Papers by Keyword: Low Angle Boundary

Abstract: The microstructures of low angle boundaries (LABs) of a third generation single crystal superalloy DD9 in as-cast state and after different heat treatment processes were studied by optical microscopy (OM) and field emission scanning electron microscopy (FESEM). The results showed that the as-cast LABs of DD9 alloy consisted of rod-like and bulk γ' phases with γ matrix between them, and there were eutectic γ-γ' precipitating at the LABs, as well as small amounts of discrete distribution of carbides. The γ' phase locateed at the grain boundaries was larger than that distributed on both sides of the grain boundaries. After the solution heat treatment, as-cast eutectic γ-γ' at LABs dissolved completely, and rod-like γ' phase was still found at some LABs. Meanwhile, the LABs were inclined to be straight compared to the as-cast state. The primary aging heat treatment made γ' phase at the LABs dissolved completely, and the secondary aging heat treatment resulted little change in the morphology of the LABs. Thus, the effect of the primary aging heat treatment on the microstructures of the LABs was greater than that of the secondary aging heat treatment.

Abstract: The microstructure of a third generation single crystal superalloy DD10 with 0°~15° grain boundary and stress rupture property at 980°C/280MPa and 1100°C/140MPa have been studied and compared in the present investigation. The results showed that the primary dendritic stems at either side of low angle boundary indicated angular differences as compared with structure of principal [001] crystal. After thermal treatment, the grain boundary changed from irregular chain structure of γ’ and γ to flat and thin γ layer. Under the condition of 980°C/280MPaand 1100°C/140MPa, stress rupture life of the DD10 alloy with 7° low angle boundary decreased little compared with [001] crystal. The rupture was non-intergranular fracture. The 9° low angle boundary did not have a remarkable effect on stress rupture property of the DD10 alloy.

Abstract: The structure of disconnections in symmetrical low- and high-angle [0001] tilt boundaries in an hcp metal are studied using atomic-scale simulation. Applied engineering strains cause such defects to move conservatively along the boundaries, producing coupled shear and migration. The Peierls stresses causing such motion are found to decrease precipitously through the transition from low- to high-angle boundaries. The reason underlying this behaviour is discussed.

Abstract: The specimens were machined from DD6 single crystal superalloy blades with low angle boundary. The misorientation of LAB was measured with EBSD technique in scanning electron microscope. The microstructures of specimens with LAB were examined in optical microscope and scanning electron microscope. The formation mechanism of low angle boundary of DD6 single crystal superalloy blades was investigated. The results showed that he formation of LAB which is caused by the deviating orientation from ideal [001] and the angle between the crystal orientation and shell is crystal selection process acted by dendrite competitive growth rule. Part of dendrites have changed their growth orientation a little to the decreasing [001] orientation departure angle because of solidification condition fluctuating during dendrites branching process. The LAB is the obvious interface between the deforming dendrites and their surrounding dendrites.

Abstract: In the work the single-crystalline alloy CMSX-4 was studied. The main aim of the study was an attempt to find correlations between images of X-Ray topography, X-ray diffraction maps of lattice parameter and misorientation angle and Scanning Electron Microscopy (SEM) images obtained by back-scattered electron (BSE) technique. Topography images were obtained by Auleytner method with wide beam. Diffractometer provided by EFG company was used for obtaining orientation and lattice parameter maps. Material for research was produced in Research and Development Laboratory for Aerospace Materials of Rzeszów University of Technology. Casts were obtained in ALD furnace by the Bridgman technique. It was found that X-ray topograms were correlated with SEM images of microstructures as well as with orientation and lattice parameter maps. X-Ray topograms showed high contrast bands which corresponded to dendrite arms. There was a correlation between low angle boundary and lattice parameter map.

Abstract: The tensile properties of DD6 alloy with twist low angle boundaries were investigated at 760°C, 850°C and 980°C, and the misorientation angle of twist low angle boundaries of the specimens of the alloy varies from 0º to 12º. The results showed that when the angle of low angle boundaries is relatively small, it has a little effect on the tensile properties of the alloy. It is notable that effects of low angle boundaries on the tensile strength are weaker than those on the tensile elongation. The characteristic of quasi-cleavage, intergranular and dimple fracture were observed on the tensile rupture surfaces of the specimens, and the tensile fracture mechanism was discussed.