Nanohardness Tester Research Articles

Investigation of Hybrid Lap Welds of TI6AL4V and Stainless Steel with Bronze Interlayer

Abstract Welding of the austenitic stainless steel AISI 304 and Ti6Al4V is complicated by hard and brittle intermetallic compound formation. In this contribution, we study a laser welding method that partially overcomes this problem using interlayer. Bronze foil (CuSn6) of thickness 100 µm and 200 µm was inserted between steel and titanium sheets and lap welds were realized on pulsed Nd:YAG laser. Representative samples were investigated by nanohardness measurement, SEM/EDS, and XRD analysis to detect the localization of the intermetallic phases. The macrostructure of the weld cross sections was displayed by optical and digital microscopy. The nano-hardness test revealed the presence of very hard intermetallic mainly around the interface between the fusion zone and bottom metal sheet. EDS mapping displayed the main elements Fe, Cr, Cu and Ti distribution in the fusion zone, EDS line scanning detected elements‘ signals in the diagonal and horizontal directions. XRD analysis revealed expected intermetallic compounds FeTi and CuTi2 and solid solution Cu0.8Fe0.2.

Influence of coherent intermetallic nano-precipitates on the nano-level mechanical and tribological properties of the Laser-Powder bed fused Scalmalloy

Scalmalloy alloys fabricated by Laser-Powder Bed Fusion (L-PBF) process are extensively used in the field of aerospace, construction, and automotive applications due to its lightweight, corrosion resistant qualities and fine microstructure. But, there was a lack of in-depth study in the nano-level mechanical properties of the Scalmalloy. So, the prime novelty of this research work is to examine the nano-level mechanical behavior with respect to nano-level precipitations due to Sc-Zr addition. In this work, the L-PBFed Scalmalloy was examined for the irregularities and the grain distributions using Optical Microscopy (OM) and Field Emission Scanning Electron Microscopy (FE-SEM) with Energy-Dispersive X-ray spectroscopy (EDX) analysis. The formation of Al3Sc precipitates was identified using X-ray diffraction (XRD) and Transmission Electron microscopy (TEM) analysis. Further, the influence of precipitates on the grain orientation was evaluated through Electron Backscatter Diffraction (EBSD) analysis. The nano-hardness and nano-wear testing was performed on the L-PBFed Scalmalloy. The maximum nano-hardness and reduced modulus of 2.19 GPa and 87.50 GPa was obtained from the average of 400 indentations. The nano-hardness mapping and reduced modulus mapping proved the homogenous dispersion of the precipitation. From the topographic wear tracks in the nano-wear analysis, the average worn-out height of 250.89 nm was observed and the fluctuation in the co-efficient of friction (CoF) confirms the formation of ceramic phase Al3Sc precipitates which resists the worn-out height. Tensile strength of the L-PBFed Scalmalloy was evaluated based on the 3 strain rates (3.3 × 10−5, 1.6 × 10−5 and 2 × 10−4 s−1) and the outcome shows that the Scalmalloy exhibits negative strain rate and serration caused by Portevin-Le Chatelier effect on the Al3Sc precipitates and the Mg content.

Performance improvement of magnetorheological finishing using chemical etchant and diamond-graphene based magnetic abrasives

Thermally sprayed tungsten carbide coating is extensively engaged in wear resistance applications due to its good tribological properties. For some applications in aerospace, automotive, printing and forming industries, these coated components require a nanolevel surface finish. In the current investigation, magnetorheological fluid based finishing (MRF) process is carried out on the pre-polished tungsten carbide coating using standard magnetorheological (MR) fluid which contains diamond powder as the abrasive particles. In this case, the lower gripping strength of non-magnetic abrasives into the chain structures of carbonyl iron particles (CIPs) is responsible for inadequate material removal rate (MRR) and irregular polishing. To overcome these problems, MRF is conducted with a chemical etchant and that leads to a higher finishing rate due to the integrated effect of etching and polishing. However, it is perceived that the ability of normal MRF technique and MRF with chemical etchant is somehow restricted at a higher wheel velocity. To address these challenges of MRF process, CIP-diamond and CIP-diamond-graphene composite abrasives are introduced in this investigation. Due to the resilient attraction force among the composite abrasives, a much higher yield stress is observed and that leads to higher MRR and less spilling of MR fluid even at an elevated wheel speed. Composite magnetic abrasives are characterized using nanohardness tester, magnetometer and rheometer to assess its mechanical and magnetic behaviours. The lowest surface roughness (Sa) of 55 nm and highest MRR are attained using MRF with CIP-diamond-graphene abrasives.

