Orowan Looping Research Articles

Precipitation Refinement via Aging Time Modification for Enhancing Wear Resistance in Ti–V–Nb Microalloyed High‐Manganese Steels

It is imperative to ensure an even distribution of refined precipitates to enhance wear resistance. Herein, different heat treatments are to control the size and distribution of precipitates. The treatments include water quenching at 1100 °C followed by aging at 400 °C for 24, 60, and 84 h, designated as AT24, AT60, and AT84, respectively. The microstructure, mechanical properties, and impact wear properties of high‐manganese steel are investigated under solution and aging conditions using scanning electron microscopy, field‐emission scanning electron microscopy, tensile testing, and impact abrasive wear testing. Notably, the absence of nanoscale precipitates largely accounts for the poor wear resistance of as‐casting steel, whereas the strengthening effect of larger micrometer‐sized precipitates is insufficient. After the solution and aging treatment, nanosized precipitates continuously form within the matrix, conducive to the formation of the deeper work‐hardening layer, thereby improving the wear resistance. The fine micrometer‐sized precipitates and evenly distributed nanoscale precipitates in AT60 actively contribute to toughness. Additionally, these precipitates interact with slip dislocations, providing stronger strengthening via the Orowan looping mechanism. The wear mechanisms of steel can be transformed from wide, deep pits to shallow grooves and microcutting by extending the aging time.

Tensile and creep resistance improvement of GH4975 alloy for turbine discs via electron beam smelting layer solidification technology

A difficult-to-deform superalloy for turbine disks, which can be used at 850 °C for a long time, was prepared by electron beam melting layer solidification (EBSL) technology with high purity and fine structure. Subsequently, the ingot was processed by hot extrusion technology instead of conventional hot forging, and then the tensile and creep tests were performed after standard heat treatment. The results show that the EBSL alloy exhibits excellent high-temperature strength and creep rupture life compared to the conventional preparation method. Among them, the yield strengths at 20 °C and 850 °C are 8.1 % and 5.2 % higher than those in the literature, and the creep rupture life at 850 °C and 412 MPa is 1.53 times higher than that in the literature. The dislocation-precipitate interaction reveals that dislocation shearing γ′ phase is the major mechanism at 20 °C and 850 °C tensile, and Orowan looping and stacking fault shearing are the decisive mechanism during creep at 850 °C and 412 MPa. MC carbides remaining during solidification are the main source of cracks during deformation by fracture analysis. The reasons for refining the microstructure and improving the purity by electron beam melting are analyzed and explained. We believe this work can provide new ideas and methods for preparing superalloys.

Mechanical properties of scCu-rGO /Cu composites reinforced with Cu2O transition layer constructed by supercritical CO2 deposition

Reduced graphene oxide (rGO) with surface-loaded Cu particles (scCu-rGO) was prepared by supercritical CO2 deposition, and Cu matrix composites with scCu-rGO as a reinforcement (scCu-rGO/Cu composites) were successfully prepared by ball milling for different times and spark plasma sintering (SPS). The scCu-rGO/Cu composites prepared with a ball milling time of 20 h exhibited high electrical conductivity (96.3 % IACS), tensile strength (240 MPa), and elongation (37 %). The outstanding properties are mainly ascribed to the uniform distribution of rGO by the ball milling process and rGO promoted by loading Cu particles onto its surface through supercritical deposition, which led to an interfacial reaction between rGO and Cu, resulting in the formation of a Cu2O transition layer with a load-transferring effect that enhanced the mechanical properties of the composites. Based on the experimental results, the strength of scCu-rGO/Cu composites is mainly enhanced by synergistic strengthening through grain refinement, Orowan looping and load transfer strengthening. This study demonstrates that the use of supercritical deposition to construct Cu2O transition layers can result in a strength-plasticity and high electrical conductivity match in scCu-rGO/Cu composites. The findings presented here offer new insights for innovative design of Cu matrix composites for advanced engineering applications by using supercritical deposition.

