Phase Transformations and Microstructural Evolution: Non-Ferrous Alloys
Sponsored by: TMS Materials Processing and Manufacturing Division, TMS: Phase Transformations Committee
Program Organizers: Mohsen Asle Zaeem, Colorado School of Mines; Ramasis Goswami, Naval Research Laboratory; Saurabh Puri, VulcanForms Inc; Eric Payton, University of Cincinnati; Megumi Kawasaki, Oregon State University; Eric Lass, University of Tennessee-Knoxville

Wednesday 8:30 AM
March 2, 2022
Room: 255B
Location: Anaheim Convention Center

Session Chair: Ramasis Goswami, Naval Research Laboratory

8:30 AM  
Precipitation Behavior of Strengthening Phases in a High Temperature Aluminum-cerium Alloy: Opemipo Adetan1; Dinc Erdeniz1; 1University of Cincinnati
    The use of cerium as a major alloying element for aluminum is gaining more attention in recent years due to the castability of this binary alloy system and the high-temperature stability of the Al11Ce3 intermetallic phase, which forms upon eutectic solidification and provides strengthening. Despite the apparent advantageous properties of these alloys, they still suffer from high creep rates at elevated temperatures, due to a lack of strengthening within the aluminum solid-solution channels. Micro-alloying with scandium and zirconium enables additional strengthening via the formation of L12– ordered, tri-aluminide precipitates, which improves the creep resistance. In this work, castable Al-Ce-Sc-Zr alloys are designed using the CALPHAD methodology and subjected to various heat treatments. The precipitation and thermal stability of these two strengthening phases, Al11Ce3 and Al3(Sc,Zr), are investigated using micro/nano characterization techniques. Compression creep tests are carried out to evaluate the effect of the tri-aluminide precipitates on high temperature strength.

8:50 AM  
Time Resolved In-situ Small Angle X-ray Scattering Clarifies the Competition between Continuous and Discontinuous Precipitation in U-6wt%Nb: Nathan Peterson1; Erik Watkins2; Don Brown2; Bjorn Clausen2; Travis Carver2; Jun-Sang Park3; Sean Agnew1; 1University of Virginia; 2Los Alamos National Laboratory; 3Argonne National Laboratory - Advanced Photon Source
    During the initial stages of the monotectoid phase transformation in U-6wt%Nb, both continuous (intragranular) and discontinuous (lamellar, grain boundary) precipitation occur, in a competitive fashion. In order to better understand the competition between these two modes, in-situ small-angle x-ray scattering (SAXS) measurements were performed to probe the relevant (10-150nm) precipitate length scales. Simultaneous wide-angle x-ray scattering (WAXS, diffraction) measurements were also performed, which provided quantitative phase volume fractions and compositions (critical for quantifying scattering contrast). These experiments reveal two distinct microstructural length scales which correspond to the two modes of precipitation, providing greater clarity regarding the temporal competition between these two modes at various temperatures above and below the nose in the TTT diagram.

9:10 AM  
The Role of Non-hydrostatic Stress State in the α to ω Phase Transformation in Ti: Khanh Dang1; Laurent Capolungo1; Carlos Tome1; 1Los Alamos National Laboratory
    While the crystallography and orientation relationships of the pressure-induced martensitic α to ω transformation in Ti have been well-documented, the transformation mechanism and governing parameters are not fully understood. For instance, the transition pressure at room temperature exhibits a great discrepancy, varying from 0.25 to 7.0 GPa, which could be due to (1) impurities and defects or (2) non-hydrostatic stress effects. Here, MD and DDD simulations are utilized to explore the role of the non-hydrostatic stress states in the α to ω phase transformation in Ti. First, a spherical ω nucleus within a α domain is generated and subjected to different loading conditions to determine the effects of non-hydrostatic stress states on the stability of the ω nucleus. Second, the sources of non-hydrostatic stress states are determined by studying the effect of defects such as prismatic dislocation loops and {101$2}〈1$011〉 twins on the stability of the ω nucleus.

