Nanohardness Values Research Articles

Deformation and wear in a H21 (3Cr2W8V) steel die during hot forging: simulation, mechanical properties, and microstructural evolution

Deformation and wear in a hot-forging die made of H21 steel was investigated using finite element analysis, nanoindentation, microhardness, optical scanning method, electron backscattering diffraction, and transmission electron microscopy. The results showed that deformation and wear were concentrated more in some die regions during the hot-forging process. In these regions, the processing parameters such as strain, strain rate, and temperature were suitable for the occurrence of different softening mechanisms such as the formation of blocky ferrite phase, recovery of dislocations, tempering, and dynamic recrystallization. In addition, dynamic recrystallization happened by both the continuous and discontinuous mechanisms causing the formation of fine and equiaxed grain with a low density of dislocations. These softening mechanisms reduced nano hardness values from 6.69 GPa in base material to 3.91 GPa in deformed regions. The results of this study may help scientists and engineers understand the origin of the failure of hot-forging dies for industrial applications.

Role of Fe2Al5 in fracture of novel dissimilar aluminum-steel resistance spot welds using multi-ring domed electrodes

In a comparative study of resistance spot welded (RSW) 1.2 mm AA6022 joined to 2.0 mm high strength low alloy (HSLA) steel and 1.2 mm AA6022 joined to 2.0 mm low carbon steel (LCS) it was found that quasi-static tensile tests and mini shear tests exhibited similar intermetallic compound (IMC) strength but different load capacity, i.e., nominal shear strength in tensile shear tests. This phenomenon was related to the Fe2Al5 structure and properties at the Al-steel interface which were unique for each stack-up. The thicker Fe2Al5 layer in 1.2 mm AA6022-2.0 mm LCS was comprised of fewer but larger grains which contributed to a larger difference between the Young's modulus of FeAl3 and Fe2Al5 than in 1.2 mm AA6022-2.0 mm HSLA. The Fe2Al5 in the AA6022-LCS stack-up was more brittle and rigid with greater nanohardness values and smaller variation in elastic modulus that may have contributed to lower overall joint strength with large variation. In addition, AA6022-LCS welds produced with non-optimized and optimized weld schedules produced different IMC shear strengths which was attributed to the different mismatch in Young modulus values that accentuated the differences in shear stresses at the FeAl3/Fe2Al5 interface.

An investigation into microstructure, tribological and mechanical properties of cold sprayed Inconel 625 coatings

In this study, Inconel 625 coatings were successfully deposited on 6061 aluminum alloy using a high-pressure cold spray process. The microstructure, mechanical and tribological properties of the coatings were systematically studied. The cold sprayed Inconel 625 coatings had a low porosity level due to the severe plastic deformation of the splats. EBSD analyses revealed that grain refinement occurred within the coatings and substrates (near the substrate-coating interface), which could be attributed to strain accumulation and fragmentation process. Good adhesion strength of above 57.0 MPa was achieved between the coatings and substrates. Nano-hardness and micro-hardness values were higher than those of bulk Inconel 625 and were uniform along the thickness of the coatings. The effects of normal load and sliding velocity on the tribological properties of cold sprayed Inconel 625 coatings were investigated by sliding wear tests . The wear results demonstrated that both increased sliding velocity and normal load led to higher specific wear rates, which could result from the combined effects of tribo-film delamination , adhesive wear , abrasive wear, and thermal softening. Lower coefficients of friction of the coatings measured under 5 N compared to those measured under 2 N with the same sliding velocity could be explained by transition of wear mechanisms as well as larger coverage of tribo-film on the wear tracks. • Inconel 625 coating was successfully cold sprayed onto aluminum alloy 6061. • Hardness of the coating was much higher than the bulk Inconel 625 alloy. • The adhesion strength greater than 57 MPa was achieved. • Coefficient of friction decreased with increasing normal load. • Wear mechanisms at varying normal load and sliding velocity were revealed.

