Elevated Temperature Strength Research Articles

A novel NbTaV0.5Hf0.1 complex concentrated alloy with superior room-temperature tensile plasticity and elevated-temperature strength

Refractory complex concentrated alloys (RCCAs) encounter difficulties in balancing room-temperature ductility and high-temperature strength, which restricts their applications. Here, a novel NbTaV0.5Hf0.1 RCCA was prepared through vacuum arc melting for the first time. The as-cast alloy exhibited a stable body-centered cubic phase structure with a small amount of micro-scale dispersed Hf-rich oxides. As a result, the designed alloy exhibits a room-temperature tensile fracture strain of 14.9 %, and superior compressive yield strength values under elevated temperatures (472 MPa under 1200 ℃, 358 MPa under 1400 ℃, respectively). A synergy between room-temperature tensile ductility and exceptional high-temperature strength was achieved in RCCAs.

Failure mechanism of steel fiber pullout in UHPC affected by alternating cryogenic and elevated variation

This paper investigates the pullout response of straight and hooked-end steel fiber embedded in Ultra-high Performance Concrete (UHPC) subjected to alternating cryogenic (−170 °C) and elevated (200 °C) temperature variation. The temporal evolution of Acoustic Emission (AE) parameters and failure behavior during the pullout process were monitored in situ using the AE test. Additionally, changes in the UHPC microstructure were also evaluated. Results showed that in addition to the UHPC matrices exposed to elevated temperature, the compressive and flexural strength of UHPC matrices subjected to single or multiple cycles were generally higher than those at ambient temperature. Whereas the bond strength/pullout energy of straight fiber increased with a single cycling exposure of UHPC specimens to either cryogenic or elevated temperature, the improvement in the pullout performance of the hooked-end fiber was obtained only after the post-cryogenic thawing of specimens. Moreover, the exposure to an increased number of temperature-variation cycles caused the pullout strength and energy of both fiber groups to gradually decrease. Nonetheless, the pullout performance of the hooked-end fiber was significantly and consistently superior to that of the straight fiber, regardless of the exposure temperature or cycles. The AE test confirmed that the pullout process of both fibers was mainly characterized by tensile failure, with a marginal occurrence of shear failure for the hooked-end fiber. When the UHPC was exposed to various temperatures, the fiber pullout behavior was predominantly influenced by the physical structure of the fibers, thermal deformation proclivity of the matrix, and the competition between mechanisms such as pore moisture phase change, secondary hydration, and the composition of hydrates.

A Zr-45Ti-54Al-3V alloy with excellent elevated temperature mechanical properties: Millimeter-scale coarse grains with initial subgrains

For improved elevated temperature mechanical properties, a Zr-45Ti-54Al-3V alloy with initial subgrains microstructure and millimeter-scale coarse grains is prepared herein via an electric field-assisted high-temperature compression process at temperatures of 1200 °C and 1400 °C. After the treatment at 1400 °C, the tensile strength and elongation of the alloy at 500 °C are increased by 25.2% and 21.7%, respectively, compared with those of the as-forged 47Zr. Both treatment temperatures lead to a compressive strength of 1400 MPa, along with good elevated temperature compression deformation ability. The rapid grain growth is attributed to the promotion of atomic diffusion by the pulsed current, which also results in a uniform distribution of each solute element. The dynamic recovery and continuous dynamic recrystallization during hot deformation are the main reason of elevated temperature plasticity improvement of EFHC sample. The elevated temperature strength of EFHC sample is higher than that of as-forged sample because it has more α phase and LAGB than as-forged sample

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.

Effect of microstructure and temperature on the bulk and small-scale deformation behavior of 2nd and 3rd generation advanced intermetallic TiAl alloys

