Instrumented Indentation Testing Research Articles

Selected properties of X120Mn12 steel welded joints by means of the plasma-MAG hybrid method

The article describes properties of welds made of high wear resistance X120Mn12 steel obtained by the hybrid PTA-MAG (plasma transferred arc – metal active gas) method. The specimens were 8 mm thick rectangular (200 mm × 350 mm) sheets metal. The analyzed butt welds were made with the parameters selected according to the criterion of smallest cross-sectional area of welds and the narrowest HAZ (heat affected zone). The outcome of metallographic tests of weld, HAZ and parent material, hardness distribution and XRD (X-ray diffraction) patterns of selected areas are presented. The IIT (Instrumented Indentation Test) method was used to describe the distribution of mechanical properties shaped by thermal cycle annealing of the welding process. The investigation shows that the application of the PTA-MAG hybrid heat source for welding manganese steel enables the use of the filler material ER307 (AWS-A5.9). The hybrid PTA-MAG welding system has the relatively high potential to be an efficient alternative to welding standard processes for X120Mn12 steel due to the HAZ overheating limitation. The zone of high-risk weld cracking is the part of the HAZ close to the fusion area that has been reheated during weldment formation. Heat input about 0.6 kJ/mm is needed to provide full deep penetration butt weld without defects and with a vapor capillary of wide enough to cover the weld gap. The increase of hardness in the welded joint is smooth distributed and going up to 10% compared to the base material. The width of HAZ was <1 mm. Intensive carbides precipitation in HAZ has been avoided successfully.

Wear Rate, Tribo-Corrosion, and Plastic Deformation Values of Co-Cr-Mo Alloy in Ringer Lactate Solution.

This study investigates the tribocorrosion performance of a cast Co-Cr-Mo alloy prepared using casting and electromagnetic stirring (EMS) at specific frequencies. The tribocorrosion behaviour of the alloy was evaluated when exposed to Ringer's lactate solution to optimize the EMS parameters and improve its properties. The research focuses on biomedical implant applications and explores how EMS affects alloy wear and corrosion resistance. As did the friction coefficient and wear volume, the wear rate of samples produced with EMS frequencies of 75 Hz and 150 Hz decreased. These improvements are attributed to the ability of EMS to refine grain size and homogenize the microstructure, thereby increasing the resistance to tribocorrosion. Techniques such as scanning electron microscopy (SEM) and profilometry were used for surface and wear analysis, while mechanical properties were evaluated through instrumented indentation tests. The findings confirm that EMS improves the alloy's durability and tribocorrosion resistance, making it highly suitable for demanding biomedical applications such as joint replacements. This highlights the importance of advanced manufacturing techniques in optimizing biomedical alloys for simulated body conditions.

A new nanometre resolution method for probing densification ratio at nanoindentation sites in glass: Unravelling discrepancies in the literature

The region of permanent densification beneath a Berkovich indentation imprint in silica glass is investigated using a novel chemical dissolution technique. The use of the similitude regime in sharp indentation testing allows one to record reliable data with a good spatial resolution that makes it possible to deal with low loads (typically below 10 mN) and, more importantly, crack-free imprints. The densified zone dissolves more quickly than the non densified regions. The analysis of the results, along the vertical axis, indicates that the densification zone is rather homogeneous with a steep transition to the non densified zone. The size of the densification zone, with respect to the initial free surface, is estimated to be around two times the maximum penetration depth of the instrumented indentation test. These findings are compared with those obtained by numerical simulations using different constitutive equations from the literature. A very good concordance between Raman spectroscopy and chemical probe results is found for imprints made with no or few cracking events during indentation testing.

