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1. Effect of Post Processing Heat Treatment Routes on Microstructure and Mechanical Property Evolution of Haynes 282 Ni-Based Superalloy Fabricated with Selective Laser Melting (SLM)

   https://doi.org/10.3390/met10050629  

   Deshpande, Anagh; Deb Nath, Subrata; Atre, Sundar; Hsu, Keng (May 2020, Metals)

   Selective laser melting (SLM) is one of the most widely used additive manufacturing technologies. Fabricating nickel-based superalloys with SLM has garnered significant interest from the industry and the research community alike due to the excellent high temperature properties and thermal stability exhibited by the alloys. Haynes-282 alloy, a γ′-phase strengthened Ni-based superalloy, has shown good high temperature mechanical properties comparable to alloys like R-41, Waspaloy, and 263 alloy but with better fabricability. A study and comparison of the effect of different heat-treatment routes on microstructure and mechanical property evolution of Haynes-282 fabricated with SLM is lacking in the literature. Hence, in this manuscript, a thorough investigation of microstructure and mechanical properties after a three-step heat treatment and hot isostatic pressing (HIP) has been conducted. In-situ heat-treatment experiments were conducted in a transmission electron microscopy (TEM) to study γ′ precipitate evolution. γ′ precipitation was found to start at 950 °C during in-situ heat-treatment. Insights from the in-situ heat-treatment were used to decide the aging heat-treatment for the alloy. The three-step heat-treatment was found to increase yield strength (YS) and ultimate tensile strength (UTS). HIP process enabled γ′ precipitation and recrystallization of grains of the as-printed samples in one single step. 

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2. The origin of microtwinning in HAYNES® 244® superalloy

   https://doi.org/10.1038/s43246-025-01030-8  

   Tucker, Victoria; Mann, Thomas R; Roginski, Andrew; Fahrmann, Michael G; Monclús, Miguel A; LLorca, Javier; Titus, Michael S (December 2026, Communications Materials)

   Abstract Superalloys exhibit varying deformation mechanisms at differing temperatures and strain rates. The HAYNES^®244^®superalloy stands out due to its consistent mechanism of planar fault formation. This distinctive behavior is attributed to the presence of the Ni₂(Cr, Mo, W)$${\gamma }^{{\prime\prime} {\prime} }$$ ${\gamma }^{″\prime }$intermetallic phase, wherein stacking faults form by partial dislocations and subsequently thicken into microtwins via the transmission of partials on adjacent planes. Here we find that, in contrast to conventional$${\gamma }^{{\prime} }$$ ${\gamma }^{\prime }$-strengthened superalloys where deformation begins in theγmatrix, twinning in the 244 alloy initiates at theγ–$${\gamma }^{{\prime\prime} {\prime} }$$ ${\gamma }^{″\prime }$interface within the$${\gamma }^{{\prime\prime} {\prime} }$$ ${\gamma }^{″\prime }$precipitates and then extends outward into the matrix. Our study supports previous hypotheses on twin formation using advanced techniques such as high-resolution scanning transmission electron microscopy, in-situ transmission electron microscopy, and high-strain-rate testing. Contrary to conventional literature, where twinning is often considered detrimental, our work highlights twinning as a unique and significant behavior across temperatures up to the precipitate dissolution temperature and strain rates as high as 500 s⁻¹. In-depth analysis of this alloy at the onset of plasticity and characterization of theγ–$${\gamma }^{{\prime\prime} {\prime} }$$ ${\gamma }^{″\prime }$interface highlights a new and additional structural driving force for the stability of the deformation twinning mechanism. 

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3. Heat Treatment Post-Processing for the Improved Mechanical Properties of Scalmalloy® Processed via Directed Energy Deposition

   https://doi.org/10.3390/cryst14080688  

   Boillat-Newport, Rachel; Isanaka, Sriram Praneeth; Liou, Frank (August 2024, Crystals)

