Nanoindentation Hardness Testing Research Articles

Microstructural changes in He-irradiated V-Cr-Ti alloys with low Ti addition at 700 °C

V-Cr-Ti alloys with reduced Ti contents are expected to be good candidates as recyclable structural materials for fusion reactors. Herein, He irradiation was applied to V-4Cr-xTi (x = 0 to 4) alloys to investigate the additional effect of Ti and gas interstitial impurities on their microstructural evolution and irradiation hardening. Following He irradiation of the specimens at 700 °C with a maximum damage depth of 0.5 dpa, transmission electron microscopy and nanoindentation hardness tests were conducted. The microstructural evolution of the titanium-oxycarbonitride (Ti(CON)) precipitates formed during He ion irradiation was observed. The behavior of irradiation hardening is explained by the formation process of Ti(CON) precipitates and the magnitude of irradiation hardening depends on the amount of gas interstitial impurities that contribute to precipitate formation.

Helium ion irradiation-induced damage of powder metallurgy-hot isostatic pressed Ni-based alloy GH3535 for molten salt reactor applications

Powder metallurgy-hot isostatic pressing (PM-HIPing) is a promising technology for the manufacturing of components for nuclear reactors. In this study, Ni-based alloy GH3535 for molten salt reactor applications, was processed via PM-HIPing, and irradiation damage behaviors of the PM-HIPed GH3535 along with its forged counterparts were studied with He+ ions irradiation and microstructural characterization. The irradiation-induced defects in the samples, such as helium bubbles and dislocation loops, were characterized using transmission electron microscope (TEM). The mechanical responses of irradiated specimens were studied by nano-indentation. The results show that the PM-HIPed GH3535 exhibits a comparable irradiation resistance to its forged counterparts. Size of the helium bubbles and dislocation loops are larger for samples irradiated at high temperature than those irradiated at room temperature, irrespective of processing methods. However, number density of these defects is smaller for the high temperature irradiated samples than those irradiated at room temperature, which is particularly evident for the forged sample. The samples show significant hardening after irradiation, evidenced by the nano-indentation hardness test results. The experimental results and the calculations based on dispersed barrier hardening (DBH) model are in general agreement. This study will provide important data to support the application of the PM-HIPed materials or components in the nuclear reactors.

Interplay between microstructure, micromechanical, and tensile properties in wire arc additive manufactured nickel-aluminum bronze: As-built and heat treated

The generalized hardness-strength relationship in additively manufactured materials may differ from that observed in cast/wrought materials. To investigate this, the present study focuses on wire-arc additive manufactured (WAAM) Nickel-Aluminum Bronze (NAB) in both its as-built state and three distinct heat-treated conditions. Tensile tests and nanoindentation hardness tests were conducted simultaneously to establish a correlation between hardness and strength. Additionally, a comparison is made between the cast-NAB material and WAAM-NAB in this article. By considering the variations in grain size (coarse vs. fine) and intermetallic compounds in the cast and WAAM-NAB materials (in their as-built and post-heat treated forms), the correlation factor is found to differ based on the specific manufacturing processes and heat treatments employed. This paper aims to develop empirical equations that account for the various influencing factors, including rigid plasticity and uniform plastic work hardening conditions. Moreover, the study reports several indentation-based quantitative variables, such as the plasticity index, elastic recovery, recovery resistance, and wear resistance index of the WAAM-NAB material. By providing a comprehensive analysis of these factors, this research contributes to a better understanding of the hardness-strength relationship and the associated material properties in WAAM-NAB.

