Browsing by Author "Wei, Shen-Hung"

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Formation of omega and Ti2Ni phases in a residual Ti-Ni-Ti multilayer between stainless steel and zirconia after bonding at 1173K
(2014-10-03)
Wei, Shen-Hung
;
Lin, Chien-Cheng
;
材料科學與工程學系
;
Department of Materials Science and Engineering
Stainless steel (316L) and 8mol pct Y2O3-stabilized zirconia (8Y-ZrO2) were bonded using a Ti-Ni-Ti multilayer at 1173K (900 degrees C) for 1h. Cross-sectional transmission electron microscopy specimens were prepared by an innovative focused ion beam plus lift-out technique. In addition to acicular alpha-Ti, the dissolution of Fe, Cr, and Ni diffusing outwards from 316L into beta-Ti led to the precipitation of the omega (omega) phase with different variants in the residual Ti foil between 316L and Ni. The omega-phase was not found in the residual Ti foil between Ni and 8Y-ZrO2, while Ti2Ni precipitates were precipitated in some alpha-Ti grains owing to the exclusion of Ni from the beta-Ti.
Microstructural evolution and bonding mechanisms of the brazed Ti/ZrO2 joint using an Ag68.8Cu26.7Ti4.5 interlayer at 900 degrees C
(2014-03-14)
Wei, Shen-Hung
;
Lin, Chien-Cheng
;
材料科學與工程學系
;
Department of Materials Science and Engineering
In this study, 3 mol% Y2O3-stabilized zirconia (3Y-ZrO2) and commercially pure titanium (cp-Ti) joints were fabricated with an Ag68.8Cu26.7Ti4.5 interlayer (Ticusil) at 900 degrees C for various brazing periods. After brazing at 900 degrees C/0.1 h, Ti2Cu, TiCu, Ti3Cu4, and TiCu4 layers were present at the Ti/Ticusil interface, while TiCu and TiO layers were observed at the Ticusil/3Y-ZrO2 interface. In the residual interlayer, clumpy TiCu4 was formed along with the Ag solid phase. After brazing at 900 degrees C/1 h, Ti3Cu3O and Ti2O layers were formed at the interlayer/ZrO2 interface, while Cu2O was precipitated in the residual interlayer with [111](Cu2O)//[111](Ag) and (20 (2) over bar)(Cu2O)//(20 (2) over bar)(Ag). After brazing at 900 degrees C/6 h, a two-phase (alpha-Ti + Ti2Cu) region was observed on the Ti side with [2 (1) over bar(1) over bar0](alpha-Ti)//[100](Ti2Cu) and (0002)(alpha-Ti)//(0 (1) over bar3)(Ti2Cu), while the TiCu layer grew at the expense of Ti3Cu4 and TiCu4. The bonding mechanisms and diffusion paths were explored with the aid of Ag-Cu-Ti and Ti-Cu-O ternary phase diagrams.
Phase transformation and microstructural development of zirconia/stainless steel bonded with a Ti/Ni/Ti interlayer for the potential application in solid oxide fuel cells
(2014-04-28)
Wei, Shen-Hung
;
Lin, Chien-Cheng
;
材料科學與工程學系
;
Department of Materials Science and Engineering
The 8 mol% yttria-stabilized zirconia (8Y-ZrO2) was bonded to stainless steel 316L at 900 degrees C for 1 h in a protective Ar atmosphere using an interlayer of Ti/Ni/Ti. Interfacial microstructures were characterized using both secondary electron microscope (SEM) and transmission electron microscope (TEM), each with an attached energy dispersive spectroscope (EDS). A layer sequence of sigma-phase/TiFe2/TiFe + beta-Ti/Ti2Fe was observed at the stainless steel 316L/Ti interface, whereas a layer sequence of Ti2Ni/Ti2Ni + TiNi/TiNi3 was found at the Ti/Ni interface. Furthermore, TiO and c-ZrO2-x formed at the Ti/8Y-ZrO2 interface. An acicular alpha-Ti and a fine omega-phase existed along with beta-Ti in the residual Ti foil adjacent to the stainless steel 316L, but alpha-Ti and Ti2Ni were observed within beta-Ti in the other residual Ti foil adjacent to the 8Y-ZrO2. The orientation relationships of the omega-phase and beta-Ti were ${left[ {1bar 10} right]_{{rm{ beta {hbox-} Ti}}}}//{left[ {1bar 210} right]_{rm{omega }}}$ and ${left( {111} right)_{{rm{beta {hbox-} Ti}}}}//{left( {0001} right)_{rm{omega }}}$ , respectively. The microstructural development was elucidated with the aid of Fe-Ti and Ni-Ti binary phase diagrams.