Nanoindentation Results Research Articles

Characteristics of Ancient Ship Wood from Taicang of the Yuan Dynasty.

In this study, wood samples extracted from the Taicang ancient ship, dating back to the Yuan Dynasty, were investigated to study the characteristics of waterlogged archaeological wood. The macroscopic characteristics and microscopic structures were used to identify the wood species. To assess the degree of degradation of the waterlogged archaeological wood, X-ray diffraction (XRD), nanoindentation (NI), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM) were used to compare the new and ancient wood samples from the same species. The microscopic structures of the samples were identified as Pinus massoniana. The XRD and nanoindentation results revealed that the crystallinity index of the cellulose decreased from 41.07% to 33.85%, the elastic modulus was reduced by 20.90%, and hardness was reduced by 55.6% compared with the new wood. The FTIR spectra revealed that biological deterioration occurred in the cellulose and hemicellulose, but there was no noticeable change in the lignin content. These results provide helpful information for the conservation and restoration of ancient ships.

Fabrication and interface optimization of continuous CF/Al composites with different reinforcement volume fraction

Interface is the key factor to determine the properties of composites. In this work, the Ni coated continuous CF/Al composites were fabricated via twin-roll casting method. After interface optimization, the interfacial bonding strength was enhanced and the dispersion of carbon fibers was improved. The effect of reinforcement volume fraction on microstructure, mechanical properties and strengthening mechanism of CF/Al composites was studied. The microstructural showed that the increase of reinforcement volume fraction was easy to cause more defects in composites. Transmission electron microscopy (TEM) and thermodynamic calculation were used to characterize the interfacial phase composition of composites after interface optimization. The results revealed that the exterior of carbon fibers bundle was mainly composed of Al3Ni intermetallic phase, and there was no obvious Al4C3 phases were found interior of the CFs bundle. In addition, the composites with 13.6 vol% CFs had the best UTS of 218.7 MPa and well dispersion. Furthermore, Vickers hardness test and Nano-indentation results showed that Al-Ni intermetallic compound can enhance the whole hardness of CF/Al composites. Dislocation strengthening in the Al-Ni intermetallic compound region was observed by TEM. The interface evolution mechanism of CF/Al composites were revealed for the first time.

A multiscale study on gel composition of hybrid alkali-activated materials partially utilizing air pollution control residue as an activator

This paper provides a detailed underlying mechanism of gel composition of hybrid alkali-activated fly ash/slag (AAFS) pastes prepared by utilizing the air pollution control residue (APCr, a highly alkaline waste containing 38.3% of Na2O content by mass) as a partial replacement (8%, 16% and 24% replacement by mass) of energy-intensive commercial sodium silicate (CSS) activator. AAFS pastes containing APCr as a partial replacement of CSS showed the strength, micromechanical and microstructure properties equivalent to the reference AAFS paste without APCr (R-0). SEM-EDS, FTIR spectral subtraction, and nanoindentation results showed that reaction products in AAFS pastes were composed of geopolymer gel (N-A-S-H), cross-linked gel (C–N-A-S-H) and alkali-activated gel (C-A-S-H) contributing to 60–66% of paste volume. Reaction products were more dominated by calcium-rich gels (C-A-S-H or C-(N)-A-S-H) as compared to N-A-S-H gel in all AAFS pastes. The heat of hydration and thermogravimetric results confirmed the slow rate of reaction of APCr-AAFS pastes at the early age but a higher rate of reaction at the silater stage which contributed to achieve a similar strength as control paste (R-0).

