| Budget Amount *help |
¥3,700,000 (Direct Cost: ¥3,700,000)
Fiscal Year 2005: ¥1,100,000 (Direct Cost: ¥1,100,000)
Fiscal Year 2004: ¥2,600,000 (Direct Cost: ¥2,600,000)
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| Research Abstract |
Heavily cold-rolled foils of L1_2-type Ni_3(Si,Ti), Ni_3Al and Co_3Ti ordered intermetallic alloys were successfully fabricated by the newly designed thermomechanical processing using conventional polycrystalline ingots. Also, thin sheets of B2-type FeAl, NiAl, CoTi and CoZr intermetallic compounds were fabricated by the two-step hot-rolling. Microstructure including texture and grain boundary character, and mechanical properties of these thin sheets or foils were studied. Main results obtained from the present study are as follows : (i)Texture development during cold rolling of Ni-based L1_2 ordered alloys (i.e., Ni_3(Si,Ti), N_3Al and Ni_3Fe) as well as fcc disordered nickel was investigated by means of the orientation distribution function (ODF). The cold rolling texture of these Ni-based L1_2 ordered alloys was found to be a copper-type with a prominent component of Bs {011}<211> orientation. In addition, intensity of rolling texture of L1_2 alloys was relatively weak in comparison
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that of fcc nickel. These results can be interpreted by consideration of cross slips for superlattice dislocations and ordinary dislocation whose width are estimated by energies of stacking-fault-like defect (SFLD) (i.e., antiphase boundary (APB) in the case of L1_2 ordered structure and stacking fault (SF) in the case of fcc disordered structure). (ii)Grain boundary character distribution (GBCD) of the recrystallized L1_2 ordered alloys and fcc disordered alloys was determined by the electron backscatted diffraction (EBSD) method. A number of annealing twin boundaries (i.e., Σ3 boundaries) were observed in both the L1_2 and fcc alloys. It was suggested that the frequency of Σ3 twin boundary was primarily dominated by the stacking fault energy, regardless of L1_2 ordered or fcc disordered alloys. On the other hand, the difference in the feature of grain boundaries between L1_2 ordered and fcc disordered alloys could be interpreted by the energetic consideration for the grain boundary in which the APB energy (i.e. the ordering energy) due to the wrong bonds is incorporated into. (iii)Mechanical property of the L1_2 thin foils were evaluated by tensile test at room temperature as well as at high temperature. It was found that owing to heavily cold-rolling and proper annealing, these intermetallic foils showed high tensile strength and considerable elongation at room temperature, and also that their high temperature tensile strength was superior to that of conventional metallic materials such as nickel alloys and stainless steels. (iv)Texture evolution during hot-rolling and recrystallization of B2 type FeAl, NiAl and CoTi intermetallic compounds were investigated by means of X-ray pole figure and EBSD methods. The hot-rolling textures of FeAl, NiAl and CoTi are commonly composed of a ND//{111} textural component. The orientations of the recrystallized gains were evolved within the orientation distribution of the deformed matrix, but were more dispersive than those of the deformed grains. It was suggested that the non-selected grain growth was responsible for the observed weak recrystallization textures of the present compounds. (v)B2-type CoZr intermetallic compound was hot-rolled and subsequently recrystallized. Tensile test was revealed that CoZr with recrystallized microstructure exhibited a notable tensile ductility at room temperature as well as at elevated temperature. Furthermore, the recrystallized CoZr was possible to be cold rolled to 70% reduction. These results is strongly suggested that B2 CoZr phase is substantially ductile whereas most of B2-type intermetallic compounds show poor ductility, particularly at room temperature. Less
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