Showing papers on "Grain boundary strengthening published in 1985"
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TL;DR: In this article, both the relatively simple problem of the interaction between a single particle and a grain boundary, and the much more complicated problem of deriving a restraining force from the many particles on the grain boundary have been considered.
680 citations
TL;DR: In this article, a model for growth of secondary grains into a uniform matrix of columnar normal grains is presented, which indicates that secondary grain growth rates should increase with grain boundary energy, surface energy anisotropy, grain boundary mobility, and temperature.
Abstract: Secondary grain growth in thin films can lead to grain sizes much greater than the film thickness. Surface energy anisotropy often provides an important fraction of the driving force for secondary grain growth, especially in the early stages of growth. Surface‐energy‐driven secondary grain growth leads to the development of large grains with restricted crystallographic textures. A model is presented for growth of secondary grains into a uniform matrix of columnar normal grains. The model indicates that secondary grain growth rates should increase with grain boundary energy, surface energy anisotropy, grain boundary mobility, and temperature. While final secondary grain sizes will decrease with film thickness, their growth rates will increase. The final secondary grain sizes and orientations will be strongly affected by grain sizes and orientations in the initial film. The models presented here provide analytical tools for experimental study of secondary grain growth in thin films. They will be used in for...
263 citations
TL;DR: In this paper, the growth of abnormally large grains is modelled under two conditions: 1) where the driving force is provided solely by curvature and 2.1 where the difference in the gas-metal surface energy between grains of different crystallographic orientation.
262 citations
TL;DR: In this paper, a Monte Carlo computer simulation technique has been developed which models grain growth for the case in which the grain boundary energy is anisotropic, and the grain growth kinetics, as represented by the growth exponent n ( R = Ct n ), is found to decrease continuously from 0.42 ± 0.02 to 0.25 ± 1.02 as the anisotropy is increased.
229 citations
TL;DR: In this paper, a complex analysis of experimental results on the structure and properties of grain boundaries in different materials has been analyzed on the basis of the original works available by the present time.
155 citations
TL;DR: In this article, the effect of the substitutional third elements on the mergranular embrittlement of the Ni 3 Al compound was systematically investigated at room temperature, where various kinds of third elements ranging from groups IIIa to V b in the periodic table were selected and alloyed in the Ll 2 structure range.
147 citations
TL;DR: In this article, the authors investigated the grain boundary fracture behaviors at ambient temperature on the binary Ll 2 -type A 3 B ordered alloys, which consist of the elements of group VIII in the first row of the periodic table as the A atom and the widely different elements ranging from groups IV a to IV b as the B atom.
133 citations
TL;DR: In this article, the authors investigated the dynamic recrystallisation mechanisms in a magnesium alloy during uniaxial large strain compression at T = 0.7−0.95 Tm (Tm = melting temperature).
127 citations
TL;DR: In this article, a review of the structural and electrical properties of polycrystalline silicon grain boundaries is presented, with a focus on grain boundary properties in other semiconducting materials.
Abstract: Significant progress in the understanding of the structural and electrical properties of semiconductor grain boundaries has been made in the last ten years. Much of this work was stimulated by promising technological applications of poly crystalline semiconductors, such as cheap solar cells ( 1 ), large area device arrays for display use (2), integrated circuit gates and interconnections (3), and voltage-controlled resistors (varistors) (4). In addition to industrial research support for these studies, government funding in this area has been readily available. A large part of this interest has focused on polycrystalline silicon, not only because of its attractiveness for many of the above-mentioned uses, but also because it is the best characterized, purest semiconductor available, which allows the researcher to concentrate on grain boundary rather than bulk properties. While this review mainly focuses on this material, it will become clear that many of the concepts discussed can be (and have been) carried over quite successfully to model grain boundary properties in other semiconducting materials. The organization of the text is straightforward; it logically follows the concepts needed to understand the rather complex properties of a given piece of polycrystalline silicon. However, as will become apparent to the reader, our present, somewhat incomplete level of understanding in this area was not acquired in the same simple order that is presented here. While grain boundaries affect the mechanical and chemical properties of silicon in important ways, their major effect-and the one that most influences the operation of the devices mentioned above-is on the
115 citations
TL;DR: In this paper, the authors calculated the contiguity of liquid phase sintered materials for various interfacial energies, grain size ratios, and volume fractions of solid phase, and correlated the results to prior observations on cemented carbides.
