Ultrasonic Fatigue of Radical Nitrided Ni-Base Superalloy

2009 ◽  
Vol 417-418 ◽  
pp. 209-212
Author(s):  
K. Yamane ◽  
Norio Kawagoishi ◽  
Kazuhiro Morino ◽  
K. Fukada
Keyword(s):  
Fatigue Strength ◽  
Fracture Surface ◽  
Fatigue Tests ◽  
Loading Frequency ◽  
Bending Fatigue ◽  
Fatigue Process ◽  
Rotating Bending Fatigue ◽  
Ultrasonic Fatigue ◽  
Rotating Bending ◽  
Base Superalloy

Ultrasonic and rotating bending fatigue tests were carried out for aged and nitrided Ni-base super alloys to investigate the effects of loading frequency and nitriding on fatigue strength. Loading frequencies were 19.5 kHz under ultrasonic and 50 Hz under rotating bending, respectively. Fatigue strength under ultrasonic was higher than that under rotating bending in both alloys. Moreover, in both tests, fatigue strength was improved by nitriding. The increase in fatigue strength by nitriding was large in ultrasonic fatigue. These results were discussed through the successive observation of fatigue process at specimen surface and fracture surface observation.

Effect of Radical Nitriding on Fatigue Strength of Ni-Base Superalloy

2009 ◽  
Vol 417-418 ◽  
pp. 205-208 ◽  
Author(s):  
Kazuhiro Morino ◽  
Norio Kawagoishi ◽  
K. Yamane ◽  
K. Fukada
Keyword(s):  
Fatigue Strength ◽  
Base Alloy ◽  
Compound Layer ◽  
Fatigue Tests ◽  
Bending Fatigue ◽  
Propagation Behavior ◽  
Initiation And Propagation ◽  
Rotating Bending Fatigue ◽  
Rotating Bending ◽  
Base Superalloy

In order to investigate the effect of nitriding on the crack initiation and propagation behavior of Ni-base super alloy, Alloy 718, rotating bending fatigue tests were carried out until 108 cycles at room temperature. By nitriding at 500°C for 12h, compound layer of about 5μm in thickness was formed and the initiation of a fatigue crack was strongly suppressed causing the increase in fatigue strength. A crack initiated in brittle manner at the compound layer in all of fractures. However the crack propagated in ductile manner controlled by the property of the base alloy. That is, there is no or little influence of nitriding on the crack growth rate of the alloy.

scholarly journals FATIGUE CRACK GROWTH OF AGE-HARDENED Al ALLOY UNDER ULTRASONIC LOADING

2012 ◽  
Vol 06 ◽  
pp. 275-281
Author(s):  
Q. CHEN ◽  
N. KAWAGOISHI ◽  
K. KARIYA ◽  
Y. NU ◽  
M. GOTO
Keyword(s):  
Fatigue Strength ◽  
Crack Growth ◽  
Shear Mode ◽  
Al Alloy ◽  
Loading Frequency ◽  
Time Saving ◽  
Bending Fatigue ◽  
Rotating Bending Fatigue ◽  
Ultrasonic Fatigue ◽  
Rotating Bending

An age-hardened and extruded Al alloy 7075-T6 was fatigued under both ultrasonic loading (20kHz) and rotating bending (50Hz) in the environments of controlled humidity, distilled water and oxygen gas respectively, to investigate the availability of ultrasonic fatigue test as a time-saving tool for the reliability evaluation of materials subjected to conventional frequency loading. Although fatigue strength decreased slightly at relative humidity below 60-70%, it degraded significantly when the humidity was increased beyond that level, irrespective of the loading frequency. However, the mechanisms of strength degradation involved in high humidity are quite different. Under rotating bending, fatigue strength decreased because crack growth was accelerated due to brittle fracture, whileas the decrease in fatigue strength under ultrasonic loading was caused by crack propagation transition from tensile mode to shear mode cracking.

Effect of Humidity on Fatigue Strength of Age-Hardened Al Alloy

2009 ◽  
Vol 417-418 ◽  
pp. 373-376
Author(s):  
T. Fukudome ◽  
Norio Kawagoishi ◽  
K. Kariya
Keyword(s):  
Fatigue Strength ◽  
Fracture Mechanism ◽  
Fatigue Tests ◽  
Shear Mode ◽  
Al Alloy ◽  
Bending Fatigue ◽  
Rotating Bending Fatigue ◽  
Ultrasonic Fatigue ◽  
Rotating Bending ◽  
The Difference

Ultrasonic and rotating bending fatigue tests were carried out using plain specimens and specimens with a small blind hole for an extruded and age-hardened Al alloy 7075-T6 in different environments in order to investigate the effect of humidity on fatigue strength and fracture mechanism. Fatigue strength was decreased by high humidity under both tests. The effect of humidity on fatigue strength was larger in ultrasonic fatigue. The humidity affected both of crack initiation and propagation processes. Crack propagated in tensile mode then changed to shear mode macroscopically in all environments under ultrasonic fatigue, though it was only in tensile mode under rotating bending fatigue. These differences in fracture mechanism related to the difference in environmental effect on fatigue strength in both tests.

