Abstract
A series of tensile tests were conducted at room and elevated temperatures on specimens of the alloy known as IC221M (Ni-8.2Al-7.6Cr-1.5Mo-2.1Zr, wt%). Specimens were tested in the as-cast condition or after aging in either air or Ar for up to 1000 h at 900-1100�XC. Room temperature yield strength decreased continuously with aging time at 900�XC from the as-cast value of 530 MPa to 320 MPa after 1000 h. A similar trend was found for hardness. The strength reductions with aging time at 900�XC were similar for aging in either air or Ar. For aging at 1050�XC and 1100�XC, aging in air caused significant strength loss that was attributed to aggressive oxidation. The room temperature yield strength of specimens aged in Ar increased for aging at 1050�XC and 1100�XC. Microhardness testing also showed that specimens aged at 1100�XC had higher hardness than those aged at 900�XC. Analysis using equilibrium thermodynamics suggested that the increases of yield strength and hardness resulted from increasing the amount of fine ���S precipitation in the alloy matrix. For testing at elevated temperatures, the as-cast alloy had room temperature yield strength of 530 MPa that increased continuously up to a value of 650 MPa at 700�XC. Aging in Ar for 1000 h at 900�XC resulted in a room temperature yield strength of 320 MPa that increased to 560 MPa at 700�XC and decrease slightly to 550 MPa at 900�XC. Aging in Ar for 1000 h at 1100�XC produced room temperature yield strength of 435 MPa that increased to 550 MPa at 500�XC and decreased continuously at high test temperatures. The behavior of these specimens was also rationalized using equilibrium thermodynamics to estimate the fractions of coarse and fine ���S particles in the microstructures.