Abstract: Contiguity is a measure of the dispersed phase contact area in a composite microstructure and is particularly important to the properties of liquid phase sintered materials. For an assumed spherical geometry, the contiguity is calculated for various interfacial energies, grain size ratios, and volume fractions of solid phase. The volume fraction solid is linked to the dihedral angle to indicate conditions where grain shape accommodation is necessary. The effect of a distribution in solid phase grain sizes is to lower slightly the contiguity from the monosized grain value. Coalescence is linked to the occurrence of curved boundaries at intergrain contacts involving differing grain sizes. The results are correlated to prior observations on cemented carbides.
101 citations
TL;DR: In this paper, it was shown that slip continuity is related to the magnitude of the residual dislocation at the boundary and the dissociation of residual into smaller grain boundary dislocations, and a smaller residual and a larger Burgers vector of the grain boundary dislocation enhances the probability of slip continuity across the interface.
TL;DR: AES analysis of intergranular fracture surfaces of Ni3Al showed that grain boundaries are free from any detectable amount of impurity segregation as discussed by the authors, and it was suggested that grain boundary brittleness is not due to the segregation of harmful elements.
Abstract: AES analysis of intergranular fracture surfaces of Ni3Al showed that grain boundaries are free from any detectable amount of impurity segregation. From this finding it was suggested that grain boundary brittleness in Ni3Al is not due to the segregation of harmful elements. X-ray diffraction and SEM observation of the fracture surfaces detected a plastically strained layer of which thickness is compa-rable to grain size.
TL;DR: In this article, the authors estimate flow stresses from unbound dislocation densities and dynamically recrystallized grain sizes in the tectonite specimens in the Betic Movement Zone (Betic Cordilleras, Spain).
TL;DR: In this paper, the number of domains that can exist in a given size grain is determined based on the nucleation of domain walls at grain boundaries for materials free of crystalline defects.
TL;DR: In this article, the serrated grain boundary formation potential of a large number of conventionally forged, powder processed, and investment cast Ni-based superalloys is reviewed and the prerequisite conditions for its occurrence are highlighted.
Abstract: The serrated grain boundary formation potential of a large number of conventionally forged, powder processed, and investment cast Ni-based superalloys is reviewed. A mechanism of serrated grain boundary formation by which grain boundaryγ′ particles move and displace the local grain boundary segment is discussed and the prerequisite conditions for its occurrence are highlighted. The practical implications of the serrated grain boundary formation are also discussed. It is suggested that modifying the existing heat-treatment cycles in some investment cast and powder processed Ni-based superalloys would improve their properties. The possibility of minimizing weld cracking in superalloys by creating serrated grain boundaries in the base metal and the heat affected zone is also discussed.
TL;DR: In this paper, a lattice model for 2-dimensional grain growth was developed in which topology and local environment are included, and the results of this model were used to simulate grain growth in thin encapsulated films.
TL;DR: In this paper, it was shown that the coherency strain energy in a diffusion layer in the retreating grain is the driving force for boundary migration in liquid phase sintered 95Mo-5Ni alloy.
TL;DR: In this article, the impact test of Fe-P-C alloys with up to 067wt% phosphorus showed intergranular fracture (IGF) by an impact test after quenching from 1073k.
