Investigation On Microstructural Stability In Ni-Mo-Cr Superalloy

Nickel-based superalloys have been widely used to make the advanced gas turbines for their excellent creep performance,fatigue resistance,corrosion resistance and good oxidation resistance at high temperature.Nickel-based superalloys consist of a variety of refractory elements which will promote the precipitation of topologically close-packed?TCP?phases during the high temperature creep.Therefore,inhibiting the precipitation of TCP phases is important for improving the property of superalloys.The interaction of elements is complex.The alloy structure is simplified in our work.Ni-Mo-Cr model superalloy including two phases?+TCP,was selected to explore the precipitation mechanism of TCP phases during thermal exposure experiments.The main results are shown as follow:1.The Ni-20Mo-10Cr?at.%?model superalloy is thermal exposured at the temperature of 800°C for different times.Plenty of shuttle like Ni₂?Mo,Cr?superlattice phases are precipitated.The size is 100²00 nm along the long axis and30⁵0 nm along the short axis.The interface between Ni₂?Mo,Cr?and matrix remained coherent.Mo or Cr atoms occupy the site of 3d?220??.The content of Mo and Cr increases with the thermal exposure time increasing.The orientation relationship between the Ni₂?Mo,Cr?phase and the matrix are determined as:[010]Ni₂?Mo,Cr?//[001]?,?002?Ni₂?Mo,Cr?//?220??;[010]Ni₂?Mo,Cr?//[001]?,?002?Ni₂?Mo,Cr?//?2???0??;[111]_Ni2?Mo,Cr?//[112]?,?0???1?_Ni2?Mo,Cr?//????11??and[1???1]_Ni2?Mo,Cr?//[112]?,?011?_Ni2?Mo,Cr?//????3?????.A small quantity of?phase and rich-Mo phase ware observed at the condition 800?/20 h.2.The TCP phases formed at 900?were identified as?phase,which was riched in Mo and short of Cr.The orientation relationship between?phase and the matrix is determined as:[1???0]?//[110]?,?110??//?200??.The morphology of?phase is rod-like,faceted blocky,and few in branch shapes.Plenty of planar defects was found in some?phases.