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Hot Cracking and Grain Boundary Weaknesses of Nickel - Based Superalloys

Joel Andersson (Institutionen för material- och tillverkningsteknik)
Göteborg : Chalmers University of Technology, 2008.
[Licentiatavhandling]

Abstract Grain boundary weaknesses of nickel-based superalloys not only materialize during service in the hot turbine engine sections but also during the weld manufacturing. The performance, in this respect, of the most commonly used alloys at Volvo Aero Corporation (VAC), 718 and the higher temperature capacity Waspaloy, are therefore the main subjects for this thesis. The emerging Allvac 718® PLUSTM (718 Plus) is also included due to the prospect of replacing the expensive Waspaloy. The overall emphasis is on weldability through Varestraint testing but limited work was initially carried out on notch rupture sensitivity of 718 Plus. The notch rupture testing of 718Plus emphasized the importance of the secondary phases like delta-phase in the grain boundaries. Hot cracks were observed in all alloys with re-solidified products on the liquated and re-solidified grain boundaries. Grain boundary liquation and segregation of alloying elements was considered to be the primary reason for liquation of HAZ grain boundaries which caused cracking. Evidence of constitutional liquation of Nb rich MC type carbides in alloy 718 and 718 Plus were found in the region adjacent to the fusion zone and also on the cracked grain boundaries. The resolidified products along the hot cracks consisted of γ + MC type carbide and γ + Laves eutectics.

Nyckelord: Superalloys, Grain boundary weaknesses, Notch rupture testing, Varestraint testing, Weldability, Hot cracks, Eutectic



Denna post skapades 2008-09-28. Senast ändrad 2009-01-27.
CPL Pubid: 74502

 

Institutioner (Chalmers)

Institutionen för material- och tillverkningsteknik (2005-2017)

Ämnesområden

Materialteknik

Chalmers infrastruktur

Examination

Datum: 2008-10-17
Tid: 10:00
Lokal: Delta-Gamma
Opponent: Hasse Fredriksson

Ingår i serie

Technical report - Department of Materials and Manufacturing Technology, Chalmers University of Technology