Dispersoid Size Research Articles

Intermetallic and dispersoid structures in AA3104 aluminium alloy during two-step homogenisation

During homogenisation of the AA3104 cast ingot, a phase transformation of intermetallic particles from β-Al6(Fe,Mn) orthorhombic phase to harder α-Alx(Fe,Mn)3Si2 cubic phase occurs. The large constituent intermetallic particles, regardless of phase, assist in the recrystallisation nucleation process through particle stimulated nucleation (PSN). Ultimately, this helps to refine grain size. The sub-micron dispersoids act to impede grain boundary migration through a Zener drag mechanism. For this reason, the dispersoids that form during homogenisation are critical to the recrystallisation kinetics during subsequent rolling, with smaller dispersoids being better suited to instances where the minimisation of recrystallisation is required during hot rolling. This work simulates an industrial two-step homogenisation practice with variations in the peak temperature of the first step between 560 °C and 580 °C. The effect of this temperature variation on the intermetallic particle phase evolution is investigated. The aim is to identify the ideal intermetallic phase balance and the dispersoid structure that are best suited for the minimisation of recrystallisation during hot rolling through maximising Zener drag and maintaining galling resistance. The results indicate a trend where an increase in homogenisation temperature from 560 °C to 580 °C yields, firstly, an increase in the volume fraction of the α-phase particles to greater than 50% of the total volume fraction at both the edge and the centre of the ingot and, secondly, it yields an increased dispersoid size. Thus, a lower temperature homogenisation practice produces a near-ideal combination of intermetallic particle phase distribution, as well as dispersoid size, which is critical for Zener drag and the minimization of recrystallisation during the hot rolling processes.

Limits of dispersoid size and number density in oxide dispersion strengthened alloys fabricated with powder bed fusion-laser beam

Previous work on additively-manufactured oxide dispersion strengthened alloys focused on experimental approaches, resulting in larger dispersoid sizes and lower number densities than can be achieved with conventional powder metallurgy. To improve the as-fabricated microstructure, this work integrates experiments with a thermodynamic and kinetic modeling framework to probe the limits of the dispersoid sizes and number densities that can be achieved with powder bed fusion-laser beam. Bulk samples of a Ni–20Cr ＋ 1 wt% Y2O3 alloy are fabricated using a range of laser power and scanning velocity combinations. Scanning transmission electron microscopy characterization is performed to quantify the dispersoid size distributions across the processing space. The smallest mean dispersoid diameter (29 nm) is observed at 300 W and 1200 mm/s, with a number density of 1.0 × 1020 m−3. The largest mean diameter (72 nm) is observed at 200 W and 200 mm/s, with a number density of 1.5 × 1019 m−3. Scanning electron microscopy suggests that a considerable fraction of the oxide added to the feedstock is lost during processing, due to oxide agglomeration and the ejection of oxide-rich spatter from the melt pool. After accounting for these losses, the model predictions for the dispersoid diameter and number density align with the experimental trends. The results suggest that the mechanism that limits the final number density is collision coarsening of dispersoids in the melt pool. The modeling framework is leveraged to propose processing strategies to limit dispersoid size and increase number density.

Tailoring microstructure and mechanical properties of Al-Mg-Si-Cu alloy with varying Mn and/or Cr additions

