The Effect of Calcium on the Type of Intermetallic Phases Obtainable in the Al-Cu Powder System and the Microstructure

Razieh Khoshhal

This study utilized aluminum, copper powder according to the stoichiometric ratio of Al₂Cu, and calcium powder in relation to the eutectic composition of Al-Ca at the ratio of 5.5 atomic percent. Two samples were prepared, one without calcium and another with calcium, and were analyzed to determine the impact of calcium on the formation of copper aluminide. Samples were subjected to thermal treatment at temperature of 400, 600, and 800ºC. The obtained results indicated that disappearance of Al₂Cu phase at 800ºC in calcium-free sample and existence of Al₂Cu phase in calcium sample indicating a possible role of calcium in stabilization of Al₂Cu phase. Furthermore, it was concluded that calcium influences phase formation. There was higher diffusion of aluminum in to copper resulting in formation of Al₄Cu₉ not only in the sample with calcium, but also in calcium-free sample. One more finding of the research is that calcium influences microstructure and its homogenization as well. In particular, it was found that calcium-containing sample has the least number of pores and was uniform in the structure.

Effect of Fine-Grained Area’s Dissolution after Solution Treatment Temperature on Tensile and Creep Life Enhancement of Hot Rolled Rene 65

Seyed Hossein Razavi

This study examines how solution treatment temperature affects the dissolution of fine-grained areas (FGAs) that form during hot rolling of René 65 nickel-based superalloy. These FGAs, which are rich in sub-micron to micron-sized primary γ' precipitates (γ'I) and located mainly in shear bands, remained stable after sub-solvus treatments below 1055 °C. They dissolved gradually with increasing temperature and disappeared completely above 1115 °C. The resulting microstructural changes, along with high-temperature tensile properties and creep behavior in the 1055–1115 °C range (followed by aging at 760 °C for 8 h), were evaluated. Raising the solution temperature reduced the FGA volume fraction and improved tensile elongation, while yield strength (YS) and ultimate tensile strength (UTS) remained largely unchanged. At 1095 °C, creep life at 730 °C / 530 MPa exceeded 100 h without fracture and exhibited a notably lower steady-state creep rate. These improvements appear linked to the elimination of secondary γ' depleted zones around the former FGAs, which produced a more uniform secondary γ' distribution, greater crack path deflection, and continued Zener pinning by remaining primary precipitates. However, solution treatment at 1115 °C caused grain growth and coarsening of secondary precipitates, which reduced creep performance. Overall, 1095 °C provided the best compromise for microstructural uniformity and balanced high-temperature properties in hot-rolled René 65.

Iranian Journal of Materials Science and Engineering

The Effect of Calcium on the Type of Intermetallic Phases Obtainable in the Al-Cu Powder System and the Microstructure

Effect of Fine-Grained Area’s Dissolution after Solution Treatment Temperature on Tensile and Creep Life Enhancement of Hot Rolled Rene 65