Formation and Prevention of a Surface Defect on the Aerofoil of As‐Cast Nickel‐Based Single‐Crystal Turbine Blades

Keehyun Park,Paul Withey

doi:10.1002/adem.202100302

Abstract

Surface scale is a common casting defect covering up to one‐third of the aerofoil on as‐cast single‐crystal turbine blades. To better understand and control this scale, the scaled and unscaled regions on the surface of a blade are observed. The surface of the unscaled region is covered with a relatively thick and uniform aluminum oxide layer. In comparison, the surface of the scaled region shows a different morphology, which is mainly composed of two different regions: one is a tessellated region with irregular polygons and the other with many irregular lines. The cross‐section and transmission electron microscopy samples of the scaled region clearly show that the surface is covered with double oxide layers of thickness 300–500 nm composed of several metallic oxides, which form after the normal microstructure of the base material during solidification. A specific region, which is in contact with the investment mold but remains in the scaled part, shows the possibility of this scale formation through the reaction of the initial aluminum oxide/mold wall material and the oxidation of the fresh surface of the base material. Based on these observations, the formation mechanism and the prevention of the surface scale are discussed.

Highlights

IntroductionFormation and Prevention of a Surface Defect on the Aerofoil of As-Cast Nickel-Based Single-Crystal Turbine Blades
The cross-section and transmission electron microscopy samples of the scaled region clearly show that the surface is covered with double oxide layers of thickness 300–500 nm composed of several metallic oxides, which form after the normal microstructure of the base material during solidification
The surface scale formed on the surface of as-cast turbine blades was observed by electron microscopy

Summary

Introduction

Formation and Prevention of a Surface Defect on the Aerofoil of As-Cast Nickel-Based Single-Crystal Turbine Blades. Surface scale is a common casting defect covering up to one-third of the aerofoil ensures a low diffusion rate, which means low rates of thermally activated creep.[1] To on as-cast single-crystal turbine blades. Nickel-based single-crystal superalloy different morphology, which is mainly composed of two different regions: one is a turbine blades have high mechanical tessellated region with irregular polygons and the other with many irregular lines. The cross-section and transmission electron microscopy samples of the scaled region clearly show that the surface is covered with double oxide layers of thickness 300–500 nm composed of several metallic oxides, which form after the normal microstructure of the base material during solidification. A specific approaching their melting temperature and under severe mechanical load.[1,2,4,5]

Results

Discussion

Conclusion