Introducing and maintaining the subgrain structure during thermomechanical processes is an effective approach to mitigate the strength-ductility contradiction of Al-Mg-Si-Cu alloys, which holds significant importance for their engineering application. The objective of this work is to explore the effects of individual and synergistic additions of two dispersoid-forming elements, Mn and Cr, on microstructure and associated mechanical properties of an Al-Mg-Si-Cu alloy. The results show that when compared to alloys with individual addition of either Mn or Cr, their synergistic incorporation leads to an improved dispersoid precipitation with reduced size. For instance, the 0.7Mn0.4Cr alloy exhibits a number density of 10.26 μm-2, which is twice that of the sum of 0.7Mn and 0.4Cr alloys. In response to that, the 0.7Mn0.4Cr alloy attains enhanced resistance to recrystallization, leading to a well-maintained recovery structure and exceptional mechanical properties. But an excess addition of Cr will result in the formation of primary Al45Cr7 phase, which significantly deteriorate the mechanical properties of the alloy. While notably, the 0.4Cr alloy surprisingly exhibits better recrystallization resistance compared to the 0.7Mn alloy, despite having larger dispersoid size and lower number density. This can be attributed to the coherent interface between the α-Al(Cr,Fe)Si dispersoids and matrix, providing higher pinning force that effectively impede the recrystallization.

Influences of adding Y2Ti2O7 and HfH1.98 nanoparticles on the microstructure and mechanical properties of oxide dispersion strengthen steels

Adding Y2O3 will make Al-containing oxide dispersion strengthened (ODS) steels produce coarse Y-Al-O particles, which deteriorates their mechanical properties. Herein, Y2Ti2O7 nanoparticles and Hf hydride nanoparticles (NPs) were successfully prepared by hydrogen plasma-metal reaction (HPMR) method and added together in the Fe-Cr-Al ODS steel to replace the traditional Y2O3 NPs. The microstructure of matrix and oxide in ODS steels has been characterized by scanning transmission electron microscopy (STEM) and high resolution transmission electron microscopy (HRTEM). The oxide NPs in FHYT-0.6 (Fe-14Cr-4.5Al-2 W-0.35HfH1.98–0.6Y2Ti2O7, wt%) are made of Y2Ti2O7 (semi-coherent with the matrix and about 10 nm) and HfO2 (incoherent with the matrix and about 26 nm). The size of oxide dispersoid in FHYT-0.6 is reduced to 8.8 nm and the number density is greatly increased to 9.4 × 1023 m−3 compared with FTYT-0.6 (Fe-14Cr-4.5Al-2 W-0.35Ti-0.6Y2Ti2O7, wt%) and FTY-0.6 (Fe-14Cr-4.5Al-2 W-0.35Ti-0.6Y2O3, wt%). The tensile strength at room temperature of FHYT-0.6 is 1194 MPa, which is 24.1 and 14.1% higher than the FTY-0.6 and FTYT-0.6, respectively. Our work has proved that the mechanical properties of the alloy can be significantly improved by adding Y2Ti2O7 and HfH1.98 NPs, which provides a new idea for manufacturing high-performance ODS steels.

Additive manufacturing of oxide dispersion-strengthened CoCrNi medium-entropy alloy by in situ oxide synthesis

The additive manufacturing of oxide dispersion-strengthened (ODS) alloys has been challenging due to difficulties in forming nanosized dispersoids and achieving a uniform distribution of dispersoids. To overcome these challenges, this study proposes a novel ODS feedstock preparation strategy using the surface modification and reinforcement transplant (SMART) process and an in situ dispersoid synthesis strategy that could be applied during direct energy deposition (DED). The feedstock of ODS CoCrNi was prepared with Co-Y alloy powder and NiO or TiO2 as the Y and O suppliers, respectively. To evaluate the in situ dispersoid synthesis effect, a counterpart was prepared by adding Y2O3 using an ex situ dispersoid addition approach. The addition of TiO2 to induce the supply of O and Ti led to an in situ synthesis of ODS CoCrNi with a 63.5 % reduction in dispersoid size compared to the pristine CoCrNi resulting in the strengthening of the CoCrNi MEA matrix. This study suggests that ODS alloys with an optimal microstructure can be fabricated using the DED process through in situ dispersoid synthesis aided by Ti and O suppliers.

