Investigation of Fracture Mechanisms Thermal Stability and Hot-Strength Properties of Controlled Polyphase Alloys

摘要

The results of continued investigations concerning the effect of phase particle size on tensile strength, the thermal stability and the hot tensile strength of unidirectionally solidified A1-CuA12 and A1-A13Ni eutectic alloys are reported in this quarterly report. Production of sufficient ingots for all studies at three solidification rates has been completed using a semi-automatic temperature controller in conjunction with a water-cooled crucible end plug. Thermal stability studies of an A1CuA12 ingot produced at a 2.2 cm/hr solidification rate have shown that 500 hr of annealing at 537C are insufficient to cause breakdown of the lamellar structure at other than mismatch regions. Furthermore, there has been no measurable change in lamellar spacing or crystallography. However, there has been an increase in the number of terminations, termed faults, due to the breakdown of individual plates at defects in their surface. The first set of heat treatments on an A1-A13Ni specimen solidified at 2.2 cm/hr through 100 hr at 555C have been completed and post-heat treatment studies are under way. (Author)