Advanced intermetallic TiAl alloys have attracted considerable attention as a high-temperature structural material in aerospace and automobile sectors owing to their low density, elevated temperature strength, superior creep, and oxidation resistance. The present study is focused on assessing the effect of alloy composition, heat treatment and microstructural variation on the bulk and small-scale deformation behavior of commercial grade 2nd generation and newly developed 3rd generation TiAl alloys at 25 °C (298 K), 300 °C (573 K), and 500 °C (773 K). Twinning is noted to be the dominant deformation mechanism irrespective of the temperature. The highest yield strength and hardness are noted for the as-cast 3rd generation TiAl alloy owing to the finer microstructure and compositional variation. Heat treatment however modifies the TiAl microstructure significantly resulting to unique bilamellar-biglobular (BLBG) microstructure, devoid of the brittle β0 phase. Consequently, nano twins- and micro twins-induced enhanced deformability is noted for such microstructure, as compared to the as-cast counterparts. Interestingly, an anomalous increase in strength with an increase in temperature is observed for the studied alloys owing to the presence of high-density twins and Kear-Wilsdorf locks. Most importantly, a temperature dependant hardness anomaly is noted in the TiAl alloys that opens new avenues for further research in nanoscale deformation. This piece of research potentially strengthens the understanding of the role of constituent phases and temperature in the deformation behavior of complex TiAl alloys. Twin-induced deformation mechanism noted for the novel BLBG microstructure, can also be valid for different generations of TiAl alloys to achieve enhanced deformability that paves the way for the development of next-generation material.

Rapidly achieving high-performance joining of single crystal superalloy and powder metallurgy superalloy via partial transient liquid phase diffusion bonding

A rapid and high-performance partial transient liquid phase diffusion bonding process has been proposed for the DD5 single crystal superalloy and the FGH96 P/M superalloy via a mixture of NiTi alloy and FGH96 P/M superalloy powders as interlayer. During the bonding process, isothermal solidification and homogenization of the joint were achieved through a rapid diffusion mechanism of short-range and large-area between the liquid phase of NiTi and the FGH96 particles and the base material. When bonded at 1170 °C only for 60 min of the holding time, isothermal solidification and homogenization of the joints were completed. The isothermal solidification joint consisted of a polycrystalline zone with γ/γ′ structure similar to that of FGH96 and an epitaxial growth zone (EGZ) derived from DD5. Compared with traditional brazing and transient liquid diffusion bonding process (TLP), no brittle compounds and eutectics of Si and B were presented in the joint, which ensured the joint with excellent mechanical properties. With the increase of holding time, both the tensile strength and elongation was significantly increased on account of the reduction of η-Ni3Ti. When the joints were bonded at 1170 °C for 60 min, the elevated temperature strength of 650 °C reached 880.7 MPa, which was more than 80 % and 60 %o that of the DD5 and FGH96, respectively.

Enhancing the elevated temperature strength of titanium matrix composites through a novel (α + β) TRIPLEX heat treatment

In this work, an (α + β) TRIPLEX heat treatment process was designed, as well as its impact on the microstructures and high–temperature mechanical properties of 2.5 vol% (TiB + TiC)/Ti–6Al–4Sn–7Zr–1Nb–1Mo–1W–0.2Si (wt.%) was carefully investigated. The results show that the microstructures of heat–treated TMCs consist of the primary α phase (αp) and the transformed β (βt) with a large number of nano–scale secondary α phases (αs). The TRIPLEX heat treatment encourages the effect of structural heredity, causing the residual αp lamellae to develop adequately and even mature into lamellae clusters with the same orientation, which induces a visible strengthening of the variant selection for the α phase. After the TRIPLEX heat treatment, the increase in content and size of silicides is mainly due to the process providing favorable sites and sufficient time for nucleation and growth. The longitudinal axes of some silicides exhibit an approximate 40° angle or parallel arrangement with the β/αp interfaces, which means that the silicides will grow preferentially along a specific orientation to minimize the strain energy. The (α + β) TRIPLEX heat treatment significantly increases the high–temperature strength of the TMCs with no appreciable elongation loss (as–cast TMCs: UTS = 487.6 MPa, EL = 17.4%; HT–4#: UTS = 558.1 MPa, EL = 11.5%). The strength improvement of HT–4 # is mainly related to the combined effects of αp content reduction, αs precipitation, obstruction of dislocations by the βt/αp interface, hetero–deformation strengthening, silicides precipitation strengthening, and α2 dispersion strengthening.