Investigation of nanohardness values of dual-cure, bulk-fill composite resins at different time intervals

Aim: The aim of this study was to evaluate the surface hardness of dual-cure, bulk-fill composite resins at different depths and time intervals using nanoindentation.
 Methodology: In the study, a comparison was conducted of the nanohardness values of Fill-Up, HyperFIL, and Cention N dual-cure, bulk-fill composite resins in the experimental group and Reveal HD, a light-cured, bulk-fill composite, in the control group. The dual-cure, bulk-fill composites used in the experimental group were divided into two subgroups. The first group was polymerized with an LED light source, and the second group was chemically polymerized in line with the manufacturer's instructions. The dual-cure composite resins were prepared in two different depths, 5 mm and 10 mm. In the control group, specimens with a depth of 5 mm were prepared, and their polymerization was provided by an LED light source. The nanohardness values of the lower and upper surfaces of the samples were measured using the Hysitron TI 950 Triboindenter 24 hrs and 7 days after polymerization.
 Results: Following statistical evaluations, no statistically significant difference was found between the nanohardness values measured 24 hrs and 7 days after light or chemical polymerization of the dual-cured, bulk-fill composite resins. It was observed that light polymerization of HyperFIL and Fill-Up dual-cure, bulk-fill composite resins had no effect on nanohardness values. When Cention N dual-cure, bulk-fill composite resin was polymerized with a light source, higher values of nanohardness were obtained.
 Conclusion: It was determined that the investigated dual-cure, bulk-fill composites reached their final hardness after 24 hrs. In all groups, it was observed that the highest nanohardness values belonged to Cention N for both polymerization methods.
 
 How to cite this article: Bolgül B, Özdemir E. Investigation of nanohardness values of dual cure bulk-fill composite resins at different time intervals. Int Dent Res 2021;11(Suppl.1):19-25. https://doi.org/10.5577/intdentres.2021.vol11.suppl1.4
 
 Linguistic Revision: The English in this manuscript has been checked by at least two professional editors, both native speakers of English.

Simulation and optimization of lightweight insulating geopolymer composites via dual gradient slurry deposition

High porosity over 50% is essential to achieving lightweight and thermal insulating properties in the green manufacturing of geopolymers. Recognizing that mechanical and thermal properties are highly related to pore distribution and orientation, we analyze and optimize the pore of the geopolymer composites with purposely designed different gradient variations via additive manufacturing (AM) and simulate the related properties. The results shows that adding 15 wt% diamond in the specimen reduced the heat flux and the maximum value of heat flux at 15 wt% part is 13.429 J/s. The dynamic nano hardness and Young's modulus values both increase with increasing diamond ratios in addition to the 12 wt%. Besides, the elongated shape of internal pores and throat is closely related to the layer-stacking printing method, playing a more significant role than material in the decreased thermal and ductile compressive behavior. 3D structure of Schwarz w with connected pores is proved to have the optimal mechanical and thermal performances among the eight typical triply periodic structures. This research establishes the guidelines to the pore analysis and simulation of multiple mineral composites with tailored, deigned-pore-dependent lightweight and thermal insulation properties.

Melatonin-doped polymeric nanoparticles induce high crystalline apatite formation in root dentin

ObjectiveTo investigate the effect of novel polymeric nanoparticles (NPs) doped with melatonin (ML) on nano-hardness, crystallinity and ultrastructure of the formed hydroxyapatite after endodontic treatment. MethodsUndoped-NPs and ML-doped NPs (ML-NPs) were tested at radicular dentin, after 24 h and 6 m. A control group without NPs was included. Radicular cervical and apical dentin surfaces were studied by nano-hardness measurements, X-ray diffraction and transmission electron microscopy. Mean and standard deviation were analyzed by ANOVA and Student-Newman-Keuls multiple comparisons (p < 0.05). ResultsCervical dentin treated with undoped NPs maintained its nano-hardness values after 6 m of storage being [24 h: 0.29 (0.01); 6 m: 0.30 (0.02) GPa], but it decreased at apical dentin [24 h: 0.36 (0.01); 6 m: 0.28 (0.02) GPa]. When ML-NPs were used, nano-hardness was similar over time [24h: 0.31 (0.02); 6 m: 0.28 (0.03) GPa], at apical dentin. Root dentin treated with ML-NPs produced, in general, high crystallinity of new minerals and thicker crystals than those produced in the rest of the groups. After 6 m, crystals became organized in randomly oriented polyhedral, square polygonal block-like apatite or drop-like apatite polycrystalline lattices when ML-NPs were used. Undoped NPs generated poor crystallinity, with preferred orientation of small crystallite and increased microstrain. SignificanceNew polycrystalline formations encountered in dentin treated with ML-NPs may produce structural dentin stability and high mechanical performance at the root. The decrease of mechanical properties over time in dentin treated without NPs indicates scarce remineralization potential, dentin demineralization and further potential degradation. The amorphous stage may provide high hydroxyapatite solubility and remineralizing activity.