Nanosecond Laser Induced Surface Structuring of Cadmium after Ablation in Air and Propanol Ambient.

In the present study KrF Excimer laser has been employed to irradiate the Cadmium (Cd) targets for various number of laser pulses of 500, 1000, 1500 and 2000, at constant fluence of 3.6 J cm-2. Scanning Electron Microscopy (SEM) analysis was utilized to reveal the formation of laser induced nano/micro structures on the irradiated target (Cd) surfaces. SEM results show the generation of cavities, cracks, micro/nano wires/rods, wrinkles along with re-deposited particles during irradiation in air, whereas subsurface boiling, pores, cavities and Laser Induced Periodic Surface Structures (LIPSS) on the inner walls of cavities are revealed at the central ablated area after irradiation in propanol. The ablated volume and depth of ablated region on irradiated Cd targets are evaluated for various number of pulses and is higher in air as compared to propanol ambient. Fast Fourier Transform Infrared spectroscopy (FTIR), Energy Dispersive X-ray Spectroscopy (EDS) and X-ray Diffraction (XRD) analyses show the presence of oxides and hydro-oxides of Cd after irradiation in propanol, whereas the existence of oxides is observed after irradiation in air ambient. Nano-hardness tester was used to investigate mechanical modifications of ablated Cd. It reveals an increase in hardness after irradiation which is more pronounced in propanol as compared to air.

Comparison Study of PVD Coatings: TiN/AlTiN, TiN and TiAlSiN Used in Wood Machining.

In this paper, we analyze the possibilities of the protection of tools for wood machining with PVD (Physical Vapor Deposition) hard coatings. The nanolayered TiN/AlTiN coating, nanocomposite TiAlSiN coatings, and single layer TiN coating were analyzed in order to use them for protection of tools for wood machining. Both nanostructured coatings were deposited in an industrial magnetron sputtering system on the cutting blades made of sintered carbide WC-Co, while TiN single layer coating was deposited by evaporation using thermionic arc. In the case of TiN/AlTiN nanolayer coatings the thickness of the individual TiN and AlTiN layer was in the 5–10 nm range, depending on the substrate vertical position. The microstructure and chemical composition of coatings were studied by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) method. Additionally, in the case of the TiN/AlTiN coating, which was characterized by the best durability characteristics, the transmission electron microscope (TEM) and X-ray photoelectron spectroscopy (XPS) methods were applied. The coatings adhesion to the substrate was analyzed by scratch test method combined with optical microscopy. Nano-hardness and durability tests were performed with uncoated and coated blades using chipboard. The best results durability characteristics were observed for TiN/AlTiN nanolayered coating. Performance tests of knives protected with TiN and TiAlSiN hard coatings did not show significantly better results compared to uncoated ones.

Effects of a 445 nm diode laser and silver diamine fluoride in preventing enamel demineralisation and inhibiting cariogenic bacteria

ObjectiveTo study the effects of a 445 nm diode laser (L) and silver diamine fluoride (F) on preventing enamel demineralisation and inhibiting cariogenic bacteria. MethodsThirty-three enamel slices were sectioned each into four blocks for four groups to receive L with F (LF), F, L and Water (W, control). Ten blocks from each group were used to evaluate demineralisation. Surface morphology, lesion depth and nanohardness of the blocks after pH-cycling were studied by scanning electron microscopy (SEM), nanohardness test, and micro-computed tomography, respectively. Twenty-three blocks per group were used for biofilm assessment. Morphology, viability, and growth kinetics of the Streptococcus mutans biofilm were assessed by SEM, confocal laser scanning microscopy, and the counting of colony-forming units (CFUs), respectively. ResultsSEM images of LF-treated enamel showed an intact surface compared with other groups. Nanohardness (GPa) for LF, F, L and W were 1.43±0.17, 1.01±0.11, 1.04±0.13 and 0.73±0.14, respectively (p < 0.001; LF>F, L>W). Their lesion depths (µm) were 46±8, 52±6, 88±13 and 111±9, respectively (p < 0.001; LF, F<L<W). SEM showed few bacteria for LF and F compared with other groups. Their dead-live ratio were 1.67±0.13, 1.60±0.15, 0.39±0.05 and 0.32±0.05, respectively (p < 0.001; LF, F>L>W). Log CFUs for LF, F, L and W were 4.2±0.3, 4.5±0.2, 7.9±0.3 and 9.4±0.2, respectively (p < 0.05; LF<F<L<W). Two-way ANOVA analysis revealed an interaction effect on nanohardness and Log CFUs between the laser irradiation and SDF treatment (p < 0.001). ConclusionThis study showed a superior caries preventive effect of a combined treatment of the diode laser and SDF. Because diode laser and SDF are affordable and readily available, clinicians can provide this treatment to their patients for caries prevention. Clinical significance statementDiode lasers are handy, afforable and readily avaliable to clinicians. This study provides information of use of 445 nm diode laser for caries prevetion. The laser irradiation hopefully can be added before conventional topical SDF application.

