Showing papers on "Grain boundary strengthening published in 1987"
220 citations
218 citations
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TL;DR: In this paper, a new model was presented to predict the critical grain radius (Rc) as a function of the particle radius (r) and of the volume fraction of the particles (ƒ), which was found to agree satisfactorily with the experimental results of Tweed, Hansen and Ralph.
146 citations
TL;DR: In this article, the authors investigated grain growth habits and the structure of grain boundaries using transmission electron microscopy and scanning Auger microscopy of bulk sintered samples of orthorhombic Ba 2 YCu 3 O 7-x, and proposed a model based on the highly anisotropic thermal contraction of the material during cooling from the high sintering temperatures.
128 citations
TL;DR: In this paper, Bilby, Cottrell and Swinden applied the crack model to simulate the blocking of the plastic zone at the grain boundary and to obtain the stress concentration ahead of the crack as it approaches the barrier.
Abstract: The behaviour of short cracks approaching growth barriers (eg grain boundaries) is considered The crack model of Bilby, Cottrell and Swinden is applied to simulate the blocking of the plastic zone at the grain boundary and to obtain the stress concentration ahead of the crack as it approaches the barrier The idea of the Hall-Petch type relationship that the transmission of slip across grain boundaries needs the previous achievement of a critical stress has been used By making the crack growth rate proportional to the plastic displacement at the root of the crack the deceleration behaviour of short cracks and the existence of non-propagating cracks may be explained The fatigue limit is related to the stress below which a crack growing in a single grain is unable to promote slip in the neighbouring grain The different behaviour in the so-called long crack period has been rationalized in terms of the plastic zone exceeding the grain size For this case, and in the grain completely included within the plastic zone, the Hall-Petch analysis must be applied Hence the maximum back-stress sustained by this grain cannot exceed the yield stress After this point the Bilby et al model is used with uy as a friction stress (ie the Dugdale model) Finally use is made of Fracture Mechanics to correlate the results in the long crack phase
112 citations
TL;DR: In this article, a study on grain boundary fracture failures found in Al-Si interconnects during aging tests without electric current flow is presented, showing that failures are caused by slitlike voids formed at grain boundaries during the relaxation process in AlSi conductors stressed by temperature cycling under the volume constraint of passivation films.
Abstract: This paper presents a study on grain boundary fracture failures found in Al–Si interconnects during aging tests without electric current flow. Failure rate analysis and microscopic observation by transmission electron microscopy and scanning electron microscopy indicate that failures are caused by slitlike voids formed at grain boundaries during the relaxation process in Al–Si conductors stressed by temperature cycling under the volume constraint of passivation films. Conductors are seen to fail in two modes; an open mode at bamboolike grain boundaries and a high‐resistance mode at grain boundaries having large silicon precipitates.
107 citations
TL;DR: In this article, the effect of grain size on the cyclic stress-strain response and on the fatigue life including the plastic strain fatigue limit was determined for a large number of specimens.
101 citations
TL;DR: In this article, the role played by boron in ductilizing Ni3Al is revealed when the Hall-Petch relationships for Ni3 al and B-doped Ni3al are compared.
Abstract: Ductilization of Ni3Al at room temperature by microalloying with boron has been primarily attributed to the increased grain boundary cohesion in the presence of boron.1 However, another aspect of the role played by boron in ductilizing Ni3Al is revealed when the Hall-Petch relationships for Ni3Al and B-doped Ni3Al are compared. A shallower slope for the B-doped Ni3Al compared to that for Ni3Al indicates a reduced resistance to slip propagation across grain boundaries, and therefore reduced stress concentration at boundaries, in the presence of boron. This comparison of Hall-Petch relationships was carried out by generating data for powder processed B-doped Ni3Al at various grain sizes and by compiling data for Ni3Al from the literature. In addition, the room temperature fracture of B-doped Ni3Al has been shown to initiate along certain grain boundaries. The fracture eventually occurs by transgranular ductile tearing.
