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Al–Si–Mg alloys have received widespread application in communication, transportation and other fields on account of their attractive properties, e.g. superior castability, high ductility and excellent corrosion resistance. Comprehensive understanding of relationship between morphologies and mechanical performances under combined refiner-modifier condition is the prerequisite for the applications expansion. In this work, effect of Gd and Gd/Sr on the microstructure and mechanical properties of Al-9Si-0.4 Mg alloy was systematically studied. The results indicated that Gd had excellent refinement effect on α-Al but only partial modification on eutectic Si. Whereas simultaneous addition of Gd/Sr resulted in completely refined α-Al and modified eutectic Si. Growth of eutectic Si in untreated alloys show evidence of typical facet step growth mechanism. However, eutectic Si in Gd/Sr composite modified alloy mainly grew through impurity induce twinning mechanism and twin plane re-entrant edge mechanism, and facet step growth gradually weakened until disappearance. Based on these, both ultimate tensile strength (UTS) and elongation (El) of alloys were significantly improved and reasons were explained. [ABSTRACT FROM AUTHOR]

In this work, two different types of post-heat treatment processes were developed for additively manufactured CuCrZr alloy. The effect of post-heat treatment on the microstructure and properties of as-built CuCrZr alloy was studied in detail. After the direct aging of the as-built samples, the cellular substructure was preserved and a large number of fine Cu4Zr and Cr particles were precipitated in the matrix. However, after solid solution and age-hardening treatment, the grains in the sample coarsened to hundreds of microns and the annihilation of the cellular substructure occurred. Compared with the samples after solid solution and age-hardening treatment, the directly aged samples had an excellent combination of hardness (191 ± 7 HV), strength (513 ± 8 MPa) and electrical conductivity (82.2 ± 1.5 pct IACS). The high strength of the directly aged samples can be attributed to the enhancement of the strengthening mechanism of the precipitated particles and the retention of the cellular substructure. In addition, the reduction of solid solution atoms would significantly weaken the electron scattering effect, thereby improving the electrical conductivity. [ABSTRACT FROM AUTHOR]

Oxide dispersion strengthened tungsten (ODS-W) alloy was prepared by chemical method, conventional sintering and hot-rolling method, which breaks through the research bottleneck of preparing tungsten alloys with excellent comprehensive mechanical properties. More specifically, it can exhibit ultrahigh strength and superior toughness when tested at 200°C. In addition, the nil ductility temperature (NDT) can also dramatically decrease to 100–150°C. The bimodal structure formed by the uneven distribution of yttria and the lamellar structure formed by hot rolling in this ODS-W alloy provide a feasible way to develop other engineering materials with ultra-high strength and ductility. W-Y2O3 alloy with bimodal and lamellar structures prepared by wet chemical method and hot rolling process exhibits excellent combination of ultra-high strength and toughness. [ABSTRACT FROM AUTHOR]

Al-0.5Mg-0.4Si-0.1Cu alloy possessing weather resistance and oxidation resistance can obtain good surface quality (metallic luster) without chrome plating. Therefore, it is an important material to replace polluting chrome-plated aluminum profiles for automotive decorative parts. At present, studies about the extrusion process of Al-0.5Mg-0.4Si-0.1Cu alloy are very few, which affects its further application. In this work, the effect of extrusion ratios on microstructure and mechanical properties of Al-0.5Mg-0.4Si-0.1Cu alloy is investigated by optical microscopy (OM), scanning electron microscopy (SEM), electron backscattered diffraction (EBSD), transmission electron microscopy (TEM) and tensile tests. The results showed that the dynamic recrystallization degree of the alloy gradually increased with the extrusion ratio increasing, which is attributed to the driving force provided by the large extrusion ratio. Meanwhile, due to the occurrence of dynamic recrystallization, the texture changed from <111> to <001> orientation. In addition, grains were obviously refined and uniform with the extrusion ratio increasing. Due to the fine grain strengthening mechanism, the tensile strength and elongation of the alloy with an extrusion ratio of 30 reached 152 MPa and 32.4%. [ABSTRACT FROM AUTHOR]

Herein, effect of heat treatment on the microstructure and mechanical properties of a newly developed Al–9Si–0.4Mg–0.1Cu alloy treated by Al–6Sr–7La is investigated, and optimal T6 heat treatment process parameters are determined through optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM) analysis, and quantitative statistics. The results show that the distribution of α‐Al is more uniform after T6 heat treatment (solution treated at 540 °C for 5 h and aged at 170 °C for 6 h) with eutectic silicon possessing fine grain and high roundness. Meanwhile, Al–6Sr–7La increases peak aging hardness and reduces peak aging time. During the under‐aging process, a large amount of Guinier Preston zone and a small amount of Mg5Si6 phase precipitate, which have strengthening effect on the alloy. At peak aging state, the coherent precipitated Mg5Si6 phase in α‐Al leads to the highest microhardness. Continuing to prolong aging time, the coherent relationship between metastable phase Mg5Si6 and the matrix is weakened, resulting in the decrease in microhardness. In addition, after T6 heat treatment, both tensile strength and elongation of the alloy are significantly improved and the reasons are discussed. [ABSTRACT FROM AUTHOR]

Precipitation evolution and strengthening effect of Al-15wt%Mg2Si-5wt%Cu alloy were studied by characterizing the change of morphology and tensile properties after ageing at 200 °C for various times. At the under-ageing condition (ageing for 0.5 h), metastable θ″, θ′, fine dots and σ phases are formed. After ageing for 1 h (peak-ageing condition), θ″ and θ′ are dominant phases, and the high number density of precipitates produces a significant improvement of the hardness (173 Hv) and ultimate tensile strength (356 MPa). As ageing time is prolonged (ageing for 24 h), plenty of σ phases are formed at the expense of θ"/θ′ phases and act as the main strengthening precipitates. The over-aged microstructure consequently causes a decrease in the hardness (134 Hv) and ultimate tensile strength (311 MPa) of the alloy. [ABSTRACT FROM AUTHOR]

With excellent creep resistance, good high-temperature microstructural stability and good irradiation resistance, oxide dispersion strengthened (ODS) alloys are a class of important alloys that are promising for high-temperature applications. However, plagued by a nerve-wracking fact that the oxide particles tend to aggregate at grain boundary of metal matrix, their improvement effect on the mechanical properties of metal matrix tends to be limited. In this work, we employ a unique in-house synthesized oxide@W core-shell nanopowder as precursor to prepare W-based ODS alloy. After low-temperature sintering and high-energy-rate forging, high-density oxide nanoparticles are dispersed homogeneously within W grains in the prepared alloy, accompanying with the intergranular oxide particles completely disappearing. As a result, our prepared alloy achieves a great enhancement of strength and ductility at room temperature. Our strategy using core-shell powder as precursor to prepare high-performance ODS alloy has potential to be applied to other dispersion-strengthened alloy systems. Aggregation and coarsening of the second-phase oxide particles at grain boundaries have been a bottleneck for improving mechanical properties of oxide-dispersion-strengthened (ODS) alloys. Here the authors employ core-shell nanopowder precursors to achieve uniform dispersion of oxides in ODS alloys. [ABSTRACT FROM AUTHOR]