Microstructural characterization and mechanical behavior of Aba Panu meteorite by correlative microscopy and nanoindentation

Meteorite samples that land on earth can provide important information about asteroid and meteors found in space. Thorough, multimodal, and multiscale microstructural analysis is necessary to provide clues about the formation history of these materials. Both 3D x-ray tomography and scanning electron microscopy, along with energy dispersive spectroscopy, were used to obtain detailed structural information from the Aba Panu meteorite. EDS was utilized to obtain elemental composition and identify existing minerals in the meteorite. The microstructural analysis enabled a proposed hypothesis of potential local structure formation processes supported by phase diagrams of the existing minerals. Mechanical properties of identified phases were measured using nanoindentation and Vickers hardness testing. By combining structural, compositional, and mechanical results, a comprehensive characterization and discussion of meteorite Aba Panu was obtained.

Local microstructure evolution of a V-containing Fe–Cr–Ni–Mo weld metal subjected to post-weld heat treatment

The high-strength steels are widely used in modern shipbuilding and marine facilities. However, welding of >900 MPa grade steels is particularly challenging owing to the lack of understanding of fine microstructure for the weld metal (WM). The present investigation is mainly focused on a V-containing Fe–Cr–Ni–Mo WM fabricated by gas metal arc welding (GMAW) in aspects of localized microstructure evolution during post-weld heat treatment (PWHT). Microanalysis of the localized microstructure of inter-dendritic regions (IDRs) and dendrite core region (DCRs) for WMs was conducted by transmission electron microscopy (TEM), transmission kikuchi diffraction (TKD) and atom probe tomography (APT), complimented by nanoindentation hardness testing. It is found that the microstructure of WM in as-welded (AW) and PWHT condition was characterized by elongated martensitic laths with high-density dislocations in IDRs, while that in DCRs was coarse bainitic microstructure with relatively fewer dislocations. Most of retained austenite (RA) formed during cooling after welding was decorated martensite lath boundaries within IDRs owing to the segregation of austenite stabilizing elements after solidification. For PWHT condition, more numerous and smaller nano-scale MC carbides were observed in IDRs compared to DCRs. Furthermore, V atoms were mainly responsible for the nucleation of nano-scale MC carbides, and the growth and coarsening process of them were mainly controlled by diffusion of Mo atoms. Besides, the RA could also decompose into nano-scale MC carbides during PWHT. The IDRs of the PWHT specimens showed the average nanohardness value of 7.4 ± 2.3 GPa, which was higher than that of the DCRs (4.0 ± 0.2 GPa).

Positron annihilation investigation of hardening behavior induced by Fe2+ irradiation in low-Cr FeCrAl alloys

Compared with 13Cr–FeCrAl alloy, micro-alloyed low-Cr FeCrAl alloy is expected to provide higher potential for application as accident-tolerant fuel (ATF) cladding material. In this study, low-Cr FeCrAl alloys with 7–10 wt.% Cr contents were irradiated to different doses of 1 and 5 dpa at 400 °C with 3 MeV Fe2+ ion. The 13Cr–FeCrAl alloy C35MN developed by Oak Ridge national laboratory was also studied for comparison. Samples were examined by Doppler Broadening of Annihilation Radiation (DBAR) and nanoindentation before and after irradiation. Nanoindentation hardness tests showed that irradiation hardening occurred in FeCrAl alloy samples with different Cr contents after irradiation. The hardening response of the 13Cr–FeCrAl alloy increased with the increase of irradiation dose, while the hardness of low-Cr micro-alloyed FeCrAl alloy changed little or decreased after higher dose irradiation. DBAR shows that the defect type of all samples before irradiation is the same and there are a large number of vacancy-type defects in all unirradiated samples. High temperature irradiation reduces the density of the internal vacancy defect of FeCrAl alloy, which is probably caused by the annealing-induced recovery effect on atomic displacement. The defect density of 13Cr-alloy increases with the increase of irradiation dose, while that of 10Cr–FeCrAl alloy decreases with the increase of irradiation dose. This is related to the much finer grain/precipitate size and the higher number density of precipitates, and thus the higher fraction of boundaries in the 10Cr–FeCrAl alloy. The results also showed that the vacancy recovery rate of the 10Cr–FeCrAl alloy is higher.

