서지주요정보
Fabrication process and mechanical properties of NiAl/Ni micro-laminated composites by reaction synthesis = 반응합성법에 의한 NiAl/Ni 미세적층복합재료의 제조공정 및 기계적 성질
서명 / 저자 Fabrication process and mechanical properties of NiAl/Ni micro-laminated composites by reaction synthesis = 반응합성법에 의한 NiAl/Ni 미세적층복합재료의 제조공정 및 기계적 성질 / Hee-Yeoun Kim.
발행사항 [대전 : 한국과학기술원, 2005].
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8016817

소장위치/청구기호

학술문화관(문화관) 보존서고

DAME 05029

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초록정보

Fabrication process and mechanical properties of NiAl/Ni micro-laminated composites were investigated. NiAl/Ni micro-laminated composites have the possibility of combining the good ductility and toughness of metals with the higher elastic modulus, higher strength, and lower density of intermetallics. Toughening in these composites is derived from the rupture of the Ni phase that has bridged the cracks developed in the brittle NiAl phase. Thus micro-laminated composites are particularly attractive, because no physical mechanisms exist by which the cracks in the brittle phase can bypass the more ductile metal phase. NiAl/Ni intermetallic/metal micro-laminated composites were formed by a recently developed process in which SHS reaction was initiated at the interface between Ni and Al element foils. After the reaction, one of the metal foils was entirely consumed, resulting in NiAl/Ni micro-laminated composites. First objective of this paper is to characterize the microstructure evolution during processing, investigate how the reaction proceeds, and analyze the effect of processing parameters such as thickness and thickness ratio of element foils, diffusion bonding time, and pressure. Second objective is to characterize and analyze the elastic, tensile, and fracture behaviors of the micro-laminated composites which are designed to investigate the relationship between microstructure and mechanical property. The reaction mechanism and microstructure evolution during reaction synthesis have been investigated. The reaction between Ni and Al micro-foils started with a nucleation and growth of $NiAl_3$ followed by a diffusional growth of $Ni_2Al_3$ between Ni and NiAl3. By post-heat treatment with applied pressure, the reaction products were converted to NiAl and $Ni_3Al$ having better strength at high temperature. The hardness at the center of intermetallic is lower than other positions due to shrinkage cavity and becomes more uniform through the entire intermetallic layer as the applied pressure increases. Fabrication process consisting of diffusion bonding, reaction synthesis, and post heat treatment are suggested for the fabrication of NiAl/Ni micro-laminated composite containing Ni-rich intermetallic. When the combined thickness $(λ=t_{Ni}+t_{Al})$ was below 40㎛ and thickness ratio became to 1:1, the monolithic intermetallic could be made and this intermixing criteria depended on mainly the conductive heat loss through Ni layer. The effect of initial thickness ratio and diffusion bonding on microstructure was thermodynamically calculated by using the volume fraction of un-reacted liquid Al as a parameter. As the thickness ratio (Ni:Al) and diffusion bonding time increased, the amount of un-reacted liquid Al decreased. For the characterization of mechanical properties, type I and II NiAl/Ni micro-laminated composites were prepared by using various Al thickness (100㎛, 50㎛, 25㎛) reaction-bonded with constant Ni thickness (100㎛), and various Ni thickness (75㎛, 50㎛, 20㎛) reaction-bonded with constant Al thickness (10㎛), respectively. Major intermetallic phase was Al-rich $Ni_{0.45}Al_{0.55}$ in type I, and Ni-rich $Ni_{0.58}Al_{0.42}$ and $Ni_3Al$ in type II. The elastic modulus of type II micro-laminated composites were measured by tensile test and RUS (Resonant Ultrasound Spectroscopy). As the intermetallic volume fraction increased, the elastic modulus of micro-laminated composites increased due to the higher elastic modulus of intermetallic but deviated from the linearity (Voigt model) at higher intermetallic volume fraction. Deviation from the linearity of elastic modulus caused from the texture change of Ni layer in micro-laminated composites. The texture of Ni layer at low intermetallic volume fraction showed random orientation and the texture of Ni layer at higher intermetallic volume fraction showed cube texture ((001)[100]) similar to pure Ni foil. Thickness ratio effect on thermal residual stress was analyzed by assuming the bilayer structure of Ni and $Ni_3Al$. When thickness ratio $(t_{Ni}/t_{Ni3Al}$)$ became similar, the stress gradient in Ni layer increased and showed the maximum value at the thickness ratio range of 1.5~3.0. The variation of stress gradient brought the texture change of Ni layer within this thickness range. Thermal residual stress in Ni layer measured by X-ray $sin^2Ψ$ method was the biggest at high intermetallic volume fraction. Thus, no texture change and less stress relaxation happened in this specimen was related directly the nonlinearity of elastic modulus in micro-laminated composites. Tensile and fracture properties of two types of micro-laminated composites have been investigated. They showed the different strength behavior as the intermetallic volume fraction increased. Multiple cracking during tensile loading of micro-laminated composites could be related to the shear-lag condition satisfied at the intermetallic/metal interface and the different tensile strength behavior of two types was explained by different intermetallic strength. It was confirmed by CTOD and tensile behavior that the fracture toughness enhancement of intermetallic/metal micro-laminated composites was due to bridging traction by ductile metal layer. R-curve test results showed increasing fracture toughness compared to the monolithic intermetallic and the bridging traction based on LSB model was estimated to be 250~300MPa in all specimens. These values were very well matched with three times of yield strength of annealed pure Ni foils if the plastic constraint of metal layer was considered by linear elastic fracture mechanics. Fracture mode transition from single to multiple fracture in intermetallic/metal micro-laminated composites were successfully explained by combined model of LEFM and shear lag model as applied in metal/ceramic system previously. Fracture mode transition caused by the change of stress field around crack tip according to intermetallic volume fraction and FEM results using 3D SENB specimen geometries were in good agreement with analytical solutions based on LEFM.

서지기타정보

서지기타정보
청구기호 {DAME 05029
형태사항 xvi, 179 p. : 삽도 ; 26 cm
언어 영어
일반주기 저자명의 한글표기 : 김희연
지도교수의 영문표기 : Soon-Hyung Hong
지도교수의 한글표기 : 홍순형
수록잡지명 : "Reaction synthesis and microstructures of NiAl/Ni Micro-laminated composites". Material science & engineering A, v.396, pp. 376-384(2005)
학위논문 학위논문(박사) - 한국과학기술원 : 신소재공학과,
서지주기 Reference : p. 173-179
주제 NiAl/Ni
Microlaminate
Reaction Synthesis
Fabrication Process
Mechanical Property
NiAl/Ni
미세적층복합재료
반응합성법
제조공정
기계적 성질
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