The current study has demonstrated that cation dopant segregation at matrix/oxide interface opened up a new route to refine and disperse secondary oxide particles in oxide dispersion-strengthened (ODS) alloys. Thus, a unified theory that explains the physical origins of this interfacial segregation phenomenon is needed for designing ODS alloys with excellent oxide dispersity and ensuing high performance. Here, taking W–Y2O3 system for example, we firstly assess the possible driving forces for cation dopant interfacial segregation based on the experimental observation from Sc3+-, La3+-, Ti4+-, Zr4+- and Hf4+-doped W–Y2O3 alloys. It was suggested that elastic energy, oxygen chemical potential gradient and interfacial energy reduction are three main driving forces for the cation dopant segregation at W/Y2O3 interface. Then, an analytical model was developed in this work to quantitatively calculate the contributions of these three factors to the total segregation energy. Finally, the coupled results are further validated with the density functional theory (DFT)-calculated total segregation energy, and the good consistency confirms again the underlying mechanism behind cation dopant segregation phenomenon in W-based ODS alloy. On this basis, it can be predicted that a chemically expanded lattice and a large oxygen affinity will promote dopant interfacial segregation and enable the microstructure of ODS alloys to be tailored desirably. More importantly, the results and analytical model in our work can provide theoretical guidance for choosing proper cation dopant for other ODS alloys and then enhancing their strength and ductility simultaneously. Besides, the high-temperature instability of secondary oxide particles under extreme working environment also can be solved easily using this method. [ABSTRACT FROM AUTHOR]

In this work, twin wire arc additive manufacturing (T-WAAM) combined with in-situ alloying method was developed to fabricate multi-element alloys, and biomedical Ti-6Al-7Nb alloy with a good combination of strength and ductility was successfully fabricated for the first time. The modification of microstructure and the improvement of mechanical properties of the deposited Ti-6Al-7Nb alloy caused by Nb addition were investigated. Although demonstrated here for Ti-6Al-7Nb alloy, the combined method of T-WAAM and in-situ alloying is in principle applicable to fabricate other multi-element alloys by composition design, which is conductive to expanding the application fields of WAAM. IMPACT STATEMENT Twin wire arc additive manufacturing combined with in-situ alloying was developed to fabricate multi-element alloys, and biomedical Ti-6Al-7Nb alloy with a good combination of strength and ductility was first fabricated. [ABSTRACT FROM AUTHOR]

In this paper, the interactions between interstitial oxygen atoms and substitutional atoms in Ti–Nb–O alloys were investigated by first-principles calculations based on the density functional theory. The binding energies and formation energies of oxygen atoms sited were calculated in various interstices with different geometries, element species, and atomic arrangements. The calculation results showed that there was a strong repulsive binding energy between the interstitial oxygen and the substitutional niobium atoms. On this basis, the energetically favored sites and the distribution of interstitial oxygen atoms in Ti–Nb–O alloys were discussed and demonstrated by an electron energy loss spectroscopy method. Furthermore, the diffusion activation energies of interstitial oxygen atoms based on the formation energy results were presented, and the diffusion behaviors of interstitial oxygen atoms in Ti–Nb–O alloys were also discussed. [ABSTRACT FROM AUTHOR]

Ti2AlNb‐based alloys are synthesized by spark plasma sintering from pre‐alloyed and ball‐milled Ti–22Al–25Nb powder, and the structure of the alloys is regulated by aging at 800 °C for 0.5, 1, 2, and 3 h. Comparison of phase composition, microstructure, and mechanical properties are made in this study. Aging in the B2 + O phase region refers to the reversible transformation of B2 ↔ O. Complete B2 + O Widmanstätten structure is obtained in the aged alloys synthesized from pre‐alloyed powder, and the ones from milled powder contain acicular O and B2 + O Widmanstätten structure. Ball milling eliminates the B2 + O colonies, facilitates the continuous transformation of O → B2, and induces acicular O in the alloys; however, the hardness of these alloys is decreased in contrast with that of the ones synthesized from pre‐alloyed powder. Owing to the precipitation strengthening based on a large amount of fine O‐phase precipitates, the 3 h aged alloy from pre‐alloyed powder exhibits comprehensive mechanical properties with Vickers hardness of 448 ± 9 HV, ultimate tensile strength of 730 MPa, and elongation of 0.43%. [ABSTRACT FROM AUTHOR]

In order to better understand the thermal stability and mechanical properties of the nominal Ti–22Al–25Nb alloy with different initial microstructures, microstructural evolution after long-term aging, and mechanical properties at room temperature and 650 °C of four differently heat-treated Ti–22Al–25Nb alloy were investigated. The investigation results indicated that α 2 platelets formed by aging at (α 2 +B2) region were not as stable as previous research claimed and spontaneously decomposed into fine (O+β/B2) mixture during the annealing at 650 °C. As a result, the alloy's steady-state creep strain rate dropped dramatically at the secondary creep stage and tensile strength grew. On the contrary, long time aging exposure resulted in the connection of original dispersed lenticular O precipitation and thus degraded the ductility of all specimens. Besides, the discontinuous precipitation B2→β+O caused by supersaturation of solutes in the matrix also harmed the mechanical properties. Under the condition of 650 °C/250 MPa, the steady-state creep strain rates of the Ti–22Al–25Nb specimens show a significant dependence on their grain size. Crept samples showed that most dislocation motion was restrained in the β channels under a small strain and then extended into O phase when creep strain grew over 10%. Finally, by comparing the room temperature tensile property and creep resistance of four samples, supertransus solution and furnace cooling ensured the alloy most balanced mechanical properties among lamellar samples. The supertransus then furnace-cooled sample did not only have an excellent creep resistance but also kept a moderate room temperature elongation to failure of nearly 6%. • Thermal stability and mechanical properties of four different microstructures were investigated and compared. • Metastability of α 2 phase resulted in its decomposition and promoted the creep resistance of the alloy. • Grain size including equiaxed precipitation dominates creep resistance in intermediate stress regime. • Discontinuous precipitation and piling up of dislocations promoted the interfacial cracks. [ABSTRACT FROM AUTHOR]

The Ti 2 AlNb and Mo-modified Ti 2 AlNb alloys were fabricated by hot isostatic pressing, and then underwent annealing treatment at 800 °C for 1, 2 and 3 h respectively. To evaluate the tensile properties of the two kinds of alloys, tensile tests were conducted at ambient temperature and 650 °C in this study. For the Ti 2 AlNb alloy, the room-temperature ultimate tensile strength (UTS) was 700–900 MPa, and the highest elongation to failure (ε f) reached 6.2% after aging for 2 h at 800 °C. Since the Mo addition promoted the precipitation of the coarse B2+O colony structure near the grain boundary, the Mo-modified Ti 2 AlNb alloy exhibited decreased UTS and ε f at room temperature. As for the high-temperature performance of both the Ti 2 AlNb and Mo-modified Ti 2 AlNb alloys, the UTS reached approximately 700 MPa and the ε f exceeded 3.0%. Meanwhile, the two kinds of alloys presented the same tendency that both the high-temperature UTS and ε f increased firstly and then decreased as the aging time increased. Among them the specimens after aging at 800 °C for 2 h for both alloys acquired the highest UTS and ε f. Moreover, the Mo-modified alloy exhibited a better high-temperature ductility than that at room temperature, which is associated with the B2↔O phase transformation during the loading at 650 °C. The Mo addition effectively refined the lath of the precipitates in the grain and the grain size of the matrix, and it induced abundant dislocations. Thus, the Mo-modified Ti 2 AlNb alloy aged for 1 and 3 h exhibited superior high-temperature mechanical properties than those of the Ti 2 AlNb alloy. [ABSTRACT FROM AUTHOR]

