Nanoscratch Measurements Research Articles

Mechanical responses and plastic rheological behavior of Ti–Zr-Hf-Co-Ni-Cu metallic glass thin films deposited with different substrate temperatures during nanoindentation and nanoscratch process

Ti–Zr-Hf-Co-Ni-Cu metallic glass thin films were deposited by magnetron sputtering at different substrate temperatures of 293 K, 373 K, and 473 K. All the thin films were indicated to be amorphous. The roughness was decreased from 0.71 ± 0.02 nm (293 K) to 0.65 ± 0.01 nm (473 K) and the thin film became more densified with fewer voids and defects. Consequently, the mechanical properties, plastic rheological behavior, and nanoscratch properties varied regularly with the microstructure at different substrate temperatures. The hardness and elastic modulus showed increasing trends with the elevated substrate temperature. The strain-rate strengthening effect occurred, causing the gradual disappearance of the pop-in event with the increasing strain rate. The cut-off value of strain burst size showed an increasing trend with the elevating strain rate. This trend was weakened with the elevated substrate temperature due to the decreased chaos of the interaction between atoms. The cut-off value also increased with the elevating substrate temperature. During the nanoscratch measurement, the elastic recovery ratio increased with the elevating substrate temperature. The critical stress for interface separation of the Ti–Zr-Hf-Co-Ni-Cu metallic glass thin film was improved from 1.9 N to 2.7 N with the substrate temperature rising from 293 K to 473 K.

A strong enhancement of corrosion and wear resistance of polyurethane-based coating by chemically grafting of organosolv lignin

Corrosion and wear pose significant challenges to equipment operating in harsh environments. Thus, protective coatings are needed. Anti-corrosion and anti-wear coatings are traditionally fossil-based and often contain environmentally harmful additives. Achieving anti-corrosion and anti-wear coatings based on environmentally benign and sustainable materials is important and a significant challenge. This work focused on the development of organosolv lignin-based polyurethane (OS_lignin-PU) coatings. The coatings were synthesised and evaluated for corrosion protection using electrochemical impedance spectroscopy (EIS) and for wear properties using nanoindentation and nano scratch measurements. EIS revealed that the optimal lignin content for corrosion protection purposes in the OS_lignin-PU coatings was 15 wt%. Moreover, addition of 15 wt% lignin to the OS_lignin-PU coatings also enhanced their wear resistance, as evidenced by reduced thickness loss during tribometer tests. The nano scratch measurements revealed that OS_lignin-PU coatings containing 15 wt% lignin exhibited the lowest scratch depth and friction coefficient. It is found that the developed lignin-containing coating exhibits remarkable corrosion and wear resistance, making it a promising sustainable material in various applications for pursuing sustainable development.

Tribological Characteristics of Thermomechanically Processed 7075 Al Alloy Through Nano-scratch Characterization

Age-hardenable Al–Zn–Mg–Cu (AA 7075) alloys can be fortified by precipitation solidifying because of precipitation of the MgZn2 intermetallic stages. Furthermore, grain refinement and high dislocation density can also be opted for strengthening purposes. A low-temperature deformation enhances the dislocation density and also facilitates the grains recovery to strengthen the component. The present study combines artificial aging (at 120 °C) and sub-zero (∼−20 ˚C) temperature rolling to achieve strengthening. Various sequences and combinations of these mechanical and thermal treatments are performed and the effects of these treatments on the tribological characteristics of the alloy are studied by nano-scratch measurements. The tribological characteristics are indicated by coefficient of friction ( μ), plastic energy ( PE), recovery index ( η), recovery resistance parameter ( Rs), etc. of each sample. The widths of the scratch are further utilized to calculate the scratch hardness values ( Hs), wear resistance coefficients ( Rw) and the coefficient of wear ( K) with the help of Archard's equation.

