The Development of Direct Age 718 for Gas Turbine Engine Disk Applications

Abstract

The processing trials and evaluations which led to the use of Direct Age 718 as a commercial gas turbine aircraft engine disk material are described. Initial trials performed on pancake forgings showed that high forge reductions, low forge temperatures, and heat treatment with only an age could produce very high tensile strength in Alloy 718 without degrading needed creep and stress rupture properties.As a result, trial full-scale disks were processed using this "Direct Age" technique. More extensive mechanical property testing successfully demonstrated the potential of this material for disk applications and showed that the process window was suitable for production practice. Mechanical property results for the trial pancake and disk forgings are presented and related to microstructural characteristics and processing parameters.The best combination of tensile, creep, and low cycle fatigue properties resulted from microstructures with a uniform distribution of fine recrystallized grains and a limited amount of the delta phase precipitate. The results of investigations performed to study fatigue behavior, aging response, and heat treatment effects are also discussed.

Hold Time Effects on the Crack Growth Behavior in Inco 718 Alloy

“…It was given a conventional heat-treatment (720 °C -8 h + 620 °C -8 h) directly after forging (DA). More details on the development of Inco 718 DA can be found in [22]. Inco 718 DA exhibits y FCC matrix grains with a small grain size (5 to 15 |im).…”

Application of advanced materials to aircraft gas turbine engines

“…8 The increased tensile and low cycle fatigue strengths were utilized by designers to enhance engine performance. The progressive refinement of linear elastic fracture mechanics over the last -20 years has resulted in excellent life prediction capability in !he presence of small flaws for a wide variety of component designs.…”

Deformation Mechanisms and Fatigue Behavior of Prestrained Inconel 718 Superalloy

“…Some examples of the applications within the aerospace industry include gas turbine engine components (1) and powerhead components for the Space Shuttle Main Engine (2). The extensive usage is due primarily to the good mechanical properties (tensile strength, fatigue endurance, and rupture strength), corrosion resistance, and outstanding fabricability (resistance to post-weld cracking) of the superalloy (3).…”