To investigate the effect of initial microstructure on the hot deformation behavior of a Ni 3 Al-based alloy, the isothermal compression tests were conducted on the studied alloy with two different microstructures at 1100 °C and 1200 °C with strain rate range of 0.01–1 s−1. The results show that the hot deformation behavior of the Ni 3 Al-based alloy is sensitive to the initial microstructure, particularly under low deformation temperature and high strain rate. The flow curves signified that the peak stress and the magnitude of the stress drop for the alloy with coarse γ′ precipitates are higher than those for the alloy with fine γ′ precipitates at a given temperature and strain rate. Besides, it is found that the critical conditions are affected by deformation temperature, strain rate and initial microstructure. Both the critical stress and strain of dynamic recrystallization significantly decreases with the increase of strain rate and decrease of deformation temperature. For different initial microstructures, the critical stress and strain for the alloy with coarse γ′ precipitates are higher than that for the alloy with fine γ′ precipitates. The critical ratios of the studied alloy were also determined. The dissolution of coarse γ′ precipitates easily occurs and the dissolution rate can be accelerated at the sufficiently high temperature, which leads to that the effect of initial microstructure on hot deformation behavior of the Ni 3 Al-based alloy is weakened. • Hot deformation behavior of Ni 3 Al-based alloy with two microstructures was studied. • Hot deformation behavior is sensitive to initial microstructure. • Critical stress and strain were determined at various deformation conditions. • Critical conditions affected by initial microstructure, strain rate and temperature. [ABSTRACT FROM AUTHOR]

The Snoek relaxation profiles for ternary Niobium–Vanadium–Oxygen systems were analyzed by an embedded-cell model of statistical mechanics treatment. The relaxation characteristic and broadening mechanism were systematically discussed and some conflicting interpretations in the early research were clarified. The complicated Snoek spectrums of the Nb–V–O system can be resolved into a series of effective elementary Debye peaks, which result from the transitions of interstitial oxygen atoms between adjacent octahedral sites. The relaxation parameters of each elementary peak can be determined by element species and atomic arrangements within the corresponding embedded octahedron. The Snoek relaxation characteristic in Nb–V–O systems mainly depends on the sites distributions and the transitions status of the interstitial oxygen atoms, which are controlled by the site-dependence energies and the transition probabilities, respectively. [ABSTRACT FROM AUTHOR]

Mo-modified Ti-22Al-25Nb alloys are sintered at 900 °C, 1000 °C, 1070 °C, and 1150 °C, followed by quenching and furnace cooling, respectively. We made comparisons of phase composition and microstructure between quenched and furnace-cooled alloys to interpret the phase transformation and microstructure evolution during cooling. The phase transformation was B2→O for the alloy cooled from B2+O region, and was B2→B2+O for those cooled from α 2 +B2+O, α 2 +B2, and B2 phase regions. Moreover, the morphology was B2+O colonies for those cooled from B2+O and α 2 +B2+O phase regions, and was Widmanstätten structure for those cooled from α 2 +B2, and B2 phase regions. Kinetics analysis indicated that the activation energy for the phase transformation of α 2 →B2 was 170 kJ mol−1 for Ti-22Al-25Nb, while it was 330 kJ mol−1 for Mo-modified Ti-22Al-25Nb. The retarded phase transformation in Mo-modified Ti-22Al-25Nb further led to curvy Widmanstätten structure when the alloy was furnace-cooled from single B2 phase region. The hardness of the Mo-modified Ti-22Al-25Nb alloys is up to 488 HV, while that of the Ti-22Al-25Nb alloys without Mo addition is less than 400 HV. • Diverse B2+O structures are observed in Mo-modified Ti 2 AlNb alloys. • Mo-rich kinky Widmanstätten structure corresponds to high Vickers hardness. • Kinetic analysis shows Mo addition inhibits the phase transformation of α 2.→B2. • The phase transformation during different cooling routes is reported. [ABSTRACT FROM AUTHOR]

In present work, a multiphase Ni 3 Al-based intermetallic alloy with complex components of γ'+γ dendrite comprising extremely high volume fraction (81 vol %) of γ′ phase and interdendritic β phase is investigated, the microstructure evolution and phase transformation behavior tailored by different solution cooling rates are studied by applying different cooling methods of water cooling (WC, 138 °C/s), air cooling (AC, 72 °C/s), and furnace cooling (FC, 0.05 °C/s) after solution treatment at 1200 °C for 10 h. Results show that the cubic degree, size and volume fraction of cuboidal primary γ′ as well as size of spherical secondary γ′ particles in the γ'+γ dendrite are improved by decreasing cooling rates, and the average sizes of the primary and secondary γ′ particles are found to meet logarithmic relationships with cooling rates. There are three kinds of precipitates in the interdendritic β phase resulted from different cooling methods, i.e., the rod-like Cr 3 C 2 carbides, the semi-spherical α-Cr particles, and the long acicular γ′ precipitates. The lower cooling rate decreases the number of rod-like Cr 3 C 2 carbides, increases the number and size of the semi-spherical α-Cr particles, and promotes the formation of long acicular γ′ precipitates in the interdendritic β-matrix. The semi-spherical α-Cr particles play the role of pinning dislocations in the β-matrix and have the orientation relationship of [‾110] α-Cr //[‾110] β-matrix. In addition, the precipitation of semi-spherical α-Cr particles in β-matrix is observed to accomplish in two sequential stages and grow in an onion-like ordered way. Stacking faults existed in partial of α-Cr particles due to the nanotwins in β-matrix. Microtwins are observed in the interdendritic β-matrix after water cooling, which have a bimodal configuration of nanotwins at the microtwinning boundaries and interior stacking faults. Besides, γ′-envelope formed between the γ'+γ dendrite and interdendritic β phase dependent on the solution cooling processes. Image 1 • Re-precipitation sizes of primary and secondary γ′ particles have the logarithmic relationship with solution cooling rates. • Microtwins in the β-matrix have a bimodal configuration of nanotwins at their boundary and interior stacking faults. • Precipitation pattern and growth mode of semi-spherical α-Cr particles in β-matrix phase after air cooling. • Precipitation behaviors influenced by solution cooling rates of precipitates in the interdendritic β. [ABSTRACT FROM AUTHOR]

