Processing, Microstructures and Mechanical Properties of a Ni-Based Single Crystal Superalloy

Qingqing Ding,Xinbao Zhao,Hongbin Bei,Yanfei Gao,Ze Zhang

doi:10.3390/cryst10070572

Qingqing Ding, Xinbao Zhao + Show 3 more

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https://doi.org/10.3390/cryst10070572

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Abstract

A second-generation Ni-based superalloy has been directionally solidified by using a Bridgman method, and the key processing steps have been investigated with a focus on their effects on microstructure evolution and mechanical properties. The as-grown microstructure is of a typical dendrite structure with microscopic elemental segregation during solidification. Based on the microstructural evidence and the measured phase transformation temperatures, a step-wise solution treatment procedure is designed to effectively eliminate the compositional and microstructural inhomogeneities. Consequently, the homogenized microstructure consisting of γ/γ′ phases (size of γ′ cube is ~400 nm) have been successfully produced after a two-step (solid solution and aging) treatment. The mechanical properties of the resulting alloys with desirable microstructures at room and elevated temperatures are measured by tensile tests. The strength of the alloy is comparable to commercial monocrystalline superalloys, such as DD6 and CMSX-4. The fracture modes of the alloy at various temperatures have also been studied and the corresponding deformation mechanisms are discussed.

Highlights

Ni-based single crystal (SX) superalloys have been widely used in turbine blades of aero-engines because of their excellent combination of mechanical properties and corrosion resistance under a wide range of elevated temperatures
The aim of the current work is to systemically study the processing–microstructure–property relationship of Ni-based SX superalloys, focusing on: (i) how to properly design each processing step based on microstructure evidence, and (ii) the behavior and the fracture modes of γ and γ0 phases during mechanical tests at various temperatures
After removing the ceramic mold, the rods are ready for further experiments

Summary

Introduction

Ni-based single crystal (SX) superalloys have been widely used in turbine blades of aero-engines because of their excellent combination of mechanical properties and corrosion resistance under a wide range of elevated temperatures. As a general designing strategy, to push the superalloys to an even higher temperature capability, more refractory elements are being added into these alloys [6,7,8,9], which, cause dendritic microstructures after single crystal growth and severe elemental segregation between the dendrite arms and the interdendritic regions. These segregation sites are potential places for creep failure [10,11]

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