Application of Instrumented Indentation Test and Neural Networks to determine the constitutive model of in-situ austenitic stainless steel components

Over the last few decades, Instrumented Indentation Test (IIT) has evolved into a versatile and convenient method for assessing the mechanical properties of metals. Unlike conventional hardness tests, IIT allows for incremental control of the indenter based on depth or force, enabling the measurement of not only hardness but also tensile properties, fracture toughness, and welding residual stress. Two crucial measures in IIT are the reaction force (F) exerted by the tested material on the indenter and the depth of the indenter (D). Evaluation of the mentioned properties from F–D curves typically involves complex analytical formulas that restricts the application of IIT to a limited group of materials. Moreover, for soft materials, such as austenitic stainless steel SS304L, with excessive pile-up/sink-in behaviors, conducting IIT becomes challenging due to improper evaluation of the imprint depth. In this work, we propose a systematic procedure for replacing complex analytical evaluations of IIT and expensive physical measurements. The proposed approach is based on the well-known potential of Neural Networks (NN) for data-driven modeling. We carried out physical IIT and tensile tests on samples prepared from SS304L. In addition, we generated multiple configurations of material properties and simulated the corresponding number of IITs using Finite Element Method (FEM). The information provided by the physical tests and simulated data from FEM are integrated into an NN, to produce a parametric mapping that can predict the parameters of a constitutive model based on any given F–D curve. Our physical and numerical experiments successfully demonstrate the potential of the proposed approach.

Rapid evaluation of trade-offs between strength and impact toughness of wheel steels by instrumented spherical indentation test

In this paper, an improved size-independent instrumented spherical indentation test (ISIT) method was proposed to determine tensile strength and fracture toughness on wheel rims of two different types of wheel steels. Additionally, Charpy impact specimens were taken from three specific positions on the wheel rims and subjected to standard Charpy impact testing. The resulting Charpy impact energy (CVN) were matched with the fracture toughness measured by ISIT (KIc,IT) at the same positions. There was a clear linear correlation between CVN and the square of KIc,IT, which was consistent with the established relationship between both properties as determined by conventional Charpy impact and compact tension tests. Therefore, we expanded the ISIT method to study the impact of cooling rates on the variation of yield strength and Charpy impact energy across the wheel rim. To accomplish this, we designated additional testing points on the wheel rim using the ISIT method. The investigation found trade-offs between strength and impact toughness of wheel steels under different cooling rates. The above findings demonstrated the effectiveness of using the ISIT method, which facilitated high-resolution fracture toughness measurement, to establish accurate correlation between CVN and fracture toughness of wheel steels. Moreover, this ISIT method can be employed to regulate heat treatment of material properties to meet specific application requirements.

Realization of Martens hardness method in macro range with high accuracy force and indentation depth

TÜBİTAK UME Hardness Laboratory has been working on instrumentation in the field of hardness metrology since 2005 and three generations of hardness standardizing machines were developed since then to be used as reference (calibration/standardizing) machines in Türkiye. In former designs conventional hardness methods such as Rockwell, Brinell and Vickers scales were the main scope of the projects. In the final Project that was supported and funded by TÜBİTAK UME to develop three hardness standard machines to be used as national standards for the conventional hardness scales mentioned, the Instrumented Indentation Test (IIT) was also aimed at and some parameters like Martens hardness, creep, indentation hardness, (elastic and plastic) indentation work, etc. were also implemented onto the machines developed. It was a good occasion that the measurands in Rockwell hardness and IIT were the same, force and indentation depth besides time and this made it easier to realize the IIT on the same machine with a more suitable design to achieve the highest accuracy in terms of the measurands mentioned. In this paper the new design of the Rockwell-Brinell-Vickers hardness standard machine developed also for Martens hardness in macro range (3 kgf – 150 kgf) and preliminary Martens hardness measurements are explained.

Effect of laser beam wobbling and welding speed in X80 steel wire-fed laser root welds

A wobble laser was combined with a wire feed during laser root welding of X80 pipeline steel. The enlarged laser irradiation area and molten pool resulting from the laser beam wobbling provided a better gap-bridging ability, which is critical during laser welding of thick pipes. Applying laser beam wobbling enabled better control of filler metal dilution, which determined the weld metal microstructure and mechanical properties. In the present work, more bainite along with reduced acicular ferrite was formed in the wobble laser weld, due to the effect of dilution resulting from increased base material melting during wobbling beam, along with an inhomogeneous fusion zone microstructure. The instrumented indentation testing was utilized for the first time to distinguish the local yield strength variation of different regions of the fine weld zones, allowing one to verify if the weld metal strength meet the target value in industrial standards. As the productivity being improved when the welding speed increased from 1.0 to 1.5 m/min, the presence of more low temperature transformation products generated with a faster cooling led to a 26 HV higher hardness and a 70 MPa higher yield strength in the upper region of the fusion zone.