Comparison of restorative materials and surface alterations after prebiotic and probiotic beverages: A nanoindentation and SEM study.

The purpose was to investigate the surface characteristics of various resin-based materials by immersing in probiotic beverages. A total of 420 disc-shaped samples (5 mm × 2 mm) were prepared from resin-based composites. Samples were divided into four groups and immersed for 10 min/day for 1 month in either a probiotic sachet, kefir, kombucha, or artificial saliva (control). Surface roughness was measured at baseline and 1 month. One sample of each of the tested materials was examined under nanoindentation to evaluate the reduced elasticity modulus and nanohardness scores. Scanning electron microscopy (SEM) was used to compare surface differences. Data were analyzed statistically using one-way ANOVA test and the significance was set at p < .05. The lowest roughness scores were observed in Z250, Estelite Bulk Fill, and HRi ENA in most of the test groups. Among conventional composites, Z250 group had the highest nanohardness and elasticity modulus scores. Among bulk-fill composites, Estelite Bulk Fill Flow had the lowest surface roughness after immersion in probiotic beverages and the highest nanohardness values. Reveal HD, as a bulk-fill group showed higher surface roughness and considerably lower nanohardness and elasticity modulus scores. Maximum height levels of samples were recorded. SEM images revealed voids and microcracks on the surfaces of test materials. Dentists may prefer Z250 as microhybrid and Estelite Bulk Fill Flow as bulk-fill composites for the restorations of patients who consume gut-friendly drinks regularly. When there are various types of materials, nanoindentation is a useful method for evaluating surface alterations and sensible comparisons.

Effect of Mo content on Ti-Al-Mo ternary alloys for biomedical applications

The microstructure, microhardness, nano hardness, wear-resistance, and anti-wear properties of Ti6AlxMo ternary alloys (x = 3–15 wt%) have been studied for biomedical applications. The microstructural and phase analysis have demonstrated that there is an increase in the β phase with the increase in Mo wt%, while α and α2 phases decrease. Consequently, Ti6Al15Mo alloy has the lowest elastic modulus value. The highest micro and nano hardness values were exhibited by Ti6Al6Mo alloy owing to the presence of alpha and beta colonies with low interlayer distance in the microstructure. The hardness and wear resistance properties of Ti6Al15Mo alloys were comparatively higher than existing biomaterials like Ti6Al4V and CP Ti. The Ti6Al15Mo alloy can be considered as a promising new age biomaterial.

Nondestructive measurement of the mechanical properties of graphene nanoplatelets reinforced nickel aluminium bronze composites

Nanoindentation is a viable method to assess the mechanical properties of developed alloys and composites at the nanometer scale without hampering the microstructure and integrity of materials. In this study, nondestructive measurement was conducted on spark plasma sintered nickel aluminium bronze (NAB), and graphene nanoplatelets (1, 2, 3 wt.%) reinforced NAB composites using the nanoindentation technique. The nondestructive measurements were conducted under loads of 50 mN and 100 mN to assess the nanohardness and reduced elastic modulus of the fabricated NAB alloy and composites. Further investigations were carried to evaluate the elastic recovery index, plasticity index, the nanohardness and reduced modulus ratio, and the yield pressure to reveal the nanomechanical responses of the fabricated materials. Scanning electron microscopy was used to analyze and reveal the dispersibility of the graphene nanoplatelets (GNP) in the NAB matrix. The nondestructive measurements showed that the nanohardness, reduced elastic modulus, yield pressure, resistance to elastic strain to failure and the elastic recovery index improved with the presence and increase in the concentration of GNP in the NAB matrix. The reduced elastic modulus and nanohardness values range from 34.2 – 43.0 GPa and 4407.2–6598.8 MPa respectively, which declined with nanoindentation loads. The fabricated NAB alloy experienced the maximum plastic deformation and least resistance to impact loading.

