Showing papers on "Grain boundary strengthening published in 1969"
TL;DR: In this article, the average grain size of a log-normal distribution of grain sizes with tetrakaidecahedral shape is related to the average intercept size by a proportionality constant.
Abstract: A model is proposed which realistically characterizes the grain structure of polycrystalline ceramics. The average grain size of a log-normal distribution of grain sizes with tetrakaidecahedral (truncated octahedral) shape is related to the average intercept size by a proportionality constant. This result can be used to determine the average grain size of a sintered powder compact composed of nontextured grains which shows no discontinuous grain growth.
1,732 citations
323 citations
247 citations
TL;DR: In this paper, it was shown by electron transmission microscopy that a grain boundary has a step-like structure and the steps are formed by a Frank spiral mechanism or at junction points of grain boundaries.
239 citations
TL;DR: In this paper, the migration rate of a grain boundary is calculated as a function of the orientation of the two grains relative to the grain boundary and the thermodynamic constants (driving force, enthalpy of migration etc.).
183 citations
TL;DR: In this article, the origin of the grain boundary precipitate free zone is discussed in relation to Al-Zn-Mg and Al-Cu alloys using the occurrence of homogeneously distributed precipitate as a semi-quantitative indication of the excess vacancy concentration and its variation in the quenched alloys.
153 citations
TL;DR: In this paper, the early stages of grain boundary precipitation in two aluminium alloys, Al-6 %Zu-3 %Mg and Al-7 % Mg, have been examined by transmission electron microscopy, and are discussed in relation to the heat treatment procedure and the properties of individual boundaries.
111 citations
TL;DR: In this article, it was shown that sulfur is strongly segregated to grain boundaries in nickel alloys and this segregation causes a local increase in microhardness and an unusual variation of the Petch slope k in the grain size dependence of the flow stress.
92 citations
TL;DR: In this article, a transmission electron-microscopy study of high-angle grain boundaries has been made, where thin foils are cut in precisely oriented bicrystals of aluminium and some details of the grain-boundary structure appear.
Abstract: A transmission electron-microscopy study of high-angle grain boundaries has been made. When thin foils are cut in precisely oriented bicrystals of aluminium, some details of the grain-boundary structure appear. Micrographs of symmetrical tilt boundaries around [001] show linear defects parallel to the tilt axis. Their properties are tightly bound to the geometry of the bicrystal: this provides a good support to the idea of a transitional lattice as a structure of a high-angle boundary. A theoretical interpretation of these observations is developed essentially on geometrical considerations.
86 citations
TL;DR: In this paper, a model of the growth of precipitates which nucleate at grain boundaries and grow pre ferentially along them (grain-boundary allotriomorphs) is studied.
Abstract: A model descriptive of the growth of precipitates which nucleate at grain boundaries and grow pre ferentially along them (grain‐boundary allotriomorphs) is studied. The sequential processes during growth are presumed to be volume diffusion of solute to the grain boundary, transport along the grain boundary to the precipitate, and interfacial diffusion and deposition over the surface of the growing allotriomorph. An analysis of this mode of growth is applied to the results of recent observations of the lengthening and the thickening rates of θ‐allotriomorphs in an Al‐4% Cu alloy. On the basis of these measurements the diffusivity within the grain boundary Db is found to be 0.1 exp (−18480/RT) cm2sec−1, while the diffusivity within the allotriomorph‐matrix interface, D8, is D8=1.8 exp (−22020/RT) cm2 sec−1 when the mole fraction of solute in this interface is taken to be the average of that in θ and in α at the boundary, or D8=0.06 exp (−12740/RT) cm2 sec−1 when this surface concentration is assumed to be s...
80 citations
TL;DR: In this paper, high purity nickel bicrystals with controlled grain boundary misorientations have been grown from the melt using an electron beam floating zone technique using high-resolution contact autoradiography.
Abstract: High‐purity nickel bicrystals with controlled grain boundary misorientations have been grown from the melt using an electron beam floating‐zone technique. These bicrystals have symmetrical tilt grain boundaries with 10° misorientation between {111} planes tilted about a 〈112〉 axis, and 10° twist about a {111} axis. The diffusion of nickel‐63 in these boundaries and similar sintered grain boundaries has been studied over the temperature range 600°–970°C using high‐resolution contact autoradiography. Using the dislocation pipe model for low‐angle grain boundaries, edge and screw dislocations were found to have similar activation energies of 40.7 and 44.9 kcal/mole, respectively. The value for the tilt boundaries is shown to agree well with recent work on isolated edge dislocations in nickel. It is concluded that the low‐angle tilt boundaries are composed of 〈112〉 {111} edge dislocation arrays which exhibit the same diffusion behavior as isolated edge dislocations formed by plastic deformation. Also, the hig...
TL;DR: In this paper, regular substructures were observed in grain boundaries of an annealed Fe•0.75% Mn alloy by transmission electron microscopy and a detailed analysis was made on one of the grain boundaries.
