Analysis of Grain Boundary Cavitation Damage in Copper (original) (raw)

Interface cavitation damage in polycrystalline copper

Acta metallurgica et materialia, 1992

Determination of an interface damage function (IDF) [Adams, Zhao and O'Hara, Acta metall. mater. 38, 953 (1990)], from a stereological procedure similar to that presented by Hilliard [Trans. Am. Inst. Min. Engrs 224, 1201], is described. The mathematical and experimental simplicity of the method is utilized in measuring an IDF for polycrystalline copper crept at 0.6T m under uniaxial tension. Whereas previous work focussed on a five parameter description of the local state of a grain boundary, the domain of the IDF is increased to eight degrees of freedom in the present study to include the complete geometrical description of grain boundary structure. The resulting functions identify certain types of grain boundaries which were preferentially damaged. Most of the damage occurred on interfaces oriented nearly normal to the principal stress axis. Some relatively small angle boundaries demonstrated a surprising propensity to cavitate as did certain special boundaries distinguished by a group multiplicity in misorientation space greater than one. A sequence of two dimensional projections through the eight-dimensional domain of the IDF is shown to identify a number of interface structures which are readily damaged.

Effects of grain size and boundary structure on the dynamic tensile response of copper

2011

Plate impact experiments have been carried out to examine the influence of grain boundary characteristics on the dynamic tensile response of Cu samples with grain sizes of 30, 60, 100, and 200 lm. The peak compressive stress is 1.50GPaforallexperiments,lowenoughtocauseanearlystageofincipientspalldamagethatiscorrelatedtothesurroundingmicrostructureinmetallographicanalysis.Theexperimentalconfigurationusedinthisworkpermitsreal−timemeasurementsofthesamplefreesurfacevelocityhistories,soft−recovery,andpostimpactexaminationofthedamagedmicrostructure.Theresultingtensiledamageintherecoveredsamplesisexaminedusingopticalandelectronmicroscopyalongwithmicrox−raytomography.Thefreesurfacevelocitymeasurementsareusedtocalculatespallstrengthvaluesandshownosignificanteffectofthegrainsize.However,differencesareobservedinthefreesurfacevelocitybehaviorafterthepull−backminima,whenreaccelerationoccurs.Themagnitudeofthespallpeakanditsaccelerationratearedependentuponthegrainsize.Thequantitative,postimpact,metallographicanalysesofrecoveredsamplesshowthatforthematerialswithgrainsizeslargerthan30lm,thevoidvolumefractionandtheaveragevoidsizeincreasewithincreasinggrainsize.Inthe30and200lmsamples,voidcoalescenceisobservedtodominatethevoidgrowthbehavior,whereasin60and100lmsamples,voidgrowthisdominatedbythegrowthofisolatedvoids.Electronbackscatterdiffraction(EBSD)observationsshowthatvoidspreferentiallynucleateandgrowatgrainboundarieswithhighanglemisorientation.However,specialboundariescorrespondingtoRl(lowangle,<5)andR3(1.50 GPa for all experiments, low enough to cause an early stage of incipient spall damage that is correlated to the surrounding microstructure in metallographic analysis. The experimental configuration used in this work permits real-time measurements of the sample free surface velocity histories, soft-recovery, and postimpact examination of the damaged microstructure. The resulting tensile damage in the recovered samples is examined using optical and electron microscopy along with micro x-ray tomography. The free surface velocity measurements are used to calculate spall strength values and show no significant effect of the grain size. However, differences are observed in the free surface velocity behavior after the pull-back minima, when reacceleration occurs. The magnitude of the spall peak and its acceleration rate are dependent upon the grain size. The quantitative, postimpact, metallographic analyses of recovered samples show that for the materials with grain sizes larger than 30 lm, the void volume fraction and the average void size increase with increasing grain size. In the 30 and 200 lm samples, void coalescence is observed to dominate the void growth behavior, whereas in 60 and 100 lm samples, void growth is dominated by the growth of isolated voids. Electron backscatter diffraction (EBSD) observations show that voids preferentially nucleate and grow at grain boundaries with high angle misorientation. However, special boundaries corresponding to Rl (low angle, < 5 ) and R3 (1.50GPaforallexperiments,lowenoughtocauseanearlystageofincipientspalldamagethatiscorrelatedtothesurroundingmicrostructureinmetallographicanalysis.Theexperimentalconfigurationusedinthisworkpermitsreal−timemeasurementsofthesamplefreesurfacevelocityhistories,soft−recovery,andpostimpactexaminationofthedamagedmicrostructure.Theresultingtensiledamageintherecoveredsamplesisexaminedusingopticalandelectronmicroscopyalongwithmicrox−raytomography.Thefreesurfacevelocitymeasurementsareusedtocalculatespallstrengthvaluesandshownosignificanteffectofthegrainsize.However,differencesareobservedinthefreesurfacevelocitybehaviorafterthepull−backminima,whenreaccelerationoccurs.Themagnitudeofthespallpeakanditsaccelerationratearedependentuponthegrainsize.Thequantitative,postimpact,metallographicanalysesofrecoveredsamplesshowthatforthematerialswithgrainsizeslargerthan30lm,thevoidvolumefractionandtheaveragevoidsizeincreasewithincreasinggrainsize.Inthe30and200lmsamples,voidcoalescenceisobservedtodominatethevoidgrowthbehavior,whereasin60and100lmsamples,voidgrowthisdominatedbythegrowthofisolatedvoids.Electronbackscatterdiffraction(EBSD)observationsshowthatvoidspreferentiallynucleateandgrowatgrainboundarieswithhighanglemisorientation.However,specialboundariescorrespondingtoRl(lowangle,<5)andR3(60 <111> misorientation) types are more resistant to void formation. Finally, micro x-ray tomography results show three dimensional (3D) views of the damage fields consistent with the two dimensional (2D) surface observations. Based on these findings, mechanisms for the void growth and coalescence are proposed.

