Automated Ball Indentation Research Articles

On the correlation between processing parameters, plastic deformation, and mechanical property in hard machining of H13 steel

Hard machining, as one of the sustainable manufacturing technologies, tends to introduce highly coupled thermomechanical loads into the machined surface layer, which causes materials to suffer from severe plastic deformation underneath and, thus, the alteration of the mechanical properties. In this paper, a systemic investigation was performed on the correlation of processing parameters, plastic deformation, and mechanical properties of machined surface layer for hardened H13 steel, where the cutting parameters and tool micro-geometry are varied. The plastic deformation layer was composed of an amorphous structure and plastically deformed grain. Compared to cutting parameters, edge micro-geometry significantly influences the depth of the plastic deformation layer. The automated ball indentation (ABI) technique was utilized to evaluate the mechanical properties of the machined surface layers. Finally, the relationship between processing parameters, depth of plastic deformation, and mechanical properties was revealed. The experimental findings provide a solid foundation for processing parameter selection to improve the functional performance of manufactured components.

Evaluation of strength in stainless steel weld joints using ball indentation technique

In the present study, strength variations across the type 316LN stainless steel weld joints processed by advanced hot wire tungsten inert gas, activated tungsten inert gas, and hybrid laser metal inert gas welding processes were evaluated using automated ball indentation technique. The secondary dendrite arm spacing (SDAS) associated with welding heat input and welding thermal cycles strongly influenced the strength properties across the weld joints. The strength properties were lower at 823 K compared to 298 K because of thermally activated deformations. The hybrid laser metal inert gas welding process exhibited significantly narrower weld and higher strength in the weld and heat-affected zone due to finer SDAS and grain size, respectively, than the other weld joints.

Region-wise evaluation of strength and creep behavior of AISI 904L weldments by small specimen testing techniques

Super austenitic stainless steel AISI 904L is a premium stainless steel renowned for its outstanding characteristics and the ability to be maintained even under harsh situations. This alloy is widely used in a variety of engineering applications, and hence generating creep and indentation data of the material will prove useful for those concerned. Our study investigates the impression creep (IC) and automated ball indentation (ABI) performance in activated tungsten inert gas (ATIG) and hot wire tungsten inert gas (HWTIG) weldments of 10 mm thick plates of AISI 904L. ABI-evaluated strength correlates well with the conventional uniaxial tensile test and hardness data. IC studies were performed on base metal and welds by applying a load of 60 kg on a 1 mm diameter flat-end cylindrical punch at 650 oC. Several cycles of loading followed by partial unloading were performed on ABI specimens at 25 °C using a 0.76 mm diameter tungsten carbide spherical indenter. The results indicated that the ATIG weld excelled over the HWTIG weld with higher creep resistance. During the ABI analysis, the heat-affected zone of HWTIG weldment displayed higher UTS and ABI hardness values of 499 MPa and 185 HB, respectively. Hardness values generated by the ABI analysis are 174 HB, 161 HB, and 177 HB for the base metal, ATIG weldment, and HWTIG weldment, respectively. This was found to be very much in agreement with conventional hardness test results. The results cemented the ability of IC and ABI analysis to precisely predict the creep and mechanical properties of the base metal and weldments. Data generated through this study will benefit industries and researchers associated with AISI 904L.

On the hot isostatic pressing of Inconel 625 structures built using laser powder bed fusion at higher layer thickness

This paper reports the effect of hot isostatic pressing (HIP) on the porosity, microstructure and mechanical properties of laser powder bed fusion (LPBF) IN625 structures built at a higher layer thickness of 100 µm. It is observed that the process-induced pores/voids of volume fraction (Vf) 0.43% in as-built IN625 structures are reduced significantly to ~ 0.01% after HIP treatment. The microstructure is changed from fine columnar dendrites to coarse equiaxed dendrites. The microstructural analysis of as-built structures reveals the presence of cellular/dendritic growth along with elemental segregation of Nb, Si and C and precipitation of Nb-rich carbides, whereas coarse recrystallized microstructure along with elemental segregation of Si and precipitation of Nb, Mo and Cr rich carbides is observed in hot isostatic pressed (HIP) samples. HIP structures exhibit lower tensile strength, higher ductility and lower anisotropy as compared to LPBF built structures. There is a reduction in the Vickers micro-hardness of IN625 samples after HIP, and the values are observed to be similar to their conventional counterparts. Further, an increase in the energy storage capacity of the material is observed after HIP treatment through Automated Ball Indentation (ABI®) studies. The study paves a way to develop ~ 100% dense, defect-free and isotropic engineering components using LPBF.