Stability and design of stainless steel hollow section columns at elevated temperatures

This paper investigates the stability and design of stainless steel circular, elliptical, square and rectangular hollow section (CHS, EHS, SHS and RHS) columns at elevated temperatures. Nonlinear shell finite element models are employed to conduct comprehensive parametric studies whereby extensive benchmark structural performance data on the behaviour and resistance of stainless steel hollow section columns at elevated temperatures is generated. In total, 26,760 cold-formed and hot-rolled austenitic, duplex and ferritic stainless steel CHS, EHS, SHS and RHS columns at elevated temperatures are taken into account, considering various member slendernesses, cross-section geometries, cross-section slendernesses and elevated temperature levels. New flexural buckling design rules are put forward for stainless steel hollow section columns in fire, which consistently considers the elevated temperature strength at 2% total strain f2,θ as the reference material strength for all cross-sections classes. The accuracy, safety and reliability of the proposed new design rules are assessed for a wide range of cases. Comparisons are also made against the results obtained through the column fire design rules of the European structural steel fire design standard EN 1993-1-2 [1]. It is demonstrated that the proposed new design rules furnish more accurate, safe-sided and reliable flexural buckling resistance predictions for stainless steel hollow section columns at elevated temperatures relative to the column fire design provisions of EN 1993-1-2 [1].

Significantly enhancing elevated-temperature strength and ductility of a FeMnCoCr high-entropy alloy via grain boundary engineering: Exploring multi-deformation mechanisms

The objective of the study is to elucidate the influence of grain boundary engineering (GBE) on the high-temperature properties of a metastable FeMnCoCr high-entropy alloy (HEA). Using thermo-mechanical processing (TMP), the grain boundary character distribution (GBCD) was optimized, which involved the increase of coincidence site lattice (CSL) special boundaries and multiple twinning events, and breaking of random high-angle grain boundaries (RHAGBs) network. Furthermore, the deformation strain of the alloy became more uniform at high temperature, dynamic recrystallization was suppressed, and a number of deformation mechanisms were operative. The ductility of studied HEA was significantly enhanced by over 200% at 1073 K, resulting in a remarkable 1.35-fold increase.

Precipitating thermally reinforcement phase in aluminum alloys for enhanced strength at 400 °C

Heat-resistant aluminum alloys are widely used in aerospace and automotive fields for manufacturing hot components due to their advantages in lightweight design and energy conservation. However, the high-temperature strength of existing cast aluminum alloys is always limited to about 100 MPa at 350 °C due to coarsening and transformation of strengthening phases. Here, we reveal that the yield strength and ultimate tensile strength of the T6 state Al–8.4Cu–2.3Ce–1.0Mn–0.5Ni–0.2Zr alloy at 400 ℃ increase by 34% and 44% after re-aging at 300 °C for 100 h, and its thermal strength exhibits distinguished advantage over traditional heat-resistant aluminum alloys. The enhanced elevated-temperature strength is attributed to the reprecipitation of the Ni-bearing T-Al20Cu2Mn3 phase, whose number density increases over one time. The significant segregation of Ni, Ce, and Zr elements at the interfaces helps improve the thermal stability of the T phase. The thermostable T phase effectively strengthens the matrix by inhibiting dislocation motion. Meanwhile, a highly interconnected 3D intermetallic network along the grain boundaries can still remain after long-term re-aging at 300 °C, which is conducive to imposing a drag on the grain boundaries at high temperatures. This finding offers a viable route for enhancing the elevated-temperature strength of heat-resistant aluminum alloys, which could provide expanded opportunities for higher-temperature applications.

Carbide-reinforced Re0.1Hf0.25NbTaW0.4 refractory high-entropy alloy with excellent room and elevated temperature mechanical properties

Refractory high-entropy alloy (RHEA) with high elevated-temperature strength is generally brittle at room-temperature, which greatly restricts the workability and application of the RHEA. Here, we report a novel Re0.1Hf0.25NbTaW0.4C0.25 RHEA with both excellent high-temperature strength and decent room-temperature ductility. Meanwhile, the microstructure and mechanical properties of Re0.1Hf0.25NbTaW0.4C0.25 RHEA were investigated. The microstructure of the alloy was composed of BCC matrix phase and eutectic phases (BCC+(MC + M2C)), and lots of secondary carbides were dispersedly precipitated in the BCC matrix. Due to the synergistic strengthening effect between the BCC matrix and the carbides. The alloy exhibited excellent compressive strength of 1026 MPa at 1450 °C and 523 MPa at 1700 °C, with a good compressive fracture strain of 10.2% at room-temperature. The Re0.1Hf0.25NbTaW0.4C0.25 RHEA has potential applications in the field of ultra-high-temperature structural materials.

Influence of Ion Nitriding on Microstructure and Properties of Haynes 282 Nickel Superalloy Specimens Produced Using DMLS Technique.

