Indentation Creep Behavior Research Articles

Micromechanical and microstructure evolution of leaded (SnPb) and lead-free (SAC305 and SnCu) mixed solder joints during isothermal aging

This paper studies how isothermal aging affects the micromechanical and structural properties of mixed solder joints made of 60Sn-40Pb (SnPb) with Sn-3.0Ag-0.5Cu (SAC305) and SnPb with Sn-0.7Cu (SnCu). The nanoindentation test was done to measure the micromechanical properties of SnPb/SAC305 and SnPb/SnCu mixed solder joints. These properties are hardness, reduced modulus, and stress exponent. Scanning electron microscopy (SEM) was used to look at the microstructure of a cross-section of mixed solder joints. The micrographs that were taken were then examined with open-source image processing software called ImageJ. It was found that the rate and distribution of intermetallic compound (IMC) formation and the reduction of Sn-rich phase grain size affect how the hardness and stress exponent values of mixed solder joints change after 1000 h of high temperature storage (HTS). ImageJ analysis shows that the Pb-rich phase particle count and distribution can be used to figure out how mixed solder joints respond to indentation creep and how that relates to isothermal aging. Using ImageJ, it’s clear that the indentation creep behavior of the GBS mechanism of an as soldered SnPb/SnCu mixed solder joint is caused by the highest number and size of Pb-rich phase particles that are not well distributed across the dendritic area of Sn-rich phase grain boundaries.

Indentation creep behavior of Fe–8Ni–xZr oxide dispersion strengthened alloys

Abstract This study was conducted to understand the creep behavior of two oxide dispersion strengthened alloys containing Zr as the alloying addition by performing indentation creep tests at room temperature. The oxide dispersion strengthened alloys were Fe–8Ni–xZr (x = 1 and 4 at.%, i.e., Zr-1 and Zr-4 alloys, respectively), which had been previously fabricated by mechanical alloying; followed by consolidation via equal channel angular extrusion at 1000 °C. The indentation tests were conducted under a maximum load of 100 mN with the loading rates at 300 and 400 mN min−1. The hardness was calculated by the Oliver–Pharr method, and the creep properties, such as the creep displacement, creep strain rate, creep stress, and stress exponent n, were determined. The results showed that the Zr-4 alloy was harder than the Zr-1 alloy. However, the creep resistance of the Zr-1 alloy was better than that of the Zr-4 alloy. It was further demonstrated that both the hardness and creep resistance depended on the loading rate. Moreover, a possible creep mechanism was proposed. Although the tests were performed at room temperature, they can provide insight into the effect of an oxide dispersion strengthened alloys microstructure on creep at higher temperatures.

Evaluation of room temperature creep deformation of in situ Fe-based bulk metallic glass nanocomposites by instrumented indentation

In the present work, Fe57Cr9Mo5B16P7C6 (at. %) in situ bulk metallic glass nanocomposites of varying crystallinity, i.e. 0 to 80 vol. %, were synthesized by spark plasma sintering. Room temperature indentation creep behaviour of these composites was evaluated with nanoindentation technique. Effect of crystalline phase content on overall creep behaviour of the BMG composites was evaluated. Creep resistance of the BMG composites was improved with increase in the amount of crystalline phases up to 40 vol. %. Improved creep resistance is attributed to the presence of nanocrystalline phases in amorphous matrix and lower defect concentration in the BMG composite samples. However, excess crystallinity imparted brittleness and resulted in poor creep performance of the BMG composites. Derived stress exponent values are significantly lesser for the BMG composite sample in comparison to the amorphous compact indicating the transition in the mode of plastic deformation from inhomogeneous to nearly homogeneous. Loading rate has more pronounced influence on final creep displacement of fully amorphous sample in comparison to that of BMG composite.

