The effect of solidification rate on structure and high-temperature strength of the eutectic NiAl-Cr
01 May 1970-Metallurgical and Materials Transactions B-process Metallurgy and Materials Processing Science (Springer New York)-Vol. 1, Iss: 5, pp 1221-1229
TL;DR: The eutectic NiAl-Cr, consisting of chromium rods in a NiAl matrix, was directionally solidified at rates varying from 1/4 to 30 in. per hr as discussed by the authors.
Abstract: The eutectic NiAl-Cr, consisting of chromium rods in a NiAl matrix, was directionally solidified at rates varying from 1/4 to 30 in. per hr. The inter-rod spacing and elevated temperature tensile properties were measured and the structure determined for each solidification rate. The spacing, λ, obeyed the relation λ2V= Constant, whereV is the solidification rate. AtV greater than 1 in. per hr, a cell or colony structure formed and the cell size decreased with increasing solidification rate. At 600°C, the tensile strength increased substantially with decreasing inter-rod spacing, reaching 100,000 psi at the highestV. At 800° and 1000°C, the strength first increased then decreased at the highest solidification rates reaching maximum strengths of 63,000 psi and 47,000 psi, respectively. At 1200°C, the strength decreased slightly with increasing solidification rate. Fracture occurred by shear along grain boundaries and cell walls. The decreased strength at the highest solidification rates may be related to the increased cell boundary area.
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TL;DR: In this article, the authors summarize all available mechanical and pertinent physical properties on NiAl, stressing the most recent investigations, in an attempt to understand the behavior of NiAl and its alloys over a broad temperature range.
Abstract: Considerable work has been performed on NiAl over the last three decades, with an extremely rapid growth in research on this intermetallic occurring in the last few years due to recent interest in this material for electronic and high temperature structural applications. However, many physical properties and the controlling fracture and deformation mechanisms over certain temperature regimes are still in question. Part of this problem lies in the incomplete characterization of many of the alloys previously investigated. Fragmentary data on processing conditions, chemistry, microstructure and the apparent difficulty in accurately measuring composition has made direct comparison between individual studies sometimes tenuous. Therefore, the purpose of this review is to summarize all available mechanical and pertinent physical properties on NiAl, stressing the most recent investigations, in an attempt to understand the behavior of NiAl and its alloys over a broad temperature range.
705 citations
TL;DR: In this paper, Niobium-Nb wire composites with 0.105, 0.148, and 0.182 volume fraction of Nb filaments were produced in situ and their mechanical properties measured as a function of filament size and interfilament spacing.
Abstract: Cu‐Nb wire composites with 0.105, 0.148, and 0.182 volume fraction of Nb filaments were produced in situ and their mechanical properties measured as a function of filament size and interfilament spacing. The yield stress and the ultimate tensile strength increased with both niobium volume fraction and overall composite reduction. At room temperature, the ultimate tensile strength of the Cu–18.2 vol% Nb composite reduced by 99.999% in cross‐sectional area (100–200 A filament thickness) reached the value of 2230 MN/m2 (323 ksi) and further increased to 2850 MN/m2 (413 ksi) when measured at 77 °K. These values are higher by a factor of 4 than the values predicted by the rule of mixtures based on the highest reported strength of both niobium and copper. The composite strength is as high as that of the best copper whiskers and is shown to closely approach the theoretical strength of the material. The anomalous increase in strength despite the low volume fraction of reinforcing filaments suggests that the filam...
342 citations
TL;DR: In this article, the effect of eutectic morphology on the room temperature fracture toughness of different NiAl-based alloys was evaluated, and the results showed that directionally solidified alloys exhibited superior toughness compared to binary NiAl or conventionally cast alloys, but the principal mechanism responsible for the improved toughness was dependent on the second phase morphology.
244 citations
142 citations
01 Jul 1974-Metallurgical and Materials Transactions B-process Metallurgy and Materials Processing Science
TL;DR: In this article, the stability of the bcc phase in the Mo-Al, Fe-Al and Ni-Al systems has been investigated with a comparison with limited experimental data.
Abstract: Explicit descriptions of the Mo-Al, Fe-Al and Ni-Al systems have been developed and com-bined with descriptions of seven binary systems developed previously to compute significant numbers of isothermal sections in the Mo-Al-Cr, Ni-Al-Fe, Cr-Ni-Al, Al-Ni-Mo and Ni-Al-Ti systems. Comparison of these calculations with limited experimental data yields good results and provides considerable insight into the stability of the bcc phase in these systems. The computations provide detailed information on tie-line configurations and melting minima in these systems.
122 citations
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TL;DR: In this article, the deformation behavior of polycrystalline NiAl of various compositions, and of stoichiometric single crystals with different orientations, has been studied in compression in the temperature range 77-1300° K.
Abstract: The deformation behaviour of polycrystalline NiAl of various compositions, and of stoichiometric single crystals with different orientations, has been studied in compression in the temperature range 77–1300° K. All alloys except the aluminium-rich composition (53 at.-% aluminium) were deformable down to 77°K. Plastic deformation of single crystals was strongly anisotropic. All polycrystals and single crystals exhibited the three-stage temperature-dependence of the yield stress typical of b.c.c. alloys. The main effect of non-stoichiometry was to increase the athermal contribution to the yield stress; the strengthening produced by vacancies (aluminium-rich alloys) was greater than that produced by substitutional atoms (nickel-rich alloys).
169 citations
TL;DR: In this paper, a description of the observed microstructures, with discussion of the type of dispersion occurring in unmodified eutectics and the modification of lamellar arrangements by impurity cell formation, is given.
Abstract: Directional freezing experiments have been carried out with the binary eutectic mixtures, Al–Ag2Al, Al–CuAl2, Al–Zn, Al–Al3Ni, Ag–Cu, LiF–NaF and NaF–NaCl. Various aspects of eutectic solidification are discussed with particular reference to the importance of solid interfacial energy. The work is divided into three parts. I. A description of the observed microstructures, with discussion of the type of dispersion occurring in unmodified eutectics and the modification of lamellar arrangements by impurity cell formation. II. An account of the development of preferred orientations during the directional freezing of some eutectics. III. Measurements of the interphase separations as functions of the freezing rates and a discussion of the influence of solid interfacial energy upon these.
123 citations
TL;DR: In this article, the authors studied the mechanical properties of the cadmium-zinc lamellar eutectic and found that the yield stress σy is proportional to λ − 1 2.
69 citations
TL;DR: In this article, the strength of a linear dislocation pileup depends on the nature of its barrier and is analyzed for the case in which the barrier is a second-phase particle and for that the barrier was a locked dislocation with a different Burgers vector.
Abstract: The strength of a linear dislocation pileup depends on the nature of its barrier. Analysis is given for the case in which the barrier is a second-phase particle and for that in which the barrier is a locked dislocation with a different Burgers vector.In the first case, where pileups lie in front of hard inclusions, it is shown that the Hall–Petch relation is valid and that the Petch slope increases as the ratio of the inclusion/matrix shear moduli increases. For a screw dislocation pileup, the Petch slope increases by a factor of about 2 for a modulus ratio of 3 and by about a factor of 3 for a ratio of 7. The increase for edge pileups is somewhat higher.In the second case, where the barrier is a locked dislocation with a different Burgers vector, the Petch slope may be increased (or decreased) by a factor of √m, where m is the ratio of the Burgers vector of the locked dislocation resolved in the slip plane to that of the free dislocations in the pileup.
34 citations