Page 60 - MSAM-3-2

Materials Science in Additive Manufacturing Heat treatment on bimetallic parts

was observed in the transition zone.
(ii) With extended dwell time, overall porosity decreased.
Simultaneously, carbides, an intermetallic compound
(a hard and brittle phase), exhibited a more uniform
and finer distribution after 4 h of heat treatment.
(iii) The thickness of the transition zone increased with
prolonged dwell times, resulting in enhanced bonding
strength for the bimetallic components. Empirical
data on microhardness and the theoretical parabolic
diffusion law provided supporting evidence for the
observed phenomenon.
(iv) No new phases were detected after heat treatment;
however, XRD peak shifts occurred due to stress
relaxation and precipitate formation.
(v) The microhardness of the transition zone increased
with heat treatment, reaching a maximum of 186 HV
1.0
after a 4-h holding time. The optimized heat treatment
Figure 11. Microhardness changes along the bimetallic interfaces under condition was determined to be 1150°C for 4 h to attain
various conditions. uniform microstructures and high bonding strength.
Future studies could involve complementary
With an increase in holding time, the microhardness of the computational efforts involving modeling and simulations to
transition zone initially rises, and then decreases after 4 h, as acquire insights into the mechanisms facilitating interfacial
shown in Figure 11. Heat treatment for 4 h yields the highest bonding. Particular attention should be paid to elucidating
microhardness value, approximately 186 HV , compared to the role of elemental segregation and diffusion phenomena.
1.0
the lowest value of 156 HV observed in samples without
1.0
heat treatment. This observed increase represents a nearly Acknowledgments
20% post-treatment enhancement, closely aligning with The authors extend their sincere gratitude to the anonymous
the microhardness on the IN625 side. With the increase in reviewers for their valuable comments and suggestions,
time, the size of pores reduces, and the occurrence of pores which have greatly contributed to the improvement of this
decreases. During heat treatment, oxides and carbides form paper. This work was funded by the United States National
in the transition zone, creating an intermetallic compound Science Foundation through the award CMMI-2224309.
that is both hard and brittle. Excessively long dwell times
typically result in larger grain sizes, which are detrimental Funding
to the hardness of the interface. Notably, microhardness
measurements also allow us to determine the thickness of the This work was funded by the United States National Science
transition zone in Figure 10A-D. These values are consistent Foundation through the award CMMI-2224309.
with results calculated using Equation I and EDS scan line Conflict of interest
analysis results from Table 5.
The authors declare that they have no competing interests.
4. Conclusion
Author contributions
This study investigated the effects of various heat treatment
approaches on the microstructure and mechanical Conceptualization: Yulin Liu and Fuda Ning
properties of 17-4PH/IN625 bimetallic components Formal analysis: Yulin Liu and Dayue Jiang
fabricated through the ES-AM process. The key findings Investigation: Yulin Liu
are summarized below. Methodology: Yulin Liu and Dayue Jiang
(i) The 17-4PH/IN625 bimetallic composite exhibited Writing – original draft: Yulin Liu
excellent interfacial bonding after heat treatment, Writing – review & editing: All authors
with few pores at the interface and uniform elemental All authors have read and agreed to the published version
distribution without delamination. The diffusion of the manuscript.
zone could be separated into two regions: an Fe-rich Ethics approval and consent to participate
zone and a Ni-rich zone (containing oxides and
Mo-, Nb-rich precipitates). Significant Nb segregation Not applicable.

Volume 3 Issue 2 (2024) 13 doi: 10.36922/msam.3281