Browsing by Author "Lih, WC"

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Activated diffusion brazed repair for IN738 hot section components of gas turbines
(2001-09-24)
Su, CY
;
Lih, WC
;
Chou, CP
;
Tsai, HC
;
機械工程學系
The wide-clearance activated diffusion brazing (ADB) techniques with various brazing alloys, namely DF4B and Nicrobraz 150 were applied to restore worn areas of IN738 components. In this study, the microstructure of an ADB joint and the results of thermal cyclic tests as well as tensile tests within the temperature range of from 25 to 980 degreesC were investigated and discussed. The results of the tensile tests showed that ADB specimens brazed by 40 wt.% DF4B at 1190 degreesC exhibited 85% tensile strength of the IN738 base materials at room temperature and retained the same strength as that of the base material at 980 degreesC. However, the ductility of the ADB specimens with both brazing alloys was reduced. The results of cyclic-oxidation tests showed that ADB specimens with Nicrobraz 150 as the brazing alloy decayed after 150 cycles. However, the ADB specimens with DF4B had no obvious weight change until 205 cycles. (C) 2001 Elsevier Science B.V. All rights reserved.
Microstructural characterisation of transient liquid phase zone of activated diffusion brazed nickel base superalloy
(1999-03-01)
Su, CY
;
Chou, CP
;
Wu, BC
;
Lih, WC
;
機械工程學系
Microstructural investigations of activated diffusion brazed (ADB) joints in IN738 plate were conducted. Joints of this type, which had wide gaps, were formed using the brazing alloys Nicrobraz 150, BRB, and DF4B. Tests on the wettability of the brazing alloys when associated with an IN738 surface showed that a slight degree of wetting was associated with a rapid onset of isothermal solidification and conversely a heavy degree of wetting was associated with a relatively low rate of isothermal solidification. The microstructure of the joint area was characterised using a scanning electron microscope and an electron probe X-ray microanalyser (EPMA). These showed that borides with a blocky morphology were present in joints associated with all three brazing alloys examined. A major difference in matrix phase chemistry was observed however for th three brazing alloys, e.g. an Ni-Ni3B eutectic phase was observed in Nicrobraz 150, but DF4B and BRB exhibited a coarsened gamma prime (gamma') phase and an absence of a Ni3B matrix phase.
Plasma transferred are repair welding of the nickel-base superalloy IN-738LC
(1997-10-01)
Su, CY
;
Chou, CP
;
Wu, BC
;
Lih, WC
;
機械工程學系
Plasma transferred are welding (PTA) has been considered a promising process tea restore worn areas of land-based gas turbine blades and vanes. The objective of this investigation was to study the effect of PTA welding on the repairing of IN-738LC superalloy components, Tensile tests were conducted on specimens welded with various combinations of parameters, Room temperature, 760 degrees C, and 980 degrees C were selected Its tensile test temperatures, High-temperature phase transformed, during solidification, were identified by differential thermal analysis (DTA), The weld-pool shapes and microstructures of welded specimens prepared by various welding parameters were evaluated by optical metallography (OM), a scanning electron microscope (SEM) equipped with energy dispersive x-ray spectrometer (EDS), and microhardness testing. Results of this study showed that PTA welded specimens exhibited 96% nominal tensile strength of IN-738LC base materials, Specimen failure was observed predominantly in the base materials instead of in the heat-affected zone (HAZ) for gas tungsten are weld (GTAW) repair weldments, IN-738LC is considered susceptible to weld cracking during fusion welding; however, using a low-input heat repair welding process (PTA), cracking susceptibility could be minimized by the optimized welding parameters.