Plate-like Precipitates Research Articles

Study on tensile behavior at various temperatures of the Mg-7Gd-5Y-1Nd-2Zn-0.5Zr alloy

Mg-rare earth (RE)-Zn alloys with long-period stacking ordered (LPSO) structure show excellent room temperature, elevated temperature mechanical properties. In this work, microstructure and mechanical properties of Mg-7Gd-5Y-1Nd-2Zn-0.5Zr (wt%) alloy after tensile deformation at various temperatures (room temperature (RT), 250 °C and 300 °C) were investigated. The pre-precipitated alloy exhibited tensile yield strength (TYS) of 149 MPa at room temperature, while it maintained relatively high TYS at 250 °C (154 MPa) and 300 ℃ (123 MPa). The microstructural characterizations revealed that such outstanding heat resistance is mainly attributed to the blocky LPSO structure near the grain boundary; basal plate-like precipitates, twins and kink bands inside the grain. The blocky LPSO structure exhibits a coherent boundary with one α-Mg grain, while being incoherent with other α-Mg grains or the LPSO structure. Cracks primarily occured along the incoherent interface. Basal plate-like precipitates formed during elevated temperature tensile deformation included GP zones, γ', metastable LPSO building blocks, and fine 14H-LPSO structure. A probable γ-precipitation sequence is supersaturated solid solution → GP zones (ABAB-type) → single LPSO building block (γ')→ various metastable LPSO building block clusters→ 14H-LPSO (γ). The deformation modes (sliding, twinning, kinking, grain boundary sliding, etc) modified with the tensile temperature increase. <c+a> dislocations were observed at elevated temperatures. As the temperature of tensile test increases, twins become less. Grain boundary sliding occurs at elevated temperatures.

Enhancing mechanical properties of Al-Zn-Mg-Cu alloys: The impact of high strain rate compression and subsequent heat treatment on microstructural evolution

This study presents a comprehensive examination of the Al-Zn-Mg-Cu alloy, focusing on the effects of high strain rate dynamic compression and heat treatment on its performance. The research aimed to understand the underlying microstructural mechanisms contributing to the enhanced mechanical properties of the alloy, which is critical for applications in aerospace and automotive industries. High strain rate dynamic compression tests, conducted at 3.0 × 1000 s−1, revealed a significant increase in both yield strength and ultimate compression strength of the Al alloy, which was accompanied by a increase in hardness. Post-compression microstructural analyses utilizing transmission electron microscopy and scanning- transmission electron microscopy indicated that significant changes occurred during testing. Key findings include the development of micro shear bands, alterations in the size and distribution of precipitates, and the emergence of new plate-like precipitate formations. Subsequent T6 heat treatment led to further microstructural evolution, particularly impacting the volume fraction and size of η' precipitates. The study highlights the crucial role of dislocation-precipitate interactions, where dislocations are effectively pinned by precipitates, thereby contributing significantly to the material's strength. These results demonstrate the potential of high strain rate dynamic compression coupled with heat treatment as a method to significantly enhance the mechanical properties of Al-Zn-Mg-Cu alloys. Overall, the findings provide valuable insights into the optimization of this alloy for high-performance applications, emphasizing the importance of controlled microstructural engineering.

Coupling of alloy chemistry, diffusion and structure by grain boundary engineering in Ni–Cr–Fe

The diffusion–microstructure correlations for grain boundaries (GBs) in the technologically-relevant Ni-based 602CA alloy are investigated. Prolonged annealing treatments up to 744 h create distinct GB complexions with specific segregation–precipitation–structure states. Globular M23C6-type carbides at straight GBs and plate-like carbides together with NiAl-enriched (γ′-type) particles at hackly GBs are found to co-exist. Moreover, an atomic-scale GB spinodal-like decomposition, especially at straight GBs, is observed. The co-existence of the two distinct states of general high-angle GBs, indicated by tracer diffusion experiments and verified by a detailed structure examination, is explained via state-of-the-art measurements of local elastic strains. In a course of annealing at 873 K, the relatively “fast” diffusivities are found to increase by a factor of 10 or more as a result of a coupled evolution of the GB plate-like precipitates and the irregular GB structures, whereas the relatively ”slow” diffusivites remained practically unchanged representing the contributions of straight interfaces with spherical precipitates. Thus, the diffusion properties of high-angle GBs evolve together with characteristic changes of GB complexions distinguished by a growth of carbide- and γ′-type precipitates and a concomitant generation of GB dislocation networks. The obtained results provide novel insights into grain boundary tailoring by utilizing structure – kinetics correlations involving segregation, precipitation and the evolution of interface defects.

