Размер областей когерентного рассеяния порошков варьируется от 13 до 65 нм, морфология и размер порошков зависят от способа синтеза. При нагревании до 1170 K порошки сохраняют свой фазовый состав. Средние значения коэффициентов теплового расширения при 900 К находятся в интервале (5.6–9.6) × 10 –6 K –1 , что позволяет отнести исследуемые материалы к классу среднерасширяющихся.

— Phosphates isostructural with the mineral monazite—NdPO 4 , GdPO 4 , and a La 0.3 Nd 0.5 Sm 0.1 Eu 0.1 PO 4 solid solution modeling the composition of the lanthanide components of radioactive waste—and YbPO 4 , crystallizing in the xenotime structure, have been prepared via direct precipitation from acid solutions. Under hydrothermal conditions, we have prepared the crystalline hydrate NdPO 4 ·0.67Н 2 О isostructural with the mineral rhabdophane and the YbPO 4 phosphate with the xenotime structure. The powders range in crystallite size from 13 to 65 nm. The particle morphology and size have been shown to depend on the synthesis process. During heating to 1170 K, the phase composition of the powders remained unchanged. Their average 900-K thermal expansion coefficients lie in the range (5.6–9.6) × 10 –6 K –1 , so these phosphates can be regarded as having medium thermal expansion.

The paper presents the investigation of ordinary and ternary vanadates with zircon and monazite structures. Vanadates LnVO4 and CaLnZr(VO4)3 , where (Ln = La, Nd, Sm, Eu, Gd, Dy, Yb) and solid solution La0.3Nd0.5Sm0.1Eu0.1VO4, were prepared by precipitation reaction. Bulk ceramic samples were obtained from powders by Spark Plasma Sintering (SPS). The powders and ceramics were examined with several physicochemical methods. The coefficients of thermal expansion at 900C were determined. The hydrolytic stability of ceramic materials was studied. The peculiarities of high-rate SPS of powders of ordinary and ternary vanadates were analyzed.