The Microstructure and Properties of Laser Shock Peened CMSX4 Superalloy

Magdalena Rozmus-Górnikowska,Łukasz Cieniek,Jerzy Morgiel,Jan Kusiński

doi:10.1007/s11661-021-06277-7

Abstract

The influence of laser shock peening on the surface morphology and microstructure of single-crystal CMSX4 nickel-based superalloy was investigated by optical profilometry and atomic force microscopy, scanning and transmission electron microscopy as well as scanning-transmission electron microscopy in high-angle annular dark-field mode. Maps of chemical elements distribution in the laser-affected areas were determined using energy-dispersive X-ray spectroscopy. Furthermore, after the LSP, nanohardness tests were conducted on the cross section of the treated samples as well as the untreated material. Laser shock peening caused an ablation and melting of the surface layer and hence enlarged the surface roughness. Beneath the surface, in the laser shock-peened areas, severe distortion of the regular {gamma mathord{left/ {vphantom {gamma {gamma^{prime}}}} right. kern-0pt} {gamma^{prime}}} microstructure was observed. In the surface layer, down to about 15 μm, shear bands of localized deformation were formed. Moreover, the result showed that the average nano-hardness value was obviously increased in the laser-treated region.

Highlights

CMSX4 is a second-generation Ni-base single-crystal superalloy, which is used to make blades for gas turbines in aero-engines and power plants
Laser shock peening (LSP) is an innovative surface treatment which can be used in the power generation industry to improve the fatigue life of the components.[5,6]
Structural changes in the surface layer may be considered a result of the simultaneous interaction of the temperature gradient and compressive stresses involved during LSP

Summary

INTRODUCTION

CMSX4 is a second-generation Ni-base single-crystal superalloy, which is used to make blades for gas turbines in aero-engines and power plants. Before the laser shock processing, the material is covered by a sacrificial ablating layer to prevent the surface from damage during the treatment This layer, as a black adhesive film or a metal foil, which is opaque to the laser radiation, strongly absorbs it. The transparent to laser light water layer limits free plasma expansion over the sample surface This plasma confinement generates high pressures and shock waves, which propagate into the bulk and generate compressive stresses.[11,12] Generation of the compressive stresses in the surface layer improves the fatigue life, which is very important, i.e., for turbine blades of aircraft engines.[13] When these stresses reach the yield strength of the treated metal, plastic deformation occurs. The aim of this contribution is to investigate the surface morphology and roughness, microstructure and nanohardness of the CMSX-4 nickel alloy subsurface layer after LSP

MATERIALS AND EXPERIMENTAL PROCEDURES

RESULTS AND DISCUSSION

TEM and STEM-EDS Examinations

CONCLUSIONS