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Storrs, CT : The Additive Manufacturing Center was established at the University of Connecticut (UConn) in April 2013 in partnership with Pratt & Whitney, to advance additive manufacturing research and development. The facility recently expanded their capabilities by adding a Gleeble 3500 system, equipped with the advanced Hydrawedge unit which combines high-temperature capabilities with high-speed deformation.

Gleeble systems, produced by Dynamic Systems Inc. (DSI) are material testing and simulation systems used to characterize new materials and optimize manufacturing processes. Data and insight garnered from the Gleeble can be successfully transferred to plant production lines, reducing the cost, risk and time associated with developing new processes or materials.

Of particular interest to the researchers at UConn is the Gleeble’s ability to simulate the additive manufacturing process as well as generate material performance data to better inform computer modeling simulations. This close association of physical simulation and computer modeling is critical for the refinement of metallic 3D-printing processes, alloy development and post-build material characterization.

The Gleeble’s capabilities provide industrial partners with a powerful competitive advantage – resulting in improved product quality, cost-savings and accelerated development times which ultimately lead to greater profits. UConn is well positioned to provide these competitive advantages to a growing list of industrial partners.

Dr. Rainer Hebert, Director of the Pratt & Whitney Additive Manufacturing Center, described the value the Gleeble will bring to his team’s research, “We have been looking forward to the unique Gleeble capabilities for a long time. Our new Gleeble will support R&D projects in materials development and manufacturing simulations. The role of manufacturing simulations continues to increase in many industries. However, without high quality materials data, even advanced simulation models cannot accurately predict manufacturing processes. High quality materials data needs to capture the conditions found in manufacturing processes that are often highly transient in nature.”

The Gleeble’s very fast heating and cooling rates (up to 10,000°C/sec) as well as high strain rates, combined with independent control of strain and strain rates are ideally suited to simulate manufacturing processes, in particular the stress-strain behavior of materials. The data obtained from these transient property measurements can then be used to generate constitutive models that drive computer simulations.

Gleeble systems can achieve very high heating and cooling rates, a hallmark of most additive manufacturing processes, but can also probe minute dimension changes under zero load conditions that are caused by phase transformations. These dilatometry measurements will be used for research on new alloys to be used in additive manufacturing.

Gleeble’s long history of supporting welding applications, along with the similarities between additive manufacturing and welding, promises several additional applications for additive manufacturing research. For example, liquation cracking or hot tearing are challenges well known in the welding world that limit the use of many alloys, including most of the high-strength aluminum alloys, in additive manufacturing. With the Gleeble, these phenomena can be studied experimentally. UConn researchers will combine Gleeble physical simulations with thermodynamic calculations and a new arc-melter that will yield experimental alloy samples for the Gleeble. UConn has also purchased the optional High-Temperature Mobile Conversion Unit which allows for sustained testing up to 2,300°C with a peak temperature of 3,000°C.

For those at UConn interested in microstructure analysis after testing with the Gleeble, the Thermo-Fisher Scientific Center for Microstructure and Materials Analysis will be located in the same building and will extend R&D capabilities with a suite of scanning electron microscopes, focused ion-beam milling equipment, electron backscattered diffraction, and transmission electron microscopes, including the newest FEI Titan aberration-corrected microscope.

The nearly-complete Tech Park at UConn provides researchers with a host of impressive metal printing and research equipment. The range of equipment available includes electron beam melting and laser sintering technologies, including an experimental powder bed machine with complete open architecture. UConn’s research center is focused on the underlying physics of additive manufacturing with emphasis on rapid solidification, powder spreading, and metal-atmosphere interactions. Experiments as well as ab-initio calculations are used to develop new insight into the additive manufacturing process.

UConn and DSI have a shared objective of advancing research and supporting industrial partners, not just with data but with actionable intelligence. To further this goal, UConn and DSI have created a formal Research Collaboration which will provide UConn with advanced training opportunities, a funded research project, access to new components and features with increased access to DSI R&D teams to collaborate on new projects and offerings.

