Microhardness Results Research Articles

Microstructure and material properties of 3D-printed bimetallic steels

Corroded steel components can be repaired by laser 3D printing technology. However, studies on the mechanical behaviour of repaired areas composed of a substrate and deposited material are still limited. In this study, 316L stainless steel powder was deposited on Q355B steel plates through 3D laser printing technology to form bimetallic steel plates. Uniaxial tensile tests were conducted on Q355B steel coupons, laser 3D-printed 316L stainless steel coupons, and bimetallic steel coupons. The test results revealed that ductile fracture occurred in the bimetallic steel coupons. The mechanical properties of bimetallic steel are considerably correlated with the properties of the cladding layer and substrate. During the loading process, the axial strain of the bimetallic steel coupons was uniformly distributed along the thickness direction, indicating that the substrate and cladding materials maintained excellent cooperative deformation. Bending tests and scanning electron microscopy observations indicate that a reliable and robust metallurgical bond is established at the interface between the substrate and the cladding layer. The interface area can be divided into the cladding layer, the carburising zone, the decarburised zone, and the Q355B substrate. The microhardness results indicate a considerable increase in the hardness of the carburised layer, which enhances the tensile strength of the bimetallic steel. On the basis of the experimental results, a three-stage model for predicting the stress‒strain curve of bimetallic steel was established.

The effect of direct aging treatment on microstructure and mechanical properties of the GH4099 superalloys produced by selective laser melting

The effect of direct aging (DA) treatment on microstructure and mechanical properties of the GH4099 superalloys produced by selective laser melting (SLM) was investigated by the microhardness tests, room- (RT) and high-temperature (HT) tensile tests, field emission scanning electron microscopy (FE-SEM), and electron backscattered diffraction (EBSD) in this study. Both microhardness and RT tensile results show that DA treatment improves mechanical properties more than solution-aging (SA) treatment. By analyzing the effect of the microstructural features on the yield strength, we found that the dominant strengthening mechanisms responsible for higher yield strength of the DA specimens are the grain size hardening of fine γ matrix, high-density dislocation strengthening, Orowan dislocation bypass strengthening of smaller but dense M23C6-type carbides, and chemical strengthening of smaller but dense γ΄ nanoprecipitates. Furthermore, a transgranular fracture is a dominant fracture type for RT tensile specimens produced by DA treatment. Conversely, the failure type of SA tensile specimens is a typical intergranular fracture mechanism. The underlying mechanism for the above phenomenon is attributed to the effects of transgranular and intergranular M23C6-type carbides.

Influence of a Constant Magnetic Field on the Parameters of the Magnetoplastic Effect in Aluminum Alloy B95pch

The present work is devoted to the comprehensive experimental study of the magnetoplastic effect found in the aluminum alloy B95pch aged in a weak constant magnetic field. The data on chemical composition of aluminum alloy B95pch, modes of thermal and thermomagnetic treatments and main experimentally observed regularities of changes in values of microhardness, modulus of elasticity of separate local areas and phase composition of aluminum alloy B95pch, aged at temperature 140°С, time from 2 to 8 h, in a constant magnetic field with intensity 557.0 kA/m and in its absence are presented. It was found that the constant magnetic field significantly affects the strength properties and structure of aluminum alloy B95pch. The negative magnetoplastic effect has been detected, the value of which is 21%. It is observed that the constant magnetic field does not significantly affect the average grain size, however, the size and number of observed foreign inclusions within the grain become significantly smaller compared to aging in the absence of magnetic field. In addition, the imposition of the constant magnetic field on the phase formation process leads to the formation of a more distorted structure: the half-width of diffraction lines becomes wider. The results of microhardness and modulus of elasticity measurements of aluminum alloy B95pc were found to be correlated.