THE INFLUENCE OF SILICON ELEMENT-ADDED DLC FILM ON Ti-6Al-4V

Silicon added diamond-like carbon films fabricated from C2H2:TMS mixture were used to study the influence of silicon content on the deposition and tribological properties of films prepared on Ti-6Al-4V substrate by using plasma-based ion implantation (PBII). The structure of the film was analyzed by Raman spectroscopy. Hardness and elastic modulus of the film were measured by nano-indentation hardness tester. Tribological propertiesof the film were performed by using ball-on-disk friction tester. The results indicate that with the increasing silicon content in the pure DLC film, the friction coefficient increases. The hardness and elastic modulus of Si-DLC film can increase to a value of up to 31.1 GPa and 200.1 GPa with a silicon content of 13.1 at.%. This is because the greater C content. The Si-DLC films with Si content of 13.1 at.% (C:Si/1:2) and 14.3 at.% (C:Si/1:6) shows a low friction coefficient of 0.2, which is considerable improvement in the tribological properties. This is due to the high hardness and elastic modulus.

Effect of Heat Treatment on the Mechanical and Tribological Properties of Dual-Reinforced Cold-Sprayed Al Coatings

The aluminum cold spray feedstock powder was single- and dual-reinforced with no greater than 2 vol% boron nitride nanoplatelets (BNNP) and/or nanometric boron carbide (nB4C). These powders were cold sprayed onto Al-6061 substrates and then heat-treated in an argon environment. In addition, micro- and nano-indentation hardness and wear testing were performed on the heat-treated samples. Further microscopy and optical profilometry were used to characterize the microstructure and wear track volumes. Minimal changes to the splat structure were observed after heat treatment. However, when compared to the pure Al coating, microhardness improved with reinforcement after treatment at 500 °C, while nanohardness improved only in the dual-reinforced coatings, again after treatment at 500 °C. The elastic modulus generally decreased for the reinforced coatings after treatment; however, indentation test results were mixed. The wear testing done on samples heat treated at 500 °C for one hour showed increases in the specific wear rate for single-reinforced coatings but decreases in the dual-reinforced coatings. These results indicate that both dual-reinforcement and heat treatment are required for improvements in the mechanical and tribological properties of Al nanocomposites.

Microstructural modelling and characterisation of laser-keyhole welded Eurofer 97

The novel reduced activation ferritic/martensitic steel Eurofer 97 is employed by many concept designs for the plasma-facing first wall of the EU DEMO fusion reactor. These designs feature precision joints between Eurofer 97 coolant piping, for which an advanced laser-keyhole welding technique is proposed. In this work the microstructure of these novel laser-keyhole Eurofer 97 welds is modelled by combining finite element thermal analysis with precipitate kinetics modelling. Microanalysis of a representative specimen via scanning electron and high-speed atomic force microscopy techniques is also conducted, complimented by electron backscatter diffraction, energy-dispersive X-ray spectroscopy, and nanoindentation hardness testing. Models of the weld microstructure agree well with the results of microanalysis although the precipitate diameters predicted are slightly underestimated. Several large void defects were discovered within the weld fusion zone, the cause of which is suspected to arise from the evaporation of cerium-rich oxide inclusions present in the as-cast Eurofer 97 during welding.

Preparation of ultra-large intermetallic particles in Al alloys for accurate determination of their mechanical properties

