Metal treatment – Process of modifying or maintaining internal physical... – Heating or cooling of solid metal
Reexamination Certificate
1999-02-26
2001-05-01
Yee, Deborah (Department: 1742)
Metal treatment
Process of modifying or maintaining internal physical...
Heating or cooling of solid metal
C148S555000
Reexamination Certificate
active
06224695
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of manufacturing a casting of a Ni-base directionally solidified alloy (hereinafter referred to as “Ni-base DS alloy”), which is used for forming turbine blades and turbine vanes for jet engines and industrial gas turbines.
2. Description of the Related Art
Generally known commercial Ni-base DS alloys include IN792 (9.0 wt. % Co, 12.7 wt. % Cr, 2.0 wt. % Mo, 3.9 wt. % W, 3.2 wt. % Al, 3.9 wt. % Ta, 0.21 wt. % C, 0.02 wt. % B, 4.2 wt. % Ti, 0.10 wt. % Zr, and the balance of Ni), Rene 80 (9.5 wt. % Co, 14.0 wt. % Cr, 4.0 wt. % Mo, 4.0 wt. % W, 3.0 wt. % Al, 0.17 wt. % C, 0.015 wt. % B, 5.0 wt. % Ti, 0.03 wt. % Zr, and the balance of Ni) and Mar-M247 (10.0 wt. % Co, 8.5 wt. % Cr, 0.65 wt. % Mo, 10.0 wt. % W, 5.6 wt. % Al, 3.0 wt. % Ta, 1.4 wt. % Hf, 0.16 wt. % C, 0.015 wt. % B, 1.0 wt. % Ti, 0.04 wt. % Zr, and the balance of Ni). Although inferior in strength at elevated temperature to Ni-base single crystal alloys (Ni-base SC alloys), these Ni-base DS alloys have no directional property when cast and are less subject to cracking. Therefore products of these Ni-base DS alloys are manufactured at a high yield and do not require complicated heat-treatment processes.
Raising the temperature of a combustion gas for driving turbines is the most effective method of improving the efficiency of jet engines and industrial turbines. Therefore it is desired that Ni-base DS alloys having further enhanced strength at elevated temperature, ductility and high-temperature corrosion resistance are developed.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a Ni-base DS alloy casting manufacturing method capable of manufacturing a Ni-base DS alloy casting exceptionally excellent in strength at elevated temperature, ductility and high-temperature corrosion resistance.
According to a first aspect of the present invention, a Ni-base DS alloy casting manufacturing method processes a Ni-base DS alloy casting of a Ni-base DS alloy having a composition of 10 to 14 wt. % Co, 2 to 3 wt. % Cr, 1.5 to 2.5 wt. % Mo, 5 to 6.5 wt. % W, 5.7 to 6.5 wt. % Al, 5.5 to 6.5 wt. % Ta, 4.5 to 5.0 wt. % Re, 0.01 to 1.5 wt. % Hf, 0.01 to 0.30 wt. % C, 0.01 to 0.03 wt. % B, and the balance of Ni and inevitable impurities by a two-stage aging process for aging the Ni-base DS alloy casting at a temperature in the range of 750 to 1200° C.
According to a second aspect of the present invention, a Ni-base DS alloy casting manufacturing method processes a Ni-base DS alloy casting of a Ni-base DS alloy having a composition of 10 to 14 wt. % Co, 2 to 3 wt. % Cr, 1.5 to 2.5 wt. % Mo, 5 to 6.5 wt. % W, 5.7 to 6.5 wt. % Al, 5.5 to 6.5 wt. % Ta, 4.5 to 5.0 wt. % Re, 0.01 to 1.5 wt. % Hf, 0.01 to 0.30 wt. % C, 0.01 to 0.03 wt. % B, and the balance of Ni and inevitable impurities by a solid solution treatment at a temperature in the range of 1250 to 1300° C., and then processes the Ni-base DS alloy casting by a two-stage aging process at a temperature in the range of 750 to 1200° C.
In a Ni-base DS alloy subject to &ggr;′-phase precipitation hardening by aluminum (Al), cobalt (Co) makes the component elements dissolve satisfactorily in the matrix in a solid solution treatment, and precipitate homogeneously in a fine &ggr;′-phase by the subsequent aging process, so that the Ni-base DS alloy has a high strength at elevated temperature.
