Recrystallization and Grain Growth during Alloy 718 Processing

2007 ◽  
Vol 539-543 ◽  
pp. 3094-3099
Author(s):  
Nho Kwang Park ◽  
Jeoung Han Kim ◽  
Jong Taek Yeom
Keyword(s):  
Grain Size ◽  
Grain Growth ◽  
Heat Treatments ◽  
Grain Structure ◽  
Alloy 718 ◽  
Compression Tests ◽  
Δ Phase ◽  
Grain Boundary Characteristics ◽  
The Difference ◽  
Boundary Characteristics

In Alloy 718 ingot cogging process, dynamic and metadynamic recrystallizations, and static grain growth occur, and also the presence of δ phase plays a key role in controlling the grain size. In this study, the evolution of grain structure in VIM/VAR-processed Alloy 718 ingots during post-cogging heat treatments is dealt with. Compression tests were made on VIM/VAR-processed Alloy 718 ingot at temperatures between 900oC ~ 1150oC. Heat treatments were made on the compression-tested specimens, and the variation of grain size was evaluated. Constitutive equations for the grain growth are established to represent the evolution of microstructures. Special attention is paid to the evolution of grain structure under the condition of dynamic and metadynamic recrystallizations, and grain growth. The grain growth rate depends mainly on the presence of δ-phase below the δ-solvus temperature, and on the difference in the grain boundary characteristics above it.

Grain Growth in Si3 N4-Based Materials

MRS Bulletin ◽  
1995 ◽  
Vol 20 (2) ◽  
pp. 33-37 ◽  
Author(s):  
Suk-Joong L.|Kang ◽  
Sang-Moo Han
Keyword(s):  
Grain Size ◽  
Grain Growth ◽  
Driving Force ◽  
Grain Structure ◽  
Liquid Matrix ◽  
Material Transport ◽  
The Difference ◽  
The Moment ◽  
Crystalline Forms ◽  
Critical Grain Size

The growth of Si3N4 grains in the usual sintering process occurs in an oxynitride liquid formed by reactions between sintering additives, impurity SiO2, and Si3N4. The shape of an Si3N4 grain in the liquid matrix is a hexagonal rod, although the aspect ratio (c/a) varies considerably, depending on the processing conditions and final crystalline forms of α or β. Figure 1 shows two types of microstructures observed in sintered Si3N4-based materials. The microstructure shown in Figure la is normal with unimodal grain-size distribution and that of Figure 1b is abnormal with a microstructure of exceptionally large elongated grains within fine matrix grains. When normal grain growth occurs, the microstructure varies little with sintering time, and the development may be described by a simple law. But, when abnormal grain growth occurs, a duplex grain structure with a bimodal grainsize distribution results; then no simple kinetic law can describe the microstructure development.The grain growth in the microstructures shown in Figure 1 exemplifies the growth of faceted grains in a liquid matrix. The grain growth in a matrix occurs via growth of larger grains and dissolution of smaller ones by material transport through the liquid phase. The driving force of the material transport for an individual grain is determined by the difference between its size and the critical grain size, which is invariant at the moment of observation. Since the driving force is usually low, the volume change of each grain is relatively slow and analogous to the crystal growth or dissolution in a liquid matrix under low super- or undersaturation. Therefore, knowledge of the growth behavior of faceted crystals under low supersaturation in a liquid may provide fundamental understanding of the grain growth in Si3N4-based materials.

The Effects of Thermal History on Toughness of Ni-Based Corrosion Resistant Alloys During In-Situ Hydrogen Charging

2021 ◽  
Author(s):  
Michelle Kent ◽  
Kip Findley
Keyword(s):  
Thermal History ◽  
Potential Drop ◽  
Heat Treatments ◽  
Alloy 718 ◽  
Unstable Crack ◽  
Heat Treated ◽  
Δ Phase ◽  
Incremental Step ◽  
M23c6 Carbides