The mechanical properties of intermetallic phases are important parameters for designing aluminum alloys. However, accurate measurement of these properties was obstructed by the subsidence of small intermetallic particles in the soft matrix. In this work, the alloy compositions are designed through CALculation of PHAse Diagram (CALPHAD) so that each target phase is primarily formed in a wide temperature range during slow solidification, thus intermetallic particles as large as 0.6–3 mm were prepared by the solution growth method. The hardness and elastic moduli of 6 important intermetallic phases in aluminum alloys, including Al6(Mn, Fe), Al2Cu, α-Al8Fe2Si, β-Al9Fe2Si2, Al3FeSi2 and Mg2Si were obtained. The elastic moduli and hardness values of Al6(Mn, Fe) and Al3FeSi2 were measured for the first time by nanoindentation and Vickers hardness tests as EAl6(Mn, Fe) = 171 ± 10 GPa, HAl6(Mn, Fe) = 501 ± 5 HV and EAl3FeSi2 = 199 ± 10 GPa, HAl3FeSi2 = 811 ± 12 HV. The properties measured in this work are overall higher than other experimental data and closer to theoretically predicted values. For this sake, we believe these data are most accurate for these 6 phases. In addition, this work provides a simple method to prepare ultra-large single crystal particles in Al alloys.

Micromechanical properties of hydroxyapatite nanocomposites reinforced with CNTs and ZrO2

This study examined the mechanical properties, wettability, and tribology of hydroxyapatite (HA)–zirconia (ZrO2)–carbon nanotube (CNTs) ceramic nanocomposites (with various CNT ratios (x): 1, 5, and 10 wt%). HA–ZrO2–CNT-x powders were hydrothermally synthesized. Hot isostatic pressing (HIP) and cold isostatic pressing were used to manufacture solid and dense tablets; consolidation was performed by sintering the nanocomposites under Ar gas at 1150 °C during HIP. The microstructure and morphology of the nanocomposites were characterized via transmission electron microscopy, energy-dispersive X-ray spectroscopy, powder X-ray diffractometry, Fourier transform infrared (FTIR), and scanning electron microscopy. The effects of ZrO2 and CNTs on the mechanical characteristics of the nanocomposites were examined via nanoindentation, reciprocating wear, and Vickers hardness tests. The microhardness of HA–ZrO2–CNT-1% and HA–ZrO2–CNT-5% increased by 36.8% and 66.67%, respectively, compared with that of pure HA. The nanohardness of the HA–ZrO2–CNT-1%, HA–ZrO2–CNT-5%, and HA–ZrO2–CNT-10% samples was 8.3, 9.65, and 8.02 Gpa, and the corresponding elastic modulus was 83.72, 114.34, and 89.27 GPa, respectively. Both of these parameters were higher than those of pure HA. However, in the nanocomposite reinforced with 10% CNT, as opposed to those with lower CNT ratios, their values were lower. Additionally, HA–ZrO2–CNT-10% was the most hydrophilic nanocomposite synthesized in this study with a contact angle of 48.8°.

An experimentally driven high-throughput approach to design refractory high-entropy alloys

High-entropy alloy (HEA) design strategies have been limited to theoretical/computational approaches due to their compositional complexity and extremely large compositional parameter space. In this work, we developed an experimentally driven, high-throughput, HEA design approach using a physical vapor deposition (PVD) technique and coupled it with nanomechanical testing to accelerate material design for structural applications. The PVD technique enabled the formation of a compositional gradient across a thin-film sample. Specifically, a 10 cm wafer was used to manufacture a continuous set of 80 HEA compositions within the Nb-Ti-V-Zr family using a single deposition cycle. By using the solid-solution strengthening theory and estimated parameter properties, the strength and ductility of these HEA compositions were quantitatively determined/predicted and then experimentally verified by nano-indentation hardness test. Consequently, 7 refractory HEA compositions were successfully down-selected, which has a high propensity to have a balanced mechanical property.

Evaluating the irradiation hardening of reactor pressure vessel steels by nanoindentation hardness test and micropillar compression test