Precipitate-domain wall topologies in hardened Li-doped NaNbO3

Ferroelectric hardening is an absolute requirement for potential applications of piezoceramics in high-power devices. A very recent work demonstrates that ferroelectric hardening by pinning domain walls with precipitates introduced during processing is feasible, akin to precipitation hardening in metals. With the precipitation of plate-like LiNbO3 in Li-doped NaNbO3 piezoceramics, ferroelectric hardening was achieved, exhibiting an enhanced mechanical quality factor (Qm). The specific morphology and corresponding orientation of the LiNbO3 platelets, exhibiting {110}PC habit planes, were characterized by transmission electron microscopy (TEM). The experimentally revealed crystallographic structures and strain incompatibility were found to correlate well with the thermodynamic simulation of the minimum-energy aspect ratio. In particular, the topology of the precipitate-domain wall assembly was clarified, revealing a full pinning on the domain walls by the incorporated plate-like precipitates. The revealed topology provides a fundamental basis for future optimization strategies for platelet hardening in new lead-free piezoceramics for high-power applications.

Crystal plasticity evaluation of the effect of grain morphology on compressive deformation behavior of AA2099 Al–Li alloy

The strip-like grain shape is one of three important factors (the strip-like grain shape, strong crystallographic texture and plate-like T1 precipitate) influencing the mechanical properties of the third-generation Al–Li alloys. However, studies on its effect have seldom been investigated to date. In the present study, an extended crystal plasticity finite element (CPFE) framework considering the strain gradient effect via incorporating the geometrically necessary dislocation (GND) density is constructed to investigate the compressive deformation behavior of studied AA2099 Al–Li alloy with strip-like grain shape. Good consistency with respect to the true stress-strain curve and texture characteristics between experimental and predicted results confirms the validity of constructed CPFE framework, as well as these fitted material parameters. Simulation results show the occurrence of aggregation for GND density not only near grain boundaries but also at grain interiors, which benefits in blocking the motion of the statistically stored dislocation (SSD) and the occurrence of obvious stress concentration in the constructed polycrystalline model. This demonstrates that the strip-like grain shape could exsert a nonnegligible influence on the mechanical response of studied AA2099 Al–Li alloy. Moreover, the difference between the predicted orientation distribution functions (ODFs) and the difference about the evolution of accumulative shear strain in 12 slip modes collectedly confirm that the strip-like grain shape does exert some influence on slip activities of studied AA2099 Al–Li alloy.

Strengthening via Orowan Looping of Misfitting Plate-like Precipitates

Many common engineering alloys are strengthened by precipitates with plate-like geometries. The mechanics of precipitation strengthening, while well resolved with spherical precipitates, are less well understood for plate-like geometries. In this work, we employ discrete dislocation dynamics simulations to study precipitation strengthening by θ′ precipitates in AlCu. We show that Orowan looping with parallel plate-like precipitates can be fundamentally different from spheres because it is governed by a steady-state glide process rather than a single critical dislocation geometry. We develop a model based on the formation of a dislocation dipole across the precipitate thickness to explain the observed strengthening. Finally, we show that while the precipitate misfit field can lead to both strengthening and weakening, strengthening is more common because of the steady-state process by which Orowan loops form.

Datasets from "Strengthening via Orowan Looping of Misfitting Plate-like Precipitates"

Datasets from "Strengthening via Orowan Looping of Misfitting Plate-like Precipitates"

Hardening effects of sheared precipitates on {112¯1} twinning in magnesium alloys