Abstract Hydrogen embrittlement (HE) susceptibility was investigated for Alloy 718 and Alloy 945X specimens heat treated to a set of conditions within the specifications of API Standard 6ACRA. Heat treatments were selected to simulate the potential variation in thermal history in thick sections of bar or forged products and produce various amounts of discontinuous grain boundary δ phase in Alloy 718 and M23C6 carbides in Alloy 945X, while maintaining a constant hardness in the range of 35-45 HRC for Alloy 718 and 34-42 HRC for Alloy 945X. Time-temperature-transformation (TTT) diagrams and experimentation were used to select a set of heat treatments containing no δ phase, a small quantity of δ, and a larger quantity of δ in Alloy 718. The presence of δ phase has not been verified for the moderate condition. A similar approach was taken regarding M23C6 carbides in Alloy 945X. Incremental step loading (ISL) tests were conducted under in-situ cathodic charging on circular notch tensile (CNT) specimens in a 0.5 M H2SO4 solution. During the test, the direct current potential drop (DCPD) was measured across the notch to determine the stress intensity associated with unstable crack growth. Results indicate that even very small quantities of δ phase in Alloy 718 are detrimental to HE resistance. Both Alloy 718 and Alloy 945X show decreases in HE resistance with aging, with a greater degradation in Alloy 718.

Grain Growth in (Ga, Mn)-Codoped ZnO Ceramics

2011 ◽  
Vol 492 ◽  
pp. 250-255
Author(s):  
Bing Shen ◽  
Hua Wang ◽  
Shuai Li ◽  
Jiang Hong Gong
Keyword(s):  
High Temperature ◽  
Grain Growth ◽  
Sintering Temperature ◽  
Sintered Sample ◽  
Grain Structure ◽  
Growth Exponent ◽  
Growth Equation ◽  
Temperature Ranges ◽  
The Difference ◽  
Zno Ceramics

Grain growth in Ga2O3and MnO co-doped ZnO was investigated for sintering from 950° to 1250°C in air. Microstructural observation revealed that the samples sintered at lower temperatures consist of uniform equiaxed grains while the samples sintered at higher temperatures consist of plat-like grains, implying that the grain growth mechanism for the examined ZnO ceramics changes when the sintering temperature increases above about 1150°C. The traditional kinetic grain growth equation was employed to analyze the variation of grain size with sintering temperature and sintering holding time. It was shown that the grain growth exponent,n, increases from 2.17 for samples with uniform equiaxed grain structure to 4.30 for samples with plate like grain structure, while the apparent activation energy,Q, increases from 237 kJ/mol for low-temperature-sintered sample to 405 kJ/mol for high-temperature-sintered samples. The increases in bothnandQwere mainly attributed to the difference between the grain morphologies in low- and high-temperature ranges. The underestimation of the sizes of the plate-like grains was also considered to be another important origin for the higher values ofnandQfor the high-temperature-sintered samples.

Microband-To-Microshear Band Transition near Grain Boundaries in BCC Steel

2007 ◽  
Vol 558-559 ◽  
pp. 873-878 ◽  
Author(s):  
Dorothée Dorner ◽  
Yoshitaka Adachi ◽  
Kaneaki Tsuzaki
Keyword(s):  
Grain Boundary ◽  
Crystal Orientation ◽  
Electron Backscatter Diffraction ◽  
Early Stage ◽  
Compression Tests ◽  
Grain Boundary Characteristics ◽  
Band Transition ◽  
Boundary Characteristics ◽  
Backscatter Diffraction ◽  
Initial Crystal

Compression tests were performed on Fe-3%Si specimens with few grains. The deformation microstructure and microtexture were investigated by electron backscatter diffraction (EBSD) and related to the initial crystal orientation and grain boundary characteristics. Groups of microbands were found that are characterised by a periodic change in crystal orientation, shear at the grain boundary, and the formation of new grains. It is supposed that these microband groups represent an early stage of microshear band development.