Micromechanical study of raw earth stabilization using instrumented indentation

Alkali-activated slag is used as a stabilizer in earthen materials to improve their mechanical properties and to reduce their sensitivity to water. The efficiency of this stabilization is assessed through the mechanical characterization of samples made of three stabilized raw earths (RE) with different mineralogical compositions and equilibrated under five different hygrometric conditions. Instrumented indentation tests are used to evaluate the cohesion of the stabilized samples as this testing method allows the characterization of the mechanical properties of brittle porous materials at a local scale. The results show an increase in hardness and elastic modulus and a strong decrease in water sensitivity of the three different RE with increasing slag and activator contents.

Effect of printing orientation on mechanical properties of 3D-printed orthodontic aligners.

The purpose of this study was to assess differences in the fundamental mechanical properties of resin-made three-dimensional (3D) printed orthodontic aligners according to the printing orientation. Twenty resin 3D-printed dumbbell-shaped specimens and 20orthodontic aligners were fabricated and postcured in nitrogen. Half of the specimens and aligners were built in horizontal (H), the other half in vertical (V)directions. The dumbbell-shaped specimens were loaded in atensile testing machine, while parts of the aligners were embedded in acrylic resin, ground, polished, and then underwent instrumented indentation testing (IIT). Mechanical properties that were assessed included the yield strength (YS), breaking strength (BS), plastic strain (ε), Martens hardness (HM), indentation modulus (EIT), elastic index (ηIT), and indentation relaxation (RIT). Data were analyzed statistically with independent t‑tests or Mann-Whitney tests at α = 5%. No significant differences were found between specimens or aligners printed either in ahorizontal or avertical direction (P > 0.05 in all instances). Overall, the 3D-printed aligners showed acceptable mechanical propertied in terms of YS (mean 19.2 MPa; standard deviation [SD] 1.7 MPa), BS (mean 19.6 MPa; SD 1.2 MPa), ε (mean 77%; SD 11%), HM (median 89.0 N/mm2; interquartile range [IQR] 84.5-90.0 NN/m2), EIT (median 2670.5 MPa; IQR 2645.0-2726.0 MPa), ηIT (median 27.5%; IQR 25.9-28.1%), and RIT (mean 65.1%; SD 3.5%). Printing direction seemed to have no effect on the mechanical properties of 3D-printed resin aligners, which are promising for orthodontic use.

Nanoscale and Tensile-Like Properties by an Instrumented Indentation Test on PBF-LB SS 316L Steel.

The mechanical properties of a defect-free laser melting (PBF-LB) deposit of an AISI 316L steel alloy were assessed by means of an instrumented indentation test (IIT), at both the macro- and nano-scales. The inherent non-equilibrium microstructure of the alloy was chemically homogenous and consisted of equiaxed grains and large-elongated grains (under the optical microscope) with irregular outlines composed of a much finer internal cell structure (under the scanning electron microscope). Berkovich and Vickers indenters were used to assess the indentation properties across individual grains (nano) and over multiple grains (macro), respectively. The nano-indentation over the X-Y plane revealed nearly constant indentation modulus across an individual grain but variable on average within different grains whose value depended on the relative orientation of the individual grain. The macro-indentation test was conducted to analyze the tensile-like properties of the polycrystalline SS 316L alloy over the X-Y and Y-Z planes. The macro-indentation test provided a reliable estimate of the ultimate tensile strength (UTS-like) of the alloy. Other indentation properties gave inconsistent results, and a post factum analysis was, therefore, conducted, by means of a new approach, to account for the presence of residual stresses. The already existing indentation data were supplemented with new repeated indentation tests to conduct a detailed analysis of the relaxation ability of compressive and tensile residual stresses. The developed methodology allows the effect of residual stresses and the reliability of measured macro-indentation properties to be examined as a function of a small group of indentation parameters.