Grain Boundary Cavitation Under Various States of Applied Stress

Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences, 1976

Submicrometre grain boundary cavities are produced in Nimonic 80A when plastic deformation in any of three different stress states is followed by a short anneal. Tension, torsion and compression specimens were plastically strained in a systematic manner and then annealed for 2 h at 750 °C. Detailed quantitative observations with a 1 MV microscope showed that the number of cavities per unit volume was a function of the shear strain and independent of the stress state. Furthermore the measurements revealed the surprising result that most cavities were on those grain boundaries which were parallel to the maximum principal stress axis. However, Preferential cavity growth occurred during subsequent tensile creep and cavities on these parallel boundaries either remained constant in size or diminished while those on boundaries which were orthogonal to the applied stress axis grew relatively quickly, thus producing the usual appearance of cavitated tensile samples. Plastic strain was more d...

Heterogeneity of intergranular damage in Copper Crept in Plane-Strain Tension

Metallurgical Transactions A, 1992

An interface damage function (IDF), which statistically describes the area fraction of interface damage as a function of up to eight parameters defining crystallite interfaces, was determined for commercial purity copper specimens crept in plane strain tension. The IDF was determined from stereological parameters measured on plane sections cut through damaged specimens. The eight-dimensional space of the function was investigated by analyzing two-dimensional projections of the complete domain. Certain "special" interfaces were observed to damage preferentially. A low planar density of atoms near crystallite interfaces apparently increased the propensity for the occurrence of damage. Other microstructural mechanisms contributing to the observed heterogeneous distribution of damage are also considered.

The role of the structure of grain boundary interfaces during shock loading

2012

In order to understand the role of interface structure during shock loading, and specifically the role of interfaces in damage evolution due to shock, four copper bi-crystal grain boundaries (GBs) were studied under shock loading and incipient spall conditions. These boundaries, two [100]/[111] boundaries and two [100]/[100] boundaries, were characterized prior to deformation using optical microscopy (OM), electron back scattered diffraction (EBSD), and transmission electron microscopy (TEM) to determine axis/angle pair relationships and interface plane. Samples containing these boundaries were then subjected to incipient spall at 2.1 GPa and shock loading at 10 GPa, respectively, in an 80 mm gas gun. Samples were soft recovered and characterized post-mortem via EBSD and TEM. Preliminary results indicate that typical GBs readily form damage during shock loading but that special boundaries, such as twin boundaries, are resistant to failure. Differences in slip and defect transmissibility across these types of boundaries likely play a role in the failure modes.

Macro, Micro, and Nano Level Analysis of Cavitation Damage Mechanism in FCC Materials

2016

The aim of this paper is to demonstrate the analysis of cavitation damage mechanism in FCC (Face Centered Cub ic ) materials , and to establish a possible application of the cavitation phenomenon as an efficient method to modify surface properties. Three FCC materials ( c opper, AlMg - alloy and stainless steel ( St.St.316 ) ) were subjected to high speed submerged cavitating jets under certain working conditions, for different time periods. The force generated by cavitation is employed to deform and to damage the surface in scales ranging from nano to micro and macro . The target surface s were investigated with various techniqu es. Results indicate that at short exposure times, the observed characteristic features in the microstructure – hills, holes and wavy configuration – can be related to the start of the plastic deformation of the specimen surface. By increasing the exposur e time , the surface s bec a me eroded, the damaged area is characterized by many rings , with differen...