90 citations
TL;DR: In this article, the effect of Al2O3 inclusions with a greater average size (0.6 μm) than the average particle size of the major phase powder (0,3,5,10, and 20 vol%) on grain gowth was examined by sintering ZrO2/Al 2O3 composites at 1400°C and then heat treating at temperatures up to 1700°C.
Abstract: The effect of Al2O3 inclusions with a greater average size (0.6 μm) than the average particle size of the major phase powder (<0.1 μm) on grain gowth was examined by sintering ZrO2/Al2O3 composites (0,3,5,10, and 20 vol%) at 1400°C and then heat-treating at temperatures up to 1700°C. Normal grain growth was observed for all conditions. The inclusions appeared to have no effect on grain growth until the ZrO2 grain size was ∼1.5 times the average inclusion size. Grain growth inhibition increased with volume fraction of the Al2O3 inclusion phase. At temperatures 1600°C, the inclusions were relatively immobile and most were located within the ZrO2 grains for volume fractions <0.20; at higher temperatures, the inclusions could move with the grain boundary to coalesce. Grain growth was less inhilited when the inclusions could move with the boundaries, resulting in a larger increase in grain size than observed at lower temperatures. Analogies between mobile voids, entrapped within grain at lower temperature due to abnormal grain growth during the last state of sintering, and the observations concerning the mobile inclusions are made suggesting that grain-boundary movement can “sweep” voids to grain boundaries and eventually of four-grain junctions, where they are more likely to disappear by mass transport.
87 citations
TL;DR: In this article, the size of ferrite grains dα formed by continuous cooling transformation from polygonal austenite has been measured as a function of cooling rate and grain size dγ.
Abstract: Ferrite grain refinement by accelerated cooling has been studied in a carbon steel. The size of ferrite grains dα formed by continuous cooling transformation from polygonal austenite has been measured as a function of cooling rate and austenite grain size dγ. In the cooling rate range studied (q= 0·05–5 K s−1), dα was found to be proportional to q−0·26dγ 0·46. The mechanism of grain refinement by accelerated cooling is discussed, and it is shown that this occurs in the transformation where the ratio of nucleation to growth rate increases with a decrease in temperature. The austenite grain size dependence of ferrite grain size is shown to become progressively large as the nucleation mode changes from homogeneous to grain surface to edge to corner. A theoretical estimation of ferrite grain size formed by continuous cooling transformation was attempted on the basis of nucleation and growth rates. In the alloy studied, ferrite grain size was theoretically estimated to be proportional to q−0·17dγ 0·33...
82 citations
TL;DR: In this paper, the effect of boron on the mechanism of strain transfer across grain boundaries in Ni/sub 3/Al has been investigated by dynamic recording of events occurring during in-situ straining in the transmission electron microscope.
Abstract: The effect of boron on the mechanism of strain transfer across grain boundaries in Ni/sub 3/Al has been investigated by dynamic recording of events occurring during in-situ straining in the transmission electron microscope. Boundaries in both doped and undoped material can act as effective barriers to dislocation motion, large numbers of dislocations being incorporated into the boundary without any plastic strain occurring in the adjacent grain. In the undoped material, the grain-boundary strain is relieved by the sudden failure of the grain boundary. In the doped material the strain is relieved by the sudden generation and emission of large numbers of dislocations from the grain boundary. This effect may be understood by boron either increasing the grain-boundary cohesion or reducing the stress required to operate grain-boundary dislocation sources, rather than easing the passage of slip dislocations through the grain boundary.
TL;DR: In this article, the thermal expansion of grain boundaries in copper polycrystals was measured by a newly developed method compared with a comparison with small (17 μm) and large (19 mm) grain sizes, which was deduced to be 40 to 80·10−6K−1 which is about 2.5 to 5 times the expansion coefficient of a copper crystal suggesting large anharmonic atomic vibrations in grain boundaries.