Effect of heat treatment on the microstructure and properties of CoCrFeNiMo0.2 particles reinforced titanium matrix composites

In this paper, the influence of heat treatment process on the microstructure and properties of CoCrFeNiMo0.2/Ti composites was studied by heat treatment of the composites. The structure and composition of CoCrFeNiMo0.2/Ti composites were characterized by X-ray diffraction and optical microscope. The distribution of elements of the interface layer was explored by electron probe. The mechanical properties of the composites were analyzed by nano indentation experiment and hardness tester. The relationship between irregular particles and the thickness of the interface layer was studied. The results are as follows: when the heat treatment temperature is 770 °C, the morphology of the high entropy alloy does not change significantly. As the temperature rises to 830 °C, the shape of the particles deforms and the thickness of the diffusion layer increases significantly. With the increase of the heat treatment temperature, the Young’s modulus and hardness of the interface layer have increased. When the heat treatment temperature rises to 890 °C, the particles completely diffuse into the matrix. Overall, the distance of the particles from the inscribed circle and the thickness of the interface layer are positively correlated.

Characterization of KrF Excimer Laser Ablation of Cadmium in Different Liquids for Biomedical and Industrial Applications

Liquid-assisted laser ablation (LALA) has gained substantial attention as a method that can achieve desired chemical and physical properties. The fabrication of carbides (CdCO3), oxides (CdO), and hydro-oxides (Cd(OH)2) on Cd surfaces make them more useful in industrial and biomedical applications due to the enhancement of their physical properties. For this purpose, LALA of Cadmium (Cd) is performed using a KrF Excimer laser (248 nm, 20 ns) at varying numbers of pulses from 500 to 2000 at constant fluence (3.6 Jcm−2) in deionized water (DI) and ethanol. A comparison of the ablation behavior of Cd in DI water and alcohol (ethanol) environments is discussed in the present work. The surface structuring and enhancement of mechanical properties are also discussed in correlation with the changes produced in its crystallinity due to the increase in the chemical reactivity of Cd in both ambient environments. The surface features, chemical composition, structural and compositional analysis, and mechanical properties of irradiated targets are evaluated using a Scanning Electron Microscope (SEM), X-ray Diffraction (XRD), Fast Fourier Transform Infrared spectroscopic (FTIR), Energy Dispersive X-ray Spectroscopy (EDS), and a Nano-hardness tester. Pores, cavities, hillocks, wave-like ridges, nanoparticles, flake-like structures, and periodic surface structures are distinguished features on the Cd surface after irradiation. However, the density and size of pores and cavities are higher in water, whereas ethanol is favorable for the growth of craters and ripples. These features are attributable to various thermal and chemical phenomena induced by laser heating at the solid–liquid interface. Ethanol-assisted ablation is more favorable for enhancing the hardness of Cd as compared to DI water-assisted ablation due to the presence of maximum compressive stresses and minimum crystallite size (C.S.) caused by the diffusion of carbon into the target surface.