Superior mechanical properties of additively manufactured FV520B matrix composites by microstructure tailoring

The additively manufactured martensitic stainless steel (SS) parts often manifest the strength-ductility trade-off dilemma, which severely limits their practicality. In this study, the TiC-reinforced FV520B metal matrix composites (MMCs) were deposited via laser powder bed fusion (LPBF), and the as-built MMCs exhibited a superior strength-ductility synergy (ultimate tensile strength of 1,389±29 MPa, and fracture elongation of 30.1±0.6 %) when compared to their matrix alloy. This strength-ductility synergy can be attributed to a high-density of well-dispersed TiC nanoparticles, in-situ grain boundary engineering induced by TiC particles, fully austenite structure, and progressive transformation-induced plasticity effect. Furthermore, the microstructure, and mechanical properties of the MMCs annealed at 400–700 °C were compared. As the annealing temperature increases, the matrix progressively transforms from a fully austenite structure to a fully martensite structure, enabling substantial enhancements in tensile strength and work hardening capabilities. Notably, a high number density of the Cu-rich precipitates (CRPs) can be observed in the high-temperature annealed specimen, which can yield considerable strengthening through the Orowan looping mechanism. This work paves a pathway to fabricate structural materials with unique microstructures and excellent mechanical properties for practical engineering applications.

Temperature dependence tensile behaviors of additively manufactured GH4099 Ni-based superalloy

Additive manufacturing was currently widely used to fabricate complex-shaped superalloy components for extreme environment applications. To replace the components prepared by the traditional approaches, it is crucial to ensure the reliability of AMed superalloys, especially in a thermal-stress environment. In this work, the high-temperature tensile properties of AMed GH4099 nickel-based superalloy are studied to establish the relationships among deformation temperatures, mechanisms, and failure responses. The results show that the deformation mechanisms at 600 °C are mainly cross-slip of the slip bands and arrays, which induced a ductile fracture. Increasing the tensile temperature will cause a shift of the dislocation movement from cross-slip to Orowan looping and stacking fault shearing to dislocation entangles-recovery-recrystallization, and the fracture mode transformed from pure ductile to mixed ductile-brittle. Additionally, the neighboring grain boundaries and the carbide-grain boundary bondings will also change with the temperature, which is further linked to the mediate-temperature brittleness and high-temperature abnormal plasticity of this superalloy.

A novel under-aging design to improve the creep rupture life of a precipitation-strengthened Fe–Ni-based superalloy

The under-aging, peak-aging, and over-aging microstructures of a precipitation-strengthened Fe–Ni-based alloy were designed by applying different heat treatment procedures. Tensile creep tests were conducted at 700 °C and 250 MPa on samples exhibiting different strengthening γ′ precipitate volume fractions and diameters. The creep life of the alloy in the under-aged state was increased by more than 10% compared to the peak-aged condition, which provided a new approach to designing the heat treatment regime that improve the creep rupture life and plasticity of precipitation-strengthened alloys. The improvement in creep properties of the under-aged state was attributed to the transition from shearing to Orowan looping of γ′ particles by matrix dislocations during the dynamic precipitation and coarsening of γ′ phase, increasing intragranular deformation resistance. The under-aged microstructure design allowed reducing the grain boundary sliding contribution to overall strain during creep. As a result, the steady-state creep stage of the alloy in the under-aged state was extended. Additionally, relationships between applied stress and nucleation, growth, and coarsening of the γ′ phase have been evidenced.