Stabilization of durable tetragonal phase and barrier regions in y-123 ceramic systems with partial substitution mechanism

This study examines the impact of Tb and Zn doping on the Y-123 superconducting system by analyzing crack propagation mechanisms through Vickers microhardness measurements. The measurements are conducted at various application forces ranging from 0.245 N to 2.940 N. The microhardness measurements are used to determine the role of impurity addition on Vickers hardness, modulus of elasticity, brittleness index, fracture toughness, and yield strengths. It is found that impurity ions serving as strong barrier regions improve the surface residual compressive stress sites and interactivity between the adjacent layers. Similarly, the sensitivity to the external forces reduce significantly with the substitution mechanism due to the induced new slip systems and ionic bond formations. Accordingly, all the mechanical performance properties are recorded to increase significantly with the impurity ions. Especially, the replacement of Zn by Cu ions in the Y-123 matrix exhibits higher resistance to failure, mechanical strength, and stabilization of the durable tetragonal phase. Accordingly, Zn/Cu substitution in Y-123 ceramics paves the way for the applications of ceramic compounds in the fields of heavy-industrial technology and industrial power systems. All the ceramic materials also exhibit indentation size effect feature based on the recovery mechanism. Additionally, load-independent microhardness parameters are semi-empirically modeled by Meyer's law, Hays-Kendall, indentation-induced cracking, elastic–plastic deformation, and proportional sample resistance model for the first time. According to the comparisons, the IIC model is identified as the most suitable for interpreting the real microhardness results of newly produced Y-123 ceramic matrices.

Performance of low shrinkage Bis-EFMA based bulk-fill dental resin composites

ObjectivesThe purpose of this study was evaluating the performance of new Bis-EFMA based bulk-fill composites with common methacrylate based composites and commercial dental composites. MethodsThe Bis-EFMA monomer was synthesized and the novel Bis-EFMA based bulk-fill composites were prepared. The resin composite samples were co-cultured with human gingival epithelial cells and human dental pulp stem cells to test the biocompatibility. The edge adaptation was observed under a combination of stereoscope and scanning electron microscope. The internal hardness was measured using a Vickers microhardness tester after one-time filling of cavities prepared in extracted teeth. After friction and wear test on the surface of the resin composites, the surface morphology and volume wear of each group were measured by the optical profilometer. The color stability was measured by a colorimeter. ResultsDirect contact with human gingival epithelial cells and human dental pulp stem cells did not cause significant changes in their growth density and morphology, indicating good biocompatibility of Bis-EFMA group (p > 0.05). The continuous margin proportion of the Bis-EFMA group was as good as commercial bulk-fill composites (p > 0.05). The sectional microhardness results showed that the Bis-EFMA group had the highest microhardness. After the friction and wear test, the volume wear of the Bis-EFMA group was minimal, indicating its good wear resistance and mechanical strength. Color changes in all resin groups after 28 days of immersion were within the clinically acceptable range. SignificanceThe addition of Bis-EFMA demonstrated excellent biocompatibility, edge adaptation and color stability comparable to commonly used clinical bulk-fill composites, along with preferable mechanical strength, friction and wear resistance. Bis-EFMA based bulk-fill composites have the potential to be employed as a bulk filling material in commercial dental composite applications.

