Room Temperature Yield Strength Research Articles

Regulating the mechanical properties of (μm B4C+nm SiC)/7075Al composites via nano-SiC content

In this study, micron B4Cp (m-B4Cp) and nanometer SiCp (n-SiCp) reinforced 7075Al composites were prepared by high-energy ball milling, hot press sintering, and hot extrusion. The microstructures and mechanical properties of composites were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), tensile testing, and synchrotron radiation computed microtomography (SR-μCT). The results showed that n-SiCp and m-B4Cp were uniformly distributed in the aluminum matrix without interfacial reaction. The optimal grain refinement was achieved by adding 1.5 wt.% n-SiCp, improving the strength and ductility of composites. The room temperature yield strength (YS) and ultimate tensile strength (UTS) of M5N1.5 composites were increased from 350 MPa and 460 MPa of 7075Al to 401 MPa and 502 MPa, respectively. The results revealed that the YS and UTS of composites decreased, but elongation increased with increasing temperature. When the temperature increased to 200 °C, the elongation of 7075Al and M5N1.5 increased from 5.9% and 4.7% to 8.7% and 10.9%, respectively. Quantitative analysis revealed that dislocation strengthening and grain refinement strengthening caused by the addition of n-SiCp are the dominating strengthening mechanisms at both room and high temperatures, while the contribution of m-B4Cp to the strengthening of the composites is very small.

Solution temperature influence on CRSS of the secondary γ′ phase in nickel-based superalloy FGH4096

Nickel-based superalloy components are capable of being manufactured by direct hot isostatic pressing (HIP) process with near-net shape and nearly 100 % raw materials utilization. However, they cannot be applied directly, due to the poor mechanical properties of HIPed components. Fortunately, heat treatment can improve the properties via regulating the microstructure. Therefore, the effects of varied solution temperatures on the tensile properties of FGH4096 nickel-based superalloy disk at room and high temperatures were studied. The results revealed that the disk after sub-solution treatment (1130 °C) has higher tensile properties (room temperature yield strength: 1194 MPa, elongation: 15.5 %; high temperature yield strength: 1075 MPa, elongation: 10.5 %). The antiphase boundary (APB) shear stress, Orowan bypass stress, stacking faults (SF) shear stress, and micro-twins (MT) shear stress affected by the size and distribution of the secondary γ′ phase were calculated. The results show that the main strengthening mechanism at room temperature is APB shear, and the APB shear stress of solution treatment at 1190 °C is the highest. The high temperature strengthening mechanism is due to SF shear and MT strengthening effects. The difference in SF shear stress between various solution temperatures is minimal. 1190 °C has a higher MT strengthening effect than 1090 °C. This is consistent with the actual result that the tensile properties at 1190 °C are superior to those at 1090 °C. The conclusion is that the combination of high strength reflected by several critical resolved shear stresses and considerable plasticity reflected by the MT strengthening effect can lead to a comprehensive improvement in alloy tensile properties.

Strengthening a non-equiatomic quaternary high-entropy alloy via concurrent gradient structures of nanotwin and dislocation cell

One main drawback of FCC high-entropy alloys (HEAs) is their insufficient room temperature yield strength. In this work, concurrent gradient structures of nanotwins and dislocation cells have been introduced into a non-equiatomic quaternary Fe40Ni20Co20Cr20 (at. %) high-entropy alloy by ultrasonic shot peening to meet this challenge. The gradient alloy exhibits a significantly enhanced yield strength, i.e., from the original 204 MPa to 559 MPa, combining with a well-retained ductility of 29 % and a good work hardening ability. Strengthening mechanisms at different depths (5, 30, 200, 400 μm) are also carefully discussed. The current work presents a strategy for hardening FCC HEAs significantly while maintaining the single solid solution microstructure.