ABSTRACT Ultra-small testing technologies (USTTs), such as nanoindentation hardness tests and micropillar compression tests, can be potentially used to measure the mechanical properties of irradiated materials. However, the hardness and yield strengths of USTTs are different from those of standardized methods on bulk samples. In addition, irradiation-induced defects can affect the size dependence on the mechanical properties. This study examined A533B reactor pressure vessel steels before and after 5 MeV electron irradiation using USTTs. The depth dependence of the nanoindentation hardness was analyzed using the Nix-Gao model to evaluate the bulk-equivalent nanoindentation hardness and confirm its good linear relationship with the Vickers hardness. The compression yield strength was evaluated with a truncated square pyramid shape micro-pillars where the edge length (d) of the top surface and the height (L) of the micropillars were made similar: (d, L) = (1,2), (2,4), (3,6), (4,8), and (8,16) in μm. The size dependence of the yield stress in the micropillars has a minimum at d = 2 µm, which remained unaffected by electron beam irradiation up to 22 mdpa. The average yield stress of the d = 4 and 8 µm specimens was similar to that of the bulk tensile specimens.

Shock-induced large-depth gradient microstructure in commercial pure titanium subjected to explosive hardening

Explosive hardening of commercial pure titanium plate was conducted by a thin-layer high-detonation-velocity explosive. The nanoindentation and Vickers hardness tests of the treated titanium plates along the depth of shock loading were performed. The microstructures along the depth were characterized by using different methods, including X-Ray Diffraction, Optical Microscopy, Electron Back-Scattered Diffraction and Transmission Electron Microscopy. Experimental results showed that large-depth gradient hardness distribution with depth of 2.5 mm was produced in CP titanium by explosive hardening. There are two gradient hardenedlayers, ultra-hardened layer with a depth of 0–40 μm and a hardness increase of ∼400%, sub-hardened layer with a depth of 40 μm-2500 μm and a hardness increase of 54.3%. Gradient microstructures with different characteristics were observed, including gradient α-ω phase transition, gradient grain size, gradient twining and gradient dislocation. The area of gradient microstructure is consistence with that of gradient hardness distribution. Grain refinement/α-ω phase transition mainly contributed to hardness sharply increasing in ultra-hardened layer. High-density dislocation/twining mainly contributed to hardness increasing in the sub-hardened layer. Finally, the formation mechanism of gradient microstructures and grain refinement mechanism was detailly discussed.

Room-temperature wear resistance of tungsten carbide composite layers produced on grey cast iron by diffusion-controlled in situ reactions

To improve the tribological properties of substrate surfaces, tungsten carbide composite layers were deposited on an iron-based alloy by diffusion-controlled in situ reaction (DIR) at different temperatures. The microstructure, phase composition and worn morphology of the composite layer were characterized by utilizing scanning electron microscopy/energy-dispersive spectroscopy (SEM/EDS), X-ray diffraction (XRD) and confocal laser scanning microscopy (CLSM). A thin tungsten carbide layer with an interface crack was obtained at 1000 °C. At 1100 °C, the structure of the optimized composite layer contains a thin tungsten plate, a thicker tungsten carbide layer (300 μm) and a broad composite zone (2.5 mm) from top to bottom. The indexed phase composition for the carbide layer includes WC and α-Fe, and the composite zone consists of α-Fe, Fe6W6C, FeC and graphite. The tribological properties and mechanical properties of the composite layers were evaluated by using a ball-on-disk tribometer and a nanoindentation hardness tester. The average nanohardness of the tungsten plate, carbide layer, composite region and substrate is approximately 6.4 ± 1.0 GPa, 24.1 ± 3.4 GPa, 13.5 ± 2.4 GPa and 9.6 ± 1.2 GPa, respectively. Friction wear tests of all samples against GCr15 balls were performed at room temperature under 5, 10, 15 and 20 N normal loads. The carbide layer exhibits an average coefficient of friction of 0.39–0.63, which is higher than that of the substrate under an identical load due to the lubricating effect of the flake graphite phase in the substrate during the wear process. The specific wear rate of the carbide layer with a value of 2.69–4.33 is 18.5–34.3% of that of the substrate. The results of the worn morphology presence of particle deformation, extraction and crushing reveal that abrasive wear is a dominant abrasion mechanism for the carbide layer. For the substrate, adhesive wear plays an important role and is accompanied by abrasive wear.

