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RISS 인기검색어
- 검색키워드
- 저자 : Peter K. Liaw (검색결과 3 건)
- 무료
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Fracture Behavior of Ceramic Matrix Composites during Monotonic and Cyclic Loadings
Kim, Jeong Guk,Liaw, Peter K. Trans Tech Publications, Ltd. 2007 Key Engineering Materials Vol.345-346 No.-
<P>The fracture behavior of ceramic matrix composites (CMCs) was investigated using the infrared (IR) thermography nondestructive evaluation (NDE) technique during monotonic and cyclic loadings. The CMCs used for this investigation are continuous Nicalon (silicon carbide fiber) fiber reinforced calsium aluminosilicate (CAS) glass-ceramics matrix composites. During monotonic tension and cyclic fatigue loadings, IR camera was used for in-situ monitoring of temperature evolution, and the temperature changes during testing were measured. Microstructural characterizations using scanning electron microscopy (SEM) were performed to investigate fracture modes and failure mechanisms of Nicalon/CAS samples. In this investigation, the NDE technique and SEM characterization were employed to facilitate a better understanding of damage evolution and progress of Nicalon/CAS composites during monotonic and cyclic loadings.</P>
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Lijing Lin,Xin Xian,Zhihong Zhong,Yucheng Wu,Peter K. Liaw 대한금속·재료학회 2020 METALS AND MATERIALS International Vol.26 No.8
The effect of long-term thermal exposure at 700 °C on the microstructure and mechanical behavior of as-castCrMnFeCoNiAl0.25was investigated. Results indicated that microscopically, the as-cast alloy was not an equilibrium alloyto maintain a single FCC structure after long-term aging. The strip-like sigma phase (Cr-rich σ phase) and B2 phase (NiAl)precipitated in the FCC matrix and coarsened when the exposure time was increased. Due to the increased volume fractionand the strengthening of these precipitates, the yield strength and Vickers hardness increased considerably with increasingthe thermal exposure time up to 2000 h. The yield strength increased from 272 MPa for the as-cast alloy to 993 MPa for thealloy exposed for 2000 h. The hardness increased up to 322 Hv for the alloy exposed for 2000 h. However, the yield strengthdecreased to 664 MPa for the alloy exposed for 4000 h, owing to the coarsening of precipitates. The alloy maintained a goodcompressive plasticity after long-term aging.
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Jingbo Qiao,Hongmin Zhang,Haoyan Meng,Fanchao Meng,Yang Tong,Daiyi Chao,Peter K. Liaw,Shuying Chen 대한금속·재료학회 2024 METALS AND MATERIALS International Vol.30 No.2
The equiatomic high entropy alloy (HEA) NiCoCrFePd crystalizes as a single face-centered cubic (FCC) phase with stronglocal lattice distortion due to large atomic size mismatch between Pd element and other constitute elements. To betterunderstand this quinary alloy, a family of single FCC phase equiatomic alloys made from the constituent elements of theNiCoCrFePd HEA, including the binary NiPd alloy, medium entropy alloys (MEAs) of NiCoPd, NiCrPd, and NiFePd, andthe quinary NiCoCrFePd HEA with fully-recrystallized microstructure was experimentally investigated to understand thechemical effects on grain growth kinetics and solid solution hardening. With the principal elements increasing from two tofive, the grain growth was increasingly inhibited in the annealing temperature range of 800–900 °C, while at 1000 °C andabove, the NiCrPd MEA showed the slowest grain growth, which may attribute to the higher melting temperature of Crand negative mixing enthalpy between Cr and other constituent elements, increasing the activation energy of grain growth. Moreover, the hardness depending on the grain size complied with the Hall-Petch relationship, in which NiCoPd exhibitedthe lowest hardness, while NiPd had a comparable hardness with NiCrPd and NiFePd. The above results suggested thatthe number of alloying elements was not the sole factor determining the sluggish diffusion and hardness. Instead, thetype of constituent elements in the Pd-containing multicomponent alloys played more critical role. Furthermore, it wasconcluded that the strength of MEAs and HEA should depend on the combination of atomic size and modulus mismatchand electronegativity difference.
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