Age-hardening behavior in the spray formed Ni-based superalloy

The microstructural features and age-hardening behaviors of spray formed Ni-based superalloy have been investigated. The alloy was solutioned at 1140℃ for 8 h followed by ageing at 780℃ for various time in the range of 2 h to 12 h. The microhardness, γ' precipitates size, morphology, electrical conductivity and positron annihilation lifetime as a function of ageing time were measured. The results show that the microhardness reaches a maximum after ageing for 8 h; at that time, the γ' precipitates grow up to a critical size of 56 nm. However, when the size of γ' precipitates is beyond the critical size, the microhardness decreases. The electrical conductivity rapidly increases up to its maximum value of 32%IACS with further increase of ageing time of 6 h, but the positron annihilation lifetime drops down to its minimum of 149 ps at this moment, and a maximum of 297 ps is reached after ageing for 10 h. The results are attributed to the changes of defect concentration and γ' precipitates size evolution during the ageing process.