Abstract: Fe-P alloys containing up to 067wt% phosphorus show intergranular fracture (IGF) by an impact test after quenching from 1073K Additions of up to about 001wt% of carbon to the alloys prevents the intergranular fracture caused by the grain boundary segregation of phosphorus, and lowers the ductile-brittle transition temperature (DBTT) This effect is due to the segregation of carbon at grain boundaries Aging at 873K of the quenched specimen with 052% P and 00008% C lowers DBTT and increases the degree of grain boundary segregation of carbon while it does not affect the degree of grain boundary segregation of phosphorus The grain boundary segregation of carbon strengthens the grain boundary cohesion and prevents intergranular fracture without removing phosphorus from grain boundariesDBTT of the Fe-P-C alloys are analyzed in terms of the degree of grain boundary segregation of carbon and phosphorus and the solution hardening by phosphorus (the bulk concentration of phosphorus) The site-competition between carbon and phosphorus is taken into account in the calculation of the degree of segregation It is found that the increase in the boundary cohesion by the carbon segregation is an important factor in preventing IGF
TL;DR: In this article, the longitudinal creep behavior of two heats of coarse grained INCONEL* MA 754 has been examined at temperatures of 1000 °C and above, and the results show that at high stresses, dislocation creep is observed and high stress exponents (n ∼40) are measured.
Abstract: The longitudinal creep behavior of two heats of coarse grained INCONEL* MA 754 have been examined at temperatures of 1000 °C and above. Both heats exhibit a pronounced transition in deformation behavior. At high stresses, dislocation creep is observed and high stress exponents (n ∼40) are measured. Fracture in this regime is transgranular with high creep ductilities. At lower stresses, the stress exponents are low and fracture is intergranular. In this regime, the stress exponent depends strongly on the grain morphology. Heat 1, with a uniform fiber grain morphology, exhibits significantly higher stress exponents than Heat 2, which has a duplex grain morphology consisting of coarse grains along with pockets of fine, equiaxed grains. Microstructural examination of specimens deformed at the lower stresses provides evidence that cavitation of the transverse grain boundaries occurs by means of diffusive cavity growth. In the heat with the uniform fiber morphology, cavity growth is constrained by creep of adjacent grains. Cavity growth for the heat with the duplex grain morphology is apparently limited by the sliding of pockets of fine grains. The implications of these results for optimizing creep resistance of MA 754 are discussed.
TL;DR: For polycrystalline metals undergoing creep at high temperatures, the nucleation, growth and coalescence of grain boundary cavities are investigated in this paper, with main focus on the influence of grain boundaries sliding.
Abstract: For polycrystalline metals undergoing creep at high temperatures the nucleation, growth and coalescence of grain boundary cavities is investigated, with main focus on the influence of grain boundary sliding. Both the local stress state and the average rate of opening of a cavitating facet can be rather strongly affected by sliding on the grain boundaries emanating from the edges of this facet. A number of numerical solutions of axisymmetric model problems are used to study the combined influence of sliding and cavitation. The time to creep rupture by cavity coalescence is significantly reduced by grain boundary sliding, as is seen by comparison with analyses that disregard sliding. The numerical results are compared with predictions of a set of constitutive relations for creep in polycrystals with grain boundary cavitation.
TL;DR: In this article, a new model of structural superplasticity is proposed on the basis of recent experimental data on the operative deformation mechanisms and the results of investigations of grain boundary properties.
Abstract: A new model of structural superplasticity is proposed on the basis of recent experimental data on the operative deformation mechanisms and the results of investigations of grain boundary properties. The concepts of hardening and recovery are used to analyse the superplastic nature, the development of these processes being associated with grain boundaries. According to the proposed model during superplastic flow the hardening due to easy generation of lattice dislocations (LD's) in the boundaries at the formation of grain boundary dislocation pile-ups is insignificant while the rate of the recovery whose kinetics is determined by LD absorption by boundaries is high. On the basis of these conceptions a system of equations of the dislocation kinetics is obtained which describes the experimental curve of superplastic deformation and the principal causes of a number of structural effects which have not been satisfactorily explained before are given.
[Russian Text Ignored].