Evaluation of tensile properties using uni-axial and ball indentation testing and correlation with microstructure variations across the 316LN stainless steel weld joints

Automated ball indentation (ABI) tests were conducted across the 316LN stainless steel (SS) weld joints at 298 K, and 823 K. Zone wise tensile properties of 316LN SS weld joints such as weld metal, heat affected zone (HAZ), and base metal region are evaluated in this work. Uniaxial tensile tests were conducted to assess the effect of welding processes on the tensile properties. The weld joints were initially fabricated using arc based and laser based welding processes. The variations of tensile properties such as yield strength, ultimate tensile strength and strain hardening component values across the heterogeneous microstructure zones of the weld joints were evaluated. The correspondence between the microstructure variations and the tensile properties have been studied. The variations in grain size, secondary dendrite arm spacing (SDAS) and δ-ferrite content are found to be the primary cause of tensile strength variation across the weld joints. The gradient in tensile strength across the weld joints was higher at 298 K than at 823 K which was attributed to the microstructural changes at higher temperature causing material softening. It was noticed that the 316LN stainless steel weld joint made by hybrid laser MIG welding exhibited the highest values of strength and ductility among all the weld joints. It was attributed to the combined effect of higher δ-ferrite content and finer SDAS values. Therefore, the HLM welding process is recommended for welding of 316LN stainless steel components from the point of view of better tensile properties.

Evaluation of bond interface characteristics of rotary friction welded carbon steel to low alloy steel pipe joints

In the present investigation, rotary friction weld joints were prepared between carbon steel and low alloy steel pipes. These types of similar and dissimilar configurations are in general, used for drill pipe joining. Low alloy steel for the friction welding in dissimilar configurations were used in two different microstructure state; a) as-received and b) quenched and tempered. The friction weld joints showed three distinct weld microstructure characteristics; a) radial plastic flow, b) axial plastic flow and, c) partial heat affected zone, for joining configurations. In general, microstructure characterization revealed grain size refinement and carbide precipitation in the vicinity of bond interface for all types of similar and dissimilar steel joining conditions. A characteristic bond layer width of ~2 μm was developed between the dissimilar steel weld joints whereas it was found to be absent for the similar weld joints. These weld joints were evaluated for their mechanical properties by using conventional tensile tests and furthermore by automated ball indentation technique. The study has also shown that in the case of dissimilar steel joints the mechanical properties of the bond interface can be obtained aptly by using an automated ball indentation technique. The quench and temper treatment given to the low alloy steel resulted in the improved bond interface strength. The improvement of the mechanical properties of the weld joints was attributed to the synergistic effect of grain size refinement and tempered martensite microstructure.

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.

Evaluation of tensile properties of thermally aged 316LN stainless steel with varying nitrogen content using ABI technique

Abstract Type 316LN stainless steel (SS) with varying nitrogen content (0.07, 0.14 and 0.22 wt%) was thermally aged at 873 K and 923 K for 20,000 h. The microstructures of thermally aged steels revealed secondary phases such as M23C6 carbides and Fe–Cr–Mo intermetallics at all the nitrogen contents and Cr2N nitrides additionally at 0.14 and 0.22 wt% N. The amount of precipitates increased with increase in nitrogen content and aging temperature. The effect of thermal aging on the tensile properties of 316LN SS was evaluated using automated ball indentation (ABI) technique at 298 K. The flow curves of the steels aged at 873 K were lower than those obtained under unaged condition. Whereas due to ageing at 923 K, the flow stress response gradually increased above the unaged condition with increasing nitrogen content. The ultimate tensile strength varied similarly at 873 K aging condition for all nitrogen levels and was observed to recuperate upon aging at 923 K, except for 0.07 wt% N. Yield strength was not strongly affected by thermal ageing, except the considerable increase in 316LN SS with 0.22 wt% N aged at 923 K. The addition of nitrogen generally imparted interstitial solid solution strengthening to 316LN SS. The higher the nitrogen content and ageing temperature, the higher is the precipitation strengthening due to ageing, which was reflected in the tensile behavior. Transmission electron microscopy examination of ABI deformed zone revealed dislocation-precipitate interactions, precipitate-shear band interaction and pile-up of dislocations at precipitates, influencing the tensile properties.

Evaluation of tensile properties of various regions of creep exposed dissimilar weld joint using miniature specimen testing

Strength variations in various regions of a dissimilar weld joint made between 316LN stainless steel (SS) and P91 steel after creep exposure at 550 °C and stress of 200 MPa was estimated using automated ball indentation (ABI) test. The ABI results were used to derive equivalent uniaxial tensile flow behaviour using established correlation factors. A comparison of the results obtained in the creep tested and post weld heat treated (PWHT) samples showed loss of strength in the P91 steel side. It was observed that, creep exposure under this testing condition strengthened the 316LN SS side of the weld joint. ABI derived results showed that, the inter critical-heat affected zone (IC-HAZ) of P91 steel is the weakest region across the weld after creep exposure. The narrow IC-HAZ created a strain constraint which caused the specimen to fail in the P91 steel base metal region.

