Development of Light Weight Alloys and Composites : On-Demand Oral Presentations
Program Organizers: Ramasis Goswami, Naval Research Laboratory; Nikhil Gupta, New York University; Tanjore Jayaraman, United States Air Force Academy; Aashish Rohatgi, Pacific Northwest National Laboratory
Friday 8:00 AM
October 22, 2021
Room: On-Demand Room 12
Location: MS&T On Demand
Invited
Surge for Design and Development of Low-density High Entropy Alloys and Composites: Nandini Singh1; Yagnesh Shadangi1; Vivek Kumar Pandey1; Vikas Shivam1; Nilay Mukhopadhyay1; 1Indian institute of Technology (BHU) Varanasi
The demand for advanced lightweight materials for various engineering applications has brought a paradigm shift in alloy-development strategies. In recent times multi-principal element alloys (MPEA), also known as high entropy alloys (HEAs) have gained much of attention due to their promising potential. In the present investigation, attempts were made to study a few equiatomic MgAlSiCrFe, MgAlSiCrFeNi, MgAlSiCrFeCuZn and MgAlMnFeCu low-density high entropy alloys (LDHEAs), processed through mechanical alloying (MA) and spark plasma sintering (SPS). The sequence of phase evolution during MA and SPS was ascertained through XRD and TEM. The microstructure and chemical composition of milled powder and SPSed samples were investigated through SEM equipped with EDS. The mechanical properties of these LDHEAs evaluated by instrumented microhardness and compressive testing were found to exhibit excellent mechanical strength, especially high strength to density ratio. Thermodynamic modelling including CALPHAD modelling were considered for discussing phase evolution and stability during MA and SPS.
Grain Boundary Relaxation in Nanocrystalline Aluminum: Leslie Mushongera1; Wenye Ye1; Jake Hohl1; Pradeep Menezes1; Mano Misra1; 1University of Nevada Reno
The excess free volume in grain boundaries (GBs) of pure nanocrystalline aluminum leads to grain coarsening, which degrades their desirable mechanical properties. The decoration of GBs with dopants is proposed to stabilize the nanostructure. Thermodynamic modeling is used to identify the specific dopant type with the highest potential to segregate to grain boundaries in nanocrystalline aluminum. Various elements are evaluated as potential dopants and magnesium is identified to have the highest tendency to partition preferentially to the GBs. To shed light on the stabilization mechanisms, we present results from virtual mechanical tests on nanocrystalline aluminum samples with similar grain sizes but different magnesium dopant contents. It is found that the deformation pathways are influenced by the local GB state as modified by the dopants. The segregation of magnesium decreases the excess free volume within the GB which prohibits the nucleation and propagation of intergranular cracks.
Effect of Copper Contents on Corrosion of High Performance ACMZ Cast Aluminum Alloys: Jiheon Jun1; Amit Shyam1; J. Allen Haynes1; Yi Feng Su1; 1Oak Ridge National Laboratory
ACMZ cast Al alloys were developed to realize higher temperature strength and fatigue performance for the fabrication of cylinder heads for higher-efficiency engines. ACMZ alloys contain relatively high Cu contents (6~8 wt.%) which may impact the corrosion behavior of the alloys. This work aims to compare the aqueous corrosion resistance of different classes of ACMZ alloys and two commercial Al cast alloys, A319 and A356 with 0.5 wt.% Cu in as-cast and aged conditions. The evaluation of corrosion resistance was primarily performed in NaCl solutions at ambient temperatures using a suite of electrochemical techniques including corrosion potential, anodic/cathodic polarizations and electrochemical impedance spectroscopy measurements. Corrosion mass change measurement of selected Al alloys was also conducted by NaCl solution immersion tests. The experimental results indicated that the corrosion resistance of as-cast and aged ACMZ alloys was comparable or slightly higher than the resistance of commercial Al alloy counterparts.
Invited
Precipitation of Stable Icosahedral Quasicrystalline Phase in Mg-Al-Zn Alloys: Alok Singh1; Takanobu Hiroto1; Machiko Ode1; Karel Tesar2; Hidetoshi Somekawa1; Toru Hara1; 1National Institute for Materials Science; 2Czech Technical University in Prague
Precipitation of stable icosahedral quasicrystalline (i-) phase in a ZA63 Mg-Zn-Al alloy has been discovered, possibly for the first time involving a stable i-phase. It is shown that the stable i-phase forms during solidification of ZA63 alloy. It reversibly transforms to liquid at eutectic temperature near 350°C during heating and cooling. Calculation of phase diagram showed a solvus boundary involving i-phase at the Mg-end. The i-phase goes into solution on prolonged heating/annealing, whereby cooling below 300°C causes precipitation of the i-phase. The precipitates are sharply faceted and show definite orientation relationships with the matrix. Nucleation and transformation characteristics as well as formation of interfaces have been studied using DSC, in-situ XRD and TEM. The findings will be presented and discussed. This discovery opens doors to new studies, such as exploring properties effected by volume fraction of i-phase and its interfaces in a periodic crystal matrix.
Coarsening of Strengthening Phases in Al(Cu) Alloys: Correlated Atomic-Resolution Microscopy and Composition Analysis: Ujjval Bansal1; Mahander Singh1; Shyam Sinha1; Sukla Mondol2; Kamanio Chattopadhyay1; 1Indian Institute of Science; 2NIT Warangal
Strengthening by shear resistant θ"/θ' plates is the basis for developing high-temperature Al-Cu alloys. The addition of transition metals (TM) in Al(Cu) alloys form a coherent L12 ordered Al3TM phase that can further improve the microstructural stability and mechanical properties of these alloys. This talk will discuss the interaction between the evolved L12 and θ"/θ' precipitates leading to a coarsening resistant microstructure. STEM-EDS compositional studies show the enrichment of TM in the θ' plates. The presence of TM decreases the interfacial energy (thermodynamic factor) and act as a kinetic diffusion barrier to Cu atoms due to Zener drag (kinetic factor), eventually delaying the coarsening of θ' plates. Aberration-corrected STEM HAADF microscopy also detected anti-phase boundaries in L12 ordered precipitates which initiate phase transformation to a different phase on long-term ageing.