In this work, we creatively introduced MAX additives (Ti 2 AlC) into W alloy system to break the development bottleneck of ball milling technology: a large amount of oxygen impurities and large-sized second phase particles at grain boundaries (GBs). Unlike traditional oxides/carbides, Ti 2 AlC can undergo self-decomposition during high-temperature sintering stage (>1400 °C) on the basis of hydrogen sintering, and continue to adsorb a number of stubborn oxygen impurities to form various smaller, more dispersed, and stronger in-situ Ti x C y , TiO x , Al 2 O 3 , and Al x Ti y O z nanoparticles. Furthermore, these in-situ nanoparticles could maintain stable coherent interfaces with W, thereby more effectively refining, purifying, and strengthening matrix. Compared to traditional W-carbide/oxide alloys, MAX additives render our alloy with high hardness (521 ± 24 HV 0.2), a remarkable combination of high compressive strength (1262.9 ± 35.1 MPa) and large ductility (9.88%). This work provides a new perspective for the preparation of high-performance refractory metals and relevant engineering application. • The MAX phase (Ti 2 AlC) is innovatively added into W alloys. • The Ti 2 AlC phase decomposes at above >1400 °C and forms in-situ nanoparticles. • The Ti 2 AlC phase continues to adsorb stubborn oxygen impurities at sintering stage. • In-situ nanoparticles could maintain stable coherent interfaces with W. • The W-Ti 2 AlC alloy possess excellent mechanical properties. [ABSTRACT FROM AUTHOR]

The effect of the Ni/Cu-rich aluminides on the strength of Al–15%Mg 2 Si–Cu–Ni alloys at room and elevated temperatures was analyzed and revealed. The contribution of aluminides to alloys' strength is promoted with the temperature increasing from 25 °C to 350 °C. Both Mg 2 Si and aluminides strengthen Al matrix and carry the load at room temperature (25 °C). The thermal stable and interconnected aluminides play the leading role in load-carrying and load-transfer capacity at high temperature (350 °C), resulting in the pronounced contribution to alloys' strength. At 450 °C, aluminides lose load-bearing capacity and have no effect on the increase of alloys' strength. • Both Mg 2 Si and aluminides can effectively strengthen the Al matrix and carry the load at 25 °C. • The thermal stable and interconnected aluminides play the leading role in load-carrying and load-transfer capacity at 350 °C. • At 450 °C, the loss of load-bearing capacity of aluminides leads to a significant decrease of alloy's strength. [ABSTRACT FROM AUTHOR]

In order to further refine W particles and improve properties of traditional W-Cu alloys, an innovative freeze-drying and subsequent solid phase sintering technology was employed to fabricate ultrafine W-10/20/30Cu alloys in our work. Compared with W-Cu powder precursors synthesized by traditional technologies, the freeze-dried powders (35 nm) are finer and better dispersed, which possess ultrahigh sintering activity. After solid phase sintering, the relative density of prepared W-Cu alloys is as high as above 98%. Meanwhile, the Cu network possesses complete continuity and the W particles keep ultrafine size (178 nm), which is much smaller than W particles in W-Cu literatures. Compared with other traditional technologies, freeze-dried W-Cu alloys in our work possess the highest hardness (499 HV 0.2), taking into account high thermal conductivity (246.9 W/mk) and electrical conductivity (48.3% IACS), which provides a new insight for the further development of W-Cu alloy industries. [Display omitted] [ABSTRACT FROM AUTHOR]

The precipitation and evolution of intersected plate-like γ′ (γ′ P) phase within interdendritic β during long-term aging and its relevant influence on the creep behavior of a multiphase Ni 3 Al-based intermetallic alloy are investigated. Results show that the precipitation and growth of the γ′ P precipitates during 800 °C aging of original as-cast alloy are significantly rapid, which can be fully precipitated in 60 min to form the intersected morphology and continue to coarsen and grow during the extended aging and subsequent 800 °C creep processes. The γ′ P precipitates have the Bain orientation relationship (OR) of (100)γ′ P //(100) β and [0-11]γ′ P //[001] β with the interdendritic β-matrix. The precipitation of intersected γ′ P phase is sensitive to the elemental fluctuations in β-matrix, and the preceding high-temperature annealing treatment can significantly reduce the elemental inhomogenization and inhibit its generation within the interdendritic β. Precipitation of adequate intersected γ′ P phase can effectively inhibit the dislocation proliferation and crack initiation in the brittle interdendritic β during creep, resulted in the improved creep properties. Slightly rafted γ′ after long-term aging at 800 °C transitioned into R-type γ′-raft structure during creep at 800 °C/220 MPa, and can induce larger creep resistance than N-type γ′-raft structure. [ABSTRACT FROM AUTHOR]

In present work, the unique envelope structure (about 1.1 μm in width, and ~3 vol%) in an as-cast multiphase Ni 3 Al-based intermetallic alloy was characterized in detail, its formation mechanism during solidification and widening behavior during long-term aging process were analyzed, and relevant effects on creep behaviors of this Ni 3 Al-based intermetallic alloy under 800 oC/220 MPa were evaluated. Results show that the envelope structure located between the γ'+γ dendrite and interdendritic β phase is γ′-Ni 3 Al phase with ordered face-centered L1 2 structure, which plays a vital role in adjoining the heteroid γ'+γ dendrite/interdendritic β phases. The γ′-envelope possesses a coherent orientation relationship of [101] γ'-envelope //[01‾1] dendritic-γ with the dendritic-γ phase (face-centered A1 structure) due to their similar face-centered lattice type, while there exists a semi-coherent transition region between the γ′-envelope (face-centered L1 2 structure) and interdendritic β phase (body-centered B2 structure) to accommodate their relative lattice mismatching. The formation of γ′-envelope during solidification process is induced by nickel enrichment in the residual liquidoid after interdendritic β phase, and its widening during long-term aging at 800 oC is mainly controlled by the diffusion of Ni, Al, Hf and Mo atoms at the interfaces between γ'+γ dendrite/γ′-envelope/interdendritic β phase under thermal activations, involving the relevant phase transformation of β (NiAl) + γ (Ni) → γ' (Ni 3 Al). The widening of γ′-envelope resulted in a decrease of interdendritic β phase and an increase of γ′ phase in volume fraction, benefited in the improved creep rupture life and reduced steady-state creep rate. However, the γ′-envelope widening also plays a positive role in crack initiation during creep deformation, since besides the GBs and the semi-coherent interfaces of the γ′-envelope/interdendritic β, cracks are also found to initiate near the Cr 23 C 6 carbides surrounded by the widened γ′-envelope. [ABSTRACT FROM AUTHOR]