9:30 AM  
Precipitation Behavior in a Laser-glazed Powder-processed Icosahedral-phase-strengthened Aluminum Alloy: Mingxuan Li1; Hannah Leonard1; Sarshad Rommel1; Cain Hung1; Thomas Watson2; Tod Policandriotes3; Rainer Hebert1; Mark Aindow1; 1University of Connecticut; 2Pratt & Whitney; 3Collins Aerospace
    Laser glazing experiments were performed on a powder-processed Al-Cr-Mn-Co-Zr alloy with a nano-composite FCC Al matrix plus I-phase dispersoid microstructure to evaluate the potential of the alloy for use in metal additive manufacturing (MAM). Electron microscopy studies on the microstructures of single laser tracks revealed the formation of I-phase dispersoids in the melt pools at appropriate combinations of processing parameters. Subsequent experiments were performed using overlapping melt tracks, to more closely represent the conditions that might prevail in MAM. The overlapping melt pools exhibited a more complex microstructure than the single laser tracks particularly in the remelted regions. In-situ TEM experiments were performed on FIB-cut samples of single laser tracks using the same parameters as those for the overlapping laser track experiments to study the precipitation behavior caused by the interaction of adjacent melt tracks. The potential for developing new alloys for MAM based on such systems will be discussed.

9:50 AM Break

10:10 AM  
Shuffle Transformation in Titanium Alloys: Wenrui Zhao1; Dian Li1; Yufeng Zheng1; 1University of Nevada-Reno
    Shuffle transformation is a distinct class of displacive transformation, accomplished by the rearrangement of atom positions within the unit cell, with little or no pure strain of the lattice. In titanium alloys, body-centered cubic (bcc) beta phase to hexagonal omega phase transformation is a prototype shuffle transformation, in which every two of three adjacent {111} planes shuffle towards to the intermediate plane of the two leaving the third plane unaltered. In this work, we report another shuffle transformation in titanium alloys, the bcc beta phase to orthorhombic O’ phase transformation. The structure of O’ phase was directly characterized using atomic resolution aberration-corrected scanning transmission electron microscopy. The orthorhombic structure is generated by the shuffle of every other {110} planes of bcc lattice along the <1-10> directions. This work is supported by the Research Enhancement Grant from University of Nevada Reno.

10:30 AM  
The Effect of Grain Size on Quasi-static and Dynamic Strength: Jenna Krynicki1; Laszlo Kecskes1; Christopher DiMarco1; Jake Diamond1; Zhigang Xu2; K.T. Ramesh1; Timothy Weihs1; 1Johns Hopkins University; 2North Carolina A&T State University
    The use of lightweight metals in structural applications has sparked revived interest in Mg alloys, as they can offer high specific strengths. Under extreme, high-rate loading conditions, spall strength and dynamic strength determine performance. In such applications, attempts to strengthen Mg alloys with precipitates may prove ineffective as second phase particles can serve as void nucleation sites that decrease spall strength. Therefore, we focus on grain refinement with a minimal number of precipitates, using a Mg-1Zn-0.2Ca (wt%) alloy as an alternative to precipitation strengthening. The alloy was first processed via Equal Channel Angular Extrusion (ECAE) to refine the grain size to ~5 microns; subsequently, samples were then annealed to generate grain sizes of ~25 and 80 microns. We report on the resulting microstructures, identifying corresponding grain size distributions and texture. Additionally, we compare the quasi-static and dynamic mechanical behavior of these samples, as a function of grain size.

10:50 AM  
NOW ON-DEMAND ONLY - The Impact of Al on the SRO, LRO, and Clustering of Elements within a CoFeNi High Entropy Alloy: Jaimie Tiley1; Soumya Nag1; Ke An1; Joerg Neuefeind1; Jonathan Poplawsky1; Sriswaroop Dasari2; Rajarshi Banerjee2; 1Oak Ridge National Laboratory; 2University of North Texas
    Microstructure evolution in a base equi-atomic CoFeNi alloy and samples containing 4, 8, and 12 at% Al was investigated using neutron scattering and diffraction coupled with TEM and APT. Al was specifically chosen since it has a large negative enthalpy of mixing with Ni, Fe, and Co, and therefore expected to introduce ordering tendencies (B2 structure). Previous solution thermodynamic modeling indicated the potential for forming phases within these materials that were stable at higher temperature. Select samples were cold rolled at 50 and 85% to provide heterogeneous nucleation sites, followed by water quenching. The resulting material was characterized at multiple length scales to identify probability distribution functions and chemical segregation. Results demonstrate the advantages of coupling multiple characterization techniques and illustrate the impact of Al on the short-range ordering and composition gradients within the alloy. In addition, the use multiple characterization methods identified strengths associated with coupling techniques.