Recycle of ceramic substrate of PDMS/ceramic composite membranes towards alcohol-permselective pervaporation

Nowadays, membrane recycling has received increasing attention in water treatment, gas separation and pervaporation. Compared with polymeric substrates, inorganic substrates possess higher mechanical and thermal stability, which can be reused to balance the high cost. In this work, for the first time, we studied the recycle of inorganic substrate that was used for fabricating polymeric composite membranes. A facile approach was proposed to recycle ceramic substrate from PDMS/ceramic composite membranes with thermal degradation followed by ultrasonic cleaning. The thermal degradation compositions of PDMS membrane under air or nitrogen atmosphere were investigated by using TGA-IR, XRD and XPS analysis. Influence factors of the recycle approach including degradation conditions, cleaning approach and multi-recycle process were explored to optimize the transport properties of ceramic substrate and PDMS/ceramic composite membrane. The interfacial morphologies and adhesion of the PDMS membrane coated on the recycled ceramic substrate were characterized by SEM and nano-scratch measurement. The results demonstrated that PDMS composite membrane fabricated on the ceramic substrate with 10 times recycle by thermal degradation in nitrogen at 800 °C for 4 h and ultrasonic cleaning could still achieve >92% separation performance and interfacial adhesive force of the fresh PDMS/ceramic composite membrane. Specifically, the membrane exhibited stable flux of 1.2 kg/m2h and separation factor of 8.1 for 120 h continuous pervaporation separation of 5 wt% ethanol/water at 40 °C. Additionally, ∼75% energy saving relative to synthesizing fresh ceramic substrate was estimated for applying the feasible recycle approach.

Mechanism of Adhesion of Natural Polymer Coatings to Chemically Modified Siloxane Polymer.

Surface coatings play an important role in improving the performance of biomedical implants. Polydimethylsiloxane (PDMS) is a commonly used material for biomedical implants, and surface-coated PDMS implants frequently face problems such as delamination or cracking of the coating. In this work, we have measured the performance of nano-coatings of the biocompatible protein polymer silk fibroin (SF) on pristine as well as modified PDMS surfaces. The PDMS surfaces have been modified using oxygen plasma treatment and 3-amino-propyl-triethoxy-silane (APTES) treatment. Although these techniques of PDMS modification have been known, their effects on adhesion of SF nano-coatings have not been studied. Interestingly, testing of the coated samples using a bulk technique such as tensile and bending deformation showed that the SF nano-coating exhibits improved crack resistance when the PDMS surface has been modified using APTES treatment as compared to an oxygen plasma treatment. These results were validated at the microscopic and mesoscopic length scales through nano-scratch and nano-indentation measurements. Further, we developed a unique method using modified atomic force microscopy to measure the adhesive energy between treated PDMS surfaces and SF molecules. These measurements indicated that the adhesive strength of PDMS-APTES-SF is 10 times more compared to PDMS-O2-SF due to the higher number of molecular linkages formed in this nanoscale contact. This lower number of molecular linkages in the PDMS-O2 indicates that only fewer numbers of surface hydroxyl groups interact with the SF protein through secondary interactions such as hydrogen bonding. On the other hand, a larger number of amine groups present on PDMS-APTES surface hydrogen bond with the polar amino acids present on the silk fibroin protein chain, resulting in better adhesion. Thus, APTES modification to the PDMS substrate results in improved adhesion of nano-coating to the substrate and enhances the delamination and crack resistance of the nano-coatings.

Corrosion behavior of diverse sputtered coatings for the helium cooled pebbles bed (HCPB) breeder concept

Abstract The present paper studies the corrosion behavior of several sputtered coatings (nanostructured W, SiC and Al2O3) under the working conditions expected for the helium cooled pebbles bed breeder concept to be used in future nuclear fusion reactors. To this purpose, coatings were evaluated during 240 h at a temperature of 550 °C in Helium atmosphere with 120 ppms of water to simulate the purge gas in the presence of ceramic pebbles whose composition was a mixture of lithium silicate/titanate. The 3-D topography, morphology, microstructure and elemental composition of the coatings were studied prior to and after the corrosion tests. Results evidence that coatings show quite different corrosion behavior: Because of oxidation, nW is completely ruled out for such application, the corrosion behavior of Al2O3 coating is questionable whereas, SiC coating is shown to act as a real corrosion barrier. Nanoscratch measurements of this last coating show that it also has a good adhesion to the Eurofer substrate both prior to and after the corrosion test.

