Akira Yoshinari

Development of novel Ni-based single crystal superalloys for power-generation gas turbines

Abstract In advanced industrial gas-turbine systems, there has been a great demand for new single crystal (SC) superalloys with an excellent combination of high-temperature creep strength, hot-corrosion resistance and oxidation resistance. In this study, 12 nickel-based SC superalloys were designed with the aid of the d-electrons concept. Their chemical compositions were in the range of 1.2–1.5%Ti, 3.8–6.5%Cr, 11%Co, 0–1.4%Mo, 0–3.0%Ru, 6.5–7.4%Ta, 5.0–6.4%W, 3.6–5.4%Re, 5.1–5.5%Al, 0.12–0.14%Hf and balanced Ni in wt%. A series of experiments such as creep rupture tests, burner rig tests and cyclic oxidation tests were conducted with the heat-treated SC specimens of these alloys. Almost all the designed alloys were found to be superior in creep rupture life to a second generation superalloy currently used in the world. For hot-corrosion resistance, estimated from the burner rig tests, any of the designed alloys were comparable or even superior to a second generation superalloy. The oxidation resistance was very different among the designed alloys, but some of them showed better resistance than the second generation superalloy. Thus the SC alloys containing about 4–5 wt%Re had about 30°C or more higher temperature capability than the second generation superalloy, while exhibiting excellent hot-corrosion resistance and good oxidation resistance.

Development of Ni based single crystal superalloys for power generation gas turbine blades

Abstract In advanced industrial gas turbine systems, there has been a great demand for new single crystal (SC) superalloys with an excellent combination of high temperature creep strength, hot corrosion resistance and oxidation resistance. In the present study, twelve nickel based SC superalloys were designed with the aid of the d-electrons concept. Their chemical compositions were in the range 1·2–1·5%Ti, 3·8–6·5%Cr, 11%Co, 0–1·4%Mo, 0–3·0%Ru, 6·5–7·4%Ta, 5·0–6·4%W, 3·6–5·4%Re, 5·1–5·5%Al, 0·12–0·14%Hf and balanced Ni in wt-%. A series of experiments such as creep rupture tests, burner rig tests and cyclic oxidation tests were conducted with the heat treated SC specimens of these alloys. Almost all the designed alloys were found to be superior in creep rupture life to a second generation superalloy currently used in the world. In the hot corrosion resistance estimated from the burner rig tests, any designed alloys were similar or even superior to a second generation superalloy. The oxidation resistance was very different among the designed alloys, but some of them showed better resistance than the second generation superalloy. Thus the SC alloys containing about 4–5 wt-%Re had ∼30°C or more higher temperature capability than the second generation superalloy, while exhibiting excellent hot corrosion resistance and good oxidation resistance.

Multiaxial Low Cycle Fatigue for Ni-Base Single Crystal Super Alloy at High Temperature

This paper presents multiaxial low cycle fatigue lives of YH61 Ni-base single crystal superalloy at elevated temperature. Tension-torsion low cycle fatigue tests were performed using hollow cylinder specimens with aligning the specimen axis to [100] direction at 1173 K. Biaxial tension-compression low cycle fatigue tests were also performed using cruciform specimens whose x and y axes were aligned to \(\langle 110\rangle \) directions. The effect of strain multiaxiality on the multiaxial low cycle fatigue lives was discussed. Couples of multiaxial stress and strain parameters were applied to the experimental data for correlating the multiaxial low cycle fatigue lives of both types of the specimens. The strain parameters yielded a large scatter in the correlation and Mises equivalent stress was only the parameter to give a satisfactory correlation of multiaxial low cycle fatigue lives of the superalloy.

Nickel Base Superalloys Single Crystal Growth Technology for Large Size Buckets in Heavy Duty Gas Turbines

A larger size bucket with superior high temperature strength is required for future land based gas turbines. From the viewpoint of high temperature mechanical properties, single crystal alloys are rather promising. To grow larger sized single crystals of nickel base superalloys, a two stage heating and bypass process in which single crystal growth paths are incorporated into large cross sectional positions such as platforms has been developed. It results in successful single crystal growth of alloys for buckets with a total length of 170mm and large lateral cross section. Characteristics of single crystal buckets made by the bypass process and properties of an alumina mold prepared for a single crystal casting are described herein.Copyright

High Temperature Multiaxial Creep-Fatigue Life Prediction for YH61 Nickel-Base Single Crystal Superalloy

This paper discusses an evaluation method of creep-fatigue lives of YH61 single crystal superalloy under multiaxial loading at high temperature. Three types of creep-fatigue tests were performed using three types of the single crystalsuperalloy specimens at 1173K. They were push-pull tests using solid bar specimens, tension-torsion tests using hollow cylinder specimens and biaxial tension-compression tests using cruciform specimens. Anisotropic strain and Mises stress in combination with frequency modified fatigue equation were applied for evaluating the creep-fatigue lives in the three types of tests. The former parameter gave a relatively large scatter but the latter parameter a small scatter in the correlation.