Processing and mechanical properties of in-situ composites from the NiAlCr and the NiAl(Cr,Mo) eutectic systems

In-situ composites based on the NiAlCr eutectic system have been successfully produced by containerless processing and evaluated. Molybdenum additions of 0.6 to 6 at.% were used to change the eutectic microstructure. The NiAlCr alloys had a fibrous microstructure, while the NiAl(Cr,Mo) alloys containing 1 at.% or more of molybdenum exhibited a lamellar structure. The room temperature fracture toughness of the different eutectic alloys was evaluated. The toughness values of the directionally solidified eutectics were similar regardless of composition or eutectic morphology, but all the directionally solidified alloys exhibited superior toughness compared to binary NiAl or conventionally cast eutectics. However, the principal mechanism responsible for the improved toughness of the directionally solidified alloys was dependent on the second phase morphology. The effect of eutectic morphology on the 1300 K creep strength was also investigated by testing a typical fiber reinforced and a lamellar reinforced eutectic. A molybdenum-doped alloy with the lamellar eutectic morphology exhibited the best creep resistance. Due to the promising creep behavior of this NiAl-28Cr-6Mo alloy at 1300 K, additional creep testing was performed at 1200 and 1400 K. This NiAl(Cr,Mo) eutectic displays promising high temperature strength while still maintaining a reasonable room temperature fracture toughness when compared to other NiAl-based eutectics.