Microstructure Evolution and Grain Boundary Characteristics of Oriented Silicon Steel during Primary Recrystallization in a Pulsed Magnetic Field

2013 ◽  
Vol 690-693 ◽  
pp. 139-146 ◽  
Author(s):  
Li Hua Liu ◽  
Li Juan Li ◽  
Qi Jie Zhai
Keyword(s):  
Magnetic Field ◽  
Grain Size ◽  
Magnetic Fields ◽  
Grain Boundary ◽  
Microstructure Evolution ◽  
Silicon Steel ◽  
Pulsed Magnetic Field ◽  
Magnetic Annealing ◽  
Grain Boundary Characteristics ◽  
Boundary Characteristics

The effects of a 2 T pulsed magnetic field primary annealing process on microstructure evolution and grain boundary characteristics in two-stage cold-rolled silicon steel were examined. Pulsed magnetic annealing increased grain size through the application of relatively smaller intensity of magnetic fields (2 T), compared to steady magnetic annealing. The effect of increasing grain size may be attributed to the magnetic acceleration effect of boundary motion under magnetic pulse conditions. Pulsed magnetic annealing may serve to enhance the relative intensity of the {111} component and decrease the frequency of low-angle misorientations. Repeated magnetostriction induced by pulsed magnetic field applications may accelerate overall dislocation motion. These findings suggest that pulsed magnetic fields require relatively lower intensities than steady magnetic fields to achieve superior results, providing a potentially viable alternative for industrial annealing processes for electrical steels.

Annealing Treatment for Superplastic Forming of Twin Roll Casted AZ31 Magnesium Sheet

2011 ◽  
Vol 239-242 ◽  
pp. 50-54 ◽  
Author(s):  
Guo Dong Shi ◽  
Jun Qiao
Keyword(s):  
Grain Size ◽  
Grain Growth ◽  
Mechanical Test ◽  
Dynamic Balance ◽  
Annealing Treatment ◽  
Optical Microscope ◽  
Grain Structure ◽  
Average Grain Size ◽  
Az31 Sheet ◽  
Twin Roll

Annealing treatments at 200°C, 250 °C, 300°C, and 350°C were conducted on a twin-roll casted AZ31 sheet with an initial average grain size of 10.11 mm. Microstructure and mechanical behaviors were studied by optical microscope observation and tensile mechanical test. Expermeintal results show that grain size experienced three stage evolution during 180 min annealing at each temperature: recrystallization refinement, stabilization under dynamic balance of recrystallization and grain growth, and grain growth. The minimum average grain size of 5.96 μm was achieved after 120 min annealing at 200°C. The refined grain structure causes a decrease of ultimate tensile strength and an increase of elongation, and facilitates superplastic deformation of the material.

Electroplated Cu Recrystallization in Damascene Structures at Elevated Temperatures

1999 ◽  
Vol 564 ◽  
Author(s):  
Qing-Tang Jiang ◽  
Michael E. Thomas ◽  
Gennadi Bersuker ◽  
Brendan Foran ◽  
Robert Mikkola ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Grain Size ◽  
Film Thickness ◽  
Grain Growth ◽  
Elevated Temperatures ◽  
Retardation Effect ◽  
Cu Films ◽  
Grain Sizes ◽  
Geometrical Constraints ◽  
The Difference

AbstractTransformations in electroplated Cu films from a fine to course grain crystal structure (average grain sizes went from ∼0.1 µm to several microns) were observed to strongly depend on film thickness and geometry. Thinner films underwent much slower transformations than thicker ones. A model is proposed which explains the difference in transformation rates in terms of the physical constraint experienced by the film since grain growth in thinner films is limited by film thickness. Geometrical constraints imposed by trench and via structures appear to have an even greater retardation effect on the grain growth. Experimental observations indicate that it takes much longer for Cu in damascene structures to go through grain size transformations than blanket films.

Microstructural Evolution and Mechanical Properties of Pure Magnesium during Multi-Axial Compression

2015 ◽  
Vol 713-715 ◽  
pp. 2759-2764 ◽  
Author(s):  
Xiao Hui Yang ◽  
Song Ni ◽  
Min Song
Keyword(s):  
Mechanical Properties ◽  
Grain Size ◽  
Grain Growth ◽  
Axial Compression ◽  
Microstructural Evolution ◽  
Pure Magnesium ◽  
Compression Tests ◽  
Axial Deformation ◽  
Lower Strain ◽  
Significant Difference