Mechanical Properties of Direct Composite Resins and CAD/CAM Composite Blocks

The widespread application of CAD/CAM technology in contemporary dentistry led to the development of promising restorative materials, such as resin composite blocks (RCBs). Thus, the present study aims to evaluate the mechanical properties of RCBs, comparing this material to the direct composite resin from the same manufacturer. Samples retrieved from three CAD/CAM resin composite blocks (Tetric CAD (TC), Ivoclar Vivadent, Grandio blocs (GB), VOCO GmbH and Brilliant Crios (BC), Coltene/Whaledent) and four direct composite resins (Tetric EvoCeram (TEC), Ivoclar Vivadent, GrandioSO (GS), VOCO GmbH, Brilliant EverGlow Translucent (BET) and Universal Shade (BEU), Coltene/Whaledent) were submitted to three-point bending flexural test and Vickers microhardness test. The resulting data of the flexural strength were analyzed using one-way ANOVA considering Bonferroni correction for post hoc tests (α = 0.05). The flexural modulus and Vickers microhardness results were analyzed using Welch’s ANOVA considering Games–Howell correction for post hoc tests (α = 0.05). Regarding results, flexural strength and flexural modulus values ranged from 81.1 MPa (BEU) to 246.5 MPa (GB) and 10.6 GPa (BEU) to 20.3 GPa (GB), respectively. GS (121.2) and GB (136.2) groups were associated with the highest microhardness values. According to the post hoc tests, statistically significant differences in flexure strength were found in RCBs (BC, GB, and TC) compared to all direct composite resins. Flexural modulus and Vickers microhardness of RCBs (BC, GB, TC) were also significantly different from the direct composite resin (BET, BED, and TEC), except when comparing GS and GB for microhardness. In conclusion, differences between RCBs and direct composite resins were observed regarding flexural strength, flexural modulus, and microhardness, revealing that RCBs have enhanced mechanical properties compared to direct composite resins.

Effect of Heat Source on the Formation of Welding Zone Structure between Carbon Steel and Stainless Steel Applied in Shipbuilding

This work presents the influence of heat sources on forming the weld zone structures between carbon steel and stainless steel. The results show that the weld structure includes the melting, transition, and heat-affected zones. The microstructure on the stainless-steel side is in the form of δ-Ferrite with thin fibers and clusters of Widmantes Austenite formed due to the high cooling rate in this area. On the carbon steel side, the influence of the concentration gradient and cooling rate changes the crystallization pattern from A-A-FA. The structure obtained from the melting boundary is a completely Austenite to Austenite + δ-Ferrite zone with δ-Ferrite varying from cylindrical, dendritic, and axial crystal forms. The δ-Ferrite content is inversely proportional to the hardness. In the melting zone, the change in the ratio value between temperature gradient and crystallization rate is the cause of the change in δ-Ferrite in this region. The HAZ region has Widmanstet phases, Bainite, and Martensite, which are phases with high hardness and brittleness. This area is thus easily destroyed. The results on the microhardness of the weld in the transition zone on the carbon steel side show that the microhardness result is 390HV in the fusion boundary area, the hardness value in the weld metal area ranges from 160 to 173HV, and the primary metal hardness value of carbon steel is from 134 to 146HV.

Constitutive modeling and tensile behavior of a fully austenitic gradient nanostructured stainless steel

The constitutive relationship can effectively describe and predict the deformation behavior of materials, and it is critical to establish appropriate constitutive relationships to obtain the mechanical response of gradient nanostructured (GNS) metallic materials during deformation. In this work, a general method for establishing the multi-layer constitutive relationship of the GNS metallic materials was proposed. A fully austenitic 310S stainless steel specimen with a thickness of 1.4 mm was fabricated by surface mechanical rolling treatment (SMRT) technology, and its depth-dependent microstructures and macroscopic mechanical properties were experimentally investigated. Based on the experimental results of uniaxial tensile and microhardness, using the quantitative relationship between microhardness and flow stress, the reverse analysis was conducted using a separation parameter method to establish the constitutive relationship of the 28 thin shells of the GNS310S specimen. Finite element analysis (FEA) confirmed that GNS310S was in a multiaxial stress state at low strains, and the evolution of stress and strain gradients during non-uniform deformation was analyzed. The method for establishing the constitutive relationship is independent of the microstructure and synergistic strengthening factors, and the experiment performs conveniently and has great generalizability, which can provide a useful guide for the mechanical modeling of the GNS metallic materials to obtain the intrinsic mechanical response.

The Influence of Precipitated Particles on the Grain Size in Cold-Rolled Al-Mn Alloy Foils upon Annealing at 100-550 °C.