For more information on the Pratt & Whitney Additive Manufacturing Center at UConn, please visit: www.amic.uconn.edu

Gleeble Workshop South America (GWSA) Meeting Recap:

Gleeble users from across South America gathered in Campinas, Brazil at the Brazilian Nanotechnology National Laboratory (LNNano) to share knowledge and learn from other Gleeble researchers. The meeting included two days of presentations from researchers from universities, industry and research institutions, as well as demonstrations and discussions about testing best practices. The ability to interact with other users and share experiences allows for a deeper knowledge of thermal mechanical physical simulation.

LNNano is part of CNPEM, the Brazilian Center for Research in Energy and Materials, and operates two Gleeble systems, including a Gleeble 3800 with a Torsion Mobile Conversion Unit and another Gleeble that has been customized for use within the Brazilian Synchrotron Light Laboratory (LNLS).

We would like to thank the attendees that participated in the meeting and helped make the event a success. We are grateful to the the staff at LNNano for their hospitality in hosting our group and providing an excellent venue and learning environment. We would like to especially thank Leonardo Wu with CNPEM and Fulvio Siciliano from DSI for their efforts in organizing both a productive and enjoyable two-day event.

If you were not able to attend this user meeting, we hope that will be able to attend a future event. Typically, user meetings occur once or twice a year. Upcoming meetings are scheduled for Early August in Xi'an, China and September, 2018 in Erlangen, Germany. Details will be posted on our website (www.Gleeble.com) and outlined in future Gleeble eNewsletters.

For more information on CNPEM / LNNano and the Brazilian Synchrotron at LNLS, please visit http://www.lnls.cnpem.br.

Analysis of the deformation behavior of Ti-6Al-4V at elevated temperatures
Marion Merklein, Hinnerk Hagenah, Markus Kaupper, Adam Schaub
Friedrich-Alexander-Universität Erlangen-Nürnberg, Manufacturing Technology

Abstract: Titanium alloys, such as Ti-6Al-4V, offer favorable characteristics as significant strength, biocompatibility and metallurgical stability at elevated temperatures. These advantages afford the application of parts out of Ti-6Al-4V in a wide field within aerospace, astronautic and medical technologies. Most applied shaping operations for parts out of titanium alloys are forging, casting, forming and machining. In order to develop and improve forming operations numerical simulations are applied during preprocessing. For that purpose mechanical properties of the material such as yield stress and Lankford parameter have to be determined. Due to the two-phase (α + β) microstructure of Ti-6Al-4V, forming operations have to be carried out at elevated temperatures to reduce the required forming force and extend forming limits. Taking the temperature and stress state dependency of the material into consideration, uniaxial tensile and compression tests are accomplished at elevated temperatures, ranging from 400 to 600 °C. Furthermore, the experimenttally determined yield stress and Lankford parameter are approximated with the yield loci model proposed by Barlat 2000. The model predicts the flow response of the material, thus provides input data for the finite element analysis of forming processes at different temperature levels.

Phase Transformation Behaviour in P91 During Post Weld Heat Treatment: A Gleeble Study
Transactions of the Indian Institute of Metals
April 2017, Volume 70, Issue 3, pp 875–885
G. Vimalan - Welding Research Institute, Bharat Heavy Electricals Limited Tiruchirappalli, India
Ravichandran - Welding Research Institute, Bharat Heavy Electricals Limited Tiruchirappalli, India
V. Muthupandi - MME Department, National Institute of Technology Tiruchirappalli, India

Abstract: Grade P91 is a creep strength enhanced ferritic steel used widely at high temperature applications in thermal power plants. P91 weldments are subjected to post weld heat treatment (PWHT) at a typical temperature of 760 °C for stress relieving purpose and to obtain optimal mechanical properties. In general PWHT temperature is about 30–50 °C lower than the lower critical temperature (Ac1). Depending on the chemical composition (particularly Ni + Mn), heating rate and prior austenite grain size, Ac1 temperature can vary from 780 to 860 °C. In this investigation an attempt was made to understand the effect of surpassing the typical PWHT temperature of 760° and approaching Ac1 of the material. The investigation was based on physical simulation conducted using 3500 Gleeble thermo mechanical simulator. The study was performed on cylindrical specimens which were extracted from weld metal and parent metal. Specimens were subjected to normalizing treatment at 1050 °C for achieving austenitisation and to determine the Ac1 temperature and then to different PWHT temperatures in the range of 790–850 °C at suitable intervals. American Society for Testing and Materials (ASTM) A1033-10 based procedure was used to find Ac1 temperature for the parent metal and weld metal at slow heating rate condition to compare with practical heat treating condition. Dilatometry plots, microstructure and hardness tests performed on the specimen were used to analyse the phase transformation. Results indicated that alpha ferrite phase and fresh untempered martensite could be formed in P91 steel when PWHT temperature was about 12 °C less than the Ac1 temperature. It was also seen that the heating rate had strong influence on the Ac1 temperature. At the heating rate of 28°/hr, Ac1 was about 792 °C for weld metal, while Ac1 was about 812 °C for the heating rate of 220 °C/hr.

