Automated Ball Indentation Test Research Articles

Influence of heat treatment on the microstructure evolution and elevated temperature mechanical properties of Hastelloy-X processed by laser directed energy deposition

The microstructure and elevated temperature mechanical properties of Hastelloy-X (Hast-X) bulk structures built using Laser Directed Energy Deposition (LDED) based Additive Manufacturing is investigated in as-built (AB) and heat-treated (HT) conditions. Microscopic analysis show the presence of fine cellular and dendritic growth in AB samples and recrystallized and coarsened equiaxed grains in HT samples. The AB samples revealed random grain orientation with slightly preferred texture along the< 100 >plane, unlike in the HT samples. Further, the AB samples revealed the elemental segregation of Mo, Si and C and precipitation of Mo-rich carbides, which are absent in the HT samples. Micro tensile test results at ambient temperature showed excellent agreement with the mechanical properties obtained from automated ball indentation (ABI) tests of LDED built Hast-X in AB condition. Subsequently, ABI tests are used to evaluate the mechanical properties in AB and HT conditions from ambient temperature to 873 K. It is observed that the strength and ABI hardness decreased with increase in test temperature, while the strain hardening exponent and uniform ductility showed an opposite trend. The yield strength (YS) of AB sample is higher than conventional sample, while YS of HT sample is similar to the YS of conventionally processed wrought Hast-X taken from literature at all test temperatures. Further, the indentation size and material pile up around the indentation also increased with heat-treatment and increase in the test temperature. This study paves a way towards the successful deployment of LDED built Hast-X for various applications in hostile conditions.

Experimental Studies on Laser Additive Manufacturing of Inconel-625 Structures Using Powder Bed Fusion at 100 µm Layer Thickness

This paper reports process development and material characterization studies of Inconel-625 (IN625) using laser powder bed fusion (LPBF)-based additive manufacturing at higher layer thickness (100 µm). Conventionally, layer thickness up to 50 µm is used in LPBF due to process instability issues at higher layer thickness. However, successful development of LPBF with higher layer thickness will yield higher build rate. Therefore, systematic parametric investigations are carried out by varying laser power (P), scan speed (v) and hatch spacing (h) from 150 to 450 W, 0.02 to 0.08 m/s and 0.150 to 0.350 mm, respectively, with 100 µm layer thickness. The obtained results are compiled as a function of combined parameter—laser energy density (LED). Samples with relative area density > 99% are achieved for LED of 150, 240 and 360 J/mm3. Geometrical studies show that the deviation from nominal length and range of height of the sample decreases and increases with an increase in LED, respectively. X-ray diffraction shows the presence of face-centered cubic γ-phase at all the conditions with fine crystallites. The microstructure is a mix of cellular and dendritic with the primary arm width increasing with LED. Micro-hardness studies show that the hardness decreases slightly with an increase in LED, while automated ball indentation tests indicate the increase in energy storage capability with increase in LED. The micro-hardness, yield strength and ultimate tensile strength of LPBF built IN625 structure at 100 µm are found to be higher than that of the conventional and laser directed energy deposited IN625 structures and similar to that of the LPBF built IN625 structures at lower layer thickness. The study provides insight into LPBF of IN625 at 100 µm layer thickness and paves way for fabricating components at higher layer thickness with favorable mechanical properties.

Experiment characterization and formulation estimation of tensile properties for selective laser melting manufactured 304L stainless steel

Additive manufacturing (AM) becomes more and more prevalent and offers enormous benefits on account of its inherent layer-by-layer nature. Material characterizations of such printed metal alloy are essential and necessary to understand the unique process-properties maps of different structures. From which, the tensile performance is one of the most demanding and concerning behaviors by diverse requirements from industries. In this study, experimental methodologies (uniaxial tensile testing and automated ball indentation testing) and constitutive relations (Holloman, Swift, Voce, and Ludwigson formulation) studies were performed to AISI 304L stainless steel. A comparative study was presented between selective laser melting fabricated parts and conventional counterparts. Outputs indicated the Swift formulations provided the best estimations of the flow curve. All four formulations provided reasonable estimations of ultimate tensile strength. Anisotropic study in tensile strength and work hardening exponent with varying build orientations were correlated to grain structures. The non-destructive automated ball indentation test yielded the acceptable tensile strength with the accurate determination of plastic chordal diameter. However, the automated ball indentation test demonstrated an insensitive manner on the anisotropy.

