Weldability of superalloys alloy 718 and ATI® 718Plus™ – A study performed by Varestraint testing

Jonny Jacobsson; Joel Andersson; Anssi Brederholm; Hannu Hänninen

doi:10.3139/120.111049

Article

Weldability of superalloys alloy 718 and ATI® 718Plus™ – A study performed by Varestraint testing

Jonny Jacobsson , Joel Andersson , Anssi Brederholm and Hannu Hänninen

Published/Copyright: August 28, 2017

Published by

Become an author with De Gruyter Brill

Submit Manuscript Author Information

From the journal Materials Testing Volume 59 Issue 9

Abstract

In this study, the old and well-known alloy 718 is compared with the newly developed ATI® 718Plus™ from the weldability point of view. This is done in order to gain new information that have not been documented and established yet among the high-temperature materials with high strength, oxidation resistance, thermal stability and sufficient weldability, yet. ATI® 718Plus™ shows a lower sensitivity to hot cracking than alloy 718 with approximately 10 mm total crack length (TCL) difference in Varestraint testing. In the solution-annealed condition at 982°C for 4.5 h followed by air cooling, the crack sensitivity is decreased as compared to the mill-annealed condition. Along the crack path and also ahead of the crack tip, γ-Laves eutectic is present in both alloys. The microhardness measurements showed similar hardness level of 250 HV in the weld metal of both alloys and even in the parent material of alloy 718. ATI® 718Plus™ parent metal had hardness of 380 HV and a small increase of less than 50 HV was observed for both studied alloys in the heat affected zone (HAZ). For the same grain size of ATI® 718Plus™ (8.3 μm) and alloy 718 (15.6 μm), the susceptibility to liquation cracking may increase with increasing grain size. With a small grain size, there is a possibility to accommodate more trace elements (B, S, P) due to the larger grain boundary area. The impurity elements were found in relatively small precipitates, typically borides (0.2 μm), phosphides (0.1 to 0.5 μm) and carbo-sulphides. The solidification sequence of alloy 718 and ATI® 718Plus™ is relatively similar, where the liquid starts to solidify as γ-phase followed by γ/MC reaction at about 1260 °C and then final γ/Laves eutectic reaction at around 1150 °C. Detailed knowledge about weldability of alloy 718 and ATI® 718Plus™ can be used for material selection.

Kurzfassung

In dieser Studie wird die Schweißbarkeit der bekannten Legierung Alloy 718 mit der neu entwickelten Legierung ATI® 718Plus™ verglichen. Dies wurde durchgeführt, um neue Informationen über diese Hochtemperaturwerkstoffe mit hoher Festigkeit, Oxidationsbeständigkeit, thermischer Stabilität und hinreichender Schweißbarkeit zu erzielen. Die Legierung ATI® 718Plus™ zeigt eine geringere Heißrissempfindlichkeit als die Legierung Alloy 718. Zwischen beiden Legierungen betrug im Varestraint-Heißrisstest die Differenz der Gesamtrisslänge (TCL) 10 mm. Im lösungsgeglühten Zustand bei 954 °C für 1 h wird die Rissempfindlichkeit im Vergleich zum stabilgeglühten Zustand verringert. Entlang des Risspfades und auch vor der Rissspitze ist in beiden Legierungen ein γ-Laves-Eutektikum existent. Die Mikrohärte-Messungen zeigten einen ähnlichen Härtegrad von 250 HV im Schweißgut beider Legierungen und sogar im Grundwerkstoff der Legierung Alloy 718. Der Grundwerkstoff der Legierung ATI® 718Plus™ hatte eine Härte von 380 HV. In der Wärmeeinflusszone (WEZ) wurde eine geringe Härtezunahme von weniger als 50 HV für beide untersuchten Legierungen beobachtet. Für eine Korngröße der Legierung ATI® 718Plus™ (8,3 μm) und der Legierung 718 (15,6 μm) kann die Anfälligkeit für Wiederaufschmelzrissbildung mit zunehmender Korngröße ansteigen. Bei einer kleinen Korngröße besteht aufgrund des größeren Korngrenzenaufkommens die Möglichkeit mehr Spurenelemente (B, S, P) aufzunehmen. Die Verunreinigungen wurden in relativ kleinen Ausscheidungen detektiert, typischerweise Boride (0,2 μm), Phosphide (0,1 bis 0,5 μm) und Carbonsulfide. Die Verfestigungsmechanismen der Legierungen Alloy 718 und ATI® 718Plus™ sind relativ ähnlich – die Schmelze erstarrt als γ-Phase, gefolgt von einer γ/MC-Reaktion bei etwa 1260 °C und schließlich der eutektischen γ/Laves-Reaktion bei etwa 1150 °C. Detaillierte Kenntnisse über die Schweißbarkeit von Alloy 718 und ATI® 718Plus™ können für die Werkstoffwahl genutzt werden.

*Correspondence Address, Assoc. Prof. Joel Andersson, Head of Division in Welding Technology, Department of Engineering Science, The Production Technology Centre, University West, SE-461 86 Trollhättan, Sweden, E-mail: Joel.andersson@hv.se, jonny.jacobsson@chalmers.se

Jonny Jacobsson is a PhD student at Chalmers University of Technology in the Department of Industrial and Material Science, Gothenburg, Sweden. His work is mainly done in collaboration with GKN Aerospace Sweden at the Production Technology Centre in Trollhättan and is focused on weldability of precipitation hardening Ni- or Ni-Fe based superalloys.