The effect of ZnO nanoparticles on nanomechanical behavior of Hydroxyapatite electrodeposited on NiTi biomedical alloy

This paper aims at surface characterization, chemical composition, and mechanical properties of Hydroxyapatite/ZnO (HA/ZnO) nanocomposite coatings on NiTi biomedical alloy. Morphological observations by FESEM and AFM techniques showed that ZnO NPs were responsible for a uniform, porous HA matrix. XRD analysis proved the pure HA phase synthesis in the presence of ZnO NPs; without them, there were other secondary CaP phases. XPS chemical state investigations firmly confirmed the presence of ZnO NPs by showing peaks at 531.05 eV (O ─ Zn bond) and 1021.82 eV (Zn ─ O bond). Nano-hardness test highlighted a significant enhancement in hardness of composite coating (0.37 GPa) compared to pure HA coating (0.19 GPa). The notable point was that HA/ZnO nanocomposite exhibited more plasticity than HA simple coating. This is beneficial as it provides a comfortable spot for cellular activities. Last but not least, the nano-scratch analysis revealed a great effect of ZnO inclusion on reducing friction coefficient by around 40%. The critical load was also much higher for HA/ZnO composite coating (91.4 mN) than HA coating (58.5 mN). Owing to higher plasticity and lower friction coefficient, HA/ZnO composite managed to ease the movement of the indenter tip on its surface, thereby suffering less shear stress.

Investigation of HVOF sprayed novel Al1.4Co2.1Cr0.7Ni2.45Si0.2Ti0.14 HEA coating as bond coat material in TBC system

The present study aims to investigate non-stoichiometric Al1.4Co2.1Cr0.7Ni2.45Si0.2Ti0.14 high entropy alloy (HEA) as a bond coat material for the TBC (Thermal Barrier Coating) system. The mechanical activated synthesized HEA was sprayed on a Ni-based superalloy substrate by High-velocity oxy-fuel (HVOF) spraying, and 8 mol% Yttria Stabilized Zirconia (YSZ) was deposited on HEA by Air Plasma Spray (APS). X-Ray Diffraction (XRD) analysis and Scanning Electron Microscopy (SEM) were used to investigate the phases and microstructure of the as-synthesized HEA powder, Ni superalloy/HEA-bond coat, and Ni superalloy/HEA-bond coat/YSZ topcoat. The mechanical properties of the coating like microhardness, Young’s modulus and residual stress between bond coat and YSZ top coat was evaluated using the Nano-Hardness Tester (NHT). The TBC system was investigated for cyclic oxidation at 1050 ℃ for 100 cycles, and its cross-sections were analyzed for TGO (Thermally grown oxides) layer composition, thickness and interdiffusion of elements. The properties of the TBC system containing HEA as a bond coat were compared with those of the conventional TBC system comprising of MCrAlY (AMDRY 365–4) as a bond coat. It was observed that HEA containing TBC displayed exceptional high temperature properties and were comparable to MCrAlY.

Role of Nitrogen and Yttrium Contents in Manufacturing (Cr, Y)Nx Film Nanostructures.

The high-power impulse magnetron sputtering (HiPIMS) technique was applied to deposit multilayer-like (Cr, Y)Nx coatings on AISI 304L stainless steel, using pendular substrate oscillation and a Cr-Y target and varying the nitrogen flow rate from 10 to 50 sccm. The microstructure, mechanical and tribological properties were investigated by scanning and transmission electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, instrumented nano-hardness, and wear tests. The columnar grain structure became highly segmented and nanosized due to pendular substrate oscillation and the addition of yttrium. The deposition rate increased continuously with the growing nitrogen flow rate. The increase in nitrogen flow from 10 to 50 sccm increased the hardness of the coatings (Cr, Y)Nx, with a maximum hardness value of 32.7 GPa for the coating (Cr, Y)Nx with a nitrogen flow of 50 sccm, which greatly surpasses the hardness of CrN films with multilayer-like (Cr, Y)Nx coatings architecture. The best mechanical and tribological performance was achieved for a nitrogen flow rate of 50 sccm. This was enabled by more elevated compressive stresses and impact energies of the impinging ions during film growth, owing to an increase of HiPIMS peak voltage with a rising N2/Ar ratio.