The present work investigates the change in the microstructure and the improvement in the microhardness in the Mo-modified Ti 2 AlNb alloys induced by solution treatment. Typical Widmanstätten O + B2 structure was observed in the alloys directly aged in the O + B2 phase region, with a lower hardness value compared to that of the alloy without Mo addition. Well-arranged O + B2 colonies were observed in the specimen solution treated in single B2 phase region, and it exhibited a favorable hardness performance of up to 620 HV. Besides the precipitation hardening of the O phase, the solution of Mo in B2 phase should be responsible for the enhancement of hardness. Further microstructural observation proved that the substitution of Mo for Nb in the lattice of B2 phase induced the lattice distortion mainly the (200) and (211) planes, and the induced entanglement of dislocations also contributed to the enhancement of hardness. Image 1 • Well-arranged O + B2 structure is obtained in Ti 2 AlNb alloys by Mo addition. • Solution treatment and ageing enhanced hardness of Mo-modified Ti2AlNb alloys. • Lattice distortion of B2, especially along (211) face, is induced by adding Mo. • Orientation relationship of (211) B2 //(26 1 ¯ ) O is identified in the aged Ti 2 AlNb alloy. [ABSTRACT FROM AUTHOR]

In this study, the dissimilar TLP bonding joints of Inconel 718 nickel-base alloy and AISI 316LN stainless steel free of brittle athermal solidification zone (ASZ) were obtained. It was recognized that a good metallurgical bonding is achieved at the interface between the isothermal solidification zone (ISZ) and diffusion affected zone on the side of IN718 alloy (hereafter referred to as DAZ-IN718), while the interface of ISZ and DAZ-316LN is more sensitive to crack initiation. A lot of precipitates were found in DAZ on both sides near the base metal, which were identified as Cr 2 B, Cr 5 B 3 , Nb 3 B 2 , and BN. Moreover, two different sizes of voids form at the ISZ/DAZ-316LN interface. The bigger voids are caused by BN phases, while the smaller voids were identified as Kirkendall voids. The tensile test results indicate that the tensile strength and elongation decrease with increasing bonding time. In-situ tensile tests and digital image correlation (DIC) analysis indicate that there are two factors that cause the fracture of dissimilar TLP bonding joints at the ISZ/DAZ-316LN interface. The first factor is the brittle BN phases and Kirkendall voids at the ISZ/DAZ-316LN interface. During tensile tests, dislocations slide along the slip surface until they are blocked by precipitates in the DAZ, resulting in extremely high-stress concentrations at these locations. Moreover, the second factor is the poor ability of DAZ-316LN to resist plastic deformation. The high degree of strain concentration in DAZ-316LN also promotes the formation of microcracks at the ISZ/DAZ-316LN interface. • Lots of precipitates, such as Cr 2 B, Cr 5 B 3 , Nb 3 B 2 , and BN are found in DAZ. • The interface of ISZ and DAZ-316LN is sensitive to crack initiation. • BN phases and Kirkendall voids are the key to the fracture of the TLP joint. • High-stress concentrations in DAZ-316LN promotes the formation of microcracks. [ABSTRACT FROM AUTHOR]

Abstract The effect of dual aging treatment on phase morphology, composition, and microstructure evolution of a pre-deformed Ti 2 AlNb-based alloy were investigated in this study. The 1040 °C-pre-deformed alloys were dual aged at different temperature in O + β /B2 region followed by 750 °C-aged treatment. The experimental results show that coarse O lath and lamellar O + β /B2 were formed when the aging temperature is lower than 950 °C while globular O appeared when aging temperature is higher than 950 °C. The size and content of the O phase increase and decrease with the aging temperature, respectively. Widmanstätten O + β /B2 laths were obtained after secondary aging treatment at 750 °C when the first aging temperature is higher than 910 °C. Complete lamellar O + β /B2 precipitation and coarse O lath, in particular, were obtained in the 910 °C and 750 °C dual aged alloy with no Widmanstätten O + β /B2 laths appeared. The phase content is closely related to the aging temperature. When the 970 °C-aged alloy put into the secondary aging at 750 °C, coarse O laths which were fragmented or partially spheroidized and globular O during 970 °C-aged process were dissolved and the Widmanstätten O began to precipitate inside. Highlights • Effect of dual aging treatments on phase transformation and morphology of pre-deformed Ti 2 AlNb-based alloy was presented. • No Widmanstätten O + β /B2 laths appeared in the 910 °C and 750 °C dual aged alloy. • Dissolution and regeneration of O phase during aging treatment was discovered. [ABSTRACT FROM AUTHOR]

The natural oxidation of amorphous Cu x Zr 1- x ( x  = 0.33, 0.5, 0.67 and 0.75) alloys has been studied by X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy and cross-sectional transmission electron microscopy. It is revealed that passivation behavior occurs for amorphous Cu x Zr 1- x alloys where x  ≤ 0.67, which provides an effective composition range of amorphous CuZr alloys for long time service. A thin (2–5 nm) ZrO 2 film is formed on top of amorphous alloys, with a Cu-enriched amorphous alloy layer at below. Surprisingly, tetragonal ZrO 2 nucleates between the oxide film and the alloy at room temperature in the naturally oxidized am-Cu 0.33 Zr 0.67 alloy. Amorphous Cu 2 O layer forms on top of the oxide film and surface segregation forming metallic Cu occurs for amorphous Cu x Zr 1- x when x ≥ 0.75. [ABSTRACT FROM AUTHOR]

The microstructural evolution during long-term thermal exposure of Alloy 617 is investigated in detail. During processing, various precipitation phases were formed, including MC, M 23 C 6 , M 6 C and γ', in which the M 23 C 6 carbide is the primary strengthening phase and determines the hardness of Alloy 617. The M 23 C 6 carbides can either form from decomposing MC or precipitate directly from the γ matrix, but they most eventually transformed to M 6 C carbides after long-term aging. In addition to the phase transformation among various carbides, the morphology evolution of M 23 C 6 carbide is found to have a significant effect on the formation of γ' phase, which is closely related to the redistribution behavior of Al and Ti between M 23 C 6 and γ matrix. We also identified a faster evolution kinetic of the precipitates at grain boundary than those in grain interior, which is caused by the different local diffusion rates. This work elucidates the transformation sequence among different precipitates and the corresponding alloy element redistribution behavior during aging Alloy 617, which shed lights on the strengthening phase design and can in turn optimize the mechanical properties of Alloy 617. • The study reveals the variation of precipitates during long-term aging and its strong link to the element diffusion and redistribution behaviors. • The morphology evolution of M 23 C 6 carbide can promote the precipitation of γ' particles. • The evolution between different precipitated phases is much faster at grain boundary than that in grain interior. • M 23 C 6 carbide is mainly strengthening phase, which determines the hardness of Alloy 617. [ABSTRACT FROM AUTHOR]

Cold-worked Inconel 718 alloy has successful applications in turbine engines due to its elevated strength. Otherwise, cold working will bring about the undesired ductility degradation accompanied with strength improving. Meanwhile, the susceptibility to δ precipitation is increased with modified morphology. To address these issues, this work aims expressing the effect of cold-rolling on hot ductility and the role of δ phase regarding differential morphologies in tensile behavior of Inconel 718 alloy at 650 °C. The results revealed that the ductility degradation can be attributed to the interactions of necking, microstructure instability and oxidation process tailored by cold-rolling. Nevertheless, appropriate cold-rolling is proved to enhance the resistance to crack propagation. The needlelike δ phase in strain-free structure tightly hindered the migration of horizontal GBs to enhance the strength but promote the intergranular brittle cracking, resulting in the degradation of ductility. In contrast, the δ phase with modified granular morphology in cold-rolled structures showed good deformation compatibility with horizontal GBs, playing a positive role in delaying necking occurrence and impeding crack propagation. In summary, the granular δ precipitation endowed cold-rolled Inconel 718 alloy with a superior combination of strength and ductility at 650 °C. [ABSTRACT FROM AUTHOR]

