Nanoindentation Results Research Articles

Physical and mechanical characterization of mechanically treated AlTiN coatings deposited using novel arc enhanced HIPIMS technique

This work investigates the variation in surface and sub-surface characteristics of the AlTiN coated tools in comparison to the micro abrasive blasted AlTiN coated tools. The coatings were deposited through a newly developed hybrid technique that combines the benefits of the two conventional physical vapour deposition techniques. The coated inserts were subjected to micro abrasive blasting (MAB) at 0.1 MPa and 0.2 MPa blasting pressure using alumina (Al2O3) abrasive grains. The physical, metallurgical and mechanical properties of the AlTiN films were studied using various characterization techniques. The deposited film is free from surface defects like holes or pores. MAB of these films lead to surface flattening at localized sites leading to the film surface uniformity. The impact of hard abrasives onto the film surface has also improved subsurface properties along with an escalation in the surface roughness value. Nano-indentation results showed that the nano-hardness exhibited by the AlTiN coated tools subjected to micro blasting is high, around 35 GPa, in comparison to only coated samples, which show a value of around 29 GPa. MAB of films also resulted in an improvement of film crystallinity. These results indicate that the micro blasted films have improved properties and hence may be more beneficial in enhancing the machining performance of the tools.

Effect of the varied nitrogen vacancy concentration on mechanical and electrical properties of ZrNx thin films

ZrNx films were deposited with reactive magnetron sputtering in different [Ar]/([Ar] + [N2]) atmospheres and analyzed using X-ray photoelectron spectroscopy, glancing incidence X-ray diffraction, scanning electron microscopy, high-resolution transmission electron microscopy, nanoindentation techniques, and four-point probe meter. N vacancy concentration is defined as VN = 1- x, where x is N/Zr ratio in ZrNx. Results showed that the VN ranged from 0.02, through 0.08, 0.13, 0.24 to 0.30. The glancing incidence X-ray diffraction results showed a decrease in lattice parameter a0 from 4.582, through 4.578, 4.571, 4.564 to 4.548 Å with the increase of VN from 0 to 0.30. Berkovich nanoindentation results showed that the hardness of ZrNx films increased from 18 ± 1.3 GPa to 24 ± 1.2 GPa with the increase of VN from 0 to 0.24, which is due to vacancy-induced hardening. However, further increase of VN to 0.30, a drop-in hardness was observed, which was attributed to vacancy-induced softening. Both hardening and softening proved the existing of a turning point at VN around 0.24. In addition, the fracture toughness and sheet resistance of ZrNx films also presented the same tendency. The experimental results agreed with first principle predictions that the metal-N (d-p) bonds, ZrZr (d-d) σ bonds and the valance electron density around Zr atoms had changed greatly due to the varied VN.

Microstructure and corrosion characteristics of CrCuFeMoNi HEA coatings with different compositions in high-temperature and high-pressure water

Surface modification technology consists of a coating technique is one important method to improve the operational performance of nuclear fuel cladding. In this paper, different compositions of a CrCuFeMoNi high-entropy alloy (HEA) coating were deposited on a Zr-4 substrate by magnetron co-sputtering. The microstructures, mechanical properties and high-temperature corrosion behaviors of the CrCuFeMoNi HEA coatings were investigated. All as-deposited HEA coatings have an fcc structure and are well adhered to the Zr-4 substrate. The nanoindentation and autoclave test results showed that the as-deposited Cr0.26Cu0.3Fe0.1Mo0.15Ni0.19 HEA coating had superior hardness (12.5 GPa) and high-temperature corrosion resistance relative to others. The corrosion mechanisms of the CrCuFeMoNi HEA coatings with different compositions are also discussed.

Electron beam assisted physical vapor deposition of very hard TiCN coating with nanoscale characters

Abstract The work concerns electron beam assisted physical vapor deposition (EB-PVD) of titanium carbo-nitride (TiCN) on D2 tool steel. First, D2 steel substrate was heat treated to support and improve the load bearing capacity of the coating. To reduce the intrinsic gap between D2 substrate and TiCN coating and to improve the adhesive strength of the coating, a thin bond coat of Ti was EB-PV deposited on D2 steel prior to TiCN coating. The deposited coating was characterized in depth using XRD, SEM, AFM, profilometry and nanoindentation; its performance was assessed by the wear tests. The results demonstrated that EB-PVD process is successful in uniform deposition of nanograined (5.7 nm) TiCN coating; this character of the coating enhances its mechanical responses and cohesive strength. AFM topographic characterization confirms nanoscale smoothness of the TiCN coating which is a key factor in upgrading the wear resistance and tribological behavior of the coating. Nanoindentation results showed that the deposited coating is very hard; it is also tough enough. The hardness of the TiCN in this work is too much higher than those reported in the literature by similar works. AFM and nanoindentation results showed that a TiCN coating with thickness of 1.6 μm and roughness of 22 nm exhibits a hardness of 3552 HV which is much higher than those hardnesses reported in previous works. The wear tests showed that the deposited TiCN coating has a higher wear resistance than the D2 steel as well as TiN coating; this better performance is attributed to the modifications made in the coating process and its nanoscale characters.

