Constitutive Characteristics, Microstructure, and Texture Evolution of As-Cast 42CrMo Alloy in Nonisothermal Multipass Compression

The nonisothermal multipass deformation behavior of as-cast 42CrMo alloy was studied with declining temperature, constant pass strain, varying strain rate, and interval time. The stresses are used to develop the constitutive model. As the finishing temperature increases from 990°C to 1070°C, the stress decreases gradually and the softening effect increases, which results in a large grain size and inhomogeneous microstructure. The low angle grain boundaries transform into high angle grain boundaries through absorbing dislocations. The noticeable stress softening in a high strain rate is attributed to the thermal softening, dynamic recovery, and dynamic recrystallization. The thermal softening is no longer considered to be the main interpass softening mechanism at a low strain rate. The interval time has a negligible effect on the stress, but the significant changes in grain size and texture component are caused by the interpass softening. The average grain size is approximately 40 μm, and the distorted grain boundaries and small fine grains are found in the interval times of 0.5–5 s, implying the dynamic recovery and grain growth. The near {001}<110> and {110}<112> orientation exerts an important influence on the grain refinement.

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Superplasticity and Microstructural Evolution of a Large-Grained Mg Alloy

10.1115/imece2000-1818 ◽

2000 ◽

Author(s):

Yi Liu ◽

Kelly Shue ◽

Xin Wu ◽

Zhicheng Li ◽

Yongbo Xu

Keyword(s):

Grain Size ◽

Electron Microscope ◽

Strain Rate ◽

Grain Boundaries ◽

Grain Growth ◽

Large Angle ◽

Dislocation Creep ◽

Rate Dependent ◽

Average Grain Size ◽

Elongation To Failure

Abstract Commercial Mg-3Al-Zn alloys (AZ31) with initial large grains (∼250μm) has been found superplastic at a strain rate of 0.5×10−2s−1 and at 350–500 C. The maximum elongation to failure of 170% at 500°C was obtained. Scanning electron microscope observations with electron back-scattering diffraction technique (SEM-EBSD) indicate that during deformation significant grain size reduction occurred, the average grain size reduced from about 250μm before deformation to about 50μm after deformation at temperatures from 300 C to 400°C, it reduced to about 100μm if deformed at above 400°C. The observed grain refinement at lower temperature and grain growth at higher temperature during the superplastic deformation is believed to be the result of the competing processes between dynamic recrystallization and dynamic grain growth, which are temperature and strain rate dependent. Transmission electron microscope (TEM) observations indicates that most of the grain boundaries are large-angle grain boundaries, though small amount of small-angle grain boundaries are also observed. The density of dislocations in the grains is very low in these superplasticlly deformed samples. It is evident that grain boundary played a role as the source and sink of the dislocation, being responsible for combined dislocation creep and diffusional creel. Therefore, the very large elongation obtained at the very high strain rates and high temperatures is attributed to dynamic dislocation hardening, recovery and recrystallization.

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Superplastic Behavior of a Cu-Cr-Zr Alloy Subjected to ECAP

Materials Science Forum ◽

10.4028/www.scientific.net/msf.838-839.404 ◽

2016 ◽

Vol 838-839 ◽

pp. 404-409

Author(s):

Roman Mishnev ◽

Iaroslava Shakhova ◽

Andrey Belyakov ◽

Rustam Kaibyshev

Keyword(s):

Grain Size ◽

Dislocation Density ◽

Strain Rate ◽

Temperature Interval ◽

Rate Sensitivity ◽

Tensile Tests ◽

Superplastic Behavior ◽

Average Grain Size ◽

Gauge Section ◽

Zr Alloy

A Cu-0.87%Cr-0.06%Zr alloy was subjected to equal channel angular pressing (ECAP) at a temperature of 400 °C up to a total strain of ~ 12. This processing produced ultra-fine grained (UFG) structure with an average grain size of 0.6 μm and an average dislocation density of ~4×1014 m-2. Tensile tests were carried out in the temperature interval 450 – 650 °C at strain rates ranging from 2.8´10-4 to 0.55 s-1. The alloy exhibits superplastic behavior in the temperature interval 550 – 600 °C at strain rate over 5.5´10-3 s-1. The highest elongation-to-failure of ~300% was obtained at a temperature of 575 °C and a strain rate of 2.8´10-3 s-1 with the corresponding strain rate sensitivity of 0.32. It was shown the superplastic flow at the optimum conditions leads to limited grain growth in the gauge section. The grain size increases from 0.6 μm to 0.87 μm after testing, while dislocation density decreases insignificantly to ~1014 m-2.