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.

COMPARISON OF TWO TECHNIQUES FOR EVALUATING SPHERICAL INDENTATION DATA

Flow curves of 15Kh2MFA, Sv 08Kh19N10G2B and 08Kh18N10T steels used for fabrication of WWER-440 nuclear reactor pressure vessel and core internals were obtained using the automated ball indentation (ABI) test technique and compared with flow curves evaluated from the same measured load-displacement data and widely used Oliver-Pharr method. Differences in results obtained by both studied methods do not exceed 12 % and are attributed to the amount of material pile-up.

Parametric investigation and characterization of laser directed energy deposited copper-nickel graded layers

One of the exciting applications of laser directed energy deposition (LDED) is the fabrication of complex-shaped engineering components involving graded composition. In the present work, a 2 kW fibre laser-based LDED system is used to deposit copper-nickel (CuxNi(100−x) (x = 25, 50, and 75)) layers on copper (Cu) substrate. The single tracks are deposited at different combination of laser power, scan speed, and Cu-Ni compositions. Track geometry (width and height) indicates direct and inverse dependence with laser power and scan speed, respectively. For same LDED processing parameters, there is lower track height and wider track width with increasing Cu in Cu-Ni composition due to improved wettability. Further, analysis of variance (ANOVA) shows that laser power and scan speed are more significant for track width and track height, respectively. Graded bulk structures built at identified process parameters are characterized using optical microscopy, microhardness, and single cycle automated ball indentation (SC-ABI). Deposited Cu-Ni graded bulk has a density of > 99% with pure Cu and Ni phase. The microscopy analyses reveal defect-free deposition with fine dendritic growth in the bottom and middle layers, while equiaxed grains are observed in top layers. Microhardness measurements show a smooth hardness transition from deposit to the substrate with higher hardness. SC-ABI presents an increase in energy storage capacity by 2.25 times with the increase in Cu percentage. This work paves a way for fabricating Cu-Ni graded components for manufacturing engineering components.

The Impact of Alloying Elements Addition on the Flow Behavior of Aluminum Alloys

The effect of alloying addition on the flow behavior of aluminum alloys was investigated. Three compositions were produced for this study including pure aluminum; aluminum–10wt% copper; and aluminum–10wt% copper–5wt% titanium. The bulk samples of these alloys were fabricated by mechanical alloying and hot consolidation. The flow behavior of the alloys under investigation was studied at room temperature by Stress–Strain-Microprobe® system and its Automated Ball Indentation® (ABI®) test method. The ABI experiment results were used to display the behavior of load-versus-depth of indentation (L–D), stress-versus-strain (S–S) behavior, yield strength, ultimate tensile strength, and ABI hardness. Pure aluminum revealed the lowest resistance to penetration and the weakest mechanical strength. The addition of copper to pure Al produced a higher resistance to penetration and augmented alloy strength. Adding Cu and Ti to pure Al exhibited the highest resistance to penetration and the strongest mechanical strength.

Online Acoustic Emission Monitoring of Cyclic Ball Indentation Testing - Correlation with Hysteresis Area Response

Fatigue has been one of the most researched subjects as most of the critical component failures are traced to fatigue. While fatigue data generation for design purposes is carried out using ASTM or equivalent standard specimens, the use of miniature or small specimens to estimate the fatigue properties is considered as a tool for extending the remaining life of in-service components. Cyclic automated ball indentation (Cyclic ABI) is one of the non-conventional test techniques used for fatigue performance assessment of pristine and in-service damaged materials. This method uses compression-compression cyclic loading of a flat specimen using a tungsten carbide spherical indenter; continuous monitoring of load-displacement (measured close to the indentation location) data provides an idea about the fatigue life of the material. Apart from this, hysteresis in load-displacement is used as an indicative energy parameter to detect fatigue failure in an Inconel 617 alloy using an off-line data analysis. To ensure on-line tracking of failure events, a specially tuned, miniature acoustic emission (AE) sensor was used during cyclic indentation testing. The AE parameters were extracted in the format of counts, absolute energy; the result processed in terms of cumulative counts, cumulative energy as well as first derivative of acoustic emission counts vs. fatigue cycles was used to cross-correlate failure events with other sensor responses. The failure cycles identified from AE were found to be in good agreement with the hysteresis area under the load-displacement curves, as well as extensometer displacement during cyclic loading.