The paper investigates the influence of the ion-nitriding process on the microstructure, corrosion resistance, and tensile strength at elevated temperatures of Haynes 282 nickel superalloy specimens produced by the Direct Metal Laser Sintering (DMLS) technique. The study was performed for two conditions, i.e., as-built by DMLS method and as-built by DMLS method + covered by a layer containing CrN + Cr2N phases. An analysis of the surface morphology revealed that the ion-nitriding process significantly affects the physical and chemical phenomena occurring on the specimen's surface. The XRD measurement of the specimens showed that preparing them with the DMLS method as well as following a nitriding process produced residual tensile stresses. Based on the measurement of the nanohardness distribution through the layer approximatively of 7 μm in width and the superalloys substrate, the results of the nanohardness showed the maximum values of 27 GPa and 13.5 GPa for the nitrided layer and the substrate, respectively. The surface protection from the nitrided layer proved a positive effect on the corrosion resistance of the DMLS specimens in the solution of 0.1 M Na2SO4 + 0.1 M NaCl at room temperature. The results of the tensile tests at 750 °C showed that the ion-nitriding process did not significantly affect the elevated-temperature tensile strength of the superalloy specimens produced with the DMLS technique.

A physically-based model for elevated temperature strength prediction of (TiBw + (Ti, Zr)5Si3)/Ti-6.5Al-2Zr-1Mo-1V composite

In this paper, effects of heat treatment temperature and soaking time on the microstructure and elevated temperature mechanical properties of the (TiBw+(Ti, Zr)5Si3)/Ti-6.5Al-2Zr-1Mo-1V composite were studied. A physically-based model capable of predicting microstructure and yield strength was established. Results show that acicular martensite forms in the transformed β microstructure, the size of (Ti, Zr)5Si3 increases obviously, while the morphology of TiBw remain unchanged. With the increase of heat treatment temperature, the fraction of primary α phase and (Ti, Zr)5Si3 decreases, while the fraction of βT increases. The yield strength and ultimate tensile strength of the composite are improved by 34% and 46% after heat treatment at 975 °C. The yield strength can be accurately predicted by the model. The mean relative error (MRE) of yield strength calculated by the model was 1.20% under the condition of heat treatment at 900 °C and 1050 °C. Using the model, martensitic strengthening accounts for the largest proportion in yield strength. The variation tendency of yield strength with temperature is predominantly decided by the variation tendency of martensitic strengthening. And the heat treatment temperature affects the yield strength through the factors including the fraction of βT and the lamellae thickness of martensite.

Tailoring precipitates in Mg–12Gd-3Y alloys by Sn addition to obtain superior elevated temperature mechanical properties

The precipitation phase was tailored by adding different Sn contents to the Mg-12Gd-3Y alloy to achieve multiphase composite strengthening. Adding different Sn contents has different effects on the microstructure and mechanical properties. Adding 1.0 wt% Sn to the Mg-12Gd-3Y alloy produced Mg5RE, Sn3RE5, and β′ precipitates, which were uniformly diffusely distributed within the alloy. When Sn elements were added up to 1.5 wt%, Mg5RE and Sn3RE5 precipitates increased and aggregated into lumps. The prepared Mg-12Gd-3Y-1.0Sn alloy exhibited excellent room and elevated temperature (ET) mechanical properties. The ultimate tensile strengths (UTS) of Mg-12Gd-3Y-1.0Sn alloy after extrusion and aging (E-A) treatment were 476, 415, 383 MPa at RT, 200 °C, and 250 °C, respectively. The fine grain size inhibits dislocation sliding, and the uniformly diffuse multi-scale phase structure inhibits the expansion of grain boundary cracks, resulting in excellent strength of Mg-12Gd-3Y-1.0Sn at room temperature (RT). The excellent ET strength of the Mg-12Gd-3Y-1.0Sn alloy is derived from the homogeneous diffusion of multi-scale heat-resistant precipitates within the alloy.

Eutectic MoNbTa(WC)x Composites with Excellent Elevated Temperature Strength

To develop materials with a promising utilization future in the extreme environments of aerospace, the MoNbTa(WC)x composites were prepared by vacuum arc melting, of which the crystal structure, microstructure, and compression properties at elevated temperature were investigated. The MoNbTa(WC)x composites had eutectic structures that consisted of body-centered cubic (BCC) phase and eutectoid structures. The lamellar fine eutectoid structures were composed of BCC-structured high entropy alloy (HEA) Mo-Nb-Ta-W and FCC-structured carbide Mo-Nb-Ta-W-C. It was demonstrated that the ductility and elevated temperature strength was enhanced simultaneously combined with the effect of eutectic structures and WC addition. The optimal true yield strength and true fracture strain reached 1205 MPa and 29.2% in MoNbTa(WC)0.9 at 1200 °C, meanwhile, the fracture strain at ambient temperature was 13.96%. Distinct strain hardening was observed at the initial deformation stage of MoNbTa(WC)0.9 at 1200 °C. The compression performances of MoNbTa(WC)x were superior in comparison with most refractory high entropy alloys.