THE MICROSTRUCTURE AND MECHANICAL PROPERTIES OF THE Al–Mg–Fe–Ni–Zr–Sc ALLOY AFTER MULTIDIRECTIONAL FORGING

The influence of multidirectional isothermal forging on the grain structure and secondary phase particles of solidification origin and dispersoids in Al–4.9Mg–0.9Ni–0.9Fe–0.2Zr–0.1Sc alloy has been studied. The finite element simulation was used to analyze a strain distribution in the sample during forging in a die. A proposed method considered the influence of friction and the changes in a strain rate to recalculate true stress-strain curves for multidirectional forged alloy. An increase in a number of forging cycles at a temperature of 350°C ensured a twice decrease in a mean size of the particles of solidification origin, provided a mean grain size of 1.3 ± 0.2 μm, and insignificantly changed the size of dispersoids. The isothermal multidirectional forging increased the yield strength of the alloy by 60%, tensile strength by 20%.

Investigation of Phase Transformation and Mechanical Properties of A356 Alloy with Cu and Zr Addition during Heat Treatment

Cast A356(Al-Si-Mg) alloys are widely used in automotive and general applications because of their mechanical properties and castability. Al-Si-Mg-(Cu) alloys typically lose their strength above 170 o C due to coarsening of precipitates, which limits their application to components. To maintain their strength at elevated temperature, Al-Si-Mg-(Cu) alloys are modified by adding transitional metals. Several studies have been carried out to evaluate the effect of Zr addition on the high temperature mechanical properties of cast Al-Si alloys because Zr can form thermally stable phases such as Al3Zr. Despite the relative studies on the influence of Cu and Zr on the mechanical properties of cast Al-Si-Mg-(Cu) alloys, investigations of the effect of Zr on the phase transformations and the mechanical properties during heat treatment remains limited. In this study, the effects of added Cu and Zr on the phase transformations and the mechanical performance during heat treatment of A356 cast alloy were investigated. Needle-like and block-like (Al,Si)3(Ti,Zr) dispersoids formed as some Si and Ti replaced Al and Zr in Al3Zr crystal structures were generally observed. Furthermore, with increasing solution treatment time, the size of Zr dispersoids was reduced, and smaller Zr particles were precipitated at the same time, which caused a decrease in the area fraction of the Zr dispersoids. In addition, the metastable L12 structures of Zr dispersoids in Al-Si-Mg-Cu-Zr alloys were transformed into stable D023 during solution heat treatment as the Cu addition accelerated the transformation. Tensile and low-cycle fatigue (LCF) tests were performed to reveal the effects of (Al,Si)3(Ti,Zr) dispersoids on mechanical properties. As a result, elongation at elevated temperature was highly increased, while maintaining strength, according to the increase in solution heat treatment time, which improved low-cycle fatigue properties.

Effects of CrxMo(0.2-x) addition on the dispersoids evolution and mechanical properties of Al–Cu–Mg–Ag–Mn alloy

Unlike the rod-like T–Al20Cu2Mn3 dispersoids, the spherical Al7(Cr, Mn) and Al6(Fe, Mn, Mo) precipitated in Al–Cu–Mg–Ag–Mn alloys with CrxMo(0.2-x) addition, retained the deformed substructure, and acted as a dispersion reinforcement. In this study, the precipitation behavior of dispersoids in Al–Cu–Mg–Ag–Mn alloys with various CrxMo(0.2-x) (x = 0.15, 0.10, 0.05 wt.%) at 400 °C/12 h + 515 °C/24 h homogenization was investigated. The compositional and structural evolution of dispersoids in Al–Cu–Mg–Ag–Mn alloys were investigated by optical microscopy and atomic resolution high-angle annular dark-field scanning transmission electron microscopy. The effects of CrxMo(0.2-x) addition on morphology, size and number density of dispersoids inhibited the recrystallization behavior and improved the mechanical properties of alloys in varying degrees. When x = 0.15 in CrxMo(0.2-x), the large amount of Al7(Cr, Mn) precipitates to refine the T–Al20Cu2Mn3, and dispersoid-free zones (DFZ) significantly decreases. As x decreases to 0.05, the homogeneous Al6(Fe, Mn, Mo) dispersoids present the opposite precipitation trend of T–Al20Cu2Mn3 to compensate for the DFZ. During the deformation and subsequent heat treatment, the Al–Cu–Mg–Ag–Mn alloy with Cr0.05Mo0.15 addition maintains the highest substructure and dislocation density owing to the highest number density of spherical dispersoids, demonstrating excellent mechanical properties at ambient and elevated temperatures.

