JMEPEG (2014) 23:2120–2130 The Author(s). This article is published with open access at Springerlink.com
DOI: 10.1007/s11665-014-0988-6 1059-9495/$19.00
Incorporation of Y2O3 Particles into 410L Stainless Steel
by a Powder Metallurgy Route
A. Zeybek, S. Pirfo Barroso, K.B. Chong, L. Edwards, and M.E. Fitzpatrick
(Submitted September 10, 2013; in revised form March 21, 2014; published online April 11, 2014)
Addition of yttria to steels has been proposed for the fabrication of oxide-dispersion-strengthened materials
for nuclear power applications. We have investigated materials prepared from 12 Cr martensitic stainless
steel, AISI 410L, produced by powder metallurgy. Materials were produced with and without yttria
addition, and two different sizes of yttria were used, 0.9 lm and 50 nm. Tensile and mini-creep tests were
performed to determine mechanical properties. Optical microscopy, SEM, TEM, and EDX analysis were
used to investigate the microstructures and deformation mechanisms and to obtain information about non-
metallic inclusion particles. SiO2, MnS, and Y2Si2O7 inclusion particles were observed. An SiO2 and Y2O3
interaction was seen to have occurred during the ball milling, which impaired the final mechanical prop-
erties. Small-angle neutron scattering experiments showed that the matrix chemistry prevented effective
dissolution of the yttria.
with components fabricated with high-Cr martensitic steel (Ref
Keywords advanced characterization, creep and stress rupture,
mechanical, powder metallurgy 2). Austenitic stainless steels are not preferred for advanced
nuclear reactor applications because of high swelling rates and
high thermal stresses caused by low thermal conductivity and
high thermal expansion coefficient.
Structural materials for future nuclear applications have to be
1. Introduction stable at elevated temperatures and have good resistance to
irradiation. This resulted in focussing structural materials
research on ferritic-martensitic (F/M) steels. Presently, F/M
The current most common commercialized nuclear fission
 steels are the primary candidate for components of advancedreactors work at a temperature range of 250-300 C, a pressure
reactor systems such as fuel cladding and duct materials.
range of 7-15 MPa, and displacement per atom (dpa) in core
Precipitates are a major source of strength in F/M steels.
structural components of 10-25. Future innovative nuclear systems
Processing procedures that decrease the size of precipitates and
and technologies have designs muchmore demanding onmaterial
increase their number density could enhance mechanical prop-
performance. Some so-called ‘‘Generation IV’’ designs have
 erties. This is akin to the so-called oxide-dispersion-strengthenedoperating requirements up to 1100 C, 24 MPa, anddpa up to 150.
(ODS) steels, where particles are dispersed into the steel matrix
Efforts to develop new Fe-Cr-Mo-type heat-resistant steels
resulting in an increase in strength at higher temperatures (higher
were initiated for steam generators in the early 1970s. During
creep resistance). ODS steels have been visualized as an
the development of high-chromium (9 to 12%) steels for high-
alternative to increase the creep resistance of the ferritic,
temperature application, the use of stainless steel for nuclear
martensitic, or F/M steels (Ref 3). Powder metallurgy is the
applications was demonstrated. This included attempts to
most commonly used method of producing ODS steels.
replace Mo with W to reduce the radio-activation of the
The dispersion particles are generally Ti O and/or Y O .
material (Ref 1). Since then, much experience has been gained 2 3 2 3
The first ODS steels were of high chromium (12 up to 20% Cr).
Attempts to solve the anisotropy problems caused by grain
A. Zeybek, Materials Engineering, The Open University, Walton Hall, structure and a strong deformation texture resulted in the use of
Milton Keynes MK7 6AA, UK; and Defence Industries Research and 9-11% Cr, 2-3% W and by the austenite-to-martensite trans-
Development Institute (TÜBI_TAK-SAGE), 16 06261 Mamak, Ankara, formation (through cooling from the austenization treatment
Turkey; S. Pirfo Barroso, Materials Engineering, The Open University, temperature). The Cr content is also optimized to achieve
Walton Hall, Milton Keynes MK7 6AA, UK; K.B. Chong, Materials higher toughness and lower ductile-to-brittle transition temper-
Engineering, The Open University, Walton Hall, Milton Keynes MK7 atures. The resulting steels have outstanding tensile properties
6AA, UK; and High Performance Computing Centre, University
Malaysia of Computer Science & Engineering, Persiaran APEC, and reduced anisotropy, but the creep-rupture properties are
Cyberjaya Flagship Zone, 63000 Cyberjaya, Selangor Darul Ehsan, reduced compared to the high-chromium ODS steels (Ref 3, 4).