In DELTA processing of Inconel 718 alloy, δ phase plays a vital role in final grain refinement, whose precipitation during intermediate thermal cycles is tailored by prior wrought structure. Therefore, it is necessary to renew insights into the effect of wrought structure on the morphology and quantity of δ phase. From this point, this work was conducted to investigate the δ precipitation behaviors in wrought Inconel 718 alloy. The results show that the δ precipitation behaviors are tailored by prior dynamic recrystallization (DRX) degree. Under partial DRX, δ precipitation exhibits twofold characteristics of preferential GB-precipitation accompanied by sluggish intragranular precipitation; while modified into predominant homogeneous GB-precipitation by fully DRX, in spite of the presence of few intragranular δ precipitates. After hot deformation, the equilibrium δ content is improved and inversely proportional to DRX degree. After 24 h aging at 900 °C, the volume fraction of δ phase is 38.6% and 27.9% for partial and fully DRX, respectively, compared to 15.1% for strain-free state. The GB-δ nucleation process is accelerated due to the occurrence of DRX, and firstly finished in few minutes; differently, the intragranular δ nucleation is grain-dependent, that promoted within unrecrystallized grains but inhibited within DRX grains. The “encounter” phenomena are observed during δ growth, and some particular coalescence mechanisms are proposed. [ABSTRACT FROM AUTHOR]

The solid solubility of Si in a quaternary Al–4Mg–1Cu–0.5Si (wt%) alloy has been found to be only about 0.061 at% at 520 °C, and 0.093 at% at 560 °C, less than 1/10 of that in the ternary Al–Mg–Si system. The excess Si in the alloy remains as coarse Mg 2 Si dispersoids which produce no significant age-hardening effect. Interestingly, a small change of Si content (from 0.061 at.% to 0.093 at.%) in the solid solution of the alloy has been found to be effective in modifying precipitation microstructure by promoting the formation of fine Guinier–Preston–Bagaryasky (GPB) zones and postponing the formation of the S phase during ageing at 200 °C. Consequently, the quaternary alloy exhibits an enhanced age-hardening response during earlier-stage ageing. [ABSTRACT FROM AUTHOR]

The microstructure control of multiphase Ni 3 Al-based intermetallic alloy by traditional heat treatment is still limited, especially size and volume fraction of interdendritic β phase cannot be effectively reduced, due to the limitation of interdendritic β phase dissolution temperature close to the melting point of the alloy. In present work, the temperature gradient and solidification rate of the alloy under different laser remelting parameters were calculated by the Rosenthal equation. Afterward, the as-cast multiphase Ni 3 Al-based intermetallic alloy (19.4 vol% of interdendritic β phase) was remelted under different laser parameters of 3000–4500 W laser power and 5–20 mm/s laser scanning rate. And the effects of different laser remelting parameters on the microstructure, room temperature, and 980 °C high-temperature tensile properties of multiphase Ni 3 Al-based intermetallic alloy were studied. The results show that laser remelting treatment with the appropriate parameters (4000 W laser power and 10 mm/s laser scanning rate) can effectively reduce the size and volume fraction of interdendritic β phase and the morphology and size of γ′ phase in the γ′+γ dendrite, and significantly refine the microstructure of alloy, thus effectively improving the room temperature and 980 °C tensile properties of multiphase Ni 3 Al-based intermetallic alloy. Under the optimum laser remelting parameters of 4000 W-10 mm/s, the tensile strength at room temperature and 980 °C of the corresponding laser remelting alloy can reach 1215 MPa and 280 MPa, respectively, and the elongations after fracture of the corresponding alloy are 14.09% and 6.41%, respectively. [ABSTRACT FROM AUTHOR]

In this work, eutectic Si modification grade formula was established and effect of Sr element on modification level and mechanical properties of Al-9Si-0.4Mg-0.1Cu alloy was studied. Thermal analysis, SEM, EPMA and TEM were applied to analyze cooling curves, microstructure and Si twinning of the alloys. The results showed that precision and accuracy of eutectic Si modification grade formula were significantly improved and quantitative evaluation modification level of eutectic Si could be achieved. Modification level of eutectic Si increased first and then decreased with Sr content increasing. Though twin plane re-entrant edge (TPRE) mechanism and impurity induced twinning (IIT) mechanism were effective under certain conditions, they cannot fully explain the modification mechanism of eutectic Si in Al-9Si-0.4Mg-0.1Cu alloy. Sr element caused constitutional undercooling at the front of solid-liquid interface, promoted the formation of fine Al 2 Si 2 Sr phases and nano-precipitates, resulting in the changes of size and morphology of eutectic Si. With the improvement of eutectic Si modification level, the UTS and El of the alloys increased. While, adding excessive Sr led to the formation of coarse Al 2 Si 2 Sr, which was detrimental to the improvement of modification level and mechanical properties of alloy. • Modification level function suitable for quantitatively evaluate modification grade of eutectic Si was established. • Fine Al 2 Si 2 Sr phases and nano-precipitates change the size and morphology of eutectic Si. • Coarse Al 2 Si 2 Sr reduces the modification level of eutectic Si and the mechanical properties of alloy. [ABSTRACT FROM AUTHOR]

The Mo based alloys with minor Ti additive were fabricated by successive processes of simple ball-milling and low-temperature sintering. Different from traditional titanium oxides additive, the minor Ti additive will adsorb nearby oxygen impurities to form TiO 2 or Ti 8 O 15 during above process, thus purifying Mo matrix. The size of formed titanium oxides (approximately 540 nm) is also close to that reported in relevant literatures. What's more, the Ti additive could availably refine the Mo powder particles during ball-milling process and improve its sintering activity. While maintaining high densit (> 99%), the sintered Mo based alloys with minor Ti additive possess finer grain (13.17 μm → 4.44 μm) and higher hardness (249 HV 0.2 → 332 HV 0.2) compared with pure Mo. • Minor Ti additive was innovatively introduced into Mo alloys. • The Ti could adsorb oxygen impurities to purify Mo matrix. • The Ti finally forms TiO 2 or Ti 8 O 15 phases. • The Ti could availably refine Mo grains. • The Ti could availably improve Mo alloy hardness. [ABSTRACT FROM AUTHOR]