When the Co content is less than 10% by weight, only a narrower temperature range is available for solid solution treatment. If the Co content is more than 14% by weight, the precipitated &ggr;′-phase decreases and the strength at an elevated temperature is lowered. The Co content is preferably in the range of 11 to 13% by weight.
Chromium (Cr) is added to the Ni-base DS alloy to give Ni-base DS alloy oxidation resistance and corrosion resistance. The alloy has a low high-temperature corrosion resistance if the Cr content is less than 2% by weight, and a detrimental TCP structure (topologically closed packed structure) is formed if the Cr content is more than 3% by weight. A preferably Cr content is in the range of 2.5 to 3% by weight.
Molybdenum (Mo) dissolves in the matrix and increases strength at an elevated temperature and provides strength at an elevated temperature by precipitation hardening. Raft effect produced by making misfit between the &ggr;-phase and the &ggr;′-phase negative, is insufficient if the Mo content is less than 1.5% by weight and the TCP structure is produced if the Mo content is more than 2.5% by weight. A preferable Mo content is in the range of 1.8 to 2.2% by weight.
Tungsten (W) promotes solid solution hardening and precipitation hardening. Incomplete solid solution hardening occurs and the creep strength decreases if the W content is less than 5% by weight, and a TCP structure is formed if the W content is more than 6.5% by weight. A preferable W content is in the range of 5.5 to 6.2% by weight.
Aluminum (Al) is necessary for the precipitation of the &ggr;′-phase. The amount of the precipitated &ggr;′-phase is excessively smaller and the strength at an elevated temperature decreases if the Al content is less than 5.7% by weight, and the amount of the precipitated eutectic &ggr;′-phase is excessively larger and the solid solution treatment becomes difficult if the Al content is more than 6.5% by weight. A preferable Al content is in the range of 5.9 to 6.1% by weight.
Tantalum (Ta), similarly to Mo, contributes to the enhancement of the strength at an elevated temperature by the solid solution hardening and the &ggr;′-phase precipitation hardening. The solid solution hardening effect of the &ggr;′-phase is insufficient and the strength at an elevated temperature decreases if the Ta content is less than 5.5% by weight, and the amount of the eutectic &ggr;′-phase increases excessively and the solid solution hardening treatment becomes difficult if the Ta content is more than 6.5% by weight. The Ta content is preferably in the range of 5.7 to 6.2% by weight.
Hafnium (Hf) contributes to crystal stressing during columnar crystallization by directional solidification. The crystal stressing effect of Hf is unavailable and longitudinal cracks develop along grain boundaries during solidification if the Hf content is less than 0.01% by weight, and Hf combines with oxygen to form an oxide in the alloy and cracks develop if the Hf content is more than 1.5% by weight. The Hf content is preferably in the range of 0.01 to 0.3% by weight and more preferably in the range of 0.05 to 0.2% by weight.
Rhenium (Re) contributes to phase stabilization. The solid solution hardening of the &ggr;′-phase is insufficient and the strength at an elevated temperature decreases if the Re content is less than 4.5% by weight, and a TCP structure is formed and the range of temperature suitable for the solid solution hardening treatment is narrowed if the Re content is more than 5% by weight. The Re content is preferably in the range of 4.7 to 5% by weight.
Carbon (C) contributes to crystal stressing. The effect of C on crystal stressing is insignificant if the C content is less than 0.01% by weight, and the ductility is reduced if the C content is more than 0.3% by weight. The C content is preferably in the range of 0.05 to 0.1% by weight.
Boron (B), similarly to C, contributes to crystal stressing. The effect of B on crystal stressing is insignificant if the B content is less than 0.01% by weight, and the ductility is reduced if the B content is more than 0.03% by weight. The B content is preferably in the range of 0.01 to 0.02% by weight.
Zirconium (Zr) may be added to the Ni-base DS alloy in a Zr content of 0.3% or less by weight for crystal stressing.
One or some of titanium (Ti), niobium (Nb) and vanadium (V), which are added generally to Ni-base superalloys, may be added to the Ni-base DS alloy. It is desirable that the Ti content is 2% or less by weight, the Nb content is 2% or less by weight and the V cont
Harada Hiroshi
Kobayashi Toshiharu
Koizumi Yutaka
Nitta Seiya
Tamura Akira
National Research Institute for Metals, Science and Technology A
Oliff & Berridg,e PLC
Yee Deborah
LandOfFree
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