Simultaneous intermetallics suppression and residual-stress relaxation of heat-resistant Nb-interlayer-inserted Ti-6Al-4V/Si3N4 joints via one-step transient liquid phase bonding and brazing

• One-step bonding of Ti-6Al-4V/Nb/Si 3 N 4 joints by simultaneous transient liquid phase bonding and brazing. • Suppression of intermetallics in Ti-6Al-4V/Nb side of joints by transient liquid phase bonding. • Tailoring of filler's thickness for sound interfacial bonding in Nb/Si 3 N 4 side of joints. • Enhancement of residual-stress relaxation with highly ductile Ag-rich filler. • Elevated temperature strength of joints determined by tradeoff between stress relaxation and filler's weakening. This work has successfully proposed a solution to produce robust Nb-interlayer-inserted Ti-6Al-4V/Si 3 N 4 joints optimized for a maximum operating temperature of 873 K; transient liquid phase bonding (TLPB) of Ti-6Al-4V/Nb side was carried out with Cu and Ni fillers to suppress brittle intermetallic compounds (IMCs), whereas brazing of Nb/Si 3 N 4 side was performed using a highly ductile Ti-added Ag-rich filler for effective residual-stress relaxation. A sound yet simple one-step bonding process incorporating simultaneous TLPB and brazing was achieved with a relatively short holding time of 10 min at 1213 K. TLPB of Ti-6Al-4V/Nb side with Cu and Ni foils of 2-µm-thick each as a laminated filler suppressed brittle Ti-based IMCs and developed a homogenized microstructure consisting mainly of (α + β)-Ti via isothermal solidification. Meanwhile, brazing of Nb/Si 3 N 4 side with 100-µm-thick SILVER-ABA filler (92.75Ag-5Cu-1Al-1.25Ti mass%) foil enhanced interfacial bonding with sufficient total Ti content and accommodated residual stress better than conventional eutectic Ag-Cu-based fillers, and it was verified by finite element analysis with consideration of materials’ temperature-dependent elasto-plastic properties. All joints with a bonding area of 10 mm × 10 mm were tested via symmetrical four-point bending from room temperature (RT) to 873 K fractured from Nb/Si 3 N 4 side. When re-heating the joints from RT to 673 K, fracture initiation gradually shifted from Si 3 N 4 towards interfacial-compounds/Si 3 N 4 interface and bending strengths maintained ∼220 MPa as weakening of SILVER-ABA filler was compensated by residual-stress relaxation in Si 3 N 4 . When tested at 873 K, joints fractured mainly across the Ag-rich solid solution in a ductile manner and bending strength degraded by ∼20% to 171 MPa as weakening of SILVER-ABA filler dominated.

Influence of Ni on the Microstructures and Mechanical Properties of Heat-Treated Al-Cu-Ce-Mn-Zr Alloys

In order to enhance the high-temperature mechanical performance to meet service requirements, the microstructures and tensile properties of heat-treated Al-8.4Cu-2.3Ce-1.0Mn-0.2Zr-xNi (x = 0, 0.5, 1.0, 2.0, 4.0 wt.%) were investigated. The metallographic analysis techniques have been used to examine the microstructural changes with different Ni contents. Results show that after adding 0.5% Ni to the Al-8.4Cu-2.3Ce-1.0Mn-0.2Zr alloy, the spheroidized Al7Cu4Ni phase is formed. With Ni content further increasing, the Al8CeCu4 and Al24MnCu8Ce3 phases disappear, and the nano-sized Al20Cu2Mn3 and Al2Cu phases decrease gradually. When Ni content reaches 4.0%, the Al3CuNi phase appears. It turns out that the addition of 0.5% Ni has significantly improved the tensile properties at 400 °C. The ultimate tensile strength, yield strength, and elongation of Al-8.4Cu-2.3Ce-1.0Mn-0.2Zr-0.5Ni alloy at 400 °C reach 103 MPa, 93 Mpa, and 18.0%, respectively, which makes the alloy possible to be employed at 400 °C. The intermetallic micro-skeleton, composed of thermostable Al8CeCu4, Al24MnCu8Ce3, Al16Cu4Mn2Ce, and Al7Cu4Ni phases at the grain boundaries as well as nano-sized Al20Cu2Mn3 and Al2Cu precipitates in the grains, contributes to the good elevated-temperature tensile strength. The fracture mechanism is changed from quasi-cleavage at ambient temperature to coexistence of quasi-cleavage and dimple at 400 °C.

