Microstructure And Properties Of Large Nickel-Base Superalloys Castings Processed By Different Derectinal Solidification Techniques

In order to realize the industrialized application of liquid metal cooling(LMC) technique,the large DSM11 castings were fabricated using high rate solidification(HRS) and liquid metal cooling(LMC) techniques,and the effect of the directional solidification technique on both microstructures and properties of the large DSM11 castings was investigated.The effect of Sn element served as cooling medium in LMC process on microstructure and properties of the DSM11 alloys was also studied by adding different contents of Sn to the DSM11 alloy in HRS process.Furthermore,the heat treatment rule for the DSM11 alloys under different directional solidification techniques and different Sn contents was determined.The experimental results show that the finer and more homogenous microstructure can be achieved by LMC technique.In the LMC castings,small primary and secondary dendrite arm spacing as well as few tertiary dendrite are observed.Both volume fraction and size ofγ/γ′eutectic get reduced,and the finer and more uniformly-distributedγ′and carbides form.Moreover,the LMC process can reduce the micro-segregation of alloying elements and restrain the precipitation of the blockyηphase.The room temperature tensile strength of the DSM11 alloys processed by LMC technique gets improved.For the DSM11 alloys processed by LMC,the transverse stress rupture properties at 980℃/220MPa as well as the longitudinal stress rupture properties at 980℃/220MPa and 750℃/850MPa are higher,while the transverse stress rupture elongation at 980℃/220MPa is lower for the DSM11 alloy near the cooling plate.Moreover,the microstructures and properties of the DSMll alloys processed by LMC technique exhibit the good stability.For the DSM11 alloys processed by HRC technique and with different Sn contents,the primary and secondary dendrite arm spacing,volume fraction and size ofγ/γ′eutectic as well as the morphologies ofγ′and carbides are nearly same.The morphology of most carbides shows skeleton-like,and the few carbides are blocky.Tin is mostly segregated in boride near eutectics,and a few in the carbide and eutecticγ′phase,but hardly in the dendrite arms. Tin distributes homogenously in the DSM1l alloy after heat treatment.The room temperature tensile properties as well as the stress rupture properties at 980℃/220MPa and 750℃/850MPa for the DSM11 alloys processed by HRS technique and with different Sn contents are similar.Furthermore,the incipient melting temperature of the alloy processed by HRS technique is lower than that of the alloy processed by LMC technique.The solution temperature of the alloys processed by LMC technique gets increased due to reducing the segregation of the alloying elements.The addition of Sn in the DSM11 alloy decreases the incipient melting temperature because of forming the phases with low melting point.