6 research outputs found
Investigation of the microstructure of the fine-grained YPO:Gd ceramics with xenotime structure after Xe irradiation
The paper reports on the preparation of xenotime-structured ceramics by the
Spark Plasma Sintering (SPS) method. Phosphates YGdPO
(YPO:Gd) were obtained by the sol-gel method. The synthesized nanopowders
are collected in large agglomerates 10-50 mkm in size. Ceramics has a
fine-grained microstructure and a high relative density (98.67%). The total
time of the SPS process was approximately 18 min. High-density sintered
ceramics YPO:Gd with a xenotime structure were irradiated with Xe
ions (E = 167 MeV) to fluences of - cm.
Complete amorphization at maximum fluence was not achieved. As the fluence
increases, an insignificant increase in the depth of the amorphous layer is
observed. According to the results of grazing incidence XRD (GIXRD), with an
increase in fluence from - cm, an
increase in the volume fraction of the amorphous structure from 20 to 70% is
observed. The intensity of XRD peak 200 YPO:Gd after recovery annealing
(700C, 18 h) reached a value of ~80% of the initial intensity I0.Comment: 16 pages, 10 figure
Non-Equilibrium Evolution Thermodynamics Theory
Alternative approach for description of the non-equilibrium phenomena arising
in solids at a severe external loading is analyzed. The approach is based on
the new form of kinetic equations in terms of the internal and modified free
energy. It is illustrated by a model example of a solid with vacancies, for
which there is a complete statistical ground. The approach is applied to the
description of important practical problem - the formation of fine-grained
structure of metals during their treatment by methods of severe plastic
deformation. In the framework of two-level two-mode effective internal energy
potential model the strengthening curves unified for the whole of deformation
range and containing the Hall-Petch and linear strengthening sections are
calculated.Comment: 7 pages, 1 figur
Effect of grain boundary state and grain size on the microstructure and mechanical properties of alumina obtained by SPS: A case of the amorphous layer on particle surface
The effect of temperature modes and heating rates (Vh) on the shrinkage
kinetics of submicron and fine aluminum oxide powders has been studied. The
objects of research comprised (i) submicron alfa-Al2O3 powder, (ii) submicron
alfa-Al2O3 powder with an amorphous layer on particle surface, (iii) fine
alfa-Al2O3 powder. The alumina ceramic specimens were produced by Spark Plasma
Sintering (SPS). Equally fine powders (i) and (ii) were used to analyze the
effect of an amorphous layer on sintering kinetics. Powders (i) and (iii) were
used to analyze the effect of the initial particle size on shrinkage kinetics.
Shrinkage curves were analyzed using the Young-Cutler and Coble models. It has
been shown that sintering kinetics is determined by the intensity of grain
boundary diffusion for submicron powders and by simultaneous lattice and grain
boundary diffusion for fine powders. It has been determined that an amorphous
layer on the surface of submicron alfa-Al2O3 powder affects grain boundary
migration rate and the Coble equation parameters at SPS final stages. It has
been suggested that abnormal characteristics of the alumina ceramics sintered
from a submicron powder with an amorphous layer on the particle surface are
associated with an increased concentration of defects at grain boundaries that
were formed during crystallization of the amorphous layer.Comment: 62 pages, 20 figures, 5 tables, 67 reference