A high strength and high electrical conductivity copper based composite enhanced by graphene and Al2O3 nanoparticles

The rapid development of electrical and electronic engineering requires to further surmount the trade-off between the electrical conductivity and strength of Cu matrix composite. In this study, the surface of Cu–Al2O3 powder is selective for carbon sources, and only α-naphthol can prepare graphene. Graphene and Al2O3 particles are simultaneously incorporated into Cu matrix by hot-press sintering Cu–Al2O3 powders by internal oxidation coated with in-situ grown graphene. This composite exhibits a good combination of strength and conductivity (600 MPa of ultimate tensile strength and 81.7 % IACS of electrical conductivity) due to synergistic effect of graphene and Al2O3 particles. This composite fabricated by such synergistic more effectively retains the microstructure induced by plastic deformation during the cold-rolling process. Both graphene and Al2O3 particles uniformly distribute in Cu matrix. Coherent Al2O3 particles and graphene in situ grown can be well enhance to Orowan looping mechanism effect, and the addition of graphene in Cu matrix composite with Al2O3 particles can improve dislocation strengthening and dispersion strengthening at the same time. Our study provides an effective route to achieve simultaneously high strength and conductivity of Cu matrix composites.

Evolutionary mechanisms in the plastic deformation of γ'-Ni3(Al, Ti)-strengthened additively manufactured nickel-based 939 superalloys at intermediate temperatures

Tensile interruption experiments with different strains were conducted on additively fabricated nickel-based Inconel 939 superalloys at 700 ℃ to investigate the evolution of multiple deformation mechanisms. The microstructures of different strain groups captured by transmission electron microscopy (TEM) were analyzed, and it was concluded that a total of four various deformation mechanisms were identified, of which the first to be activated was the Orowan loop bypassing γ', and a tendency of transition from double to single loop was observed. Anti-phase boundary (APB) shearing was subsequently initiated, with a needed critical resolved shear stress level of approximately 195.82 MPa. Stacking faults (SFs) and deformation twinnings (DTs) were observed at higher stress, accompanied by the dissociation of dislocations. In addition, the magnitude of the stacking fault energy of AM 939 superalloys at intermediate temperature was calculated and estimated by matching the experimental phenomena with the critical shear stress.

An additively manufactured near-eutectic Al-Ce-Ni-Mn-Zr alloy with high creep resistance

A new additively manufactured (AM) Al-7.5Ce-4.5Ni-0.4Mn-0.7Zr (wt.%) near-eutectic alloy is reported, which shows unprecedented creep resistance up to 400 °C (a homologous temperature of 0.72). The eutectic solidification microstructure comprises ∼ 27 vol% of coarsening-resistant second phase network with an ultrafine (<100 nm) inter-phase spacing. Both Mn and Zr contribute to creep resistance of the alloy. Small amount of Mn addition promotes selection of coarsening resistant phases without compromising the alloy processability. Zr not only improves hot-tearing resistance, but further enhances the second phase coarsening resistance resulting in improved creep resistance. Neutron diffraction performed during creep deformation reveals that the underlying mechanism for creep resistance in this alloy is impedance to dislocation motion stemming from the ultrafine eutectic solidification microstructure, whereas load transfer strengthening becomes less effective as the creep temperature increases. The second phase forms a continuous network in the as-fabricated condition, which is maintained during long-term creep at 300 °C. However, this network is fragmented into fine dispersoids at higher temperatures. It is proposed that the rate-limiting deformation mechanism at 300–400 °C is (i) dislocation climb for the alloy with fragmented second phase dispersoids and (ii) Orowan looping for the alloy with a continuous second phase network. The present design of an AM-processable multicomponent eutectic alloy with high creep resistance can be applied to other metallic systems exhibiting eutectic reactions, with expected extreme creep resistance.

Microstructure and Properties of Aluminum-Graphene-SiC Matrix Composites after Friction Stir Processing.

