M. S. Kaiser, A. S. W. Kurny,
Volume 8, Issue 4 (12-2011)
Abstract
Microstructure and properties of the Al-6Si-0.3Mg alloys containing scandium (0.2 to 0.6wt %) were investigated. The microstructure was observed by optical microscopy, the hardness was determined by Vickers tester and phase transformation was investigated by differential scanning calorimetry (DSC) technique. The results showed that scandium can refine dendrites, enhance hardness in the aged alloys and suppress softening effect during prolonged ageing treatment.
Seyed Hossein Razavi, Mehdi Safavi, M. Reza Aboutalebi, Seyed Mehdi Abbasi,
Volume 21, Issue 0 (3-2024)
Abstract
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.