Modeling and experimental investigation of indentation creep behavior of hypoeutectic Sn-Bi and Sn-Bi- Sb2O3 alloys using genetic programming approach

This study employs genetic programming (GP) to model the impact of aging temperature and the addition of nano-sized Sb2O3 particles on the mechanical properties of hypoeutectic Sn-5 wt% Bi alloy. Vickers hardness measurements were used to investigate the indentation creep behavior of the alloy under different testing conditions, comparing Sn-5 wt% Bi (alloy A) and Sn-5 wt% Bi-0.5 wt% Sb2O3 (alloy B). Microstructure development was studied using a scanning electron microscope (SEM). A MATLAB code was employed to optimize the GP parameters during the training process. Two GP models were developed to describe the indentation creep behavior of alloys A and B, respectively, as a function of dwell time, aging temperature, and applied load, using experimental data with errors of 0.0844 and 0.086 and a correlation coefficient greater than 0.9. The equations generated by the GP approach demonstrate excellent agreement with the experimental findings, and the GP model predicts the data with high accuracy.

Prediction of nanoindentation creep behavior of tungsten-containing high entropy alloys using artificial neural network trained with Levenberg–Marquardt algorithm

This paper describes the synthesis of tungsten-containing high-entropy alloys (HEAs). The synthesis method involves a powder metallurgy process, and spark plasma sintering (SPS) is used to compact the powder. XRD and SEM analyses of synthesized HEAs showed that the main phases formed were body-centered and face-centered cubic phases, and a sigma phase was also observed after sintering at 900 ℃. Furthermore, nanoindentation showed that the introduction of tungsten in HEA resulted in high hardness and elastic modulus, which ranged from 8.31 to 13.57 GPa and 197.21–209.43 GPa respectively. The indentation creep behavior was ascertained at room temperature. The HEAs exhibited a significant benchmark after the addition of a specific amount of W for further investigation because of their lower creep rate. Experimental creep displacement data were used for modeling by artificial neural networks (ANNs) in which the training has been performed by the Levenberg–Marquardt algorithm. The experimental creep displacement data and the ANN model predictions have an excellent agreement. The ANN model is reliable and can accurately forecast the room temperature creep behavior of HEAs. HEAs are promising candidates for use in elevated and wear-resistance applications, owing to their unique combination of high hardness and high creep resistance.

High through-put nanoindentation mapping and indentation creep behavior of P-TIG welded CpTi and Inconel 718 using a Nb-interlayer

The high-speed correlative study of the local mechanical properties and indentation creep of different zones of the P-TIG welded CpTi (Commercially pure Ti) and IN718, with Nb as an interlayer has been studied. The results showed contrasting mechanical properties (nanohardness and elastic moduli) to a width of 35 µm and 60 µm at the Nb/CpTi and the Nb/IN718 interfaces with hardness of ∼9 GPa and ∼15 Gpa, respectively. This was owing to the strengthening of the interfaces due to the interdiffusion of Nb into the base alloys. The Nb/IN718 and Nb/CpTi interfaces, exhibited significantly higher resistance to creep deformation than the Nb-Interlayer. The stress exponent at the Nb/CpTi interface and in different zones of Nb/IN718 side indicated dislocation climb as the creep deformation mechanism.

Corrigendum to “Indentation creep behavior of pulsed Tungsten inert gas welded Ti-5Al-2.5Sn alloy joints by nanoindentation and atomic force microscopy”

Corrigendum to “Indentation creep behavior of pulsed Tungsten inert gas welded Ti-5Al-2.5Sn alloy joints by nanoindentation and atomic force microscopy”

Phase selection and characterization of Fe-based multi-component amorphous composite

Phase selection and amorphous transition play a significant role for controlling of the microstructure and properties of multi-component alloys. In the present work, the solidified microstructure evolution of Fe52-xCo20NixB19Si5Nb4 (x = 7,12, labeled as 7 Ni, 12 Ni) alloys were studied in a wide range of cooling rate, and the effect of phase constitutions on the magnetic and micromechanical properties were systematically investigated. The results show that the microstructures of the two master alloys are composed of α-Fe, γ-Fe, Fe2B and Nb6Co16Si7 phases. As the solid solubility increases, the content of the intermetallic Nb6Co16Si7 phase decreases or even disappears, while the metastable Fe3B phase and Fe23B6 phase grow competitively. With the rise of the cooling rate, there is a transition from eutectic microstructure to internal amorphous structure plus peripheral crystalline/amorphous composite, and then to complete amorphous state in the two alloys. For the 7 Ni alloy, when the droplet diameter reduces, the coercivity of the alloy decreases continuously. As the content of the main magnetic α-Fe phase decreases, the saturation magnetization of the alloy diminishes firstly, and then slightly heightens when it is completely amorphous. From the perspective of solid solubility, the difference in hardness of the α-Fe and Fe2B phases with the undercooling is clarified. The hardness of the amorphous phase is slightly lower than that of the Fe2B phase. Finally, the nanoindentation technique was used to explore the indentation size effect and creep behavior of amorphous composite under different peak loads and different loading rates. As the peak load decreases or the loading rate increases, the hardness and elastic modulus of the alloy enhance, while the maximum creep displacement, stress factor and activation volume all increase with the rise of the peak load.