Finite Element Simulation of Plastic Deformation of 316LN Stainless Steel during Automated Ball Indentation Test

Abstract The automated ball indentation (ABI) technique has been used to obtain the tensile properties of 316LN stainless steel (SS). In order to study the complex state of stress prevailing during plastic deformation in the ABI test specimen under spherical indenter, finite element analysis (FEA) was carried out on an axisymmetric model of ABI indenter and specimen. The stresses that were obtained along the surface confirmed the requirement of finite interplanar spacing to be maintained between successive indentations. The evolution of plastic zone has been studied using von Mises yielding criterion. The plastically deformed zone existed up to the depth approximately equal to 1.5 times the diameter of indenter. The accumulation of strain in the specimen close to the indenter tip was inferred similarly from both FEA and the strain map experimentally determined using electron backscatter diffraction. The stress–strain curves for 316LN SS at 298 K and 923 K were predicted by combining FEA procedures with ABI testing.

Quantitative evaluation of mechanical properties of machined surface layer using automated ball indentation technique

Machining-induced microstructure alteration in the machined surface layer possibly tends to result in the change of mechanical properties in this area that are different from the bulk material. It is very important to evaluate quantitatively mechanical properties of machined surface layer. In the present research, the nondestructive automated ball indentation (ABI) technique equipped with stress-strain microprobe system was employed to evaluate the mechanical properties of the machined surface layer generated by hard milling of AISI H13 steel. Through performing ABI tests, the mechanical properties including the true stress-strain curve, yield strength, ultimate tensile strength (UTS), strain hardening exponent and Brinell hardness were quantitatively acquired before and after hard milling. In addition, the fracture toughness can be determined by analyzing the continuous loading and unloading curves on the basis of the continuum damage mechanics (CDM). It indicates that the ABI technique can be exploited as a nondestructive technique for mechanical property evaluation of machined surface layer.

Nondestructive measurements of flow properties of nanocrystalline Al-Cu-Ti alloy using Automated Ball Indentation (ABI) technique

The Stress-Strain Microprobe® (SSM) system and its Automated Ball Indentation® (ABI®) test technique were applied in the present study for the purpose of determining the flow properties of the alloy under study in a non-destructive manner. ABI tests were applied at 21 °C to the consolidated nanocrystalline Al-10 wt% Cu-5 wt% Ti alloy samples which were subjected to three and six hours of milling. The samples processed for six hours of milling were further tested at elevated temperatures of 200 °C and 400 °C. The results of the ABI tests of the alloy under study include the indentation load versus depth of penetration curves, true stress versus true-plastic-strain curves, determination of yield strength curves, ultimate tensile strength values, and ABI Brinell hardness number (BHN). X-Ray Diffraction (XRD) was applied to investigate the microstructure of the Al-10 wt% Cu-5 wt% Ti alloy subjected to different milling time before and after consolidation. XRD analysis includes identification of the main phases/elements present and calculating the crystallite size in the processed alloy for 3 and 6 h of milling before and after consolidation. Apreo Field Emission Scanning Electron Microscope was applied to characterize the size and morphology of the indentation area after conducting the ABI tests. In addition, the same technique was applied to reveal the elemental distribution in the indentation area of the tested samples.

High temperature tensile properties of 316LN stainless steel investigated using automated ball indentation technique

Type 316LN stainless steel (SS) is the principal structural material for the components of sodium cooled fast reactors operating under elevated temperature conditions. In order to assess the degradation in strength of service exposed components using a small specimen testing technique such as automated ball indentation (ABI), it is necessary to carry out prior detailed ABI studies on the virgin material. In this investigation, the tensile behaviour of as-received 316LN SS were investigated at several temperatures in the range 298–973 K using ABI technique. The load-depth of indentation data measured from ABI tests was analyzed using semi-empirical relationships to obtain the tensile properties. The yield stress and the flow curves were determined by correlating ABI results with corresponding uniaxial tensile test results. Trend curve for tensile strength with temperature, as estimated from ABI tests, exhibited a plateau region in the temperature around 823 K, similar to uniaxial tensile tests. The variations of strength coefficient, strain hardening exponent, yield ratio, hardness and uniform ductility with temperature were evaluated from ABI tests. The ABI technique was found to estimate the influence of temperature on tensile properties sensitively.

