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The influence of thermal cycle stress loading on hybrid bonding, which was formed by sintering a mixture of Cu nanoparticles and a eutectic Bi-Sn solder powder, has been investigated. A Si chip and a directly bonded aluminum (DBA) substrate were bonded using the hybrid bonding layer. The bonded sample was evaluated using a thermal cycle test (− 40°C and 250°C). The degradation process of the sample during the test was observed nondestructively using synchrotron radiation x-ray computed laminography. The thermal cycle stress loading had a minimal effect on the microstructure of the bonding layer, which has a high bonding strength owing to the liquid phase sintering and high decomposition melting temperature of the Cu-Sn compound formation. This property reduced the Al deformation of the DBA substrate caused by the thermal cycle loading, resulting in the suppression of the bonding layer degradation. Therefore, hybrid bonding can be instrumental in achieving the reliable operation of power modules at high temperatures.

Probing polycrystals' stress The way that a polycrystalline material deforms is in part determined by internal stresses between and within crystal grains. Hayashi et al. developed an x-ray method for mapping the intragranular stresses in a polycrystalline material. They found surprisingly large stresses, which are important for the fundamental understanding of how these materials will fail. This method will work for other materials and provides important information for multiscale deformation modeling. Science , this issue p. 1492

Since lead-free solder was adopted for in-vehicle electronic components, a sufficient number of years have passed to allow examining the condition of lead-free solder joints in components used in the field. For this paper, using an EBSD analysis technique, solder joint degradation analysis was conducted on specimens subjected to accelerated testing and field-aged components. Degradation indicators of the level of grain refining and the amount of strain in the Sn phase in solder were obtained from specimens subjected to accelerated testing. The analysis results of field-aged components revealed increases in the degradation indicators commensurate with the age of components, thereby we were able to estimate field stress from the recovered components.

The effects of high-temperature aging on a novel hybrid bonding layer were investigated. The hybrid layer, which consisted of Cu nanoparticles and a eutectic Bi-Sn solder powder, was formed by a sintering reaction of the solid-phase Cu nanoparticles and a chemical reaction involving the liquid-phase Bi and Sn in combination. The layer was used to bond a SiC chip to a direct bonded aluminum substrate. A conventional Cu nanoparticle-based bonding layer was also prepared as a reference. Samples with these bonding layers were evaluated using the thermal aging test (225 or 250 °C, 100 h). Bonding strength and synchrotron radiation computed laminography (SRCL) measurements were performed both before and after the thermal aging test. It was observed that thermal aging greatly decreased the bonding strength of the conventional layer. In contrast, the bonding strength of the hybrid layer was reduced only slightly by the thermal aging treatment. SRCL images showed that the conventional layer exhibited numerous cracks, which acted as passages for oxidation. On the other hand, in the hybrid layer, the liquid-phase Bi and Sn densified the Cu sintering phase through the formation of an alloyed Cu-Sn phase. As a result, the hybrid layer contained fewer passages for oxidation as compared to the conventional layer and maintained its bonding strength even against thermal aging. Therefore, the hybrid layer, which is highly stable against thermal aging, will be useful for the high-temperature operation of intelligent power modules.

The degradation process in a sintered Cu nanoparticle layer was studied by synchrotron radiation computed laminography (SRCL), which allows the high-resolution nondestructive observation of internal cracks in flat devices. A Cu layer was produced by sintering Cu nanoparticles between a Si chip and a direct bonded aluminum (DBA) substrate. This layer was then stressed by applying multiple thermal cycles, after which SRCL measurements were repeatedly performed. Images of the distributions of sintered Cu densities reconstructed from the SRCL observations show cracks with tortuous shapes generated around the dense Cu nanoparticles; these cracks propagated along the direction from the DBA substrate to the Si chip during thermal stress testing. Whereas crack propagation in typical soldering materials occurs along grain boundaries, the similar process in Cu nanoparticle layers is regulated by their sintered density distributions.

The formation of high resistivity phases of nickel silicide in a small silicide area is a problem for the uniformity of the sheet resistance. It was found that implementing furnace annealing method, as the first annealing step, improves the nickel silicide sheet resistance uniformity at small areas. Low ramp rate and prolonged annealing duration by furnace anneal promote grain size growth of Ni 2 Si phase, which decreases the free energy change and suppresses the formation of high resistivity phases of nickel silicide. Increasing the first anneal temperature was also found to improve the sheet resistance uniformity of only p + active areas. Furthermore, increasing the temperature of Ni PVD stage or second anneal, promotes the formation of NiSi 2 phase.