Elimination of delamination cracks in ceramics manufactured using LCD stereolithography

LCD stereolithography of ceramics allows the creation of ceramic parts with unprecedented resolution for various applications from medical tooling to archeological restoration. However, the manufacturing of a delamination cracks-free sintered part using LCD stereolithography has been an arduous challenge in both industrial and academic research. This contribution is a guide for the elimination of such delamination cracks. Photo-rheology, instrumented indentation tests, UV/Vis spectrophotometry and multiple microscopy techniques were used to analyze the formation of delamination cracks and to identify their culprits. It was found that proper particle dispersion, sufficient air extraction, optimized slurry formulation, optimized printing parameters and sound design principles jointly contribute to the manufacturing of a delamination cracks-free ceramic part using LCD stereolithography. This research addresses each of the aforementioned factors, with the goal of improving the quality of ceramic parts and increasing their functionality for various applications.

Evaluation of mechanical properties and tribological behavior of DLC/WC/WCN/W multilayer coatings deposited by HiPIMS

In the present research, thin films of diamond-like carbon (DLC), tungsten carbide (WC), tungsten carbonitride (WCN) and tungsten (W) were deposited onto the surface of an AISI 52100 steel using the PVD process by HiPIMS. A (DLC/WC/W), B (DLC/WCN/W) and C (DLC/WC/WCN/W) coating systems were evaluated through mechanical and tribological tests to establish the optimal system for its application in the bearing industry. The physicochemical characterization was carried out using SEM and EDS. On the other hand, the mechanical properties were obtained by Berkovich instrumented indentation tests, where it was observed that the synergy between the WC/WCN intermediate bilayer in Coating C increased the hardness and elastic modulus concerning the WC and WCN intermediate monolayers. Finally, the coating systems were evaluated through the linear reciprocating wear test. Coating C presented the highest wear resistance and the lowest values of coefficient of friction, due to the positive synergy between the WC/WCN intermediate bilayer.

Effect of heat treatment and nitrogen atmosphere during post-curing on mechanical properties of 3D-printed orthodontic aligners.

Three-dimensional (3D)-printed aligners present a promising orthodontic treatment modality, whose clinical success largely depends on the material's mechanical properties. The aim of this study was to evaluate the mechanical properties of resin-made 3D-printed aligners and assess the effect of two different post-curing conditions. Forty dumbbell-shaped specimens and 40 resin aligners were 3D-printed and divided into four equal groups according to post-curing conditions: presence or absence of oxygen during post-curing and water heat treatment at 85°C for 15 s or none. Samples from the central incisor of the aligner (n = 5/group) were studied by Attenuated Total Reflection Fourier-transform infrared spectroscopy (ATR-FTIR). The dumbbell-shaped specimens were loaded up to fracture under tensile mode and yield strength, ultimate tensile strength, elastic and plastic strain were calculated. The first mandibular molar area from 3D-printed aligners (n = 10/group) was cut and embedded in acrylic resin and then underwent metallographic grinding and polishing followed by instrumented indentation testing to determine the following mechanical properties: Martens hardness, indentation modulus, elastic index, and indentation relaxation. After descriptive statistics, differences according to each post-curing protocol, as well as their combination, were analyzed with linear regression modeling at a 5% significance level. All groups showed identical ATR-FTIR spectra, while no statistically significant effects were seen for either post-curing protocol (N2 presence and heat treatment) or their combination (P > .05 in all instances). The mechanical properties of 3D-printed resin aligners were not considerably affected either by post-curing in N2 atmosphere or heat treatment.

An uncertainty-based quality evaluation tool for nanoindentation systems

Instrumented Indentation Test (IIT) is a nonconventional mechanical tests allowing multi-scale mechanical characterisation. It is employed for research and quality control in strategic manufacturing fields for developing edge technologies. The state-of-the-art lacks a robust methodology to assess quality of indentations and benchmark indentation devices. This is limiting the application of IIT for specifying and verifying tolerances. This work proposes an uncertainty-based quality evaluation tool for IIT. A non-parametric uncertainty evaluation of calibration contribution is proposed. The method shows the statistical significance of indentation sets modelled by the bootstrap samples. The uncertainty is then propagated according to the law of uncertainty propagation for the evaluation of mechanical characteristics. The methodology is applied to five case studies. Results show that the uncertainty evaluation model can achieve robust and sensitive quantification of the indentation results and system quality, thus providing a useful practical tool for industrial and academic practitioners within a metrological framework.