The Al-Mn alloy heat exchanger fin production process includes a brazing treatment at s high temperature of 600 °C, in which coarse grains are preferred for their high resistance to deformation at elevated temperatures by decreasing the grain boundary sliding. In this study, Al-1.57Mn-1.57Zn-0.58Si-0.17Fe alloy foils cold rolled by 81.7% (1.1 mm in thickness) and 96.5% (0.21 mm in thickness) were annealed at 100-550 °C for 1 h to investigate their recrystallization behavior, grain sizes, and precipitates by increasing the annealing temperature, using micro-hardness measurement, electron back-scattered diffraction (EBSD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) techniques. The micro-hardness results showed that the recrystallization finishing temperatures for the two samples were almost the same, 323 ± 2 °C. The EBSD results showed that when the annealing temperature decreased from 550 to 400 °C, the recrystallized grain sizes of the two samples were nearly identical-both increased slightly. Further decreasing the annealing temperature from 400 to 330 °C caused the grain sizes to increase more, with the thinner foil sample having a more significant increase. The SEM and TEM observations showed that the micron-sized primary-phase remained unchanged during the annealing process. The nano-sized secondary phase precipitates formed during the hot-rolling process experienced a coarsening and dissolving process upon annealing. The particle size of the secondary phase increased from 32 nm to 44 nm and the area fraction decreased from 4.2% to 3.8%. The nucleation analysis confirmed that the large primary-phase could act as a nucleation site through particle stimulated nucleation (PSN) mode. The relatively dense secondary phase precipitates with small sizes at lower temperatures could provide higher Zener drag to the grain boundaries, leading to fewer nuclei and thereafter coarser grains. The coarsening of the recrystallized grains in the foils could be implemented through thickness reduction and/or precipitation processes to form densely distributed nano-sized precipitates.

Effect of Heat Treatments on Microstructure and Mechanical Properties of Fe-Mn-Ni-Al-Gd Shape Memory Alloy

There are significant scientific and industrial efforts to develop and optimize Iron-based shape memory alloys (SMA) such as FeMnNiAl for cost-sensitive applications. This alloy system shows shape memory and superelastic properties across a large temperature range. However, many studies have pointed out the need for rather complex thermo-mechanical treatments for the optimization of the SMA properties. In addition, works considering the effects of alloying on the development of microstructures that are more conducive to pseudo-elasticity in this system remain limited. Hence, systematic studies aiming at the investigation of the microstructural evolution of the FeMnNiAl(Gd) system are of great interest. In this study, solution heat treatment is done to tune the microstructure for optimum mechanical properties. The effect of phase distribution on mechanical properties is investigated at different heat treatments. Whereas cyclic heat treatment induced abnormal grain growth (AGG) in all samples, so large grains were obtained. The phase variation and elemental composition are analyzed by X-ray diffraction and Energy Dispersive Spectroscopy, respectively. The microstructure and phase distribution are observed using Scanning Electron Microscope and then related to the microhardness results. The microstructure has a good correlation with mechanical properties where the fine distribution of phases results in a higher hardness number.

Does the whitening dentifrice containing activated charcoal interfere with the properties of dental enamel? Microhardness, surface roughness and colorimetry analyzes.