Analytical modeling of surface roughness in precision grinding of particle reinforced metal matrix composites considering nanomechanical response of material

Grinding is usually applied for particle reinforced metal matrix composites (PRMMCs) to achieve high ground surface quality. However, the surface quality especially surface roughness is difficult to predict theoretically due to different mechanical properties of two or more phases inside the PRMMCs. In this study, an analytical model of the surface roughness of ground PRMMCs is developed based on an undeformed chip thickness model with Rayleigh probability distribution by considering the different removal mechanism of metal matrix and reinforcement particles in grinding. GT35, a typical kind of steel based metal matrix composite reinforced with TiC particles is investigated as an example. Nanoindentation experiments are employed for the investigation of nanomechanical properties and cracking behavior of GT35 and the nanoindentation results are integrated in the model. Single factor surface grinding experiments of GT35 are also carried out to understand the material removal mechanism of GT35 and validate this novel surface roughness prediction model. The predicted surface roughness from this model shows good agreement with the experimental results.

Composition-dependent mechanical property changes in Au-ion-irradiated borosilicate glasses

The mechanical property changes in three kinds of ternary borosilicate glasses (named NBS glasses) induced by 8.0-MeV Au3+ were studied by nanoindentation measurements. For these borosilicate glasses, the molar ratio R = [Na2O]/[B2O3] is varied (1.34, 0.75, and 0.40 for NBS1, NBS2, and NBS3, respectively), while their molar ratio K = [SiO2]/[B2O3] is fixed at 4.04. The nanoindentation results indicate that both the hardness and reduced Young modulus were decreased after irradiation. No obvious difference in both hardness and modulus variations of these three NBS glasses was observed. Based on the main structures of their pristine samples, the reedmergnerite groups containing Si-O-BIV may be the structural origin of Au-ion-irradiated mechanical property changes in the homogeneous glasses with R > 0.5. However, the modification of the silica network and phase separation may dominate the mechanical property changes for glasses with R ≤ 0.5. The ion- and electron-irradiation-induced mechanical property changes of these NBS glasses were also compared in this study. The extended incubation dose and the slower decreasing rate can be observed in electron-irradiation-induced hardness and modulus variations, which may be caused by the different mechanisms between both irradiation scenarios.

Nanoindentation characterization of aging gradient of mastic in asphalt mixtures

Abstract Understanding the aging behavior of asphalt mixtures is of great significance to the design, construction and maintenance of asphalt pavements. Numerous studies have been conducted on the aging phenomenon and its effects on mixture properties. However, conventional testing methods focus mainly on the global view or average value of the performance of aged mixtures, while the inner aging gradients are seldom addressed. The aging gradient, referring to the differences of aging effects in asphalt mixtures due to different accessibilities to aging conditions, represents the true aging behavior of asphalt mixtures. Hence, a micromechanical testing technique, nanoindentation, was used in this paper to investigate this issue. The effects of mixture gradation and polishing in sample preparation process on nanoindentation results were explored first. Then the vertical changes of modulus of asphalt mastic in asphalt mixture samples were characterized by nanoindentation to describe the aging gradient in different aged mixture samples. Dynamic modulus test was also performed for data supplement and comparison. Results show that gap-graded mixtures are suitable for nanoindentation test and a careful and standard polishing treatment will not affect the reliability of nanoindentation data. Nanoindentation can well characterize the age-hardening behavior of asphalt mastic and the aging gradient in long-term aged asphalt mixtures is approximately in a logarithmic curve form. Nanoindentation modulus results indicate that 8d of laboratory long-term aging in this paper can only affect the upper sections of dense asphalt mixtures. This paper suggests that nanoindentation can achieve a quantitative, mechanical and precise characterization of aging gradient in asphalt mixtures and is therefore promising in further research of asphalt materials.