The effects of multi-axial compression (MAC) on the microstructures and mechanical properties of pure magnesium were investigated. It has been shown that grain refinement and grain growth occurred simultaneously during the MAC process. After 5 MAC passes, the grain size is mainly distributed in the range of 5~25 μm. The hardness of the specimens increases with increasing the strain (MAC pass), with the increment at lower strain being more obvious than that at higher strain. Compression tests showed that the samples show significant difference in mechanical properties along different directions due to the texture development. With increasing the MAC pass, the texture has been weakened due to multi-axial deformation.

scholarly journals Grain Boundary Properties and Grain Growth: Al Foils, Al Films

2004 ◽  
Vol 819 ◽  
Author(s):  
Katayun Barmak ◽  
Wayne E. Archibald ◽  
Anthony D. Rollett ◽  
Shlomo Ta'asan ◽  
David Kinderlehrer
Keyword(s):  
Grain Size ◽  
Grain Boundary ◽  
Grain Growth ◽  
Misorientation Angle ◽  
Driving Forces ◽  
Boundary Energy ◽  
Orientation Imaging Microscopy ◽  
Solute Drag ◽  
Grain Structure ◽  
Two Dimensional

AbstractRelative grain boundary energy as a function of misorientation angle has been measured in cube-oriented, i.e., <100> fiber-textured, 120 [.proportional]m-thick Al foil using orientation imaging microscopy and a statistical multiscale method. The energies of low-angle boundaries increase with misorientation angle, in good agreement with the Read-Shockley model. The relative energies of high-angle boundaries exhibit little variation with misorientation. Examination of the grain structure of <111> fiber-textured, 100 nm-thick Al films annealed at 400°C for 0.5-10 h shows 5 and 6 sided grains to be the most frequent, and the fraction of four-sided grains to be significant. The mean number of sides is slightly lower than the expected value of 6 for two- dimensional structures. Of lognormal, gamma and Rayleigh distributions, gamma gives the best fit to the grain size data in the films; however, the difference between gamma and lognormal is small. Grain growth is not self-similar and stagnates after one hour of annealing. The evolution of the grain size distribution with time indicates that the growth stagnation in the films is neither consistent with boundary pinning by grooving nor with conventional treatments of solute drag. Surface, elastic-strain and plastic-strain energy driving forces do not play a significant role in the grain growth and the subsequent stagnation since the films are strongly textured even in the as- deposited state. The steady-state distributions of reduced grain area for two-dimensional, Monte Carlo and partial differential equation based simulations show excellent agreement with each other, even when anisotropic boundary energies are used. However, comparison with experimental distributions reveals a significantly higher population of small grains in the experiments.

HIGH POTENTIAL GRADIENT OF Y2O3-DOPED THICK FILM VARISTORS

2009 ◽  
Vol 16 (03) ◽  
pp. 387-391 ◽  
Author(s):  
L. KE ◽  
D. M. JIANG ◽  
X. M. MA
Keyword(s):  
Grain Size ◽  
Tensile Stress ◽  
Thick Film ◽  
Doping Concentration ◽  
Lattice Distortion ◽  
Potential Gradient ◽  
High Potential ◽  
Microstructural Properties ◽  
Grain Boundary Characteristics ◽  
Boundary Characteristics

The electrical and microstructural properties of a series of ZnO -based thick film varistors (TFVs) doped with 0.00, 0.02, 0.04, 0.06, 0.08, and 0.10 mol% Y 2 O 3 were studied. It was found that sample doped with 0.08 mol% Y 2 O 3 showed the highest potential gradient of 3159.4 V/mm with a leakage current of 36.4 μA and a nonlinear exponent of 13.1. The ZnO grain size decreased with increasing Y 2 O 3 content, which was the origin for the increase in potential gradient. Raman spectra results showed that the tensile stress increased linearly with Y 2 O 3 doping. Larger tensile stress was considered to result from the lattice distortion and inevitably influenced the grain boundary characteristics. While the Y 2 O 3 doping concentration was beyond 0.08 mol%, the effect of residual stress on electrical properties was much more remarkable than that of grain size, leading potential gradient to be weakened. As a result, high potential gradient of ZnO -based TFVs could be obtained with Y 2 O 3 doping concentration of 0.08 mol% and qualified as excellent candidates for high voltage varistor application.

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