Optimization of the grain boundary network and tensile properties of powder metallurgy-hot isostatic pressed Ni-based alloy Inconel 625

Powder metallurgy-hot isostatic pressing (PM-HIPing) is an advanced manufacturing technology for large-sized and complex-shaped components for nuclear applications. In the present study, a novel PM-HIPing strategy was proposed to optimize the grain boundary network and tensile properties of Ni-based alloy Inconel 625, and it was verified by a series of experiments. Samples with 69 % and 74 % of coincidence site lattice (CSL) grain boundaries were obtained when the narrow-size ranged powder was consolidated at 1140 °C and 1180 °C, respectively. The fraction of CSL grain boundaries was further increased to ∼78.5 % after a high temperature solution treatment. Room temperature yield strength and ultimate tensile strength of PM-HIPed alloy 625 were comparable to that of the wrought specimens, elongation of the specimens was ∼56–60 %, the samples all featured with dimple ductile dominant fracture mode.

Improving fatigue resistance of ultrafine bainitic steel by exploiting segregation-induced bands

An ultrafine bainitic steel was designed with segregation-induced martensitic/austenitic (MA) bands. The steel comprises almost 21 % retained austenite (RA); the rest is mainly bainitic ferrite and a small fraction of martensite. The steel exhibits room temperature (RT) yield strength of ∼914 MPa, ultimate tensile strength of ∼1969 MPa, and total elongation to failure of ∼11.5 %. Low cycle fatigue (LCF) behavior was investigated under a fully reversed strain-controlled waveform at RT, with a loading-axis parallel to the MA bands. LCF stress response reveals initial cyclic hardening followed by softening or saturation, depending on the applied strain amplitude. This is attributed to the interplay of strengthening mechanisms, which include RA transforming to martensite and dislocation multiplication/interactions and the softening effects of dislocation annihilation and crack formation/propagation. Damage studies reveal a mixed fracture mode, displaying brittle striations, secondary cracks, quasi-cleavage facets, and dimples. The secondary cracks mainly appear to originate from the main crack and propagate predominantly along the matrix-bands interphase regions or within MA bands. Additionally, surface-initiated cracks along their propagation path were deflected and branched around the interphase regions. This tortuosity reduces the crack propagation rate. Overall, the significant work hardening capability of the steel, along with its banded microstructure, contributes to its superior fatigue resistance compared to non-banded bainitic steels reported in the literature.

Microstructural evolution and mechanical behavior of novel TiZrTaxNbMo refractory high-entropy alloys

The refractory high-entropy alloy (RHEA) with a body-centered-cubic (BCC) solid-solution structure has excellent high-temperature softening resistance, which has attracted wide interest in the field of high-temperature alloys. However, its limited room-temperature plasticity has greatly hindered its engineering application. To obtain an excellent strength-plasticity matching relationship, in this reported study, the Ta content in the high-entropy alloy (HEA) was adjusted to rectify this shortcoming. A series of TiZrTaxNbMo (x = 1.0, 0.9, 0.8, 0.7, and 0.6 at. percent, at%) RHEAs were prepared using the vacuum arc-melting technique, and the microstructure and mechanical properties of these RHEA alloys were systematically investigated. The experimental results show that the TiZrTaxNbMo RHEAs are composed of main BCC1 and minor BCC2 phases, which exhibit a dendritic structure. By reducing the Ta content, the elemental segregation caused by the non-equilibrium solidification is reduced. In terms of mechanical properties, with the decrease of Ta content, the hardness and room-temperature yield strength of the alloy decreases slightly, but the room-temperature plasticity increases significantly. The Ta0.7 alloy has the highest plasticity (34.8 %), which is about twice that of the equimolar Ta 1.0 alloy, while the yield strength remained at 1297 MPa. The excellent mechanical properties of the alloys can be attributed to solid-solution strengthening and the formation of moderate amounts of interdendritic regions. The interaction between slip bands and dislocations formed during compression of the Ta0.7 alloy decreased its work hardening. Moreover, the theoretical model of solid-solution strengthening elucidates that the calculated values of the alloy’s yield strength are consistent with that obtained experimentally.

