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Title: Hardness and microstructural inhomogeneity at the epitaxial interface of laser 3D-printed Ni-based superalloy

Abstract

Here in this letter, microstructural and mechanical inhomogeneities, a great concern for single crystal Ni-based superalloys repaired by laser assisted 3D printing, have been probed near the epitaxial interface. Nanoindentation tests show the hardness to be uniformly lower in the bulk of the substrate and constantly higher in the epitaxial cladding layer. A gradient of hardness through the heat affected zone is also observed, resulting from an increase in dislocation density, as indicated by the broadening of the synchrotron X-ray Laue microdiffraction reflections. Lastly, the hardening mechanism of the claddin g region, on the other hand, is shown to originate not only from high dislocation density but also and more importantly from the fine γ/γ' microstructure.

Authors:
 [1];  [2];  [1]; ORCiD logo [1]; ORCiD logo [1];  [2]; ORCiD logo [3];  [4];  [1];  [1]
  1. Xi'an Jiaotong Univ., Shaanxi (China). State Key Lab. for Mechanical Behavior of Materials
  2. Xi'an Jiaotong Univ., Shaanxi (China). State Key Lab. for Manufacturing Systems Engineering
  3. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Advanced Light Source (ALS)
  4. Xi'an Jiaotong Univ., Shaanxi (China). State Key Lab. for Manufacturing Systems Engineering
Publication Date:
Research Org.:
Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
OSTI Identifier:
1377476
Grant/Contract Number:
AC02-05CH11231; 51671154; 51302207; 51275392; 11132006; 2016YFB0700404; 2015CB057400; 2015gjhz03
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Applied Physics Letters
Additional Journal Information:
Journal Volume: 109; Journal Issue: 10; Journal ID: ISSN 0003-6951
Publisher:
American Institute of Physics (AIP)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; Hardness; Cladding; Epitaxy; Dislocations; Nanopowders

Citation Formats

Qian, Dan, Zhang, Anfeng, Zhu, Jianxue, Li, Yao, Zhu, Wenxin, Qi, Baolu, Tamura, Nobumichi, Li, Dichen, Song, Zhongxiao, and Chen, Kai. Hardness and microstructural inhomogeneity at the epitaxial interface of laser 3D-printed Ni-based superalloy. United States: N. p., 2016. Web. doi:10.1063/1.4962485.
Qian, Dan, Zhang, Anfeng, Zhu, Jianxue, Li, Yao, Zhu, Wenxin, Qi, Baolu, Tamura, Nobumichi, Li, Dichen, Song, Zhongxiao, & Chen, Kai. Hardness and microstructural inhomogeneity at the epitaxial interface of laser 3D-printed Ni-based superalloy. United States. doi:10.1063/1.4962485.
Qian, Dan, Zhang, Anfeng, Zhu, Jianxue, Li, Yao, Zhu, Wenxin, Qi, Baolu, Tamura, Nobumichi, Li, Dichen, Song, Zhongxiao, and Chen, Kai. 2016. "Hardness and microstructural inhomogeneity at the epitaxial interface of laser 3D-printed Ni-based superalloy". United States. doi:10.1063/1.4962485. https://www.osti.gov/servlets/purl/1377476.
@article{osti_1377476,
title = {Hardness and microstructural inhomogeneity at the epitaxial interface of laser 3D-printed Ni-based superalloy},
author = {Qian, Dan and Zhang, Anfeng and Zhu, Jianxue and Li, Yao and Zhu, Wenxin and Qi, Baolu and Tamura, Nobumichi and Li, Dichen and Song, Zhongxiao and Chen, Kai},
abstractNote = {Here in this letter, microstructural and mechanical inhomogeneities, a great concern for single crystal Ni-based superalloys repaired by laser assisted 3D printing, have been probed near the epitaxial interface. Nanoindentation tests show the hardness to be uniformly lower in the bulk of the substrate and constantly higher in the epitaxial cladding layer. A gradient of hardness through the heat affected zone is also observed, resulting from an increase in dislocation density, as indicated by the broadening of the synchrotron X-ray Laue microdiffraction reflections. Lastly, the hardening mechanism of the claddin g region, on the other hand, is shown to originate not only from high dislocation density but also and more importantly from the fine γ/γ' microstructure.},
doi = {10.1063/1.4962485},
journal = {Applied Physics Letters},
number = 10,
volume = 109,
place = {United States},
year = 2016,
month = 9
}

