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Deformation behaviour in the Nickel-base superalloy 625 has been studied by tensile testing at four temperatures: 295, 223, 173 and 77 K. The microstructure has been investigated using TEM, FIB-SEM, EBSD and ECCI techniques. Deformation in the alloy turns out to be a competitive course of events between at least two deformation mechanisms, namely dislocation slip and deformation twinning. Slip is the predominant deformation mechanism at higher temperatures. While at 77 K, deformation induced twinning gives an extra degree of freedom as one of the main deformation mechanisms, i.e., the material shows a twin induced plasticity, TWIP, behaviour. Ab initio calculations indicate that the influence of cryogenic/sub-zero temperatures on the stacking fault energy of this alloy can be limited and therefore the formation of deformation twins cannot be determined solely by the stacking fault energy. The results implies that critical strain and strain hardening rate influences the deformation twinning onset and twinning rate. [ABSTRACT FROM AUTHOR]

Deformation behaviour in the Nickel-base superalloy 625 has been studied by tensile testing at four temperatures: 295, 223, 173 and 77 K. The microstructure has been investigated using TEM, FIB-SEM, EBSD and ECCI techniques. Deformation in the alloy turns out to be a competitive course of events between at least two deformation mechanisms, namely dislocation slip and deformation twinning. Slip is the predominant deformation mechanism at higher temperatures. While at 77 K, deformation induced twinning gives an extra degree of freedom as one of the main deformation mechanisms, i.e., the material shows a twin induced plasticity, TWIP, behaviour. Ab initio calculations indicate that the influence of cryogenic/sub-zero temperatures on the stacking fault energy of this alloy can be limited and therefore the formation of deformation twins cannot be determined solely by the stacking fault energy. The results implies that critical strain and strain hardening rate influences the deformation twinning onset and twinning rate. [ABSTRACT FROM AUTHOR]

Micro-alloying of Ca in Mg–1Zn-0.3Nd (wt.%) alloy is found to significantly improve tensile strength and process high ductility simultaneously. It closely correlates with grain refinement and the increased coherent nano Mg 2 Ca and (Mg, Zn) 3 Nd precipitates. Ca addition enhances alloying elements co-segregation at grain boundary and promotes grain refinement. Furthermore, nano Mg 2 Ca particles induced by Ca addition can significantly promote the precipitation of (Mg, Zn) 3 Nd phase via the heterogeneous nucleation mechanism owing to their excellent coherency relationship and ultimately lead to the pronounced strengthening effect. In addition, both fine grains and the coherent characteristics between Mg 2 Ca, (Mg, Zn) 3 Nd, and Mg matrix facilitate strain coordination during deformation and yield relatively high ductility. • Micro-alloying Ca in Mg–Zn-Nd alloy significantly increases tensile strength while keeping high ductility. • Ca addition enhances the co-segregation of alloying elements at grain boundary and refines grain size. • Nano Mg 2 Ca particles and the induced (Mg, Zn) 3 Nd precipitates with excellent coherency relationship lead to the pronounced strengthening effect. [ABSTRACT FROM AUTHOR]

Here, the microstructure and mechanical properties are investigated for the designed Mg-4Gd-0.5Zr-xZn (x = 0, 0.2, 0.5, 1.0 and 1.5 wt%) alloys with special emphasis on the effect of Zn. The results show that the designed Mg-4Gd-0.5Zr-xZn alloys exhibit the exceptional ductility. Among them, the Mg-4Gd-0.5Zr-1.0Zn and Mg-4Gd-0.5Zr-1.5Zn alloys show the elongation to fracture as high as 35.2% and 32.5%. Furthermore, a good strength-ductility balance is achieved in the alloys, which is basically ascribed to the grain refinement, texture softening and the precipitation of Zn-containing second phases. As Zn content increases from 0 to 1.5 wt%, the grain sizes of the extruded Mg-Gd-Zr-Zn alloys decrease from 6.02 to 3.05 μm, while the maximum texture intensity decreases from 11.13 to 5.24 m.r.d. Moreover, the Zn 2 Zr 3 and Mg 3 Zn 3 Gd 2 precipitates, which exhibit the completely coherent and semi-coherent orientation relationship with Mg matrix, are induced by the addition of Zn. These coherent and semi-coherent precipitates lead to noticeable strengthening effect and are not easy to become the source of crack, contributing to the high ductility in Mg-4Gd-0.5Zr-1.0Zn and Mg-4Gd-0.5Zr-1.5Zn. • The designed Mg-4Gd-0.5Zr-xZn (x = 0, 0.2, 0.5, 1.0 and 1.5 wt%) alloys all exhibit the exceptional ductility. • The Mg-4Gd-0.5Zr-1.0Zn and Mg-4Gd-0.5Zr-1.5Zn alloys exhibit a good strength-ductility balance. • The orientation relationship between the precipitates and Mg matrix was studied. [ABSTRACT FROM AUTHOR]