Orientation dependent pinning of (sub)grains by dispersoids during recovery and recrystallization in an Al–Mn alloy

The recrystallized grain size and texture in alloys can be controlled via the microchemistry state during thermomechanical processing. The influence of concurrent precipitation on recovery and recrystallization is here analyzed by directly correlating (sub)grains of P, CubeND and Cube orientation with second-phase particles in a cold-rolled and non-isothermally annealed Al–Mn alloy. The recrystallized state is dominated by coarse elongated grains with a strong P, weaker CubeND and even weaker Cube texture. The correlated data enables orientation dependent quantification of density and size of dispersoids on sub-boundaries and of subgrains in the deformation zones around large constituent particles. A new modified expression for the Smith–Zener drag from dispersoids on sub-boundaries is derived and used. The results show that drag on (sub)grain boundaries from dispersoids is orientation dependent, with Cube subgrains experiencing the highest drag after recovery and partial recrystallization. The often-observed size advantage of Cube subgrains is not realized due to increased drag, thereby promoting particle-stimulated nucleation (PSN). Relatively fewer and larger dispersoids in deformation zones around large particles give a reduced drag on PSN nuclei, further strengthening PSN. Observations substantiating stronger P texture compared to CubeND texture are higher frequency of P subgrains and faster growth of these subgrains. The applied methodology enables a better understanding of the mechanisms behind the orientation dependent nucleation and growth behavior during recovery and recrystallization with strong concurrent precipitation in Al–Mn alloys. In particular, the methodology gives new insights into the strong P and CubeND textures compared to the Cube texture.

Correlated subgrain and particle analysis of a recovered Al-Mn alloy by directly combining EBSD and backscatter electron imaging

Correlated analysis of (sub)grains and particles in alloys is important to understand transformation processes and control material properties. A multimodal data fusion workflow directly combining subgrain data from electron backscatter diffraction (EBSD) and particle data from backscatter electron (BSE) images in the scanning electron microscope is presented. The BSE images provide detection of particles smaller than the applied step size of EBSD down to 0.03 μm in diameter. The workflow is demonstrated on a cold-rolled and recovered Al-Mn alloy, where constituent particles formed during casting and dispersoids formed during subsequent heating affect recovery and recrystallization upon annealing. The multimodal dataset enables statistical analysis including subgrains surrounding constituent particles and dispersoids' location with respect to subgrain boundaries. Among the subgrains of recrystallization texture, Cube{001}〈100〉 subgrains experience an increased Smith-Zener drag from dispersoids on their boundaries compared to CubeND{001}〈310〉 and P{011}⟨5¯6¯6⟩ subgrains, with the latter experiencing the lowest drag. Subgrains at constituent particles are observed to have a growth advantage due to a lower dislocation density and higher boundary misorientation angle. The dispersoid size per subgrain boundary length increases as a function of misorientation angle. The workflow should be applicable to other alloy systems where there is a need for analysis correlating grains and grain boundaries with secondary phases smaller than the applied EBSD step size but resolvable by BSE imaging.