Refined microstructure to improve the mechanical properties of the as-cast NiCoCr multi principal element alloy via mechanical vibration

The NiCoCr multi principal element alloy (MPEA) show excellent ductility at cryogenic temperatures and corrosion-resistance properties under the condition that it prepared by thermal–mechanical processing. However, the coarse as-cast grains negatively impact mechanical properties significantly and grain refinement is necessary for forming complex castings. Most grain refining methods need extra alloying elements, which may result in loss of ductility by brittle second phases. In this work, a significant microstructure refinement of the as-cast NiCoCr MPEA was achieved by pollution-free vacuum mechanical vibration, with the average grain size refined from the initial value of 620 μm to 140 μm. As a result, the room-temperature yield strength was increased by 54 % (from 255 MPa to 392 MPa) without loss of elongation compared to the as-cast condition without vibration.

Cryo-pre-straining contributes to achieving high yield strength in high-entropy alloys

In this study, we propose an effective and feasible strategy to significantly improve the room-temperature yield strength of the Co35Cr20Fe15Mn15Ni15 HEA by 338%, from 281 MPa (as-recrystallized, before CR) to 1231 MPa (30% CR) through cryo-pre-strain-inducing defects such as dislocations, stacking-faults (SFs), nano-twins, Lomer-Cottrell (L-C) locks, and HCP martensite, while maintaining good ductility (16.4% elongation in 30% CR). Additionally, the contribution of these defects to the yield strength enhancement was quantified. This study offers a new perspective for the preparation of advanced FCC high-entropy alloys.

Study of microstructure evolution and strengthening mechanisms in Mox(Nb3TaTi3Zr)100−x high-entropy alloys

A new series of high-entropy alloys denoted as Mox(Nb3TaTi3Zr)100−x, has been designed for aero-engine applications. The study focused on investigating the microstructural evolution and strengthening mechanisms of the alloys in response to varying Mo content. Results indicate that the alloys primarily display a BCC crystal structure. Notably, an FCC phase precipitates in the alloy when the Mo content reaches 30%. Furthermore, as the Mo content increases, the strength of the alloys significantly increases while their plasticity diminishes. The room-temperature yield strength of the alloys shows a substantial increase from 729 MPa (x = 0) to 1202 MPa (x = 25), while the yield strength at 1200 °C rises from 62 MPa (x = 0) to 498 MPa (x = 30). Concurrently, the microhardness of the alloys also increases from 247 HV (x = 0) to 471 HV (x = 30). The observed strengthening mechanisms include solid solution strengthening, fine grain strengthening, and precipitated phase strengthening.

Effect of Al content on microstructure and mechanical properties of Alx(Nb3TaTi3Zr)100-x refractory high-entropy alloys

In this study, seven refractory high-entropy alloys of Al x (Nb3TaTi3Zr)100-x (x = 0, 5, 10, 15, 20, 25, 30) were synthesized by vacuum arc melting and characterized by various techniques, including XRD, SEM, EDS, compression tests at both 1200 °C and room temperature, as well as hardness tests. The analysis revealed that the alloys exhibit a single BCC structure when the Al content is between 0 and 15%, while the B2 phase appears at 20% and a mixed structure of BCC + B2 + σ phase at 30%. As the Al content increases, the hardness, stiffness, and room temperature yield strength of the alloy increases, while the plasticity decreases. Notably, the alloy with 25% Al content displayed the highest yield strength of 1400 MPa and Young’s modulus of 75.94 GPa at room temperature. Moreover, the hardness of the seven alloys increased from 247 HV to 490 HV with Al content from 0 to 30%. Furthermore, the alloy containing 30% Al exhibited a notable elevated-temperature yield strength of 143 MPa at 1200 °C.