Instrumented microindentation – a versatile technique in the field of wood science and technology

Hardness is an important mechanical property of wood or other wood-based materials and it is also very important in the case of wood coatings. Different indentation methods for measurements of hardness and other mechanical properties have been utilised already for a long time. In the last 50 years the instrumented indentation was developed. Here, an indenter tests the surface of a specimen with a controlled load and movement, in order to assess its mechanical properties. Three ranges of instrumented indentation tests are distinguished. In the macro range, the force is higher than 2 N, in the micro range it is below 2 N and the depth of indentation must exceed 0.2 μm. When the indentation depth is lower than 0.2 μm, the indentation technique is called nanoindentation. There can be found thousands of scientific papers about applications of instrumented nanoindentation in research of a large variety of materials. Instrumented microindentation remained somehow in the shadow of nanoindentation, but yet, it is a highly versatile technique with potentials to study various (micro)mechanical properties. In this review, examples of possible applications of instrumented microindentation are presented, with a focus on investigations of wood, wood-based composites, surface coated wood and polymeric films. In the second part of this paper, as an illustration, investigations of a self-healing wood paint are shown. The cyclic method and a single-load indentation confirmed the different mechanical properties and good scratch resistance of the self-healing paint.

Surface, microstructural and mechanical characterization of contemporary implant abutment screws

ObjectivesThe aim of the present work was to evaluate six commercially available abutment screws by characterising roughness parameters, microstructure and mechanical properties. MethodsSix abutment screws from each implant system, were used. The surface roughness parameters (Sa, Sq, Ssk, Sku, Spk, Sk and Svk) were identified by an optical interferometric profiler. Microstructural observations and crystallographic analysis were performed using a scanning electron microscope (SEM) equipped with an energy dispersive X-ray spectroscopy (EDX) device for elemental analysis and an X-ray diffractometer (XRD), respectively. The Martens Hardness (HM), Indentation Modulus (EIT), elastic index (ηIT) and Vickers hardness (HV) of all specimens were determined by instrumented indentation testing (IIT). The results were analyzed by one-way ANOVA and Tukey multiple-comparison tests (a=0.05). ResultsEDX and XRD showed the abutment screws to be mixed α- and β-phase titanium alloys. Microstructural analysis revealed a fine homogeneous microstructure without porosity, consisting of fine dispersoid rods of β-phase embedded in a continuous α-phase matrix. Statistically significant differences were found among the mechanical properies and surface roughness parameters apart from Sq, Spk and Svk. ConclusionsThe tested abutment screws showed significant differences in the probed properties, and, thus, differences in their clinical behaviour are anticipated.

Temperature dependence of pressure sensitive flow in bulk metallic glass composites

The constraint factor, C, defined as hardness, H, to the yield strength, σy, ratio, is an indirect measure of the pressure sensitivity in materials. Previous investigations determined that while C is less than 3 for crystalline materials, and remains invariant with change in temperature, it is greater than 3 for bulk metallic glasses (BMGs) and increases with increasing temperature, below their glass transition temperature, Tg. In this study, the variations in C for two BMG composites (BMGCs), which have an amorphous matrix and in situ precipitated crystalline β-Ti dendrites, which in one case transforms under stress to α”-Ti and deforms by slip in the other, as a function of temperature are examined and compared with that of a BMG. For this purpose, instrumented indentation tests, with a Berkovich tip, and uniaxial compression tests were performed to measure the H and σy, respectively, on all alloys and their constituents at temperatures in the range of 0.48Tg and 0.75Tg. σy and H of the BMGC with transforming dendrites (BMGC-T) increase and remain invariant with increasing temperature, respectively. Alternately, in BMG and the BMGC with non-transforming dendrites (BMGCNT), the same properties decrease with increasing temperature. BMGC-T has the highest C of ∼4.93 whereas that of BMGCNT and BMG are ∼3.72 and ∼3.28, respectively, at 0.48Tg. With increasing temperature, C of the BMG and BMGCNT increases with temperature, but that of the BMGC-T decreases. The values of C and their variations as a function of temperature were explained by studying the variation of pressure sensitivity of the amorphous phase and concluding that the plastic flow in BMGCs under constrained conditions, such as indentation, is controlled by the flow resistance of the amorphous matrix whereas that in uniaxial compression, which is only partially constrained, is controlled by plasticity in both the dendrites and matrix.