Nano oxide particles in 18Cr oxide dispersion strengthened (ODS) steels with high yttria contents

Oxide dispersion strengthened (ODS) steels containing yttria are candidate materials for fuel cladding tubes in future nuclear reactors. Their performance is determined by the size, distribution and volume fraction of the oxide dispersoids. The addition of yttria leads to a significant loss in ductility of steel limiting the yttria content in most ODS steels to 0.35%. This limitation may be overcome by powder forging of ODS steel powders. Two steels having nominal compositions (in wt%) of Fe-18Cr-2W-0.285Ti-0.5Y 2 O 3 and Fe-18Cr-2W-0.571Ti-1Y 2 O 3 were prepared by mechanical alloying of elemental powders with yttria powder in a Simoloyer attritor. The alloy powders were consolidated by powder forging at 1473 K in a flowing hydrogen atmosphere. The microstructure of powder forged ODS steels was characterized by electron microscopy. Both the steels exhibited a fine-grained recrystallized microstructure after forging. Fine (<10 nm) cuboidal oxide particles were found to be present in a ferrite matrix. A few coarse oxide particles were also observed. These coarse (>10 nm) oxide particles were present mainly along the ferrite grain boundaries. The crystal structure of oxide particles was determined by applying fast fourier transformation (FFT) on the fringes observed by high resolution transmission electron microscopy. The extracted FFTs were indexed to identify the crystal structure. The coarse particles were found to be Y 2 O 3 , TiO 2 and Cr 2 O 3 . The fine particles were identified as Y 2 TiO 5 and Y 2 Ti 2 O 7 . The face centre cubic Y 2 Ti 2 O 7 oxide particles were semi coherent whereas the orthorhombic Y 2 TiO 5 oxide particles were found to be incoherent with the ferrite matrix. The number fraction, average size and size distribution of these oxide particles was determined for both the alloys. Cr rich shells were observed around most of the particles which may prevent the coarsening of oxide particles at elevated temperatures. Reasons for this are discussed. • High yttria 18Cr ODS steels were successfully developed through novel hot powder forging route. • Recrystallized equiaxed grains with a uniform distribution of nano oxides particles were observed in the forged alloys. • A majority of oxides present were Y 2 TiO 5 or Y 2 Ti 2 O 7 oxides. Cr-rich shells were associated with these complex oxides. • The cuboidal Y 2 TiO 5 oxides were incoherent while the spherical Y 2 Ti 2 O 7 oxides were semi-coherent with the ferrite matrix. • HR-TEM also confirmed the formation of nano oxide particles such as Y 2 O 3 , TiO 2 and Cr 2 O 3 . These too were analysed.

Manufacturing oxide-dispersion-strengthened steels using the advanced directed energy deposition process of high-speed laser cladding

In this work, we demonstrate the feasibility of manufacturing an iron-based oxide-dispersion-strengthened (ODS) PM2000 composite material with the chemical composition of Fe20Cr4.5Al0.5Ti + 0.5Y2O3 (in wt.%) via the advanced directed energy deposition (DED) process of high-speed laser cladding (HSLC). The characteristic high solidification rates of HSLC processes allow the successful dispersion of nano-scaled yttrium-based oxides in the ferritic stainless steel matrix. The effective suppression of nano-particle agglomeration during the melting stage, which is frequently observed in conventional DED processes of ODS materials, is reflected by smaller dispersoid sizes and corresponding higher hardness of manufactured specimen compared to DED-manufactured counterparts.

Oxide dispersion-strengthened silver: manufacturing and properties

Abstract Novel oxide dispersion-strengthened (ODS) silver alloys were synthesised by mechanical alloying and subsequent consolidation via hot pressing in protective atmosphere. The effect of dispersoid size and volume fraction on the electrical and mechanical properties is exemplified with Cr2O3, CaO and Y2O3 as model candidates for a systematic study of the principles of particle selection. The results for the development of the microstructure under different processing conditions show that control of the impurity level is of primary importance for achieving high-quality, fully dense material. Hence, a modified cryo-milling technique at liquid-N2 temperature was applied. Data at ambient temperature are presented, revealing that the mechanical and electrical properties can be tailored within a wide range as a function of the microstructure. These results are explained by microstructural concepts for room temperature yielding and electrical conductivity.

