Characterization of Inconel® 625 and Ti-6Al-4V Laser Deposited Builds Manufactured with Varying Dwell Times

Open Access
Author:
Foster, Bryant Klein
Graduate Program:
Engineering Science and Mechanics
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
None
Committee Members:
  • Todd Palmer, Thesis Advisor
Keywords:
  • Directed Energy Deposition
  • Laser Processing
  • Additive Manufacturing
  • Inconel® 625
  • Ti-6Al-4V
Abstract:
Directed energy deposition (DED) additive manufactured (AM) builds were created in previous experiments using 0, 20, and 40 s interlayer dwell times out of Inconel® 625 and Ti 6Al 4V. In-situ deformation and temperatures were measured along with residual stresses. This study characterized the varying dwell time builds through optical microstructure analysis and mechanical tensile testing. A direct correlation was found between dwell time, cooling rate, microstructure, and mechanical properties for each material. For both materials, the addition and increase of an interlayer dwell increased the cooling rate during the solidification of the melt pool. In Inconel® 625, this increased cooling led to reduced secondary dendrite arm spacing in the 20 s and 40 s builds. The finer microstructure of the 20 s and 40 s dwell builds had increased ultimate tensile strength (UTS) and yield strength over that found in the 0 s dwell build. Each nickel based AM build became embrittled, losing ~20% elongation at failure, but showed yield strength above that of the base Inconel® 625 material. The addition and increase of an interlayer dwell in Ti 6Al 4V builds caused a reduction in alpha lath width in the basketweave microstructure. Each of the titanium alloy builds showed UTS and yield strengths that were within ~10% of the base alloy values and increased with dwell time. These results reinforce the fact that path planning is vital to tailoring the final part microstructure and resulting mechanical properties.