Optimizing nanostrands-inserted graphene oxide membrane with polyelectrolyte protective layer for enhanced ethanol pervaporation dehydration

Graphene oxide (GO) composite membranes were fabricated on polyacrylonitrile (PAN) substrates via inserting copper hydroxide nanostrands (CHNs) between GO sheets and coupling with an ultrathin hydrophilic sodium alginate (SA) top-layer. The prepared membranes were characterized by using FESEM, FTIR, XRD, water contact angle and nanoscratch measurements. The intercalation of CHNs could enlarge ultrafast water permeation channels in base GO membrane without destroying its interlayered structure. Hydrogen bonding and electrostatic interaction ensured SA layer could firmly adhere onto base GO membrane, which should be conducive to swelling prevention and selective moisture enrichment. The dehydration performance was investigated as a function of SA deposit, CHNs intercalation, and feed temperature. Under optimal SA deposit, the permeation flux could be improved by 30 wt% after the intercalation of CHNs between GO sheets. The permeation flux through the prepared membrane could reach up to 3.65 kg m−2h−1 with an excellent separation selectivity (99.70 wt% water content in permeate) at 70 °C for 10 wt% water–ethanol solution. The permeation flux and separation selectivity both increased with elevated temperatures, revealing the complete anti-trade-off behavior. The prepared membrane also possessed enhanced mechanical strength and firm interfacial adhesion, which ensured its integrity in practical operating conditions.

New insights into the role of Al2O3 nano-supplements in mechanical performance of PMMA and PMMA/HA bone cements using nanoindentation and nanoscratch measurements

ABSTRACT This work was performed to investigate the mechanical and tribological properties of polymethyl methacrylate (PMMA)-based bone cement strengthened by nano-alumina (Al2O3) and nano-hydroxyapatite (HA) particles. Seven cement groups with different amounts of Al2O3 (3 and 5 wt. %) and HA (5 and 10 wt. %) nano-particles were prepared and the nanoindentation and nanoscratch tests were employed to obtain the results. Substantial improvement/reduction in mechanical properties was observed for the addition of 3 wt. % of Al2O3 /5 wt. % of Al2O3 plus 10 wt. % of HA into the PMMA matrix. The additives had almost no obvious effects on the friction of PMMA (~0.3). This research revealed that only the specific weight percent of Al2O3 (here 3 wt. %), compared to other PMMA/Al2O3 and PMMA/HA/Al2O3 cement nanocomposites, had great potential as an added component in PMMA bone cement to provide a significant increase in the mechanical properties of the cement.

Conformal MgO film grown at high rate at low temperature by forward-directed chemical vapor deposition

MgO thin films are deposited by chemical vapor deposition from the precursor magnesium N,N-dimethylaminodiboranate, Mg(H3BNMe2BH3)2, and water at a substrate temperature of 270–350 °C. Highly conformal coatings with 98% step coverage in trenches of aspect ratio 9 are obtained at a substrate temperature of 270 °C and a growth rate of 7.5 nm/min, most notably through the use of a forward-directed flux, in which some of the precursor molecules travel ballistically down the recessed feature, strike the bottom, and are scattered there to create a virtual source. The deposition conditions can also be adjusted to afford a growth rate up to 200 nm/min with reduced conformality. Most of the films have a dense and column-free microstructure with low surface roughness; the film density, measured by a combination of Rutherford backscattering spectrometry and scanning electron microscopy, is 82%–86% of bulk. Films grown on Si substrates have good adhesion and a low coefficient of friction (∼0.1) in nanoscratch measurements. The refractive index of the films is slightly lower than that of bulk MgO, consistent with the reduced physical densities. Depending on the growth conditions, the C content in the films varies between 0.7 and 6 at. %, and the B content ranges from 1 to 16 at. %. B in the film is present in the B2O3 chemical state; after subtracting the O content in B2O3, the O/Mg ratio = 1.02 in the MgO matrix. A film grown at a temperature of 270 °C and a growth rate of 6 nm/min has a dielectric constant of 9.5 and a breakdown strength of 6 MV/cm.

Characterization of Ti/W, Ti/Cr, and Ti/Pt thin flims-Part II: Nano-scratching and tribological properties

The present paper, Part ІІ in a two-part series, describes the scratching behaviors and tribological properties of Ti/W, Ti/Cr, and Ti/Pt thin films annealed at 400, 500, and 600°C that were evaluated by a nano-scratch measurement technique. The results of the nano-scratch tests indicate that the Ti/W film annealed at 400°C exhibited high scratch resistance, good adhesion to the substrate, and a low friction coefficient. On the other hand, cracking and delamination phenomena appeared in the Ti/W films annealed at 500 and 600°C. The Ti/Cr films annealed at 500 and 600°C were better able to withstand the indenter tip than the Ti/Cr film annealed at 400°C, but their tribological performance in terms of friction coefficient was worse than that of the Ti/Cr film annealed at 400°C. The delamination phenomenon did not appear in any of the Ti/Cr films. The Ti/Pt film annealed at 500°C exhibited the highest elastic recoverability and scratch resistance among the Ti/Pt films. The friction coefficient of the Ti/Pt film annealed at 600°C was higher than that of the Ti/Pt films annealed at 400 and 500°C; this was caused by the hillocks formed on the Pt surface as confirmed in Part І. The delamination and cracking phenomena were not observed at all in the Ti/Pt films. Based on the experimental results of Part І and ІІ, the Ti/W film annealed at 400°C among the thin films investigated in this study is the most appropriate for metallization under physical contact conditions in MEMS devices.