This work proposed an innovative technology to fabricate Mo–La–O nanoparticles strengthened Mo alloys with ultrafine nano grains via freeze-drying and low temperature sintering. These novel nano Mo–La–O particles including La 7 Mo 7 O 30 , La 5 Mo 3 O 16 , La 6 Mo 2 O 15 , La 5 Mo 4 O 12 , La 4 Mo 2 O 11 and La 2 (MoO 6) remain coherent or semi-coherent interfaces with Mo matrix to strengthen their phase boundaries. Moreover, nano Mo–La–O particles enriched in excess oxygen absorb nearby impurity oxygen and then lead to the purification of Mo matrix. Furthermore, the low temperature sintered Mo–La x Mo y O z alloys possess high relative density (98.1%), which is due to the high sintering activities of ultrafine powders (56 nm). Comparing with available literature which involves oxide-dispersion-strengthened-molybdenum alloys (ODS-Mo), the freeze-dried Mo–La x Mo y O z alloys in our work possess the finest grain size (440 nm), the finest oxide particle size (mainly <5 nm), the highest hardness (495 HV 0.2) and high strength (1201 MPa) at 30% deformation. [ABSTRACT FROM AUTHOR]

In the present study, a two-phase Ti 2 AlNb-based alloy with a nominal composition of Ti–22Al–25Nb (at%) comprising the dominant O + B2/β phase was explored. The microstructural evolution and tensile properties are studied by applying different heat treatment methods of water-cooling (WC, 140 °C/s) and furnace-cooling (FC, 0.08 °C/s) after heat treatment at 1015 °C for 40 min, followed by aging treatment at 800 °C for 1, 5, and 100 h. The results indicated that the morphologies of solution-treated alloys after different cooling methods have a significant distinction. The WC alloy consists of a continuous B2/β phase and a few remnant O phase, whereas the FC alloy comprises a mass of lath O phase and discontinuous B2/β phase. The Widmanstätten O + B2 structures were generated in the following aging treatment. The α 2 phase was not detected during the heat treatments in the present work. The B2 phase and O phase in the aged WC and FC alloys follow the classical orientation relationship: (110) B 2 / / (001) O , [ 1 ‾ 11 ] B 2 / / [ 1 1 ‾ 0 ] O. The room-temperature ultimate tensile strength (UTS) and elongation to failure (EL) of the FC and aged FC alloys are higher than the WC and aged WC alloys, except for the 100 h-aging condition. On the contrary, the high-temperature UTS and EL of the aged WC alloys are higher than the aged FC alloys. The existence of the O/O phase boundaries, the coarsening of the B2 grain boundary and discontinuous precipitation harmed the performances of the studied alloys. Beyond that, the fracture mode of the explored alloys with different heat treatment methods was also analyzed. • The morphologies of solution-treated Ti 2 AlNb-based alloys after different cooling methods have a significant distinction. • The B2 phase and O phase in the studied alloys follow the classical orientation relationship: 110B2//001O, [111]B2//[110]O. • Tensile properties and fracture mode are significantly influenced by different cooling rates and aging treatments. • The O/O boundaries, coarsening of the grain boundary and discontinuous precipitation harmed the properties of the alloys. [ABSTRACT FROM AUTHOR]

The effect of primary O phase on thermal compressive deformation behavior of a Ti 2 AlNb-based alloy are investigated at temperatures from 990 °C to 1020 °C and strain rate range from 0.001 s−1 to 1 s−1. The results indicated that the primary O phase has a significant effect on the hot deformation behavior of the studied alloy. The peak stress and the degree of the stress descent of the specimen with primary O lath and Widmanstätten O + B2 structures are higher than those of the specimen with Widmanstätten O + B2 structures under higher strain rate. Besides, both the critical stress and critical strain for the onset of dynamic recrystallization (DRX) of the studied alloy upsurge with increasing the strain rate or decreasing the deformation temperature. The specimen with primary O lath and Widmanstätten O + B2 structures exhibits greater critical stress and critical strain than the specimen with Widmanstätten O + B2 structures. The strain rate sensitivity exponents of the investigated alloy with primary O lath and Widmanstätten O + B2 structures is higher than that of the alloy with Widmanstätten O + B2 structures at low temperature (990 °C), while the reverse is true at high temperature (1020 °C). Beyond that, the DRX mechanisms of the explored alloys with different morphologies of O phase were also investigated by EBSD and TEM analysis. • Thermal deformation behavior of Ti 2 AlNb-based alloy with two morphologies of O phase was studied. • The existence of primary O lath results in more significant effect of flow softening. • Critical conditions for the onset of DRX is sensitive to morphology of O phase. • The studied Ti 2 AlNb-based alloys with different morphologies of O phase undergo DDRX in all deformation conditions. [ABSTRACT FROM AUTHOR]

Oxygen evolution reaction (OER) is crucial for electrochemical water splitting. However, corrosive issues in the alkaline environment impede its applications. Here, we explore the corrosion-resistant multiphase Ni 3 Al-based intermetallic alloy (Ni 3 Al alloy) as self-supported OER catalysts for the first time. A two-step treatment, annealing at high-temperature followed by acid oxidation is performed to improve the catalytic activity. Further investigations demonstrate that the annealing process can tune the size of γ′ precipitates, which will modify the strain effects caused by γ/γ′ lattice mismatch to boost the OER activity. The oxidation of Ni during the acid pretreatment can facilitate the formation of active high-valent Ni sites during the OER process, and further enhance the OER performance. The optimized electrode exhibits a low overpotential of 280 mV at 10 mA cm−2, a small Tafel slope of 73.5 mV dec−1 and long-term stability of 180 h in 1 M KOH solution. The findings in this paper will inspire the exploration of high stability OER catalysts and the functional application of Ni 3 Al alloy. • Ni 3 Al high-temperature alloy shows high OER activity and stability. • The boosted OER activity was ascribed to modified strain effect at γ/γ′ interface. • The formation of active high-valent Ni sites also promotes the catalytic activity. • Ni 3 Al alloy treated by acid oxidation has better catalytic performance for OER. [ABSTRACT FROM AUTHOR]

In the present work, strain-controlled low cycle fatigue (LCF) tests were performed at 704 °C using 0.25 Hz in cyclic frequency with tension-compression loading on the forged alloy 718Plus to investigate the fatigue performances determined by structures, and the corresponding microstructure evolutions and deformation mechanisms were analyzed through techniques of scanning electron microscope (SEM) and transmission electron microscope (TEM). The fatigue specimens from different locations (core and rim) showed similar response on cycle stress, but smaller grain size contributed to superior fatigue performance. Fatigue deformation induced the generation of η precipitates in grain interior and promoted the growth of grains and η precipitates, but brought insignificant change on the morphology of spherical γ′ phase and slightly increase in particle size and γ′/γ lattice misfit, indicating its excellent mechanical stability at 704 °C. A transition area was observed between the η precipitates and γ matrix, which was determined to be γ phase via high resolution transmission electron microscopy (HRTEM) and elements mapping techniques. Twinning and dislocation planar slip bands were confirmed to be the primary fatigue deformation modes of alloy 718Plus. Dislocations piled up and formed networks at the edges of η precipitates during the fatigue process, inducing the initiation and propagation of micro-cracks. As the cycle accumulated, the η and γ′ precipitates were sheared by gliding dislocations, resulting in weakened resistance to deformation and fatigue softening. [ABSTRACT FROM AUTHOR]