Abstract The interactions between a plate-like precipitate and two twin boundaries (TBs) ( { 10 1 ¯ 2 } , { 11 2 ¯ 1 } ) in magnesium alloys are studied using molecular dynamics (MD) simulations. The precipitate is not sheared by { 10 1 ¯ 2 } TB, but sheared by { 11 2 ¯ 1 } TB. Shearing on the (110) plane is the predominant deformation mode in the sheared precipitate. Then, the blocking effects of precipitates with different sizes are studied for { 11 2 ¯ 1 } twinning. All the precipitates show a blocking effect on { 11 2 ¯ 1 } twinning although they are sheared, while the blocking effects of precipitates with different sizes are different. The blocking effect increases significantly with the increasing precipitate length (in-plane size along TB) and thickness, whereas changes weakly as the precipitate width changes. Based on the revealed interaction mechanisms, a critical twin shear is calculated theoretically by the Eshelby solutions to determine which TB is able to shear the precipitate. In addition, an analytical hardening model of sheared precipitates is proposed by analyzing the force equilibrium during TB-precipitate interactions. This model indicates that the blocking effect depends solely on the area fraction of the precipitate cross-section, and shows good agreement with the current MD simulations. Finally, the blocking effects of plate-like precipitates on the { 10 1 ¯ 2 } twinning (non-sheared precipitate), { 11 2 ¯ 1 } twinning (sheared precipitate) and basal dislocations (non-sheared precipitate) are compared together. Results show that the blocking effect on { 11 2 ¯ 1 } twinning is stronger than that on { 10 1 ¯ 2 } twinning, while the effect on basal dislocations is weakest. The precipitate-TB interaction mechanisms and precipitation hardening models revealed in this work are of great significance for improving the mechanical property of magnesium alloys by designing microstructure.

Precipitation sequence in Al-Sc-Zr alloys revisited

Sc and Zr additions to Al provide significant strengthening through the formation of Al3(Sc,Zr) L12 dispersoids. Fe impurities are always present in commercial Al alloys and the effect of these impurities on precipitation mechanisms in Al-Sc-Zr alloys remain poorly understood. This is particularly relevant when considering recycled aluminium as recycling results in the build-up of impurities. We used a combination of resistivity and thermo-electric power (TEP) measurements to monitor the evolution of solid solution during ageing of an Al-Sc, Al-Zr and Al-Sc-Zr alloy. Sc first comes out of solution to form Al3Sc dispersoids, followed by Zr to form Al3Zr. A range of Al3Sc-core/Al3Zr-shell faceted morphologies were observed with high angular annular dark field scanning transmission electron microscopy (HAADF-STEM). The presence of a new class of Fe-rich plate-like precipitates in the {100}Al was revealed via HAADF-STEM. The ordered positions of the precipitate and matrix reflections in the selected area diffraction pattern and in high-resolution TEM images reveal that these precipitates display a multi-layered structure. The centre of the plates is pseudo-icosahedral with apparent five-fold symmetry, and is rich in Fe. The outside layer has a L12 structure and is rich in Sc and Zr. The layered structure allows complete coherency with the aluminium matrix. These precipitates are highly anisotropic with a thickness of 5-10 nm and a length up to ∼1000 nm. This is the first report of the formation of this type of coherent pseudo-icosahedral precipitates in isothermal conditions which is named the D-phase.

Coherent Precipitates with Strong Domain Wall Pinning in Alkaline Niobate Ferroelectrics.

High-power piezoelectric applications are predicted to share approximately one-third of the lead-free piezoelectric ceramic market in 2024 with alkaline niobates as the primary competitor. To suppress self-heating in high-power devices due to mechanical loss when driven by large electric fields, piezoelectric hardening to restrict domain wall motion is required. In the present work, highly effective piezoelectric hardening via coherent plate-like precipitates in a model system of the (Li,Na)NbO3 (LNN) solid solution delivers a reduction in losses, quantified as an electromechanical quality factor, by a factor of ten. Various thermal aging schemes are demonstrated to control the average size, number density, and location of the precipitates. The established properties are correlated with a detailed determination of short- and long-range atomic structure by X-ray diffraction and pair distribution function analysis, respectively, as well as microstructure determined by transmission electron microscopy. The impact of microstructure with precipitates on both small- and large-field properties is also established. These results pave the way to implement precipitate hardening in piezoelectric materials, analogous to precipitate hardening in metals, broadening their use cases in applications.

A new modeling framework for anisotropic yield strength of Al-Li alloy sheet with inhomogeneous plate-like T1 precipitates

