Influence Of Heat Treatment On Microstructure And Mechanical Properties Of Nickel-base Superalloys

Influence of heat treatment on microstructures and mechanical properties of Ni-base superalloys K445, K35 and DZ417G superalloys has been investigated including the morphology, distribution and volume fraction ofγ' precipitates and their influence on mechanical properties.The microstructure and properties of hot corrosion-resistant Ni-base superalloy K445 on different heat treatment was investigated. As cast alloy was composed of matrix (γphase), main strengthing phase(γ'-Ni3Al), eutecticγ/γ' and MC which locate at interdendrite region. Solution temperature influence the size and morphology ofγ' phase. Hardness changes with the increase ofγ' phase(first reduce then increase). The influence of solution time onγ' and hardness is slight. Through influence the morphology and volume fraction ofγ' phase cooling manner after solution treatment influence hardness strongly. After ageing treatment the changes of hardness is similar with before ageing treatment.Stability of microstructure and mechanical properties after long-term ageing was investigated. With the increase of temperature and ageing time,γ' phase coarsening occurs during long-term ageing. Kinetics ofγ' phase coarsening is accord with Ostwald ripening and the energy of coarsening is 290kJ/mol. The influence ofγ' phase coarsening on tensile are discussed. Needle-like phase was observed during long-term ageing in K35 Ni-base superalloy. It was seem that the needle-like phase is sigma phase. And it's influence on rupture life was discussed.Influence of cooling rate, circular heat treatment and long-term ageing on microstructure and mechanical property in DZ417G was investigated. Cooling rate after solution influence the precipitate ofγ' phase strongly in DZ417G. The fast cooling is better for nucleate ofγ' phase but restrain its growth. On contrast the slow cooling is better for the precipitate of secondγ' phase sufficiently, but bad for the precipitate of thirdγ' phase. Moderate cooling rate create the best match of second and third, which heighten the tensile and perdure properties strongly. The volume fraction of bigger ofγ' phase reduce with increase of cyclic times. Especially, there only exist a little biggerγ' phase vicinage eutecticγ/γ' after 5th cycle. Influence of cyclic times on eutecticγ/γ' and MC carbide is little. Influence of cyclic times on tensile property is little, but the endurance reduce quickly after 4th cycles. During ageing at 800-900℃for 10000 hours,γ' phase's coarsening and decompose of MC occurs. But no TCP phase was observed. Those indicate that DZ417G has better microstructure stability. Tensile strength raise and yield strength reduce tensile plastic when tinseling at room temperature with raising of ageing temperature and lengthen of ageing time.