Unique Yttria Nanoparticle Strengthening in an Inconel 718 Superalloy Fabricated by Additive Manufacturing

AbstractOxide dispersion strengthened (ODS) nickel (Ni)‐based superalloys are advanced materials known for their outstanding tensile and creep performance at temperatures exceeding 1000 °C. Nevertheless, their conventional synthesis presents a longstanding challenge in cost‐effectively producing intricate components for critical applications. In this work, electrostatic self‐assembly (ESA) of powders with the laser powder bed fusion (LPBF) process are successfully combined to produce yttria ODS Inconel 718 (IN718) alloy for the first time. This approach demonstrates a significant contribution of yttria to the strength of IN718 after the solid solution heat treatment, as evidenced by ≈50% improvement in room temperature yield strength with a 0.5 wt.% yttria addition. The addition of yttria by this process leads to a heterogeneous microstructure. This heterogeneous microstructure comprises two distinct grain areas with varying amounts of yttria nanoparticles and dislocation storage. The results show that the yield strength increase can be predicted by the combination of both Y2O3 dispersion strengthening and dislocation strengthening mechanisms. These findings offer an effective approach to tailor heterogeneous microstructures, unlocking new opportunities for cost‐effectively producing high‐performance ODS Ni‐based superalloy products with excellent mechanical properties.

Unusually high room and elevated-temperature tensile properties observed in direct aged wire-arc directed energy deposited Inconel 718

Wire-arc directed energy deposition (DED) processed Inconel (IN) 718 is known to have coarse columnar grains, strong texture, and significant chemical and microstructural inhomogeneity in the as-fabricated condition. Homogenization treatment is commonly used prior to aging to eliminate the inhomogeneity and detrimental precipitation for better mechanical properties. In this study, however, direct aging (DA) at 700 °C without homogenization has resulted in room-temperature yield strength, ultimate tensile strength (UTS), and elongation that are comparable to wrought condition and among the highest reported properties for wire-arc DED IN718. The DA samples at between 650 and 750 °C aging also demonstrates remarkable ductility when deformed at elevated temperatures. In addition, when aged below 750 °C the DA IN718 possesses significantly higher UTS compared to those with homogenization treatment. These superior mechanical properties are highly likely due to the non-uniform and hierarchical precipitation consisting of disk-shaped γ″ in diameter from a few to tens of nm in the dendritic core area and micron-sized Laves phase and carbides in the inter-dendritic region.

Metal matrix composite with superior ductility at 800 °C: 3D printed In718+ZrB2 by laser powder bed fusion

We investigated the microstructure and mechanical properties of ZrB2 fortified Inconel 718 (In718+ZrB2) superalloy metal matrix composite (MMC), which was produced via Laser Powder Bed Fusion (LPBF). 2 vol% ZrB2 nano powders (below 100 nm in diameter) were decorated on the surfaces of Inconel 718 alloy powders by high-speed blender. Microstructural analysis of the as-printed specimens showed that the ZrB2 decomposed during LPBF, which promoted the formation of homogeneously distributed (Zr, Ni)-based intermetallic and (Nb, Mo, Cr)-based boride nanoparticles in the matrix. The 3D printed In718+ZrB2 has remarkably lower porosity and smaller grain size compared to 3D printed In718 fabricated under the same LPBF conditions. The mechanical performance of the as-printed and heat-treated In718+ZrB2 showed significantly higher room temperature (RT) hardness, RT yield strength (σYS), and RT ultimate tensile strength (σUTS) compared to In718. High-temperature tensile tests at 800 °C showed that In718+ZrB2 has ∼10 times higher tensile ductility with higher σYS (by 10 %) and σUTS (by 8 %) than pure In718.

Low-cycle Fatigue Behavior and Microscopic Morphology of Fatigue Crack Structure of Al-Cu-Ag-Fe-Mg-Zr-Er Alloy in The Aging Treatment

Al-Cu-Ag-Fe-Mg-Zr-Er alloy with different content of Er addition was prepared by using metallurgy processing. The Al-4.5%Cu-0.5%Ag-0.35%Fe-0.38%Mg-0.1%Zr-xEr alloy phase and its refinement mechanism were studied with SEM. Tensile and fatigue tests were performed for the alloy in the state of deformation treatment condition. The microstructural observations reveal that the addition of 0.2% rare earth Er can effectively refine the grain structure of Al-Cu-Ag-Fe-Mg-Zr-Er alloy. It improves room temperature tensile strength, yield strength, and elongation at break. Under the condition of low cycle fatigue loading, Al-4.5%Cu-0.5%Ag-0.35%Fe-0.38%Mg-0.1%Zr-0.2%Er alloy shows a cyclic strain hardening in the cyclic stress response curves, which mainly depends on forming complex dislocation configurations. The accumulation of slip bands at the front of the grain boundary will lead to intergranular fracture of the material.