Quantification of the carbon content of single grains in martensite-ferrite dual phase steel by UHV-EDXS

The detection and quantification of carbon by conventional energy dispersive X-ray spectroscopy (EDXS) performed under standard conditions is not feasible due to occurring contaminations in common electron microscopes. In contrast, novel ultra high vacuum EDXS (UHV-EDXS) was used to acquire elemental mappings of carbon on dual phase (DP) steel, which exhibits a microstructure consisting of ferrite and martensite. These phases differ in hardness, local dislocation density and, most importantly, in their carbon content. Since the UHV conditions in combination with a customized windowless EDXS detector ensured a minimization of hydrocarbon contamination during the measurements and a maximization of the sensitivity for the detection of light elements, UHV-EDXS carbon mappings could successfully be obtained, which clearly reflect the ferrite and martensite microstructure of the investigated DP steels, as confirmed by electron back scatter diffraction (EBSD). Most importantly, it was possible to quantify the carbon content of individual grains with concentrations as low as 0.25 wt%. Furthermore, nano-hardness tests were performed on the very same grains which were characterized by UHV-EDXS and EBSD. It is shown that the hardness of the martensite grains is correlated to their carbon content, as directly determined by UHV-EDXS. With this new method an additional tool for advanced material characterization of multiphase materials on the level of individual grains is now available. • Quantification of low carbon concentrations is obtainable by EDXS under UHV conditions. • The carbon content of single martensite grains was determined by UHV-EDXS in DP steels. • Nanoindentation was equally performed on individual martensite and ferrite grains of the DP steels. • Correlation between the hardness of the grains, the martensite volume fraction and the carbon content in the martensite was proven.

Selective Laser Melting of 304L and 316L Stainless Steels: A Comparative Study of Microstructures and Mechanical Properties

In article 2100664, Zhou, Nai, and co-workers show that 304L and 316L have similar compositions. However, a selective laser melted 304L and 316L show a significant difference in grain size and morphology. Their microstructures and mechanical properties are compared using a scanning electron microscope, electron backscattered diffraction, nanohardness, and tensile tests. This comparative study proposes a method for grain refinement and microstructure tuning in additive manufacturing.

Tribotechnical properties of experimental hard alloys with modified cobalt binder

Introduction. This paper discusses tribomechanical characteristics of experimental hard alloys with a modified cobalt binder under friction without lubrication on hard-to-cut materials – stainless steel and titanium alloy. The research objective is to evaluate the process of friction interaction for each friction pair according to a number of parameters, and to determine the optimal combinations of “experimental hard alloy – structural material” on the basis of the established tribological indicators.Materials and Methods. Tribological tests of hard alloys were carried out using a cylinder-to-disc friction scheme for different sliding speeds and temperatures under constant load without the use of lubricants. Comparison of the friction interaction process was carried out by the frictional force, volumetric wear and roughness of the friction tracks on the counterbody. Stainless steel 12H18N9Т and titanium alloy ВТ3-1 were used as counterbody materials. The resistance of experimental compositions to the abrasive type of wear was determined through measuring the surface dynamic microhardness on a scanning nanohardness tester by analyzing the thickness of the scratches caused by the indenter.Results. According to the results of surface microindentation, the experimental alloys 2.22 (binder 5.65% Co + l.8% Mo + 0.6% Ti) and 2.23 (binder 5.1% Co + 2.7% Mo + 0.61 % Ti) are characterized by the highest microhardness. For these materials, the average scratch width at various forces was minimal. During tribological tests, the best frictional characteristics were recorded for stainless steel in combination with experimental alloy 2.22, and for the friction pair “titanium alloy VT3-1 — hard alloy 2.23”. The friction of this combination of materials was characterized by low friction coefficients with a low level of fluctuations, minimal wear of samples, and changes in the initial microrelief of their surfaces.Discussion and Conclusions. As a result of the research, the optimal friction pairs from the point of view of tribological interaction were established, specifically “titanium alloy VT3-1 — hard alloy 2.23” and “stainless steel 12X18N9T – hard alloy 2.22”. The frictional interaction for these combinations of materials is characterized by minimal volumetric wear, which will contribute to increasing the wear resistance of the tool in the areas of elastic contact on the front and rear surfaces.

Evaluation of microstructure, nanoindentation and corrosion behavior of laser cladded Stellite-6 alloy on Inconel-625 substrate