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What is Behind the Inverse Hall-Petch Behavior in Nanocrystalline Materials?

MRS Proceedings ◽

10.1557/proc-976-0976-ee01-04 ◽

2006 ◽

Vol 976 ◽

Author(s):

Christopher Carlton ◽

P. J. Ferreira

Keyword(s):

Grain Size ◽

Yield Strength ◽

Strain Rate ◽

Grain Boundaries ◽

Nanocrystalline Materials ◽

Critical Value ◽

Petch Relationship ◽

And Diffusion ◽

Critical Grain Size

AbstractAn inverse Hall-Petch effect has been observed for nanocrystalline materials by a large number of researchers. This result implies that nanocrystalline materials get softer as grain size is reduced below a critical value. Postulated explanations for this behavior include dislocation based mechanisms and diffusion based mechanisms. In this paper, we report an explanation for the inverse Hall-Petch effect based on the statistical absorption of dislocations by grain boundaries, showing that the yield strength is both dependent on strain rate and temperature, and that it deviates from the Hall-Petch relationship at a critical grain size.

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Effect of Mo doping on the microstructure and properties of an Fe36Ni Invar alloy

International Journal of Modern Physics B ◽

10.1142/s0217979220502975 ◽

2020 ◽

Vol 34 (31) ◽

pp. 2050297

Author(s):

Liming Dong ◽

Zhaopeng Yu ◽

Xianjun Hu ◽

Fang Feng

Keyword(s):

Grain Size ◽

Thermal Expansion ◽

Grain Boundaries ◽

Coefficient Of Thermal Expansion ◽

Solution Temperature ◽

Microstructure And Properties ◽

Invar Alloys ◽

Average Grain Size ◽

Mo Content ◽

Hot Rolled

The effects of doping with different Mo contents on the microstructure and properties of Fe36Ni Invar alloys were investigated. The results show that when 0.9 wt.% Mo and 1.8 wt.% Mo were added to Fe36Ni, the tensile strengths of the hot rolled alloys were 46 and 61 MPa higher than that of the 0 wt.% Mo sample, respectively. With an increase in Mo content from 0.9 to 1.8 wt.%, the solution temperature of the highest hardness after heat treatment increased from 800[Formula: see text]C to 850[Formula: see text]C, respectively. The addition of 0.9 wt.% Mo refined the average grain size from 37 to 15 [Formula: see text]m, and an excessive amount of Mo (1.8 wt.%) did not refine the grains further. After Mo was added, the precipitates on the original grain boundaries changed into nanoprecipitates dispersed in the grain boundaries and inside the grains. Mo was present in the alloy in the form of a carbide and in solid solution, which affected the magnetic lattice effect and increased the thermal expansion coefficient of the alloy. However, upon comparing the samples doped with 0 wt.% Mo, 0.9 wt.% Mo and 1.8 wt.% Mo, it was found that the addition of 0.9 wt.% Mo not only refined the grain size and improved the mechanical properties of the alloy but also led to a low coefficient of thermal expansion (CTE) over the range from 20[Formula: see text]C to 300[Formula: see text]C.

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Microstructure and Mechanical Properties of 4Al Alumina-Forming Austenitic Steel after Cold-Rolling Deformation and Annealing

Materials ◽

10.3390/ma13122767 ◽

2020 ◽

Vol 13 (12) ◽

pp. 2767 ◽

Cited By ~ 1

Author(s):

Chenchen Jiang ◽

Qiuzhi Gao ◽

Hailian Zhang ◽

Ziyun Liu ◽

Huijun Li

Keyword(s):

Grain Size ◽

Cold Rolling ◽

Grain Boundaries ◽

Austenitic Steel ◽

Rolling Reduction ◽

X Ray Diffraction ◽

Transmission Electron ◽

Cold Rolling Reduction ◽

Average Grain Size ◽

Cold Rolled

Microstructural evolutions of the 4Al alumina-forming austenitic steel after cold rolling with different reductions from 5% to 30% and then annealing were investigated using electron backscattering diffraction (EBSD), X-ray diffraction (XRD) and transmission electron microscopy (TEM). Tensile properties and hardness were also measured. The results show that the average grain size gradually decreases with an increase in the cold-rolling reduction. The low angle grain boundaries (LAGBs) are dominant in the cold-rolled samples, but high angle grain boundaries (HAGBs) form in the annealed samples, indicating that the grains are refined under the action of dislocations. During cold rolling, high-density dislocations are initially introduced in the samples, which contributes to a large number of dislocations remaining after annealing. With the sustaining increase in cold-rolled deformation, the samples exhibit more excellent tensile strength and hardness due to the decrease in grain size and increase in dislocation density, especially for the samples subjected to 30% cold-rolling reduction. The contribution of dislocations on yield strength is more than 60%.