Study on the microstructures and tensile creep behaviors of extruded dilute Mg–Mn–Zn alloys

In this work, creep behaviors of dilute Mg–Mn–Zn alloys were investigated in extruded rods (ER) with bimodal grain microstructures and extruded sheets (ES) with homogeneous microstructures. Tensile creep tests were carried out at 423 K along the extrusion direction (ED) and transverse direction (TD). For brevity, the samples were named as ER-ED, ER-TD, ES-ED and ES-TD, respectively. All samples' creep is dominated by dislocation movement, and different types of dislocation slip are seen in the different samples under loading along each direction. For the ER sample, the creep mechanisms of the ER-ED sample were determined to be cross-slip accompanied by pyramidal <c+a> slip. Differently, the creep of the ER-TD sample was dominated by basal slip and accompanied by grain boundary bulging, which induced the worst creep resistance. For the ES alloy, the creep mechanisms were pyramidal <c+a> and cross-slip, but the cross-slip density of the ES-ED sample was higher. Accordingly, the creep test results indicated that the creep resistance was ranked in an order of ES-TD/ED > ER-ED » ER-TD. Furthermore, bimodal grain microstructure accelerates creep at a similar texture effect level, where grain boundary bulging was clearly observed, as well as the decreased KAM and increased fraction of M/HABs (middle-to-high angle boundaries). These typical softening characteristics might be responsible for weakening the ER-ED sample from the highest room-temperature yield strength to the inferior creep resistance to ES-TD/ED samples, meaning the thermal instability of this strong heterogeneous microstructure.

The evolution of dual-phase core–shell structure and mechanical properties induced by Co addition in as-cast high-entropy intermetallic

In this work, three as-cast L12-type HEIs with different content of Co element were carefully examined combined with TEM, SEM and XRD technologies. The main matrix of three alloys was L12 ordered phase, and Si,Ti-rich grain-boundary precipitate phase generated with the addition of Co. In Co1 alloy, distinct dual-phase core–shell structure was found within grain due to the precipitation of extra FCC disordered secondary phase, which leads to a better strength-plasticity combination (compressive strength of 3441 ± 50 MPa, and fracture strain of 46.0 ± 1.5%) than Co0 and Co0.5 alloy at room temperature. With the increase of temperature, particular anomalous yield effect was discovered in Co1 alloy. It is clear that SFs became main deformation substructure in Co1 alloy at elevated temperature, and the interaction between non-coplanar SFs motivated the generation of L-C Locks, which assists the K-W Locks to pin dislocations movement and enhance the yield strength from room temperature to about 650 ℃. In addition, the interaction between SFs resulted in the formation of nano-spaced SF network, which contributes to the dynamic Hall-Petch effect. Finally, excellent high-temperature yield strength was achieved in as-cast Co1 alloy, which is higher than room-temperature yield strength until 950 ℃.

Synergetic regulation of hierarchical microstructure to improve the 704 ℃ tensile property in laser directed energy deposition IN718Plus superalloy

IN718Plus superalloy with hierarchical microstructure has been successfully manufactured by laser directed energy deposition (LDED). Along building direction, microstructure varies from composing of epitaxial columnar grains oriented along <001>γ direction to equiaxed grains in flower like configuration. Striped Laves phase and fine γ'/γ'' precipitates form in the columnar grains, and would transform into fine Laves phase particles and nanoscale γ' precipitates at equiaxed layer. To improve the compositional homogeneity and microstructural stability, high temperature solution treatment has been explored on the superalloy. The treatment would not affect the morphology and orientation of columnar grains, but would redissolve Laves phase precipitates. Double aging treatment has also been performed to obtain homogeneous distributed γ' precipitates, and the synergistic regulation of microstructure enhances the mechanical property significantly, as causing the room temperature yield strength and tensile strength increased from 0.88 GPa and 1.14 – 1.04 GPa and 1.28 GPa, respectively. Moreover, the excellent mechanical property would be maintained upon 704 ℃, with yield strength of 0.93 GPa, tensile strength of 1.04 GPa and high elongation of 27.3%.