Journal Article:
Free Publicly Available Full Text
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  • Synchrotron X-ray microdiffraction was employed to investigate the inhomogeneous distribution of defect and residual strain in the transitional region between the dendritic and stray grains in a laser-assisted 3D printed Ni-based superalloy. The dendritic region was found to be under tensile strain transversely to the primary dendrite arm directions. The dendrite edges, where high level of strains and geometrically necessary dislocations were detected, were discerned as low angle grain boundaries. Lastly, high angle grain boundaries were observed in the stray grain region, and the orientation of the strain tensor in this region varied dramatically at the micron scale, in contrastmore » with the more or less homogeneous distribution in the dendritic region.« less
  • Ductility-dip cracking in Ni-based superalloy, resulting from heat treatment, is known to cause disastrous failure, but its mechanism is still not completely clear. A statistical study of the cracking behavior as a function of crystal orientation in a laser 3D-printed DL125L Ni-based superalloy polycrystal is investigated here using the synchrotron X-ray microdiffraction. The dislocation slip system in each of the forty crystal grains adjacent to the 300 μm long crack has been analyzed through Laue diffraction peak shapes. In all these grains, edge-type geometrically necessary dislocations (GNDs) dominate, and their dislocation line directions are almost parallel to the crack plane.more » Based on Schmid's law, the equivalent uniaxial tensile force direction is revealed normal to the trace of the crack. A qualitative mechanism is thus proposed. Thermal tensile stress perpendicular to the laser scanning direction is elevated due to a significant temperature gradient, and thus locations in the materials where the thermal stress exceeds the yield stress undergo plastic deformation mediated by GND activations. As the dislocations slip inside the crystal grains and pile up at the grain boundaries, local strain/stress keeps increasing, until the materials in these regions fail to sustain further deformation, leading to voids formation and cracks propagation.« less
  • Laser additive forming is considered to be one of the promising techniques to repair single crystal Ni-based superalloy parts to extend their life and reduce the cost. Preservation of the single crystalline nature and prevention of thermal mechanical failure are two of the most essential issues for the application of this technique. Here we employ synchrotron X-ray microdiffraction to evaluate the quality in terms of crystal orientation and defect distribution of a Ni-based superalloy DZ125L directly formed by a laser additive process rooted from a single crystalline substrate of the same material. We show that a disorientation gradient caused bymore » a high density of geometrically necessary dislocations and resultant subgrains exists in the interfacial region between the epitaxial and stray grains. This creates a potential relationship of stray grain formation and defect accumulation. In conclusion, the observation offers new directions on the study of performance control and reliability of the laser additive manufactured superalloys.« less
  • Laser additive forming is considered to be one of the promising techniques to repair single crystal Ni-based superalloy parts to extend their life and reduce the cost. Preservation of the single crystalline nature and prevention of thermal mechanical failure are two of the most essential issues for the application of this technique. Here we employ synchrotron X-ray microdiffraction to evaluate the quality in terms of crystal orientation and defect distribution of a Ni-based superalloy DZ125L directly formed by a laser additive process rooted from a single crystalline substrate of the same material. We show that a disorientation gradient caused bymore » a high density of geometrically necessary dislocations and resultant subgrains exists in the interfacial region between the epitaxial and stray grains. This creates a potential relationship of stray grain formation and defect accumulation. The observation offers new directions on the study of performance control and reliability of the laser additive manufactured superalloys.« less