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Hot compression tests were conducted using a Gleeble 3500 thermomechanical simulator at temperatures ranging from 1,000 to 1,200°C with the strain rate ranging from 0.1 to 10 s−1. Electron backscatter diffraction (EBSD) technique was employed by investigating the microstructure evolution during hot deformation. Microstructure observations reveal th...
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... specimen for EBSD investigation was electropolished in a 20% H 2 SO 4 and 80% methanol solution under 15-30 V for 5-15 s at room temperature. Figure 1 shows the original microstructure of the solution-treated superalloy at 1,200 ° C for 120 min by EBSD. The OIM map of the solution-treated superalloy is shown in Figure 1A. ...
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... 1 shows the original microstructure of the solution-treated superalloy at 1,200 ° C for 120 min by EBSD. The OIM map of the solution-treated superalloy is shown in Figure 1A. The grain boundaries with misorientation angles below 10 ° are defined as low-angle grain boundaries (LAGBs). ...
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... grain boundaries with misorientation angles between 10 ° and 15 ° are defined as medium-angle grain boundaries (MAGBs) ( Wang et al., 2008;Li et al., 2011;Zhang et al., 2015a). In Figure 1A, the black and blue lines represent HAGBs and MAGBs, respectively. Moreover, red and green lines represent LAGBs. ...
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... red and green lines represent LAGBs. It is noted that equiaxed grains with HAGBs are presented in the solution-treated superalloy, and some annealing twins also exist, as shown in Figure 1A. The grain size distributions are shown in Figure 1B. ...
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... is noted that equiaxed grains with HAGBs are presented in the solution-treated superalloy, and some annealing twins also exist, as shown in Figure 1A. The grain size distributions are shown in Figure 1B. The average grain size of the solution-treated superalloy is 88.4 μm. Figure 2 shows typical true stress-strain curves of different temperatures at a strain rate of 0.1 s −1 and different strain rates at a temperature of 1,100 ° C. It can be seen from Figure 2 that the shape of the flow curves is significantly affected by the temperature and strain rate. ...
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... microstructures of the Co-Ni-Cr-W-based superalloy deformed to the true strain of 0.7 at different temperatures with the strain rate of 0.1 s −1 were examined by EBSD. to 1,150 ° C, the recrystallized microstructures become uniformly equiaxed grains, as shown in Figure 3D1. It is also found that the grain size begins to coarsen at 1,150 ° C. The degree and grain size of DRX increase with the increase of deformation temperature, as shown in Figures 3A1-E1. ...
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... microstructures of the Co-Ni-Cr-W-based superalloy deformed to the true strain of 0.7 at different temperatures with the strain rate of 0.1 s −1 were examined by EBSD. to 1,150 ° C, the recrystallized microstructures become uniformly equiaxed grains, as shown in Figure 3D1. It is also found that the grain size begins to coarsen at 1,150 ° C. The degree and grain size of DRX increase with the increase of deformation temperature, as shown in Figures 3A1-E1. It is generally known that the grain boundary migration rate is related to the deformation temperature. ...
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Citations
... Nickel-based superalloys usually undergo work hardening, dynamic recovery (DRV), and dynamic recrystallization (DRX) during thermal deformation. [6] DRX is an effective way to refine grains and soften metals, and can reduce the deformation resistance of materials through DRX. [7] Therefore, DRX behavior is one of the issues that need to be considered in thermal compression tests. ...
Incoloy 800H alloy has excellent high‐temperature mechanical properties and broad application prospects. However, the dynamic recrystallization (DRX) behavior of this alloy at different deformations has been little studied. The thermal deformation characteristics and DRX mechanisms of Incoloy 800H alloy are studied by thermal compression tests. Quantitative analysis of grain size, DRX fraction, misorientation distribution, and twin boundaries under different deformation degrees is conducted using electron‐backscattered diffraction. Furthermore, the evolution characteristics of dislocations and grains are observed through transmission electron microscopy. It is found that the proportion of DRX improves with increasing deformation significantly. In the DRX process, discontinuous DRX (DDRX) is the main nucleation mechanism, while continuous DRX (CDRX) serves as an auxiliary nucleation mechanism. As the deformation increases, the CDRX + DDRX mechanisms can also be observed simultaneously in the high‐density dislocation region near the grain boundary. In addition, the ratio of ∑3 boundaries first decreases and then increases as the deformation increases. The initial twins gradually disappear due to the increase in deformation, and new twins are formed within the DRX grains. Twins can promote grain boundary bulging, provide more nucleation sites for DRX, and have a significant promoting effect on DRX.
... Representative bioimplants include artificial joints for patients whose bones are damaged owing to aging or accidents. The metal materials predominantly used for artificial joints are cobalt-chromium-molybdenum alloys owing to their excellent mechanical properties, corrosion resistance, and biocompatibility [1][2][3][4]. Co-Cr-Mo alloys are known to have two structures: face-centered cubic (FCC) γ-phase at high temperatures and hexagonal close-packed (HCP) ε-phase at low temperatures. Many research results have demonstrated that adding nitrogen considerably changes the phase transformation behavior. ...
We investigated the improvement of mechanical properties of biograde Co–28Cr–6Mo–0.11N alloy prepared by electron beam melting through grain refinement via multiple reverse transformations. While the effects of single and double reverse transformation treatments on the microstructure have been investigated in previous studies, we investigated the effects of multiple reverse transformation heat treatments. The particle size was refined to 1/4, and the yield strength, tensile silence strength, and elongation were enhanced to 655 MPa, 1234 MPa, and 45%, respectively, satisfying ASTM F75 standards. Moreover, a mixed phase of ε and γ was observed to provide higher yield strength than a single γ structure. The dominant behavior in the γ → ε phase transformation at 1073 K was obvious. Grain growth was suppressed by the grain-boundary pinning effect of the Cr2N phase during reverse transformation to the γ phase. Because no fracture was caused by precipitates such as σ, η, and Cr2N phases, the influence of the precipitates on the tensile properties was small.
... This is because the higher deformation temperature accelerates dislocation annihilation and rearrangement, which promotes the transition from LAGBs to HAGBs through MAGBs. It has been reported that the presence of MAGBs is necessary for the occurrence of subgrain rotation, which is an important feature for the occurrence of CDRX [55,56]. Subgrain boundaries gradually form LAGBs by continuously absorbing dislocations, and finally, new grains are formed. ...
Lightweight structural alloys have broad application prospects in aerospace, energy, and transportation fields, and it is crucial to understand the hot deformation behavior of novel alloys for subsequent applications. The deformation behavior and microstructure evolution of a new Al-Zn-Mg-Li-Cu alloy was studied by hot compression experiments at temperatures ranging from 300 °C to 420 °C and strain rates ranging from 0.01 s−1 to 10 s−1. The as-cast Al-Zn-Mg-Li-Cu alloy is composed of an α-Al phase, an Al2Cu phase, a T phase, an η phase, and an η′ phase. The constitutive relationship between flow stress, temperature, and strain rate, represented by Zener–Hollomon parameters including Arrhenius terms, was established. Microstructure observations show that the grain size and the fraction of DRX increases with increasing deformation temperature. The grain size of DRX decreases with increasing strain rates, while the fraction of DRX first increases and then decreases. A certain amount of medium-angle grain boundaries (MAGBs) was present at both lower and higher deformation temperatures, suggesting the existence of continuous dynamic recrystallization (CDRX). The cumulative misorientation from intragranular to grain boundary proves that the CDRX mechanism of the alloy occurs through progressive subgrain rotation. This paper provides a basis for the deformation process of a new Al-Zn-Mg-Li-Cu alloy.
