Indentation Tests Research Articles

Deep Indentation Tests of Soft Materials Using Mobile and Stationary Devices.

Measurements of the properties of soft materials are important from the point of view of medical diagnostics of soft tissues as well as testing the quality of food products and many technical materials. One of the frequently used techniques for testing such materials, attractive due to its non-invasive nature, is the indentation technique, which does not puncture the material. The difficulty of testing soft materials, which affects the objectivity of the results, is related to the problems of stable positioning of the studied material in relation to the indentation apparatus, especially with a device held by the operator. This work concerns the comparison of test results using an indentation apparatus mounted on mobile and stationary handles. The tested materials are cylindrical samples of polyurethane foams with three different stiffnesses and the same samples with a 0.5 or 1 mm thick silicone layer. The study presented uses an apparatus with a flat cylindrical indenter, with a surface area of 1 cm2, pressed to a depth of 10 mm (so-called deep tests). Based on the recorded force changes over time, five descriptors of the indentation test were determined and compared for both types of handles. The tests performed showed that the elastic properties of foam materials alone and with a silicone layer can be effectively characterized by the maximum forces during recessing and retraction and the slopes of the recessing and retraction curves. In the case of two-layer materials, these descriptors reflect both the characteristics of the foams and the silicone layer. The results show that the above property of the deep indentation method distinguishes it from the shallow indentation method. The repeatability of the tests performed in the mobile and stationary holders were determined to be comparable.

Thermal runaway of Li-ion batteries caused by hemispherical indentation under different temperatures: Battery deformation and fracture

Thermal runaway (TR) of Li-ion batteries (LIBs) presents a disastrous safety hazard and a significant barrier to the wider adoption of electric vehicles (EVs). Internal short circuit (ISC) induced by mechanical abuse is one of the causes of battery TR. This paper uses hemispherical indentation tests to trigger ISC in the battery at different temperatures and studies the battery deformation and fracture mode. Results show as the initial temperature increases, the battery hardness and strength decrease, and the fracture mode of the laminar structure changes from shear fracture to localized rupture. In the shear fracture mode, the ISC homogeneously heats the battery, and it does not directly trigger TR. In the localized rupture mode, the ISC is only induced at the layers close to the indenter and generates a hot spot exceeding 200 °C, leading to the initiation of TR. Therefore, the mechanical properties of batteries under different conditions need to be studied in more detail to develop batteries that are safer under mechanical abuse.

A mechanical TiAl/TiAlN multinanolayer coating model based on microstructural analysis and nanoindentation

A finite element model reproducing the mechanical behaviour during nanoindentation tests on Ti0.67Al0.33/Ti0.54Al0.46N multilayer coatings was developed. Coatings with two different nanoperiods (10 and 50 nm) were deposited by radio-frequency magnetron sputtering from a single sintered titanium/aluminium target using the reactive gas pulsing process. X-ray diffraction and transmission electron microscopy confirmed the multilayer stacking of the coatings. The finite element models of coatings with these two stacking periods were built considering successive hypotheses: equal thicknesses for metal and nitride nanolayers stacked without transition layer, equal thicknesses stacking with a transition layer between each metal and nitride nanolayer and finally imbalanced thicknesses stacking with a transition layer. The elastic and plastic properties of the stacked nanolayers were determined on thick monolithic coatings of metal and nitride using indentation testing and the finite element model updating method respectively. The elastic-plastic properties of the interface were introduced in the multilayer model as a rule of mixtures of the metal and nitride properties using two hypotheses: parallel or serial. For 50 nm-period film, the interface has a negligible effect on the overall indentation response. On the other hand, for the 10 nm period, the imbalanced stacking model with precise knowledge of the transition layer thickness obtained by N K-edge electron energy loss spectroscopy is required to reproduce the experimental indentation curve. Compared to classical analytical models accounting for hardness, not only the hardnesses but also the indentation moduli appear to be well predicted and evaluated in this work.

Characterisation and Application of Bio-Inspired Hybrid Composite Sensors for Detecting Barely Visible Damage under Out-of-Plane Loadings.