For engineering components with cracks, it is very important to evaluate the reliability for fracture. The X-ray diffraction method is now widely used to measure non-destructively the loading and residual stresses in crystalline materials. Synchrotron radiation sources provide the X-rays with extremely high intensity as well as a narrow divergence. The high intensity X-rays with a narrow divergence enables stress measurements in a localized region. The strain distribution near the fatigue crack in the steel plate with ultrafine-grained surface layers, called SUF plates, was measured by the polychromatic X-ray from synchrotron radiation at SPring-8. The spatial resolution in the direction parallel to the crack propagation direction was 0.1 mm. The strain distributions at several applied stress levels were determined for six diffraction planes. The measured strain distribution was compared with the result calculated by the FE analysis. The average value of the measured strains for several diffraction planes agreed well with the calculated results.

The compressive stress distribution below the specimen surface of severely surface deformed steels by shot peening was investigated by using laboratory X-rays and high-energy X-rays from a synchrotron radiation source, SPring-8 in the Japan Synchrotron Radiation Research Institute. Medium carbon steel plates were heat treated in two different conditions. The Vickers hardness of materials A and B after heat treatment is 408 and 617 HV, respectively. The specimens were shot peened with fine cast iron particles of the size of 50 μm. The coverage was selected to be 5000%. For the synchrotron radiation, by using the monochromatic X-ray beam with several energy levels, the stress values at the arbitrary penetration depth were measured by the constant penetration depth method. The shot-peened specimens were fatigued under four-point bending. The improvement of fatigue strength of material A was not so large because of large surface roughness. On the other hand, for material B, the surface roughness was smaller and the fatigue strength was higher than that of ground specimens.

Three kinds of copper thin films were fabricated by RF-magnetron sputtering. The target power was selected to be 10 and 150W to change the properties of the films. Thin glass sheet was used as a substrate. For the target power of 150W, the deposition time was selected to be 7 and 40min. The thickness was 0.6μm and 2.9μm, and the grain size measured was 243nm and 450nm, respectively. The grain size of thicker film was larger than that of thinner one. On the other hand, for the target power of 10W, the thickness and grain size were 2.4μm and 54nm, respectively. The grain size depends on the target power, too. The residual stress distribution in the films was measured by X-ray method. Several methods such as the grazing incidence X-ray diffraction method, the constant penetration depth method and the conventional sin2ψ method were adopted. The measured weighted average stress increased with increasing depth. After taking the maximum value at about 0.3μm from the surface, the value decreased with increasing depth. The stress distribution near the surface in the films deposited at 150W was almost identical irrespective of thickness. On the other hand, for the target power of 10W, the stress distribution shifted to compression side. The reason could be explained by the effect of the thermal residual stress. The real stress distribution was estimated by using the optimization technique. The stress took the maximum value at 0.5μm from the surface, and was compressive near the substrate.

TiN thin films were deposited on the polyimide films by reactive RF magnetron sputtering in Ar and N2 gas atmosphere. Most of the films possess strong or fiber texture. The properties such as the fiber texture, residual stress and tensile strength of the film were estimated by using X-ray method. The fiber texture of the film was strongly influenced by the N2 gas flow ratio and changed from to with increasing gas flow ratio. This change of the fiber texture affected on the grain size, residual stress and tensile strength. As orientation become strong, the grain size and compressive residual stress increased. Stress distribution below the surface was also measured by using the constant penetration depth method and the grazing incidence X-ray diffraction (GIXD) method. Compressive residual stress was measured near the substrate and surface of the film. On the other hand, tensile residual stress was observed in the intermediate region. In-situ tensile tests were carried out for each specimen in order to estimate the strength of the films. The maximum X-ray stress measured during tensile loading process increased with decreasing grain size. When compared at the same grain size, oriented films tend to show the larger strength than oriented films.

The internal stress in solid-oxide fuel cells (SOFCs) was evaluated during the thermal, reduction and re-oxidation cycles by using high-energy X-ray synchrotron radiation of about 70 keV at Beam line BL02B1 of SPring-8. The oxidized cell has a compression of about 400 MPa in the c-ScSZ electrolyte and a tension of 50-100 MPa in the NiO-YSZ anode at room temperature. In-situ measurement during the thermal cycle in an air atmosphere, the internal stress decreased with increasing temperature, becoming approximately zero at 1000 K. After the thermal cycle, the internal stress returned to its initial value. In the measurement during the reduction cycle, the internal stress was smaller than that measured during the cooling cycle after the anode was reduced from NiO-YSZ to Ni-YSZ. In the re-oxidation cycle of a reduced cell, the internal stress in the electrolyte went into tension above 800 K when the anode was re-oxidized from Ni-YSZ to NiO-YSZ. This tensile stress is responsible for possible fracture of unit cells in SOFCs.

