Strength of Intermetallic Matrix Composites by Controlling Interface Reactions

点击翻译按钮获取中文摘要

Based on the obtained results in the proceding years, model composites of B doped Ni-rich Ni_3Al reinforced with W fibers are successfully fabricated by isothermal forging Ni_3Al plates sandwiching W fibers at 1373K to 1473K.It is found that isothermal forging of cold rolled Ni_3Al plates enables better consolidation and lower forging temperature than that of recystallized Ni_3Al plates. No reaction zone is formed at interfaces of as-fabricated composites. However, SEM/EDX result reveals that W and Ni diffuse each other, suggesting that strong bonding is produced at the interfaces.A stress-strain curve of the composite tensile tested at ambient temperature exhibits serrations resulting from brittle failure of W fibers. No pull-out of W fiber are observated in a fracture surface, indicating that cohesive strength between W fibers and matrix is very high.Deformation and fracture behavior of the composites at elevated temperatures are influenced by those of monolithic Ni_3Al alloys. Yield … More strength is higher in the composites than in the monotilluc alloys at all temperatures tested (ambient to 1323K). Especially, increase in strength by the reinforcement is remarkable (1.5 to 2 times) in the low (ambient to 973K) and high (above 1273K) temperature region. Strengthening is not attained in the intermediate temperature region (1073 to 1173K) because of brittle intergranular fracture in the matrix.Tensile strength in the low temperature region (e.g. 873K) is lower than that calculated by the low of mixtures, suggesting that B segregation to the W/Ni_3Al interfaces leads to decrease in B content at grain boundaries in the matrix. Tensile strength in the high temperature region (e.g. 1323K) is in fairly good agreement to the calculated value.It is revealed that W/Ni_3Al composites posses high strength over monolithic Ni_3Al alloys at temperatures up to 1323K.Holding above 1373K produces an interface place W_3Ni and Kirkendall voids, thereby reducing strength of the composites. Less