11 research outputs found
Effect of the Sc/Zr ratio on the corrosion resistance of Al-Mg cast alloys
The results of investigations of the corrosion resistance of Al-Mg-Sc-Zr
alloys with varying Mg content and different Sc/Zr ratios are presented. The
objects of investigations were the Al-Mg-Sc-Zr alloys with total Sc + Zr
content of 0.32 wt%. The concentration of Sc and Zr in the alloys varied with
the increments of 0.02 wt%. The alloys were produced by induction casting. The
effect of annealing temperature on the microhardness and electrical resistivity
of the Al-Mg-Sc-Zr alloys was investigated. Corrosion tests were carried out in
a medium simulating intergranular corrosion in aluminum alloys. Electrochemical
studies and mass loss tests were performed. An increase in the Sc concentration
and a decrease in the Zr one were shown to result in an increase in the
corrosion rate. The primary Al3(ScxZr1-x) particles were found to have the main
effect on the corrosion resistance of Al-Mg-Sc-Zr alloys. The dependence of the
corrosion current on the annealing temperature of the Al-Mg-Sc-Zr alloy was
found to have a non-monotonous character (with a maximum).Comment: 29 pages, 2 tables, 11 figures, 58 reference
Corrosion fatigue crack initiation in ultrafine-grained near-a titanium alloy PT7M prepared by Rotary Swaging
The study focuses on corrosion fatigue processes taking place in an
ultrafine-grained (UFG) near-a-titanium alloy Ti-2.5Al-2.6Zr (Russian
industrial name PT7M) used in nuclear engineering. UFG structure formed with
Rotary Swaging is found to increase resistance to corrosion fatigue. Parameters
of the Basquin's equation are defined and the slope of the fatigue curve
Sa-lg(N) is shown to depend (nonmonotonic dependence) on the UFG alloy
annealing temperature. This effect can be explained with the patterns of
microstructural evolution in a UFG alloy PT7M during annealing: (1) reduced
density of lattice dislocations, (2) precipitation and dissolution of zirconium
nanoparticles, (3) release of a''-phase particles causing internal stress
fields along interphase (a-a'')-boundaries, and (4) intensive grain growth at
elevated annealing temperatures. It is shown that the fatigue crack closure
effect manifested as changing internal stress fields determined using XRD
method may be observed in UFG titanium alloys.Comment: 54 pages, 2 tables, 19 figures, 64 referance
Investigation of the effect of the grain sizes on the dynamic strength of the fine-grained alumina ceramics obtained by Spark Plasma Sintering
The results of dynamic strength tests of the alumina ceramics with various
grain sizes are presented. The ceramics were obtained by Spark Plasma Sintering
(SPS) of industrial submicron and fine Al2O3 powders. The heating up was
performed with the rate of 10 oC/min; the grain sizes in the ceramics was
controlled by varying the SPS temperature and the heating rate as well as by
varying the initial sizes of the Al2O3 particles in the powders. The ceramics
had a high density (over 98%) and a uniform fine-grained microstructure (the
mean grain sizes varied from 0.8 to 13.4 mkm). The dynamic compressing tests
were carried out by modified Kolsky method with using split Hopkinson pressure
bar. The tests were performed at room temperature using a 20-mm PG-20 gas gun
with the strain rate of ~10^3 s-1. The dependence of the dynamic ultimate
strength of alumina on the grain size was found for the first time to have a
non-monotonous character (with a maximum). The maximum value of the dynamic
ultimate compression strength (SY = 1060 MPa) was provided at the mean grain
size of ~2.9-3 mkm. The reduction of SY for alumina in the range of submicron
grain sizes was shown to originate from the reduction of the relative density
of the ceramics sintered at lower SPS temperatures.Comment: 16 pages, 1 table, 6 figures, 28 reference
Effect of severe plastic deformation realized by rotary swaging on the mechanical properties and corrosion resistance of near-a-titanium alloy Ti-2.5Al-2.6Zr
The research aims to analyze the impact that severe plastic deformation
arising during Rotary Swaging has on mechanical properties and corrosion
resistance of a near-a-titanium alloy Ti-2.5Al-2.6Zr (Russian industrial name
PT7M). The nature of corrosion decay in fine-grained alloys caused by hot salt
corrosion is known to vary from pit corrosion to intercrystalline corrosion at
the onset of recrystallization processes. Resistance to hot salt corrosion in a
fine-grained titanium alloy Ti-2.5Al-2.6Zr is shown to depend on the
structural-phase state of grain boundaries that varies during their migration
as a result of covering corrosive doping elements (aluminum, zirconium)
distributed in the crystal lattice of a titanium alloy.Comment: 37 pages, 15 figures, 39 reference
Effect of annealing on the corrosion-fatigue strength and hot salt corrosion resistance of fine-grained titanium near-{\alpha} alloy Ti-5Al-2V obtained by Rotary Swaging
The corrosion-fatigue strength in 3% aqueous NaCl solution and the resistance
against hot salt corrosion (HSC) of the fine-grained near-a alloy Ti-5Al-2V
(Russian analog of Grade 9 titanium alloy with increased aluminum content) has
been studied. The properties of the Ti-5Al-2V alloy in the coarse-grained
state, in the fine-grained after cold Rotary Swaging (RS), in partly
recrystallized state, and in fully recrystallized one have been investigated.
The mechanical properties of the alloy were characterized using compression
tests and microhardness measurements. The effects of RS and of the annealing
temperature and time on the character of corrosion destruction of the surface
and on the composition of the products of the HSC were studied. RS was shown to
result in an increase in the depth of the intergranular corrosion defects while
the recrystallization annealing promotes the increasing of the corrosion
resistance of the Ti-5Al-2V titanium alloy. The parameters of the Basquin
equation for the corrosion-fatigue curves for the near-a Ti-5Al-2V alloy in the
coarse-grained state, in the severely strained one, and after recrystallization
annealing were determined for the first time. An effect of nonmonotonous
dependencies of the slopes of the corrosion-fatigue curves for the strained
near-a Ti-5Al-2V alloy on the recrystallization annealing temperature has been
observed.Comment: 46 pages, 1 table, 19 figures, 64 reference
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