GAT-2017 (Gamma Alloys Technology - 2017): Microstructure Evolution, Simulation and Prediction
Sponsored by: TMS Structural Materials Division, TMS: Titanium Committee
Program Organizers: Young-Won Kim, Gamteck LLC; Wilfried Smarsly, MTU Aero Engines AG; Junpin Lin, University of Science and Technology Beijing; Pierre Sallot, Safran Tech; Paul Withey, Rolls-Royce; Al Sommer, Del West Engineering, Inc; Rui Yang, Institute of Metal Research CAS; Florian Pyczak, Helmholtz-Zentrum-Geesthacht; Dennis Dimiduk, BlueQuartz Software, LLC

Tuesday 2:00 PM
February 28, 2017
Room: Pacific 17
Location: Marriott Marquis Hotel

Session Chair: Florian Pyczak, Helmholtz-Zentrum Geesthacht; Thomas Broderick, GE Aviation

2:00 PM  Invited
Grain Refinement and Texture Evolution in Boron Containing TiAl Alloys: Ulrike Hecht1; Silja-Katharina Rittinghaus2; 1Access e.V.; 2Fraunhofer ILT (Institute for Laser Technique)
    Boron additions in gamma alloys are known to promote grain refinement and mitigate the texture in cast components or ingots as well as in parts produced by additive manufacturing routes. This presentation reviews the roles of boron additions from several perspectives: 1) the thermodynamic background of boron partitioning and boride formation; 2) the crystallography of stable and metastable boride phases; 3) the role of ribbon borides (Ti,Nb)B with the crystal structure of NbB during the bcc-hcp phase transformation and their impact on grain refinement and texture evolution. Due distinction will be made between the solid-state bcc-hcp transformation and the peritectic bcc-hcp reaction/ transformation in the presence of borides; and 4) the phase transformations of borides during heat treatment. Finally and based on (i)-(iv) boride formation and grain refinement will be presented for the special case of additive layer manufacturing (LDM) both in as-build and heat treated samples from selected alloys.

2:25 PM  
Fine-grained FL Microstructure Evolution/Control and their Tensile Properties in a Cast Beta Gamma Alloy Material: Joon Sik Park1; Kwang Soo Choi1; Sang Lan Kim2; Young-Won Kim2; 1Hanbat National University; 2Gamteck LLC
    Some beta-solidified (BS) gamma alloys have been found to generate fine-grained (FG GS<100Ám) FL microstructures both in the cast material upon a subsequent annealing plus aging treatment cycle as well as in post-BS wrought-processed material upon a specific annealing plus aging cycle. When the FG-FL material exhibits a phase distribution within the g-rich and b-lean phase field (85-92)g-(0-2)b/B2-(15-6)a2 (vol%), the alloy composition is called a beta gamma alloy. A beta gamma alloy called 09C (Ti-43.8Al -4Nb–2Cr–xB-yC) has demonstrated a FG-FL microstructure in a wrought-processed material form that yields remarkable RT tensile properties (YS and ductility) and high high-temperature strength retention. The present experiment evaluates the FG-FL microstructure evolution in a controlled cast material form under various post-anneal cooling rates and their yield strength variations as a function of temperature. The results will be discussed and compared with those of a controlled wrought processed FG-FL material form.

2:45 PM  Invited
Processing, Microstructure and Mechanical Properties of Beta-gamma TiAl Alloy: Yuyong Chen1; Fantao Kong1; Jing Tian1; Shulong Xiao1; Xiaopeng Wang1; Ping Sun1; 1Harbin Institute of Technology
     This presentation reviews the processing, microstructure and mechanical properties of TiAl alloys in Harbin Institute of Technology. Aimed at the improvement of mechanical properties of casting TiAl alloy,the influence of B and C on the microstructure and mechanical properties were studied, also the influence of nanosize Y2O3 investaged. Finnally the TiAl casts were fabricated and the ablation test was carried out. In order to improve the hot-working character, the wrought processes of TiAl alloys were summarized. Their hot-deformation behaviors, microstructure, heat treatment process, mechanical properties and hot processing technologies were investigated systematically. Large size forged TiAl pancakes and rolled TiAl sheets were obtained successfully. Also the TiAl alloy parts were fabricated by isothermal die forging using wrought TiAl alloy.

3:10 PM  
Effect of Borides on the Beta/Alpha Phase Transformation Kinetics in Gamma Titanium Aluminide Alloys: Michael Oehring1; Andreas Stark1; Marcus Rackel1; Norbert Schell1; Florian Pyczak1; 1Helmholtz-Zentrum Geesthacht
    Pronounced microstructural refinement can be achieved in gamma alloys by the addition of B, as it is known since about two decades. For beta solidifying alloys this effect is induced by the beta/alpha transformation and only observed for rather slow cooling rates. In order to understand the microstructural refinement the phase transformations kinetics was analyzed by in situ high-energy XRD on cooling the material from the high-temperature beta phase field. An inductively heated dilatometer was used for heating and cooling specimens of the alloys Ti-43Al-5Nb and Ti-43Al-5Nb-0.2B (at.%). The specimens were cooled to room temperature with several cooling rates from 1 K/s up to 30 K/s. The phase fractions were determined by HEXRD and in addition from the length signal measured by the dilatometer. The experiments indicate a change in the transformation mechanism between 5 K/s and 10 K/s the origin of which will be discussed in the contribution.