Changes in the microstructure and mechanical properties of Ti–6Al–4V alloys induced by Fe ion irradiation at a high He generation rate

As an attractive candidate structural material for nuclear applications, the irradiation resistance of high strength double-phase titanium alloys Ti–6Al–4V has received great attention. In this study, the damage dose dependence of defect evolution and hardening behavior at a high He generation rate (95 appm/dpa) for the Ti–6Al–4V alloys were investigated by TEM and nanoindentation. The Ti–6Al–4V specimen was pre-implanted with He ions with multi-energy at ambient temperature and subsequently irradiated with Fe ions at about 420 °C to obtain a He/dpa plateau region (400–1000 nm) with average damage doses of 1.5, 7.5 and 37.5 dpa. TEM observations show that the bubble density showed a strong damage dose dependence. When irradiated to 37.5 dpa, the bubble exhibited a bimodal size distribution with the critical radius of approximately 1 nm. Meanwhile, the precipitate length showed an increasing trend with increasing depth, which is due to the effect of injected-Fe ions rather than the damage dose. In addition, no He dependence was observed for the loops and the precipitates. Nanoindentation results indicate that the irradiation hardening became more significant with the increase of damage dose. The contribution of irradiation-induced defects to the hardening was estimated by dispersed barrier-hardening (DBH) model.

In-situ synthesis of Ti5Si3-reinforced titanium matrix nanocomposite by selective laser melting: Quasi-continuous reinforcement network and enhanced mechanical performance

Titanium matrix nanocomposites (TMNCs) with quasi-continuously distributed Ti5Si3 reinforcements exhibit high material strength, good thermal stability, great tribological properties, and high fracture toughness. However, fabrication of such TMNCs via advanced additive manufacturing (AM) techniques has rarely been realized due to the presence of AM-induced large columnar grains and the cracking issue associated with the reinforcement coarsening. Here, we report a nanoparticle-mediated approach to in-situ fabricate nano-Ti5Si3 reinforced TMNC coatings by selective laser melting (SLM) of Ti powders and minor amount of SiC nanoparticles. Results showed that with the optimized SiC amount and SLM processing parameters, a crack-free and ultrahigh-strength TMNC consisted of near-equiaxed grain structure and nano-scale Ti5Si3 network at the grain boundaries was successfully produced. The optimized TMNC showed an ultrahigh surface microhardness of 706 VHN, 51.5% higher than that of SLM-fabricated SiC-free sample (466 VHN). Spherical nanoindentation results showed that the effective indentation modulus and indentation yield strength were improved by 62.6% and 57.2%, respectively. A more pronounced strain hardening phenomenon was also observed in the optimized TMNC. The dry sliding tests revealed that the wear rate was reduced by 70%, and the wear mechanism transferred from abrasion to adhesion.

Electronic, nanomechanical and smart reversible phase transition behaviours of sputtered titanium oxide-vanadium oxide composite thin films

Crystalline vanadium oxide-titanium oxide (VO-TO) composite thin films of 197 nm are developed on quartz and silicon substrates by RF magnetron sputtering technique. A thorough structural investigation of deposited thin films is carried out by field emission scanning electron microscopy (FESEM), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) techniques. Differential scanning calorimetry (DSC) and temperature-based sheet resistance measurement techniques reveals the Smart (i.e., reversible) phase transition behaviour of VO-TO films at about 45 °C. Further selective depth analysis by XPS on the VO-TO films shows the variation of the Ti doping amount along the thickness. The top region of VO-TO thin film possess lower Ti species, while beyond 50 nm thickness from the surface possess comparatively rich Ti species. This graded Ti species along the depth also results in the variation of nanomechanical properties along the depth as confirmed by nanoindentation. The simulation through the finite element approach is also carried out to depict the experimental results of nanoindentation. The nanohardness and modulus of the presently developed VO-TO composite film were measured as 6.7 GPa and 158.7 GPa, respectively at 50 nm depth. Beyond 50 nm, nanohardness and modulus were 5.6 GPa and 116.6 GPa, respectively. Further, finite element simulation predicted yield stress value of 3.52 GPa at 50 nm depth whereas higher yield stress of 4.68 GPa was predicted beyond 50 nm.