Effect of annealing on mechanical and morphological properties of Poly(L-lactic acid)/Hydroxyapatite composite as material for 3D printing of bone tissue growth stimulating implants

In this work, effect of additional annealing on mechanical and morphological properties of 3D-printed PLLA/HAp composite scaffolds of three compositions (12.5, 25, and 50 wt.% of HAp) was investigated. Morphology and Young’s modulus of 3D-printed scaffolds were investigated by scanning electron microscopy and nanoindentation. It has been shown that additional annealing does not have an effect on the homogeneous distribution of HAp powder in the PLLA-matrix. Results of nanoindentation showed growth of Young’s modulus after annealing. The maximum value of 9393 ± 709 MPa Young’s modulus was reached for the annealed composite with 50 wt.% of HAp.

Recovering the bending ductility of the stress-relieved Fe-based amorphous alloy ribbons by cryogenic thermal cycling

Fe-based amorphous alloys with excellent soft magnetic properties always suffer catastrophic annealing embrittlement. The soft magnetic and mechanical properties of a series of Fe84.3-xCoxSi2B13Cu0.7 (x = 0, 2, 4, 6, 8) amorphous alloy ribbons were investigated. With appropriate substitution of Co for Fe, the BS of the alloys shows a slight increase and the HC remains at a low level. From two-point bending tests, a sharp transition from ductility to brittleness can be observed upon annealing. The embrittlement can be attributed to localized shear bands due to shear bands branching during deformation. It is found that the ductile-brittle transition temperature increases slightly by applying cryogenic thermal cycling treatment to annealed ribbons, indicating that the annealing embrittlement can be improved to some extent by cryogenic thermal cycling treatment. According to nanoindentation results, the increased shear transformation zone volume is responsible for the bending ductility increment. Ultimately, a ductile Fe80.3Co4Si2B13Cu0.7 amorphous alloy ribbons with a BS of 1.68 T and a HC of 4.8 A/m were obtained by cryogenic thermal cycling treatment after annealing.

Anomalous microstructure and excellent mechanical behaviors of (CoCrFeNi)6-x-yCrxAly high-entropy alloy induced by Cr and Al addition

The (CoCrFeNi)6-x-yCrxAly (x = 0.5, y = 0; x = 1, y = 0; and x = 1, y = 1) high-entropy alloys were prepared, and the microstructure and mechanical behaviors were investigated. The crystal structure changed from a sole face-centered-cubic (FCC) structure to a dual-phase structure of FCC plus body-centered-cubic (BCC) structure with the increasing of Cr content. By controlling the addition of Al and Cr elements, the crystalline structure changed to a BCC structure, which was composed of two ordered BCC phase. One is (Al, Ni)-enriched, and the other is (Co, Fe, Cr)-enriched. The increment of the BCC/B2 phase could significantly enhance the hardness and yield strength with a slight sacrifice to ductility. The nanoindentation tests showed that with the increasing of the Al and Cr content, the nano-hardness increased from 4.58 GPa to 8.95 GPa, and the elastic modulus increased from 200.83 GPa to 233.76 GPa, respectively. Based on the nanoindentation results, the H/Er and H3/Er2 values were calculated, which could be used to estimate the wear resistance. Both the H/Er ratio and H3/Er2 ratio showed an increase trend with the addition of Cr and Al elements, which demonstrated that the anti-wear ability was enhanced. The compression tests indicated that the (CoCrFeNi)4Cr1Al1 alloy demonstrated excellent comprehensive compression properties, whose yield strength and fracture strain is 1653 MPa and 29.5%, respectively. Furthermore, the strengthening mechanism has been discussed. In comparison with the solid solution strengthening, the second phase strengthening is dominant.

Tribological and corrosion performance of DLC coating on sintered Al alloy

DLC formation on sintered Al alloys and its purity is obtained for automotive applications. In this work, initial evaluation of DLC coatings was performed using scratch, micro-hardness, fracture toughness and surface roughness tests on sintered Al. Raman spectra analysis confirms the DLC formation. The DLC coated sintered Al samples exhibits micro-hardness in the range of 2000 to 2300 kg mm−2 when measured using a Vickers diamond pyramid indenter of 0.5 N load applied on it. In some localized regions, even more hardness (>5000 kg mm−2) has been obtained. Scratch test results shows a fairly homogenous coating with strong adhesive nature having almost four times the average critical force compared to electro-statically deposited sample. Fracture toughness and surface roughness are well within the acceptable ranges of DLC coatings. The capability of laser sintering to produce thick DLC coatings with outstanding mechanical and tribological properties and excellent bonding with aluminium offers the possibility to tailor an extreme lightweight, strong and wear-resistant material. Nano indentation result indicates the information of plastic and elastic deformation for industry based applications.

