Comparison of Mechanical Properties of TMW Alloys, New Generation of Cast-and-Wrought Superalloys for Disk Applications

Abstract

A new kind of Ni-Co-base disk alloys, named TMW alloys, has been developed on the basis of our innovative concept. Full-scale pancakes (440 mm in diameter and 65 mm in thickness) with an average grain size of about 10 lm were successfully manufactured from TMW alloys by a conventional cast-and-wrought (C&W) processing route. The property assessments of the pancakes indicate that TMW alloys are superior to C&W U720Li alloys in tensile strength and in creep resistance, while the performances of low-cycle fatigue (LCF) and fatigue crack growth (FCG) are comparative.Turbine disks are the parts holding the rotor blades while rotating at a high speed, which require that the materials for the disk have excellent properties in fracture toughness, creep, and fatigue resistance. [1][2][3] Nickel-based alloys with c/c¢ two-phase structure are generally employed for the turbine disks. To meet the high requirements of modern engines for mechanical properties, the latest disk alloys such as Rene 95, RR1000, [4] and ME3 [5] have a high volume fraction of c¢ phase and heavily solid-solution-hardening elements, which make them produce only via the powder metallurgy process route. [4][5][6] However, the high requirement for clean powder and the cost of thermomechanical processing steps set the limit to their applications.Recently, in the High Temperature Materials 21 Project led by the Japanese National Institute for Materials Science, we proposed an innovative concept to design disk alloys. [7][8][9][10][11][12][13][14][15][16] This concept is based on combining the characters of two kinds of c-c¢ two-phase alloys (Ni-base and Co-base alloys), where Ni-base alloys offer basic mechanical properties required for disk applications and added Co-base alloys have beneficial effects on increasing the middle temperature (600°C to 800°C) strength and on widening the C&W processing window of the mixed alloys. [8] We named these C&W Ni-Co-base materials TMW alloys.In this article, we report the investigations on mechanical properties of some TMW alloys (TMW-2, TMW-24, and TMW-4M3) and a commercial C&W Nibase disk alloy (U720Li alloy). The chemical compositions of the tested alloys are listed in Table I. All specimens used were cut from the pancakes (440 mm in diameter and 65 mm in thickness) produced by a conventional C&W processing route including triple melting, billet making, and pancake forging at Mitsubishi Materials Corporation. The specimens were heat treated in the standard heat-treated condition reported for U720Li alloy (1100°C/4 h followed by oil quench (OQ) and then aging at 650°C/24 h/OQ + 760°C/16 h/OQ).All mechanical property tests were carried out at Kobe Materials Testing Laboratory, the first material testing laboratory in Japan accredited to Nadcap. (Nadcap is the only worldwide standard accreditation program of special processes and products required by aerospace prime contractors.) The tests were performed according to ASTM E8/E21, ASTM E139, ASTM E606, and ASTM E647 standard test methods for tensile, creep, low-cycle f...

On the Effect of Nb on the Microstructure and Properties of Next Generation Polycrystalline Powder Metallurgy Ni-Based Superalloys

“…[7][8][9][10] However, co-additions of Co and Ti to conventional Ni-based superalloys have been found to confer significant strength benefits to the material. [11][12][13][14][15] In one such study, increasing the concentration of Co and Ti in RR1000 resulted in yield and tensile strengths that were~20 pct greater than that of conventional RR1000. Although the creep life of the modified alloys was found to deteriorate when tested at 750°C and 460 MPa as a result of the precipitation of the TCP r phase along the grain boundaries.…”

The microstructure and hardness of Ni-Co-Al-Ti-Cr quinary alloys

“…Such modifications were shown to confer benefits to both the strength and microstructural stability of both cast & wrought [47][48][49][50][51] and powder processed [52,53] alloys. In parallel, fundamental studies of the underpinning Ni -CoAl -Ti system were performed and determined that the A1 -L1 2 two-phase field is continuous between Ni -Ni 3 Al and Co -Co 3 Ti [54,55].…”

New Quantitative Analysis of Contributing Factors to Strength of Disk Superalloys

“…Thus, substituting the equation [2]- [5] into equation [10], the effect of solution temperature on the individual strengthening mechanism contributing to the 0.2% flow stress can be summarized as shown in Figure 6.…”