TL;DR: In contrast to the voluminous literature devoted to the structure of grain boundaries in metals and, to a lesser extent, in diamond cubic semiconformal ductors, relatively few studies have been directed to elucidating the struc · ture of grain boundary in ceramic materials.
Abstract: In contrast to the voluminous literature devoted to the structure of grain boundaries in metals and, to a lesser extent, in diamond cubic semicon ductors, relatively few studies have been directed to elucidating the struc ture of grain boundaries in ceramic materials. The crystallographic studies performed have been reviewed by Balluffi and colleagues (1, 2), but these papers, reflecting the work carried out to date, have been restricted to single-phase ceramics of relatively simple crystal structures and small unit cells. Much less attention has been given to the more complicated polyphase ceramics that are of importance to ceramic scientists today. These include the structural ceramics, such as the silicon nitride alloys (3, 4) and the zirconia transformation toughened materials (5); the multicomponent sub strate ceramics; nuclear waste ceramics (6); and the dielectric and electrical ceramics. In all these materials the majority of grain boundaries have been found (7-14) to be coated with a very thin ( 1-10 nm) film of a (generally siliceous) glass. I [In many respects the microstructure of the boundaries in these materials can be likened to the microstructure envisioned in the liquid-layer grain boundary model for metals which was introduced by Rosenhain (15) and was current during the early decades of this century.] The presence of such a glass phase can have a profound eflect on the properties of such polyphase ceramics. For instance, the unique electrical properties of a number of electrical ceramics, such as the barrier-layer
TL;DR: In this article, the effect of alloy stoichiometry on the grain boundary strength and fracture behavior of L12-type A3B compounds was investigated at room temperature, and the effects of interstitial atoms of boron and hydrogen were observed.
TL;DR: In this article, the microstructural processes during dynamic recrystallization of wet bischofite are grain coalescence, grain dissection and grain migration, and the oscillatory motion of grain boundaries and sudden large changes in grain boundary migration rate were important features.
TL;DR: In this paper, the formation of surface intergranular cracks was investigated with a coarse-grained polycrystal of nickel, deformed in low-cycle fatigue at 573 K. The evolution of the cracks was followed as a function of fatigue life fractions, and the factors favoring their formation were identified.
TL;DR: In this article, the diffusional coherency strain energy is shown to be the driving force for the grain boundary migration in DIGM with the Cu melt acting as the sink for Ni atoms.
TL;DR: In this article, the grain size of 0.5% Si steels was changed from 42 to 115 μm by various combinations of several hot rolling and annealing conditions, and the core loss W15/50 in 0°, 45° and 90° directions decreases altogether with an increase in the hot-band grain size.
Abstract: Hot-band grain size of 0.5% Si steels was changed from 42 to 115 μm by various combinations of several hot rolling and annealing conditions. The hot-bands were cold rolled from 2.3 to 0.50 mm and finally annealed for 1 min at several temperatures between 750 °C and 950°C. The values of magnetic induction B50 in the directions of 0° and 90° from the rolling direction increase, whereas that of 45° direction decreases a little with an increase in the hot-band grain size. The core loss W15/50 in 0°, 45° and 90° directions decreases altogether with an increase in the hot-band grain size. The change in B50 with an increase in the hot-band grain size is caused by decreases of (110) component in the annealing texture. The change in W15/50 with an increase in the hot-band grain size is accounted for both of the grain size and texture effects.
TL;DR: In this article, a grain boundary etching method was utilized for analyzing P-segregation, and the crystallography of grain boundaries was characterized by making channelling pattern and trace analysis.
07 Apr 1987
TL;DR: In this article, the authors examined stress induced open-circuit failures in AlSi and Al-Si-Cu interconnects and found that the failure rate increases as a P-SiN film gets thinner and thinner, as an interconnect becomes narrower and thinner and as the mean grain size of an Al alloy becomes larger.