The micro addition of Ca is demonstrated to noticeably increase the strength and ductility of Mg–Zn–Ce alloy, which is closely correlated with the enhanced alloying segregation at grain boundary. Addition of Ca is found to yield the enhanced Zn segregation and co-segregation of Zn, Ce, and Ca. The mechanism behind is that Ca decreases the segregation energy while promoting the diffusion process of Zn, ultimately accelerating the thermodynamic and kinetic process of segregation. The enhanced alloying segregation induced by Ca effectively stabilizes grain boundary, which contributes to the refined grain size, retardant mobility of dislocation and ultimately improved strength. Furthermore, the intergranular fracture energy can be noticeably increased by Ca owing to the promoted alloying element segregation at grain boundary, which contributes to the improved grain boundary cohesion and ductility. The controllable segregation at grain boundary via alloying is intended to contribute to the development of advanced magnesium alloys. • The micro Ca addition noticeably increases the strength and ductility of Mg–Zn–Ce alloy. • Ca decreases the segregation energy while increasing the diffusion rate of Zn, yielding the enhanced alloying element segregation. • The enhanced alloying segregation stabilizes grain boundary and increases the intergranular fracture energy. [ABSTRACT FROM AUTHOR]

In this study, the nano-micron TiB 2 -Al 2 Y/Mg-9Y-0.6La composites were prepared by introducing nano-TiB 2 and micron-Al 2 Y particles into Mg-9Y-0.6La alloys via the addition of nano-TiB 2 /Al master alloy. The introduction of nano-micron TiB 2 -Al 2 Y particles refined the α-Mg grains, weakened the basal texture, and promoted the dynamic recrystallization of the composites. The yield strength and tensile strength of the 4.31 wt% TiB 2 -Al 2 Y/Mg-9Y-0.6La composite were increased by 69 MPa and 65 MPa, respectively, compared with the Mg-9Y-0.6La alloy. The main strengthening mechanisms of the composites were fine grain strengthening, Orowan strengthening, and coefficient of thermal expansion strengthening caused by the TiB 2 -Al 2 Y particles. [ABSTRACT FROM AUTHOR]

In this study, the nano-micron TiB 2 -Al 2 Y/Mg-9Y-0.6La composites were prepared by introducing nano-TiB 2 and micron-Al 2 Y particles into Mg-9Y-0.6La alloys via the addition of nano-TiB 2 /Al master alloy. The introduction of nano-micron TiB 2 -Al 2 Y particles refined the α-Mg grains, weakened the basal texture, and promoted the dynamic recrystallization of the composites. The yield strength and tensile strength of the 4.31 wt% TiB 2 -Al 2 Y/Mg-9Y-0.6La composite were increased by 69 MPa and 65 MPa, respectively, compared with the Mg-9Y-0.6La alloy. The main strengthening mechanisms of the composites were fine grain strengthening, Orowan strengthening, and coefficient of thermal expansion strengthening caused by the TiB 2 -Al 2 Y particles. [ABSTRACT FROM AUTHOR]

The mechanical properties of as-extruded Mg-11Gd-5Y-2Zn-0.7Zr (GWZ1152) alloy were systematically studied with respect to their microstructures at room and high temperatures. It exhibited excellent ultimate tensile strength (UTS) of 365 MPa at room temperature (RT), while it maintained relatively high UTS as the temperatures increased to 250 °C (342 MPa), 300 °C (337 MPa) and 350 °C (278 MPa) with a strain rate of 1.85 × 10−3 s−1. The microstructural characterizations revealed that such outstanding heat resistance is mainly attributed to (i) the fine dynamic recrystallized (DRXed) grains and strongly textured un-DRXed grains, (ii) the block-shaped LPSO phase and the nano-scale β precipitates, (iii) the nano-spaced basal LPSO/SFs. Compared to other heat-resistant Mg alloys, our intrinsic chemistry properties contribute to the superior high-temperature mechanical properties of GWZ1152 alloy. For the deformation modes at RT, the dislocations were mainly generated and accumulated on the block-shaped LPSO, followed by cracking and propagation. At 250 °C and 300 °C, non-basal slip inside the coarse un-DRXed was generated, the cracks and fractures were initiated along the slip trace. The main deformation mechanism of GWZ1152 alloy at 350 °C was grain boundary sliding, cracks usually occurred at grain boundaries. • Mg-11Gd-5Y-2Zn-0.7Zr alloy exhibited excellent ultimate tensile strength at 25 °C, 250 °C, 300 °C and 350 °C. • The deformation modes of the alloys were systematically studied at different temperatures. • The relationship between the deformation modes and mechanical properties were discussed at room and high temperatures. [ABSTRACT FROM AUTHOR]

