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1. Circumventing cracking in grading 316L stainless steel to Monel400 through compositional modifications in directed energy deposition

   https://doi.org/10.1016/j.mtla.2024.102283  

   Yang, Zhening; Richter, Alexander; Sun, Hui; Liu, Zi-Kui; Beese, Allison M (December 2024, Materialia)

   In joining Fe-alloys and Cu-containing alloys to access the high strength of steels and corrosion resistance of Cu-alloy, cracking is widely observed due to the significant Cu microsegregation during the solidification process, resulting in an interdendritic Cu-rich liquid film at the end of solidification. By fabricating functionally graded materials (FGMs) that incorporate additional elements like Ni in the transition region between these terminal alloy classes, the hot cracking can be reduced. In the present work, the joining of stainless steel 316L (SS316L) and Monel400 by modifying the Ni concentration in the gradient region was studied. A new hot cracking criterion based on hybrid Scheil-equilibrium approach was developed and validated with monolithic multi-layer samples within the SS316L-Ni-Monel400 three-alloy system and a SS316L to 55/45 wt% SS316L/Ni to Monel400 FGM sample fabricated by direct energy deposition (DED). The new hot cracking criterion, based on the hybrid Scheil-equilibrium approach, is expected to help design FGM paths between other Fe-alloys and Cu-containing alloys as well. 

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2. Selective laser melting of metal structures onto graphite substrates via a low melting point interlayer alloy

   https://doi.org/https://doi.org/10.1016/j.apmt.2021.101334  

   Arad Azizi, Xiaobo Chen (March 2022, Applied materials today)

   We demonstrate a process to selective laser melt a metal alloy directly onto graphite. The heat trans- fer applications of metal features printed onto annealed pyrolytic graphite are compelling, as pyrolytic graphite has the second highest in-plane thermal conductivity ( > 1500 W/m-K at room temperature) of any bulk material. While the bonding of metal alloys commonly used in selective laser melting (SLM) with graphite is relatively weak, the proper interlayer material drastically improves the wetting and bond- ing. The challenge is the alloys that typically bond to graphite require extended bonding times at elevated temperatures (minutes to hours), while the SLM process delivers only brief exposures to high tempera- tures ( ∼100 μs). In this paper, we employ a Sn3Ag4Ti alloy that rapidly forms a nanometer-thin layer of TiC, as verified by transmission electron microscopy. The influence of graphite thermal properties on interfacial bond strength is shown by mechanical testing and simulations of selective laser melting. 

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3. Tailoring compositionally graded interface of 316L stainless steel to Al12Si aluminum alloy bimetallic structures via Additive Manufacturing

   https://doi.org/doi.org/10.1021/acsami.0c21478  

   Zhang, Yanning; Bandyopadhyay, Amit (February 2021, ACS applied materials interfaces)

   null (Ed.)

   316L stainless steel (SS) to Al12Si aluminum alloy structures were processed, tailoring the compositionally graded interface on a SS 316 substrate using a directed energy deposition (DED)-based additive manufacturing (AM) process. Applying such a compositionally graded transition on bimetallic materials, especially joining two dissimilar metals, could avoid the mechanical property mismatch. This study's objective was to understand the processing parameters that influence the properties of AM processed SS 316L to Al12Si bimetallic structures. Two different approaches fabricated these bimetallic structures. The results showed no visible defects on the as-fabricated samples using 4 layers of Al-rich mixed composition as the transition section. The microstructural characterization showed a unique morphology in each section. Both cooling rate and compositional variations caused microstructural variation. FeAl, Fe2Al5, and FeAl3 intermetallic phases were formed at the compositionally graded transition section. After stress relief heat-treatment of SS 316L/Al12Si bimetallic samples, diffused intermetallic phases were seen at the compositionally graded transition. At the interface, as processed, bimetallic structures had a microhardness value of 834.2 ± 107.1 HV0.1, which is a result of the FeAl3 phase at the compositionally graded transition area. After heat-treatment, the microhardness value reduced to 578.7 ± 154.1 HV0.1 due to more Fe dominated FexAly phase formation. The compression test results showed that the non-HT and HT SS 316L/Al12Si bimetallic structures had a similar maximum compressive strength of 299.4 ± 22.1 MPa and 270.1 ± 27.1 MPa, respectively. 

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4. In situ design of advanced titanium alloy with concentration modulations by additive manufacturing

   https://doi.org/10.1126/science.abj3770  

   Zhang, Tianlong; Huang, Zhenghua; Yang, Tao; Kong, Haojie; Luan, Junhua; Wang, Anding; Wang, Dong; Kuo, Way; Wang, Yunzhi; Liu, Chain-Tsuan (October 2021, Science)

   Additive manufacturing is a revolutionary technology that offers a different pathway for material processing and design. However, innovations in either new materials or new processing technologies can seldom be successful without a synergistic combination. We demonstrate an in situ design approach to make alloys spatially modulated in concentration by using laser-powder bed fusion. We show that the partial homogenization of two dissimilar alloy melts—Ti-6Al-4V and a small amount of 316L stainless steel—allows us to produce micrometer-scale concentration modulations of the elements that are contained in 316L in the Ti-6Al-4V matrix. The corresponding phase stability modulation creates a fine scale–modulated β + α′ dual-phase microstructure that exhibits a progressive transformation-induced plasticity effect, which leads to a high tensile strength of ~1.3 gigapascals with a uniform elongation of ~9% and an excellent work-hardening capacity of >300 megapascals. This approach creates a pathway for concentration-modulated heterogeneous alloy design for structural and functional applications. 

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5. Vanadium MXenes materials for next-generation energy storage devices

   https://doi.org/10.1088/1361-6528/acc539  

   Sijuade, Ayomide Adeola; Eze, Vincent Obiozo; Arnett, Natalie Y; Okoli, Okenwa I (April 2023, Nanotechnology)

   Abstract Batteries and supercapacitors have emerged as promising candidates for next-generation energy storage technologies. The rapid development of new two-dimensional (2D) electrode materials indicates a new era in energy storage devices. MXenes are a new type of layered 2D transition metal carbides, nitrides, or carbonitrides that have drawn much attention because of their excellent electrical conductivity, electrochemical and hydrophilic properties, large surface area, and attractive topological structure. This review focuses on various synthesis methods to prepare vanadium carbide MXenes with and without etchants like hydrofluoric acid, lithium fluoride, and hydrochloric acid to remove the ‘A’ layers of the MAX phase. The goal is to demonstrate the utilization of a less toxic etching method to achieve MXenes of comparable properties to those prepared by traditional methods. The influence of intercalation on the effect of high interlayer spacing between the MXene layers and the performance of MXenes as supercapacitor and battery electrodes is also addressed in this review. Lastly, the gaps in the current knowledge for vanadium carbide MXenes in synthesis, scalability, and utilization in more energy storage devices were discussed. 

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