scholarly journals Effect of Local Recrystallized Grains on the Low Cycle Fatigue Behavior of a Nickel-Based Single Crystal Superalloy

Crystals ◽  
2019 ◽  
Vol 9 (6) ◽  
pp. 312 ◽  
Author(s):  
Xianfeng Ma ◽  
Jishen Jiang ◽  
Wenjie Zhang ◽  
Hui-ji Shi ◽  
Jialin Gu
Keyword(s):  
Crack Propagation ◽  
Single Crystal ◽  
Low Cycle Fatigue ◽  
Fatigue Behavior ◽  
Fatigue Cracks ◽  
Fatigue Crack Initiation ◽  
Initiation Site ◽  
Single Crystal Superalloy ◽  
Cycle Fatigue ◽  
Intergranular Cracking

This paper aims to understand the effect of local recrystallization (RX) on the low cycle fatigue fracture of a turbine-blade single crystal nickel-based superalloy. The fatigue life of the single crystal superalloy was evidently decreased by local recrystallization. In single crystal specimens, casting porosity is the preferential fatigue crack initiation site, which is followed by crystallographic crack propagation along one or several octahedral slip planes. For all RX specimens, fatigue cracks preferred to initiate from local recrystallized grains and propagated through the recrystallized grains in a transgranular manner, followed by crystallographic crack propagation in the substrate single crystal superalloy. Moreover, fatigue tests indicated that locally recrystallized specimens exhibited temperature dependent fracture modes, i.e., transgranular cracking dominated at 550 °C, whereas intergranular cracking was preferred at 850 °C. Evident oxidation of fracture surfaces and strength degradation of grain boundaries at 850 °C was evidenced by scanning electronic microscopic observations. The present study emphasized the need to evaluate the effect of recrystallization according to the working conditions of turbine components, i.e., the local temperature.

Low Cycle Fatigue of Electrodeposited Pure Nanocrystalline Metals

2007 ◽  
Vol 561-565 ◽  
pp. 1299-1302 ◽  
Author(s):  
Pasquale Cavaliere
Keyword(s):  
Mechanical Properties ◽  
Grain Size ◽  
Fatigue Crack ◽  
Crack Propagation ◽  
Low Cycle Fatigue ◽  
Fatigue Behavior ◽  
Fatigue Crack Initiation ◽  
Size Variation ◽  
Load Ratio ◽  
Cycle Fatigue

The fatigue behavior of metals is strongly governed by the grain size variation. As the tensile strength, the fatigue limit increases with decreasing grain size in the microcrystalline regime. A different trend in mechanical properties has been demonstrated in many papers for metals with ultrafine (< 1 m) and nanocrystalline (< 100 nm) grain size in particular in the yield stress and fatigue crack initiation and growth. The fatigue behavior of electrodeposited nanocrystalline Ni (20 and 40 nm mean grain size) and nanocrystalline Co (20 nm) has been analyzed in the present paper by means of stress controlled tests. The monothonic mechanical properties of the materials were obtained from tensile tests by employing an Instron 5800 machine by measuring the strain with an extensometer up to 2.5% maximum strain. The strain gage specimen dimensions measured 20 mm length and 5 mm width, all the specimens were produced by electro-discharge machining. The low cycle fatigue tests were performed with specimens of the same geometry of the tensile ones in tension-tension with load ratio R=0.25. The fatigue crack propagation experiments were carried out by employing single edge notched specimens measuring 39 mm in length, 9.9 mm in width and with an electro-discharge machined edge-notch of 1 mm. All the endurance fatigue and crack propagation tests were performed at 10 Hz.

LOW CYCLE FATIGUE BEHAVIOR OF Zn-22Al ALLOY IN SUPERPLASTIC REGION AND NON-SUPERPLASTIC REGION

2008 ◽  
Vol 22 (31n32) ◽  
pp. 5477-5482 ◽  
Author(s):  
ATSUMICHI KUSHIBE ◽  
TSUTOMU TANAKA ◽  
YORINOBU TAKIGAWA ◽  
KENJI HIGASHI
Keyword(s):  
Fatigue Crack ◽  
Crack Propagation ◽  
Fatigue Crack Propagation ◽  
Low Cycle Fatigue ◽  
Fatigue Behavior ◽  
Crack Tip ◽  
The Other ◽  
Al Alloy ◽  
Cycle Fatigue ◽  
Secondary Cracks

The crack propagation properties for ultrafine-grained Zn -22 wt % Al alloy during low cycle fatigue (LCF) in the superplastic region and the non-superplastic region were investigated and compared with the corresponding results for several other materials. With the Zn - 22 wt % Al alloy, it was possible to conduct LCF tests even at high strain amplitudes of more than ±5%, and the alloy appeared to exhibit a longer LCF lifetime than the other materials examined. The fatigue life is higher in the superplastic region than in the non-superplastic region. The rate of fatigue crack propagation in the superplastic region is lower than that in the other materials in the high J-integral range. In addition, the formation of cavities and crack branching were observed around a crack tip in the supereplastic region. We therefore conclude that the formation of cavities and secondary cracks as a result of the relaxation of stress concentration around the crack tip results in a reduction in the rate of fatigue crack propagation and results in a longer fatigue lifetime.

A Study on the Low Cycle Fatigue Behavior of the Steel for Shipbuilding Industry

2005 ◽  
Vol 297-300 ◽  
pp. 10-15 ◽  
Author(s):  
Kyung Su Kim ◽  
Byung Ok Kim ◽  
Young Kwan Kim ◽  
Chang Hwan Lee ◽  
Sung Won Lee
Keyword(s):  
Low Cycle Fatigue ◽  
Fatigue Behavior ◽  
Fatigue Cracks ◽  
Published Data ◽  
Cycle Fatigue ◽  
Maritime Industry ◽  
Shipbuilding Industry ◽  
Design Procedures ◽  
Calculation Results ◽  
Good Agreement

Recently, most of fatigue cracks in ship structures are reported within a few years after delivery. This type of fatigue characteristics cannot be explained adequately by the S-N curve based on high cycle fatigue. Calculation results under critical loading conditions reveal that stress magnitude higher than three times the yield stress occurs at some critical locations. It shows the fatigue cracks are related to low cycle fatigue. But the existing recommended design procedures in maritime industry do not properly cover low cycle fatigue problems. This work represents the first step in an effort to develop a design code that addresses low cycle fatigue problems. Low cycle fatigue test for uniform round specimen made of base/weld metal and for cruciform welded joint are carried out under constant amplitude alternating load, controlled by strain. Strain-cycle curves for the base metal and weld joints show good agreement with published data as well as some code recommended design curves.

Sign in / Sign up

Export Citation Format

Share Document