Characterization of Al3Zr precipitation via double-step homogenization and recrystallization behavior after subsequent deformation in 2195 Al-Li alloy

The processability and final mechanical properties of Al-Li alloys are strongly affected by the uniformity of solute element and the degree of recrystallization, which can be improved via homogenization treatments. It is essential to control the microstructure to achieve the desired properties. In this work, the optimal double-step homogenization (DH) parameters for as-cast 2195 Al-Li alloy were first determined as 460 °C/16 h + 515 °C/20 h according to the comparative analysis, which fitted well with the results predicted by the corresponding kinetics modeling. Compared with the conventional single-step homogenization (SH), DH not only prevented the occurrence of overburning but also provided a more favorable condition for Al3Zr dispersoids to precipitate uniformly. The size and number density of Al3Zr dispersoids in the DH sample are finer and higher than those in the SH sample based on quantitative statistics. Due to the sufficient driving force for nucleation, the precipitate free zone (PFZ) of Al3Zr dispersoids was much narrower after DH. As a result, the DH sample possessed a higher Zener drag pressure, leading to a remarkable inhibition on the continuous evolution of substructures. Therefore, the recrystallization behavior in the DH sample was impeded effectively during the subsequent solution treatment. These findings are expected to provide reliable theoretical guidance for the industrial processing of as-cast 2195 Al-Li alloy.

Influence of Fe and Mn on the Microstructure Formation in 5xxx Alloys-Part I: Evolution of Primary and Secondary Phases.

The increasing demands for Al sheets with superior mechanical properties and excellent formability require a profound knowledge of the microstructure and texture evolution in the course of their production. The present study gives a comprehensive overview on the primary- and secondary phase formation in AlMg(Mn) alloys with varying Fe and Mn additions, including variations in processing parameters such as solidification conditions, homogenization temperature, and degree of cold rolling. Higher Fe alloying levels increase the primary phase fraction and favor the needle-shaped morphology of the constituent phases. Increasing Mn additions alter both the shape and composition of the primary phase particles, but also promote the formation of dispersoids as secondary phases. The size, morphology, and composition of primary and secondary phases is further affected by the processing parameters. The average dispersoid size increases significantly with higher homogenization temperature and large primary particles tend to fragment during cold rolling. The microstructures of the final soft annealed states reflect the important effects of the primary and secondary phase particles on their evolution. The results presented in this paper regarding the relevant secondary phases provide the basis for an in-depth discussion of the mechanisms underlying the microstructure formation, such as Zener pinning, particle stimulated nucleation, and texture evolution, which is presented in Part II of this study.

A numerical study of a size-dependent finite-element based unit cell with primary and secondary voids

Aluminium alloys contain various types of intermetallic particles with different sizes, such as constituent particles and dispersoids. The main mechanism of ductile fracture in these materials is assumed to be nucleation of voids around the constituent particles, which grow during plastic deformation and eventually coalesce, resulting in material failure. The role of the dispersoids is less certain, but they are assumed to contribute in the last stages of the ductile fracture process. While the constituent particles are in the range of a couple of microns, the size of dispersoids is normally one order of magnitude smaller. To disclose the possible effects of the dispersoids on the ductile fracture process in aluminium alloys, this paper presents a numerical study of a finite-element based unit cell, which consists of a single spherical void embedded in a matrix material represented by a porous plasticity model with void size effects. Accordingly, the single, primary void of the unit cell is assumed to have nucleated on a constituent particle, whereas the matrix porosity is assumed to account for secondary, smaller voids nucleated on dispersoids. The effects of the intrinsic length scale of the matrix material on the void growth and coalescence are studied for a range of stress states, while the initial primary and secondary void volume fractions are kept constant. The secondary voids have a substantial effect on the behaviour of the unit cell when their size is large compared to the intrinsic material length scale, but they were not found to influence the growth of the primary void. Instead, the growth of the secondary voids promotes strain softening and influences the coalescence process of the primary voids, which gradually changes mode from internal necking to loss of load-carrying capacity of the inter-void ligament.