The high strength of Al-Li alloy is mainly attributed to precipitates, which has attracted extensive investigations on precipitation dynamics and interaction with dislocations. However, the influence of plate-like T1 precipitate on mechanical anisotropy is still not fully clarified, and an accurate corresponding modeling framework considering inhomogeneous distribution and various configurations of T1 precipitate is also needed. Here, the evolution of mechanical anisotropies in 2198 Al-Li alloy sheets is systematically studied with different distributions and thicknesses of T1 precipitates obtained via changing pre-deformation direction and artificial aging temperature. A new modeling framework based on visco-plasitic self consistant (VPSC) is proposed to predict the anisotropic yield strength under different processing conditions. The resistance of four variants of T1 precipitates which form a 'T1 precipitate forest' to dislocation movement is considered. According to the geometric relationship with slipping systems, T1 precipitates can be divided into three types: type I is parallel to slipping plane, type II is parallel to slipping direction but not slipping plane, and type III has a certain angle to both slipping plane and direction. The critical resolved shear stress (CRSS) of each slipping system can be calculated using a linear mixture law considering volume fraction and shear strength of these three types. It is found that T1 precipitate of type I plays an important role in the strengthening of 2198 Al-Li alloy sheet. The shear strengths of types I, II and III are determined to be 400 MPa, 8 MPa and 8 MPa, respectively, at artificial aging temperature of 155 °C, and reach 400 MPa, 40 MPa and 40 MPa due to the increased T1 thickness when aging temperature increases to 162 °C. The calculated anisotropy of yield strength is in good agreement with experimental results. Furthermore, a reasonable correlation between slipping activation and T1 precipitate is revealed. That is, the activation fractions of different slipping systems exhibit how the varying distribution and thickness of T1 precipitate lead to different mechanical anisotropy of 2198 Al-Li alloy sheet.

A model experiment on nano-particle stability in 12Cr-ODS steel using high-resolution high voltage microscopy

In this work, the microstructure stability of 12Cr-ODS ferritic steel under irradiation is studied using a high-resolution high voltage electron microscope up to 1.5 dpa at 300 and 500 °C. Coherent YTiO3 nanoparticles (NPs) undergo coarsening during electron irradiation and the coarsening rate is positively correlated to irradiation temperature (the third power of NPs size is proportional to the irradiation dose). He pre-implantation can significantly reduce the coarsening rate. A model coupling Ostwald ripening and irradiation enhanced diffusion is used to explain this coarsening. The fitting results between NPs size and irradiation dose show that pre-implanted He causes a lower diffusion of Y in 12Cr-ODS steel compared with the non-implanted sample. In response to the irradiation, plate-like radiation-induced precipitates appear which result in diffraction streaks in fast fourier transform (FFT) pattern. Precipitations are paralleled to [100] or [110] direction of Fe matrix and located near the interface between NPs and matrix. The hypothesis that coherent Cr precipitate along NPs/matrix interface caused diffraction streaks is proposed. Besides, He pre-implantation can also delay this precipitation.

Novel heating- and deformation-induced phase transitions and mechanical properties for multicomponent Zr50M50, Zr50(M,Ag)50 and Zr50(M,Pd)50 (M = Fe,Co,Ni,Cu) amorphous alloys

Multicomponent alloys of Zr50M50, Zr50(M,Ag)50 and Zr50(M,Pd)50 (M = Fe,Co,Ni,Cu) can be melt-spun to obtain amorphous ribbons. The maximum thickness for fully amorphous ribbons varies with composition in the range 34‒53 μm. In contrast, fully amorphous ribbons are not obtainable for binary Zr50Ni50 or ternary Zr50(Ni,Cu)50 alloys. Heating-induced crystallization occurs through: two stages of amorphous [am] →[am′ + B2] → [B2 + B33] for Zr50M50; and [am] → [am′ + B2] → [B2 + AgZr] for Zr50(M,Ag)50; and a single stage of [am] → [B2] for Zr50(M,Pd)50, while no B2 phase is formed for the binary and ternary Zr50Q50 (Q = Ni or/and Cu) alloys. As-spun amorphous ribbons have good bending plasticity. Remarkably, Zr50M50 ribbons in tension show 0.22‒0.28% plastic elongation and work-hardening (the yield stress is ∼820 MPa, the fracture stress is ∼1200 MPa). When cold-rolled at room temperature to 30% reduction in thickness, Zr50M50 ribbons show 10% increase in hardness, while retaining good bending plasticity. Cold-rolling induces precipitation of spheroidal B2 and irregular B33 particles, while deformation in tension induces B2, B33 and also plate-like monoclinic precipitates. The B2 and B33 particles form by polymorphic transformation, and include a high density of internal defects. This novel deformation-induced precipitation has not been recognized for any Zr50Q50 binary or ternary alloys. The new multicomponent systems are encouraging for future progress as structural amorphous alloys.