Obtaining multilayer coatings by the detonation spraying method

This work were studied the effect of technological parameters of detonation spraying on the phase composition and tribological characteristics on the bases of NiCr and Al2O3 coatings. As well as there was obtained and investigated multilayer coating on the bases of NiCr/NiCr- Al2O3/Al2O3 . It was determined that during detonation spraying the phase composition of Al2O3 coatings strongly depends on the degree of filling the borehole with a gas mixture. The a - Al2O3 -phase content in the coatings increases when the degree of filling is 63% and 54%. Only one CrNi3 phase is observed on the diffractograms and only increase of reflex intensity (020) at barrel filling by 58% is observed by sputtering on the bases of NiCr coatings in different degrees of barrel filling. The results of the coating nanohardness study showed that the hardness of the Al2O3 coating increases depending on the content of a- Al2O3 in it. Al2O3 coating has the maximum nanohardness values and is 16.42 GPa at the borehole is filled to 63%. The nanohardness of NiCr coating has the maximum values at barrel filling by 58% and consisting of 8.02 GPa.

The influence of Cr and Ni doping on the microstructure of oxygen containing diamond-like carbon films

Non-hydrogenated diamond-like carbon (DLC) films doped with metals and oxygen were deposited by direct current magnetron sputtering. The influence of chromium and nickel on the surface morphology, elemental composition, bonding structure, adhesion force, optical transmittance and nanohardness of the films was characterized by atomic force microscopy (AFM), energy dispersive X-ray spectroscopy (EDX), multi-wavelength Raman spectroscopy, UV–VIS–NIR spectrophotometry and nanoindenter. The surface roughness was reduced with the addition of Cr (7.4 at. %) or Ni (8.9 at. %) into DLC films. The EDX measurements indicated that the addition of Cr increased the oxygen content by ~37%, while Ni reduced it by ~50%, compared to the oxygen doped DLC film. The microRaman analysis indicated that the G band shifted to a higher wavenumbers range, became narrower and the sp3/sp2 sites fraction ratio decreased for the metals doped DLC films. The nanohardness values of the sputtered doped DLC films varied in the range of 4.5–7.6 GPa. It was observed that the Ni-DLC film showed the highest adhesion force value and was optically opaque.

The Microstructure and Properties of Laser Shock Peened CMSX4 Superalloy

The influence of laser shock peening on the surface morphology and microstructure of single-crystal CMSX4 nickel-based superalloy was investigated by optical profilometry and atomic force microscopy, scanning and transmission electron microscopy as well as scanning-transmission electron microscopy in high-angle annular dark-field mode. Maps of chemical elements distribution in the laser-affected areas were determined using energy-dispersive X-ray spectroscopy. Furthermore, after the LSP, nanohardness tests were conducted on the cross section of the treated samples as well as the untreated material. Laser shock peening caused an ablation and melting of the surface layer and hence enlarged the surface roughness. Beneath the surface, in the laser shock-peened areas, severe distortion of the regular {gamma mathord{left/ {vphantom {gamma {gamma^{prime}}}} right. kern-0pt} {gamma^{prime}}} microstructure was observed. In the surface layer, down to about 15 μm, shear bands of localized deformation were formed. Moreover, the result showed that the average nano-hardness value was obviously increased in the laser-treated region.