Traditional inspection methods often fall short in detecting defects or damage in fibre-reinforced polymer (FRP) composite structures, which can compromise their performance and safety over time. A prime example is barely visible impact damage (BVID) caused by out-of-plane loadings such as indentation and low-velocity impact that can considerably reduce the residual strength. Therefore, developing advanced visual inspection techniques is essential for early detection of defects, enabling proactive maintenance and extending the lifespan of composite structures. This study explores the viability of using novel bio-inspired hybrid composite sensors for detecting BVID in laminated FRP composite structures. Drawing inspiration from the colour-changing mechanisms found in nature, hybrid composite sensors composed of thin-ply glass and carbon layers are designed and attached to the surface of laminated FRP composites exposed to transverse loading. A comprehensive experimental characterisation, including quasi-static indentation and low-velocity impact tests alongside non-destructive evaluations such as ultrasonic C-scan and visual inspection, is conducted to assess the sensors' efficacy in detecting BVID. Moreover, a comparison between the two transverse loading types, static indentation and low-velocity impact, is presented. The results suggest that integrating sensors into composite structures has a minimal effect on mechanical properties such as structural stiffness and energy absorption, while substantially improving damage visibility. Additionally, the influence of fibre orientation of the sensing layer on sensor performance is evaluated, and correlations between internal and surface damage are demonstrated.

Inverse Method to Determine Parameters for Time-Dependent and Cyclic Plastic Material Behavior from Instrumented Indentation Tests.

Indentation is a versatile method to assess the hardness of different materials along with their elastic properties. Recently, powerful approaches have been developed to determine further material properties, like yield strength, ultimate tensile strength, work-hardening rate, and even cyclic plastic properties, by a combination of indentation testing and computer simulations. The basic idea of these approaches is to simulate the indentation with known process parameters and to iteratively optimize the initially unknown material properties until just a minimum error between numerical and experimental results is achieved. In this work, we have developed a protocol for instrumented indentation tests and a procedure for the inverse analysis of the experimental data to obtain material parameters for time-dependent viscoplastic material behavior and kinematic and isotropic work-hardening. We assume the elastic material properties and the initial yield strength to be known because these values can be determined independently from indentation tests. Two optimization strategies were performed and compared for identification of the material parameters. The new inverse method for spherical indentation has been successfully applied to martensitic steel.

Parallel-beams magnetic actuator for in-situ transmission electron microscope observation of mechanical testing

Abstract Understanding the microscopic mechanisms behind mechanical fractures is essential for enhancing material properties and increasing reliability through fatigue suppression. Conventional mechanical testing methods, such as indentation tests that press a sharp needle into a specimen or tensile tests using hydraulic pumps, are unable to capture nanoscale deformations under applied forces. As a result, the microscopic mechanisms that influence mechanical properties are often inferred indirectly, and material design largely depends on the engineer’s intuition and occasional serendipity. To overcome these challenges, in-situ observation techniques utilizing transmission electron microscopes (TEMs) have been developed to enable the observation of sample deformations at the nanoscale. However, despite their high resolution, conventional TEMs are limited by a small available space -often just a few millimeters- that restricts the application of sufficient force to fracture specimens. Traditional actuation methods, such as thermal expansion, electrostatic force, and piezoelectric actuators, fail to generate significant forces within such confined spaces. In response to these limitations, our research involved the development of a micromachine with multiple parallel beams. This device leverages the Laplace force generated by an electric current passing through the beams and the magnetic field of the TEM. We demonstrated the capability to produce significant force using the magnetic field from the microscope’s magnetic lens. The actuator developed in our study successfully generated forces exceeding 50 µN, marking a significant advancement in the in-situ observation capabilities for mechanical testing.

Master Curves for Poroelastic Spherical Indentation With Step Displacement Loading

Abstract Theoretical and numerical analyses are conducted to rigorously construct master curves that can be used for interpretation of displacement-controlled poroelastic spherical indentation test. A fully coupled poroelastic solution is first derived within the framework of Biot’s theory using the McNamee–Gibson displacement function method. The fully saturated porous medium is assumed to consist of slightly compressible solid and fluid phases and the surface is assumed to be impermeable over the contact area and permeable everywhere else. In contrast to the cases in our previous studies with an either fully permeable or impermeable surface, the mixed drainage condition yields two coupled sets of dual integral equations instead of one in the Laplace transform domain. The theoretical solutions show that for this class of poroelastic spherical indentation problems, relaxation of the normalized indentation force is affected by material properties through weak dependence on a single-derived material constant only. Finite element analysis is then performed in order to examine the differences between the theoretical solution, obtained by imposing the normal displacement over the contact area, and the numerical results where frictionless contact between a rigid sphere and the poroelastic medium is explicitly modeled. A four-parameter elementary function, an approximation of the theoretical solution with its validity supported by the numerical analysis, is proposed as the master curve that can be conveniently used to aid the interpretation of the poroelastic spherical indentation test. Application of the master curve for the ramp-hold loading scenario is also discussed.