The compressive stress distribution below the specimen surface of a nanocrystalline medium carbon steel was investigated nondestructively by using high-energy X-rays from a synchrotron radiation source, SPring-8 (Super Photon ring-8 GeV) in the Japan Synchrotron Radiation Research Institute. A medium carbon steel plate was shot-peened with fine cast iron particles of the size of 50 μm. By using the monochromatic X-ray beam with three energy levels of 10, 30 and 72 keV, the stress values at the arbitrary depth were measured by the constant penetration depth method. The stress was calculated from the slope of the sin2ψ diagram. Measured stress corresponds to the weighted average associated with the attenuation of the X-rays in the material. The real stress distribution was estimated by using the optimization technique. The stress distribution was assumed by the third order polynomial in the near surface layer and the second order polynomial. The coefficients of the polynomials were determined by the conjugate gradient iteration. The predicted stress distribution agreed well with that measured by the conventional surface removal method.

Fatigue test system for thin sheets was constructed using an ultrasonic fatigue testing machine. Specimens were fixed at the location where the displacement amplitude became the maximum. The specimen was fatigued under full-reverse bending. Displacement at a fixed edge of the specimen and the deflection of the specimen were measured with a laser displacement gage during fatigue tests. Modal analysis was carried out to determine the dimensions of the specimen and to calculate the applied stress on the basis of the flexural displacement amplitude. The maximum stress was observed on the free side edge near the fixed edge. Two kinds of martensitic stainless steel sheets, SUS301-CSPH and SUS632J1-CSP, were fatigued with the fatigue test system. The thickness of the specimen was 83 and 106μm, respectively. The 3rd vibration mode was selected for fatigue tests. The fatigue cracks initiated from the free side edge of the specimen. For the case of shorter fatigue life, fatigue strength for both stainless steels were almost identical. On the other hand, for longer fatigue life, fatigue strength of SUS632J1 is higher than that of SUS301.

Both EBSD and AFM methods were used to investigate the active slip systems and fatigue crack initiation behavior in face-centered cubic polycrystalline metal, austenitic stainless steel, SUS316NG, under cyclic torsional loading. Most active slip planes are the primary slip planes having the largest Schmid factor. Grains with slip band cracks or transcrystalline cracks have larger Taylor's factors. On the basis of EBSD and AFM observations, h, the depth of intrusion vertical to the surface, S, and the component of the slip displacement perpendicular to the surface trace, SB, showed a sharp increase at the onset of crack initiation. The critical value of SB at crack initiation was 170 nm.

Electron backscattering diffraction, EBSD, technique as well as atomic force microscopy, AFM, was employed to investigate fatigue damage mechanism in ultrafine-grained copper processed by equal channel angular pressing, ECAP. The fatigue damage evolution under axial tension compression was investigated. The results show that linearly shaped fatigue damage was introduced in the scale of micrometers in spite of the average grain size of 300 nm. The linear damage was randomly oriented when the shear direction of the last ECAP-pressing in perpendicular to the loading axis. The orientation analysis by EBSD revealed that the linear damage is introduced in the area with the same crystallographic orientation in the direction of the maximum Schmid factor as in the slip deformation in coarse-grained materials. The comparison before and after fatigue tests shows the grain coarsening in the area where large linear fatigue damage was formed. It is considered that strain concentration at the edge of the slips introduced in a relatively coarse ultrafine grain causes the grain rotation and deformation in the adjacent nano-sized grains, resulting in the grain coarsening and subsequent propagation of the slips in the order of micrometers.

