Advances in Multi-Principal Elements Alloys X: Alloy Development and Properties: Structures and Mechanical Properties III
Sponsored by: TMS Functional Materials Division, TMS Structural Materials Division, TMS: Alloy Phases Committee, TMS: Mechanical Behavior of Materials Committee
Program Organizers: Peter Liaw, University of Tennessee; Michael Gao, National Energy Technology Laboratory; E-Wen Huang, National Chiao Tung University; Jennifer Carter, Case Western Reserve University; Srivatsan Tirumalai; Xie Xie, FCA US LLC; Gongyao Wang, Globus Medical

Wednesday 2:00 PM
March 2, 2022
Room: 251A
Location: Anaheim Convention Center

Session Chair: Eric Lass, University of Tennessee-Knoxville; Jeffery Gibeling, University of California, Davis

2:00 PM  
Mechanisms of Creep in NiCoCr and ODS-NiCoCr Multi-principal Element Alloys: Gianmarco Sahragard-Monfared1; Timothy Smith2; Jeffery Gibeling1; 1University of California, Davis; 2NASA Glenn Research Center
    Multi-principal element alloys (MPEA) have been proven to exhibit excellent room temperature and cryogenic strength and ductility. However, MPEAs with an FCC crystal processed by arc melting generally exhibit low strengths at elevated temperatures. Alternative manufacturing processes provide an opportunity to introduce dispersoids into the matrix to improve high temperature properties. In this study the influence of oxide dispersion strengthening (ODS) on the steady state and constant structure creep behavior of an MPEA produced by additive manufacturing (AM) is investigated. Constant stress and stress reduction creep tests were performed on AM-NiCoCr and an oxide dispersion strengthened variant containing one weight percent yttria (ODS-NiCoCr). Activation areas determined from the latter tests highlight the rate controlling mechanisms of these MPEAs. Transmission electron microscopy of specimens crept to various strains are used to characterize the evolving morphology of dislocations and their interactions with other dislocations and the dispersoids.

2:20 PM  Cancelled
Strain Partitioning Enables Excellent Tensile Ductility in Precipitated Heterogenous High-entropy Alloys with Gigapascal Yield Strength: Feng He1; 1State Key Laboratory of Solidification Processing
    High entropy alloys (HEAs) with grain-scale heterogeneous structure and coherent precipitates have shown gigapascal strength and considerable ductility. However, the origins of the excellent ductility of the HEAs with both precipitates and grain-scale heterogeneous structures are relatively less explored and not well understood. Here, through single-step heat treatment, we developed a Ni2CoCrFeTi0.24Al0.2 HEA with an excellent yield strength of ~1.3 GPa and tensile elongation of ~20%. Using multiple length-scale microstructure characterizations and micro-digital image correlation analysis, we revealed the strengthening and toughening mechanisms of the novel HEA. Our results showed that the grain-scale heterogeneous structure with L12 precipitates ranging from ~10 – 100 nm is responsible for the excellent strength-ductility combination. The good ductility is attributed to the strain-partitioning-induced additional deformation modes, i.e., deformation twinning and microbands, as well as the efficient hetero-deformation induced strain hardening effect.

2:40 PM  
Solidification Behavior and Mechanical Performance of Ductile Mn35Fe5Co20Ni20Cu20 MPEA Brazing Filler: Benjamin Schneiderman1; Andrew Chuang2; Olivia DeNonno1; Jonah Klemm-Toole1; Zhenzhen Yu1; 1Colorado School Of Mines; 2Advanced Photon Source - Argonne National Laboratory
    A novel MPEA of approximate composition Mn35Fe5Co20Ni20Cu20 was developed as a filler material for brazed joining and repair of nickel-base superalloys. A direct comparison of mechanical properties was made to a conventional boron-suppressed filler alloy commercially available for the same application, with nickel-base alloy 600 as the substrate for demonstration. Relative to the commercial filler, the MPEA offered comparable strength and one order of magnitude greater ductility, at both room temperature and 600C. Joints brazed with the boron-suppressed filler exhibited cleavage failure at less than 1% elongation, while joints brazed with the MPEA showed ductile microvoid coalescence and greater than 10% elongation. The improved ductility resulted from single-phase solidification to a face-centered cubic matrix phase in the MPEA, which prevented brittle eutectic microconstituents from populating the MPEA joint microstructure. The MPEA filler thus offers a novel approach to circumvent brittle phase formation that has plagued superalloy braze repair for decades.