Nano-, micro- and macro-indentation tests of thermal spray WC-Ni coatings with lamellar microstructure at different particle deposition temperatures

The mechanical properties of WC-Ni coatings by HVOF thermal spraying were comprehensively evaluated by indentation tests at a wide load range of 10−1-103 N, i.e. nano-, micro- and macro-indentations. The correlation between process parameters and coating microstructure and mechanical properties was characterized via particle deposition temperature. The coating microstructure changes in reduced porosity, enhanced WC phase decomposition and better splats flattening were correlated to the particle deposition temperature rising. A porosity divergence between coating surface and cross-section was found as a quantitative anisotropy indicator to coating intrinsic lamellar microstructure formed by the splats flattening and piling up. Considering the lamellar microstructure, indentation responses on coating surface and cross-section were compared for hardness and elastic modulus evaluation below 3 N. The surface hardness is higher than that of cross-section, and both increased correlatively to the particle deposition temperature rising except for the almost constant surface hardness below 1 N. An analogous particle temperature-dependent behavior was also manifested for the elastic modulus by nano-indentation below 1 N. Interestingly, the elastic modulus by coating surface micro-indentation at 30 N presented identical particle temperature dependence to that by coating cross-section nano-indentation, both consistently representing the overall coating elastic modulus change trend verified by non-destructive ultrasonic test. Indentation fracture toughness on coating surface under 1.96 kN and on coating cross-section under 49 N was comparatively evaluated, and the values had a reverse trend of dependence on the particle deposition temperature. The particle-deposition-temperature dependent mechanical properties were interpreted by the coating intra-splats and inter-splats defects reduction with enhanced carbide-metal bonding essentially determined by the melting state of the metal binder phase, providing an insight to utilize indentation tests for characterizing thermal spray coatings.

Influence of printing parameters on part density in L-BPF of Ti-6Al-4V and correlation with static mechanical properties measured using indentation testing

Abstract A complete workflow of parameter development and process qualification of a part manufactured using laser powder bed fusion (L-PBF) AM technique requires data of porosity, pore morphology, distortion and static mechanical properties. Using a combination of two non-destructive techniques: Computed tomography and indentation testing, the influence of printing parameters on defect types and part density in L-PBF of Ti-6Al-4V is described. In addition, the results using the combined method are compared to conventional testing methods.

Surface residual stress in H-section steel beams processed by quenching and self-tempering using instrumented indentation testing

Using instrumented indentation testing, we explore the measurement of surface residual stress in H-section steel beams produced through the quenching and self-tempering (QST) process. We establish a significant correlation between the plastic pile-up behavior observed during indentation and the magnitude of surface residual stress. We thoroughly clarify the distribution of plastic pile-up and residual stress, linking their variations to non-uniform phase transformation and changes in mechanical properties resulting from the QST process. Moreover, we employ an indentation curve analysis to evaluate surface residual stress, obviating the need for direct measurements of pile-up height. These findings facilitate the measurement of non-uniform surface residual stress in H-section beams, crucial for ensuring structural integrity, yet challenging to measure in situ.

Evaluation method of dynamic indentation behavior of glass based on electromagnetic induction phenomena

AbstractContact damage of glass is one of the most crucial issues for glass products. To develop strong and tough glass products and to compare damage resistance among glass compositions, a simple method for evaluating the mechanical response of glass during contact is required not only for glass mechanists but also for glass customers and suppliers. Although it is well known that the quasi‐static Vickers indentation test is one of the simplest and most useful methods to evaluate hardness and brittleness in glass, the indentation response of glass under the indenter at higher impact velocities remains to be quantitively understood because of the difficulty of measurement and limited experimental works. In this study, therefore, the dynamic indentation behavior of soda‐lime glass is evaluated by using a lab‐made free‐drop indentation set‐up with the coils for detecting electromotive forces (EMFs). The cono‐spherical indenter made of tungsten carbide attached with a neodymium magnet was employed to generate the EMFs when the indenter passed through the coils located near the glass sample. The impact load versus indentation depth curve during the impact within a few tens of microseconds was successfully obtained both for an elastic contact and for an inelastic contact. Under an elastic condition, where no residual indent nor any cracks were left on the glass surface after the test, it is confirmed that there is almost no hysteresis in the impact load versus indentation depth curve and that the curve can be reproduced by the Hertzian analytical solution. Under an inelastic condition, on the other hand, it is found that the hysteresis in the impact load versus indentation depth curve stems from inelastic phenomena, such as plastic deformation (shear flow and/or permanent densification) and cracking. These results suggest that the dynamic indentation technique based on electromagnetic induction phenomena is a useful and effective tool for evaluating the mechanical responses of glasses during the impact.