Nano-Indentation Hardness and Strain Hardening of Silicon, Sodium Chloride and Tungsten Crystals

BackgroundA previous review of micro- and nano-indentation hardness tests and their analyses gave emphasis to obtaining measurements of continuous nano-indentation load, P, versus, depth, h, recordings that monitor the full elastic–plastic deformation behavior of a localized crystal volume [1].ObjectiveAttention is given to determining the complete, indentation-based, elastic–plastic deformation properties of the local volume, including the initial crystal elastic deformation behavior and, especially to evaluation of post pop-in plastic strain hardening.MethodStress–strain calculations are presented for an initial Hertzian elastic loading and follow-on crystal micro- and nano-scale plastic deformation responses [2].ResultsApplied load, P, dependencies on contact diameters, di, of silicon crystals are compiled on the basis of elastic, plastic and cracking predictions, giving indication at the lowest P values of an indentation size effect (ISE) for the crystal hardness. Elastic–plastic stress–strain curves are presented for sodium chloride and tungsten crystals. The hardness and strain hardening calculations also demonstrate an influence of the ISE.ConclusionsThe exceptional plastic strain hardening behaviors scale dimensionally with corresponding dislocation interactions and sessile reactions within the very localized plastic indentation zones. There is usefulness in determining elastic modulus values from the initial loading record. Micro- and nano-scale dislocation interactions/reactions account for the high stress and strain hardening levels as well as the occurrence of an ISE.

Scratch-healable automotive clearcoats based on disulfide polyacrylate urethane networks

We report a novel scratch-resistant and healable automotive clearcoat that can not only protect the substrate surface but also facilitate scratch repair. A self-healable disulfide polyurethane diol adduct (DSPUDA) was synthesized via step-growth polymerization with bis(4-hydroxyphenyl) disulfide, isophorone diisocyanate, and poly(tetrahydrofuran). The reversibility of bond cleavages and associations of the synthesized DSPUDA was quantified through nuclear magnetic resonance analysis, and its healing properties were confirmed using a universal testing machine and a rheometer. The material properties of clearcoats were tuned by varying the amounts of the DSPUDA added to prepared control clearcoats. The scratch resistances of the resultant clearcoats were assessed using an Amtec-Kistler car-wash tester and a gloss-meter, and their scratch-healing performances were evaluated using a micro-scratch tester and an optical microscope. In addition, the healing efficiency was quantitatively scrutinized using a nano-scratch tester and an atomic force microscope. The thermal properties of the clearcoat samples specifically, the thermal decomposition temperature, glass-transition temperature, and degree of crosslinking were characterized by thermogravimetric analysis, differential scanning calorimetry, and dynamic mechanical analysis, respectively. The mechanical properties of the clearcoat surfaces were investigated using nano-indentation and pendulum hardness tests. The healing efficiency and mechanical properties of the prepared clearcoats exhibited an inverse trade-off relationship. Nevertheless, optimizing the proportion of reversible disulfide bonds of the DSPUDA in the polyacrylate-based urethane networks not only resulted in superior scratch healing and scratch resistance but also maintained sufficient mechanical properties for the coatings to be used as automotive clearcoats.

Effect of theobromine based dental varnish on the enamel surface microhardness- an in vitro study