Fatigue crack propagation tests of PZT ceramics were conducted by using 4 point bending of single edge-notched specimens under cyclic and static loading conditions. Domain switching (DS) in the vicinity of fatigue cracks in PZT ceramics was evaluated from the intensity ratio of 002 to 200 diffractions measured by X-ray microdiffraction. The change of the crack propagation rate with crack extension can be divided into three regions. In region I, the crack propagation rate decreases with increasing crack length, and then turn to increase in region III. In region II, the propagation rate is nearly constant. The crack propagation rate was higher in the order of cyclic fatigue with frequency of 30Hz, cyclic fatigue with 0.3Hz and static fatigue. DS near the crack tip was divided into two kinds : one is the residual DS left without load and the other was reversible during loading-unloading cycle. The amount of residual DS increased with crack extension. The decrease of crack propagation rate in region I was caused by the development of DS and interlocking between crack faces. In region III, the increase of the applied stress intensity factor became dominant, then accelerated crack propagation. Region II was the transitional region. The fatigue fracture surface made by static fatigue had the largest amount of residual DS and the largest fraction of intergranular fracture.

This paper reports a study on crystal rotation in a single crystal copper specimen by a knife edge tool indentation. A rectangle specimen was made from a single crystal copper ingot so that its edges correspond with crystal direction. Indentation tests were conducted on its {001} plane by using a knife edge tool, where the direction of tool edge were set in various direction on the {001} plane. Cross sections of the indent grooves were analyzed by FIB. Results show that indent depth depends on tool direction. Then, distribution of crystal orientation around an indent groove was analyzed by EBSD. Spin vectors of the crystal structure were calculated from EBSD data. Distribution of spin vector revealed that crystal rotation around an indent groove is separated into two zones ; the upper zone rotates to inside direction but the lower zone rotates to outside direction. Also, most of the spin vectors indicates [100] crystal orientation regardless of tool direction.

The phase stresses under loading in a monolithic aluminum alloy and an aluminum alloy reinforced with silicon carbide particles were measured by the neutron diffraction method. Under uniaxial loading, the longitudinal and transverse strains in each constituent phase were measured. The diffraction elastic constants for each diffraction plane were investigated as a function of the diffraction intensity by TOF. Single peak analysis was carried out for each diffraction profile. The measured results were compared with the theoretical micromechanical models such as the self-consistent and Mori–Tanaka method using the Eshelby theory (MTE). The accuracy of the elastic constant strongly depends on the diffraction intensity. In order to confirm the rule of mixture, the phase stress was measured by the X-ray method. The macrostress calculated by the rule of mixture agreed very well with the applied stress. Finally, fatigue damage was evaluated by the neutron method. The change of the full width at half maximum in the aluminum phase during fatigue is small. On the other hand, the value in the SiC phase increased steeply just before fracture.

A shape memory alloy TiNi actuator was used to suppress mode I and II propagation of interlaminar cracks in carbon fiber reinforced plastics, CFRP. Pre-strained TiNi sheets were attached on the surface of CFRP with the direction of the actuation strain parallel to the crack propagation direction. They were heated to introduce the recovery strain for the suppression of interlaminar crack propagation under static loading of mode I or II and cyclic loading of mode I. The change in fracture toughness and crack propagation rate with the application of the recovery strain was investigated. The results show that the fracture toughness increased due to the actuation strain and stiffness increase by the attachment of the actuator in both mode I and II. The average fracture toughness after the introduction of the actuation strain was 2.8 times larger than the initial value without the effect of stiffness increase in mode I. The improvement was more evident in mode I than in mode II, where the friction between fracture surfaces was more effective. The fatigue crack propagation rate was remarkably decreased by the introduction of the actuation strain. The difference in the crack propagation rate between specimens with and without actuators was more than an order of magnitude after the activation of the actuator. The introduction of the actuation strain by TiNi sheets attached parallel to the fiber direction of CFRP was found to be effective for the suppression of fatigue crack propagation.

Single-edge-notched specimens of ultrafine-grained steel were fatigued. The mean grain size of the steel is about 2 micrometers. Propagation behavior of fatigue cracks was observed with the crack closure. The resistance of the crack propagation of ultrafine-grained steel was larger than that of conventional steels. The crack closure acted as an important role for the larger resistance of fatigue crack propagation. After fatigue tests, stress distribution near the fatigue crack was measured by monochromatic X-rays from synchrotron radiation. The irradiated area was 100 µm x 100 µm. Residual and loading stress distributions ahead of the crack tip and on the crack wake was measured at the maximum stress intensity factor and zero applied load. The stress was determined by sin2ψ method. The measured stress was compared with the value calculated by FEM and the fatigue crack propagation model. The stress distribution at the maximum load and residual stresses agreed very well with the calculated results. The crack opening stress calculated by the residual stresses agreed with the experimental result.