3:30 PM  
Ordered ω Phase Transformations in High Nb-TiAl Alloys: Lin Song1; Junpin Lin2; Jinshan Li1; Hongchao Kou1; 1Northwestern Polytechnical University; 2University of Science and Technology Beijing
    In this study, the phase transformation behaviors of ordered ω phases in high Nb-TiAl alloys at 800~950℃ are reported. The ordered ω phases were removed at 950℃ while some ωo particles remained within βo areas after annealing at 900℃. However, in Ti-45Al-8.5Nb-0.2B alloy, the ωo phase could consume the whole βo areas after annealing at 850℃. The ωo phase also emerged in Ti-45Al-(6~10)Nb alloys after annealing at 850℃, which precipitated within α2 phase. Thus it can be concluded that the ordered ω phases are inevitable in the service condition of TiAl alloys. However, the direct evaluation of their effects on the mechanical properties is difficult because of their low volume fraction and distribution. Trace addition of other alloying elements will effectively control the morphology and stable temperatures of ordered ω phases, which may inspire new ideas on better controlling of these phase and optimizing microstructures.

3:50 PM Break

4:05 PM  Invited
3D Materials Science and Engineering: Emerging Capabilities for Gamma Alloys: Dennis Dimiduk1; Michael Uchic2; Michael Groeber2; 1BlueQuartz Software, LLC ; 2Air Force Research Laboratory
    Emulating microstructure–property relationships requires 3-dimensional (3D) models of microstructure. Automated serial sectioning methods such as Robo-Met.3D make 3D datasets more readily obtainable, but data-to-models workflows for specific characterization needs are still emerging. In this study we use mechanical serial sectioning to examine several materials, including the gamma alloy, Ti-47Al-XD. The DREAM.3D open source tool set is discussed in the context of workflows for 3D materials data analysis, quantification and model building. The talk emphasizes current capabilities and highlights emerging methods and needed improvements.

4:30 PM  
Three Dimensional Reconstruction of TiAl Microstructures: Henry Proudhon1; Anouk Briane2; Nicolas Gueninchault2; Wolfgang Ludwig3; Jerome Crepin2; Lionel Marcin4; Jean-Charles Stinville5; McLean Echlin5; Tresa Pollock5; 1MINES ParisTech / UCSB; 2MINES ParisTech; 3ESRF / INSA Lyon; 4SafranTech; 5UCSB
    Diffraction Contrast tomography (DCT) is a powerful non destructive near field X-ray technique to probe bulk cristalline materials. DCT allows to retreive the 3D grain map of millimeter sized specimens with a spatial resolution close to the micrometer. It has been used succesfully in the past to image a variety of materials and works well with rather equiaxed and undeformed mirostructures. Here, more complex TiAl microstrutures, including full gamma and duplex, are investigated. The slighly tetragonal structure of the L10 phase and the twin relationships are taken into account to improve the reconstructions and achive 3D grain maps in TiAl samples. Progress and challenges of the technique with complex microstructure of engineering materials will be detailed. Finally, the first results of destructive 3D characterization with the UCSB Tribeam system (large scale EBSD serial sectioning) of the same samples imaged earlier by DCT will be presented.

4:50 PM  Invited
Thermodynamic Modeling of the Ti-Al-Cr-Mo-Nb-B System for Aiding Gamma-TiAl Alloy Design: Fan Zhang1; Jun Zhu1; Chuan Zhang1; John Foltz2; Nick Sonnentag2; Thomas Broderick3; 1CompuTherm, LLC; 2ATI; 3GE Aviation
    Gamma (TiAl-based) alloys possess attractive attributes for structural applications. Adjustment of materials chemistry and processing conditions has been a common practice during materials development to achieve desired microstructure and properties. Traditional approaches relying on pure experimentation and trial-and-error are no longer viable due to limited resources, and materials design processes can be greatly accelerated with the aid of modeling tools. CALPHAD (stands for CALculation of PHAse Diagram), which emerged first as an approach for calculating complex phase diagrams, has now been applied to a broader field of materials science and engineering. This approach plays an important role in ICME. In this presentation, we will demonstrate how we use this approach to develop a thermodynamic database of the Ti-Al-Cr-Mo-Nb-B system. By using this database and Pandat software, we can obtain the phase stability and related properties of TNM and 48-2-2 alloys. Such information is valuable in aiding gamma-TiAl alloy design.

5:15 PM  Invited
Phase Field Simulation of Microstructure Evolution in TiAl: Dongsheng Xu1; Chunyu Teng1; Jinhu Zhang1; Yunzhi Wang2; Rui Yang1; 1Institute of Metal Research, Chinese Academy of Sciences; 2Ohio State University
    The properties of TiAl alloys depend strongly on their unique lamellar microstructures, with fully lamellae having the best combination of mechanical properties. However, the long term stability of the lamellar structure during service at elevated temperatures is a concern due to the high density of interfaces. In this study phase field simulations are carried out to study the effects of several processing and materials parameters, undercooling / supersaturation, external load, lattice mismatch and interfacial energy. The effects of these parameters on nucleation and variant selection of γ phase, in particular, the effect of the external load on lamellar thickness and interface type distribution are discussed. The simulation results may shed some light on microstructure optimization in TiAl alloys.