Nondestructive evaluation of mechanical properties of nanostructured Al−Cu alloy at room and elevated temperatures

Abstract The influence of processing variables on the mechanical properties of a nanostructured Al−10wt.%Cu alloy was investigated. Stress−strain microprobe® system (SSM) and its automated ball indentation® (ABI®) test were used for evaluating the mechanical properties of this alloy. The tests were conducted at 21 °C on the bulk samples that were mechanically alloyed for 6 h at two ball-to-powder mass ratios (BPR) of 30:1 and 90:1. Furthermore, the tests were conducted at 200 and 400 °C on the samples that were processed at BPR of 90:1. Increasing BPR resulted in raising the final indentation load from (316±26) to (631±9) N and reducing the final indentation depth from 111 to 103 μm. Regarding the samples that were processed at BPR of 90:1, increasing the test temperature from 21 to 400 °C resulted in decreasing the final load from (631±9) to (125±1) N and increasing the final depth from 103 to (116±1) μm. The sample processed at BPR of 90:1 and tested at 21 °C revealed the highest strength and the least deformability while the sample processed at BPR of 90:1 and tested at 400 °C exhibited the lowest strength and the greatest deformability, as compared to all samples under study.

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.

Mechanical behavior of nanostructured bulk aluminum at various temperatures

The mechanical behavior of nanostructured bulk aluminum samples processed by means of ball milling and hot consolidation was investigated at various temperatures. Stress-Strain Microprobe® system and its Automated Ball Indentation® (ABI®) test were used for non-destructive determination of the mechanical properties of nanostructured Al samples under various variables. High purity aluminum was processed by means of ball milling for 6 hours and ball to powders weight ratios (BPR) of 30:1 and 90:1. The sintered bulk Al samples were subjected to ABI tests at room temperature, 200 °C and 400 °C to investigate the effect of BPR and test temperature on the mechanical behavior of these samples. Aluminum samples (C90-RT) which were ball milled using high BPR of 90:1 and tested at room temperature displayed the greatest values of final indentation load (303; ± 10 N); YS (228 ± 9 MPa); UTS (394 ± 11 MPa) and ABI hardness value of 113 ± 4, as compared to all samples under examination. On the other hand, the samples tested at 400 °C (C90-400 sample) revealed the least values of final indentation load (156 ± 4 N); YS (113 ± 1 MPa); UTS (220 ± 4 MPa) and ABI hardness value of 61.

Experimental investigation on laser directed energy deposition of functionally graded layers of Ni-Cr-B-Si and SS316L

Functionally Graded Material (FGM) is necessary for successful performance of two dissimilar materials joint, specifically when there is a large difference in the thermophysical properties of the materials and the joints are subjected to cyclic loading and extreme duty conditions. Laser Additive Manufacturing using Direct Energy Deposition (LAM-DED) is one of the advanced additive manufacturing processes favored for fabrication of FGMs. In the present work, an indigenously developed LAM-DED system is deployed for fabricating FGM of Ni-Cr-B-Si and SS316L. Parametric study is performed by varying the laser power, scan speed and powder feed rate and process parameter combination is identified for depositing uniform and continuous Ni-Cr-B-Si tracks with aspect ratio greater than 5. The identified process parameter combination is deployed for fabricating FGM of Ni-Cr-B-Si and SS316L and the composition of fabricated FGM is confirmed using Energy Dispersive Spectroscopy analysis. The surface topography analysis using Scanning Electron Microscopy indicates that the amount of partially melted powders increases with the increase in concentration of SS316L. Microstructure of as-built deposit is primarily dendritic with fine dendrites of ~5 µm. Micro-hardness and Single Cycle Automated ball indentation (SC-ABI) measurements indicates higher hardness and lower energy storage capacity for Ni-Cr-B-Si rich region as compared to SS316L rich region. The highest microhardness value of 645.23 HV1.96N is observed at the top layer of the graded deposit where Ni-Cr-B-Si fraction is 100%. SC-ABI testing indicates that the energy storage capacity of the material increases with increasing concentration of SS316L with similar trend for maximum displacement of the indenter. Further, LAM-DED deposits are heat-treated in muffle furnace at 900 Deg. C for two hours. The microstructural examination of thus heat-treated samples shows recrystallized grains in the Ni-Cr-B-Si rich region while dendritic microstructure is retained at the SS316L rich region. X-ray diffraction studies shows the difference in the diffraction patterns of as-built and heat-treated deposits with the absence of Ni3B phases in heat-treated samples. Microhardness studies indicate a large difference in hardness values in as-built and heat-treated deposits with a micro-hardness of 255.6 HV1.96N for 100% Ni-Cr-B-Si. SC-ABI studies show that heat treatment improves the energy absorbing capacity of the graded deposit. This study paves a way for the fabrication of Ni-Cr-B-Si and SS316L FGM with tailored mechanical and microstructural properties.