Solid State Precipitation: Session I
Sponsored by: TMS Materials Processing and Manufacturing Division, TMS: Phase Transformations Committee
Program Organizers: Seth Imhoff, Los Alamos National Laboratory; Robert Hackenberg, Los Alamos National Laboratory; Gregory Thompson, University of Alabama

Wednesday 2:00 PM
March 1, 2017
Room: 24C
Location: San Diego Convention Ctr

Session Chair: Seth Imhoff, Los Alamos National Laboratory

2:00 PM  Invited
Understanding the Precipitation and Orientation Relationships in Transition Metal Carbides and Nitrides: Christopher Weinberger1; Hang Yu1; Bradford Schulz2; Robert Morris2; Xiao-Xiang Yu2; Gregory Thompson2; 1Drexel University; 2University of Alabama
    The group IVB and VB transition metal carbides and nitrides are a group of refractory materials that are known to precipitate a wide range of phases and associated microstructures. There has been renewed interest in this problem because one such phase, the zeta phase, has been linked to high fracture toughness. In this talk, we review experimental evidence for the precipitation pathways of these materials with emphasis on the tantalum carbide and hafnium nitride systems. To understand the orientation preference of the zeta and associated phases, we develop a model fit to density functional theory data. This model is able to predict interfacial energies, which can be used to interpret both orientation relationships as well as help explain observed microstructures. It is also able to help explain why in the tantalum carbides, the zeta phase appears as thin lathes but can form large grains more easily in the hafnium nitrides.

2:30 PM  
An Experimental and Modelling Study on Precipitation during Tempering of Martensitic Alloys: Tao Zhou1; Joakim Odqvist1; Peter Hedström1; 1KTH Royal Institute of Technology
    Precipitation of particles plays a major role in strengthening of metals and there is currently significant interest in the experimental characterization and predictive modelling of precipitation. The present work focuses on the nucleation, growth and coarsening of copper precipitates and carbide precipitates in multicomponent martensitic stainless steel and alloy steel, respectively. Quantitative assessments of precipitates during tempering are performed using advanced electron microscopy and dissolution experiments. Data on mean radius, volume fraction, number density and size distribution are collected and compared with precipitation modelling performed using the software TC-PRISMA. The modelling and experimental results on evolution of precipitates during tempering is further correlated with the evolution of mechanical properties for the alloy under specific tempering conditions. The work gives promise for further opportunities of predictive modelling of precipitation for design of alloys, optimization of heat treatments and life-time assessments of precipitation-strengthened metals.

2:50 PM  
Carbide Precipitation during Heating in Martensitic Steels: Xiaoqing Cai1; Richard Sisson1; 1Worcester Polytechnic Institute, Center for Heat Treating Excellence
    Martensitic steels must be tempered to increase their toughness and ductility. The tempering process requires heating from room temperature to the desired tempering temperature. In this presentation the effects of heating rates on carbide precipitate size distribution, chemistry and precipitate density will be discussed. As-quenched Martensite in AISI 4140 steel was heated to selected tempering temperatures in air furnaces as well as by induction. The heating times to tempering temperature vary from 20 minutes to 10 seconds. The experimental results are presented and compared to theoretical calculations based on heterogeneous nucleation theory and growth kinetics. The results for hardness measurements are analyzed using the Holloman-Jaffe parameter.

3:10 PM  
Precipitation Behavior in Ni-Ti-Zr Shape Memory Alloys: Suzanne Kornegay1; Monica Kapoor2; B. Chad Hornbuckle3; Othmane Benafan4; Ronald Noebe4; Mark Weaver1; Gregory Thompson1; 1University of Alabama; 2National Energy Technology Laboratory; 3Army Research Laboratory; 4NASA Glenn Research Center
    A series of aging studies on the precipitation in 50.3Ni-(49.7-X)Ti-XZr, where X varied from 1 to 17.5 at. %, have been conducted at 400C and 550C. It was found that two types of precipitates formed in the dilute Zr concentrations and only one type of precipitate at higher concentrations. In the dual precipitate microstructure, the known H-phase precipitate was observed along with a new, spherical precipitate denoted as the S-phase. At higher Zr concentrations, the S-phase was not found. At 1%Zr, after 10 hour/400C, only the S-phase is observed with a composition 55Ni-40Ti-5Zr. At 100 hours, the S- and H-phase are observed with the S-phase being 54Ni-43Ti-3Zr. The depletion of Zr is contributed to a potential competition of this solute with the onset of H-phase precipitation. The compositional evolution of the H-phase at other concentrations and its effect on the shape memory transformation temperature will be discussed.