The study evaluated the influence of whitening dentifrice containing activated charcoal on microhardness (MH), surface roughness (Ra) and colorimetry of tooth enamel. A total of 60 healthy bovine incisor teeth were used and divided into: G1 (regular non-whitening toothpaste), G2 (conventional whitening toothpaste), G3 (activated charcoal based whitening toothpaste) and G4 (10% carbamide peroxide gel - PC10). Groups G1, G2 and G3 underwent simulated toothbrushing for 14 days, while G4 received bleaching treatment for the same time. The readings of MH, Ra and colorimetry were performed before any intervention (T0 - baseline) and at the end of 14 days of the proposed treatments (T1). After confirming the normality of the data, the results of MH, Ra and colorimetry were subjected to 2-factor ANOVA for repeated measures (α = 5%). For MH, there were no statistical differences in G1, G2 and G3, only in G4. Considering Ra, a significant increase was observed in G2 and G3, with no statistical differences found in the other groups. Regarding colorimetry, the average color difference (ΔE) was greater in the G4 group (11.30 ± 4.31), even compared to the groups submitted to the whitening dentifrices: G2 (5.13 ± 2.75) and G3 (5.86 ± 3.66). It was concluded that the use of a whitening toothpaste containing activated charcoal caused deleterious effects on the enamel Ra, but did not affect the microhardness of the substrate, besides promoting a color change inferior to the regular non-bleaching toothpaste or PC10 gel. Key words:Whitening dentifrice, charcoal, roughness, microhardness.

ВЛИЯНИЕ ГРАФЕНА НА МИКРОТВЕРДОСТЬ И ТРИБОЛОГИЧЕСКИЕ СВОЙСТВА НАНОКОМПОЗИТНОЙ КЕРАМИКИ

The paper presents the results of microhardness depending on the graphene content in the concentration range 0-2 wt.% in nanocomposite ceramics Al2O3 was obtained by plasma spark sintering. The dependence of the wear rate and the friction coefficient at dry contact, at room temperature, in accordance with the circular motion “ball - disk" scheme of a ceramic nanocomposite with an addition of graphene 0.5%, is shown.

Microstructure and mechanical properties of WC–TiC–Co cemented carbides produced by spark plasma sintering (SPS) method

Cemented carbide 91 wt% WC–3 wt% TiC–6 wt% Co was sintered by spark plasma sintering at different temperatures of 1200 °C, 1300 °C, and 1400 °C and the effect of sintering temperature on the microstructure and properties of this type of composites, such as total density, apparent density, hardness, and fracture surface were measured and observed using Field Emission-Scanning Electron Microscopy, Optical Microscopy, X-ray diffractometry and mechanical test instruments. The results showed that the apparent density of the samples increased with increasing sintering temperature from 1200 to 1300 °C from 13.98 to 14.23 g/cm3, respectively. But in the sample sintered at 1400 °C, the density was reduced to 14.20 g/cm3. An increase in the fluidity of the cobalt phase and capillary pressure is the cause of the increase in density at higher temperatures, the cobalt phase has evaporated and the density has decreased slightly. Also, Vickers micro-hardness results showed that the hardness of sintered samples increased with the increase of sintering temperature. For the sample sintered at 1200 °C the hardness value of 1746.41 kgf/mm2 was obtained which increased with increasing sintering temperature from 1300 to 1400 °C from 2094.33 to 2280.97 kgf/mm2, respectively. The amount of core–shell structure [including TiC-core and (W, Ti)C-shell] increased with increasing the sintering temperature process. As a result, the hardness also increased. At the optimum sintering temperature, it was found that TiC inhibited the grain growth of tungsten carbide. In addition, as expected, the grain growth of tungsten carbide increased with increasing sintering temperatures. Examination of the fracture surface of sintered samples at different temperatures also showed that brittle fracture involves fracture.

Effect of SAW electrode wire preheating current on its melting rate and weldment properties of HSLA steel joint

ABSTRACT Weld strength and quality are mostly affected by process parameters, which, in turn, influence the mechanical properties of weld metal and heat affected zone. In this research work, effect of electrode wire preheating on different responses including electrode wire melting rate, wire and plate melting efficiency, width of heat affected zone, microhardness, and corrosion rate of weld metal was studied. The experiments were carried out to accumulate the response data using the optimisation techniques. Then, the quadratic mathematical models were developed and checked the significance using the tests such as ANOVA, F-test and lack of fit. The preheat current is found to be the most contributing parameter, which efficiently enhanced the wire melting rate, wire melting efficiency and microhardness of weld metal whereas reduced the plate melting efficiency, heat affected zone (HAZ) width and corrosion rate. In addition, micrographs and micro-hardness results also confirmed the significant influence of preheat current.

