Ni-Co Base Research Articles

Fatigue crack growth characteristics of a new Ni–Co-base superalloy TMW-4M3: effects of temperature and load ratio

The fatigue crack growth (FCG) behavior of a newly developed Ni–Co-base superalloy TMW-4M3 has been investigated in this study. Experiment was carried out in laboratory air with compact-tension specimen. The effects of temperature (400, 650, and 725 °C) and load ratio (0.05 and 0.5) on crack growth rate were studied in the Paris regime. The results revealed that the crack growth rate increased with increasing temperature under a given load ratio. The influence of load ratio on crack growth rate was pronounced, especially at higher temperature and low stress intensity factor range. Fractographic observations showed that fracture mode was transgranular at 400 °C, mixed transgranular and intergranular at 650 °C, and predominantly intergranular at 725 °C. The possible explanations for the crack growth behavior were discussed based on the degradation of mechanical properties and the oxidation assisted crack growth, as well as the crack closure effect. A comparison of FCG rate was also made between TMW-4M3 and the commercial superalloy U720Li.

Enhanced mechanical properties in a new Ni–Co base superalloy by controlling microstructures

We report the enhanced tensile strength and creep resistance of a new Ni–Co-base superalloy (TMW-2) by increasing the solution temperature from 1100 °C to 1140 °C. The yield strength could be improved by 60 MPa, and a temperature gain in creep resistance of about 15 °C could be achieved. The improvements in yield strength and creep resistance are mainly due to the coarsening of grain size, the increasing of the volume fraction of tertiary γ′ and of the length of annealing twin formed during the heat treatment.

THERMODYNAMIC STUDY ON EQUILIBRIUM PRECIPITATION PHASES IN A NOVEL Ni--Co BASE SUPERALLOY

Thermodynamic properties of the traditional U720Li alloy and the new Ni-Co base superalloy have been studied using JMatPro and the latest relevant database for Ni base superalloys. The effects of chemical composition on the equilibrium precipitation phases,process-ability andγ/γ' mismatch have been analyzed.It is found that theγ/γ' mismatch increases with the increase of Ti/Al (atomic ratio).The volume fraction ofγ' is proportional to the Ti+Al contents(atomic fraction). Therefore,by increasing the Ti/Al ratio and Ti+Al content,the yield strength of alloys can be improved. On the other hand,theγ' solvus temperature decreases by Co additions.As a result,the range of processing temperature is extended.Theγ/γ' mismatch also increases with Co additions,which adds additional strengthening to the alloy.Moreover,high Ti/Al ratio or low Co content promotes the precipitation ofηphase.Thus,Ni-Co base superalloys with high Ti+Al content,Ti/Al ratio and Co content bear an improved strength,phase stabilities and process-ability.

THERMODYNAMIC STUDY ON EQUILIBRIUM PRECIPITATION PHASES IN A NOVEL Ni-Co BASE SUPERALLOY

Thermodynamic properties of the traditional U720Li alloy and the new Ni-Co base superalloy have been studied using JMatPro and the latest relevant database for Ni base superalloys. The effects of chemical composition on the equilibrium precipitation phases,process-ability andγ/γ' mismatch have been analyzed.It is found that theγ/γ' mismatch increases with the increase of Ti/Al (atomic ratio).The volume fraction ofγ' is proportional to the Ti+Al contents(atomic fraction). Therefore,by increasing the Ti/Al ratio and Ti+Al content,the yield strength of alloys can be improved. On the other hand,theγ' solvus temperature decreases by Co additions.As a result,the range of processing temperature is extended.Theγ/γ' mismatch also increases with Co additions,which adds additional strengthening to the alloy.Moreover,high Ti/Al ratio or low Co content promotes the precipitation ofηphase.Thus,Ni-Co base superalloys with high Ti+Al content,Ti/Al ratio and Co content bear an improved strength,phase stabilities and process-ability.

