Studies of the Influence of Beam Profile and Cooling Conditions on the Laser Deposition of a Directionally-Solidified Superalloy

Shuo Yang,Dong Du,Baohua Chang

doi:10.3390/ma11020240

Abstract

In the laser deposition of single crystal and directionally-solidified superalloys, it is desired to form laser deposits with high volume fractions of columnar grains by suppressing the columnar-to-equiaxed transition efficiently. In this paper, the influence of beam profile (circular and square shapes) and cooling conditions (natural cooling and forced cooling) on the geometric morphology and microstructure of deposits were experimentally studied in the laser deposition of a directionally-solidified superalloy, IC10, and the mechanisms of influence were revealed through a numerical simulation of the thermal processes during laser deposition. The results show that wider and thinner deposits were obtained with the square laser beam than those with the circular laser beam, regardless of whether natural or forced cooling conditions was used. The heights and contact angles of deposits were notably increased due to the reduced substrate temperatures by the application of forced cooling for both laser beam profiles. Under natural cooling conditions, columnar grains formed epitaxially at both the center and the edges of the deposits with the square laser beam, but only at the center of the deposits with the circular laser beam; under forced cooling conditions, columnar grains formed at both the center and the edges of deposits regardless of the laser beam profile. The high ratios of thermal gradient and solidification velocity in the height direction of the deposits were favorable to forming deposits with higher volume fractions of columnar grains.

Highlights

Single crystal (SX) and directionally-solidified (DS) superalloys are increasingly being used to manufacture critical hot components in aeroengines and gas turbines
As an advanced additive manufacturing technology, laser metal deposition has been considered as an ideal process to repair such superalloy components, because the concentrated heat input from a laser beam can form a high temperature gradient, which is in favor of the oriented growth of grains in solidifying deposits
Laser deposits were made on a directionally solidified super IC 10 with two types of laser beam profile and two different cooling conditions; the geometric morphology and microstructure of the deposits obtained under different conditions were examined; and the thermal processes during the laser deposition were numerically analyzed

Summary

Introduction

Single crystal (SX) and directionally-solidified (DS) superalloys are increasingly being used to manufacture critical hot components (e.g., turbine blades) in aeroengines and gas turbines. Defects like cracks and wear are inevitable for such superalloy components due to the high temperature and high pressure service environments [1,2]. During the repairing of components made of single crystal or directionally-solidified superalloys, epitaxial columnar grains with the same orientation as that of the base metal are preferable to the equiaxed grains because of their better performance [3]. As an advanced additive manufacturing technology, laser metal deposition has been considered as an ideal process to repair such superalloy components, because the concentrated heat input from a laser beam can form a high temperature gradient, which is in favor of the oriented growth of grains in solidifying deposits. Based on the first analytical model to describe the CET in solidifying processes [4], Gaumann et al [5,6,7]

Results

Discussion

Conclusion