Assoc. Prof. Joel Andersson, born in 1981, is Associate Professor of High Temperature Materials and Head of the Division in Welding Technology at University West in Trollhättan, Sweden. The Division of Welding Technology at University West comprises about 30 people (including senior researchers, PhD students and engineers) and focuses on three main areas in relation to welding technology; metallurgy, modeling of process physics, process development and control. His field of research primarily covers welding and weldability of high temperature materials, in particular the precipitation hardening Ni- and Ni-Fe based superalloys. He is currently supervising nine PhD students in corresponding research areas.

Anssi Brederholm holds a Licentiate Science Degree of Engineering Materials from the Department of Engineering Design and Production, Aalto University in Helsinki, Finland.

Prof. Hannu Hänninen, born in 1949, is Professor of Engineering Materials in the Department of Engineering Design and Production, Aalto University, Finland, since 1990. He received his MSc and PhD degrees in 1973 and 1980, respectively. He worked at the Technical Research Centre of Finland (VTT) from 1977 to 1990. He was a visiting scientist at Materials Engineering Associates, Inc. (MEA) in Lanham, USA, from 1987 to 1996, in the European Commission, Institute for Energy, Joint Research Centre Petten, The Netherlands, in the years from 2000 to 2001, and at MIT, Department of Nuclear Science and Engineering, Cambridge, USA, during 2010 and 2011. He was Chairman of the International Co-operative Group on Environment Assisted Cracking (ICG-EAC) from 2001 to 2003. He became fellow of ASM International, USA, in 1996.

References

1 J. N.DuPont, J. C.Lippold, S. D.Kiser: Welding Metallurgy and Weldability of Nickel-Base Alloys – Precipitation-Strengthened Ni-base Alloys, John Wiley & Sons, 200910.1002/9780470500262Search in Google Scholar

2 W.-D. C., R.Kennedy: Role of chemistry in 718 type alloys – Allvac® 718Plus^TM alloy development, TMS (The Miner. Met. Mater. Soc.) (2004), pp. 91–100Search in Google Scholar

3 ASTM-International: Standard Test Methods for Determining Average Grain Size, 27 (2013) 10.1520/E0112-12.1.4Search in Google Scholar

4 J.Andersson: Weldability of Precipitation Hardening Superalloys – Influence of Microstructure, Chalmers University of Technology, Gothenburg, Sweden (2011)Search in Google Scholar

5 J.Andersson, G.Sjöberg, A.Brederholm, H.Hänninen: Solidification cracking of alloy Allvac 718Plus and alloy 718 at transvarestraint testing, EPD Congress 2008: Proceedings of Sessions and Symposia Sponsored by the Extraction and Processing Division (EPD), Ed. S. M.Howard, Wiley-Blackwell (2008), pp. 157–169Search in Google Scholar

6 K. R. R.Vishwakarma, N. L. L.Richards, M. C. C.Chaturvedi: Microstructural analysis of fusion and heat affected zones in electron beam welded ALLVAC® 718PLUSTM superalloy, Mater. Sci. Eng. A.480 (2008), pp. 517–52810.1016/j.msea.2007.08.002Search in Google Scholar

7 R.Vincent: Precipitation around welds in the nickel-base superalloy, Inconel 718, Acta Metallurgica33 (1985), pp. 1205–121610.1016/0001-6160(85)90231-7[8]Search in Google Scholar

8 J.Andersson, V. A.Corporation: Metallurgical Response of Electron Beam Welded Allvac® 718Plus^TM, Hot Cracking Phenomena in WeldsIII (2011), pp. 415–42810.1007/978-3-642-16864-2_21Search in Google Scholar

9 J.Andersson, G.Sjöberg, L.Viskari, A.Brederholm, H.Hänninen, C.Knee: Hot cracking of Allvac 718Plus, Alloy 718 and Waspaloy at Varestraint testing, Proceedings of the 47^th Conference of Metallurgists (2008), Winnipeg, Canada, pp. 401–413Search in Google Scholar

10 T. J.Kelly: Elemental effects on cast 718 weldability, Weld. J.68 (1989), pp. 44–51Search in Google Scholar

11 I.Woo, K.Nishimoto: Metallurgical factors contributing to HAZ cracking susceptibility in cast alloy 718 welds and its improvement by cerium addition, Met. Mater.7 (2001), pp. 241–24910.1007/BF03026982Search in Google Scholar

12 Y. M.Yaman, M. C.Kus: Hot cracking susceptibilities in the heat-affected zone of electron beam-welded inconel 718, J. Mater. Sci. Lett.17 (1998), pp. 1231–123410.1023/A:1006514431915Search in Google Scholar

13 X.Huang, N. L.Richards, M. C.Chaturvedi: Effect of grain size on the weldability of cast alloy 718, Mater. Manuf. Process.19 (2004), pp. 285–31110.1081/AMP-120029936Search in Google Scholar

14 R. G.Thompson, M. C.Koopman, B. H.King: Grain boundary chemistry of alloy 718-type alloys, Superalloys 718, 625 and Derivatives (1991), pp. 53–70Search in Google Scholar

15 S.Benhadad, N. L.Richards, M. C.Chaturvedi: The Influence of minor elements on the weldability of an INCONEL 718 – type superalloy, Metall. Mater. Trans. A. 33 (2005), pp. 2005–201710.1007/s11661-002-0033-5Search in Google Scholar

16 J.Andersson, G.Sjöberg: Repair welding of wrought superalloys: Alloy 718, Allvac 718Plus and Waspaloy, Sci. Technol. Weld. Join. 17 (2012), pp. 49–5910.1179/1362171811Y.0000000077Search in Google Scholar

Published Online: 2017-08-28

Published in Print: 2017-09-01

You are currently not able to access this content.

Articles in the same Issue

https://doi.org/10.3139/120.111049