Inconel-625 (IN-625) is one of the widely used high-temperature alloys in various areas of application. Its outstanding characteristics like thermal stability, low density, higher yield strength and oxidation resistance makes it to get implemented in areas including supercritical boilers, heat exchangers, nuclear and pressurized water reactors. In severe aggressive environments, the surface of this alloy is prone to wear and corrosion attacks which leads to sudden failure of the components. This work has attempted to improve the corrosion resistance of the IN-625 alloy by depositing the Stellite-6 particles through the laser cladding technique. The cladded sample was cross-sectioned to analyze the microstructure using the FESEM technique. The nanohardness test has been carried out to evaluate the hardness offered by both the base and the cladded region. The corrosion (uniform type) behavior was analyzed in an electrochemical way on both the base and the cladded samples for different time periods. In addition, the EIS technique was used to evaluate the enhancements in the corrosion resistance of the samples followed by the surface roughness examination. Results showed that the hypoeutectic structure was obtained on the cladded region due to the influence of Co-rich dendritic and Cr-rich inter-dendritic eutectic phases. The cladded region exhibited higher hardness than the base region. Moreover, the cladded sample with 17 h time interval exhibited greater resistance towards corrosion compared with the other duration samples. The formation of oxide has been the major key factor for the enhancement of corrosion resistance. In addition to that, 17 h cladded specimen experienced minimized surface roughness with increased corrosion resistance.

Tribological properties of in-situ PVD TiAlN, TiSiN, and TiAlN/TiSiN coatings under ambient air and vacuum environment

It is known that the interest in manufacturing in a vacuum environment has increased in recent years. Thus, the wear behavior of mechanical tools under vacuum conditions has critical importance. However, adhesion and cold-welding problems between tool and working piece in vacuum conditions lead to poor wear properties and severe coefficient of friction values. Surface treatment methods such as physical vapor deposition coatings can eliminate these undesirable consequences, especially transition metal nitrides. In this study, TiAlN, TiSiN, and TiAlN/TiSiN films were coated on AISI H13 tool steels employing the cathodic arc evaporation technique. Whether the coatings grown to the substrate surface have a positive contribution to the wear performance of the substrate in the ambient air and vacuum environment was answered. Scanning electron microscope, energy dispersive spectrometer, and X-ray diffractometer analyses were used to attain structural properties. The hardness was measured using a nano-hardness tester, and the adhesion properties were determined by a scratch test. The wear behavior of the substrate and coating samples are determined under 2 N constant normal load and using WC-6%Co counter bodies under ambient air and vacuum conditions. The hardness of samples improved owing to surface coatings, and the highest nano-hardness value was determined from the TiSiN coatings as 39.42 GPa, which is ∼700% greater than the substrate. It has been observed that coated samples have superior wear performance in both wear conditions. Besides, it is determined that those tested under a vacuum condition showed superior wear resistance than the samples tested under ambient air. While TiSiN film exhibits the highest wear resistance in ambient air, the TiAlN/TiSiN layer is the best in a vacuum environment. Owing to the deposited coatings, the seizure mechanism between the friction surfaces, which is frequently encountered in the vacuum environment, is prevented, and a fascinating improvement in terms of friction coefficient is achieved.

Experimental and Numerical Study on Friction and Wear Performance of Hot Extrusion Die Materials.

For the aluminium alloys produced by the hot extrusion process, the profile is shaped according to the bearing at the exit of the extrusion die. The tribological process has significant effects on the die service life, profile dimensional tolerances, and profile surface finish. Recently, new technologies have been introduced to the hot extrusion die, such as cemented carbide insert die and surface coating. However, under hot extrusion working conditions, quantitative studies on their friction and wear performances are lacking. In this work, the friction and wear performances of three typical extrusion die materials, traditional hot tool steel (H13), cemented carbide (YG8), and chemical vapour deposition (CVD) coating, were studied. Macro and nano hardness tests, Pin-on-disk friction and wear tests, optical profiler and SEM observations, and experiments and simulations of hot extrusion were conducted. The results show that the coefficients of friction of CVD coatings and H13 hot work tool steel specimens were smaller under the hot extrusion condition than at room temperature. The wear mechanisms of H13, YG8, and CVD coatings at 500 °C are adhesion, abrasive, and fatigue, respectively. Moreover, the tribology results were validated by the extrusion experiments and the finite element analysis of hot extrusion. The conclusion of this manuscript is useful not only for the numerical simulation of the hot extrusion process but also for the surface finishing of the extrusion profile.

