Ttt diagram of a newly developed nickel-base superalloy -: Allvac® 718Plus™

A new nickel-base superalloy designated as Allvac (R) 718plus (TM) has been developed by ATI Allvac to be used at 700 degrees C. For phase characterization, heat treatment selection and structure stability evaluation in high temperature range, the determination of TTT diagram for alloy 718Plus is not only a basic research issue but also an important matter for the alloy application at high temperatures. The conventional alloy 718 has been also studied for comparison. Both alloys were solution treated at 1040 degrees C for full solution of precipitated phases except stable carbide MC. After solution treatment both alloy samples were heat treated at 649 to 954 degrees C for the times from 3-6 minutes till 100 hrs. Phase identification was mainly by means of SEM, XRD and partially TEM and SAD. Hardness test was also conducted on the samples as the indication of gamma" and gamma' precipitation hardening. The experimentally determined T-T-T diagrams and discussion on the phase formation in alloys 718 and 718PIus are described in this paper.