Flow behaviour of TiHy 600 alloy under hot deformation using Gleeble 3800
Advances in Materials and Processing Technologies
Basanth Kumar Kodli, Rajamallu Karre, Kuldeep K. Saxena, Vivek Pancholi, Suhash R. Dey & Amit Bhattacharjee
Pages 490-510 | Accepted 10 Jun 2017, Published online: 19 Jun 2017

Abstract: To understand deformation behaviour of TiHy 600 alloy at higher temperatures, hot compression tests are performed in α region (1173 K), α + β regions (1223, 1248, and 1273 K) and β region (1323 K) at strain rates (0.001, 0.01, 0.1, 1 and 10/s) for up to 50% deformation in Gleeble 3800® thermo-mechanical simulator. Flow curve plots are drawn at each strain rates and temperatures and it is observed that dominant deformation mechanism at higher temperature 1323 K (β region) and strain rates (1 and 10/s) is dynamic recovery (DRV) whereas dynamic recrystallization (DRX) is mostly observed at lower strain rates (0.001, 0.01/s) in medium temperature range of 1223 K (α region) to 1248 K (α + β region). Hyperbolic sine law equation is used to calculate the activation energy (Q) and other material sensitive parameters (A, α and n1). The activation energies for DRX in α region and DRV in β region are obtained as 384 and 251 kJ/mol. Experimental peak stress values are compared with predicted peak stress values (R2 = 96.2%) and Zener-Hollomon parameter (R2 = 94.3%). The flow stress behavior up to the peak stress is verified with Cingara equation. Finally, calculated prediction results of DRX volume fraction obtained from Avrami equation is compared with experimental observed microstructure.

Mechanical characterization and modelling of Inconel 718 material behavior for machining process assessment
A.Iturbe (a), E.Giraud (b), E.Hormaetxe (a), A.Garay (a), G.Germain (a), K.Ostolaza (c), P.J.Arrazola(a)
(a)Faculty of Engineering, Mondragon University, Spain, (b) Arts et Métiers ParisTech, France, (c) ITP, Parque Tecnológico,Spain

Abstract: Nickel based alloys are extensively used in the aerospace industry due to the excellent corrosion resistance and high mechanical properties that are maintained up to elevated temperatures (600–800 °C). However, these superalloys are classified as difficult-to-cut and therefore modelling and simulation of the machining processes has become a key in the machinability assessment of nickel based alloys. The reliability of Finite Element Models (FEM) largely depends on the quality of input parameters, one of the most relevant being the constitutive material model representing work material behavior under high strain, strain rate and temperatures.

In order to develop a reliable material model, the present work deals with a complete characterization of Inconel 718. Uniaxial compression tests at testing temperatures close to those found in machining (21–1050 °C) and high strain rates (10°−102 s−1) were performed on the Gleeble 3500 testing machine. Moreover, the microstructural analysis and microhardness measurements of the testing samples were performed, in order to correlate the microstructural state with the mechanical properties of the Inconel 718. Based on this experimental work, a new coupled empirical model is proposed to describe the particular behaviour of nickel based alloys at elevated temperatures and high strain rates. This material behaviour model introduces softening phenomena as well as the coupling between the temperature and the strain rate known to occur experimentally, for machining FEM simulations with Inconel 718 superalloy.

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A New Gleeble 3500 System Expands Capabilities at the Pratt & Whitney Additive Manufacturing Center at the University of Connecticut