Malaysia; L. Edwards, Australian Nuclear Science & Technology Following initial work on ODS as potential materials for
Organisation, Locked Bag 2001, Kirrawee, Sydney, NSW 2234, nuclear applications in the 1990s, there has recently been
Australia; and M.E. Fitzpatrick, Materials Engineering, The Open significant interest in the fabrication of fuel cladding based on
University, Walton Hall, Milton Keynes MK7 6AA, UK; and Faculty ODS materials, as a replacement for zirconium alloys in
of Engineering and Computing, Coventry University, 3 Gulson Road,
Coventry CV1 2JH, UK. Contact e-mail: michael.fitzpatrick@coventry. pressurized water reactors, and also for sodium-cooled designs
ac.uk. (Ref 5). For nuclear applications, steels chosen for base alloy
2120—Volume 23(6) June 2014 Journal of Materials Engineering and Performance
are reduced-activation composition steels, so that mechanical Small-angle neutron scattering (SANS) has been found to be
properties at high temperatures such as resistance to creep and a valuable technique for the study of ODS steels, as it can
recrystallization are improved, without loss of the advantages reveal the distribution of the particles at the nanometre scale
of the ferritic or martensitic microstructures, especially the (Ref 17). Conventional neutron and x-ray diffraction methods
resistance to void swelling (Ref 6-8). The large interface area
associated with a small volume (0.25%) of yttria addition
provides ‘‘sinks’’ for radiation damage and implanted ions in a
reactor core (Ref 9). The complex, ultrafine-grained micro-
structure consists of nanoclusters that are highly tolerant to high
dose irradiation at elevated temperatures (Ref 10).
The chemistry of the base alloy can have an effect on the
stability and dissolution of the ODS particles during processing.
Titanium additions to the alloy have been found to promote
yttria dissolution during processing and stabilize the particle
size during subsequent heat treatment and forming (Ref 11).
The ODS particles effectively anchor dislocations, thus
enhancing creep resistance, manifested as a decrease in creep
ductility and an increase in creep-rupture life (Ref 12). However,
studies trying to establish the upper operating temperature limit
for these steels (Ref 13-15) are finding that the creep behavior is
very sensitive to composition and microstructure. The fatigue
properties have also been found to depend on the processing route
and final microstructure (Ref 16).
Fig. 3 410L as-received material without MA etched in Villelas
Fig. 1 Scanning electron microscope image of gas-atomized 410L reagent (a) without heat treatment (b) After heat treatment
powder
Table 1 Tensile test results at room temperature
Material Yield strength, Ultimate tensile Fracture
410L base MPa strength, MPa strain, %
HIP only 675 814 18
MA and HIP 677 842 15
ODS-0.9-lm Y2O3 695 860 12
ODS-50-nm Y2O3 690 845 10.5
Table. 2 Tensile test results at 625 C
Ultimate
Material Yield tensile Fracture
410L base strength, MPa strength, MPa strain, %
HIP without MA 270 283 16
MA and HIP 266 289 9
ODS-0.9-lm Y2O3 275 292 10
Fig. 2 SEM image of yttria powders showing a large particle. The ODS-50-nm Y2O3 273 293 5
nominal particle size was 0.9 lm
Journal of Materials Engineering and Performance Volume 23(6) June 2014—2121
Table 3 Creep results
Material Temp, C Stress, MPa Rupture time, h Elongation, % Strain rate, 10243h21
410 HIP 625 150 20 26.0 44.44
625 100 205 21.5 5.00
625 75 679 16.4 1.36
410 MA 625 150 11 30.2 118.42
625 100 117 23.7 9.37
625 75 242 22.8 4.44
ODS 0.9 lm 625 150 7.3 24.2 142.85
625 100 61 17.3 14.28
625 75 216 9.5 3.00
ODS 50 nm 625 150 2.7 8.0 230.76
625 100 27 7.4 17.14
625 75 108 6.9 4.44
Fig. 4 Larsson Miller Parameter graph for the materials from the
mini-creep tests
can also be valuable in looking at the evolution of phases and
dissolution in ODS materials (Ref 18, 19).