Effects of Manganese and Zirconium Dispersoids on Strain Localization in Aluminum Alloys

Strain localization in aluminum alloys can cause early failure of the material. Manganese and zirconium dispersoids, often present in aluminum alloys to control the grain size, have been found to be able to homogenize strain. To understand the effects of dispersoids on strain localization, a study of slip bands formed during tensile tests is carried out both experimentally and through simulations using interferometry and discrete dislocations dynamics. Simulations with various dispersoid size, volume fraction, and nature were carried out. The presence of dispersoids is proven to homogenize strain both is the experimental and numerical results.

Recognition of Suspension Liquid Based on Speckle Patterns Using Deep Learning

We presented a machine learning-based method to recognize suspension by distinguishing dispersoid-dependent speckle patterns using a convolutional neural network. The dispersoid size and concentration-related transmissive speckle patterns were recorded by a lensless camera when a coherent He-Ne laser irradiated the suspension. Firstly we realized the recognition of the polystyrene microspheres-dispersed suspensions with different particle sizes and the recognition of several common suspensions including protein powder and milk powder with similar concentration. Further recognition from three different food suspensions with unknown concentration was achieved with high accuracy of 99%. The experimental results confirm that this non-contact method could find applications in the measurement and classification of suspension liquid containing micrometers-sized particles.

The effect of Mn on the high temperature flow stress of Al–Mg–Si alloys

The demand for Al–Mg–Si extrusion alloys in the transportation sector is increasing rapidly. An important aspect of the process is high temperature extrusion and in particular, the breakthrough force for the extrusion press. The breakthrough force varies as a function of the extrusion ratio, extrusion speed and temperature, the complexity of the profile and the flow stress of the alloy. Further, Mn and Cr are often added to the alloy which form dispersoids during homogenization which precipitation strengthen the alloy at high temperature. This work presents a new approach to calculate the volume fraction of dispersoids using electron microprobe analysis, electrical resistivity measurements and transmission electron microscopy (TEM). The new method substantially increases the accuracy of the volume fraction determination compared with traditional image analysis or TEM since the volume of material sampled is much larger avoiding effects of local segregation. Using the volume fraction and dispersoid size measurements, a high temperature flow stress model based on dislocation theory has been developed. It is shown to describe the high temperature flow stress measurements to within 5% in 95% of the cases. The model was validated by independent experimentation where it predicted the flow stress within 5% accuracy. The flow stress model can be used independently based on experimental quantification of the dispersoids or as part of a through process model which includes a KWN based precipitation model for dispersoids and then implemented as constitutive equation for a FEM based model of the extrusion process.

Oxide dispersoid coherency of a ferritic-martensitic 12Cr oxide-dispersion-strengthened alloy under self-ion irradiation

Ferritic-martensitic oxide-dispersion-strengthened (ODS) alloy has shown excellent mechanical property and high radiation tolerance. However, the stability of dispersoids during displacive irradiation in the individual ferritic and martensitic phases is unclear. Here, the correlation among dispersoid coherency, size, density, and matrix phase are studied in dual-phase 12Cr ODS after 100 peak displacements-per-atom (dpa) irradiation at 475°C, using 3.5 MeV Fe2+ self-ions. The size and density changes of coherent and incoherent dispersoids were analyzed as a function of irradiation depth. The average dispersoid size decreased after irradiation in both phases, and the large incoherent dispersoids in the tempered martensite phase underwent a more dramatic change than those in the ferrite phase. The dispersoid density significantly increased in the ferrite phase within the irradiated region, mostly resulting in an increase in coherent dispersoid density. On the other hand, only a small change in density was observed in the tempered martensite phase for both coherent and incoherent dispersoids. This study shows that dispersoid evolution is dramatically different in ferrite and tempered martensite phases.