Kinetics and microstructural evolution during recrystallization of a Ni_3Al-based single crystal superalloy

The recrystallization kinetics and microstructural evolution of a Ni3Al-based single crystal superalloy were presented, especially the different recrystallization behaviors between the dendrite arm and the interdendritic region. The single crystal alloy was deformed by grit blasting. A succeeding annealing under inert atmosphere at 1280 ℃ for different time led to the formation of recrystallized grains close to the grit blasting surface. It was found that the recrystallization depth and velocity in the dendrite arm were respectively deeper and faster than those in the interdendritic region where the Y-NiMo phase existed. The recrystallization process in the interdendritic region was significantly inhibited by the Y-NiMo precipitates. However, the pinning effect gradually weakened with the annealing time due to the dissolution of the Y-NiMo phase, and the recrystallization depth in the dendrite arm was deeper than that in the interdendritic region.

Surface recrystallization of a Ni_3Al based single crystal superalloy at different annealing temperatures and blasting pressure

The effects of annealing temperature and grit blasting pressure on the recrystallization behavior of a Ni3Al based single crystal superalloy were studied in this work. The results show that the precipitation of the Y-NiMo phase occurs at 900 and 1000 °C, which precedes recrystallization. The initial recrystallization temperature was between 1000 and 1100 °C. Cellular recrystallization was formed at 1100 and 1200 °C, which consisted of large columnar γ′ and fine γ + γ′. The dendrite arm closed to the interdendritic region may act as nucleation sites during initial recrystallization by a particle simulated nucleation mechanism at 1280 °C. The size of the grains first turned large and then became small upon the pressure while the recrystallization depth increased all the time.

Microstructures and properties of transient liquid phase diffusion bonded joints of Ni_3Al-base superalloy

An investigation of transient liquid phase (TLP) diffusion bonding of a Ni 3Al base directionally solidified superalloy, IC6 alloy, was presented. The interlayer alloy employed was Ni Mo Cr B powder alloy. The results show that the microstructure of the TLP diffusion bonded joints is a combination of γ solid solution (or a γ+γ′ structure) and borides. With the bonding time increasing, the quantity of the borides both in bonding seam and adjacent zones is gradually reduced, and the joint stress rupture property is improved. The obtained stress rupture property of the TLP bonded joints is on a level with the transverse property of IC6 base materials. [

Microstructure of Carbides at Grain Boundaries in Nickel Based Superalloys

It is well known that carbides at grain boundaries play an nickel based superalloys. In order to deeply understand the mportant role in affecting mechanical properties of relationship between grain boundary structures and properties, in this work, we have investigated the microstructure of grain boundaries with different misorienta- tion angles in bicrystals of nickel based superalloys. It is found that the bicrystals with smaller misorientation angles contain denser M23C6 but sparse MC particles at grain boundaries, and this kind of bicrystals presents longer stress rupture lives. It was observed that MC carbides were decorated by M23C6 and M6C particles at grain boundaries. The formation of these carbide particles, therefore, is likely due to the local fluctuation of chemical composition around MC carbides. In addition, the orientation relationships between MC carbides and γ/γ1 matrix were also determined.

The dependence of stress and strain rate on the deformation behavior of a Ni‐based single crystal superalloy at 1050°C

Ni‐based single crystal(SX)superalloys are important high‐temperature materials used for manufacturing turbine blades in aero‐engines.During service under combinational impacts of temperature and stress,the SX superalloy may reach its life due to plastic deformation,which normally accompanies time‐dependent microstructural degradation.To reveal this dynamically mechanical response,tensile tests at 1050°C are carried out to record stress‐strain curves at five stain rates as well as creep curves at four applied stresses.Deformed microstructures and defects have been analyzed to understand mechanical behaviors and the underlying mechanism by using advanced scanning electron and scanning transmission electron microscopes.Results show that the de-formation mode of the alloy strongly depends on the strain rates/applied stresses under mechanical loading.The dislocation density inside theγphase is extremely low at all tests,indicating that theγphase is relatively weak and ready to flow at this temperature even at a very fast strain rate.The deformation behavior of theγ′phase is much complicated.At fast strain rates or high applied stresses,the dislocation density in theγ′phase is very high,contributing to high‐stress requirements to deform the material.At slow strain rates or low applied stresses,rafting microstructures develop and the de-formation mode becomes directional coarsening/diffusion‐dominated.Our results de-monstrate a comprehensive understanding of the deformation mechanism of Ni‐based SX superalloys,which may provide lifetime prediction of the mechanical fail-ure,as well as the database for superalloy applications in mechanical systems.

Effects of Al on microstructural stability and related stress-rupture properties of a third-generation single crystal superalloy

To examine the influences of minor modification of Al content on the microstructural stabilities and stress rupture properties,two alloys with minor difference in Al content were exposed isothermally at 1100℃for 100 h,500 h,and 1000 h,respectively.The microstructures were characterized before and after thermal exposure.It was found that when Al content was decreased by 0.4 wt%,the volume fractionγ'decreased by 4%,the size ofγ'increased by 40 nm,the matrix channel width increased by 5 nm,and the misfit degree ofγ/γ'phases increased by 0.006%after heat treatment(HT).During thermal exposure,the alloy with low Al content had a better resistance to coarsening ofγ'phase and precipitation ofμphase.Theγ'particles of the alloy with high AI content tended to connect each other and coarsened along<100>directions;however,theγ'particles of the alloy with low Al content remained cubic after 500 h.A serious coarsening behavior took place in the two alloys after aging for 1000 h.The structural stabilities were significantly improved.However,the change of 0.4 wt%Al content was found to have little effect on the high temperature stress-rupture properties.