Enhancing the mechanical properties of conventional ceramic particles-reinforced aluminum (Al 1060) metal matrix composites (AMCs) with lower detrimental phases is difficult. In this research work, AMCs are reinforced with graphene nanosheet (GNS) and hybrid reinforcement (GNS combined with 20% SiC, synthesized by shift-speed ball milling (SSBM), and further fabricated by two-pass friction stir processing (FSP). The effect of GNS content and the addition of SiC on the microstructure and mechanical properties of AMCs are studied. The microstructure, elemental, and phase composition of the developed composite are examined using SEM, EDS, and XRD techniques, respectively. Mechanical properties such as hardness, wear, and tensile strength are analyzed. The experimental results show that the GNS and the SiC are fairly distributed in the Al matrix via SSBM, which is beneficial for the mechanical properties of the composites. The maximum tensile strength of the composites is approximately 171.3 MPa in AMCs reinforced by hybrid reinforcements. The tensile strength of the GNS/Al composites increases when the GNS content increases from 0 to 1%, but then reduces with the further increase in GNS content. The hardness increases by 2.3%, 24.9%, 28.9%, and 41.8% when the Al 1060 is reinforced with 0.5, 1, 2% GNS, and a hybrid of SiC and GNS, respectively. The SiC provides further enhancement of the hardness of AMCs reinforced by GNS. The coefficient of friction decreases by about 7%, 13%, and 17% with the reinforcement of 0.5, 1, and 2% GNS, respectively. Hybrid reinforcement has the lowest friction coefficient (0.41). The decreasing friction coefficient contributes to the self-lubrication of GNSs, the reduction in the contact area with the substrate, and the load-bearing ability of ceramic particles. According to this study, the strengthening mechanisms of the composites may be due to thermal mismatch, grain refinement, and Orowan looping. In summary, such hybrid reinforcements effectively improve the mechanical and tribological properties of the composites.

Elucidating the tensile work hardening behaviour of precipitate containing Al0.3Co1.5CrFeNi1.5Ti0.2 high entropy alloy

A significant amount of work has been performed, since the last decade, on designing novel high entropy alloy (HEA) compositions. However, the effort on concluding a universal mechanism on the strain hardening behavior of these alloys with precipitates is limited. The current study is designed with an aim to comprehend the mechanical behavior of Al0.3Co1.5CrFeNi1.5Ti0.2 HEA in solution treated and aged conditions. The results show that the peak aged condition of sample contains two types of precipitates – B2 and L12 (γ′) of approximately 800 nm and 40 nm size, respectively. They are found to be responsible for a significant increase in strength in aged samples than solution treated ones. Deformation was found to occur mainly by planar slip on the {111} primary slip planes. Noticeable strain hardening behavior was attributed to the formation of stacking faults (SFs) and Lomer-Cottrell (LC) locks, inhibiting the dislocation motion. Numerous paired dislocations formed due to inhibition of slip by the ordered γ′ precipitates, coexist with a few Orowan loops in the peak-aged alloy after deformation. However, the primary strengthening mechanism was found to be the shearing of γ′ precipitates by partial dislocations. Shearing of nanosized γ′ precipitates by partial dislocations is energetically favourable for the system than shearing by full dislocations. Overall, this study enhances the understanding of the precipitation strengthening and strain hardening mechanisms in high entropy alloys.

Deformation behavior of nickel-based superalloys with bimodal γ′ size distribution studied by in-situ neutron diffraction combined with EVPSC modeling

Nickel-based superalloys with multimodal γ′ size distribution microstructure have been designed to employ in extreme environments due to their excellent mechanical performance. Whilst the effect of γ′ size on deformation mechanism has been studied before, little has been done to assess the deformation sequence and contribution to the load partition for different types of γ′ precipitates. In order to address this gap, this study focused on bimodal superalloys of GH4738 (containing the secondary and tertiary γ′ precipitates) and GH4720Li (containing the primary and tertiary γ′ precipitates) alloys. In-situ neutron diffraction assisted by a 2-site elastic-viscoplastic self-consistent (EVPSC) model was employed to elucidate the deformation mechanisms. The effects of different types of γ′ precipitates on the partitioning of interphase stress and the underlying mechanisms have been revealed. The findings indicated that bimodal superalloys exhibited distinct deformation behaviours compared to unimodal ones. Notably, premature load partitioning was observed in the microplasticity stage, attributable to Orowan looping for secondary γ′ precipitates or the emission of dislocations from the straight interface of primary γ′ precipitates. In the macroplasticity stage, considerable dislocations shear three types of γ′ precipitates, especially for the tertiary γ′ precipitates, which results in the decrease in the increment rate of interphase stress. These findings could contribute to a better understanding of deformation mechanisms in superalloys with multimodal γ′ size distributions and shine a spotlight on material design to modulate intergranular and interphase stresses.