Microstructure and Properties of TiAl Composite Coatings Prepared by Laser Cladding under Multi-Phase β0/CoAl2Ti Phase Strengthening

Ceramic-reinforced TiAl matrix composite coatings are fabricated by laser cladding on Ti-6Al-4V (TC4) surfaces. The present work focuses on matching of the ceramic phase with the TiAl matrix to achieve a strength–toughness matching through the multi-scale multi-phase structure. The results indicated that the structure of composites coatings, including γ, α2, β0, CoAl2Ti, and TiC phases, significantly improved the properties of the composite coatings. The TiAl composite coating reached a maximum hardness of 741.17 Hv0.2, and the 10 at% tungsten carbide (10 WC) coating has the lowest wear volume of 8.8 × 107 μm3, the friction performance was approximate five times that of TC4. Detailed explanation of the friction properties and friction mechanism of the composite coating based on crystallographic orientation relationships and nanoindentation results. The study found that strength–toughness matching is important for the improvement of friction performance. Based on the TiAl alloy generated in the non-equilibrium solidification state in this paper, the solidification process and microstructure evolution are analyzed in detail.

Bioinspired Nanonetwork Hydroxyapatite from Block Copolymer Templated Synthesis for Mechanical Metamaterials.

Inspired by Mantis shrimp, this work aims to suggest a bottom-up approach for the fabrication of nanonetwork hydroxyapatite (HAp) thin film using self-assembled polystyrene-block-polydimethylsiloxane (PS-b-PDMS) block copolymer (BCP) with a diamond nanostructure as a template for templated sol-gel reaction. By introducing poly(vinylpyrrolidone) (PVP) into precursors of calcium nitrate tetrahydrate and triethyl phosphite, which limits the growth of forming HAp nanoparticles, well-ordered nanonetwork HAp thin film can be fabricated. Based on nanoindentation results, the well-ordered nanonetwork HAp shows high energy dissipation compared to the intrinsic HAp. Moreover, the uniaxial microcompression test for the nanonetwork HAp shows high energy absorption per volume and high compression strength, outperforming many cellular materials due to the topologic effect of the well-ordered network at the nanoscale. This work highlights the potential of exploiting BCP templated synthesis to fabricate ionic solid materials with a well-ordered nanonetwork monolith, giving rise to the brittle-to-ductile transition, and thus appealing mechanical properties with the character of mechanical metamaterials.

Micro-Mechanical Properties of Slag Rim Formed in Cement–Slag System Evaluated by Nanoindentation Combined with SEM

Slag rim mainly consists of secondary precipitations such as C–S–H gel phase and hydrotalcite-like phase, which originate from the hydration of slag. In this paper, the micro-mechanical properties of slag rim were characterized by nanoindentation in combination with SEM. It was found that, compared to the C–S–H gel phase, slag rim showed about a 15 GPa higher modulus of elasticity. At the early age, slag cement paste mainly consisted of low-density C–S–H gel phase, high-density C–S–H gel phase, and unhydrated slag particles, as well as calcium hydroxide based on the results of nanoindentation; at the later age, the system contained C–S–H gel phase, slag rim (a mixture of C–S–H gel phase and hydrotalcite-like phase), and unhydrated slag particles.

Nanomechanical Characterization of High-Velocity Oxygen-Fuel NiCoCrAlYCe Coating

MCrAlY (M = Ni or/and Co) coatings have played an indispensable role in the high-temperature protection system for key components of aero-engines due to their excellent high-temperature oxidation and hot corrosion resistance. Nanoindentation is a useful and highly efficient method for characterizing the nanomechanical properties of materials. The rich information reflecting materials can be gained by load-displacement curves. In addition to common parameters such as elastic modulus and nanohardness, the indentation work and creep property at room temperature can also be extracted. Herein, nanomechanical properties of NiCoCrAlYCe coatings using high-velocity oxygen-fuel (HVOF) spraying were investigated systematically by nanoindentation. The microstructure of as-sprayed NiCoCrAlYCe coatings present mono-modal distribution. Results of nanoindentation reveal that the elastic modulus and nanohardness of NiCoCrAlYCe coatings are 121.08 ± 10.04 GPa and 6.09 ± 0.86 Gpa, respectively. Furthermore, the indentation work of coatings was also characterized. The elastic indentation work is 10.322 ± 0.721 nJ, and the plastic indentation work is 22.665 ± 1.702 nJ. The ratio of the plastic work to the total work of deformation during indentation is 0.687 ± 0.024, which can predict excellent wear resistance for NiCoCrAlYCe coatings. Meanwhile, the strain rate sensitivity determined by nanoindentation is 0.007 ± 0.001 at room temperature. These results can provide prediction of erosion resistance for MCrAlY coatings.