This work presents the results of a study on the powder
metallurgy processing of an ODS 410L alloy steel. The
microstructural evolution and mechanical properties were
examined and measured. SANS was used to examine the
dispersion and inclusion particles.
2. Experimental Details
The base material was AISI 410L powder with nominal
composition of 11.5-13 wt.% Cr, max 1 wt.% Si, max 1 wt.%
Mn, max 0.5 wt.% S, and max 0.5 wt.% P. Two different particle
sizes of yttria were used for incorporation into the material: Fig. 5 Particle clusters in the material: (a) in 410L HIP material;
50 nm and 0.9 lm. These sizes were selected to provide a (b) Fracture surface SEM images of ODS with 0.9 lm Y2O3
comparison with a particle size that is effectively comprised of
single crystallites and can be incorporated into the matrix by SEM observations on the yttria powders showed particles
dissolution (50 nm), and a larger size which offers greater scope much larger than expected, with some particles up to 30 lm in
for particle fracture during the mechanical milling process. size, with composition of pure yttrium rather than yttria. Both
Scanning electron microscope (SEM) observations on the yttria powders, nominally of 0.9 lm and 50 nm in size, show
atomized 410L powder (Fig. 1) show particle sizes smaller than these large particles, with an example shown in Fig. 2 for the
100 lm, which is suitable for subsequent powder metallurgy 0.9-lm powder.
operations. The morphology of the alloyed powder shows Materials were fabricated by Aerospace Metal Composites
spherical particles. Some larger metal powder particles have Ltd, Farnborough, by a mechanical alloying (MA), powder
many small satellites stuck to them, which ideally should be metallurgy route. The ODS material was fabricated by mechan-
eliminated for good packing and flow attributes (Ref 20). ical milling 0.25 wt.% Y2O3 with the alloy powders under inert
2122—Volume 23(6) June 2014 Journal of Materials Engineering and Performance
Fig. 6 EDX results from two sides of a compound particle, showing (a) probable MnS on one side and (b) SiO2 on the other
argon atmosphere. Two different ODS variants were produced tested to failure at room temperature and at 625 C at an
withY2O3 particles of 0.9 lmand 50 nm sizes. After milling, the extension rate of 0.01 mm/s.
powders were canned and degassed. After degassing, the canwas Creep tests were carried out by applying a fixed tensile load
sealed. Finally, hot isostatic pressing (HIPping) was performed at at various temperatures. The ‘‘mini-creep’’ samples used had
a temperature of 1120 C. Materials were also produced without dimensions of 10 mm in gage length and 2 mm in diameter.
oxide reinforcement, and one batch was prepared by simple Mini-creep tests were conducted at the Australian Nuclear
consolidation of the 410 powder without the MA stage. Science and Technology Organisation (ANSTO) facilities. All
Heat treatment was performed on the final billets to achieve tests were conducted in vacuum at 625 C under loads of 75,
a tempered martensitic structure and remove features such as 100, and 150 MPa.
residual ferrites at grain boundaries arising due to the slow The SANS experiment was performed on the KWS-1
cooling rate (furnace cooling) after HIPping. The microstruc- instrument of JCNS at FRM-II, Munich. A magnetic field was
tures of as-received unreinforced 410 material without MA, applied at 0.4 and 1.2 T with a neutron wavelength of 7 Å.
before and after heat treatment, are shown in Fig. 3. Rectangular samples were manufactured with dimension of
The heat treatment was austenitizing at 1000 C for 30 min 209 20 mm2 with thickness of 2 mm. This thickness was
followed by oil quenching to achieve a fully martensitic chosen as higher thickness can cause multiple scattering (Ref
microstructure and then tempering at 650 C for 2 h and 21). The instrument has an upper length scale limitation of
furnace cooling. The heat treatment was performed under 400 nm. A polydispersed spherical Schultz distribution/model
ambient atmosphere. In Fig. 3b, it can be seen that a fully was used for data analysis and fittings.
tempered martensitic microstructure was achieved by the heat
treatment. No residual ferrite was observed. 3. Results
Cylindrical tensile test specimens were extracted from the
longitudinal direction of the HIP billets (though it must be
noted that no direction-dependence in the properties would be 3.1 Mechanical Properties
expected). The tensile test specimens were 6.25 mm in A summary of the tensile test results at room temperature
diameter and 25 mm in gage length. The tensile samples were is shown in Table 1. Yield strength values are around
Journal of Materials Engineering and Performance Volume 23(6) June 2014—2123
Fig. 6 continued
670-690 MPa, and ultimate tensile strength (UTS) values are ODS-0.9-lm and 50-nm samples have fracture elongations of
around 815-860 MPa. Typical mechanical properties of 410L 12 and 10.5 %, respectively. Previous work has found different
produced by conventional methods (cast and machined) and trends depending on the system studied.