Micromechanical behavior of β-Al3Mg2-dispersed aluminum composite prepared by high-energy ball milling and hot pressing

The present investigation deals with the ball milling of Al–Mg, which results in the formation of metastable fcc solid solutions after 100 h that transform into more stable β-Al3Mg2 phase during subsequent annealing treatment. Powder metallurgy route was successfully employed to synthesize different weight fractions of low density β-Al3Mg2 dispersed Al matrix composites. Maximum hardness was achieved for 15 wt% β-Al3Mg2-dispersed Al composites. Compacted composites display lower hardness for higher percentage (20 wt%) of dispersing phase due to possible agglomeration. Nanomechanical properties as obtained from nanoindentation and nanoscratch measurements substantiate the results obtained from the microhardness measurements. Moreover, the significant hardening of the Al matrix was successfully achieved by incorporation of low density β-Al3Mg2 phase.

Tribological behavior of thermomechanically treated Al–Mg–Si alloy by nanoscratch measurements

Age-hardenable Al–Mg–Si alloys can be strengthened by precipitation hardening along with grain refinement and dislocation density. Low-temperature deformation not only increases the dislocation density but also arrests grain recovery and promotes precipitation hardening. In this investigation, sub-zero temperature rolling, in combination with artificial aging, was performed to achieve strengthening as well as substantial amount of plasticity. The thermomechanically treated alloys were subjected to nanoscratch measurements to study the tribological behavior in terms of plastic energy, recovery index, penetration depth and residual depth. Scratch hardness was measured and utilized to calculate the wear rate, recovery resistance, wear resistance and the wear coefficients using Archard׳s equation.

Micromechanical and Nanoscratch Behavior of SiCp Dispersed Metal Matrix Composites

Micromechanical response of silicon carbide particle dispersed Al/Mg/Ti/Cu composite, synthesized by powder metallurgy technique was investigated. A correlation between their microhardness and nanomechanical properties at submicron length scale was established. Hardening effect of SiC particles on the hardness, elastic modulus, recovery index, and plastic energy of the matrices was prominent and may be due to the interactions between geometrically necessary and statistically stored dislocations along with their impediment with dispersoids-matrix interface. The elastic recovery obtained from nanoscratch measurement was also correlated with the recovery parameter, which was derived from the nanoindentation of the composite compacts.

Effect of Aluminum Coating on the Surface Properties of Ti-(~49 at. pct) Ni Alloy

Stable porous layer of mixed Al2O3 and TiO2 has been formed on the Ti-(~49 at. pct) Ni alloy surface with an aim to suppress leaching of Ni from the alloy surface in contact with bio-fluid and to enhance the process of osseointegration. Aluminum coating on the Ni-Ti alloy surface prior to the anodization treatment has resulted in enhancement of depth and uniformity of pores. Thermal oxidation of the anodized aluminum-coated Ni-Ti samples has exhibited the formation of Al2O3 and TiO2 phases with dense porous structure. The nanoindentation and nanoscratch measurements have indicated a remarkable improvement in the hardness, wear resistance, and adhesiveness of the porous aluminum-coated Ni-Ti sample after thermal oxidation.

Interfacial composition and adhesion of sputtered-Y2O3 film on ZnS substrate

Interface engineering has emerged as a fertile and efficacious approach to turn functional properties in the field of film systems. In this work, the interfacial properties of sputtered yttrium oxide films on zinc sulfide substrate (Y2O3/ZnS) were analyzed by transmission electron microscopy (TEM), X-ray photoelectron spectrum (XPS) depth profile and nano-scratch measurement. An interface layer with the depth of 20nm between Y2O3 film and ZnS substrate was directly observed by TEM. Under different film growth conditions, although the interfacial features including interfacial width and composition distribution exhibit similar behavior, it is found that higher cohesive strength is obtained under a special substrate bias voltage of −160V at low substrate temperature. Such an enhanced mechanical property can be understood by the role of physisorbed oxygen in the interfacial region, in which less physisorbed oxygen with van der Waals bonds leads to a strong adhesion. Our results provide a favorable strategy to achieve strong adhesion between oxide and sulfide at low temperature, which are urgent in future micro-electric applications.

