Grain boundaries with high Σ value and strain in grain matrix induce crack initiation in extruded 6000 series aluminium alloys

2022 ◽  
pp. 142630
Author(s):  
Shogo Oda ◽  
Shun-Ichiro Tanaka
Keyword(s):  
Crack Initiation ◽  
Grain Boundaries ◽  
Aluminium Alloys

“Cavity” formation in superplastically deformed aluminium alloys

1990 ◽  
Vol 48 (4) ◽  
pp. 958-959
Author(s):  
A. Cziráki ◽  
E. Ková-csetényi ◽  
T. Torma ◽  
T. Turmezey
Keyword(s):  
Grain Boundaries ◽  
Aluminium Alloys ◽  
Superplastic Deformation ◽  
Volume Fraction ◽  
Superplastic Forming ◽  
Polished Surface ◽  
Cavity Formation ◽  
Stress Concentrations ◽  
Electron Microscopic ◽  
Commercial Aluminium

It is known that the formation of cavities during superplastic deformation can be correlated with the development of stress concentrations at irregularities along grain boundaries such as particles, ledges and triple points. In commercial aluminium alloys Al-Fe-Si particles or other coarse constituents may play an important role in cavity formation.Cavity formation during superplastic deformation was studied by optical metallography and transmission scanning electron microscopic investigations on Al-Mg-Si and Al-Mg-Mn alloys. The structure of particles was characterized by selected area diffraction and X-ray micro analysis. The volume fraction of “voids” was determined on mechanically polished surface.It was found by electron microscopy that strongly deformed regions are formed during superplastic forming at grain boundaries and around coarse particles.According to electron diffraction measurements these areas consist of small micro crystallized regions. See Fig.l.Comparing the volume fraction and morphology of cavities found by optical microscopy a good correlation was established between that of micro crystalline regions.

Technique d'observation de surface in situ (TOSIS) :

1996 ◽  
Vol 84 ◽  
pp. 17-22
Author(s):  
A. Ranaivoarisoa ◽  
J. M. Olive ◽  
D. Desjardins
Keyword(s):  
Aqueous Solution ◽  
Crack Initiation ◽  
Grain Boundaries ◽  
Growth Rates ◽  
Triple Junction ◽  
Crack Nucleation ◽  
Initiation Time ◽  
Mesoscopic Scale ◽  
Crack Growth Rates

An optical method named In Situ Surface Observation Technique (ISSOT) is presented in this paper. This method is used to detect crack nucleation from a flaw (here a pit) at mesoscopic scale during a triangular push-pull cycling test under the control of charge amplitude in aqueous solution ofMgCl2 at 117°C. It can be found that the crack initiation time determined by using this technique represents 2 % of that estimated from a mechanical criterion. Moreover, the follow of the crack tip evolution by the ISSOT allows to measure average local crack growth rates. It has been shown that the variations of the latter were related to the effects of barriers such as grain boundaries, twin boundaries and grain boundaries triple junction.

Microanalysis across grain boundaries in aluminium alloys

1975 ◽  
Vol 31 (2) ◽  
pp. 285-290 ◽  
Author(s):  
P. Doig ◽  
J. W. Edington ◽  
M. H. Jacobs
Keyword(s):  
Grain Boundaries ◽  
Aluminium Alloys

Analysis of Surface and Subsurface Layers after Shot Peening of Various Aluminium Alloys

2010 ◽  
Vol 89-91 ◽  
pp. 53-58
Author(s):  
Sebastjan Žagar ◽  
Janez Grum
Keyword(s):  
Surface Layer ◽  
Crack Initiation ◽  
Residual Stresses ◽  
Surface Integrity ◽  
Shot Peening ◽  
Aluminium Alloys ◽  
Surface Hardening ◽  
Hardened Layer ◽  
Operating Pressure ◽  
Subsurface Layers

In the paper two aluminium alloys, i.e. 6082 and 7075, which were cold hardened by shot peening under different conditions, are treated. Surface hardening was carried out with S170 steel shot of the same diameter, particle hardness being 56 HRC. Other conditions were the operating pressure, mass flow, which provide different Almen intensities. The hardened layer was described by surface integrity. Macroscopic and microscopic analyses consisted in analyses of hardened profiles of hardness, and residual stresses in the thin surface layer. Research results indicated that there were significant differences among the characteristics chosen to describe surface integrity and that they had an important influence on the final condition of the surface layer. With too severe settings of the peening parameters, the surface properties got worse because of damages, which resulted in crack initiation and growth of the existing cracks.

Damage Evolution and Crack Growth in Nickel-Based Alloys during Ultrasonic Fatigue

2014 ◽  
Vol 783-786 ◽  
pp. 2410-2415 ◽  
Author(s):  
Martina Zimmermann ◽  
A. Kolyshkin ◽  
C. Stöcker ◽  
J.W. Jones ◽  
H.J. Christ
Keyword(s):  
Crack Initiation ◽  
Grain Boundaries ◽  
Crack Growth ◽  
Pure Nickel ◽  
Indirect Detection ◽  
Optical Methods ◽  
Coarse Grained ◽  
Detection Techniques ◽  
Nimonic 80A ◽  
Ultrasonic Fatigue

Experimental results on the fatigue damage of quasi defect-free materials in the VHCF range are presented. For nickel-based superalloys and pure nickel the likelihood of crack initiation at favorable grain morphologies is studied. Slip band and microcrack formation at the surface was observed even in run-out samples. Hence, microcracks were evaluated regarding their propagation capabilities according to grain orientation and barrier function of grain boundaries. In the VHCF regime crack initiation can shift from surface to subsurface, consequently early crack growth has to be studied by means of optical methods and indirect detection techniques or tomographic methods. In the study presented crack initiation and crack growth was monitored through optical observation and quasi 3-D observation by means of synchrotron radiation. For an as-received and a coarse-grained condition of pure nickel Ni201 fatigue crack growth in the VHCF regime occurs at deltaK as low as 3.54 MPam1/2 for a crack growth rate da/dN = 10E-12 m/cycle. The grain size had no effect on the threshold limit but crack growth retardation at grain boundaries and crack path deflection lead to lower crack growth rates for the coarse-grained condition In the nickel-based alloy Nimonic 80A the influence of microstructure on the intercrystalline crack initiation and propagation was confirmed. Here, the combination of the misorientation angle between two adjacent grains and the orientation of their boundary with respect to the external load defines the magnitude of stress concentration at grain boundaries.

Sign in / Sign up

Export Citation Format

Share Document