Sub-Surface Fatigue Strength of a Steel

1969 ◽  
Vol 11 (4) ◽  
pp. 432-443 ◽  
Author(s):  
P. F. Bray
Keyword(s):  
Fatigue Strength ◽  
Residual Stresses ◽  
Fatigue Limit ◽  
Fatigue Tests ◽  
Bending Fatigue ◽  
Surface Fatigue ◽  
Test Pieces ◽  
Surface Failure ◽  
Rotating Bending Fatigue ◽  
Rotating Bending

Rotating bending fatigue tests on En 40B steel gave a fatigue limit for surface failure of 30·5 tonf/in2. With nitrided test-pieces sub-surface failures were produced and, with no allowance being made for residual stresses, a fatigue limit of 34·5 tonf/in2 was obtained for sub-surface failure. In the absence of residual stresses this fatigue limit would probably have been higher.

Effects of Microstructure and Humidity on Fatigue Strength of Maraging Steel

2008 ◽  
Vol 385-387 ◽  
pp. 113-116
Author(s):  
M. Miyazono ◽  
Norio Kawagoishi ◽  
Qing Yuan Wang ◽  
Eiji Kondo ◽  
Takanori Nagano
Keyword(s):  
Grain Size ◽  
Fatigue Strength ◽  
Fatigue Tests ◽  
Specimen Surface ◽  
Bending Fatigue ◽  
Maraging Steels ◽  
Initiation And Propagation ◽  
Rotating Bending Fatigue ◽  
Rotating Bending ◽  
Different Grain Size

Rotating bending fatigue tests were carried out for maraging steels with different grain size in moist air in order to investigate the effects of humidity, grain size and reversion austenite on fatigue strength of the steel. Fatigue strength was decreased by humidity, and the decrease in fatigue strength was large in larger grain sized steel. Both of the initiation and propagation of a crack were promoted by humidity. Many cracks initiated at the specimen surface and intergranular cracks were observed at specimen surface and on fracture surface when humidity was high. The decrease in fatigue strength by humidity was suppressed by formation of reversion austenite.

Improvement of Fatigue Strength of Maraging Steel by Shot Peening

2007 ◽  
Vol 348-349 ◽  
pp. 537-540
Author(s):  
Norio Kawagoishi ◽  
Takanori Nagano ◽  
M. Moriyama ◽  
Eiji Kondo
Keyword(s):  
Fatigue Strength ◽  
Maraging Steel ◽  
Shot Peening ◽  
Fine Particles ◽  
Fatigue Tests ◽  
Fracture Origin ◽  
Bending Fatigue ◽  
Rotating Bending Fatigue ◽  
Rotating Bending ◽  
Points Of View

Rotating bending fatigue tests up to 108 cycles were carried out to investigate the effects of shot peening on the fatigue strength and the fracture mechanism in an 18 % Ni maraging steel by using shot particles of various sizes or hardness. Fatigue strength was increased markedly by shot peening in the wide region of fatigue life. The S-N curves showed duplex S-N properties because of the transition of fracture origin from the specimen surface in the short life region to the subsurface in the long life one. Double shot peening by using super-hard fine particles was effective to improve the fatigue strength for surface fracture, though the fatigue strength for an internal fracture was hardly influenced. These results were discussed from the points of view of effects of surface roughness, residual stress and work hardening on the fatigue strength.

High Cycle Fatigue Behavior of Thermally Oxidized Ti6Al4V Alloy

2007 ◽  
Vol 561-565 ◽  
pp. 2179-2182 ◽  
Author(s):  
Mehmet Cingi ◽  
Onur Meydanoglu ◽  
Hasan Guleryuz ◽  
Murat Baydogan ◽  
Huseyin Cimenoglu ◽  
...  
Keyword(s):  
Fatigue Strength ◽  
Yield Strength ◽  
Thermal Oxidation ◽  
Fatigue Behavior ◽  
Surface Hardness ◽  
Ti6al4v Alloy ◽  
Bending Fatigue ◽  
Rotating Bending Fatigue ◽  
Rotating Bending ◽  
Bending Fatigue Strength

In this study, the effect of thermal oxidation on the high cycle rotating bending fatigue behavior of Ti6Al4V alloy was investigated. Oxidation, which was performed at 600°C for 60 h in air, considerably improved the surface hardness and particularly the yield strength of the alloy without scarifying the tensile ductility. Unfortunately, the rotating bending fatigue strength at 5x106 cycles decreased from about 610 MPa to about 400 MPa upon oxidation. Thus, thermal oxidation leaded a reduction in the fatigue strength of around 34%, while improving the surface hardness (HV0.1) and yield strength 85 % and 36 %, respectively.

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