submitted to similar heat treatments show strengths slightly High-temperature tensile tests on the samples were con-
lower than observed for the material presented here. The ducted at 625 C, and the results are shown in Table 2. Yield
conventionally produced steel shows yield and ultimate strength values are around 270 MPa, and UTS is around
strengths of about 589 and 767 MPa, respectively (data from 285 MPa. As expected, yield strength and UTS values are
the 410 Specification Sheet, Sandmeyer Steel Company). lower than room temperature values which were around 680
The material that was mechanically alloyed before HIPping and 840 MPa for yield and tensile strengths, respectively. Note
showed a small increase in UTS, from 814 to 842 MPa. Thus, it that the low ductility seen for the 50-nm ODS material in this
can be concluded that the MA has a small effect on the room case was influenced by some porosity seen that was attributed
temperature strength of the steel, which is in agreement with to incomplete outgassing from the powder mix before HIPping.
previous work by Morakotjinda et al. (Ref 3) and Brytan et al. Creep results are shown in Table 3. The creep lives of all the
(Ref 22). samples are relatively poor. The best creep life belongs to 410
The addition of Y2O3 did not impact significantly on the as-HIPped material, being 679 h under 75 MPa load at 625 C.
strength of the material at room temperature. The highest The worst creep life is for the ODS-50-nm sample, again owing
mechanical properties are observed for the ODS-0.9-lm to the porosity present.
material with yield strength of 695 MPa and UTS of 860 MPa. Larsson Miller parameters (LMP) have been calculated from
Conventional 410L has strain-to-failure of the order of 18%. the results obtained in mini-creep tests and are shown in Fig. 4.
The 410 HIP and 410 MA + HIP samples have fracture
elongation values of 18 and 15%, respectively. It is well known
3.2 Microstructural Characteristics and Fractography
that MA has a negative effect on ductility (Ref 23).
As expected, the yttria particles have a negative effect on All four materials show similar microstructure after heat
fracture strain due to hindering dislocation motion. Thus, the treatment. They all have tempered martensite as expected. A
ODS materials are less ductile than the non-ODS versions. The significant feature observed in the microstructure was inclusion
2124—Volume 23(6) June 2014 Journal of Materials Engineering and Performance
Fig. 7 TEM image and EDX result of one of the intermetallic particles in ODS with 50-nm Y2O3
Fig. 8 Schematic illustration of (a) void elongation and coalescence (b) crack propagation
particles, or particle clusters. They can be seen both in reduction in mechanical properties by oxides and inclusions.
metallography samples and on the fracture surfaces after tensile So, SiO2 particles are formed due to interaction between Si and
tests, as shown in Fig. 5. They are seen in both MA and non- O. MnS particles are formed on similar lines. Manganese is a
MA materials, with and without dispersed yttria. EDX analysis good desulfurizer; it is employed on alloying to form the stable
showed that these inclusions are rich in silicon-oxygen and MnS phase so that it eliminates hot-shortness or sulfur
manganese-sulfur in non-ODS materials. In the ODS materials, embrittlement. In ODS samples, due to the interaction between
some silicon-oxygen-yttrium particles were also detected. Some silicon and oxygen in the yttria particles, we observed Y-, Si-,
of the particles were a combination of two or more different and O-containing clusters as a particle comprising on one side
particles as can be seen in Fig. 5b, with compositional an Si-O part and Y-Si-O on the other side, as can be seen from
differences shown using energy-dispersive x-ray diffraction, the TEM image in Fig. 7.
in the SEM, in Fig. 6. The 410L was supplied in pre-alloyed form. Formations of
The reason for seeing the association of Si and O is due to the SiO2 and MnS particles will have occurred during the liquid
the fact that silicon is the most common oxidizing agent in stage of the steel fabrication as a result of supersaturation of the
steel. Oxygen is considered as an undesirable element, causing solution with the solutes due to dissolution of additives
Journal of Materials Engineering and Performance Volume 23(6) June 2014—2125
(deoxidation and desulfurization agents). So, this would conventional processing. The ODS materials, however, did not
suggest that these particles were in the system before the ball show improved mechanical properties at room temperature.
milling stage. These inclusions were observed in 410L HIPed They have nearly the same mechanical properties than the non-
material (without MA). However, the interaction between Si-O- ODS materials, yet they showed a lower fracture strain.
