GAT-2017 (Gamma Alloys Technology - 2017): Novel Processing - Additive Manufacturing and SPS
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

Thursday 8:30 AM
March 2, 2017
Room: Solana
Location: Marriott Marquis Hotel

Session Chair: Rui Yang, Institute of Metal Research; Rob Haun, Retech Systems

8:30 AM  Invited
Advantages of PM Processing for Gamma Titanium Aluminides: Andrzej Wojcieszynski1; Joseph Muha1; 1ATI Powder Metals
    Gamma Titanium Aluminide alloys have been known since the 1970’s. Their attractive properties: high temperature strength, creep resistance and light weight, offered a very promising property combination for the jet engine applications. However, these alloys present a big challenge during fabrication. Inherent low ductility combined with a strong tendency to segregation during ingot solidification present a number of difficulties to form these alloys into a desired form. Many of these difficulties can be overcome by PM processing. The recent development in additive manufacturing rejuvenated an interest in this alloy system. This talk will review past experience at ATI Powder Metals in producing a PM large HIP preform for forging, which was successfully forged into an engine disk. It will also discuss advantages of VIM and gas atomization for manufacturing of TiAl powders for Premium Quality (PQ) rotating applications and the characteristics of powder used for additive manufacturing technologies.

8:55 AM  Invited
Fatigue Thresholds in γ-TiAl Alloys Produced by Additive Manufacturing: Mauro Filippini1; Stefano Beretta1; Luca Patriarca1; 1Politecnico di Milano
    Additive manufacturing (AM) based on (selective) Electron Beam Melting (EBM) is considered to be a viable technology to effectively produce γ-TiAl alloys with mechanical properties suitable for the application to structural components. As in the case of other technologies (e.g. casting, forging), once material is obtained, different microstructures can be achieved for the same alloy composition by adjusting the heat treatment parameters. In this work, an overview of the fatigue properties of three different variants of gamma-TiAl intermetallics produced by additive manufacturing by selective Electron Beam Melting (EBM) is presented. Results of fatigue tests on a Ti-48Al-2Cr-2Nb alloy, on a high Nb containing and a Mo-containing alloys, each with distinctive microstructures, are compared. Fatigue crack growth experiments conducted in the threshold region reveal how the local microstructure influences the evolution of fatigue damage. The analysis presented here is aimed at providing information useful for designing against fatigue with γ-TiAl intermetallics.

9:20 AM  
Effect of Post-Processing on Microstructure and Mechanical Properties of EBM Ti-48Al-2Cr-2Nb: Mohsen Seifi1; Ayman Salem2; Daniel Satko2; Ulf Ackelid3; John Lewandowski1; 1Case Western Reserve University; 2Materials Resources LLC; 3Amable Consulting
    Both cast and wrought titanium aluminide alloys have been studied for more than four decades because of attractive properties that include low density, high specific strength, high specific stiffness and oxidation resistance up to about 700°C. Electron beam melting provides another processing approach to producing net shape components, although little work has been conducted to examine processing-microstructure-property relationships. This work examines effects of post processing and on γ-TiAl (Ti-48Al-2Cr-2Nb) specimens. Mechanical behavior studies on as-deposited and post-processed conditions included Vickers micro-hardness, compression, fracture toughness and fatigue crack growth testing. In addition, microstructural details were investigated over a range of scales using various microscopy tools. The presentation will summarize this evolving work on the characterization of AM γ TiAl and provide some comparison to other conventional (e.g. as-cast, wrought) γ-TiAl alloys.

9:40 AM  
Characterization of a High Nb-TiAl Alloy Components Fabricated by Additive Manufacturing Using Electron Beam Melting: Wenbin Kan1; Junpin Lin1; Yongfeng Liang1; Hui Peng2; Hongbo Guy2; 1University of Science and Technology Beijing; 2Beihang University of Aeronautics and Astronautics
    A high Nb-TiAl alloy(Ti–45Al–8Nb, in at%) were processed by electron beam melting (EBM). This near-net-shape additive manufacturing process produces complex parts according to a CAD design. The formation of various types of microstructural defects, including banded structures caused by the vaporization of aluminum, was investigated with respect to different processing parameters and processing strategy. The microstructure, residual porosity and the chemical composition of the samples have been investigated both immediately after EBM and after high temperature insostatic pressing(HIP) or heat treatments(HT). To avoid both micro- and macro-cracks, the use of higher preheating temperatures and an intermediate reheating process (to reheat each solidified layer during EBM) was assessed in detail. In addition, the processing conditions for the production of a fine full lamellar microstructure were identified.

