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황선근,윤의한 대한금속재료학회(대한금속학회) 1993 대한금속·재료학회지 Vol.31 No.7
The effects of powder process on combustion characteristics, microstructure and mechanical properties of the Ni₃Al compounds were studied. Ni₃Al-B allays fabricated by the combustion synthesis with the reactive sintering(RS) and self-propagating high-temperature synthesis(SHS) showed a relative density of 97% and 96%, respectively. The microstructure of the alloys by both processes consisted of equiaxed grains of 30㎛ in size and uniformly distributed pores. Proper consolidation of the alloys required an optimum range of the green density, 65∼70% of theoretical. Excessive addition of ZrO₂also impaired the sintered density and hindered complete alloying. While the particle size ratio(d_(Al)/d(Ni)) was important in combustion synthesis, the heating rate was particularly critical in reactive sintering. Ni₃Al-B-ZrO₂alloy processed by RS showed a combination of tensile yield strength, 500MPa and tensile ductility, 10%, whereas that by SHS had inferior mechanical properties due to segregation of ZrO₂particles.
분말압출된 Ni3Al-0.5B 금속간화합물의 기계적 성질에 미치는 결정립 크기의 영향
황선근,윤의한 대한금속재료학회(대한금속학회) 1993 대한금속·재료학회지 Vol.31 No.4
The grain size dependence on mechanical properties of Ni₃Al-0.5 B alloys hot extruded from elemental powders was studied. Yield strength of the Ni₃Al-0.5 B decreased with increasing grain size produced by annealing at 1000℃, but weakened at higher temperatures. The reduced grain size also diminished the extent of anomalous yielding. For the range of grain size from 6 to 103㎛, the yield strength of the alloys was given by the Hall-Petch relationship, σ_y=σ_o+ k_y·d^(-1), where n = 0.85±0.05, σ_o=420±8 MPa and k_y=2041±168 MPa·㎛^(0.85±0.05). The deviation of the relationship from n=-0.5 was explained in terms of work hardening within Lu¨ders bands and oxide dispersion hardening. Tensile elongation of the test specimens showed insignificant variation for small grain sizes but decreased moderately for the grain size larger than about 70㎛. Regardless of the grain size, all the test specimens showed predominantly ductile transgranular fracture at room temperature.
Zircaloy-4 의 상변태 특성에 따른 집합조직 분석
황선근,오성근,이재일 대한금속재료학회(대한금속학회) 1992 대한금속·재료학회지 Vol.30 No.8
The texture of Zircaloy-4 sheets induced by phase transformation was analyzed by Kearns number f_n and CODF(crystallite orientation distribution function). In order to improve the accuracy of the program which computers CODF, a two-step method for calculating the coefficients W_(lmn) of CODF from the incomplete pole figure data was introduced into the program. The odd-1 terms which cannot be acquired from the pole figure data were calculated by the Gaussian model function. The texture change accompanying phase transformation was studied with the misorientation distribution function(MODF) An MODF analysis revealed that the non-diffusional transformation phase had an orientation relationship with the diffusional transformation phase which formed before the non-diffusional transformation. The orientation relationship was attributed to the variants selection of transformation due to the anisotropy of thermal contraction, which could be explained in terms of the Schmid factor.
분말야금법에 의한 Ni3Al-0.5 B 금속간화합물의 고온 기계적 성질
황선근,윤의한 대한금속재료학회(대한금속학회) 1993 대한금속·재료학회지 Vol.31 No.4
The effects of P/M processing methods on the mechanical properties of Ni₃Al-0.5 B intermetallic compound were studied. The major gases evolved during the degassing were water vapor and hydrogen. The density of experimental alloy was improved by hot isostatic pressing (HIP) following either reactive sintering (RS) or vacuum hot pressing (VHP); a full density was obtained by hot extruding (HE) elemental powder compacts. The ambient tensile yield strength, 840 MPa and elongation, 41% of hot extruded experimental alloys with 7㎛ grain sizes were superior to those of cast alloys found in the literature. However, the peak temperatures (T_P=400∼500℃) corresponding to the maximum yield strength of experimental alloys were lower than those (T_P=600℃ ) of cast alloys. The tensile characteristics of the experimental alloys were explained in terms of grain refinement, formation of γ+γ' duplex structure and a distribution of oxides.