Indentation creep behavior of pulsed Tungsten inert gas welded Ti-5Al-2.5Sn alloy joints by nanoindentation and atomic force microscopy

Indentation creep was used to analyze the heterogeneity of the mechanical properties in base metal, heat affected zone and fusion zone of titanium alloy weldments obtained using TIG welding process which is generally employed in aerospace industries. For all the weld zones, creep deformation was analyzed using nanoindenter, AFM and microhardness testing. Nanoindentation creep depth was plotted with respect to time using data from the hold stage and CSRs were calculated using empirical relations. The analysis of creep stress exponents (CSE) was indicative of an active creep mechanism for all the weld zones however, a notable variation between the stress exponents and creep mechanism was observed among base metal, heat affected zone and fusion zone. Moreover, Vickers microindentation was used to measure creep of Ti-5Al-2.5Sn alloy weldment using Sargent-Ashby model. However, it did not give the realistic values creep behavior when compared to literature and nanoindentation measurements. It was observed that the phase change, grain size and the loading strain rate (LSR) significantly affected the creep behavior of the Ti-5Al-2.5Sn weldment.

Twinning-Induced Abnormal Strain Rate Sensitivity and Indentation Creep Behavior in Nanocrystalline Mg Alloy.

Nanocrystalline materials exhibit many unique physical and chemical properties with respect to their coarse-grained counterparts due to the high volume fraction of grain boundaries. Research interests on nanocrystalline materials around the world have been lasting over the past decades. In this study, we explored the room temperature strain rate sensitivity and creep behavior of the nanocrystalline Mg–Gd–Y–Zr alloy by using a nanoindentation technique. Results showed that the hardness and creep displacements of the nanocrystalline Mg–Gd–Y–Zr alloy decreased with increasing loading strain rate. That is, the nanocrystalline Mg–Gd–Y–Zr alloy showed negative strain rate sensitivity and its creep behavior also exhibited negative rate dependence. It was revealed that the enhanced twinning activities at higher loading strain rates resulted in reduced hardness and creep displacements. The dominant creep mechanism of the nanocrystalline Mg–Gd–Y–Zr alloy is discussed based on a work-of-indentation theory in this paper.

Rate-dependent indentation size effect on hardness and creep behavior of a titanium metallization film on alumina substrate

Nanoindentation tests were performed at room temperature to investigate the indentation size effect (ISE) and creep behavior of a titanium metallization film on alumina substrate. The ISE of hardness was examined at different loading strain rate (LSR). The effects of LSR and penetrating depth on nanoindentation creep were evaluated at the steady creep state. Inverse ISE in titanium film was observed at indentation depth below 200 nm while normal ISE was observed at penetrating depth ranging from 200 nm to 1000 nm. Elastic contact theory and strain gradient plasticity theory were applied to interpret the variation trends of hardness respectively. In addition, the intrinsic hardness and characteristic length were found to be strongly dependent on LSR. Except for creep strain rate, creep displacement and creep stress exponent showed relatively conspicuous correlations to LSR and/or penetrating depths.

Experimental study on the effects of hygrothermal aging on the indentation creep behaviors of PMMA

The effects of aging time on indentation creep behaviors of Polymethyl methacrylate (PMMA) have been investigated and the creep displacement was found to increase with aging time. However, the rate of change weakens as aging time increases. The generalized Calvin model consists of three Voigt elements that provide a good description of the indentation creep behavior of PMMA during the holding stage. Each Voigt element represents the motions with different levels i.e. molecular chain, molecular chain segments, molecular chain linkage, and branched-chain. The motions of molecular chain with different levels always have different delay times. The mechanism on the effects of aging time on the indentation creep responses is analyzed by comparing the contributions of different deformation types to total deformation. The contribution of elastic deformation to the total deformation Rhe decreases initially and then increases as aging time increases, which indicates the weakening of elastic modulus results from hygrothermal aging. With the aging time increasing, the contribution of time-dependent deformation to the total deformation i.e. Rhev+Rhvfirst increases and then decreases, which can be attributed to the different aging mechanisms at different stages. Further studies on the effects of aging time on creep compliance and time delay spectrum of PMMA during the holding stage indicates different deformation levels of PMMA characterized by different Voigt elements.