10:00 AM  
Repair of γ-TiAl Turbine Blades by Use of Laser Additive Manufacturing: Silja-Katharina Rittinghaus1; Andreas Weisheit1; Michael Mathes2; 1Fraunhofer ILT (Institute for Laser Technique); 2Access e.V.
    Powder based laser metal deposition (LMD) is an established additive manufacturing technique used for repair of high value parts, e.g. blades made of nickel or titanium alloys. Intermetallic γ-TiAl based alloys are a modern class of materials which have found first applications as low pressure turbine blades. However, so far there is no repair technology established for this alloy class. The challenge for this is very high, since TiAl is extremely brittle and prone to oxygen pick-up. In the present work, laser metal deposition is investigated for the technical alloys TNM-B1 and GE4822. A suitable machine setup, processing strategy and parameters for crack free near-net-shape repair are identified. Post-heat treatment is performed and microstructural as well as mechanical properties (tensile strength, creep) are investigated and discussed. The results show that LMD can also fit well into an automatized process chain to restore damaged and worn turbine γ-TiAl blades.

10:20 AM Break

10:35 AM  Invited
Spark Plasma Sintering of a TiAl Alloy and of Near-net Shape Blades: Alain Couret1; Jean-Philippe Monchoux1; Thomas Voisin1; Marc Thomas2; 1CEMES/CNRS; 2DMMP/ONERA
    The aim of the present study is to evaluate the Spark Plasma Sintering (SPS) as a possible route to produce TiAl blades for aircraft engines. The first part of this talk will be devoted to the development of a performing alloy, called IRIS, offering a good compromise between creep resistance at high temperature and significant plastic elongation at room temperature. We’ll start describing the optimization of its chemical composition and processing conditions. Then, microstructures and the mechanical properties will be successively presented. In the second part, we’ll depict the method used to sinter near-net shape blades by SPS, using modified graphite die and punches, which compress the powder, to obtain the final shape of the engine component.

11:00 AM  
In-situ Experiments to Determine the Creep Law Describing the SPS Densification of a TiAl Powder: Martins David1; Grumbach Fanny2; Maniere Charles2; Sallot Pierre1; Bellet Michel3; Mocellin Katia3; Estournes Claude4; 1SAFRAN; 2CIRIMAT; 3CEMEF; 4CNRS CIRIMAT
    Spark Plasma Sintering (SPS) is a process belonging to the powder metallurgy family. It consists in applying simultaneously a load and a high intensity pulsed direct current on graphite tools containing powder to sinter this latter. The originality of this study lies on the in-situ SPS compression creep tests performed on TiAl 48-2-2 dense and porous samples, completed by SPS powder densification to established the creep law of this material. Once determined, it is then used in a fully-coupled simulation tool to predict temperature field and density gradient within the samples. The experimental relative density map will be presented and the correlation with the numerical model will be analyzed, both on simple and complex shape specimens. The evolution of the microstructure during creep test as well as after densification of a complex part will be presented and correlation with numerically assessed temperature field will be discussed.

11:20 AM  Invited
Manufacturing Issues in Rapid Thermal Processing of γ-TiAl Alloys: Marc Thomas1; Alain Couret2; Jean-Philippe Monchoux2; 1ONERA; 2CEMES
    A current challenge for γ-TiAl is to manufacture robust alloys with efficient processing strategies to achieve optimized properties for high temperature applications. Despite extensive efforts, cast γ-TiAl alloys in turbine engines are limited by structural inhomogeneities, coarse microstructure and non-uniform solidification texture which lower their strength and ductility. Alternately, Powder Metallurgy, may offer grain refinement, structural homogeneity and isotropic properties. Secondary processing by HIP was successfully used for both TiAl powder densification and near-net shaping. This paper will address encouraging results in near net shaping by HIP. However, HIPing is slow and is not always flexible enough to provide optimized microstructure. Therefore, complex shape manufacturing using more rapid thermal processing has been extensively investigated in the last decade. Three innovative PM techniques will be reviewed: Metal Injection Moulding, Spark Plasma Sintering and Additive Manufacturing. This talk will highlight the critical variables of the above processes and compare the obtained alloys.

11:45 AM  Student
Properties at High Temperatures of the IRIS Alloy Densified by Spark Plasma Sintering: Soumaya Naanani1; Jean-Philippe Monchoux1; Catherine Mabru2; Alain Couret1; 1Cemes; 2ICA (Institut Clément Ader), ISAE, Université de Toulouse
    The aim of this work is to study the behavior of the IRIS alloy (Ti-48Al-2W-0.08B) densified by Spark Plasma Sintering (SPS) under solicitations reproducing the thermomechanical environment during service in aero or automotive engines. SPS is a powder metallurgy technique, for which the heating of the sample occurs by the application of a pulsed direct electric courant. The IRIS alloy microstructure is made of small lamellar grains surrounded by single-phased γ borders, as the results of the powder metallurgy route. Several properties of the IRIS-SPS alloy will be examined: i) the evolutions of microstructure and properties of the alloy under aging treatments as 9 000h at 750°C, ii) the creep properties at 800°C and 850°C under various stress levels and, iii) the low cycle fatigue behavior at temperatures higher than 700°C.