Abstract: Regular substructures were observed in grain boundaries of an annealed Fe‐0.75% Mn alloy by transmission electron microscopy. A detailed analysis was made on one of the grain boundaries. The result indicates that the analyzed grain boundary may be considered as a coincidence site grain boundary.
TL;DR: In this paper, the formation of curved grain boundaries depends upon the misfit between the two crystals, and upon their relative thickness, and the grain boundaries themselves are made up of dislocations which once accommodated misfit in the areas occupied by the curved grains.
Abstract: Diffusion between single-crystal films which are in contact and in parallel orientation is sometimes accompanied by the generation of grain boundaries. The grains enclosed by these boundaries are unusual in that their lattices are curved to accommodate the difference between the lattice parameters of the upper and lower specimen surfaces. In the regions outside these boundaries the gradient in lattice parameter is accommodated by misfit dislocations. The grain boundaries themselves are made up of dislocations which once accommodated misfit in the areas occupied by the curved grains. The formation of curved grains depends upon the misfit between the two crystals, and upon their relative thickness.
TL;DR: In this paper, an application of a general theory of grain and phase boundaries (0-lattice theory) to grain boundaries with periodic patterns of lattice points is presented.
Abstract: This work is an application of a general theory of grain and phase boundaries (0-lattice theory) to grain boundaries with periodic patterns of lattice points. It is assumed that certain boundaries of this type are stable (coincidence boundaries). A method is indicated for the search of such configurations and for the detailed calculation of the patterns as well as the dislocation networks in high angle boundaries arising from slight deviations from minimum energy patterns. Numerical results are given for the b.c.c. structure.
TL;DR: In this article, the effect of grain size on the high-temperature fatigue properties of an Mg-0·8% Al alloy has been studied, and it is shown that this effect is related to an increase in the initial plastic strain amplitude, caused by an increasing in the rate of grain-boundary sliding.
Abstract: The effect of grain size on the high-temperature fatigue properties of an Mg–0·8% Al alloy has been studied. A reduction in rupture life occurred when the grain size exceeded the specimen thickness. It is shown that this effect is related to an increase in the initial plastic strain amplitude, caused by an increase in the rate of grain-boundary sliding. It is also established that this deformation mode controls cavity growth and that failure occurs at a critical mean value of the sliding displacement, independent of applied stress and structure.
TL;DR: In this paper, the authors calculated the stress required to form a dislocation loop of the size of a grain for cases where the loop forms within a grain, at a grain boundary, and in grains adjacent to another grain where a loop is already present.
Abstract: The stress required to form a dislocation loop of the size of a grain has been calculated for cases where the loop forms within a grain, at a grain boundary, and in grains adjacent to another grain where a loop is already present. It is shown that in typical polycrystalline films this value of the stress is comparable to the observed stresses in films before plastic flow sets in. In the case of single crystal epitaxial films with a high grown-in dislocation density the plastic strain realizable is shown on the basis of a simple model to be a few percent. The model is based on a simple nearest neighbor dislocation interaction and is shown to explain the tensile behavior of thin single crystal films.
TL;DR: In this article, a polycrystalline 3% silicon iron of various grain sizes has been subjected to a hydrostatic pressure of 15 kb at 293°K, and then tested in tension at atmospheric pressure in the temperature range 77°K to 383°K.
Abstract: Polycrystalline 3% silicon iron of various grain sizes has been subjected to a hydrostatic pressure of 15 kb at 293°K, and then tested in tension at atmospheric pressure in the temperature range 77°K to 383°K. The yield stress was reduced and the strain to fracture increased over temperature ranges that are dependent on the grain size. Twinning was less pronounced in pressurized material, and was also less effective in initiating cleavage fracture. The results are explained in terms of the effect of pressurization on phenomena occurring at grain boundaries.
TL;DR: In this paper, the authors report bulk diffusion enhancement under conditions where grain-boundary migration and grain growth only take place during the time of the diffusion experiment, where grain growth occurs only during the diffusion phase.
Abstract: This paper reports bulk diffusion enhancement under conditions where grain-boundary migration and grain growth, or grain growth only take place during the time of the diffusion experiment
TL;DR: The addition of 10% Fe promotes the formation of M7W6, grain refining of the solid solution, and accelerates the transformation of the metastable Ni3Nb phase with a fcc lattice into the equilibrium modification with an orthorhombic lattice.
Abstract: 1.
Heat-resisting alloys KhN60MBVYu and KhN50MBBYu, hardened by precipitation of Ni3Nb, have high mechanical properties at room and operating temperatures.
2.
The addition of 10% Fe promotes the formation of M7W6, grain refining of the solid solution, and accelerates the transformation of the metastable Ni3Nb phase with a fcc lattice into the equilibrium modification with an orthorhombic lattice.
3.
The M7W6 phase in the grain boundaries of the KhN50MBVYu alloy provides high plasticity at maximum hardening temperatures.