Y will have started during the milling stage, because MA is the Ductility in these materials is controlled by microvoid
first step where yttria is added to the system. These facts can be nucleation and coalescence prior to fracture (Ref 24). Propa-
used to infer that a nucleation and growth process occurred. gation of a fracture is the combination of nucleation of voids
During milling, some SiO2 particles interacted with yttria and growth and/or coalescence of these voids owing to plastic
particles due to the high energy of the milling process and strain. One of the most important factors in the nucleation of
formed a new composition of Y-Si-O. In addition, during the voids is the interfacial bonds. As the inclusions in the materials
high-temperature HIP process, those particles or clusters joined tend to have very low-strength interface bonds, they are
and grew together, forming a minimum energy shape, most of potential void nucleation points. Some inclusions like MnS can
the time spherical. These clusters size could also have been also be considered as virtual voids, i.e., with very little or no
enhanced by the subsequent heat treatment. bond to the matrix surrounding them. In the case of oxides,
void nucleation starts by particle cracking; while for sulfides,
which have a lower interfacial energy between inclusion and
4. Discussion the matrix, decohesion occurs at the inclusion/matrix interface,
even at low strains.
After voids are nucleated at the inclusions owing to weak
The PM and HIP process used here for the 410L martensitic interfacial bonds, they tend to elongate along the tensile
stainless steels increased the material strength as compared to direction up to a certain limit by plastic extension. This limit is
defined as the distance between neighbor inclusions. When they
reach that limit, a slip plane is formed between voids, and they
coalesce (Ref 25). This continues through all neighboring
inclusions, and then, fracture propagates leading to complete
rupture. The fractography analyses show inclusions inside the
dimples where the microvoid nucleation has started. Figure 8
shows the mechanism of void elongation and coalescence under
plastic extension followed by crack propagation and matrix
separation leading to fracture (Ref 26). Thus, if the distance
between these inclusions is small, the plastic strain needed to
coalesce the nucleated voids will be less as well, which means
the total fracture strain will be smaller and in consequence, the
material has low ductility.
During creep, voids and cracks nucleate at grain boundaries
and follow grain boundaries until rupture. The low creep lives
observed are associated with the inclusion particles present at
grain boundaries which ease the nucleation and propagation.
Inclusion particles were clearly observed on the fracture
surfaces following creep testing, as seen in Fig. 9. There was
Fig. 9 Creep fracture surface from the ODS material with 50-nm a high density of particles observed on the creep fracture
yttria particles surfaces. It was clear that the particles had initiated multiple
Fig. 10 Illustration of crack propagation during tensile test showing inclusion density difference between fractography and metallography
samples
2126—Volume 23(6) June 2014 Journal of Materials Engineering and Performance
Fig. 11 EDX results showing Y-Si-O particles are Y2Si2O7
voiding within the material and that this had led to an early precipitate again as pure yttria in the system at high temperature
onset of tertiary creep and a concomitantly low creep life. later in the manufacturing process: this is the main mechanism
Some of the particles are composed of two or more to disperse the matrix with oxide particles to make oxide-
individual particles. Figure 10 indicates schematically why dispersion-strengthened alloys. This dissolution and precipita-
there are more particles seen on the fracture surface SEM image tion are needed for a homogeneous microstructure and size
than are present as a volume fraction in the material. control of oxide dispersions in the nanometre range (Ref 28). If
Particles were observed in both non-ODS and ODS variants yttria dissolved in the matrix and then precipitated, then there
of the materials. In the non-ODS material, the particles are should be separate particles with composition Y2O3 or complex
comprised of MnS and Si-O systems. In the ODS material, oxides such as Y2Ti2O7 if Ti was added to the system. In our
Si-O, Y-Si-O, and MnS were seen to form particle clusters. case, the yttria-containing particles studied by SEM and EDX
The Y-Si-O particles are expected to be Y2Si2O7 which is analysis are all Y2Si2O7. However, small-angle neutron
thermodynamically favorable (Ref 27). Figure 11 shows EDX scattering (SANS) experiment results showed that there are
data taken from the fracture surface of an ODS-0.9-lm sample pure Y2O3 oxide particles in the system at the nanometre level
after room temperature tensile testing. These EDX results show which cannot be detected in the SEM. SANS results from a
that the atom percentages of Y, Si, and O satisfy the condition pore-free batch of the ODS-50-nm material are shown in
of Y2Si2O7 as 1 atom for each Y and Si and 3.5 atoms for O. Fig. 12. The size of the Y2O3 particles in the as-received
Similar atomic calculations show that the other particles are condition was measured as 33 nm. So, in the system, there are
SiO2 and MnS particles. both Y2O3 and Y2Si2O7 particles together.