Elastoplastic properties of tribological layers of WC – (Fe – Mn – C) composites formed after high-speed sliding on steel

In this work, the authors studied the elastoplastic properties of the formed tribological layers of WC – (Fe – Mn – C) composites with matrices consisting of γ-iron (containing 4 % Mn (WC – 80G20)) and γ + α′ (containing 20 % Mn (WC – 80G4)) after friction on a high-speed steel disk at contact pressure of 5 MPa and sliding speeds in the range from 10 to 37 m/s. It was established that the main factor determining the morphology of the worn surface is sliding speed. At sliding speeds of 10 and 20 m/s, finely dispersed mechanically mixed tribolayers 3 – 4 µm thick are formed. As the sliding speed increases to 30–37 m/s, the thickness of the tribolayers reaches 10 – 15 µm, and the structure consists of oxidized fragments of WC – (Fe – Mn – C) composites and FeWO4 complex oxide and does not have a sharp boundary, like the tribolayers formed at lower sliding speeds. The highest values of nanohardness (~33 GPa) and effective Young’s modulus (~523 GPa) were achieved in the WC – 80G4 tribolayer after friction at 10 m/s when the nanoindenter was embedded into agglomerates of fragmented WC grains. This contrasted with the properties of the tribolayers formed at sliding speeds above 20 m/s. The results of nanoindentation showed an obvious effect of tribochemically induced softening in the emerging tribolayer after high-speed sliding at a speed of 37 m/s. Such a layer had a composite microstructure consisting of fragmented composite components cemented in-situ by tribochemically formed FeWO4 and, in addition to antifriction properties, had an increased indentation fracture resistance.

Microstructure evolution and mechanical property of high temperature solid-state diffusion bonded Cr-Zry4 with and without a 316 SS interlayer

Solid-state diffusion bonding between pure Cr and Zircaloy-4 (Zry4) was studied with and without 316 stainless steel (SS) as an interlayer at temperatures ranging from 1203 to 1573 K, followed by the detailed microstructural analysis and mechanical property evaluation at the bonding interfaces. For the samples directly bonded between Cr and Zry4, two regions were confirmed at the diffusion interface. One was a continuous block of Zr2Cr intermetallic compound formed by the inter-diffusion of Cr and Zr, and the other was a mixture of Zr2Cr and Zrα phases as the consequence of Zr-Cr eutectic reaction. For the samples with SS as an interlayer, three regions were mainly observed at the SS-Zry4 interface, consisting of (FeCr)α-, Zr(Fe, Cr)2-, and Zr2(Fe, Ni)-phase dominated layers, with (FeCr)α-phase observed at Cr-SS interface. The microstructure of the phases at diffusion interfaces were closely related to the bonding temperature. Nano-indentation results confirmed a rapid increase in hardness at Cr-Zry4 and SS-Zry4 interfaces for Cr-Zry4 and Cr-SS-Zry4 bonded specimens, respectively, due to formation of the ZrCr2/Zr(Fe, Cr)2 phase. The presence of the hard brittle intermetallic compounds at the interface infers the possible brittle fracture risk of the Cr-Zry4 interface during long-term operation under normal condition and high temperature under accident conditions.

Analysis of residual stress distribution characteristics of laser surface hardening based on Voronoi model

The laser surface hardening’s parameters have a direct effect on the residual stress of the matrix. It is important to quantitatively reveal the influence degree of process parameters on the matrix residual stress for the formulation of optimal process. In this paper, a random polycrystalline model of the matrix is established based on the Voronoi method. The grain heterogeneity is introduced according to the nanoindentation results. The divided 7 different grain attributes are randomly assigned to each voronoi cell through a python script. A thermo-mechanical coupling model for the laser quenching process of SUS301L-HT stainless steel considering grain heterogeneity was established. The thermal stress field and temperature field distribution of the single laser surface hardening are calculated with different process parameters. On this basis, the BOX-Behnen Design method was used to establish a response surface model, and the response surface method was combined with the Monte Carlo sampling calculation method to calculate the sensitivity of the process parameters. The calculation results show that the analysis value D of the residual stress is a normally distributed. Laser power and laser scanning speed are the main factors affecting the average residual stress of the grain, and the effects of the two are opposite. The laser scanning speed has a greater influence on the residual stress of the matrix than the laser power.