Microstructures and elevated temperature mechanical properties of AlSi12Cu4Ni2 fabricated by laser powder bed fusion

The key properties of cast AlSi12Cu4Ni2 alloy are elevated temperature performance. In this paper, the microstructures and mechanical properties of a multiphase AlSi12Cu4Ni2 alloy formed by laser powder bed fusion (LPBF) were investigated from ambient temperature to 350 °C. The effects of LPBF parameters and microstructure in AlSi12Cu4Ni2 samples on mechanical properties were systematically studied. The best operating conditions (P = 300 W, v = 1800 mm/s) are obtained. The results show that fine equiaxed grains can be obtained by LPBF forming. The strengthening mechanisms were revealed. The thermal stability of the Al7Cu4Ni and Al3CuNi phases are conducive to the excellent elevated-temperature tensile strength. The high temperature wear properties of AlSi12Cu4Ni2 alloy were investigated. Abrasive wear is dominant wear mechanism of AlSi12Cu4Ni2 alloy at high temperatures.

Additive manufacturing of ductile refractory high-entropy alloys via phase engineering

Refractory high-entropy alloys (RHEAs) are developed for superior elevated-temperature strength and softening resistance. Additive manufacturing of RHEAs is attracting extensive attention because of their commendable potential in many applications. Yet, most additively manufactured RHEAs are brittle and their tensile properties at room temperature have rarely been reported. Here, tensile ductile RHEAs are fabricated by laser melting deposition for the first time. In the model TiZrHfNbx (x = 0.6, 0.8, 1.0, in molar ratios) RHEAs, the as-printed alloys have an equiaxed-grained microstructure without any special process control or additional treatment. Increasing Nb contents stabilizes the body-centered cubic phase and suppresses the ω phase formation. Such phase engineering strategy transforms the mechanical performance from brittle to ductile fracture. As a result, the as-printed TiZrHfNb variant exhibits a room temperature tensile yield strength of ∼1034 MPa and ductility of ∼18.5%. The solid-solution strengthening contributes to the high tensile yield strength, the local chemical fluctuations promote dislocation interactions and give rise to the large ductility. This work offers a new avenue for additive manufacturing of ductile RHEAs, which is conducive to their industrial application.

Achieving superior elevated-temperature strength of Mg-12Gd-3Y alloys by Nd addition

There is a tremendous demand for heat-resistant Mg alloys in aerospace and automotive applications. In this paper, different Nd contents are added to Mg-12Gd-3Y alloy to design the joint action of multiple rare earth (RE) elements to improve the elevated-temperature (ET) strength. The Mg-12Gd-3Y-1.0Nd alloy after extrusion and aging (E-A) process showed excellent strength and toughness matching at room temperature (RT), 200 °C, and 250 °C. The E-Aed Mg-12Gd-3Y-1.0Nd alloy showed ultimate tensile strength (UTS), tensile yield strength (TYS), and elongation (EL) of 440 MPa, 312 MPa, and 6.2% at RT. The E-Aed Mg-12Gd-3Y-1.0Nd alloy showed UTS, TYS, and EL of 405 MPa, 306 MPa, and 12.6% at 200 °C. The E-Aed Mg-12Gd-3Y-1.0Nd alloy showed UTS, TYS, and EL of 382 MPa, 303 MPa, and 19.4% at 250 °C. The addition of Nd elements reduces the solid solubility of Gd, and Y in the Mg matrix, thus precipitating many Mg5RE and β′ phases in the alloy. The excellent mechanical properties of Mg-12Gd-3Y-1.0Nd alloy after E-A treatment come from the fine grain size, segregation at grain boundaries (GBs), and delicate dispersed second phases. The fine grain size is beneficial to inhibit crack expansion, allowing it to consume more energy during the expansion process and improve strength. Both grain boundary segregation and diffusely distributed second phase can effectively inhibit grain boundary sliding and enhance strength.