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Effect of Deformation Route and Sc and Zr Addition on Ultra-Fine Grain Formation and Superplasticity in Al-Mg Alloys

Materials Science Forum ◽

10.4028/www.scientific.net/msf.519-521.847 ◽

2006 ◽

Vol 519-521 ◽

pp. 847-852

Author(s):

Suk Bong Kang ◽

Jae Woon Kim ◽

Hyoung Wook Kim

Keyword(s):

Grain Size ◽

Strain Rate ◽

Deformation Process ◽

Mg Alloys ◽

Fine Grained ◽

Loading Direction ◽

Zr Addition ◽

Average Grain Size ◽

Multiple Deformation ◽

Al Mg Alloys

Recently the method for obtaining ultra-fine grained metallic materials has developed using severe plastic deformation (SPD), such as equal channel angular pressing (ECAP), accumulative roll bonding (ARB), torsion straining, and warm multiple deformation (WMD) etc. In order to enhance thermal stability of ultra-fine grained aluminum alloys manufactured by SPD process, the addition of Sc and Zr elements has been considered to devise fine Al3Sc, Al3Zr and Al3(Scx Zr1-x) precipitates for inhibiting the grain growth. In this study, the microstructure evolution has been investigated in Al-Mg alloys with and without Sc and Zr addition during the warm multiple deformation process. In addition Al-Mg alloys were compressed at a strain rate of 10-1 sec-1 by two different routes, that is, route A and route B. Route A is to rotate the specimen throughout 90o around the vertical axis of loading direction at every pass. Route B is to rotate the specimen throughout 90o around the parallel axis of loading direction and then rotate it again as route A. The specimen deformed by route B had finer grain size and more uniform distribution of grains than those deformed by route A. When the warm multiple deformation process repeated up to 8 passes at 673 K, the specimen consisted of ultra-fine grained structure with the average grain size less than 3 μm. The superplastic behavior can also be observed at the high strain rate and low temperature regime.

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Characterization of Zinalco Alloy Superplastically Deformed Using Orientation Imaging Microscopy

MRS Proceedings ◽

10.1557/proc-1242-s4-41 ◽

2009 ◽

Vol 1242 ◽

Cited By ~ 1

Author(s):

Ramos A. Mitsuo ◽

Martínez F. Elizabeth ◽

Negrete S. Jesús ◽

Torres-Villaseñor G.

Keyword(s):

Grain Size ◽

Grain Boundary ◽

Grain Boundaries ◽

Superplastic Deformation ◽

Orientation Imaging Microscopy ◽

Grain Boundary Sliding ◽

Boundary Misorientation ◽

Average Grain Size ◽

Grain Boundary Misorientation ◽

Misorientation Angles

ABSTRACTZinalco alloy (Zn-21mass%Al-2mass%Cu) specimens were deformed superplastically with a strain rate (ε) of 1×10-3 s-1 at homologous temperature (TH) of 0.68 (5 ). It was observed neck formation that indicate nonhomegeneus deformation. Grain size and grain boundaries misorientation changes, due superplastic deformation, were characterized by Orientation Imagining Microscopy (OIM) technique. It was studied three regions in deformed specimens and the results were compared with the results for a specimen without deformation. Average grain size of 1 mm was observed in non-deformed specimen and a fraction of 82% for grain boundary misorientation angles with a grain boundaries angles between 15° and 55° was found. For deformed specimen, the fraction of angles between 15° and 55° was decreced to average value of 75% and fractions of low angle (<5°) and high angle (>55°) misorientations were 10% and 15% respectively. The grain size and high fraction of grain boundary misorientation angles between 15° and 55° observed in the alloy without deformation, are favorable for grain rotation and grain boundary sliding (GBS) procces. The changes observed in the fraction of favorable grain boundary angles during superplastic deformation, shown that the superplastic capacity of Zinalco was reduced with the deformation.