Mechanism of negative strain rate sensitivity in metallic glass film

The observation of negative strain rate sensitivity during nanoindentation is a common, yet poorly understood phenomenon in metallic glasses. In this study, a combination of experimental investigation and atomistic simulation has been employed to understand the mechanism behind this perplexing effect. The results suggest that the negative strain rate sensitivity arises out of the influence of a slow time-dependent relaxation process during the driven deformation at a controlled rate. By complementing the experimental outcome by simulation results, it is possible to show that this unification of the rate-driven and relaxation mechanisms is the consequence of their overlapping timescales. In addition, we demonstrate that by using the numerical results of simulated nanoindentation, it is possible to calculate the size and activation volume of the shear transformation zone, which is otherwise difficult using only experimental data in the regime of negative strain rate sensitivity.

Oxidation behaviors of ZrB2 based ultra-high temperature ceramics under compressive stress

ZrB2 based ultra-high temperature ceramic (UHTC) is one of the most promising materials for thermal protection systems. This paper focuses on the oxidation behaviors of ZrB2 under compressive stress. ZrB2 UHTC is fabricated with nano-sized powders at 1500 °C, which is a relative low temperature. Nanoindentation tests are conducted to measure the basic mechanical properties of sintered samples. Results of nanoindentation show that ZrB2 is prepared with good mechanical properties. Oxidation tests are performed under different stress states and temperatures, and oxidation mechanisms and microstructure evolution are discussed. As the oxidation proceeds, ZrO2 grains grow slowly at 1000 °C, but fast at 1200 °C. When oxidized over 1400 °C, ZrO2 grains fuse and micro-sized pores form on the surface due to the release of gaseous oxidation products. The thickness of oxide layer on the samples almost keeps unchanged under various compressive loads. Compared with the stress state, microstructure has a more obvious effect on the oxidation rate. The results in this paper provide a better understanding on the oxidation mechanism of ZrB2 based UHTCs.

Experimental Study of Synthesized Co-polymer for Stent Application

Poly-L-lactic acid (PLLA), predominantly used for manufacturing bioresorbable polymeric stents, is brittle and has a considerable degradation time (over 2~3 years). To address its deficiencies, one of the employed techniques is to blend it with elastomers, typically polymers with rubber-like behaviour. The aim of this paper is to assess a co-polymer developed for potential cardiovascular application to address the limitations of PLLA. The focus is on characterisation of mechanical properties of the co-polymer using a spherical nanoindentation technique, in comparison with those of PLLA. The copolymer is a blended poly(L-lactide-co-e-caprolactone)-poly (ethylene glycol) (PLA-(PCL-PEG)), with weight ratios of 60% and 40% for PLA and PCL-PEG, respectively. The novelty of this copolymer is the addition of phosphate-glass particles (less than 2 μm in size and 10 wt%), aiming to toughen the material. The material was supplied in the form of tubing. The obtained nanoindentation results, together with the data of tensile testing, showed that the novel co-polymer (PLA-(PCL-PEG)) did not perform well in comparison to PLLA, and, hence, required further improvements in composition and processing.

MICROSTRUCTURE, MECHANICAL AND TRIBOLOGICAL BEHAVIOR OF THE TiAlVN COATINGS

In this present work, the TiAlVN coatings were deposited by magnetron sputtering using a single alloy target of Ti60Al30V10. The effect of the argon (Ar) to nitrogen (N2) gas flow ratio on the structure, morphological characteristics and mechanical properties of the TiAlVN coating were investigated. The results of X-ray diffraction show the coatings have only face-centred cubic (fcc) structures at different gas ratio of Ar:N2. FE-SEM observation analysis each of the TiAlVN coatings indicated that the change of the gas ratio affects the surface morphology. The nano-indentation results demonstrated that coatings deposited with the gas ratio of Ar:N2 being 9:1 exhibited the highest hardness and elastic modulus. Moreover, with the various gas ratio of Ar:N2, ball-on-disc against SUJ2 ball in air at room temperature indicated friction coefficient from 0.43 to 0.58 in dry condition and 0.073 to 0.12 in oil condition, respectively, which is related to the surface roughness and grain sizes of the coatings.

