Study of the interaction of a short fatigue crack with grain boundaries in a cast Al alloy using X-ray microtomography

Abstract Synchrotron Radiation X-ray microtomography is used to visualize and analyze simultaneously the three-dimensional shape of crystallographic grains containing a short fatigue crack in a cast Al alloy. The visualization of the grains is based on the decoration of Al grain boundaries by liquid Ga which serves as a selective contrast agent. The intricate three-dimensional shape of the fatigue crack, as well as the crack stops observed on the sample surface, are correlated to the grain structure of the material. Complementary measurements of the grain orientation on the sample surface by electron backscattering diffraction (EBSD) allow us to discuss and interpret the observations in terms of possible crack propagation mechanisms.

[1]  Françoise Peyrin,et al.  Observation of microstructure and damage in materials by phase sensitive radiography and tomography , 1997 .

[2]  Subra Suresh,et al.  Crack deflection: Implications for the growth of long and short fatigue cracks , 1983 .

[3]  E. Maire,et al.  Experimental study of porosity and its relation to fatigue mechanisms of model Al–Si7–Mg0.3 cast Al alloys , 2001 .

[4]  Andreas Koch,et al.  X-ray camera for computed microtomography of biological samples with micrometer resolution using Lu3Al5O12 and Y3Al5O12 scintillators , 1999, Medical Imaging.

[5]  A. B. Geltmacher,et al.  Spatial distribution of voids in HY-100 steel by X-ray tomography , 2001 .

[6]  Peter Cloetens,et al.  Characterization of internal damage in a MMCp using X-ray synchrotron phase contrast microtomography , 1999 .

[7]  D. Juul Jensen,et al.  Three-dimensional maps of grain boundaries and the stress state of individual grains in polycrystals and powders , 2001 .

[8]  L. Edwards,et al.  Measurement of plastic zones associated with small fatigue cracks by selected area channeling patterns , 1992 .

[9]  E. R. Rios,et al.  The Behaviour of short fatigue cracks , 1986 .

[10]  Takeshi Ogawa,et al.  LIMITATIONS OF LINEAR ELASTIC FRACTURE MECHANICS IN RESPECT OF SMALL FATIGUE CRACKS AND MICROSTRUCTURE , 1986 .

[11]  S. Suresh.  Fatigue of materials , 1991 .

[12]  Avinash C. Kak,et al.  Principles of computerized tomographic imaging , 2001, Classics in applied mathematics.

[13]  F. C. Thompson,et al.  Mechanical Properties of Matter , 1965, Nature.

[14]  A. Pineau,et al.  SHORT CRACK BEHAVIOUR IN NODULAR CAST IRON , 1984 .

[15]  E. R. Rios,et al.  THE EFFECT OF GRAIN SIZE ON FATIGUE CRACK GROWTH IN AN ALUMINIUM MAGNESIUM ALLOY , 1995 .

[16]  Laurent Babout,et al.  Characterization by X-ray computed tomography of decohesion, porosity growth and coalescence in model metal matrix composites , 2001 .

[17]  J. Lankford.  THE INFLUENCE OF MICROSTRUCTURE ON THE GROWTH OF SMALL FATIGUE CRACKS , 1985 .

[18]  Wolfgang Ludwig,et al.  Penetration of liquid gallium into the grain boundaries of aluminium: a synchrotron radiation microtomographic investigation , 2000 .

[19]  Angus J. Wilkinson,et al.  A crystallographic mechanism for fatigue crack propagation through grain boundaries , 2000 .

[20]  K. Ravichandran.  THREE‐DIMENSIONAL CRACK‐SHAPE EFFECTS DURING THE GROWTH OF SMALL SURFACE FATIGUE CRACKS IN A TITANIUM‐BASE ALLOY , 1997 .

[21]  W. Ludwig.  Development and Applications of Synchrotron Radiation Microtomography , 2001 .

[22]  K. Miller.  THE SHORT CRACK PROBLEM , 1982 .

[23]  F. Meyer,et al.  Mathematical morphology: from two dimensions to three dimensions , 1992 .

[24]  W. Morris,et al.  The Effect of Grain Size on Fatigue Growth of Short Cracks , 1983 .

[25]  Eric Ziegler,et al.  Design and performance of graded multilayers as focusing elements for x-ray optics , 1999 .

[26]  James Lankford,et al.  THE GROWTH OF SMALL FATIGUE CRACKS IN 7075–T6 ALUMINUM , 1982 .

[27]  Stuart R. Stock,et al.  Direct observation of crack opening as a function of applied load in the interior of a notched tensile sample of AlLi 2090 , 1997 .

[28]  E. R. Rios,et al.  THE EFFECT OF GRAIN SIZE ON THE FATIGUE OF COMMERCIALLY PURE ALUMINIUM , 1995 .

[29]  P. Cloetens,et al.  Characterisation by X-ray micro-tomography of cavity coalescence during superplastic deformation , 2000 .

[30]  P. Withers,et al.  A synchrotron X-ray study of a Ti/SiCf composite during in situ straining , 2001 .

[31]  K. Ravichandran,et al.  Fracture mechanical character of small cracks in polycrystalline materials: concept and numerical K calculations , 2000 .

[32]  Günter Möbus,et al.  3D determination of grain shape in a FeAl-based nanocomposite by 3D FIB tomography , 2001 .

[33]  Henning Friis Poulsen,et al.  Tracking: a method for structural characterization of grains in powders or polycrystals , 2001 .