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Influence of Annealing Time on Microstructure of Ni-W Alloys

Materials Science Forum ◽

10.4028/www.scientific.net/msf.747-748.613 ◽

2013 ◽

Vol 747-748 ◽

pp. 613-618

Author(s):

Qiao Zhang ◽

Shu Hua Liang ◽

Chen Zhang ◽

Jun Tao Zou

Keyword(s):

Electron Microscopy ◽

Solid Solution ◽

Grain Size ◽

Grain Boundaries ◽

Annealing Time ◽

Single Phase ◽

X Ray Diffraction ◽

X Ray ◽

Average Grain Size ◽

Scanning Electron

The as-cast Ni-W alloys with 15wt%W, 25wt%W and 30wt%W were annealed in hydrogen at 1100. The effect of the annealing time on the microstructure of Ni-W alloys was studied, and the phase constituents and microstructure of annealed Ni-W alloys were characterized by the X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results showed that no any phase changed for Ni-15%W, Ni-25%W and Ni-30%W alloys annealed for 60 min, 90 min and 150 min, which were still consisted of single-phase Ni (W) solid solution. However, microstructure had a significant change after annealing. With increase of annealing time, the microstructure of Ni-15%W alloy became more uniform after annealing for 90 min, and the average grain size was 95μm, whereas the grain size of Ni-15%W alloy increased significantly after annealing for 150 min. For Ni-25%W and Ni-30%W, there was no obvious change on the grain size with increase of annealing time, and the amount of oxides at grain boundaries gradually reduced. After annealing for 150 min, the impurities at grain boundaries almost disappeared. Subsequently, the annealing at 1100 for 150 min was beneficial for the desired microstructure of Ni-25%W and Ni-30%W alloys.

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Variable Elastic-Plastic Properties of the Grain Boundaries and Their Effect on the Macroscopic Flow Stress of Nano-Crystalline Metals

MRS Proceedings ◽

10.1557/proc-1224-ff10-37 ◽

2009 ◽

Vol 1224 ◽

Author(s):

Malgorzata Lewandowska ◽

Romuald Dobosz ◽

Krzysztof J Kurzydlowski

Keyword(s):

Grain Size ◽

Flow Stress ◽

Grain Boundaries ◽

Size Distribution ◽

Grain Size Distribution ◽

Distribution Functions ◽

Boundary Misorientation ◽

Plastic Properties ◽

Nano Crystalline ◽

Average Grain Size

AbstractThe paper reports new experimental results describing properties and microstructure of nanocrystalline metals. Nano- and sub-micron aluminium has been produced by hydrostatic extrusion at ambient tempearture. The structures have been quantified in terms of size of grains and misorientation of the grain boundaries. Different average size of grains, variable normalized width of grain size distribution and changing grain boundary misorientation distribution functions have been revealed depending on processing parameters. The results of the tensile tests showed that the average grain size, grain size distribution and the distribution function of misorientation angles influence the flow stress of obtained nano-metals. In order to explain the observed difference in the properties of nano- and micro-sized aluminium alloys, a Finite Element Method models have been developed, which assumes that both grain boundaries and grain interiors may accommodated elastic and non-linear plastic deformation. These models assumed true geometry of grains (which differed in size and shape). Also, variable mechanical properties of grain boundaries have been taken into account (elastic modulus, yield strength and work hardening rate). The results of modelling explain in a semi-quantitative way macroscopic deformation of nano-crystalline aggregates. In particular, they illustrate the importance of the interplay between properties of grain boundaries and grain interiors in elastic and plastic regime.

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Influence of Mo Segregation at Grain Boundaries on the High Temperature Creep Behavior of Ni-Mo Alloys: An Atomistic Study

Materials ◽

10.3390/ma14226966 ◽

2021 ◽

Vol 14 (22) ◽

pp. 6966

Author(s):

Qian Li ◽

Jiayong Zhang ◽

Huayuan Tang ◽

Hongwu Zhang ◽

Hongfei Ye ◽

...

Keyword(s):

Grain Size ◽

Grain Boundary ◽

Strain Rate ◽

Grain Boundaries ◽

Creep Strain ◽

High Stress ◽

External Stress ◽

Creep Strain Rate ◽

Creep Process ◽

Boundary Slip

Based on molecular dynamics simulations, the creep behaviors of nanocrystalline Ni before and after the segregation of Mo atoms at grain boundaries are comparatively investigated with the influences of external stress, grain size, temperature, and the concentration of Mo atoms taken into consideration. The results show that the creep strain rate of nanocrystalline Ni decreases significantly after the segregation of Mo atoms at grain boundaries due to the increase of the activation energy. The creep mechanisms corresponding to low, medium, and high stress states are respectively diffusion, grain boundary slip and dislocation activities based on the analysis of stress exponent and grain size exponent for both pure Ni and segregated Ni-Mo samples. Importantly, the influence of external stress and grain size on the creep strain rate of segregated Ni-Mo samples agrees well with the classical Bird-Dorn-Mukherjee model. The results also show that segregation has little effect on the creep process dominated by lattice diffusion. However, it can effectively reduce the strain rate of the creep deformation dominated by grain boundary behaviors and dislocation activities, where the creep rate decreases when increasing the concentration of Mo atoms at grain boundaries within a certain range.

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