Embedding strain-rate sensitivities of multiple deformation mechanisms to predict the behavior of a precipitate-hardened WE43 alloy under a wide range of strain rates

A rare earth Mg alloy, WE43, exhibits high strength, good ductility, low anisotropy, and moderately high strain rate sensitivity. As such, the alloy is a viable candidate for high strain rate applications. In this work, a comprehensive set of mechanical and microstructure data recorded during quasi-static, high strain rate split Hopkinson bar (SHB), and impact tests on specimens of WE43 Mg alloy reported in (Savage et al., 2020b) is simulated and interpreted using an advanced Taylor-type crystal plasticity finite element (T-CPFE) model. The T-CPFE model is formulated physically to embed two sources of strain-rate sensitivities inherent to each slip and twinning mode in WE43, one that occurs under constant structure and another that affects structure evolution. The model parameters are established for the alloy by achieving agreement in the stress-strain response and microstructure evolution under quasi-static and SHB tests. Density functional theory calculations of anti-phase boundary (APB) energy are carried out to explain origins of the unusually large initial slip resistance for basal dislocations, which shear precipitates in the alloy. The initial slip resistances of the prismatic and pyramidal dislocations are, instead, rationalized by Orowan looping around precipitates. After calibration and validation, the model is shown to successfully predict WE43 response at much larger strain rates than those used for model calibration. Specifically, mechanical response, specimen geometry changes, twin volume fractions, and texture evolution are predicted for different orientations of the Taylor cylinders. Details of the modeling framework, comparison between simulation and experimental results, and insights from the results are presented and discussed.

Microstructure and mechanical properties of hybrid nano-titanium carbide-carbon nanotubes (nano-TiC-CNT) reinforced aluminium matrix composite

To use Al composites in structural applications, we need to improve strength and ductility at the same time. In this article, we explore three main concepts to solve this problem: improving the dispersion uniformity of CNTs in Al powder without damaging its structure by solution coating technique, fabricating a hybrid composite by reinforcing Al with nano-TiC-CNT, comparing the properties of nano-TiC-CNT and micron-TiC-CNT hybrid composites. Microstructure observation by SEM, TEM, and XRD revealed well-dispersed and preserved CNTs without the formation of a second phase. The Al-0.5CNT composite showed good tensile strength and elongation at break of 278 MPa and 14%, respectively. Further improvements in tensile strength and ductility of 285 MPa and 23%, respectively, were measured after the addition of 2.5 wt%; (1.4 vol%) TiC nanoparticles to Al-0.5CNT composite. However, the introduction of 2.5 wt-% TiC macroparticles only improved the tensile strength by 48% but elongation at break was up to 32%. The improved strength and ductility are attributed to the introduction of geometrical necessary dislocation and Orowan looping of dislocations leading to back stress strengthening. The new Al composite is expected to find application in automotive and aerospace component manufacture and thermal management.

Temperature dependence of deformation mechanisms of a new Ni-based superalloy and high-temperature property optimization

The influence of temperature on the deformation mechanisms of a new Ni-based superalloy named K4800 containing 35 vol% γ′ were investigated. We studied the temperature dependence of deformation mechanisms and used the alloying method to optimize the high-temperature properties of the alloy. By analyzing slightly deformed microstructures, the dominant deformation mechanisms of alloy K4800 at the yielding stage were identified as: the anti-phase boundary (APB) shearing from RT to 600 °C, stacking faults (SFs) shearing and Orowan looping at 600–800 °C, and Orowan looping/cross-slip/climbing above 800 °C. We found that it was the activation of thermally assisted processes declined the strengthening effect of γ′ phase and impaired the high-temperature strength of the alloy above 800 °C. First-principles calculations were employed to investigate the effects of alloying elements on the formation and stability of stacking faults in K4800 alloy by using a 48-atom Ni3(Al, Ti) orthorhombic supercell. Considering the effectiveness of elements in lowering stacking faults energy, Co and W elements were chosen to alleviate the strength degradation of K4800 alloy above 800 °C. The deformation mechanism and properties of these three alloys at elevated temperature were also revealed and discussed.