Introduction: Theobromine in recent years has been used as a remineralization agent. It demonstrates increased enamel hydroxyapatite crystal size that strengthens the enamel thus making it resistant to acid attack. Hence in the present study theobromine-based dental varnish was developed and its effect on enamel surface microhardness was assessed. Methods: In this in-vitro study, 45 freshly extracted healthy human first premolar teeth were randomly allocated into three groups of 15. Group 1 was Placebo varnish, Group 2 was Standard 5% Sodium fluoride varnish which was commercially available, and Group 3 was Novel theobromine nanoparticles containing dental Varnish. The enamel blocks were prepared from the randomly selected teeth. Baseline surface microhardness of the prepared enamel blocks were measured at three different points on the polished surface using both Vickers hardness tester and nano-indentation hardness tester. The prepared enamel blocks were immersed in a demineralizing solution for 7 days. At the end of the 7th day, the enamel blocks were removed and cleaned thoroughly. Again, the enamel blocks microhardness was recorded. After demineralization, all the enamel blocks were treated with three different varnishes for 28 days. After the 28th day, the readings were recorded using both Vickers hardness tester and nano-indentation hardness tester again. The results were analyzed by one-way analysis of variance (ANOVA), repeated measures ANOVA, and Bonferroni’s post hoc analysis. Results: The mean enamel surface microhardness between the three groups at baseline (P>0.001) and after demineralization (P>0.001) were not statistically significant whereas after application of dental varnishes the mean enamel surface microhardness values showed significant differences between the groups (P<0.001). Group 3 showed significantly more enamel surface microhardness values after its application on demineralized enamel surface as compared to Group 1 and Group 2 respectively. Conclusions: Theobromine nanoparticles containing dental varnish can significantly increase the enamel surface microhardness after its application on the demineralized early white spot lesion. Keywords: Theobromine, Remineralization, Nanoparticles, Surface microhardness

Strengthening Mechanisms in CoCrFeNiX0.4 (Al, Nb, Ta) High Entropy Alloys Fabricated by Powder Plasma Arc Additive Manufacturing

In high entropy alloys (HEAs), the addition of large-size atoms results in lattice distortion and further leads to solid solution strengthening or precipitation strengthening. However, the relationship between atomic radius, solid solution strengthening and precipitation strengthening has not been discerned yet. In this work, CoCrFeNiX0.4 (X = Al, Nb, Ta, with an equi-atomic radius) HEAs were prepared by powder plasma arc additive manufacturing (PPA-AM) and evaluated for their mechanical properties. Compression and nano-indentation hardness tests showed that the HEA with Ta showed the best properties. The influence of atomic radius and solid solubility on solid solution strengthening was investigated and the main strengthening mechanism that determines the mechanical properties of the developed HEAs was analyzed. The results showed that (i) the CoCrFeNiAl0.4 alloy did not show any solid solution strengthening effect and that a clear relation between solid solution strengthening and atomic size was not observed; (ii) in both CoCrFeNiTa0.4 and CoCrFeNiNb0.4 HEAs, precipitation strengthening and grain boundary strengthening effects are observed, wherein the difference in mechanical properties between both the alloys can be mainly attributed to the formation of fine eutectic structure in CoCrFeNiTa0.4; and (iii) from the microstructural analyses, it was identified that, in the CoCrFeNiTa0.4 HEA, the location containing a fine eutectic structure is accompanied by the formation of low-angle grain boundaries (LAGBs), which is also the region where deformed grains gather, giving rise to improved mechanical strengthening.

Evaluation of irradiation hardening in ODS-Cu and non ODS-Cu by nanoindentation hardness test and micro-pillar compression test after self-ion irradiation

Abstract Oxide dispersion strengthened (ODS) Cu alloys are expected to have high strength and superior irradiation resistance that are necessary characteristics for the divertor components of fusion reactors. The present study investigated the irradiation hardening after a self-ion irradiation experiment that was carried out at 100 °C with 5.1 MeV Cu2+ ions up to three displacements per atom in ODS-Cu and compared it to that of non-ODS Cu materials such as mechanically alloyed (MAed) Cu and single crystal (SC) Cu. Nanoindentation hardness tests and micro-pillar compression tests on 1 μm cubic pillars were carried out to evaluate the mechanical strength before and after the ion-irradiation. Both MAed-Cu and ODS-Cu showed good resistance against irradiation hardening, while SC-Cu showed a larger increase in the nanoindentation hardness and in the micro-pillar compression yield stress. Relationships between the nanoindentation hardness, Vickers hardness and micro-pillar yield stress were discussed considering the effects of both specimen/indentation size and irradiation hardening.