3:30 PM Break

3:50 PM  
Kinetics of Discontinues Precipitation upon Age-hardening of Deformed and Recrystallized Invar-Sn Alloys: Maryam Akhlaghi1; Olena Volkova1; 1Institute of Iron and Steel Technology, Technische Universität Bergakademie Freiberg
    Fe-Ni Invar alloy is well recognized for its remarkable dimensional stability upon temperature variations. In order to enhance the mechanical performance of this material at high temperatures, alloying elements such as Sn is added to the binary alloy. Development of alloying element precipitates upon age-hardening increases the strength and hardness of this material. In this research, evolution of precipitation upon age-hardening of the deformed and recrystallized ternary Fe-Ni-Sn alloys has been investigated. Upon prolonged age-hardening of both microstructures, the tiny semi-coherent precipitates are replaced by the lamellar microstructure, so-called discontinues precipitate (DP), consisting of the incoherent coarse precipitates and the matrix. Kinetics of DP development upon age-hardening of both microstructures have been traced and compared using X-ray diffraction technique. Faster progress of DP reaction during age-hardening of the recrystallized specimens as compared to the deformed ones has been associated with the easier migration of DP reaction boundaries in recrystallized materials.

4:10 PM  Invited
Prediction of Size, Temperature and Composition-dependent Precipitate/Matrix Interfacial Energies: Ernst Kozeschnik1; Bernhard Sonderegger2; 1TU Wien; 2TU Graz
    The predictive simulation of precipitate formation based on classical nucleation theory requires the precise knowledge of the interfacial energy as the most important and sensitive input parameter. Although the majority of researchers use this quantity as a fitting parameter to get precipitation kinetics simulation in accordance with experiment, recent developments in modeling provide a framework that allows for a prediction of interfacial energies purely from thermodynamic databases. In the present work, the models for calculation of the planar sharp interface energy as well as the further developments to account for interface curvature and diffuse interfaces as developed by the present authors is reviewed. Successful examples of application of the models are discussed in the second part of the presentation.

4:40 PM  
Predicting Orientation Relationships: A Simple Algorithm for Generating Near-coincidence Site Lattices in General Bravais Lattice Systems: Srikanth Patala1; Arash Banadaki1; 1North Carolina State University
    Orientation relationships between the parent and the product phase are essential for understanding the crystallography and for building predictive models of microstructure evolution during phase transformations. Experimentally observed orientation relationships usually correspond to transformations that generate a plane with minimal interfacial energy and lattice strain across the adjoining phases. Hence, a simple algorithm generating the Near-Coincidence Site Lattices for the heterophase interfaces will provide a powerful tool in predicting such orientation relationships. Grimmer, in a series of articles, has proposed the generating functions for determining the coincidence site lattices for homophase interfaces (grain boundaries) of cubic, hexagonal, trigonal and tetragonal Bravais lattices. These generating routines become increasingly complexity as the underlying symmetry of the lattice is reduced. In this talk, I will present a simple algorithm for computing near-CSL rotations between any two Bravais lattice systems (i.e. both homo-phase and hetero-phase interfaces).

5:00 PM  
Investigating the Formation Path of Delta Hydrides in Zirconium Fuel Rod Claddings by Multi-Phase Field Modeling: Jacob Bair1; Mohsen Asle Zaeem1; 1Missouri University of Science and Technology
    Precipitation of ζ, γ, and δ hydride phases in nuclear fuel claddings is studied by developing a multi-phase field model. Non-conservative structural field variables are used to represent each phase including α-Zr matrix, ζ-hydrides, γ-hydrides (one structural field variable for each of the three orientation variants), and δ-hydrides. Concentration of Hydrogen is controlled using a conserved field variable. The Ginzburg-Landau and Cahn-Hilliard equations are used for the evolution of field variables and concentration, respectively, and the mechanical equilibrium equations are imposed to consider the effects of elastic strain energy. Results from simulations both in the basal plane and perpendicular to the basal plane with and without applied stresses indicate that the initial morphology of δ hydrides is significantly dependent on the intermediate phases. Simulations conducted including only α and δ phases showed significantly different results from simulations including the intermediate phases.

5:20 PM  
Morphology and Phase Stability of Pt Nanostructures in Dense Transition Alumina Formed by Solid-state Precipitation: Arielle Clauser1; Zachary McClure1; Raquel Giulian2; Andreas Glaeser3; Melissa Santala1; 1Oregon State Unviersity; 2 Universidade Federal do Rio Grande do Sul; 3University of California, Berkeley
    Pt nanoprecipitates were formed in dense transition alumina through solid-state precipitation into amorphized regions of sapphire wafers. Amorphization was achieved during the high-energy ion implantation process used to introduce Pt into the sapphire. Subsequent thermal annealing caused the formation of Pt nanoprecipitates and epitaxial recrystallization of the amorphous alumina. Annealing between 750 – 1200°C results in the re-crystallization of the amorphized alumina as a transition phase, rather than the stable corundum structure (α-alumina). At higher temperatures, θ-alumina formed and precipitates took the form of faceted tetrahedra and truncated tetrahedra bound by (111) Pt planes. The presence of a high density of Pt nanoprecipitates appears to stabilized the transition alumina, as θ-alumina was observed to persist for hundreds of hours of annealing at 1200°C, a temperature at which rapid conversion to α-alumina would be expected in the absence of nanoprecipitates.