Formation and nanomechanical properties of intermetallic compounds in electrodeposited Cu–Sn–Co multilayers

The properties of the intermetallic compounds (IMCs) formed at the interface between the solder and the Under Bump Metallization (UBM) are crucial for the reliability of solder joints. Cobalt (Co) is a potential candidate for UBM since it can act as a diffusion barrier and hence can improve the performance of tin-based solder joints. Growth kinetics, mechanism of formation, and properties of IMC in the copper-tin-cobalt (Cu–Sn–Co) system that is encountered with Co UBM are presented in this paper. Cu–Sn–Co systems were prepared by electrodeposition of Cu, Sn and Co multilayers on Cu substrates followed by reflow at 250 °C for varying durations (1–30 min). Microscopic observation revealed the formation of defect-free (Co,Cu)Sn3, crack-containing (Cu,Co)6Sn5 and thin irregular Cu3Sn IMCs after 1 min reflow. As reflow duration increased, (Co,Cu)Sn3 and Cu3Sn grew at the expense of (Cu, Co)6Sn5. The consumption of the entire Sn layer after 1 min and the calculated effective interdiffusion coefficient of (Co,Cu)Sn3 suggested that the growth of (Co,Cu)Sn3 after 1 min is controlled by solid-state diffusion of Sn. The average Young’s Modulus values of (Co,Cu)Sn3, (Cu,Co)6Sn5 and Cu3Sn are 99.5 ± 3.2 GPa, 110.8 ± 7.3 GPa and 109.4 ± 0.3 GPa, respectively, while the nanohardness values are 4.15 ± 0.34 GPa, 6.74 ± 0.62 GPa and 4.96 ± 1.09 GPa, respectively. Increasing the reflow duration in the Cu–Sn–Co system is expected to improve the performance of the solder joint, through the replacement of the crack-containing (Cu,Co)6Sn5 by the defect-free (Co,Cu)Sn3.

Fabrication of graphite reinforced TiCxNy by spark plasma sintering technique: A comparative assessment of microstructural integrity and nanoindentation properties

This study investigated the fabrication of three different binderless TiCxNy (where the values of x and y are 0.5, 0.7, 0.9 and 0.5, 0.3, 0.1 respectively) reinforced with 0.5 wt%, 1.0 wt%, and 1.5 wt% graphites. The reinforcement particles were dispersed in TiCN matrix using the high energy ball milling technique, and the admixed powders were sintered using the novel spark plasma sintering method. The phase analysis and the structural morphologies of the starting powders and sintered specimens were analyzed using field emission scanning electron microscope (FE-SEM), Transmission electron microscope (TEM), and X-ray diffractometer (XRD), respectively. The milling process outcomes showed that the composite powders contain some isolated graphite powders distributed around the matrix as titanium carbonitride. The stoichiometry of the processed powders gave some consistency in the carbon-rich phase. The significant improvement in the properties of as-sintered composites, including microstructure, elastic modulus, fracture toughness, and hardness, was due to the presence of graphite in the ceramic composite. The graphite were also observed to improve the relative densities of specimens as the optimum relative density was achieved at 99.56% when 1.5 wt% of graphite was dispersed in TiC0.9N0.1. The nanohardness and elastic modulus values of the most improved composites are as follow; From the nanohardness test, the composites with 0.5 wt% graphite + TiC0.5N0.5, 1.5 wt% graphite + TiC0.7N0.3 and 1.0 wt% graphite + TiC0.9N0.1 had their nanohardness values recorded as 34.5 GPa, 33.3, and 35.1 GPa, respectively, while the highest elastic modulus of 350 GPa was recorded in TiC0.5N0.5 and TiC0.7N0.3 with respective reinforcement addition of 0.5 and 1.5 wt% graphite respectively. There is a clear increase in grain growth and graphite segregation when 1.5 wt% of graphite was dispersed in TiC0.9N0.1. However, the uniform distribution of grains was observed when the same (1.5 wt% graphite) proportion of nanoparticle was dispersed in TiC0.5N0.5 and TiC0.7N0.3 composites.