Creep damaged microstructure and mechanical properties of Cr–Mo–V steel subjected to long-term service exposures

Evaluating the degree of creep damage is of high importance for the residual life assessment of high temperature and pressure steam piping systems of power plants. This study aims at assessing creep damaged microstructure and mechanical properties of low alloy Cr–Mo–V steel after long-term service exposures. Variations in mechanical properties have been assessed by means of tensile tests, hardness measurement and instrumented indentation testing (IIT). Optical and scanning electron microscopies were employed for the identification of creep damaged microstructure. The effect of heat treatment on the recovery of microstructure and mechanical properties was also studied. Correlations of IIT and hardness results between surface and bulk values have been obtained. The results of IIT agree well to the results of tensile tests. Moreover, relationships between hardness and tensile properties have been assessed. Eventually, the evaluation of the degree of creep damage by employing IIT and hardness measurement was attempted.

Effect of loading/unloading rate on instrumented indentation measurements in alloy Cu-2%Be

The influence of the loading/unloading rate on the indentation strain rate, hardness and elastic modulus in Cu-2wt%Be samples subjected to different aging treatments was analyzed. Homogenized samples were aged for 1 and 10 h at 400 °C to induce the formation of γ′ and γ precipitates, and instrumented indentation tests were performed at different loading rates between 0.15 and 1 mN s−1. The indentation curves of all the samples were influenced by the loading/unloading rate, but the behavior of the samples with precipitates was different from that of the homogenized samples. Strain rate levels during loading were also influenced by the loading rate. The strain rate increased almost linearly with the loading rate in the homogenized sample and the sample with γ′ nanoprecipitates, while it experienced a decelerated increase with the loading rate in the sample with γ phase. The hardness and reduced modulus were estimated from the indentation curves using the Oliver and Pharr method. Hardness remained almost constant at approximately 2.4 GPa as the rate was varied in the homogenized sample. On the other hand, the samples with γ′ and γ phase exhibited higher hardness values at 0.15 mN s−1, while it remained approximately constant for the other rates. The reduced modulus increased with the loading/unloading rate and this increase was more pronounced for the sample with γ precipitates, with a higher sensitivity of the reduced modulus increase.

Interface microstructure and mechanical response of similar and dissimilar joints of (γ + α2) titanium aluminide and α-titanium alloy produced by diffusion bonding

Titanium aluminides are one of the potential materials for aerospace applications because of their high specific strength and good resistance to creep and oxidation at elevated temperatures. However, it is quite challenging to obtain similar and dissimilar joints with these materials by fusion welding due to their high crack sensitivity, limited ductility, and low thermal conductivity. In this study, joints of (γ + α2)-titanium aluminide (TiAl) to itself and with α-Ti alloy were produced by solid-state diffusion bonding performed under vacuum in the temperature range of 750–950 °C and pressure of 10–20 MPa for 10–30 min. The resultant interface microchemistry and microstructures were examined in-detail by scanning electron microscope in conjunction with energy dispersive spectroscopy and electron backscattered diffraction. Instrumented indentation and shear testing were employed to examine hardness variation across the interface and to evaluate the bond strength of the joints, respectively. The TiAl/TiAl joint possessed a single thin interface layer of α2 (Ti3Al), whereas two interphase layers comprised, viz. α + α2 (layer 1) and α2 (layer 2) were formed at interface of the α-Ti/TiAl joint. The minimum bonding temperatures of 900 °C and 800 °C were identified for producing metallurgically sound joints of TiAl/TiAl and α-Ti/TiAl, respectively, under an applied pressure of 10 MPa for 30 min. The bond strength of ∼400 MPa, which is ∼90% shear strength of TiAl base alloy, was achieved for TiAl/TiAl joints produced at 900 °C and above. The α-Ti/TiAl joint produced at 950 °C showed a maximum bond strength of ∼504 MPa. The intimate contact of surfaces through the complete collapse of their asperities and formation of phases, similar to that present in TiAl base alloy, at the interface led to enhanced joint strengths. The fracture surface of the shear tested specimens displayed a transition in failure mode from brittle to transgranular failure of the interface along with TiAl base alloy with an increase in bonding temperature.