Characterisation of precipitates in a stainless maraging steel by three-dimensional atom probe and small-angle neutron scattering

Abstract Two complementary techniques, namely three-dimensional atom probe and small-angle neutron scattering, were employed to study precipitation phenomena in a stainless maraging steel (Fe-12.3 %Cr-8.9%Ni-0.6 %Si-1 %Mo-0.6 %Al-0.8%Ti, wt.%) during ageing at 475 °C. Atom probe investigations revealed the precipitation of a single Ni-rich phase exhibiting an average particle diameter of 2.5 nm after 12 h. After ageing for 100 h these precipitates had grown to an average size of 4 nm. In addition, needle-or plate-like Ni-rich precipitates larger than 15 nm were present. Their compositions differ mainly in the amount of Fe, Ni and Ti. Furthermore, Cr-rich precipitates were observed. The size ranges and the number densities of the precipitates match well with those observed by small-angle neutron scattering.

Precipitation behavior of M23C6 in high nitrogen austenitic heat-resistant steel

The precipitation behavior of M23C6 carbides in LF25 high nitrogen austenitic heat-resistant steel was investigated from 700 °C to 850 °C. The results demonstrated that the precipitates in LF25 steel included Nb (C, N) and M23C6 during the aging treatment. M23C6 carbides with four morphologies formed during aging followed a sequence of intergranular precipitates, parallel plate-like precipitates, cellular precipitates, and intragranular precipitates with increasing aging temperature. The four types of morphologies of M23C6 retained a cube-on-cube crystallographic relation with the matrix. Firstly, the M23C6 precipitated as discontinuous particles along the grain boundaries due to the faster diffusion rate of the elements. With the aging temperature increasing, intergranular M23C6 grew and connected to form a film-like morphology. The partial dislocations slipped out from the non-coherent twin boundaries due to the stresses resulting from quenching and elastic modulus together with atomic volume difference between the M23C6 and austenite matrix. M23C6 nucleated at the slipped dislocations and grew along the (111) or (110) planes to form a parallel plate-like morphology. Cellular precipitates were precipitated from supersaturated austenite matrix and then formed an alternating morphology of lamellae M23C6 and austenite during the discontinuous precipitation reaction. Due to high resistance to intracrystalline growth, the intragranular precipitates were short rods or granules with small sizes.

Strong in-plane anisotropy of creep ageing behavior in largely pre-deformed Al-Cu alloy: Experiments and constitutive modeling

Deformation anisotropy is one of the key factors affecting the dimensional accuracy and performance consistency of components manufactured from aluminum alloys. Understanding and modeling their anisotropic creep ageing behavior is thus essential for achieving precise creep age forming of Al alloy components. Creep ageing responses along varying loading directions have been investigated in an Al-Cu alloy heavily cold-rolled by 82.6% at room temperature. Although the large pre-deformation imparts markedly enhanced creep formability and strength-ductility balance, significant in-plane creep anisotropy (with an index of 49%) and slight anisotropy of the obtained yield strength (with an index of 5.6%) are observed for the creep ageing at 140 ℃ under 150 MPa. The creep deformation decreases evidently with the increasing angle between the loading direction and the rolling direction. The microstructure (grain morphology, texture, dislocation and precipitation, etc.) of the largely pre-deformed Al-Cu alloy before and after creep ageing are characterized in detail by X-ray diffraction, Electron backscattered diffraction and Scanning transmission electron microscopy. The multi-scale examinations unveil a hierarchical structure consisting of flattened grains, dislocation sub-structures considerably elongated along the rolling direction and plate-like precipitates in the investigated alloy. This comparative analysis suggests the strong creep anisotropy is mainly determined by the preferential alignment of dislocation cells with a width of ∼500 nm rather than the texture and precipitation. By introducing an orientation-dependent creep resistance caused by back-stress of the elongated dislocation nanostructure, a mechanism-based constitutive model is established to accurately describe the in-plane creep anisotropy. This work also provides guidance for tuning the creep anisotropy in largely pre-deformed Al-Cu alloy.

Insight of high-entropy alloy particles-reinforced 2219 Al matrix composites via the ultrasonic casting technology