Thermal stability of (HfCo)90(NbMo)10 and (HfCo)75(NbMo)25 refractory high entropy alloys with a bcc + B2 structure

The effect of long-term (700 h) annealing at 1000 °С on the structure and mechanical properties of the as-cast (HfCo)90(NbMo)10 and (HfCo)75(NbMo)25 (in at.%) refractory high entropy alloys was examined. The as-cast alloys consisted of a mixture of (Nb, Mo)-rich bcc and (Hf, Co)-rich B2 phases with bcc / B2 ratios close to NbMo / HfСo ratios. Annealing did not result in the formation of additional phases, which agreed with the Thermo-Calc predictions. However, annealing led to the formation of (i) B2 / bcc nanoprecipitates inside the initial bcc / B2 phases and (ii) separate Nb-rich and Mo-rich bcc phases. Annealing also caused significant strengthening of the alloys; for example, the room-temperature yield strength of the (HfCo)90(NbMo)10 alloy increased from 640 to 1340 MPa. Hardening was induced by the bcc nanoprecipitates in the B2 phase according to the Orowan mechanism. The results obtained suggest novel routes for the development of refractory high entropy alloys with a stable bcc + B2 structure.

Microstructure and mechanical properties of a novel polycrystalline Ni3Al-based intermetallic alloy

A polycrystalline Ni3Al-based intermetallic alloy was successfully prepared via vacuum induction melting processing. Next, the microstructural evolution and mechanical properties of the intermetallic alloy were investigated by solution treatments at temperatures ranging from 1230 to 1290 °C. The results showed that the as-cast polycrystalline Ni3Al-based intermetallic alloy consisted of dendrite γ+γ′ with interdendritic distribution, matrix γ′ phase, and eutectic γ–γ′, and the total volume fraction of γ′ phase was ∼83.2%. After solution treatment at 1270 °C, the size and morphology of the γ′ phase changed and the secondary γ′ phase precipitated in the γ channel. The maximum room temperature yield strength, tensile strength and elongation reached 488 MPa, 686 MPa, and 5.2%, respectively. At 1100 °C, the high-temperature tensile strength of sample subjected to solution treatment at 1250 °C reached 203 MPa. It was found that solution treatment did not eliminate the incipient γ′m, resulting in the weaker interdendritic boundary area in the alloy. Moreover, noteworthy, α-Cr particles were found in the γ′m of the polycrystalline Ni3Al-based intermetallic alloy, revealing an orientation relationship such as [123]α-Cr∥[123]γ' and (1–21)α-Cr∥(11–1)γ'. The α-Cr particles have the strengthening effect of second-phase particles through pinning dislocations, which can improve the high-temperature creep performance of the alloy.

Machine learning approach for predicting yield strength of nitrogen-doped CoCrFeMnNi high entropy alloys at selective thermomechanical processing conditions

The yield strength property is important to consider while designing high entropy alloys (HEAs). In order to obtain the desired yield strength of HEAs through the experimental method it is a difficult, expensive, and time-consuming process due to the broad composition space available. The room temperature yield strength property of nitrogen-doped (CoCrFeMnNi)100-x-Nx HEAs at preferred thermomechanical conditions was predicted using the machine learning (ML) technique based on the linear regression model in the present investigation. The yield strength prediction result of 2% nitrogen-doped CoCrFeMnNi HEA subsequently cold-rolled 91 (%) and annealed at 850 °C temperature consisting of 563.6 MPa is consistent with the experimental value of 556 MPa. It implies that the yield strength predictions of (CoCrFeMnNi)100-x-Nx HEAs are accurate. As a result, selecting suitable models and material parameters to design a wide range of materials with superior properties attributed to various compositions of HEAs through ML technology could be a potential approach.