Mouse Dspp frameshift model of human dentinogenesis imperfecta

Non-syndromic inherited defects of tooth dentin are caused by two classes of dominant negative/gain-of-function mutations in dentin sialophosphoprotein (DSPP): 5′ mutations affecting an N-terminal targeting sequence and 3′ mutations that shift translation into the − 1 reading frame. DSPP defects cause an overlapping spectrum of phenotypes classified as dentin dysplasia type II and dentinogenesis imperfecta types II and III. Using CRISPR/Cas9, we generated a Dspp−1fs mouse model by introducing a FLAG-tag followed by a single nucleotide deletion that translated 493 extraneous amino acids before termination. Developing incisors and/or molars from this mouse and a DsppP19L mouse were characterized by morphological assessment, bSEM, nanohardness testing, histological analysis, in situ hybridization and immunohistochemistry. DsppP19L dentin contained dentinal tubules but grew slowly and was softer and less mineralized than the wild-type. DsppP19L incisor enamel was softer than normal, while molar enamel showed reduced rod/interrod definition. Dspp−1fs dentin formation was analogous to reparative dentin: it lacked dentinal tubules, contained cellular debris, and was significantly softer and thinner than Dspp+/+ and DsppP19L dentin. The Dspp−1fs incisor enamel appeared normal and was comparable to the wild-type in hardness. We conclude that 5′ and 3′ Dspp mutations cause dental malformations through different pathological mechanisms and can be regarded as distinct disorders.

Structure and properties of Ta–Si–N coatings obtained by pulsed magnetron sputtering

Pulsed magnetron sputtering of a TaSi2 ceramic target 120 mm in diameter was used to deposit coatings on model silicon substrates at a gas flow rate ratio of Ar/N2 = 1/2 and frequencies of 5, 50, and 350 kHz. The structure and composition of coatings were investigated using scanning electron microscopy, energy dispersive analysis and glow discharge optical emission spectroscopy. The phase composition was determined by X-ray diffraction analysis using CuKα radiation. Mechanical properties were measured by the nanoindentation method using a Nano Hardness Tester equipped with a Berkovich indenter at a load of 4 mN. The heat resistance of coatings was evaluated by isothermal annealing in the air in a muffle furnace at 1200 °С, and oxidation resistance was estimated by the structure and thickness of the oxide layer. The results of structure studies have shown that the coatings are X-ray amorphous and have a dense homogeneous structure. Increasing the frequency from 5 to 350 kHz led to a decrease in the thickness and growth rate of the coatings. Samples deposited at 5 and 50 kHz showed high mechanical performance: hardness at the level of 23–24 GPa, elastic modulus of 211–214 GPa, and elastic recovery of 75–77 %. The coating obtained at the maximum frequency had a hardness of 15 GPa, elastic modulus of 138 GPa, and elastic recovery of 65 %. Annealing led to the formation of protective SiO2, Ta2O5, TaO2 oxide layers. A pronounced crystallization of the TaSi2 phase was observed, which is confirmed by the X-ray diffraction analysis data. Samples deposited at 5 and 50 kHz showed a small oxide layer thickness of 0.9 and 1.1 μm, which indicates the good heat resistance of coatings at 1200 °С.

Sintering parameters study of a biphasic calcium phosphate bioceramic synthesized by alcoholic sol-gel technique

In the sintering of biphasic calcium phosphate bioceramics (BCP) can occur phases transformations accompanied by a sudden thermal expansion due to different coefficients of thermal expansion of each phase, which generates internal stress concentrations inducing undesired cracks within the sample. Therefore, this work aimed to study the sintering parameters of a BCP, composed of hydroxyapatite (HAp) and β-tricalcium phosphate (β-TCP), synthesized by the alcoholic sol-gel technique, in order to evaluate the better conditions for avoiding defect generation. BCP powders were uniaxially cold-pressed at 300 MPa and air-sintered at 1070 °C/2 h (BCP1070 sample) and 1130 °C/2 h (BCP1130 sample), with heating rates of 10 °C/min and 5 °C/min, respectively. Samples were characterized by X-ray diffraction, Fourier-transform infrared spectroscopy, scanning electron microscopy, relative density determination, Vickers hardness test, and nanohardness tests. The results displayed that the assessed sintering parameters were suitable for promoting a satisfactory particle consolidation. The transformation from HAp to β-TCP occurred simultaneously with grain growth and material densification under all conditions. The mechanical tests revealed that BCP1070 and BCP1130 samples have different behaviour when analyzed micro or nanostructurally. But, the heating rate (10 °C/min) combined with the sintering temperature (1070 °C) anabled to obtain a suitable sinterability with samples presenting smaller grain size and without defects. Further, it kept the microporosity which is an essential property for application in bioceramic materials.