Microstructural evolution and yield strength of a novel precipitate-strengthened Fe-based superalloy during thermal aging at 700 °C

Microstructures and compressive yield strength of a novel γ′-strengthened Fe-based superalloy with about 55 wt% iron are investigated after aging at 700 °C for various durations. We found that the γ′ particle always displays a spherical shape and its size increases only from 9 ± 1.6 to 51 ± 14.0 nm with increasing the aging time up to 10,000 h. Meanwhile, the distribution of carbides at grain boundaries is always discontinuously, and no topologically close-packed phases are visible in the alloy during aging. Compressive deformation tests disclose that the yield strength of the experimental alloy at 700 °C increases firstly and then decreases with particle size. Microstructural observations uncover that the predominant deformation mechanism changes from shearing of γ′ particles by weekly-coupled dislocations to shearing by strongly-coupled dislocations and then to Orowan looping with enlarging particle size at the beginning of plastic deformation. Based on these results, it is deemed that the evolution of microstructure and deformation mechanism with aging time leads to the changes in the yield strength during thermal aging.

Temperature-dependent tensile deformation and plasticity loss mechanism of a novel Ni-Cr-W-based superalloy prepared by laser powder bed fusion

The Ni-Cr-W-based Haynes 230 alloy fabricated by laser-beam powder bed fusion (PBF-LB) has garnered considerable attention for its ample shaping freedom and remarkable strength-plasticity synergy at room temperature. However, the limited strengthening effects provided by solid-solution atoms and carbides might restrict the practical applications of the alloy at high temperatures. In this paper, the high-temperature microstructural evolution and tensile properties of a novel γ′-strengthened based on Haynes 230 prepared by PBF-LB were systematically explored. The γ′ strengthening mechanism at 25–1000 °C and plasticity loss mechanism at 800–900 °C were first discussed. The results show that the precipitation of nanoscale γ′ phases after heat treatment (HT) can significantly improve the alloy strength at 25 °C, but dramatically sacrifice the alloy plasticity. With the testing temperature increasing, the ultimate tensile strength (UTS) and yield strength (YS) of the HT sample continue to decrease, while its elongation (EL) decreases first and then increases. A sharp decrease in EL appears at 900 °C, which is mainly attributed to the formation of acicular δ phases. The YS of the as-built (AB) sample from 25 °C to 800 °C increases, even higher than that of the HT sample, which is ascribed to the appearance of nanosized γ′ particles. The precipitation of γ′ particles and δ phases in the AB sample is the main reason for the more significant plasticity loss at 800–900 °C. Due to the increase in γ′ size and decrease in γ′ volume fraction, the dominant deformation mechanism in the HT sample changes from SF shearing at 25–800 °C to Orowan looping at 900–1000 °C.

Simultaneously enhancing the strength and ductility of as-extruded AlN/AZ91 composites via nano-precipitation and pyramidal slip