γ/γ′二相組織を有する Ni-Co 基多結晶超合金の粒成長モデル

γ/γ′二相組織を有する Ni-Co 基多結晶超合金の粒成長モデル

開発 Ni-Co 基鍛造超合金を用いた模擬タービンディスクの機械的特性

New kinds of cast and wrought (C & W) Ni-Co base superalloys (TMW alloys) have been developed based on the innovative concept of combining two kinds of γ-γ′ two-phase alloys, Ni-base and Co-base alloys, for the applications of turbine disks and high-pressure compressor blades. The results based on testing 20 kg ingots indicate that TMW alloys show excellent high temperature strength and formability, may provide 50°C temperature advantage in 630 MPa/100 h creep performance over C & W alloy U720Li. In this paper, we report our new results on the full-scale pancakes manufactured through the C & W process for real components. The results indicate that TMW alloys had good process-ability in the ingot making and forging into disk pancakes. Pancake disks with fine grain size of about 10 μm were successfully obtained for TMW alloys. TMW alloys provide 58°C to 76°C temperature advantages in 0.2% creep strain life under the 630 MPa condition, over alloy U720Li.

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

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 μm 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.

Creep behavior of new kinds of Ni–Co-base superalloys

This paper concerns our recent work on developing a new kind of advanced disk alloys based on the mixtures of two kinds of two-phase superalloys, Co-base Co-16.9 wt.%Ti and Ni-base U720Li superalloys, for the latest turbine design. The tensile creep behavior of these new Ni–Co-base superalloys at temperatures in the range of 650–760 °C and at initial applied stresses of 480–830 MPa were investigated. Comparing a new Ni–Co-base alloy (TMW-4) to U720Li by a Larson–Miller plot shows that a temperature gain in stress-rupture strength of 30 can be expected in a TMW alloy with fine-grained microstructure (10 (m).

Phase Constituents and Compressive Yield Stress of Ni-Co Base Alloys

Phase constituents and compressive yield stress of Ni-Co base alloys have been investigated. The results showed that two-phases of and 0 were the main constituents in all the alloys. Ni3Ti-type ( ) phase was observed in the alloys with lower Co and Ti content (alloy20); while a new intermetallic (Ni,Co,Cr)3(Ti,Al) phase with a hexagonal structure was detected in the higher Co and Ti containing alloy(alloy50). At temperatures lower than 1023K, the compressive yield stress increased with increasing Co content up to 28.6mass% and Ti content up to 7.4mass%, but decreased with more Co and Ti addition. At temperatures higher than 1273K, all the alloys showed similar yield stress. [doi:10.2320/matertrans.MBW200703]

Development of New Generation Turbine Disk Superalloys in the HTM21 Project

A new kind of cast & wrought (C&W) Ni-Co base superalloys named as “TMW alloys” was developed recently for compressor and turbine disk of gas turbine engines in the High Temperature Materials 21 Project at the National Institute for Materials Science (NIMS) in Japan. These Ni-Co base superalloys combine the characters of two kinds of γ- γ’ two-phase alloys (Ni-base and Co-base superalloys) and can be fabricated by cheap cast and wrought processing route. The results showed that some of these TMW alloys have superior tensile strength at temperatures up to 750 °C and higher creep resistances up to 725 °C than commercial UDIMET 720 LI alloy.

New Ni–Co-base disk superalloys with higher strength and creep resistance

A new kind of Ni–Co-base superalloys with a γ/γ′ two-phase structure has been proposed recently for turbine disk applications. Some of these Ni–Co-base superalloys are assessed by tensile tests. The results show that the Ni–Co-base alloys can be processed by cheap cast and wrought route and show superior tensile strength at temperatures up to 750 °C and higher creep resistances up to 725 °C than those of the UDIMET 720 LI alloy.

Powder Metallurgy Processing of Ni-Co Base Electrodes for Application in Water Electrolysis

Electrodes of Co, Ni and Ni 50 Co 50 were produced by powder metallurgy techniques aiming at their application as cathodes for water electrolysis system. Sintering was carried out in vacuum/argon atmosphere at low temperature to keep some residual porosity to enhance surface electroactivity by an increase of the geometric area. The Ni-Co alloying was obtained by mechanical synthesis, making use of the appropriated route. The final electrodes presented porosity around 12 % where the electrochemical tests presented increasing in the critical peak when compared with electroplated flat samples.

A Potentiostatic Evaluation of the Corrosion of a Ni-Co Base Amorphous Alloy

Abstract Corrosion of a Ni40Co20Cr12Mo6Fe6B16 amorphous alloy in deaerated sulfuric acid was evaluated by potentiostatic polarization measurements. Effects of acid concentration, sequence of polari...