Arc-enhanced glow discharge ion etching of WC-Co cemented carbide for improved PVD thin film adhesion and asymmetric cutting edge preparation of micro milling tools

Wear-resistant thin films on cutting tools require effective ion etching to enhance adhesion and thus extended tool service life. Arc enhanced glow discharge (AEGD) ion etching, characterized by high ionization degrees and high etch rates, was applied to ultrafine-grained WC-Co cemented carbide, commonly used for micromilling cutters. The effect of AEGD ion etching on the surface integrity of WC-Co and the resulting adhesion behavior of a TiAlSiN thin film was investigated by varying the etching time in comparison with conventional glow discharge (GD) ion etching. In addition, the impact of intensive etching on the cutting edge geometry of micro end cutters and, in turn, on the cutting performance in micromilling of hardened and annealed high-speed steel was evaluated.AEGD achieves remarkable etch rates of 12 nm/min at extended etching times, which are 100 times greater than conventional glow discharge (GD) ion etching. Prolonged AEGD ion etching for ≥30 min removes entire near-surface WC grains and exposes carbides beneath, resulting in increased surface roughness. After the etching process, polished WC-Co substrates exhibit a slight reduction in residual compressive stresses, which steadily decrease with increasing AEGD ion etching time. Furthermore, a TiAlSiN thin film demonstrates high adhesion on AEGD-etched surfaces compared to GD ion etching. Even a brief 5 min AEGD ion etching ensures the highest adhesion class according to the Rockwell C indentation test. Moreover, the intensive material removal results in significant changes in cutting edge geometry of micro end cutters, yielding substantial cutting edge rounding and an asymmetrical shape with form-factors Κ ≥ 2. In cutting tests, the resulting cutting edge geometries effectively reduce the wear formation and the associated wear-related increase in process forces during micromilling hardened and tempered powder metallurgical high-speed steel. In summary, AEGD ion etching emerges as a highly effective method for both enhancing thin film adhesion and preparing adapted asymmetrical cutting edge geometries for micromilling tools.

Quantification of artificially induced microcracks and their effects on hard rock fragmentation performance and mechanical response characteristics

Microcracks have a significant effect on the physical and mechanical properties of rocks. Inducing artificial microcracks in rocks can reduce rock strength and decrease the energy required for rock fragmentation. Nevertheless, few attempts have been made to investigate the effect of microcracks on rock fragmentation performance and mechanical behavior, especially from the perspective of microcrack quantification. For this end, we heated granite samples to induce different degrees of microcracks. However, the parameters of microcracks are difficult to control. For the purpose of accurately characterizing the distribution of microcracks, we measured the microcrack parameters in detail. We visualized microcracks using the fluorescent epoxy method and quantified the microcrack parameters by image processing. Such a method suffered at the expense of losing some of the extremely small microcracks. But, on the other hand, a much larger field of view area is assured, allowing the data to be more representative. After the quantification of microcracks, we performed indentation tests on samples containing microcracks to analyze the mechanical response of tool-rock interaction and crater parameters. The results show that the lengths of individual thermally induced microcracks are distributed between 0.2 and 1.1 mm. At higher temperatures, thermal microcracks are dominated by intragranular microcracks leading to a more uniform distribution. The presence of microcracks can affect the fracture characteristics of rocks and a threshold exists. Compared with the unheated sample, a fivefold increase in the density and total length of microcracks reduces the peak force by 88% and 54%, and the absorbed energy by about 90% and 68%, respectively. Additionally, the comprehensive parameter (i.e., fractal dimension) is not an effective parameter in analyzing microcracks, and a single absolute metric (e.g., crack density, length, number, etc.) is recommended. This study is expected to provide a new perspective to understanding the relationship between microcrack parameters and rock fragmentation, and to provide a reference for applied research on new drilling techniques.Our study enhances the efficiency of drilling in hard rocks for geothermal resources by elucidating the role of microcracks in rock fragmentation. This research aligns with the goals of sustainable and cost-effective subsurface engineering, contributing to a net-zero energy future.

