Higher Microhardness Values Research Articles

Corrosion Behavior of CW6MC Nickel Cast Alloy (Inconel 625) Welded by Shielded Metal Arc Welding

The aim of this study concerns the effect of multi-pass shielded metal arc welding (SMAW) on the corrosion behavior of CW6MC cast nickel alloy. Using optical and SEM techniques the welded joint is analyzed. Vickers microhardness mapping and potentiodynamic polarization in NaCl and H2SO4 solutions are also evaluated. Both the Laves phase and NbC-type carbides are identified in the base metal (BM) and weld metal (WM) regions. The main microstructural difference observed between these regions is the morphology aspect and fineness of the dendritic arrays. The welding process promotes the finer columnar grains formation with refined intermetallic particles in the WM than equiaxed grains of the BM, which in turn results in higher microhardness values in the former region. However, no substantial changes were observed in the corrosion behavior between the BM and WM regions, considering both acid and saline media. Nevertheless, during the multi-pass SMAW process, some non-metallic micrometric inclusions (Mo and S-rich regions) can be constituted to occur in the WM region. This is associated with a significant drop in the corrosion performance of this region when the electrochemical tests are evaluated.

CОЗДАНИЕ МЕХАНИЧЕСКИМ ЛЕГИРОВАНИЕМ Ti-Al ПОКРЫТИЙ С ДОБАВКАМИ КОБАЛЬТА И НИКЕЛЯ

The work is dedicated to the formation of TiAl titanium aluminide coatings with cobalt and nickel additives by means of the method of mechanical alloying with the further maturing at high temperature in vacuum. Coatings were applied with the use of the ball mill of the planetary type upon VT1-0 titanium alloy substrate which were placed in the mill cup filled with metal powders. There is studied growth kinetics, a coating thickness is measured. A specific rate of metal powder sedimentation upon a titanium substrate makes from 4.6 to 11 g/(min•m2). Deposited layers have a mean thickness 70-180 mkm. There are studied thoroughly compositions and microstructure of mechanical-alloyed coatings. For that there were used methods of X-ray diffractometry and raster electronic microscopy. It is defined that the inner structure of coatings is heterogeneous. After deposited layer thermal treatment a metal interpenetration takes place first aluminum into particles of titanium, cobalt or nickel. Coatings are composite material the basis of which makes aluminide of RiAl titanium, and as inclusions there are other inter-metallides, titanium, cobalt or nickel and also aluminum oxide. Mean values of micro-hardness of coatings obtained are 1.2 - 3.4 times higher than of titanium substrate. The highest values of micro-hardness (more than 6.5 GΠa) after thermal treatment in vacuum are observed in TiAl-5%Co and TiAl-10%Co coatings. Micro-hardness of VT1-0 titanium alloy after annealing, vice versa, decreases by 1.3 times.

Wear and Thermal Behavior of TiAlN Thin Films onto Ti6Al4V Alloy Manufactured by Selective Laser Melting Method.

In this study, it was targeted to enhance the tribological and thermal properties of Ti6Al4V alloys, which were manufactured with three different build orientations and hatch spacing by using the selective laser melting (SLM) method and a traditional method (casting). In addition, the surfaces of the samples produced by these two methods were coated with the TiAlN thin film by using the cathodic arc physical vapor deposition (CAPVD) method. After the experimental investigations, the lowest wear rate was obtained for the 60-90° sample, and the highest microhardness value was measured as ∼1070 HV0.1 for the 90-45° sample. It was specified that the wear rate rose as the hatch spacing increased among the same build orientation Ti6Al4V alloys produced by SLM method. According to thermal analysis results, among the same hatch spacing values, it was determined that as the build orientation value increased, the specific heat capacity and thermal conductivity values decreased. Among the coated samples, the highest thermal conductivity and specific heat capacity values were obtained for casting samples as 5.63 (W/m·K) and 560.4 (J/kg·K), respectively.

Fabrication of (TixZr1−x)B2-(ZrxTi1−x)N composites by reactive spark plasma sintering of ZrB2-TiN

In this study, microstructural and mechanical properties of (ZrxTi1−x)N-(TixZr1−x)B2 composite fabricated by reactive spark plasma sintering (SPS) of ZrB2 and TiN was investigated. ZrB2 and TiN starting materials with equimolar ratio were sintered at 2000 °C for 8 min under a pressure of 30 MPa. An expansion (about 4%) was observed during the sintering process of the composite in the temperature range between 1290 °C and 1625 °C, which was attributed to the reaction of the starting materials. XRD pattern of the fabricated composite revealed the formation of TiB2 and ZrN phases after the sintering process. It was found that (Ti0.91Zr0.09)B2 and (Zr0.92Ti0.08)N phases are formed after sintering. High values of Vickers microhardness (28 ± 0.2 GPa), flexural strength (706 ± 51 MPa) and fracture toughness (8.49 ± 0.92 MPa m1/2) were achieved for this composite. Fracture of the (ZrxTi1−x)N and (TixZr1−x)B2 phases and crack path deflection mechanisms was founded as dominant toughening mechanisms in this composite.