Anisotropic nanoscratch resistance of WC grains in WC–Co composite

The influence of the crystal orientation of WC grains on their nanoscratch resistance in WC–Co system was investigated. Instrumented nanoindentation with Berkovich tip was used for nanoscratch measurement. Electron backscatter diffraction (EBSD), atomic force microscopy (AFM) and scanning electron microscopy (SEM) investigations were performed to determine the orientation of WC grains and to study the surface morphology after the scratch test. The scratch resistance of the WC grains exhibits significant angle dependence with higher resistance of grains close to the basal orientation in comparison to the grains close to prismatic orientation.

Scratching by pad asperities in copper electrochemical-mechanical polishing

Low dielectric constant materials/Cu interconnects integration technology provides the direction as well as the challenges in the fabrication of integrated circuits (IC) wafers during copper electrochemical-mechanical polishing (ECMP). These challenges arise primarily from the mechanical fragility of such dielectrics, in which the undesirable scratches are prone to produce. To mitigate this problem, a new model is proposed to predict the initiation of scratching based on the mechanical properties of passive layer and copper substrate. In order to deduce the ratio of the passive layer yield strength to the substrate yield strength and the layer thickness, the limit analysis solution of surface scratch under Berkovich indenter is used to analyze the nano-scratch experimental measurements. The modulus of the passive layer can be calculated by the nano-indentation test combined with the FEM simulation. It is found that the film modulus is about 30% of the substrate modulus. Various regimes of scratching are delineated by FEM modeling and the results are verified by experimental data.

A Methacrylic Anhydride Difunctional Precursor to Produce a Hydrolysis-Sensitive Coating by Aerosol-Assisted Atmospheric Plasma Process

In this paper, we focused our attention on the elaboration of a hydrolyzable plasma-polymer produced by aerosol-assisted atmospheric pressure plasma process. A dielectric barrier discharge (DBD) was hence fed with a commercial methacrylic anhydride precursor – bearing an anhydride hydrolyzable function and two methacrylates groups aiming at producing a highly cross-linked deposit – to produce thin coatings of plasma-polymerized (pp) methacrylic anhydride. IR and NMR were performed to highlight the retention of the hydrolyzable group. After immersion in water, mass spectrometry analysis was conducted on the aqueous medium to characterize the end-products and consequently confirm the occurrence of a hydrolytic degradation. A huge 80% thickness decrease was finally pointed out by nanoscratch measurements after 10 days.

Tribological properties of biocompatible Ti–10W and Ti–7.5TiC–7.5W

This study investigates and compares the microstructure, biocompatibility, and tribological properties of two different Ti-based composites, Ti–10W and Ti–7.5TiC–7.5W, with those of pure Ti for their potential use in biomedical applications. In particular, cold and hot isostatic-pressing and arc-melting methods were utilized and compared for the microstructure of the composites. Nano-scratch measurements and pin-on-disk wear tests were employed to understand their tribological behavior. As compared to pure Ti, Ti–10W and Ti–7.5TiC–7.5W showed significantly improved nano-scratch resistance (by 85 and 77%, respectively) and wear resistance (by 64 and 66%, respectively), in good agreement with hardness measurements. For biocompatibility examination, both microculture tetrazolium test (MTT) and water soluble tetrazolium (WST-1) test were used to quantify the cell viability of human osteoblasts and mouse fibroblasts on the materials. Both of the Ti-based composites showed acceptable biocompatibility in comparison with the pure Ti control.

Emission stability enhancement of a tip-type carbon-nanotube-based field emitter via hafnium interlayer deposition and thermal treatment

Carbon nanotubes (CNTs) were deposited on a tip-type tungsten substrate via electrophoretic deposition, in which a hafnium thin film was used as an interlayer. The long-term (up to 24 h) emission stability of the CNT-based field emitter was remarkably enhanced when the hafnium interlayer was coated and thermally treated. This is attributed to the enhanced adhesion between the substrate and the CNTs. An x-ray photoelectron spectroscopy study and nano-scratch measurement provided a convincing evidence of the increase in the adhesive force.