In this study, a novel alloy designing concept, refining grain size and depressing intergranular deformation (inter-GD) simultaneously, is put forward to prepare the Mg alloy with preeminent strength-ductility synergy. A basic alloy, Mg–1Sb–1Mn (SM11), is extruded at 220 °C to attain ultrafine microstructure. Thereafter, the co-addition of Sn and Zn is conducted to inhibit the inter-GD which is the softening mechanism of the ultrafine-grained SM11 alloy. Compared with SM11 alloy, the tensile yield strength, ultimate tensile strength and compressive yield strength of Mg–1Sb–1Mn–1Sn-0.2Zn (SMTZ1110) alloy increases from 196 MPa, 245 MPa and 193 MPa–301 MPa, 361 MPa and 273 MPa MPa respectively, without the loss of tensile elongation. With the co-addition of Sn and Zn, the grain size is refined from 1.07 μm to 0.82 μm. The narrower network spacing of Mg 3 Sb 2 in the as-cast SMTZ1110 alloy promotes particle-stimulation nucleation during extrusion, resulting in finer grains of the extruded SMTZ1110 alloy. The in-situ experiments unveil that the deformation mechanisms in the SM11 alloy are mixed inter-GD and intragranular deformation, while the deformation mechanisms of the SMTZ1110 alloy shift to the modes predominated by intragranular deformation. The transmission electron microscope results show the segregations of Sn and Zn which pin and stabilize grain boundaries and further depress the inter-GD. Under the combining effects of depressing inter-GD and fine-grain strengthening, the strength of the extruded SMTZ1110 alloy is significantly improved. This study provides new insight into the development of Mg alloy with an excellent balance between strength and ductility. [ABSTRACT FROM AUTHOR]

The influence of Y on the microstructure and mechanical properties of Mg-4Gd-0.5Zr alloy is investigated. The results show that by increasing the Y content from 0 to 1.2 wt%, the grain size gradually reduces in both as-cast and as-extruded state, whilst the maximum texture intensity noticeably decreases. In addition, nanoscale particles of Mg 24 (Gd, Y) 5 phase start to precipitate at relatively high Y content. The designed Mg-4Gd-0.5Zr- x Y (x = 0, 0.5, 0.8 and 1.2 wt%) alloys exhibit exceptional ductility and moderate strength. As increasing Y content from 0 to 1.2 wt%, the elongation of Mg-4Gd-0.5Zr-based alloy decreases slightly from 44.6% to 39.0% along the extrusion direction, while the yield strength substantially increases from 87.9 to 134.1 MPa. The main strengthening mechanisms are demonstrated to be solid solution strengthening in combination with the grain refinement. Furthermore, the exceptional ductility maintained in Y-containing alloys is found to closely correlate with the activation of pyramidal slip. • The designed Mg-4Gd-0.5Zr- x Y (x = 0, 0.5, 0.8 and 1.2 wt%) alloys exhibit high ductility and moderate strength. • Massive nanoscale particles of Mg 24 (Gd,Y) 5 phase start to precipitate at relatively high Y content. • The addition of Y in the Mg-4Gd-0.5Zr alloy promotes the activation of pyramidal slip. [ABSTRACT FROM AUTHOR]

Herein, the microstructure and mechanical properties of newly developed Mg-4Gd-0.5Zr-xNd (x = 0, 0.5, 1 and 1.5 wt%) extruded alloys are investigated systematically. All the extruded alloys exhibit the complete dynamically recrystallized (DRXed) microstructure. The addition of Nd weakens the texture and decreases the intensity of double peak texture apparently from 13.08 to 8.78 m.r.d (at 1.5 wt%). With increasing the Nd content from 0 to 1.5 wt%, the grain sizes of Mg-4Gd-0.5Zr alloys gradually decrease from 11.02 to 7.90 μm, accompanying with massive fine dispersed Mg 41 Nd 5 and Mg 12 (Nd,Gd) particles in the matrix. In terms of mechanical properties, the yield strength increases substantially without the loss of elongation-to-failure basically as increasing the Nd content from 0 to 1.5 wt%. Of those, the Mg-4Gd-0.5Zr-1.5Nd alloy possesses the highest yield strength (160.2 MPa), which is 82.3% higher than that of Mg-4Gd-0.5Zr alloy (87.9 MPa). Meanwhile, the Mg-4Gd-0.5Zr-1.5Nd alloy presents an outstanding ductility (39.3%). • With the increase of Nd content, the YS of VK41 alloy increases substantially without the loss of EL. • The VK41-1.5Nd alloy possesses the highest YS of 160.2 MPa and outstanding EL of 39.3%. • Massive fine dispersed Mg 41 Nd 5 and Mg 12 (Nd,Gd) particles exist in the matrix. [ABSTRACT FROM AUTHOR]