Abstract: Stress induced open-circuit failures in Al-Si and Al-Si-Cu interconnects are examined in detail. The failure rate increases, as a P-SiN film gets thicker, as an interconnect becomes narrower and thinner and as the mean grain size of an Al alloy becomes larger. In failure analyses, two kinds of voids in the interconnects are observed. One is the slit-like void which is a very thin crack perpendicular to the Al lines. Open failure sites are always observed at slit-like voids. The other is a wedge shaped void which is formed along a grain boundary at the edge of the interconnects. The addition of Cu as low as 0.1%, substantially depresses the open failures. However, further Cu addition causes little change in the failure rate. The failures are suppressed not by Cu precipitates but by Cu atoms dissolved in Al grains. The wedge shaped void and the slit-like void are formed mainly by grain boundary diffusion and lattice diffusion of vacancies, respectively. In Al-Si-Cu alloys, dissolved Cu atoms are bonded to vacancies and suppress the lattice diffusion, resulting in enhancement of the lifetime.
TL;DR: In this paper, the influence of misorientation angle and structure of a grain boundary on the sensitization and grain boundary corrosion of austenitic and ferritic stainless steels was reported.
Abstract: This paper reports on the influence of misorientation angle and structure of a grain boundary on the sensitization and grain boundary corrosion of austenitic and ferritic stainless steels. To establish grain boundary atomic structure, orientation information of the adjacent grains, obtained with the electron backscattering (EBS) technique, was combined with the SEM image of the surface to obtain the orientation of the grain boundary. Modeling of the grain boundary structure was based on ideal crystallography and the coincident site lattice concept. The results support the concepts (1) of a threshold misorientation angle whose value is a function of the aging time and temperature, below which boundaries are of sufficiently low energy that sensitization does not occur, and (2) of a major role of grain boundary structure in explaining the wide variation in sensitization that occurs in grain boundaries of misorientation angle greater than the threshold value. It was also found that the grain boundary corrosion mechanism is not simply the dissolution of chromium depleted alloy since the observed groove widths were 10 to 100 times larger than the Cr-profile widths.
TL;DR: In this article, the influence of polycrystal grain size on ductile fracture toughness and fatigue threshold stress intensity in Armco iron has been studied over a grain size range 40 to 1050 μm.
TL;DR: In this paper, a new model based on the concept of the localization of the core of a spread-out extrinsic grain boundary dislocation and its subsequent roles as a stress concentrator is proposed.
TL;DR: In this paper, the scale microstructures were examined by parallel and transverse cross section transmission electron microscopy (TEM) and X-ray diffraction (XRD) and the mean boundary curvature per grain provided a guide to the tendency for grain growth, except in the region of the Ni-NiO interface, where the boundaries were thought to be pinned.
Abstract: In systems such as the oxidation of nickel, in which grain-boundary diffusion in the oxide can control the rate of oxidation, understanding of the factors governing the grain structure is of importance. High-purity mechanically polished polycrystalline nickel was oxidized at 700°C, 800°C, and 1000°C for times up to 20 hr in 1 atm O2. The scale microstructures were examined by parallel and transverse cross section transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Texture coefficients were found by X-ray diffraction (XRD). Each grain in the transverse section grain boundary networks was systematically analyzed for width parallel to the Ni-NiO interface and perpendicular length, for boundary radius of curvature and for number of sides. The variation of these parameters with depth in the scale was examined. In particular, grains were increasingly columnar (i.e., with ratio of grain length to width >1) at higher temperatures and longer times. Columnar grain boundaries tended to be fairly static; the columnar grain width was less than the rate controlling grain size predicted from the oxidation rate. The mean boundary curvature per grain provided a guide to the tendency for grain growth, except in the region of the Ni-NiO interface, where the boundaries were thought to be pinned.
TL;DR: The nucleation of creep cavities in iron containing controlled additions of C, P and S has been studied using slow strain rate tensile tests ( ϵ = 1.1 × 10 −6 and 4.4 × 10−5s−1) at te and 800°C as discussed by the authors.