Microstructural Template Consisting of a Face-Centered Cubic Matrix with Ordered Precipitates: Microstructural Evolution and Properties: Other FCC Based Alloys
Sponsored by: TMS Materials Processing and Manufacturing Division, TMS: Phase Transformations Committee
Program Organizers: Rajarshi Banerjee, University of North Texas; Eric Lass, University of Tennessee-Knoxville; Ashley Paz Y Puente, University of Cincinnati; Tushar Borkar, Cleveland State University; Keith Knipling, Naval Research Laboratory; Sophie Primig, University of New South Wales

Tuesday 2:00 PM
February 25, 2020
Room: 30D
Location: San Diego Convention Ctr

Session Chair: Tushar Borkar, Cleveland State University

2:00 PM  Invited
Novel fcc-Cu Matrix Based High Temperature Alloys Strengthened by Ordered Precipitates: Suman Sarkar¹; Prafull Pandey¹; Surendra Kumar Makineni¹; Kamanio Chattopadhyay¹; ¹Indian Institute of Science, Bangalore
    Ordering represents great opportunity for designing high temperature alloys as super-dislocations are needed to cut through ordered particles. Thus, below the critical temperature of ordering, these particles have the ability to retain strength. In this talk, we present a pathway utilizing ordered precipitates to develop Cu-based alloys that have desired conductivity as well as mechanical strength at high temperature for heat flux applications. We show that introduction of the coherent ordered particles are much more effective design approach for copper alloys in comparison to strategies like inducing nano-twins in pure fcc-Cu and introducing second phase particles. A new class of alloys that contain transition metal alloying additions like Fe and Co with further tuning by the addition of Si and Al will be demonstrated. The optimization of the alloys not only result in exceptional thermal conductivity at high temperatures but also provides opportunities for imparting good oxidation resistance.

2:30 PM
Mapping the Mechanical Property Space of Al-Cu-Mn-Zr (ACMZ) Cast Aluminum Alloys with Superior Microstructural Stability: Sumit Bahl¹; Jiahao Cheng¹; Eric Hoar¹; Xiaohua Hu¹; Allen Haynes¹; Amit Shyam¹; ¹Oak Ridge National Laboratory
    Al-Cu-Mn-Zr (ACMZ) is a new class of cast Aluminum alloys engineered to have exceptional microstructural stability up to 350 °C for automotive applications. These materials are expected to endure complex thermo-mechanical loading cycles throughout service. Mechanical property requirements such as strength, ductility and fatigue resistance vary with specific components in an automotive engine. This presentation will elaborate on the mechanical behavior of a series of ACMZ alloys with Cu content varying between 6.0 - 9.0 wt. %. Tensile, low cycle fatigue and creep properties will be discussed as a function of alloy composition and thermal history. The effects of grain boundary intermetallic particles and fine strengthening precipitates on tensile, low cycle fatigue and creep properties will be discussed.

2:50 PM
Stress Induced Sensitization in HAZ of 304 LN Austenitic Stainless Steel: Nikki Barla¹; Sourav Das¹; ¹IIT Roorkee
    Stress induced sensitization in HAZ of 304 LN austenitic stainless steel was studied using Gleeble 3800. The test was performed at 650⁰ C at different stress level i.e. 0, 100 and 200 MPa. The response of sensitization was studied through the observation on change in microstructure, hardness measurement, TEM test, EBSD and electrochemical properties. Transmission electron microscopy confirmed the presence of Cr23C6 precipitation at the grain boundary for all the samples. EBSD result showed higher CSL boundary for sample without stress as compared to the sample with stress. Microstructure study, Hardness measurement and Electrochemical test indicated that chromium carbide nucleation was much in sample with induced stress. It was observed through this work that presence of stress enhances the sensitization.

3:10 PM Break

3:40 PM  Cancelled
Thermodynamic Simulation and Experimental Validation of Phase Stability in Ni-based Superalloys: Kyle Ventura¹; David Beaudry¹; Alex Aviles¹; Gerhard Fuchs¹; ¹University of Florida
    Phase stability of superalloys is necessary for their application as a structural material at high temperatures. In this study, the stable phases and transformation temperatures of commercially available and novel Ni-based superalloy compositions were calculated using Thermo-Calc software. Transformation temperatures of these simulations were compared to a differential scanning calorimetry (DSC) study of all the alloys. DSC was used to develop a heat treatment in order to solution and precipitate the phases in each alloy. All alloys then underwent heat treatments to precipitate and grow carbides, 𝛾′, and topologically close-packed (TCP) phases. Each heat treatment step was carried out for 100 hours to precipitate equilibrium phases. The volume fraction and approximate elemental composition of all phases was determined using scanning electron microscopy, energy dispersive spectroscopy, and quantitative metallography. These values were then compared to the calculated values to gain an understanding of the effectiveness of the calculation.

4:00 PM  Cancelled
Enhanced Creep Resistance via Strain-induced Massive Nanoprecipitation in Alumina-forming Austenitic Stainless Steels: Zhao Wuxin¹; Zhaoping Lu¹; ¹University of Science and Technology Beijing
    Due to their outstanding corrosion resistance arisen from the compact alumina scale, alumina-forming austenitic (AFA) stainless steels are promising for service in hash environments. In this work, effects of pre-straining on the precipitation behavior of secondary NbC and creep performance of a typical AFA steel were investigated. It was found that, a proper amount of pre-straining would induce sufficient defects into the matrix, acting as the preferable nucleation sites for semi-coherent secondary NbC due to the reduced nucleation barrier energy. The nucleation rate was thus enhanced and the precipitation kinetics was accelerated. Our long-term thermal aging experiments over 10000 h also demonstrated that the nanoprecipitates of NbC about 10 nm exhibited ultrahigh thermal stability and extreme coarsening resistance at 1023 K. We have successfully enhanced the creep lifetime of the current alloys at 1023K/100MPa from 1000 h to over 4500 h due to the increased massive precipitation of nanosized NbC.

4:20 PM  Cancelled
Site Preference of the Alloying Additions on Mechanical Properties of L1₂ Ni₃Co Alloys: Peng Liu¹; Dengfu Chen¹; Pei Xu¹; Mujun Long¹; Huamei Duan¹; ¹Chongqing University, China
    The site preference and alloying effects of transition-metal elements M (M=W, Nb, Ta) on mechanical properties of L1₂ Ni₃Co alloys are investigated using density functional theory. The formation enthalpy (ΔH_f) and substitution formation enthalpy (E_site) are calculated to prediction the site preference of M. The results indicate that the three elements all tend to replace a Ni site and form Ni₂₃MCo₈ intermetallics. The mechanical properties (elastic properties and hardness) calculations show that the alloying elements deteriorate the ductility and remarkably improve the hardness of the Ni₃Co alloys. Ni₂₃NbCo₈ possesses the lowest ductility and the highest hardness. Ni₂₃TaCo₈ displays the highest shear modulus (G) and Young’s modulus (E). The anisotropic factors, 3D directional Young’s modulus predict Ni₂₃MCo₈ alloys are all anisotropic materials and the degree of anisotropy is small. Further analyses on electron localization function (ELF) demonstrate that mechanical properties are closely connected with the bonding nature of the alloys.