Influence of copper addition on corrosion properties and hardness of Al–Cu/Al two-layered-structure composites

An experimental investigation has been observed on hardness, sintered density and corrosion behaviour of two-layered structured Al-xCu/Al sample through powder metallurgical route under hot compaction condition. The samples were prepared with different percentages of Cu content (x: 5 wt. %, 10 wt. % and 15 wt. %) in the aluminium matrix with a constant pressure of 400 MPa with different hot-pressed temperatures (500 °C, 550 °C and 600 °C) at a dwelling time of 3 h. The developed two-layered samples microstructure was analysed using the optical and scanning electron microscope. The highest value of micro-hardness (100.6 HV) was obtained at interface region of 15% of copper at 550 °C. The corrosion rate of Al-Cu/Al two-layered samples at the interface were analyzed through the potentiodynamic polarization test and found that with addition of copper content the susceptibility of corrosion increases. The Electrochemical Impedance Spectroscopy (EIS) test was conducted to know the equivalent circuit model, which provides a minimum chi-square value and that circuit model taken as best-fit circuit model. From the EIS results, it was found that 10 wt. %Cu sample circuit provides minimum chi-square value.

A new approach to thermo-mechanical treatment of steel T91 by multiple upsetting-extrusion in a ferritic range

The microstructure and mechanical properties of the ferritic-martensitic steel T91 after severe plastic deformation (SPD) and subsequent thermal treatment are investigated. SPD was realized by the method of multiple “upsetting-extrusion” (MUE) in temperature range of stability of ferritic phase (750-575 °C), thermal treatment of SPD specimens was carried out at temperatures 550–730 °C during 1–100 h. It is revealed that decrease of temperature of “upsetting-extrusion” and increase of cycle number to 5 induces the decrease of mean grain size to 145 nm and increase of degree of microstructure homogeneity. At the same time microhardness increases from 1800 MPa to 2850 MPa. Composition, shape, size and density of carbide precipitates in steel after SPD and thermal treatment are determined. Obtained submicron grain ferritic microstructure with high value of microhardness is stable at exposure temperature of 550 °C. It is shown that temperature variation of thermal treatment induces the considerable change in grain size and mechanical characteristics.

Influence of laser irradiation parameters on the ultrafine-grained Ti 45Nb alloy surface characteristics

In the present study surface alterations of the high pressure torsion (HPT)-deformed Ti45Nb (mass%) alloy induced by laser irradiation treatment are presented. The alloy was irradiated in air, argon, and nitrogen atmosphere using the Nd:YAG laser. Laser-induced surface modifications were analyzed by field-emission scanning electron microscopy (FE-SEM), energy-dispersive spectroscopy (EDS), profilometric analysis, and Vickers microhardness measurements. Alloy irradiation under a low laser output energy and a low number of accumulated pulses resulted in the formation of shallow surface craters. An increase of these irradiation parameters caused the appearance of more pronounced surface craters with microcracks and hydrodynamic effects in the form of wave-like structures, ripples, and solidified droplets and consequently caused an increase in the surface roughness. The highest value of the surface roughness of 3.062 μm was attained during the alloy irradiation in argon atmosphere under 15 mJ with 150 accumulated pulses. Interaction of the laser beam with the alloy surface was accompanied by plasma formation and surface ablation due to the irradiation energy absorption. The maximal ablated target material volumes of 5.5 × 1014 nm3 and 2.6 × 1014 nm3 were observed after the irradiation under 15 mJ with 150 accumulated pulses in argon and air atmosphere, respectively. Moreover, attainment of high temperatures at the alloy surface induced its chemical composition alterations. Formation of mixed Ti- and Nb-oxide surface film and absence of nitride particles at the alloy surface was detected irrespective of the irradiation atmosphere. Irradiation in air resulted in the appearance of the most pronounced surface oxide layer with the highest microhardness value which can in great merit influence an increase of the alloy bio-integration abilities and its tribo-corrosion resistance.