Microalloying of an Al-15%Mg 2 Si alloy (wt%) with 1%Cu produced an enhanced age-hardening response, increasing peak hardness and ultimate tensile strength due to a modified precipitation process. The solid solubility of Cu in Al-15%Mg 2 Si alloy effectively promotes the formation of the high number density of Guinier-Preston-Bagaryasky (GPB) zones combined with S precipitates. It suppresses β′ and β″ formation during ageing at 200 °C. Consequently, Al-15%Mg 2 Si-1%Cu alloy with the high density of GPB zones and S phase exhibited high peak hardness (121 HVN) and ultimate tensile strength (284 MPa), 42.4% and 49.5% higher than that of the Al-15%Mg 2 Si alloy, respectively. • The addition of 1% Cu in Al-15%Mg 2 Si alloy has a significant influence on precipitation during ageing at 200 °C. • Cu addition promotes the formation of GPB zones and S phase, instead of β′ and β″ precipitates. • The high number density of GPB zones and S phase produces an enhanced age-hardening response. [ABSTRACT FROM AUTHOR]

The microstructure evolutions during 1000 °C-1000 h long-term aging and relevant 800 ~ 840 °C/220 ~ 300 MPa creep behaviors of a novelly designed multiphase Ni 3 Al-based intermetallic alloy were investigated. Results showed this alloy presented excellent intermediate temperature creep properties even after 1000 °C-1000 h long-term aging. A kind of bimodal R-type γ′ rafting structures were observed in the 800 °C/220 MPa creep process of the long-term aged alloy, and the creep resistance levels of three kinds of γ′ rafting structures were evaluated to be in the order of bimodal R-type γ′ rafting structures > R-type γ′ rafting structure > N-type γ′ rafting structure. The 1000 °C-1000 h long-term aging can promote the inhomogeneous precipitation of Cr 4.6 MoNi 2.1 phase at the edge γ′+γ dendrite area, which can play the role of pinning dislocations and inhibiting the further rafting and coarsening of the R-type γ′ rafts during creep. Differed from Ni-based alloys and other Ni 3 Al-based alloys, this long-term aged alloy exhibited abnormal four-stage creep characteristics, which consisted of atypical short steady-state creep stage with step fluctuant feature and atypical long accelerated creep stage with creep rate increasing at a constant rate. [ABSTRACT FROM AUTHOR]

This study aims to understand the thermal stability and annealing hardening behavior of nanocrystalline Ni(Mo) alloys at the Mo solubility limit. The microstructural and microhardness evolution of these alloys is investigated at different annealing temperatures. A rather stagnant grain growth, along with the gradual crystallization of amorphous nanostructures, in the Ni(Mo) alloys has been observed at high temperatures. The Ni(Mo) alloys with Mo content above the solubility limit exhibit an abnormal secondary hardening behavior at high temperatures, accompanied by nanosized MoNi precipitates. It demonstrates that the residual amorphous nanostructures play an important role in the thermal stability of nanocrystalline alloys. It also implies that the addition of the solute up to a solubility limit in the nanocrystalline alloys can help achieve superior strength at high temperatures. [ABSTRACT FROM AUTHOR]

Oxide dispersion strengthened tungsten (ODS-W) alloys are a class of important materials that widely used for high temperature applications due to their unique physical and mechanical properties. However, the insufficient ductility of ODS-W alloys at low or high temperatures limits their widespread application, especially as structural materials. It is always a great challenge to efficiently disperse oxide second phase nanoparticles within W matrix for achieving ODS-W alloy with excellent balance of strength and ductility. Here we report an innovative strategy for the fabrication of high-performance ODS-W alloy with strength of up to 1134 MPa and total elongation over 30% at 700 °C. The innovative route involves the preparation of W–Y 2 O 3 composite powder precursor via alkaline hydrothermal method and subsequent low-temperature sintering in hydrogen atmosphere. The internal flake structure with uniformly dispersed Y component and external coating of W component on this flake structure can be formed in alkaline hydrothermal product and then be passed on to the reduced W–Y 2 O 3 composite nanopowders. As a result, the distribution of second phase oxide particles in the low-temperature sintered alloys using these composite nanopowders as precursor is optimized significantly including an increase in the volume fraction of intragranular oxide particles and a decrease in the size of both intergranular and intragranular oxide particles. Besides, the average W grain size is also refined dramatically (410 nm). More importantly, the intragranular oxide particle / W matrix interface is regulated to be coherent relationship. The combined action of these microstructural factors is responsible for the significantly enhanced strength and ductility of ODS-W alloy. These results indicate that the newly developed alkaline hydrothermal method in our work is a promising way to fabricate high performance ODS tungsten based alloys. [ABSTRACT FROM AUTHOR]

• The fundamental role of atomic structure on thermal oxidation of alloys is revealed. • Al-Zr was selected as the model alloy system to circumvent preferential oxidation effect. • Structural order of parent alloys influences strikingly oxide compositions and oxidation kinetics. • Underlying mechanisms were disclosed by molecular dynamics simulations. • The study offers a new perspective in the field of surface engineering. To reveal the fundamental role of structural order of the parent alloy on the oxidation mechanism, thermal oxidation of amorphous and crystalline Al–Zr alloys with identical compositions were investigated in detail. An (Al 0.68 Zr 0.32)O 1.66 amorphous oxide emerged on crystalline Al 2 Zr, whereas an (Al 0.33 Zr 0.67)O 1.83 amorphous oxide formed on amorphous Al 68at.% Zr 32at.% under the same conditions. Oxidation kinetics was fast and linear for crystalline Al 2 Zr but slow and parabolic for amorphous Al 68at.% Zr 32at.%. The underlying mechanisms of such striking differences were disclosed by molecular dynamics simulations. The findings thus offer new prospects in the field of surface engineering. [ABSTRACT FROM AUTHOR]

The microstructural evolution and phase transformation behavior of a designed multiphase Ni 3 Al-based superalloy in as-cast and spray casting states were investigated under thermal exposure at various temperatures. For the exposure temperatures range from 600 °C to 900 °C, the average size of γ′ precipitates in the dendritic dual (γ+γ′) areas of the two states alloys increases, and the morphology of γ′ changes to irregular shapes due to merging of neighboring particles and Ostwald ripening. After thermal exposure at 600 °C or 900 °C, bulky γ′ precipitates generate in the interdendritic regions of as-cast alloy, and the γ′ envelope develops a curved interface by aggregation. For the spray casting sample, high density of microtwins in γ′ precipitates are 'inherited' from the preceding L1 0 -type martensite phases after thermal exposure at 600 °C. However, the γ′ precipitates without any microtwins form after thermal exposure at 900 °C. • For as-cast alloy, bulky γ′ precipitates generate in β phase after thermal exposure at 600 °C or 900 °C. • For the spray casting sample, high density of microtwins in γ′ precipitates are 'inherited' after thermal exposure at 600 °C. • The γ′ precipitates without microtwins form in spray casting alloy after thermal exposure at 900°C. [ABSTRACT FROM AUTHOR]