3:00 PM  
Investigation of Al2 (Co, Crx, Fey, Ni)14 Precipitation Strengthened Transition Metal High Entropy Alloys: Serena Beauchamp1; Eric Lass1; T. G. Nieh1; 1University of Tennessee Knoxville
    High entropy alloys (HEA) or Multi-principal elements alloys (MPEA), particularly precipitation-strengthened alloys, have great promise for structural applications. In this study, several alloys based on Al2 (Co, Crx, Fey, Ni)14, where 1≤x,y≤2 and x+y=3, are investigated to determine their mechanical properties, aging response, and precipitation behavior. Samples were initially homogenized, followed by water quenching, and then aged at 400 C with periodic hardness measurements. The susceptibility of the alloys to hot rolling deformation and its effect on precipitation behavior was also investigated. Microstructural and phase characterization was carried out using x-ray diffraction, scanning electron microscopy, hardness testing, and transmission electron microscopy. Hardness measurements (or the aging curve) were directly related to microstructural evolution, for example, precipitate size, density, and its distribution. Precipitation behavior was modelled using ThermoCalc and subsequently validated through experimental work.

3:20 PM Break

3:40 PM  
Improved Properties of Non-equiatomic MnFeCoNiCu HEA Compared to Its Equiatomic Counterpart: Tibra Das Gupta1; Artashes Ter-Isahakyan1; Thomas Balk1; 1University of Kentucky
    In this study, we argue that within a high entropy alloy (HEA) system the most stable composition is not always equiatomic. Other favorable compositions may exist that will exhibit superior phase stability and improved mechanical properties. We demonstrate this by cooling an equiatomic CrMnFeCoNiCu from the melt over a period of three days. This results in large Cr-rich precipitates and a nearly Cr-free matrix with compositions within the MnFeCoNiCu system. Leveraging this result, we argue that the most stable composition lies in the MnFeCoNiCu system rather than the CrMnFeCoNi system. Taking MnFeCoNiCu as a basis for new alloys, we compared the mechanical properties between the equiatomic and non-equiatomic counterparts, using nano-indentation and a custom-built micro-specimen test system. These approaches yielded bulk alloys that exhibited improved mechanical properties in comparison to their equiatomic counterparts.

4:00 PM  
Tailoring High Entropy Alloys for Advanced Technology Fuel (ATF) Coatings: Jack Wilson1; Lee Evitts1; Michael Rushton1; William Lee1; David Goddard2; Simon Middleburgh1; 1Bangor University; 2National Nuclear Laboratory
    The zirconium-water reaction is a concern for LWRs, especially during a loss-of-coolant accident (LOCA) where cladding outer temperatures are significantly higher than during normal operation. The prevention or reduction of this reaction is sought with the use of certain Advanced Technology Fuels (ATFs) concepts. High-entropy alloys (HEAs) are being investigated as a candidate material for this purpose. In this work, we investigate the potential for HEAs as an interlayer between the protective Cr and Zr substrate. We examine key properties of HEAs including thermal expansion, interdiffusion and thermodynamics, ensuring brittle phase formation is avoided. We have shown that atomic scale modelling techniques such as density functional theory can be used to reliably predict thermal expansion of a range of BCC HEAs relevant to this innovation and thermodynamic and kinetic information is being combined to ensure the optimal material is selected.

4:20 PM  
Effect of Valence Electron Concentration on the Mechanical Properties of Non-equiatomic Refractory Multi-principal Element Alloys: Taohid Bin Nur Tuhser1; Daryl Chrzan2; Andrew Minor2; Mark Asta2; Thomas Balk1; 1University of Kentucky; 2Lawrence Berkeley National Laboratory
    The superior strength of refractory multi-principal element alloys (RMPEAs) at elevated temperature is often paired with poor room temperature ductility. The intrinsic ductility of RMPEAs can be improved by reducing the Valence Electron Concentration (VEC). In this work, we examined the effects of VEC on the mechanical properties of the VNbMoTaW system by substituting Gr VI elements (Mo,W) with Gr V (Nb,Ta).Thin films were deposited on Kapton dogbones and silicon substrates by magnetron sputtering. Nanoindentation at three different strain rates was used to determine hardness, elastic modulus, and strain rate sensitivity, while in-situ fragmentation tests revealed certain effects of the VEC on tensile properties. By controlling the residual stress, thickness, and grain size of thin films on dogbones, we were able to extract ‘intrinsic’ ductility of these configurations. Finally, bulk samples were prepared, and corresponding mechanical properties were compared with the thin film counterparts.