Effect of Graphene Content on the Micromorphology, Microhardness and Micro Frictional Resistance of Co-Ni-Graphene Composite Coating

In order to obtain the alloy composite material with high hardness, good anti-friction property and low friction coefficient, the electrodeposition technology was used to prepare nanocrystalline Co-Ni-graphene composite coating on the surface of low carbon steel by means of ultrasonic dispersion combined with mechanical agitation. The influence of graphene content in electrolyte on composite coating was studied. The surface microstructure, composition, phase structure, micro-hardness and micro-wear properties of composite coating were measured by scanning electron microscopy, energy spectrometer, X-ray diffractometer, micro-hardness tester and UNMT-1 comprehensive mechanical testing system for micro-nanometer materials. The results show that with the increase of the content of graphene in the electrolyte the graphene particles were embedded in the alloy coating, which changes the crystal structure of the alloy coating and improves the microhardness and micro friction resistance of the coating. When the content of graphene in the electrolyte was 0.9g/L the microstructure of the composite coating was fine and uniform, the highest microhardness value was 678 HV, the minimum average friction coefficient was 0.15, and the composite coating had good wear resistance.

Mechanical characterization of the enamel microstructure treated with non alcoholic drinks

In previous studies, it has been shown that the microstructure of prismatic dental enamel presents differences between the external and internal zone. Radial enamel is found in the outer third of enamel and has higher microhardness values than enamel with Hunter- Schreger Bands (HSB) that occupies the inner 2/3. Our aim was to evaluate the mechanical behavior of radial enamel and HSB due the action of a non-alcoholic beverage in vitro. Longitudinal sections of dental crowns were embedded in polymer, worn and polished with sandpapers of decreasing granulation. The samples were immersed in a flavoured natural water for 12 minutes. Nanohardness tests (Triboindenter Hysitron) were performed on the radial and HSB enamel before and after the exposure to the drink. Hardness determinations "H", reduced modulus "Er" and contact depth "hc" were obtained. The percentage of reduction of hardness was determined. The values found in healthy radial enamel were H: 5.48±0.23 GPa; Er: 86.97±8.11 GPa; hc: 149.73±4.25 nm and in HSB H: 4.24±0.43 GPa; Er: 75.24±7.09 GPa; hc: 176.36±11.29 nm. After exposure to beverage, it was found in the radial enamel H: 2.22±0.31 GPa; Er: 58.73±10.79 GPa; hc: 270.29±21.22 nm, and in HSB H: 1.54±0.42 GPa; Er: 48.11±6.54 GPa; hc: 350.10±63.33 nm. After the drink action, the values of hardness of the radial enamel and HSB decreased and the trend observed in healthy enamel remained, where the highest values corresponded to the radial enamel. The percentage reduction of H in the radial enamel was 59.48% and in the HSB enamel it was 63.67%. The contact depth increased by about 50%.The decrease in hardness is related to the mineral loss produced by the acids contained in the drink. We conclude that the action of the non-alcoholic beverage produces a decrease in the mechanical properties in both the radial enamel and the HSB. The lower values in the reduced module Er indicate the formation of a superficial softened layer, the enamel with HSB being more vulnerable.

FEATURES OF THE STRUCTURE FORMATION OF SPODUMENS-CONTAINING GLASS-CRYSTAL MATERIALS AFTER HEAT TREATMENT

The promising areas of application of spodumene–containing glass–crystalline materials in various branches of science and technology, in particular, to increase the defense capability of the state, have been determined. The relevance of the development of lightweight high–strength sitalls based on them, taking into account the aspects of energy saving for obtaining armored elements, has been determined. It has been established that the use of IR spectroscopy is promising for studying the nanostructure of glass–crystalline materials. The compositions of lithium aluminum silicate glasses and the modes of their heat treatment have been developed. The features of the structure formation of spodumene–containing glass–crystalline materials obtained under the conditions of two–stage low–temperature heat treatment have been investigated. Taking into account the analysis of the nature of the IR spectra of chain silicates, the structure of glass–crystalline materials was investigated according to the IR spectra and the nature of structure formation was established depending on the initial composition of the glass. It has been established that the formation of a structural glass network with the participation of tetrahedra [AlO4], [BO4] and [SiO4] and the presence of cybotaxic groups [Si2O6] allows, under conditions of two–stage low–temperature treatment, to provide bulk crystallization of spodumene–containing glass–crystalline materials. It has been established that the formation of the vitrified structure of glass–crystalline materials allows to ensure their high values of Vickers hardness, microhardness and crack resistance and by the presence of a glass phase, which plays the role of a damper, to ensure their high armor resistance. This will increase the efficiency and make it possible to use them as an energy–destructive and energy–absorbing layer in the composition of the armor element «metal alloy – ceramics – sitall». The introduction of spodumene–containing glass–crystalline materials will increase the competitiveness of competitive domestic armored elements for personal protection.