Age hardening is often used to optimize the mechanical properties of as-deformed Mg-based materials in industry, whereas the improvement of strength is usually accompanied by the significant loss of ductility, which hinders the application of Mg-based materials in structural components. In the present work, high strength-ductility synergy (the yield strength of 263 ± 9 MPa, ultimate tensile strength of 398 ± 7 MPa and elongation to fracture of 34% ± 1%) was realized in as-extruded AlN/AZ91 composites after optimizing aging processes. Microstructural characterization shows that AlN particles induced a large number of geometrically necessary dislocations around the AlN/Mg interface during extrusion, which decreased the nucleation barrier and provided more heterogeneous nucleation sites for γ-Mg17Al12 continuous precipitation. Meanwhile, 95% of residual dislocations in as-extruded AlN/AZ91 composites were annihilated during peak-aging, suppressing the growth and coarsening of continuous precipitates. Therefore, high density of nano-sized γ-Mg17Al12 continuous precipitates was produced in as-extruded AlN/AZ91 composites after peak-aging. During tension, gliding dislocations bypassed spherical γ-Mg17Al12 nano-precipitates by Orowan looping rather than cutting mechanism, which induced a strong block on dislocation motion. So high yield strength was mainly attributed to the high density of non-shearable γ-Mg17Al12 nano-precipitates with spherical morphology, which was different from other Mg-Al-based systems. The results of texture evolution and slip trace analysis demonstrated that the suppression of extension twinning and less basal slip was due to the enhanced activity of pyramidal 〈c + a〉 slip in as-extruded AlN/AZ91 composites after peak-aging during the room temperature tension, meanwhile, the dislocation density of as-extruded AlN/AZ91 composites was significantly decreased during peak-aging, then higher elongation to fracture was achieved.

Strengthening model development and effects of low diffusing solutes to coarsening resistance in aluminum alloys

A modified Orowan strengthening model is proposed to account for finite rod-shaped precipitates with hemispherical caps in aluminum alloy systems. A combined computational and experimental approach is used to study the influences of anisotropic Orowan looping and solute-dislocation interaction on temperature-dependent yield strength. The strengthening model is validated with a dataset containing 297 experimental precipitate geometries, chemistries, temperatures, and strength measurements, and achieves a strong predictive correlation of 0.8713 with experimentally measured yield strengths. Under conditions that are applicable to coarsening, constant particle volume fraction and aspect ratio, the model predicts that short rod precipitates provide far superior strengthening effects compared to plate precipitates. A cast Al-Si-Mg-Cu alloy with rod-shaped Q-phase (Al3Cu2Mg9Si7) precipitates was developed with a novel chemistry exploring the use of low-diffusivity elements (Mn, Ni, V, Zr) to limit precipitate coarsening. The thermodynamic behavior of Mn, Ni, V, and Zr across the Q-phase interface is examined using transmission electron microscopy (TEM), first-principles density-functional theory (DFT) calculations. and atom-probe tomography (APT). DFT calculations utilizing TEM identified Q-phase/Al-matrix interfaces show that Mn, Ni, V, and Zr preferentially segregate to the Q-phase precipitate boundaries which suggests inhibition of precipitate coarsening and higher strengths after temperature exposure. Atom-probe tomography confirms solute atom partitioning/segregation at the Q-phase/Al-matrix interface, found in the modified commercial AS7GU alloy (A356 +0.5%Cu), which supports these observations.

Investigation on tensile deformation and fracture behavior of a Ni-based superalloy specially designed for additive manufacturing

A nickel-based superalloy special developed for additive manufacturing (AM) were prepared by laser directed energy deposition (LDED) technology. Through tensile test at different temperatures, the ultimate tensile strength (UTS), yield strength (YS), and elongation were obtained; The corresponding microstructure and fracture morphologies were characterized as well as the properties. The results show that the abnormal peak values of UTS and YS were found at 700 °C, accompanying with poor ductility. Furthermore, the value of flow stress is little affected by strain rate in the temperature range of 23–700 °C, while it is very sensitive for that of 800–1100 °C. The dominant deformation mechanism of the former is anti-phase boundary (APB) shearing, and the fracture is featured by shear fracture without obvious necking; while for the latter, the dislocation climbing, cross-slip and Orowan looping is dominant, and the fracture mechanism is mainly characterized by the aggregation and growth of micropores and crack propagation, and postmortem specimen exhibit distinct necking phenomena. The abnormal peak values of UTS and YS at 700 °C could be attributed to the formation of Kear–Wilsdorf locks (K-W locks). The experimental results will support the application of the investigated alloy as well as design new alloy for AM.