Mechanical properties of Fe-based amorphous–crystalline composite: a molecular dynamics simulation and experimental study

A new Fe-based amorphous–crystalline composite without non-metallic elements, Fe55Cr15Mo15Ni10W5, was prepared by melt-spinning. The formation ability and structure information were investigated by X-ray diffractometer (XRD), energy-dispersive spectrometer (EDS) and scanning electron microscope (SEM). The mechanical properties of the amorphous–crystalline composite were investigated by nanoindentation. A molecular dynamics simulation study was performed to simulate the formation of Fe55Cr15Mo15Ni10W5 amorphous alloy. The mechanical properties were obtained by compression simulations simultaneously. The results indicate that the Fe55Cr15Mo15Ni10W5 ribbon is an amorphous–crystalline composite structure with good ductility, and the hardness of the amorphous–crystalline composite is about 75% higher than that of master ingot. The simulation mechanical properties are in good agreement with the results of nanoindentation at the nanoscale.

Generalisation of the oxide reinforcement model for the high oxidation resistance of some Mg alloys micro-alloyed with Be

The present work studied how Be influences Mg alloy oxidation. Be microalloying significantly decreased the oxidation rate at 500 °C and increased the ignition temperatures of as-cast Mg-2Zn, Mg-2Sn, AS21, and ZC63. However, Be addition had little effect on the oxidation resistance of as-cast ZK20, AM60 and Mg-2Y. Based on the nanoindentation results, the present results can be well understood and explained using the recently proposed oxide layer reinforcement model, which indicates that the mechanical strength of the initially formed oxide controls Mg alloy oxidation.

Method for highly spatially resolved determination of residual stress by using nanoindentation

Measurement of highly spatially resolved residual stresses is a crucial task for tailoring the stress state during manufacturing to improve mechanical performance of metallic objects. Especially in sheet metal forming or blanking with sheet thicknesses down to 0.1 mm, a highly resolved pattern of the stress distribution over the sheet thickness is required for optimisation. For this purpose, a method which uses an extended Hertzian theory for calculating residual stresses from the results of nanoindentation is used to measure the stress profile in metallic cylinders. For verification of the indentation results, hole drilling is utilised to determine residual stresses in the near-surface area. This method provides similar assumptions about the stress state (biaxial). The measuring principle is also based on correlations between mechanical behaviour of the material and the residual stress distribution. The results yield a good accordance of the measured values despite the different scales of measurement. Therefore, a highly spatially resolved measurement of residual stresses with nanoindentation is possible and shows comparable values to the classic hole drilling technique.

Microstructure and tribological properties of TiTaHfNbZr high entropy alloy coatings deposited on Ti[sbnd]6Al[sbnd]4V substrates

We report on the microstructure and tribological behavior of equimolar TiTaHfNbZr high entropy alloy (HEA) thin films deposited on the biomedical Ti6Al4V substrates by RF magnetron sputtering. Results of nanoindentation and sliding wear experiments were evaluated along with the microstructure and topographical information obtained from scanning electron microscopy and atomic force microscopy. The findings clearly demonstrate that the TiTaHfNbZr HEA not only forms a homogenous and dense coating mechanically compatible with the Ti6Al4V substrates, but also provides a significantly enhanced surface protection against wear and cracking, which could prove valuable especially in long-term orthopedic implants that bear dynamic contact loading, such as in the cases of hip or knee joints.

Spark plasma sintered Al-0.5 wt% MWCNT nanocomposite: Effect of sintering pressure on the densification behavior and multi-scale mechanical properties

The current study aims to understand the effect of sintering pressure on densification behaviour and mechanical properties of multi walled carbon nanotube (MWCNT) reinforced aluminum (Al) based nanocomposite synthesized via spark plasma sintering (SPS). Physio-chemical functionalization, a novel dispersion technique, was followed which led to homogenous dispersion of MWCNTs in Al matrix. The crystallite size and density of the synthesized Al-0.5 wt% MWCNT nanocomposites increased with increase in sintering pressure. The relative density increased from 90.4% to 95.1% upon increasing the sintering pressure from 30 MPa to 80 MPa. To understand the densification behaviour, the movement of graphite punch within the die filled with Al-MWCNT powder mixture during sintering was monitored. Higher sintering pressure led to early onset of sintering and the total punch displacement during sintering increased from 0.38 mm to 1.48 mm upon increasing the applied pressure from 30 MPa to 50 MPa. The impact of high sintering pressure, leading to enhanced densification, was also translated in the improvement in mechanical properties. Compressive strength and microhardness increased by ~30% and ~13%, respectively as sintering pressure was increased from 30 MPa to 80 MPa. Higher sintering pressure leading to significantly enhanced mechanical properties at micro and macro scale was also replicated at nano-scale as confirmed by the results of nanoindentation and nanoscratch tests.