Multi-scale indentation creep behavior in Fe-based amorphous/nanocrystalline coating at room temperature

This work reports first ever investigation on multi-scale room temperature creep behavior of Fe-based amorphous/ nanocrystalline coatings, synthesized via plasma spraying at varying plasma power. Micro- and nano-indentation testing at different loading scales was carried out to reveal the combined effect of microstructural heterogeneities viz. porosity and constituent phases, as well as the individual contribution of amorphous and crystalline phases on the creep behavior of the coatings. Microindentation creep tests revealed higher creep resistance for the coating deposited at elevated power, ascribed to lower porosity and higher degree of crystallinity. Nanoindentation creep tests showed that mixed (amorphous and intermetallic) phase possessed lower creep displacement and retardation spectra compared to fully amorphous one, indicating better creep resistance. The present work provides valuable insight into the effect of microstructural features on the creep deformation behavior of amorphous-nanocrystalline coatings.

Nanoindentation creep properties of lead-free nanocomposite solders reinforced by modified carbon nanotubes

In this research, creep properties and thermal behavior of Sn-3.5Ag-0.7Cu (SAC)/multi-walled carbon nanotubes (MW-CNTs) lead-free nanocomposite solders was studied by conducting the nanoindentation testing at different temperatures, in the range of 292–312 K. Solder materials were prepared by mechanical alloying followed by powder consolidation routes. Furthermore, nickel coating was electro-less plated on the surface of nanotubes to enhance their metallurgical compatibility with the SAC solder matrix. The content of Ni-coated MW-CNTs varied in the range of 0–0.2 wt%. Addition of Ni-coated nanotubes resulted in an improvement of the indentation creep behavior of SAC solder alloy in comparison with the non-coated agents. By increasing the fraction of Ni-coated MW-CNTs up to ~0.1 wt%, the creep resistance of solder nanocomposite was continuously enhanced. However, the higher contents of reinforcing agents led to the deterioration of creep behavior due to the aggregation of nanotubes and a considerable heterogeneous refinement of the microstructure. The activation energy for softening during localized deformation behavior of nanocomposite solders was estimated by two approaches based on Dorn constitutive and Lucas-Oliver creep models and found to be in the ranges of 8.8–18.2 kJ/mol and 17.3–48.4 kJ/mol, respectively. By changing in the activation energy for diffusion and sliding of grain boundaries, in dependency with the extent of grain structural refinement and generation of dislocations due to altering the content of nanotubes as the reinforcing agent, the time-dependent under-loading deformation phenomenon in terms of creep can be controlled. The experimental results revealed that modified carbon nanotubes which are located on sub-grain boundaries can reduce their chemical potential tremendously, suppress the sliding-based creep deformation up to an optimized content of ~0.1 wt%.

Depth-Sensing Indentation Creep Behavior of Nanostructured Thermal Barrier Coatings from As-Synthesized t'-8YSZ Feedstocks.

Nano-indentation is a popular method to characterize the micromechanical properties of nanostructured 8YSZ coatings. However, little research has focused on the creep behavior of nano-indentation and only the elastic modulus and nanohardness have been analyzed. Herein, for the first time, the nano-indentation creep behavior of plasma-sprayed nanostructured 8YSZ coatings using as-prepared nanostructured non-transformable tetragonal (t’) feedstocks was investigated. The indentation creep behavior can be well characterized by the power-law equation and the strain rate sensitivity has been calculated in light of the equation. The strain rate sensitivity was sensitive to the load and the reasons were analyzed in detail. The current results can further guide and design thermal barrier coatings from the point of indentation creep property.