Microstructural Effects on Damage Nucleation in Shock-Loaded Polycrystalline Copper

Metallurgical and Materials Transactions A, 2014

Polycrystalline copper samples with varying thermomechanical histories were shock loaded to induce spall via laser-driven plate impacts at low shock stress (<6 GPa). Electron backscattering diffraction was used to obtain statistics on grain boundary (GB) misorientations within the spall plane and at all GBs that contained damage. Specimens with pre-existing plastic deformation showed dominant intergranular damage at boundaries in the 25 to 50 deg misorientation range, while heat-treated samples had mixed trans-and intergranular damage with a lessened misorientation influence at damaged GBs. 3-D X-ray tomography data were used to analyze global volume statistics and qualitatively inspect the shape of voids present in samples of varying thermomechanical histories. It was found that annealed samples had a mixed mode of sphericaland sheet-like voids, indicative of trans-and intergranular damage, respectively, and the microstructure with the highest number of R3 twin boundaries had the highest concentration of spherical voids. Data from a plastically pre-strained sample showed a dominance of needle-and sheet-like voids, indicating primarily intergranular damage due to the higher strength of the bulk material forcing the damage to nucleate at weaker defects, in this case GBs.

Grain boundary diffusion in copper under tensile stress

Arxiv preprint cond-mat/0307065, 2003

Stress enhanced self-diffusion of Copper on the Σ3 twin grain boundary was examined with molecular dynamics simulations. The presence of uniaxial tensile stress results in a significant reduction in activation energy for grain-boundary self-diffusion of magnitude 5 eV per unit strain. Using a theoretical model of point defect formation and diffusion, the functional dependence of the effective activation energy Q on uniaxial tensile strain ǫ is shown to be described by Q(ǫ) = Q0 − E0V * ǫ where E0 is the zero-temperature Young's modulus and V * is an effective activation volume. The simulation data agree well with this model and comparison between data and model suggests that V * = 0.6Ω where Ω is the atomic volume. V * /Ω = 0.6 is consistent with a vacancy-dominated diffusion mechanism.

Nucleation and growth of voids in shock loaded copper bicrystals

SHOCK COMPRESSION OF CONDENSED MATTER - 2019: Proceedings of the Conference of the American Physical Society Topical Group on Shock Compression of Condensed Matter, 2020

Understanding the evolution of damage and deformation due to spall at grain boundaries can provide a basis for connecting micro-to macroscale failure behavior in metals under extreme conditions. Copper bicrystal samples were shock loaded using flyer-plate impacts in a light gas gun with shock stresses ranging from 3 to 6 GPa. Pulse duration as well as crystal orientation along the shock direction were varied for a fixed boundary misorientation to determine their effects on void nucleation and coalescence. Samples were soft recovered and cross-sectioned to characterize damage using electron backscattering diffraction and scanning electron microscopy to gather information on damage characteristics at and around the GB, with emphasis on growth of boundary and bulk voids. Chemistry and composition analysis were also performed on samples to determine if trace elements present in a sample affected the threshold for void nucleation. Results show that the kinetics of damage growth at the boundary are strongly affected by stress level and impurities. It was found that the boundary selected had a similar or even lower tendency to show damage than the bulk at low pulse durations and amplitudes. As pulse duration and amplitude increased damage localized at the boundary, which was found to consist of many small voids, indicating that the boundary experienced rapid void nucleation and coalescence. The presence of impurities correlated strongly with scatter on damage evolution.

The role of interfaces on dynamic damage in two phase metals

2012

For ductile metals, the process of dynamic fracture during shock loading is thought to occur through nucleation of voids, void growth, and then coalescence that leads to material failure. Particularly for high purity metals, it has been observed by numerous investigators that voids appear to heterogeneously nucleate at grain boundaries. However, for materials of engineering significance, those with inclusions, second phase particles, or chemical banding it is less clear what the role of grain boundaries versus other types of interfaces in the metal will be on nucleation of damage. To approach this problem in a step-wise fashion two materials have been investigated: high purity copper, and copper with 1% lead. These materials have been shock loaded at 1.4 GPa and soft recovered. In-situ VISAR and post mortem metallography reveals significantly less damage in the metals with no lead. The role of lead at grain boundary triple points and its behavior during shock loading will be discussed.