Synergistic impact of corrosion pitting on the rotating bending fatigue of additively manufactured 316L stainless steel: Integrated experimental and modeling analyses

In this study, the ex-situ rotating bending corrosion fatigue behavior of laser powder bed fused stainless steel (SS) 316L has been studied incorporating experimental analyses and modeling. The findings revealed significant variations (almost 20 %) in fatigue lifetime in pre-corroded specimens relative to non-corroded (virgin) specimens because of corrosion-derived pitting phenomena on the surface. To this end, the fatigue strength of virgin (non-corroded) and pre-corroded SS 316L were recorded at 242 MPa and 203 MPa, respectively. Upon conducting the fatigue tests and extracting stress-life trends, advanced microstructural characterization and postmortem analyses were used to quantify fatigue crack behavior and fracture surface. An empirical model is also developed employing depth-sensing indentation testing, linear elastic fracture mechanics, and computer tomography scans to propose an optimum predictive trend. The analysis comparing existing models with our proposed model demonstrates reasonable agreement between experimental findings and the predicted life for the studied laser powder bed fused SS 316L material exposed to corrosion rotating bending fatigue test. The findings of this research carry important contributions to the structural integrity and longevity of marine engineering, ship construction, naval operations, and naval aviation where materials and components are exposed to cyclic loading and corrosion.

Experimental study on composite spherical-roof contoured-core (SRCC) sandwich panels under the V-shaped quasi-static indentation loading

The paper investigated the experimental study of composite spherical-roof contoured-core (SRCC) sandwich panels under a V-shaped quasi-static indentation (QSI) test. The carbon fiber, glass fiber, aramid fiber, hybrid carbon/aramid, and glass fiber chopped strand mat sheets were used to manufacture the composite cores, which used the hand layup and hot compression techniques. The polylactide (PLA) core was fabricated using fused deposition modelling (FDM). The V-shaped indenter had a 65° angle and was set at 1 mm/min as indentation speed in the experimental test. It was found that the maximum indentation deflection was 35.49 mm on the SRCC sandwich panel with a hybrid carbon/aramid core compared to other composite cores. Furthermore, it was localized fiber fracture, matrix damage, delamination, inwards fronds, and debonding damage mode on composite SRCC sandwich panels, which was visually shown at the central SRCC core unit cell. It is highlighted that aramid fiber and hybrid carbon/aramid materials can provide outstanding impact characteristics, which have great potential to be used as impact-resistant sandwich structures.

Enhancing wear resistance, anti-corrosion property and surface bioactivity of a beta-titanium alloy by adopting surface mechanical attrition treatment followed by phosphorus ion implantation

A two-step method of surface mechanical attrition treatment (SMAT) followed by phosphorous (P) ion-implantation was adopted to treat Ti-25Nb-3Mo-2Sn-3Zr (named as TLM) alloy. The initial SMAT process refined the grains from micrometer-scale to about 10–30 nm, and begot the TLM surface much rougher with apparently improved hydrophilicity. The subsequent P ion-implantation led to the formation of a hybrid structure of the TiP, β-Ti nanograins and P-interstitial amorphous in the surface layer of the TLM alloy, and resulted in a slight decrease of the surface roughness and wettability of the SMAT-processed alloy. The indentation, tribology and potentiodynamic polarization tests indicated that the SMAT procedure concurrently enhanced the microhardness, wear-resisting property and corrosion resistance of the TLM alloy, and the followed P-ion implantation could further improve these tested properties. Moreover, the P-ion implanted TLM alloy was verified to exhibit much better surface bioactivity (including biomineralization in the simulated body fluid (SBF) and in-vitro cell adhesion) as compared to the original TLM alloy. With the remarkable improvements of the wear resistance and anti-corrosion property as well as the surface bioactivity of the P ion-implanted TLM alloy, our study provides an alternative avenue to fabricating new-type Ti-based orthopedic implants with superior comprehensive performance.