Agglomeration of the inclusions, resulting in a much bigger In the literature, it is reported that up to 15 wt.% yttria has
overall particle size, has a negative effect when compared to been dissolved in ball milling in Fe-24 wt.% Cr steel (Ref 29).
particles of smaller sizes. Such larger particles tend to form Since the material being investigated contains 0.25 wt.% yttria,
voids at lower strains than smaller particles, which impairs it can be assumed that it is highly likely that yttria could be
rather than improves the mechanical properties. fully dissolved. On the other hand, some research on ODS
There is an important point about the Y-Si-O interaction and manufacturing shows that yttria does not ‘‘dissolve’’ during ball
formation of Y2Si2O7 particles. It is quite common that yttria milling, rather the effect is a reduction in size to a few
particles dissolve in the matrix during ball milling and nanometres due to fracturing or amorphization of the yttria
Journal of Materials Engineering and Performance Volume 23(6) June 2014—2127
Fig. 13 SANS data from ODS 0.9 lm in the (a) as-received (b)
Fig. 12 SANS data from ODS 50 nm in the (a) as-received (b) heat-treated condition
heat-treated condition
level in some cases, which is clearly not desirable. It has
which takes place at the interfaces of the matrix (Ref 18, 30). In previously been observed that yttria particles in ODS steels
many ODS analyses, the size of the oxide clusters was found to have an affinity for Si (Ref 36).
be around 1-4 nm after dissolution and precipitation (Ref 31- As shown in Fig. 12, the size of the particles changed with
35). Even after heat treatment and coarsening of the particles, heat treatment. The mean size of the Y2O3 increased from 33 to
oxide clusters of size around 10 nm are observed (Ref 35). So, 52 nm after heat treatment, whereas the mean size of the
it is not likely that oxide particles of 33 nm are formed by complex oxide Y2Si2O7 decreased from 261 to 197 nm. It is
dissolution and precipitation mechanisms, because even ini- expected to have larger clusters after heat treatment as particles
tially, the yttria particles were reported as 50 nm. It is more coarsen at high temperatures. However, the size of the complex
likely that the formations of oxide clusters seen here are a result oxide decreased. It can also be seen that the peak of pure yttria
of interaction between the yttria and SiO2 particles during ball (Y2O3) broadened and the peak of the complex oxide (Y-Si-O)
milling. The pure Y2O3 particles (33 nm) detected by SANS became narrower after heat treatment. The results also suggest
can be attributed to size reduction of the particles owing to that larger complex oxide particles dissolved prior to small ones
fracturing in the MA process. The size of the yttria particles because it is shown that minimum size of the complex particles
should decrease to some extent for dissolution to occur, as in increased in heat-treated condition from around 100 to 150 nm
theory Y and O are thought to enter the matrix lattice. but the average size together with the maximum size decreased.
The presence of SiO2 will, therefore, have a significant So, this can be attributed to preferential dissolution of larger
effect on the microstructure of ODS steels by preventing particles.
dissolution of the yttria and/or leading to nucleation (if there is SANS results from the ODS 0.9 lm are shown in Fig. 13.
dissolution and precipitation) of complex Y2Si2O7 oxides. This As the maximum size of the particles that can be measured by
complex oxide should not be mistaken with Y2Ti2O7 or Y2TiO5 the available SANS instrument was limited to 400 nm, only the
which are known to be better in strengthening ODS systems, as start of the size distribution graph of Y2O3 particles is obtained.
Ti is added to ODS systems purposely to improve mechanical However, when compared to heat-treated and as-received
performance. The sizes of the complex Y2Si2O7 particles are results, it can be noted that the minimum size of the Y2O3
relatively large due to their formation from the relatively large particles increases with heat treatment. Complex particles in
SiO2 inclusions, with the size of the particles reaching 2-lm this case are much larger than 400 nm; so, these are not shown
2128—Volume 23(6) June 2014 Journal of Materials Engineering and Performance
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