TL;DR: In this paper, the influence of temperature and grain size on the tensile ductility of AISI 316 stainless steel has been examined in the temperature range 300-1223 K for specimens with grain sizes varying from 0.025 to 0.650 mm at a nominal strain rate of 3 × 10 −4 s −1.
TL;DR: In this paper, a metallographic study of DIGBM and DIR was performed on thin copper layers diffused into α-CuZn between 200 and 550 °C.
TL;DR: In this paper, it was shown that a threshold shear stress is needed for cavity nucleation on grain boundary particles during grain boundary sliding, and the particle sizes and spacings were assumed to obey a log-normal distribution, and a program was developed to calculate the fraction of particles which can serve as nucleation sites.
TL;DR: A Hall-Petch microstructural stress intensity (k = 30 N/mm 3 2 ) derived from microhardness tests of electrodeposited ultrafine grain size chromium material, extending to a smallest grain diameter of 0.15 μm, is shown to compare favorably with that reported for compression test results of material swaged and recrystallized over a conventional range of grain diameters as discussed by the authors.
TL;DR: In this article, a short discussion of previous data on transport properties along grain boundaries in germanium bicrystals was carried out and it was pointed out that the system is suitable to study the metal-insulator transition.
Abstract: After a short discussion of previous data on transport properties along grain boundaries in germanium bicrystals it is pointed out that the system is suitable to study the metal-insulator transition. Complications in the interpretation of transport data arise because the conducting layers are p-type and two-dimensional. The magneto-transport data of space charge layers adjacent to tilted grain boundaries show anomalous behaviour which can be attributed to electron-electron interaction effects. Under usual conditions in [100] medium angle tilted bicrystals two hole subbands are occupied. This is the result of self-consistent subband calculations in the Hartree approximation.
TL;DR: In this article, the role of grain boundary and shearable matrix precipitates in promoting low ductility in Al-10.7at.%Li-0.22at.%.
01 Jan 1985
TL;DR: In this article, the authors present methods for the determination of the density of states at grain boundaries in polycrystalline semiconducting films and bicrystals, based on measurements of the electronic transport of majority carriers.
Abstract: This contribution discusses methods for the determination of the density of states at grain boundaries in polycrystalline semiconducting films and bicrystals. All methods are based on measurements of the electronic transport of majority carriers. The doping method reveals the dominance of band tails in the density of states of fine-grained films of Si and GaAs. This is confirmed by photocapacitance measurements at a grain boundary in a Si bicrystal. Ac-measurements on bicrystals are described within the framework of the “trap transistor model”. General solutions of this model are given in graphical form. It allows for the evaluation of the density of states and the capture cross section for majority carriers. Moreover, potential fluctuations at grain boundaries are resolved and a correlation of electronic and structural properties can be carried out. The application of this technique to a grain boundary in a Si bicrystal indicates that the interface charge is caused by secondary dislocations.
TL;DR: The effect of cold work in the range of 21.9 pct to 94.2 pct reduction in area by swaging on the recrystallization behavior and grain size distribution in Ti was investigated in this paper.
Abstract: The effect of cold work in the range of 21.9 pct to 94.2 pct reduction in area by swaging on the recrystallization behavior and grain size distribution in Ti (0.2 pct Oeq) was investigated. In keeping with commonly observed behavior, increasing amounts of cold work lead to an increase in hardness prior to annealing and a decrease in the subsequent recrystallization temperature and grain size. Also, there occurred for the recrystallized grains a decrease in the standard deviation of the grain volume distribution In Σv deduced from the one-dimensional linear intercept measurements. The decrease in In Σv with cold work in swaged Ti is in good accord with that reported by Rhines and Patterson following uniaxial deformation of Al. Considering the results for both Al and Ti, it appears that the largest decrease in In Σv occurs for true strains up to R ~0.5, the change with larger strains being more gradual. The reason for the decrease in In Σv with increased cold work is not completely clear. The increased rate of grain growth with reduction in amount of cold work can be understood in terms of the larger number of three-edged grain faces which occur with the greater spread in the recrystallized grain volume distribution.