Creep resistance and strain-rate sensitivity of a CoCrFeNiAl0.3 high-entropy alloy by nanoindentation

The indentation creep behavior and creep strain-rate sensitivity (SRS) of the CoCrFeNiAl0.3 (Al0.3 for simplicity) high-entropy alloy are investigated by nanoindentation. Al0.3 exhibits much higher modulus and nanohardness values than CoNi due to the addition of Al. A significant creep resistance and a lower SRS value for Al0.3 are obtained as compared with CoNi. For high loading rate, the SRS value is enhanced by one order of magnitude, and the introduced Kelvin model is successfully applied to the constitutive description of the current creep behavior.

Room temperature nanoindentation creep of nitrocarburised AISI 4140 steel

ABSTRACTRoom temperature indentation creep behaviour of different regions of nitrocarburised AISI 4140 steel is investigated by employing the nanoindentation creep testing method in the present study. A structure consisting of a compound layer, a diffusion layer and a substrate is observed in the nitrocarburised AISI 4140 steel. The stress exponents are calculated from the loading curve produced by nanoindentation during the holding time. The results indicate that with the increase in distance from the material surface, the obtained stress exponent decrease. From the compound layer to the diffusion layer to the substrate, the stress exponent decreases rapidly first, and then decreases gradually revealing a deeper test point that yields a lower creep resistance. The correlations between the room temperature creep behaviour and the corresponding microstructure of nitrocarburising surface are discussed.

Mechanical behavior of electroplated mossy lithium at room temperature studied by flat punch indentation

We report the Young's modulus and deformation behavior of electroplated mossy lithium at room temperature investigated by flat punch indentation inside an argon-filled glovebox. The Young's modulus of the mossy lithium with a porosity of about 62.3% is measured to be about 2 GPa, which is smaller than that (∼7.8 GPa) of bulk lithium. Both the mossy and bulk lithium show clearly an indentation creep behavior. Despite its highly porous microstructure, the impression creep velocity of the mossy lithium is less than one-thirtieth of that of bulk lithium under the same stress. We proposed possible mechanisms for the significantly higher deformation and creep resistance of the mossy lithium over bulk lithium. These findings are key to developing mechanical suppression approaches to improve the cycling stability of lithium metal electrodes.

Indentation creep and tribological characterization of AISI 321, AISI 431 and FDMA borided and non-borided steels

In this paper, the mechanical properties, the creep and the tribological behaviours of three borided and non-borided steel materials were analysed. The alloy steel substrates were borided by a powder-pack boriding process during 8 h at 950 °C. The creep process during the holding stage of nanoindentation test was analysed using various mathematical models. The tribological properties of the studied materials were investigated by wear experiments on a ball disc test wearing. It was found that the corresponding indentation creep behaviour can be correctly described by a power-law relationship. Furthermore, based on the selected power-law creep function, the stress exponents and the corresponding strain rate sensitivity (SRS) indices were also determined. In particular, boride layers showed excellent mechanical properties and they were found to be more creep and wear resistant compared to base steel substrates. Furthermore, with an increase in applied load, the wear tests revealed an increase in wear loss and a decrease in the friction coefficient.

Vickers microhardness and indentation creep studies for erbium-doped ZnO nanoparticles

The effect of erbium (Er) doping on the structural, magnetic and mechanical properties of Zn1−xErxO, with 0.00 ≤ x ≤ 0.10, samples was studied using X-ray powder diffraction, M–H magnetic hysteresis and digital Vickers microhardness tester, respectively. The samples were prepared by wet chemical co-precipitation method. Vickers microhardness (Hv) measurements were carried out at different applied loads (0.25–10 N) and dwell times (t = 10–60 s) to study the mechanical performance of the samples. Experimental results of Hv were analyzed using Meyer’s law, and modeled according to Hays–Kendall, elastic/plastic deformation, modified proportional specimen resistance (MPSR) and Indentation Induced Cracking models. It was observed that the MPSR model was the most appropriate model for describing the load independent microhardness data of Er-doped ZnO nanoparticle samples. Indentation creep behavior of Zn1−xErxO samples was studied at room temperature by measuring the variation of Hv with the dwell times (t = 10–60 s) at fixed applied loads F = 1, 5 and 10 N, respectively. The results showed that Er-doped ZnO nanoparticles samples possessed grain boundary sliding and dislocation climbs at low loads followed by dislocation creep for higher loads within the operative creep mechanism.