Process Development and Mechanical Properties of Alloy U720LI for High Temperature Turbine Disks

Abstract

Recent interest in nuclear high temperature reactor combined with a closed-cycle helium gas turbine provides the need for developing creep-resistant superalloys for the turbine disks and blades. Superalloy Udimet 720LI TM has been selected as a candidate material to produce the large diameter turbine disks because of its high creep strength and industrial maturity. Studies were performed on both Powder Metallurgy (P/M) and Cast & Wrought (C&W) billet samples. The effort was focussed on tailoring the microstructure to ensure a high creep strength and a good thermal stability. A new P/M process route has been developed to increase the grain size of the alloy and to ensure a good workability of P/M U720 with conventional forging route. The creep deformation and damage of P/M Udimet 720 was analysed to develop a creep predictive model based on physical damage parameters.

Mechanical properties and development of supersolvus heat treated new nickel base superalloy AD730TM

“…Creep lives obtained on coarse grain AD730 TM are in good agreement with those obtained with U720 [6] and significantly better than those obtained with 718Plus due to its finer grain size and its lower gamma prime fraction.…”

“…Grain size was close to ASTM 7. Results obtained on cast & wrought U720 were also used for comparison [6]. The pancake had a similar thickness (80 mm) and was supersolvus heattreated as follows : 1157…”

Grain Boundary and Intragranular Deformations during High Temperature Creep of a PM Nickel-Based Superalloy

“…ISB's are interpreted as resulting from high activity of plastic deformation in narrow bands, as observed for instance during tensile deformation of single crystal superalloys [12]. Such bands were also observed in PM nickel-base superalloys [13,14,15] during creep at 650 and 700°C under high stress. T = 850°C, σ = 350 MPa, ε = 1% T = 700°C, σ = 700MPa, ε = 1% Figure 8.…”

Review and Analysis of Powder Prior Boundary (PPB) Formation in Powder Metallurgy Processes for Nickel-based Super Alloys

“…The increasing trend of higher operating temperatures and pressure ratios in aero engines require nickel-based super alloys with even higher alloying content to give increased levels of creep resistance, greater low cycle fatigue resistance, with micro structural stability and damage tolerance at the elevated temperatures [1]. However due to the complex chemistry and high alloying content of these super alloys, macro segregation and coarse grain size occurs in the convectional cast and wrought processes [3]. A powder metallurgy (PM) route can eliminate macro segregation since the biggest amount of segregation in the parts produced by PM methods is limited by particle size [4].…”