   As high-strength aluminum alloys present several processability issues with additive manufacturing (AM), Scalmalloy®, an Al-Mg-Sc-Zr-based alloy, has been developed. This alloy is age-hardenable, allowing it to precipitate out a strengthening precipitate phase, Al3(Sc,Zr). The manufacturer recommends a single-stage aging treatment at 325 °C for 4 h; however, the majority of the literature studies utilize a powder bed processing known as selective laser melting (SLM) over powder-fed processing directed energy deposition (DED). This study addresses the lack of information on heat treatments for DED fabrication by exploring the application of artificial aging temperatures of 300–400 °C for 2, 4, and 6 h to: 1. determine the impact on the microstructural evolution and mechanical performance and 2. determine whether the recommended treatment for Scalmalloy® is appropriate for DED fabrication. Tensile testing determined that low-temperature treatments exhibited no visible dependence on time (2–6 h); however, time becomes influential at higher temperatures starting at 350 °C. The temperature plays a considerable role in the mechanical and microstructural behaviors of DED Scalmalloy®. The highest tensile strength was noted at 300 °C (384 MPa, 21.6% increase), but all heat-treated cases resulted in an improvement over the as-built case. This investigation established that increasing the treatment temperature resulted in a decreasing trend for the tensile strength that held over time. Elongation at 2 h displayed a near parabolic trend that peaks at 350 °C (20%) and falls with higher temperatures. At the 4 h treatment, a slight decreasing trend was noticed for elongation. No visible change was observed for elongation at 6 h, with elongation values remaining fairly consistent. The microstructural evolution, including micron-sized and nano-sized Al3(Sc,Zr) and grain size, was examined, and coarsening effects were noted with the increase in the temperature. It is recommended that treatment be conducted at 300 °C to achieve the precipitation of the strengthening Al3(Sc,Zr) phase while minimizing coarsening. 

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4. Heat Treatments for Minimization of Residual Stresses and Maximization of Tensile Strengths of Scalmalloy® Processed via Directed Energy Deposition

   https://doi.org/10.3390/ma17061333  

   Boillat-Newport, Rachel; Isanaka, Sriram Praneeth; Kelley, Jonathan; Liou, Frank (March 2024, Materials)

   Scalmalloy® is an Al-Mg-Sc-Zr-based alloy specifically developed for additive manufacturing (AM). This alloy is designed for use with a direct aging treatment, as recommended by the manufacturer, rather than with a multistep treatment, as often seen in conventional manufacturing. Most work with Scalmalloy® is conducted using powder bed rather than powder-fed processes. This investigation seeks to fill this knowledge gap and expand beyond single-step aging to promote an overall balanced AM-fabricated component. For this study, directed energy deposition (DED)-fabricated Scalmalloy® components were subjected to low-temperature treatments to minimize residual stresses inherent in the material due to the layer-by-layer build process. X-ray diffraction (XRD) indicated the possibility of stress minimization while reducing the detriment to mechanical strength through lower temperature treatments. Microstructural analyses consisting of energy dispersion spectroscopy (EDS) and electron backscatter diffraction (EBSD) revealed the presence of grain growth detrimentally affecting the strength and elongation made possible by very small grains inherent to AM and rapid solidification. Tensile testing determined that treatment at 175 °C for 1 h provides the best relief from the existing residual stresses; however, this is accompanied by a diminishment in the yield and tensile strength of 19 and 9.5%, respectively. It is noted that treatment at 175 °C for 2 h did not provide as great of a decrease in residual stresses, theorized to be the result of grain growth and other strengthening mechanisms further stressing the structure; however, the residual stresses are still significantly diminished compared with the as-built condition. Furthermore, a minimal reduction of the tensile strengths indicates the possibility of finding a balance between property diminishment and stress state through the work proposed here. 

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5. Structure-Property Relationships of Differently Heat-Treated Binder Jet Printed Co-Cr-Mo Biomaterial

   https://doi.org/10.1016/j.mtcomm.2023.107716  

   Khademitab, M; Rodriguez_de_Vecchis, P; Staszel, P; Vaicik, M_K; Chmielus, M; Mostafaei, A (November 2023, Materials Today Communications)

   This investigation systematically examines the influence of sintering temperature and aging treatment on the density, microstructure evolution, phase formation, and mechanical properties of a binder jet printed Co-Cr-Mo biomedical alloy. Sintering at 1380 °C for 2 h yielded a near-fully dense part (99.1%) with favorable mechanical properties (up to 325 HV0.1 hardness and up to 693 MPa ultimate tensile strength). The grain size remained unchanged after aging at 800 °C for 24 h (89 ± 21 µm). Aging resulted in increased microhardness and tensile strength due to phase formation (Cr23C6, CrMo, and ε phase), but a significant decrease in ductility. Consequently, the sintered and aged specimen exhibited higher hardness (522 HV0.1), yield strength (641 MPa), and ultimate tensile strength (854 MPa) compared to cast Co-Cr-Mo alloy. Biocompatibility testing with fibroblasts showed a cell viability of 95 ± 2%, indicating that binder jet printing did not affect the biocompatibility of the Co-Cr-Mo alloy. Exemplary printed parts including hip-joint, partial denture, and small-scale knee joint were successfully demonstrated. This study highlights the comparable properties of binder jet Co-Cr-Mo alloy to the cast alloy, affirming its potential for biomedical applications. 

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