Influence of some Test Parameters on Automated Ball Indentation Test Results

Automated Ball Indentation (ABI) technique has the potential to evaluate tensile and fracture properties of materials by testing a small volume of material. ABI testing involves various parameters such as surface finish of test specimen, maximum depth of indentation, number of loading-unloading cycles and material of indenter. As ABI test is yet to be standardized, it is necessary to assess and understand the consequences of the various test parameters. In this investigation, the influence of the above test parameters on the tensile properties of 316LN SS has been investigated at 298 K. It was found that by increasing the maximum depth of indentation, number of loading-unloading cycles and surface finish of test specimen at the cost of time and efforts, ABI results were not altered significantly. The selection of indenter material has to be done judiciously, according to test temperature.

Evaluation of strength property variations across 9Cr-1Mo steel weld joints using automated ball indentation (ABI) technique

The variations of strength properties across 9Cr-1Mo steel weld joints fabricated by different arc welding processes such as shielded metal arc welding (SMAW), tungsten inert gas (TIG) and activated tungsten inert gas (A-TIG) have been evaluated employing automatic ball indentation (ABI) technique. ABI tests were conducted at 298K across various zones of the weld joints comprising of base metal, weld metal, heat affected zone (HAZ) and intercritical HAZ (ICHAZ) regions. The flow curves obtained from ABI tests were correlated with corresponding conventional tensile test results. In general, the tensile strength decreased systematically across the weld joint from weld metal to base metal. Inter critical HAZ exhibited the least strength implying that it is the weakest zone. The incomplete phase transformation in the ICHAZ during weld thermal cycle caused the softening. The A-TIG weld metal exhibited higher UTS and strain hardening values due to higher carbon in the martensite. The strain hardening exponent exhibited only slight variation across the various regions of the weld joints. A-TIG weld joint exhibited higher weld metal and HAZ strength, marginally higher UTS to YS ratio in the weld metal and HAZ compared to that of the other two processes. Hence, among the three welding processes chosen, A-TIG welding process is found to be superior in producing a 9Cr-1Mo steel weld joint with better strength properties.

Constitutive Equations and ANN Approach to Predict the Flow Stress of Ti-6Al-4V Alloy Based on ABI Tests

The flow behavior of Ti-6Al-4V alloy was studied by automated ball indentation (ABI) tests in a wide range of temperatures (293, 493, 693, and 873 K) and strain rates (10−6, 10−5, and 10−4 s−1). Based on the experimental true stress-plastic strain data derived from the ABI tests, the Johnson-Cook (JC), Khan-Huang-Liang (KHL) and modified Zerilli-Armstrong (ZA) constitutive models, as well as artificial neural network (ANN) methods, were employed to predict the flow behavior of Ti-6Al-4V. A comparative study was made on the reliability of the four models, and their predictability was evaluated in terms of correlation coefficient (R) and mean absolute percentage error. It is found that the flow stresses of Ti-6Al-4V alloy are more sensitive to temperature than strain rate under current experimental conditions. The predicted flow stresses obtained from JC model and KHL model show much better agreement with the experimental results than modified ZA model. Moreover, the ANN model is much more efficient and shows a higher accuracy in predicting the flow behavior of Ti-6Al-4V alloy than the constitutive equations.

Uporaba ABI tehnike za merjenje mehanskih lastnosti aluminijevih zlitin: vpliv pogojev toplotne obdelave na mehanske lastnosti zlitin

Effects of chemical composition and heat treatment on the microstructures and mechanical properties were investigated with automated ball-indentation tests, scanning and transmission electron microscopy, and energy-dispersive X-ray analysis. In this work, the automated ball-indentation (ABI) technique was compared with the standard mechanical tests. The ABI method is based on load-controlled multiple indentations into a polished surface by a spherical indenter. The indentation depth is progressively increased to the specified maximum limit with intermediate partial unloading. This technique allows us to measure the yield strength, the stress-strain curve, the strength coefficient and the strain-hardening exponent. For all the test materials and conditions, the ABI-derived results were in very good agreement with those obtained with conventional standard test methods. We analyzed the effect of heat treatment on the alloys with different chemical compositions. Heat treatment leads to changes in the mechanical properties of the alloys, which are the results of several processes.