Ultratough Hydrogen-Bond-Bridged Phosphorene Films.

The rapid development of flexible electronic devices, especially based on 2D materials, has triggered the demand for high-strength materials. Mono- or few-layer phosphorene with excellent electronic properties has attracted extensive attention. However, phosphorene is affected by its low Young's modulus when applied to flexible electronic devices. Here, a strategy via ion intercalation to significantly improve the mechanical properties of black phosphorus to generate hydrogen-bond-bridged phosphorene films with Young's modulus as high as 316GPa is reported. This value is several times larger than the theoretical values of 166GPa in the zigzag direction, 44GPa in the armchair direction, and the averaged Young's modulus among all directions of 94GPa. The impact of intercalation on mechanical properties is also explored. Experimental nanoindentation results obtained by atomic force microscopy indicate that the relationship between the ratio of intercalated ions to phosphorus atoms and the corresponding Young's modulus satisfies the formula . Furthermore, a flexible NO2 gas sensor device based on this ultratough material presents excellent performance, even after 10000 bending cycles. The results provide new insight into the potential for practical applications of black phosphorus devices.

Mechanism of chemical and mechanical mutual promotion in photocatalysis-assisted chemical mechanical polishing for single-crystal SiC

Single-crystal SiC has become the third-generation semiconductor material with the most development potential due to its many outstanding physical and chemical properties, but excellent surface quality is the prerequisite for its application. Therefore, atomic mechanism of chemical and mechanical mutual promotion in hydroxyl radical ·OH aqueous was researched through reactive molecular dynamics simulation for obtaining nano-smoothed surface with photocatalysis-assisted chemical mechanical polishing (PCMP). The behavior of nanoparticles promoting chemical reaction during the nanofinishing process was studied vias a single abrasive sliding on the surface of SiC. A combination method of mechanical action and chemical action was adopted to compare effect of material oxidation and material removal. Si/C atoms are mainly fractured or escaped in the forms of SiO, CO, chain, SiO2, and CO2, and more residual oxidation products were observed on the substrate. Furthermore, XPS and nanoindentation results also support the mechanism of chemical and mechanical mutual promotion in PCMP through the detection of the oxidized products and surface hardness. This process activated and removed the SiC materials and generated a smooth and non-damaged surface (Ra 0.269 nm and Rmax 0.807 nm). The research results may reveal the removal mechanism of Si/C atoms, and provide new theoretical and technical support for the ultra-precision machining of single crystal sapphire, silicon nitride and diamond etc.

A modeling approach to predict the mechanical response of materials to irradiation damage from external sources: Nanoindentation of Pb-implanted ZrSiO4

Materials exposed to external irradiation undergo damage and detoriation of mechanical properties that decays with the distance from the surface. Finite element simulations are used to predict the hardness and Young´s modulus as function of depth. The model incorporates the homogenized mechanical properties and the volumetric swelling, determined from micromechanical simulations, as function of the locally induced damage. Predicted Young's modulus data showed a good agreement with nanoindentation results and confirmed the established mapping of damage into depth dependent amorphous phase fraction in form of sigmoidal functions. The comparison of predicted hardness profiles with experimental data suggests a relaxation mechanism that removes the residual stress in the damaged surface layer during the ion implantation process. Furthermore, the results support the hypothesis that mechanical properties determined from intrinsic damage can be used to model also external radiation damage. The presented model is applicable to other types of materials and irradiation sources.

