Abstract
The relaxation behavior of wrought high chromium Ni-base alloys Nimonic 80A, Nimonic 101 and Nimonic 105 was studied at different temperatures. All of these alloys exhibited increase in the residual stress during the relaxation tests e.g. at 450°C for Nimonic 80A and 650°C for Nimonic 105. The observed increase in the residual stress is a manifestation of the known phenomenon of “negative creep”. The stress free aging of specimens of these alloys exhibited dimensional contraction at different temperatures ranging from 450°C to 650°C. The abnormal relaxation behavior of these alloys and the observed contraction were attributed to the precipitation and ordering of the intermetallic phase Ni2(Cr,Mo) at the test temperature. The differential thermal analysis i.e. DTA results, demonstrated endothermic peaks to correspond with the order–disorder reaction of Ni2(Cr,Mo).
Highlights
High chromium Ni-base wrought superalloys such as Nimonic 80A, Nimonic 101 and Nimonic 105 have found extensive use in turbo-machinery applications due to their high strength and corrosion resistance [1,2,3]
The main strengthening phase in these superalloys is γ Ni3(Al,Ti) [3]. Another group of high chromium nickel alloys consists of Hastelloy C-276, Hastelloy C-22HS, Nimonic 75, IN617, IN625, IN686 and Haynes 242, is being used in different components in the power generation industries
The second process is the precipitation and ordering of the intermetallic Ni2Cr or Ni2(Cr, Mo) that causes the constrained specimen to contract which results in stress increase
Summary
High chromium Ni-base wrought superalloys such as Nimonic 80A, Nimonic 101 and Nimonic 105 have found extensive use in turbo-machinery applications due to their high strength and corrosion resistance [1,2,3]. The critical temperature i.e. Tc of the order-disorder transformation of the intermetallic Ni2(Cr,Mo) depends on the chemical composition of the alloy [6].The ordering of this phase gives rise to:- (a) dimensional instability resulting in “negative creep“ and (b) changes in the mechanical properties due to increased resistance to dislocations movement. The aim of the present investigation is:- studying the relaxation behavior, at intermediate temperatures, of the following alloys;- Nimonic 101, Nimonic 105 and Nimonic 80A, and correlate such behavior to the ordering of the Ni2(Cr,Mo) intermetallic phase.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