Comparison of ABI Technique and Standard Methods in Measuring Mechanical Properties of Aluminium Al-aloys

Mechanical properties and chemical composition of aluminium alloys were investigated by automated ball indentation tests, scanning electron microscopy and energy dispersive X-ray analysis.In this work, Automated Ball Indentation (ABI) technique was compared with the standard mechanical tests. ABI method is based on the load controlled multiple indentations into a polished surface by a spherical indenter. The indentation depth is progressively increased to a maximum user specified limit with intermediate partial unloading. This technique allows to measure the yield strength, stress-strain curve, strength coefficient and strain hardening exponent.For all these test materials and conditions, the ABI derived results were in very good agreement with those obtained from conventional standard test methods.

Uporaba tehnike ABI za merjenje mehanskih lastnosti aluminijevih zlitin: vpliv kemijske sestave na mehanske lastnosti zlitin

The effects of the chemical composition on the microstructure and mechanical properties were investigated using automated ball-indentation tests, scanning electron microscopy and energy dispersive X-ray analysis. It was observed that the mechanical properties change with the presence of the eutectic and varying excess content of elements. In this work, the automated-ball-indentation (ABI) technique was compared with the standard mechanical tests. The ABI method is based on controlled multiple indentations into a polished surface by a spherical indenter under load. The indentation depth is progressively increased to the maximum, user-specified limit, with intermediate partial unloading. This technique allows to measure the yield strength, stress-strain curve, strength coefficient and strain-hardening exponent. For all these test materials and conditions, the ABI-derived results were in very good agreement with those obtained with the conventional, standard test methods.

Comparison of Conventional Mechanical Testing with Innovative Techniques for Determination of Mechanical Properties of Nuclear Power Plant Components Materials

Within the nuclear power plant operational life management, components lifetime extension requires information on structural material degradation. Innovative testing methods of Small punch testing and Automated ball indentation test are based on the determination of material properties from sub-sized specimens. Present paper is focused on the employment of these techniques in the NPP irradiated materials testing and evaluation at the accredited hot cell testing laboratory of ÚJV Řež, a. s., Mechanical testing department. Comparison with the testing results from the conventional methods is depicted.

Evaluation of variation of tensile strength across 316LN stainless steel weld joint using automated ball indentation technique

Tensile strength variation across 316LN stainless steel fusion welded joint comprising of base metal, deposited weld metal and heat affected zone (HAZ) has been evaluated by Automated Ball Indentation (ABI) technique. Automated Ball Indentation tests were conducted on the various zones of the steel weld joint at 300, 523 and 923 K. The flow curves obtained from ABI results were consistent with corresponding conventional uniaxial tensile test results. The HAZ exhibited higher tensile strength than the other regions of the steel weld joint at all investigated temperatures. The ratio of ultimate tensile strength to yield stress (YS), which represents the work hardening behaviour, increased with an increase in temperature for the base metal and HAZ; whereas it remained nearly the same for the weld metal.

A comparative study on Johnson–Cook constitutive modeling for Ti–6Al–4V alloy using automated ball indentation (ABI) technique

In this study, automated ball indentation (ABI) technique has been employed to explore the flow behavior of Ti–6Al–4V alloy at low strain rates and elevated temperatures. Isothermal ABI tests have been performed in a wide range of temperatures (293K, 493K, 693K, and 873K) and strain rates (10−6, 10−5 and 10−4s−1). Based on the experimental true stress–plastic strain data derived from the ABI tests, Johnson–Cook (J–C) constitutive model has been employed to predict the flow behavior of Ti–6Al–4V alloy at low strain rates and elevated temperatures. A comparative study has been made to verify the applicability of current J–C models at low strain rate based on finite element method (FEM). The results show that the predicted values by the Johnson–Cook constitutive model agree well with the experimental data, and the automated ball indentation (ABI) technique could give a precise prediction of the flow behavior of Ti–6Al–4V alloy at low strain rates and elevated temperatures.