The microstructure and mechanical properties of metallic composites can be favorably modified by the introduction of various reinforcing particles. Different contents of high-entropy AlCoCrFeNi alloy particles (HEAps) were individually injected into the 2219 Al alloys via ultrasonic casting technology. Some irregular HEAps were observed along the grain boundaries. They served as reinforcing factors and provided numerous potential heterogeneous nucleation sites on the α-Al matrix. The average grain size of the HEAps-reinforced aluminum matrix composites (HEAps/AMCs) reduced dramatically from 136.08 μm (0 wt%) to 34.95 μm (1.5 wt% HEAps). Several rich-Al, Co, Fe, Cr, Ni, Cu elements with needle-shaped phases accompanied by some distinctive plate-like precipitates were observed in the Al matrix. Additionally, the optimal addition of HEAps was approximately 1.5 wt%, for any excess was detrimental to the microstructure and properties. The HEAps had a substantial influence on the mechanical properties, namely 1.5 wt% corresponding to the optimum tensile strength (217.4 MPa), and 3 wt% ascribing to the maximum micro-hardness (120.5 HV). The primary strengthening mechanisms were explored, revealing the grain refinement, solute, and precipitate strengthening to be the dominant factors. However, ∆ σ CTE and ∆ σ EMM showed very limited contribution. Meanwhile, ∆ σ Load , ∆ σ WH1 , and ∆ σ WH2 offered marginal increments to the yield strength. Theoretically, a novel strengthening model was established, and the yield strength of the HEAps/AMCs in an optimal HEAps addition range was effectively predicted. • AlCoCrFeNi HEAps/2219 Al matrix composites are fabricated via ultrasonic casting. • HEAps were stochastically distributed along the grain boundaries. • Novel model was established to predict the yield strength of HEAps/AMCs.

New insights into fine equiaxed zone of laser-welded 2A97 Al-Li alloy

In this study, the concept of fine equiaxed band (FEQB) was proposed for the first time, and the distribution range of the fine equiaxed zone (FEQZ) was redefined. Characterization techniques including scanning electron microscopy, electron backscattered diffraction, energy dispersive spectroscopy, and transmission electron microscopy were employed to analyse the microstructures, orientations, micro-segregations, and precipitates within the grain of the FEQZ. The results indicate the existence of tiny precipitates, mainly T1 and θ′ along with a small amount of δ′ within the randomly oriented fine equiaxed grain with spherical morphology, and no obvious dendrite structure was observed. The micro-segregation of Cu and Mg occurred at the grain boundaries, resulting in the generation of intermetallic phases at grain boundaries derived mainly by eutectic action. The dominant intermetallic phase enveloping that grain is T1, and a small amount of plate-like precipitate S′ is formed at the junction of three or more grains. The bands formed by these closely connected grains are called FEQB. Furthermore, the region covered by the FEQBs is called FEQZ.

The effect of heat treatments on mechanical properties of M789 steel fabricated by laser powder bed fusion

The microstructural evolution during the aging heat treatment of a newly developed steel (designed to be employed in the laser powder bed fusion), known as M789, was evaluated. The electron-backscatter diffraction (EBSD) analysis suggests that the as-printed sample contains a fully martensitic phase with random crystallographic texture. The samples were then solutionized at 1000 °C for 1 h, followed by aging at a temperature range of 400–600 °C and holding times from 40 to 120 min. The maximum hardness and tensile strength were achieved at aging temperatures of 450 °C and 500 °C for 2 h, with the latter temperature generated the highest amount of Ni3Ti precipitates (η-phase) with no traces of reverted austenite. Then, the heat-treated sample underwent transmission electron microscopy (TEM) and atom probe tomography (APT) analyses, which revealed the nano-scale, plate-like and spherical precipitates with number densities of 1.11 × 1024 m−3 and 0.93 × 1024 m−3, respectively. These precipitates contributed to the increase in tensile strength, from 1019 MPa (as-printed) to 1798 MPa (heat-treated), a net increase of 779 MPa. As a consequence of enhanced strength, the elongation decreased from 16% to 9%. Generally, the results of all experiments are consistent with simulations; the errors were identified to be less than 5%.

Microstructural stability of TMS-238TM Ni-base superalloy during long-term exposure at high temperature

The microstructure evolution in Re–Ru containing high generation Ni-base single crystal superalloy has been investigated during long-term isothermal exposure at 1000°C. The chemical and physical characteristics are determined by means of differential scanning calorimetry (DSC), X-ray diffraction (XRD), scanning electron microscopy (SEM) and Transmission electron microscopy (TEM) measurements. In addition to the initial γ/γ’ phase structure, formation of HCP-structured Re–Ru–Ni-rich phase is confirmed. Based on high-resolution TEM imaging and phase structure analysis the theoretical atomistic model presenting the interfaces between the phases was constructed and evaluated with respect to precipitation kinetics. Growth of plate-like precipitates occurs mainly through the plate edge area due to stacking fault sequences between the surrounding matrix and the precipitates, while thickening is very limited due to good coherency with the surrounding phase in the longitudinal direction.