Fine-Tuning Melt Pools and Microstructures: Taming Cracks in Powder Bed Fusion—Laser Beam of a non-weldable Ni-base Superalloy
Journal article, 2024

Powder Bed Fusion – Laser Beam (PBF-LB) of high γ’ strengthened Ni-base superalloys, such as CM247LC, is of great interest for high temperature applications in gas turbines. However, PBF-LB of CM247LC is challenging due to the high cracking susceptibility during PBF-LB processing (solidification cracking) and heat treatment (strain age cracking, mostly caused by residual stresses). This study focuses on understanding the impact of process parameters on microstructure, residual stresses and solidification cracking. Laser power (P), speed (v) and hatch spacing (h) were varied while the layer thickness (t) was fixed. The melt pool size and shape were found to be key factors in minimizing solidification cracking. Narrower and shallower melt pools, achieved using a low line energy density (LED = P/v ≤ 0.1 J/mm), gave low crack densities (0.7 mm/mm2). A tight hatch spacing (h = 0.03 mm) resulted in reduced lack of fusion porosity. Electron backscatter diffraction investigations revealed that parameters giving finer microstructure with 〈100〉 crystallographic texture had low crack densities provided they were processed with a low LED. Atom probe tomography elucidated early stages of spinodal decomposition in the as-built condition, where Cr and Al cluster separately. The extent of spinodal decomposition was found to be affected by the LED and the hatch spacing. Samples with low LED and small hatch spacing showed higher degrees of spinodal decomposition. X-ray diffraction residual stress investigations revealed that the residual stress is proportional to the volumetric energy density (VED = P/(v. h. t)). Although low residual stresses can be achieved by using low VED, there is a high risk of lack of fusion. Hence, other parameters such as modified scan strategy, build plate pre-heating and pulsed laser mode, must be further explored to minimize the residual stresses to reduce the strain age cracking susceptibility.

CM247LC

Ni-base superalloy

Powder bed fusion - laser beam

Non-weldable superalloy

Solidification cracking

Author

Ahmed Fardan Jabir Hussain

Chalmers, Industrial and Materials Science, Materials and manufacture

Andrea Fazi

Chalmers, Physics, Microstructure Physics

Ru Lin Peng

Linköping University

Tatiana Mishurova

Bundesanstalt für Materialforschung und -Prüfung (BAM)

Mattias Thuvander

Chalmers, Physics, Microstructure Physics

Giovanni Bruno

Bundesanstalt für Materialforschung und -Prüfung (BAM)

Håkan Brodin

Siemens Energy

Eduard Hryha

Chalmers, Industrial and Materials Science, Materials and manufacture

Materialia

25891529 (eISSN)

Vol. 34 102059

Materials for green hydrogen fueled gas turbines through additive manufacturing

VINNOVA (2021-01005), 2021-05-03 -- 2024-04-30.

Driving Forces

Sustainable development

Subject Categories

Manufacturing, Surface and Joining Technology

Other Materials Engineering

Metallurgy and Metallic Materials

Areas of Advance

Materials Science

DOI

10.1016/j.mtla.2024.102059

More information

Latest update

5/24/2024