Implementation of Semi-Destructive Mechanical Testing Techniques for Quantification of Irradiated NPP Components Materials Operational Degradation

In the terms of nuclear power plant operational life management, current trend of components lifetime extension requires precise and credible information of structural material degradation. Present-day standard conventional methods of mechanical testing are usually based on the use of large specimens and higher consumption of testing material, whose availability and volume is often limited. For determination of material properties, sampling of the necessary volume of material is in most cases connected with affecting the integrity or even destruction of the assessed component. Moreover, several components are not usually covered surveillance programs, e.g. reactor pressure vessel internals.Innovative testing methods of Small Punch Testing (SPT) and Automated Ball Indentation Test (ABIT) are based on the determination of material properties from miniaturized testing specimens and their semi-destructive approach is very promising for the possibility of present data base of irradiated materials testing results enlargement and enable the option of component in- situ testing (ABI testing). Presentation is focused on description of the process of employment of these techniques in the process of irradiated NPP materials testing and evaluation at the accredited hot cell testing laboratory of UJV Rez, Mechanical Testing Department. Comparison with testing results from conventional mechanical testing methods is also depicted.

Determination of correlation parameters for evaluation of mechanical properties by Small Punch Test and Automated Ball Indentation Test for Zr–2.5% Nb pressure tube material

Empirical correlation parameters for evaluation of key mechanical properties of anisotropic Zr–2.5% Nb pressure tube (PT) material have been determined for Small Punch Test (SPT) and Automated Ball Indentation (ABI) Test. Parameters have been developed as a function of loading direction due to highly anisotropic nature of the material. Slopes of the linear fit correlations established for the SPT and ABI tests, showed good sensitivity of these techniques to wide range of microstructures in the alloy that resulted due to different heat treatment conditions. In the case of ABI, the difference in yield strength offset constant between the two directions of loading studied, represented the effect of texture. Similarly in the case of SPT the difference in intercept values of the, linear fit correlations established for evaluation of yield strength (YS) and the ultimate tensile strength (UTS) with respect to two directions of loading studied, clearly indicated the effect of anisotropy in the material. Comparison of tensile strength data, the ABI and SPT derived σy and σUTS data obtained for heat treated specimens used in the study, through currently established correlation parameters showed good agreement with each other for both the directions of loading, indicating proper standardisation of ABI and SPT techniques and proper values of empirical parameters have been arrived at for evaluation of key mechanical properties of Zr–2.5% Nb material. The overall study established that, the direction of loading bears significance while dealing with anisotropic material like Zr–2.5% Nb alloy and hence, direction specific correlations need to be used for evaluation of true mechanical properties for a given miniature test.

Numerical simulation with finite element and artificial neural network of ball indentation for mechanical property estimation

A combined mechanical property evaluation methodology with ABI (Automated Ball Indentation) simulation and Artificial Neural Network (ANN) analysis is evolved to evaluate the mechanical properties for Carbon Manganese Steel (SA-333 Grade-6) and Stainless Steel (SS-304LN). The experimental load deflection data is converted into meaningful mechanical properties for these materials and their evaluated property is verified with experimental tensile specimen results. An ANN database is generated with the help of contact type finite element analysis by numerically simulating the ABI process for various magnitudes of yield strength (σ yp ) (200 MPa–400 MPa) with a range of strain hardening exponent (n) (0.05–0.5) and strength coefficient (K) (600 MPa–1600 MPa). For the present problem, a ball indenter of 1.57 mm diameter having Young’s modulus higher than test piece is used to minimize the error due to indenter deformation. Test piece dimension is kept large enough in comparison to the indenter configuration in the simulation to minimize the deflection at the outer edge of the test piece. Further, this database after the neural network training; is used to analyse measured material properties of different test pieces. The ANN predictions are reconfirmed with contact type finite element analysis for an arbitrary selected test sample. The methodology evolved in this work can be extended to predict material properties for any irradiated nuclear material in the service. Extensions of the ABI tests and the associated database analysis could lead to evaluation of the indentation energy to fracture needed for the structural integrity assessment of aged components.

Application of Automated Ball Indentation for Property Measurement of Degraded Zr2.5Nb

In this work, Automated Ball Indentation (ABI) technique is based on load controlled multiple indentations (at a single penetration location) of a polished surface by a spherical indenter (0.7 to 1.46 mm) and indentation depth is progressively increased to a maximum user specified limit with intermediate partial unloading. This technique permits measurement of yield strength, stress-strain curve, strength coefficient and strain hardening exponent. ABI Testing was carried out on samples of Zr-Nb2.5 (Pressure Tube Material) with different heat treatment conditions in which temperature was varying (550 degree to 900 degree and retention time was varying 0.5 to 6 hour and furnace cooled. For all these test material and conditions, the ABI derived results were in very good agreement with those from conventional standard test methods.