Synthesis of a waterproof geopolymer adhesive applied in DUV LEDs packaging

This paper presents the synthesis of a waterproof geopolymer based on the modification of silicon phosphate (Si3(PO4)4) that adheres to alumina and quartz glass substrate, which can replace traditional organic polymers for packaging deep-ultraviolet light-emitting diodes. The waterproof property of geopolymer strongly depends on the Si3(PO4)4 loading amount due to its hydrolysate H+ substitutes Na+, which is vulnerable to water. FESEM and microhardness results show that aging by 85°C/85% relative humidity for 100 h, the optimal waterproof geopolymer adhesive is successfully synthesized when the mass ratio of metakaolin, water glass, and Si3(PO4)4 is equal to 0.48: 1: 0.08 respectively, and the corresponding adhesion strength of 6.41 MPa to alumina substrate is achieved after the reliability testing. The rheological properties show that the optimal waterproof geopolymer adhesive, with shear thinning behavior and good thixotropy, is suitable for processing while holding the original shape.

Analysis of Premature Failure of a PVC Water Pipe

A case study of the failure analysis of a PVC drinking water pipeline is presented. One week after installation in a construction zone of a building, a longitudinal cracking, and pressure drop occurred in an underground pipeline, and an investigation was carried out to determine the causes of the event. Based on the results of visual inspection, dimensional metrology, plastography, microhardness, fractography, FTIR analysis, and stress analysis, the failure mechanisms of the pipe were identified as creep and slow crack growth. The cause of the development of these failure mechanisms was the exposure of the pipe, to a mixture of paint thinner and polyurethane paint, which generated plasticization, with the corresponding deterioration of the mechanical properties. The source of the plasticizer could have been an accidental spill or an incorrect final disposition of this chemical residue during the construction process of the building.

A study on the mechanical, electrochemical and microstructural behaviour of AA5052 welded sheets

Aluminium 5xxx series alloys are most robust non-heat-treatable aluminium alloy and mostly used in aerospace, automotive components and body structures due to its high corrosion resistance, good strength and light weight. The alloy used in this work is AA5052 H32 (cold rolled) of 1 mm thickness to highlight the precedence of friction stir welding (FSW) over fusion welding technique, i.e., Tungsten Inert Gas welding (TIG). In TIG, the selected input variable parameter is welding speed and the other parameters such as inert gas flow rate, welding speed and frequency were kept constant during the study. In FSW, the selected input variable is feed rate, and the parameters such as plunge depth and tool rotational speed were kept constant after conducting several trials. Mechanical, Electrochemical, and Microstructural behaviour of both welded samples were studied. It was found that Friction stir welding samples has better mechanical properties than TIG welding due to solidification cracks and porosity defects. The tensile and microhardness results of FSW were 7.3 % and 5.4% more than TIG due to solidification cracks, porosity defects and intermetallics formed. The corrosion behaviour of both FSW and TIG were less than the base material due to precipitate dissolution. In the present study a comparative study of FSW and TIG is studied and reported.

An extensive investigation of crystalline, nonlinear, piezoelectric, optical, phase purity and electro-optic properties of doped ammonium dihydrogen phosphate single crystals

Pure single crystals of ammonium dihydrogen phosphate (ADP) and crystals containing 1, 3, and 5[Formula: see text]mol% of itaconic acid (ITA) were generated by the slow evaporation of an aqueous solution. With the help of powder X-ray diffraction and Fourier transform infrared spectroscopy, we were able to show that doping puts a lot of stress on crystals. According to the of Vickers microhardness results, the addition of ITA causes the ADP to have a greater degree of abrasiveness. The SHG efficiency of ITA-doped ADP is greater than that of pure ADP. The presence of dopant was established using the energy-dispersive spectroscopy. The [Formula: see text]-scan method was used to investigate the third-order nonlinear optical characteristics of ITA–ADP crystals formed by the slow evaporation method on a variety of planes. A He–Ne laser with a wavelength of 632.8[Formula: see text]nm was used to carry out the investigation. The nonlinear absorption coefficient, nonlinear refractive index, and third-order nonlinear susceptibility of the ITA–ADP crystals were also plotted in detail. The piezoelectric charge coefficient of pure ADP is lower than that of the ITA-doped ADP. Analysis of the electro-optic investigation reveals lesser half-wave voltage of doped ADP.

