Creep and Creep-Rupture Behavior of Alloy 718

Abstract

Data obtained from creep and creep-rupture tests conducted on 18 heats of Alloy 718 were used to formulate models for predicting high temperature time dependent behavior of this alloy. Creep tests were conducted on specimens taken from a number of commercial product forms including plate, bar, and forging material that had been procured and heat treated in accordance with ASTM specifications B-670 or B-637. Data were obtained over the temperature range of 427 to 760°C and at test times to about 87,000 h. Comparisons are given between experimental data and the analytical models. The analytical models for creep-rupture included one based on lot-centering regression analysis, which uses a single heat constant to distinguish between behavior of individual heats, and one based on the Minimum Commitment Method, which used two heat constants. A 'master" curve approach was used to develop an equation for estimating creep deformation up to the onset of tertiary creep.

Creep-Fatigue and Thermo-Mechanical Fatigue of Friction-Welded IN 718/MarM247 Dissimilar Joint

“…In the other words, why did the DFW not fail at the "weaker" HAZ under these conditions? Comparing creep resistance of IN 718 with that of M247, the latter could be appreciably higher than the former at the present test temperature range [14,15]. In this work, cyclic loading is repeated under strain-controlled conditions for DFW specimens consisting of the two materials.…”

Structural analyses of Stirling power-convertor heater head for long-term reliability, durability, and performance

“…Because of time constraints, creep testing must be restricted to no more than about a 2-yr duration, far short of the required 10 yr or more. Fortunately, about three decades ago, an extensive longterm creep and creep-rupture data base had been generated (Brinkman, Booker, and Ding, 1991) on Inconel 718 by the Oak Ridge National Laboratories (ORNL) in support of terrestrial electric power generation. Certain aspects of their results are being used extensively in the current evaluations, namely, long-term results and measured statistical variations.…”

“…The new thickness values under consideration range from 0.89 to 1.14 mm. By contrast, the ORNL data (Brinkman, Booker, and Ding, 1991) were generated using test specimens on the order of 20 times thicker (≈10 mm) than those used by Glenn. Creep resistance for wrought alloys generally decreases dramatically with decreasing specimen thickness (below about 20 grain diam.)…”

“…It utilizes the large creep data base generated by ORNL (Brinkman, Booker, and Ding, 1991) for various heats, heat treatments, and product forms of Inconel 718. Although there are differences between the material used for the ORNL tests and that to be used in the current heater head, the proposed methodology captures the differences and accounts for their effect on creep behavior.…”

Creep rupture of alloy 718 after thermal aging

“…Experimental data were shown to fit the model very well. 7 Aging effects at 593°C, 649°C, 704°C, and 760°C for times up to 27,000 h are addressed briefly in Reference 7, which shows aging at 649°C and above to be quite detrimental to the rupture life of Alloy 718 tested at 593°C or 649°C. Current results show new data at 593°C, 621°C, and 649°C and for longer thermal exposures.…”