Browsing by Author "Wu, BC"

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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.