The misorientation introduced into an austenitic stainless steel (SUS 316) by plastic deformation was masured with the electron back scattering diffraction (EBSD) and the X-ray diffraction (XRD) techniques. Three parameters related to miorientation distribution, i.e. grain orientation spread (GOS), grain average misorientation (GAM) and kernel average misorientation (KAM), were calculated from the orientation measurements by EBSD. The misorienation between neighboring measured points, KAM, was larger close to the grain boundary where the slip propagation was difficult. The average of misorientation between neighboring points within one grain is GAM. The GAM value averaged over the measured reagion increased proportionally with the plastic strain to about 20%, and leveled off at higher strains. The average of the misorientation spread within one grain, GOS, also showed similar increase like GAM. The total misorientation of a grain measured by XRD also showed a proportional increase with the plastic strain to about 10%, and it was difficult to measure the total misorientation above that strain because Debye ring became continuous ring. Both EBSD and XRD can be used as a tool to measure the plastic strain in the local area, and the limit of strain to be measured was 30% for the former and 10% for the latter.

Ultrafine-grained specimens with the average grain size of less than 2µm and medium-grained specimens were prepared from steel plates produced by an advanced thermo-mechanical control process. The smooth specimens were fatigued under axial tension compression at room temperature in air. The fatigue crack initiation process was investigated by orientation imaging microscopy based on EBSP in combination with atomic force microscopy and scanning electron microscopy. The results show that fatigue cracks initiated in the simple slip lines in the medium-grained specimens. On the other hand, in the ultrafine-grained specimens, complex slip deformation was formed in the vicinity of the grain boundaries prior to the fatigue crack initiation. Fatigue cracks were nucleated at the boundary between the grains with the concentrated complex slip deformation. The crystallographic orientation analysis revealed that the complex slip deformation was formed by the cross slip of active slip systems with the largest Schmid factors. It was found that the relation between the fatigue limit and grain size of the ultrafine-grained specimens does not conform to the Hall-Petch relation of conventional ferritic-pearlitic steel due to the texture and cross slip.

The propagation behavior of fatigue cracks emanating from pre-cracks was numerically simulated to evaluate the development of crack closure with crack growth. Plasticity-induced crack closure was analyzed for two dimensional through cracks and penny-shaped cracks in plane stress, plane strain and Tresca's yield condition. The plastic constraint factor of penny-shaped cracks in Tresca's yield condition decreases with increasing applied stress. When compared at the same amount of crack extension, the development of crack opening stress with crack extension for through cracks and penny-shaped cracks in plane strain condition was nearly close. The crack opening stress intensity factor at the threshold can be simply approximated as a function of the applied stress and the amount of crack extension. The cyclic resistance-curve method was used to predict the fatigue thresholds of pre-cracked components. When compared at the same initial crack length, the fatigue limit for fracture of penny-shaped cracks in plane strain condition is larger than that of through cracks. On the other hand, the relation between the initial crack length and the fatigue limits for fracture is nearly independent of the defect type.

The fatigue strength of reinforced and unreinforced aluminum alloys with silicon carbide particles or whiskers increases in proportion to the ultimate tensile strength. The proportional constant is slightly larger for composites than for unreinforced alloys. The threshold stress intensity range ΔKth tends to decrease with increasing tensile strength. When compared at the same tensile strength, ΔKth tends to be larger for composites than for unreinforced alloys. The effective threshold stress intensity range, ΔKeffth, is fairly constant irrespective of the tensile strength. The characteristic defect sizes, a′0 and a0, tend to be smaller with increasing tensile strength. When compared at the same tensile strength, a′0 is larger for composites, which indicates a low notch sensitivity of composites.

Smooth and notched specimens of reactive-sintered Ti-45at%Al-1.6at%Mn intermetallic compound with lamellar and equiaxed γ microstructures were fatigued under cyclic axial tension compression at room temperature. The effect of microstructures on the crack propagation behavior was investigated in comparison with cast Ti-47.2at%Al with larger grain size.Fatigue crack paths were tortuous in the lamellar microstructure in contrast to the straight crack paths in the equiaxed γ microstructure. In comparison with cast TiAl, reactive-sintered TiAl exhibited higher crack propagation rates when compared at the same stress intensity range. The values of stress intensity range at threshold were greater in cast TiAl. Those threshold values had a tendency to increase with the roughness of the fracture surface. The rate of increase in crack opening stress intensity factor at threshold with non-propagating crack length was smaller than that of cast TiAl. Predicted fatigue limits for crack initiation and propagation based on the fatigue-crackgrowth resistance-curve method were in agreement with the experimental results. The fatigue limits of notched specimens were smaller than those of cast TiAl in spite of the superior mechanical properties of reactive-sintered TiAl.