Theobromine versus casein phospho-peptides/Amorphous calcium phosphate with fluoride as remineralizing agents: effect on resin-dentine bond strength, microhardness, and morphology of dentine

BackgroundThis study aimed to assess the impact of theobromine and casein phospho-peptides/amorphous calcium phosphate with fluoride (CPP-ACPF) on the resin-dentine bond strength, microhardness, and dentine morphology.MethodsA total of 18 sound human molars for micro-tensile bond strength (µTBS), 20 sound human premolars for microhardness, and 30 premolars for Scanning electron microscopy/energy-dispersive X-ray spectroscopy (SEM/EDX) were used. Based on the pre-treatment used, teeth were split into six groups; sound dentine, demineralized dentine, and demineralized dentine treated with theobromine (Sigma Aldrich) and MI paste plus (GC International, USA) for two-time intervals; 5 min and 1 month. The bonded teeth were sectioned to produce 1 mm2 resin-dentine sticks which were evaluated for µTBS using a universal testing device (Instron 3365, USA). The dentine microhardness was tested by using the Vickers microhardness tester (Nexus 4000 TM, Netherlands). The pre-treated dentine surface was examined using SEM/EDX (Neoscope JCM-6000 plus Joel benchtop SEM, Japan). µTBS results were analysed with two-way ANOVA. Microhardness and EDX results were analysed with two-way mixed model ANOVA. The significance level was set at (p ≤ 0.05).ResultsWhile both remineralizing materials at the two-time intervals demonstrated µTBS comparable to sound dentine (46.38 ± 12.18), the demineralized group demonstrated statistically the lowest µTBS (p < 0.001). Whether used for 5 min or 1 month, theobromine significantly increased the microhardness (50.18 ± 3.43) and (54.12 ± 2.66) respectively (p < 0.001), whereas MI paste only increased the hardness (51.12 ± 1.45) after 1 month (p < 0.001).ConclusionsThe pre-treatment of demineralized dentine with theobromine for 5 min or 1 month could enhance its bond strength and microhardness while for MI paste plus, only 1-month application was efficient to ensure remineralization.

Tailoring role of Al and Ti particles in the microstructure and property of electrodeposited Ni matrix nanocomposite coatings

Ni–Al–Ti nanocomposite coatings were synthesized by electrodeposition. The tailoring role of Al and Ti particles in the co-deposition behaviors of nanocomposite coatings was comprehensively investigated by analyzing the time-dependent current density and electric field near the co-deposited particles. The results showed that the Al and Ti particles caused different co-deposition behaviors of Ni deposits, consequently bringing in the gradual increase in the surface dendritic structure, the refinement of grain sizes, and the decrease in the [200] fiber texture of the nanocomposite coatings with the decrease in the Al/Ti weight ratio. COMSOL simulations verified the different co-deposition mechanisms of Ni grains near the two kinds of particles, which was vitally determined by the different conditions of current density and electric field near the particles. The micro-hardness results revealed that the decreased Al/Ti weight ratio led to enhanced micro-hardness of the nanocomposite coating; in addition, the maximum hardness of the nanocomposite coating was 604.3 HV0.2 for an Al/Ti weight ratio of 1:4. Thus, the time-dependent current density and electric field near co-deposited Al and Ti particles determined the microstructure and property of the Ni–Al–Ti nanocomposite coatings.