摘要 :
Single crystal sheets of niobium with initial orientations of (001)[110], (110) [110] and (111) [1 10] were rolled at room temperature in the strain range of 25-50%. The deformed specimens were vacuum annealed at temperatures of 8...
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Single crystal sheets of niobium with initial orientations of (001)[110], (110) [110] and (111) [1 10] were rolled at room temperature in the strain range of 25-50%. The deformed specimens were vacuum annealed at temperatures of 800 ℃, 1000 ℃, and 1200 ℃ for 3h. TEM, SEM-OIM and optical microscopy revealed orientation stability in (001) and (110) rolled samples with no recrystallization observed after annealing. Samples rolled along (111) partially recrystallized after annealing at 1000 ℃and 1200℃ A relatively small increase was observed in hardness of (001) rolled crystals between 25% and 50% strain, implying low work hardening rates. (111) rolled samples showed higher hardening rates, and enhanced recovery in hardness values after annealing, due to partial recrystallization. Conditions have been identified for the deformation and annealing of niobium single crystals, enabling the preservation of single crystal structure and near-complete recovery of mechanical properties. A simple crystallographic model is proposed, giving an explanation for the observed orientation stability in (001) and (110) rolled samples, and the tendency towards instability and recrystallization in (111) rolled samples.
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摘要 :
A set of stereological procedures has been developed for the rigorous quantification of microstructural features resolvable using scanning electron microscopy in α + β-processed α/β titanium alloys. This paper identifies the f...
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A set of stereological procedures has been developed for the rigorous quantification of microstructural features resolvable using scanning electron microscopy in α + β-processed α/β titanium alloys. This paper identifies the four microstructural features that most likely influence the mechanical properties in α +β processed titanium alloy, including: the size of the equiaxed alpha, the volume fraction of the equiaxed alpha, the volume fraction of total alpha, and the thickness of the Widmanstatten alpha laths. The details regarding the quantification methodologies are provided, as are the origins of the associated uncertainties.
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摘要 :
Thin films of nominal composition Ni-25at%Al have been sputter deposited from a target of the intermetallic compound Ni_3Al at different substrate deposition temperatures. The film deposited on an unheated substrate exhibited a st...
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Thin films of nominal composition Ni-25at%Al have been sputter deposited from a target of the intermetallic compound Ni_3Al at different substrate deposition temperatures. The film deposited on an unheated substrate exhibited a strongly textured columnar growth morphology and consisted of a mixture of metastable phases. Nanoindentation studies carried out on this film exhibited a strong strain hardening tendency. In contrast, the film deposited at 200℃ exhibited a recrystallized non-textured microstructure consisting of grains of a partially ordered Ni_3Al phase. At higher deposition temperatures (～400℃), larger grains of the bulk equilibrium, long-range ordered, Ll_2 Ni_3Al phase were observed in the film. Unlike the film deposited on an unheated substrate, the films deposited at elevated temperatures did not exhibit any dependence of the hardness on the indentation depth and, consequently no strain hardening. The average hardness of the film deposited at 200℃ was higher than the one deposited at 400℃. In addition to monolithic Ni-25Al thin films, multilayered Ni/Ni3Al thin films were also deposited. Multilayers deposited non-epitaxially on unheated substrates exhibited a strong {111} fiber texture while those deposited epitaxially on (001) NaCl exhibited a {001} texture. Free-standing multilayers of both types of preferred orientations as well as of different layer thicknesses were deformed in tension untill fracture. Interestingly, the {111} oriented multilayers failed primarily by a brittle fracture while the {001} multilayers exhibited features of ductile fracture.
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