MOBERLYCHAN et al: ROLES OF AMORPHOUS GRAIN BOUNDARIES 1631 HP@1780°c/1hr x;计 的:2话a Hexoloy 0-6H 1. 5nm Fig. 6. HR-TEM es of amorphous grain boundaries. (a) Between an -4H 22110) orientation) and a B grain(<3 from a( 110)orientation) in ABC-SiC he sed at I780°C for I h. The amorphous phase in ABC-SiC was typically < I nm thick. (b) Between two a-6H grains in xoloy-SA(upper and lower grains within 5 of a (8 10 2 3)and a(2110)orientation, respectively) Although some thick amorphous grain boundaries existed in Hexoloy-SA, the amorphous phase was typically <2 nm thick tained ternary Al-o-C phases [36]. The Auger in materials often not experimentally signal at 180 eV was at the detection limit (2-5%) detected [20, 32, 35]. Weak beam dark field ima- in Fig. 7(a)and 7(b), thus the existence of B in the ging, which has been utilized in some material sys- grain boundary layer was inconclusive. (The ma- tems to depict amorphous films at all grain jority of the B in this ABC-SiC is incorporated in boundaries, was unsuccessful at imaging the grain the ternary Alg B C7 phase [17, 21, 8, 36]; however, boundaries in ABC-SiC. The difficulties with dark Bs influential role in sintering and grain boundaries field imaging were due to a combination of the pretained ternary Al0O0C phases [36]. The Auger signal at 180 eV was at the detection limit (2±5%) in Fig. 7(a) and 7(b), thus the existence of B in the grain boundary layer was inconclusive. (The ma￾jority of the B in this ABC±SiC is incorporated in the ternary Al8B4C7 phase [17, 21, 8, 36]; however, B's in¯uential role in sintering and grain boundaries in materials is often not experimentally detected [20, 32, 35].) Weak beam dark ®eld ima￾ging, which has been utilized in some material sys￾tems to depict amorphous ®lms at all grain boundaries, was unsuccessful at imaging the grain boundaries in ABC±SiC. The diculties with dark ®eld imaging were due to a combination of the pre￾Fig. 6. HR-TEM images of amorphous grain boundaries. (a) Between an a-4H grain (<58 from a h2110i orientation) and a b grain (<38 from a h110i orientation) in ABC±SiC hot pressed at 17808C for 1 h. The amorphous phase in ABC±SiC was typically <1 nm thick. (b) Between two a-6H grains in Hexoloy±SA (upper and lower grains within 58 of a h8 10 2 3i and a h2110i orientation, respectively). Although some thick amorphous grain boundaries existed in Hexoloy±SA, the amorphous phase was typically <2 nm thick. MOBERLYCHAN et al.: ROLES OF AMORPHOUS GRAIN BOUNDARIES 1631