Fabrication and characterization of monocrystalline-based composite Pb(Zr, Ti)O3 thin film patterned with a polycrystalline crack stopper structure

This paper presents a novel form of Pb(Zr,Ti)O3 (PZT) thin film with a structure in which monocrystalline (Mono) PZT is sectioned with narrow mesh-like polycrystalline (Poly) PZT. The motivation is to overcome the inherent brittleness of piezoelectric Mono thin films. The design assumes that the Poly pattern will stop crack propagation within the Mono area. As a proof of concept, a Mono-Poly PZT composite thin film with a 20 μm-pitch and 2 μm-wide Poly pattern was sputter-deposited on a patterned underlayer on a Si substrate. Its piezoelectric properties were close to those of pure Mono PZT thin films, while its dielectric constant was significantly lower than those of pure Poly PZT thin films. Indentation tests confirmed the Poly patterns effectively stops crack propagation, which is likely to improve the mechanical durability of the overall film.

Microstructure, mechanical properties, and wettability of CrN and CrSiCN coatings with graded architectures

Protective CrN-based coatings are of interest for applications requiring a combination of corrosion resistance and toughness. Here, the processing-microstructure-properties relationships for metallic Cr, binary CrN, and quaternary CrSiCN coatings are reported. Hexamethyldisilazane (HMDS) was used as a single-source organosilicon precursor for Si and C during plasma-enhanced magnetron sputtering (PEMS). By varying the availability of reactive species during coating growth, graded coating architectures were produced. Scanning and transmission electron microscopy revealed that as Si and C content increased, the coating microstructure evolved from a coarse, columnar growth structure (0 at.% Si), to a nanocolumnar structure (3 at.% Si), and, finally, to a dense, nanoscale structure (6 at.% Si). Coating surface topography was characterized using optical microscopy and atomic force microscopy. While the CrSiCN coating deposited at the highest HMDS flow rate exhibited the lowest nanoscale surface roughness (Rq = 6.74 nm), it also had the greatest area fraction of microscopic surface defects. Evidence of the formation of secondary Cr2N phases within the graded interlayers of the coatings was acquired from selected area electron diffraction analysis. However, the practical adhesion of the coatings, as evaluated by the Rockwell C indentation test, was not adversely affected. Nanoindentation testing revealed that greater incorporation of Si and C into the CrN-based coatings increased coating hardness from 25.4 ± 1.6 GPa to 30.7 ± 1.8 GPa and decreased apparent elastic modulus from 295 ± 14 GPa to 284 ± 12 GPa. Contact angle goniometry was conducted to determine the wettability of the coatings. It was found that sessile water contact angles decreased from 86.5° ± 1.6° to 77.3° ± 2.1° as coating Si and C content increased.

Implications of using simplified finite element meshes to identify material parameters of articular cartilage

The objective of this work was to determine the effects of using simplified finite element (FE) mesh geometry in the process of performing reverse iterative fitting to estimate cartilage material parameters from in situ indentation testing. Six bovine tibial osteochondral explants were indented with sequential 5 % step-strains followed by a 600 s hold while relaxation force was measured. Three sets of porous viscohyperelastic material parameters were estimated for each specimen using reverse iterative fitting of the indentation test with (1) 2D axisymmetric, (2) 3D idealized, and (3) 3D specimen-specific FE meshes. Variable material parameters were identified using the three different meshes, and there were no systematic differences, correlation to basic geometric features, nor distinct patterns of variation based on the type of mesh used. Implementing the three material parameter sets in a separate 3D FE model of 40 % compressive strain produced differences in von Mises stresses and pore pressures up to 25 % and 50 %, respectively. Accurate material parameters are crucial in any FE model, and parameter differences influenced by idealized assumptions in initial material property determination have the potential to alter subsequent FE models in unpredictable ways and hinder the interpretation of their results.

Effects of Crystal Orientation and External Stress on the Static Recrystallization Behavior of an Ni-Based Single-Crystal Superalloy.

The deformation mechanism and static recrystallization (SRX) behavior of an Ni-based single-crystal superalloy are investigated. Indentation tests were performed to investigate the effects of crystal orientation and external stress on SRX behavior. Following solution heat treatment, the depth of the SRX layer below the indentation increases with a deviation angle (β) from the [001] orientation. The slip analysis indicates that an increased deviation angle leads to an increase in the resolved shear stress on the slip plane and a decrease in the number of active slip systems. In addition, the variation pattern of the SRX layer depth with the deviation angle is consistent for different external stresses. The depth of the SRX layer also increases with external stress. The coarse γ' phases and residual γ/γ' eutectics obviously enhance the pinning effects on the expansion of recrystallized grain boundaries, resulting in slower growth rates of the recrystallized grains in interdendritic regions than those in dendrite core regions.