The propagation behavior of microstructurally small fatigue cracks was numerically simulated on the basis of the plasticity-induced crack closure model. By assuming that the crack growth rate was controlled by the crack tip openin displacement, ΔCTOD, the simulation of the propagation of a crack nucleated in the weakest grain was conducted. The grain size, the critical value of microscopic stress intensity factor at grain boundary and the frictional stress of dislocation motion were given as random variables following two-parameter Weibull distributions. When the crack approached grains with higher frictional stresses, ΔCTOD decreased, however the crack opening stress, σop, increased. The grain boundary blocking and higher frictional stress act as a resistance of crack propagation. The scatters of ΔCTOD and σop diminished as the crack length becomes longer. When compared at the same stress intensity range, ΔCTOD increased with stress ratio. On the other hand, the relation between ΔCTOD and the effective stress intensity range was unique irrespective of the stress ratio. The crack propagation life was calculated as a function of ΔCTOD. The life of the crack propagation and fatigue limit increased with decreasing grain size and with increasing critical value of microscopic stress intensity factor. The effect of the stress ratio on the fatigue limit was analyzed by the simulation. The fatigue limit as a function of the mean stress follows a modified Goodman relation.

✓ The authors describe two occurrences of idiopathic spinal cord herniation, an entity that has been reported previously in only 11 cases. The patients described in this report presented in midlife with Brown—Séquard syndrome. Computerized tomography myelography and magnetic resonance (MR) imaging showed ventral displacement of the spinal cord with no apparent dorsal mass. Intraspinal cerebrospinal fluid (CSF) flow studies in which phase-contrast pulse sequence cine MR imaging was used displayed a normal pattern dorsal to the spinal cord. Percutaneous intrathecal endoscopic observation did not disclose dorsal intradural cysts, but ventral adhesions were seen between the spinal cord and the dura. Microsurgical intradural exploration revealed ventrolateral herniation of the cord and a ventral root through a dural defect into an epidural arachnoid cyst. The adhesions were released, the cord was repositioned intradurally, and the dural defect was patched. The patients showed gradual improvement postsurgery, as did most of the patients in the previously reported cases. The CSF flow and endoscopic studies were found to be particularly informative, and dural patching with surgical membrane is recommended.

An engineering diffractometer for investigations of stresses and crystallographic structures within engineering components is now being developed at J-PARC project. The diffractometer is designed to view a decoupled-poisoned liquid H 2 moderator providing neutrons with good symmetrical diffraction profiles in the acceptable wavelength range. The diffractometer will have a primary flight path of 40 m and a secondary flight path of 2.0 m for 90° scattering detector banks, and will include a curved supermirror neutron guide to avoid intensity loss due to the long flight path and to reduce backgrounds from fast neutrons and gamma rays. Therefore, stresses with sufficient accuracies in many engineering studies are quite promising. The diffractometer involves a sample translator which is able to handle large and heavy real industrial-scaled components. Detailed design works are being continuously promoted. The optimization of the diffractometer has been performed with a Monte Carlo simulation, and an appropriate resolution of less than 0.2% in Δ d / d has been confirmed.

A microstructural effect on the fatigue crack growth behavior of long cracks in cast Ti 47.2 (at%) Al at room temperature was investigated. Various heat treatments were employed to produced by the nearly lamellar, duplex and near-γ microstructures. The fatigue crack growth resistance exhibited by the nearly lamellar microstructure is superior to that of the duplex and near-γ microstructures. This property of the nearly lamellar microstructure is attributed to crack branching, microcracking, and roughness-induced crack closure due to tortuous crack paths and to crack shielding due to crack bridging. The crack propagation behavior strongly depends on its volume fractions of lamellar and equiaxed grains.

In this paper, plastic deformation properties and recrystallization process of single crystal metallic materials are studied, where the scale of deformation is in the micrometer range. Nano plastic forming test was conducted on single crystal specimens using a 60 degree wedge tool. Cross-sections of the indented grooves were produced by FIB machining, and variation of their crystal orientation in the plastic deformation zone was analyzed by EBSD measurement. Furthermore, the nano formed specimens were annealed under various conditions, and recrystallized grains in the vicinity of indented grooves were observed by SIM. The effects of plastic deformation and annealing conditions on recrystallization process are discussed.