Determination of shale macroscale modulus based on microscale measurement: A case study concerning multiscale mechanical characteristics

Shale mechanical properties are important for shale gas production, but the magnitudes are difficult to estimate, standard size cores are hard to sample, and secondary interstice generation is inevitable. This paper proposes a method for determining shale macroscale modulus, which is determined at a hierarchy of scales from the nano-to macro-scales. Microscale measurements are upscaled to estimate the corresponding magnitudes at the macroscale. A case study is conducted with Silurian shale samples, using the hierarchy scales, gridding nanoindentation, atomic force microscopy (AFM), mineral liberation analysis (MLA), X-ray diffraction (XRD), and uniaxial compression tests. The mineral compositions are analyzed using MLA and XRD, and the shale composition is described in terms of clay minerals, organic matter, and siliceous and carbonate contents. The variation in the Young's modulus is analyzed based on the recorded indentation depth curves and modulus distributions. The nanoindentation and AFM results are upscaled to the centimeter scale through the Mori–Tanaka method. The upscaled results exhibit satisfactory fitting with the conventional uniaxial compression results, although the fitting of the upscaled AFM results is better than nanoindentation. The proposed approach can be applied to promptly and comprehensively predict the shale mechanical parameters during shale gas exploration.

Mechanical properties of Li2MoO4 single crystals

Mechanical properties of lithium molybdate single crystals, Li2MoO4, are studied from room temperature to 650 °C. Density functional theory calculations gave the seven elastic constants of the rhombohedral crystal at 0 K. Brillouin light scattering experiments delivered comparable values at room temperature, and measurements up to 650 °C show a linear decrease in the constants with temperature. Nano-indentation results were typical of a brittle material with a low Young modulus and allowed deriving Young's moduli, for c (63 GPa) and m (48 GPa) faces, in agreement with those computed from measured elastic constants. Compressive rupture tests were performed. At 650 °C, the rupture stress was in the range 2–7.5 MPa. No clear evidence of a plastic regime was observed before cracking, even at temperatures close to the melting point.

Effect of a-C:H:Si interlayers on the mechanical and superlubricious properties of hydrogenated amorphous carbon films

Diamond-like carbon is a promising material due to its outstanding properties. Among them, hydrogenated amorphous carbon (a-C:H) film has attracted many researchers’ interests because of its ability to achieve superlubricity (friction coefficient μ<0.01) in special environments. However, the a-C:H films generally have high internal stress and low chemical affinity with metal alloy substrates, which limits the wide use of a-C:H films in industrial application. In this work, we studied in detail the effects of interlayers on the mechanical properties of a-C:H film, especially the adhesion properties. Different Si-doped a-C:H (a-C:H:Si) interlayers were introduced between a-C:H layer and substrates using ion vapor deposition and prepared by varying the gas flow ratio of Si(CH3)4/C7H8 and the layer number of the interlayer. The gas flow ratio of the interlayer has a great influence on the adhesion of a-C:H film, resulting in different peeling off patterns during the scratch test. The cross-sections of the scratched deformation zone of the ACH-5 (the a-C:H:Si interlayer possesses four sublayers and all contain silicon-dopants) film were analyzed by transmission electron microscope. It was found that there were different failure mechanisms on the titanium and magnesium alloy substrates used. The results of Raman spectra, nanoindentation, nano-scratch and friction tests showed that the ACH-5 film exhibited the lowest ID/IG ratio, the highest hardness, and the strongest adhesion to the substrate and the best superlubricious performance (μ∼0.006).

Effect of Ca/Si and Al/Si on micromechanical properties of C(-A)-S-H

Calcium silicate aluminate hydrate (C(-A)-S-H) is the main hydration product used in cement-based materials. It plays a specific role in both the mechanical properties and volumetric deformation of the cement matrix. This study aims to clarify the effect of porosity and chemical composition of C(-A)-S-H on its micromechanical properties using nanoindentation. The results showed that porosity significantly affected the indentation, elastic, and creep moduli of the porous C(-A)-S-H compacts. Micromechanical properties of the “pure” C(-A)-S-H were improved by decreasing the Ca/Si ratio. The incorporation of Al slightly altered the creep modulus by affecting the volume of the large gel pores, basal spacing, and mean chain length (if no cross-linking occurred in C(-A)-S-H). Finally, the nanoindentation results of the mixed C(-A)-S-H and Al(OH)3 confirmed the distinct contribution of the individual component characteristics to the overall properties of porous mixtures.