Liquation cracking in Inconel 617 alloy by Laser and Laser-Arc Hybrid welding

ABSTRACT The present study investigates susceptibility of Inconel 617 to liquation cracking in laser-based welding techniques such as autogenous laser welding (ALW) and laser-MIG hybrid welding (LHW) with variation in heat input. Advanced characterization techniques such as high-speed Nano-Indentation testing and micro X-ray diffraction techniques were utilized to analyze microstructural variations in correlating mechanical behavior of low-melting eutectics formed in partially melted zone (PMZ). Results indicated that the liquation cracking in PMZ was associated with the constitutional liquation reaction between intermetallic carbides and austenite matrix. With increase in heat input, its susceptibility reduced, although with enhancement in grain-boundary liquid film formation and was associated with the constitutional liquation of (Cr, Mo)-rich M23C6 carbides and γ matrix. Combined effect of induced thermal stress with presence of low-melting eutectics in partially melted zone was found to greatly influence liquation-cracking susceptibility in both the welding processes. Indeed, ternary eutectic comprising metallic carbides of Cr and Mo and austenite-matrix with low nano-hardness values compared to that of hard carbides present in base metal and weld fusion zone re-confirmed their influence on cracking susceptibility. Increase in heat input enhanced dissolution of Mo-rich M6C carbides that attributed to stress-relaxation and thereby reduce cracking propensity.

Structural and mechanical properties of Ta-based coatings deposited on polymers for biomedical applications

The polypropylene meshes currently used for hernioplasty induce severe chronic inflammatory reactions over a long-term period of use. These processes lead to scarring and have a negative effect on the connective tissue and the abdominal walls. It is well-known that the biocompatibility of polymer surfaces might be improved by surface modification. We report on the structure and composition of nanostructured Ta, Ta2O5 and TaON coatings deposited on polypropylene in correlation with their mechanical properties. The elemental distribution and chemical composition of the coatings were analyzed by energy dispersive X-ray spectroscopy. The coatings cross-sectional structure and morphology were observed by electron scanning microscopy. Mechanical tests were performed of the polypropylene and of the samples with Ta-based coatings to evaluate the Vickers hardness and the elastic modulus. The coated samples exhibited higher nano-hardness and elasticity values, significantly exceeding the values of untreated polypropylene samples. The Ta-based coatings deposited by magnetron sputtering improve the mechanical characteristics and biocompatibility of the polypropylene materials in view of, e.g., hernia repair.

ИССЛЕДОВАНИЕ СОПРОТИВЛЕНИЯ МЕХАНИЧЕСКОЙ ДЕФОРМАЦИИ ЭПИТАКСИАЛЬНЫХ СЛОЕВ α-Ga2O3 МЕТОДОМ НАНОИНДЕНТИРОВАНИЯ

Gallium oxide (Ga2O3) is a wide-band semiconducting material with an energy gap width Eg=4.8–5.0 eV, high conductivity (λ~10.9–27.0 W/(m·K)), and radiation and chemical resistance. Its energy gap width and conductivity allow in the future using the material in the structures of power equipment and optoelectronic devices to increase their energy performance, i.e. to decrease heating and increase productive capacity. Radiation resistance, high breakdown field, and optical asymmetry of Ga2O3 make it attractive for application when designing UV-photoelectric receivers and space systems. The electrical and optical properties of Ga2O3 are amply studied, but there are no systematic data on its physical and mechanical properties (hardness, Young’s modulus, and crack resistance). The paper investigated the deformation in α-Ga2O3 epitaxial layers during nanoindentation. For indentation, the authors used NanoTest (Micro Materials Ltd.) hardness meter. The surface (0001) of α-Ga2O3 crystalline layers produced in the process of chloride gas epitaxy on sapphire (Al2O3) substrates with basic (0001) orientation was investigated. For the first time, the authors experimentally obtained the values of α-Ga2O3 hardness and Young’s modulus using the Oliver-Farr method. The dependences of the indentation load on the penetration depth demonstrated the deviation from linearity, including stress relaxation coming from the pop-in phenomenon. The average values of nanohardness H and Young’s modulus E were 17 and 281 GPa, respectively. The obtained H and E values demonstrate higher characteristics compared to the formerly studied β-Ga2O3 epitaxial layers. This discrepancy can be explained by the more close-packed arrangement of the α-Ga2O3 structure (the corundum type) than one of monoclinic β-Ga2O3. The study shows that α-Ga2O3 leaves the majority of semiconducting materials behind in its mechanical properties conceding only to gallium nitride (GaN) and sapphire (Al2O3)

