Nimonic 263 has been developed for the improved ductility in welded assemblies and is a candidate material for gas turbine combustor and transition pieces along with its good weldability and mechanical properties at room and elevated temperatures. In this study, the tensile behavior of an as-welded Nimonic 263 specimen at room temperature and 1053 K (780°C) was examined in conjunction with microstructural evolution during welding and postweld heat treatment (PWHT). With the welding and the PWHT, the yield strength (YS), ultimate tensile strength (UTS), and tensile elongation of Nimonic 263 varied in a complex manner. It was observed that the PWHT of resolutionization at 1423 K (1150°C) for 2 hours gave the highest YS and UTS values, whereas the tensile elongation was the lowest, at both testing temperatures. With increasing resolutionization time, the YS and UTS tended to decrease along with the increase in tensile ductility. The tensile behaviors of as-welded Nimonic 263 specimens was affected by several factors, including grain size, residual stress, possible microsegregation of c¢ forming elements, a tendency for interdendritic or intergranular fracture and a morphological change in both M 23 C 6 and MC type carbides, depending on the testing temperature and the PWHT. The complex changes in tensile properties of Nimonic 263 with welding and PWHT at room temperature and 1053 K (780°C) were discussed based on the micrographic and fractographic observations.
A proto-model of an off-axis reflective fore-optics in a new hyperspectral sensor onboard a small unmanned aerial vehicle (UAV) is developed for low-altitude coastal remote sensing. In spite of the substantial advantages of off-axis optics over refractive or on-axis reflective optics, it is difficult to fabricate and align the mirrors in off-axis systems because of their asymmetric configurations. The fore-optics is designed by Korea Institute of Ocean Science & Technology (KIOST) as a three-mirror system including aspheric primary and secondary mirrors, with an entrance pupil diameter of 70 mm and F-ratio of 5.0. The off-axis mirror is fabricated by a single point diamond turning machine (SPDTM) with a form accuracy of 89.3 nm (RMS) and surface roughness of 7.2 nm (Ra). Coarse alignment of this three-mirror off-axis optical system is accomplished by using a designated base plate and a coordinate measuring machine. The optical performance is tested using the point spread function of the returned collimated beam of a Fizeau interferometer.
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