Predicting Flow Curves of Q&amp;amp;P Steel Using Sharp Pyramidal Nanoindentation on Constituent Phases: Isostrain Method

In this research, a method is presented for predicting macroscopic plastic flow behavior of a quench and partitioning (Q&amp;P) steel using data of nanoindentation experiments.The method is based on Tabor’s model in which nanohardness values obtained with indenters of different angles to be connected to the flow behavior of the indented material. The process consists of two steps: (i) the macroscopic flow relation of each microphases assessed based on the characteristic strain and constraint factor, (ii) the total flow curve of the steel extracted through an isostrain manner. A rationally successful prediction of the macroscopic plastic flow of the Q&amp;P steel is obtained from the constituent phases properties due to consideration of the indentation size effect and application of a rule of-mixture. Eventually, the accuracy of the estimation is verified by comparing the predicted stress-strain curve to the tensile curve obtained from a standard bulk sample.

Effect of element Te on alterations of microstructure and mechanical property of nickel-based superalloy Inconel 718 through alloy infiltration

Alloying elements have significant effects on material physical and mechanical properties. The present work studies the effect of element Te on the alterations of microstructure and mechanical property of nickel-based superalloy Inconel 718. Te was diffused into the surface layer of treated samples with a new alloy infiltration method. The microstructure and element distribution within the modified layer were tested and quantitatively characterized with scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). The depth of infiltration layer presented an approximately linear relationship with the treating temperature range from 700 °C to 900 °C. Furthermore, the mechanical property of the modified layer was evaluated through nano-indentation experiments. The results show that the Te infiltration into the surface layer of Inconel 718 presents a gradient distribution from the outmost surface to the matrix, and it results in a substantial weakening of the modified layer. A gradual decrease in nano-hardness was detected from the surface to the matrix, and the nano-hardness value of infiltration layer was weakened by 31% for the Te infiltration treatment at 900 °C. The underlying weakening mechanism of Te on the superalloy Inconel 718 was revealed. Te element penetrates along the grain boundary leading to the formation of new intercrystalline phases. Consequently, the grain boundary is “opened” which causes the embrittlement of grain boundaries and weakening of the treated surface. This study can not only help to understand the influence of alloying elements on the variation of material properties, but also provide guidance for design of material compositions.

Dentin erosion preventive effects of various plant extracts: An in vitro atomic force microscopy, scanning electron microscopy, and nanoindentation study.

The overall consumption of acidic beverages has become more common, making the prevention and treatment of dental erosion an important consideration. The aim of this in vitro study was to evaluate the effect of various plant extracts in preventing dentin erosion. Seven experimental groups (fluoride-free water, fluoride-containing mouthwash [Colgate Plax], green tea, rosehip, clove, pomegranate, and grape seed) were formed, each consisting of 20 bovine dentin samples. The specimens were exposed daily to demineralization and remineralization cycles three times per day over 5 days through a 5-min plant extract application before each erosive episode. Surface roughness, nanohardness values, and morphological changes on dentin surfaces were examined using atomic force microscopy (AFM), nanoindentation, and scanning electron microscopy (SEM). The data were subjected to Kruskal-Wallis and Friedman tests (p < .05). There were statistically significant differences between the groups in terms of nanohardness values (p < .05), except for the pomegranate and grape seed groups. The highest nanohardness value was observed in the clove group (1.24 ± 0.34 GPa), whereas the lowest nanohardness value was noted in the grape seed group (0.20 ± 0.04 GPa). The nanohardness values of positive and negative control groups after erosion cycles were statistically higher than the initial nanohardness values (p < .05).There was no statistically significant difference between the groups in surface roughness values (p > .05). Macromolecular deposits were observed both in the SEM and AFM images of the pomegranate, Colgate, and rosehip groups. It can be concluded that the clove extract group is more successful in preventing dentin erosion than the other groups. Green tea is also effective in preventing dentin erosion, similar to clove extract. The application of plant extracts may be a new treatment strategy in preventing dentin erosion. Plant extracts may also reduce the severity of existing dentin erosion. Clove and green tea extracts may present novel natural therapy potential by inhibiting dentin erosion.