The Effect of Heat Treatment on the Performance of Antiwear Steel Coatings Deposited on AISI 1015 Steel Substrates

The critical components of mining equipment generally work in relative motion and in an abrasive environment. Under these circumstances, wear by friction represents the largest portion of the cost associated with failure and maintenance of sliding bearings. Thus, antiwear coatings are extensively applied aimed at returning such equipment to its initial condition. Tamping machines are a typical type of equipment working in this condition and the focus of the present research work, whose goal is to investigate the performance of conjugates made of an MnSi low-alloy steel coating deposited on an AISI 1015 low-carbon steel substrate and subjected to three distinct heat treatment routes (normalizing and deep and surface hardening). Coating deposition was performed using gas metal arc welding. The performance assessment is based on microhardness and residual stress distributions, friction coefficient, wear mechanisms, and wear rate. The results indicate that ferritic and pearlitic microstructures were obtained after normalizing, whereas deep and surface hardening produced lath martensite. Consequently, the value of surface microhardness of the coating was 176 HV after normalizing, 356 HV after deep hardening, and 466 HV after surface hardening. Normalizing induced shallower compressive residual stresses of lower intensity, whereas surface hardening induced compressive residual stresses of higher intensity to reach deeper beneath the coating surface. More refined grains (martensite laths) were associated with higher microhardness values and compressive residual stresses of higher intensity, thus suggesting that this condition leads to higher wear resistance. The normalized conjugate presented the lowest friction coefficient and the highest wear rate, and the hardened coatings presented similar behaviors with regard to wear resistance.

The Effect of Arabian Coffee, Black Tea and Orange-juice on Microhardness and Color Stability of Hybrid Composite Resins. An in vitro Study

The main aim of the present in-vitro study is to assess the effect of daily consumable drinks on the aesthetics of the dental composite resin materials. Sixty-four microhybrid and nanohybrid direct composite resin (3M™ Filtek™ Z350 XT Universal Restorative, Filtek™ Bulk Fill Flowable Restorative, USA) block samples were made with a dimension of 15mm X 2mm and are allocated into four groups. Each sample was immersed in test media such as Arabic coffee, black tea, orange-juice and distilled water as control group at room temperature for 15 days (n = 16). The color stability and microhardness measurements were taken at pre-immersion and after two weeks of immersion in test media. These parameters were assessed by electro spectrophotometerusing the CIE (Commission Internationale de l'Eclairage) system and Vickers microhardness indenter respectively. Each group was immersed in its test media for the complete duration of the study. On completion of 15 days, the samples were blot dried out with absorbent paper and microhardness dimensions and color stability measures were performed. The collected data was subjected to statistical analysis to formulate the results. Significant discoloration was observed with the Arabic coffee, black tea and orange-juice compared with control group. The Arabic coffee caused most significant discoloration followed by black tea and orange-juice. Although the highest values of microhardness was noted in the Arabic coffee followed by black tea and orange juice, whereas the lowest values were noted in the control. The color stability and microhardness of the composite resin restorations is affected by the everyday drinks that are consumed, from some more than others. Some of the everyday drinks affect the color stability and microhardness of the composite resin restorations more than the others.

The Effect of Welding Current and Electrode Force on the Heat Input, Weld Diameter, and Physical and Mechanical Properties of SS316L/Ti6Al4V Dissimilar Resistance Spot Welding with Aluminum Interlayer.

Welding parameters obviously determine the joint quality during the resistance spot welding process. This study aimed to investigate the effect of welding current and electrode force on the heat input and the physical and mechanical properties of a SS316L and Ti6Al4V joint with an aluminum interlayer. The weld current values used in this study were 11, 12, and 13 kA, while the electrode force values were 3, 4, and 5 kN. Welding time and holding time remained constant at 30 cycles. The study revealed that, as the welding current and electrode force increased, the generated heat input increased significantly. The highest tensile-shear load was recorded at 8.71 kN using 11 kA of weld current and 3 kN of electrode force. The physical properties examined the formation of a brittle fracture and several weld defects on the high current welded joint. The increase in weld current also increased the weld diameter. The microstructure analysis revealed no phase transformation on the SS316L interface; instead, the significant grain growth occurred. The phase transformation has occurred on the Ti6Al4V interface. The intermetallic compound layer was also investigated in detail using the EDX (Energy Dispersive X-Ray) and XRD (X-Ray Diffraction) analyses. It was also found that both stainless steel and titanium alloy have their own fusion zone, which is indicated by the highest microhardness value.

Effect of autogenous GTAW on the reciprocating sliding wear behavior of a carbon martensitic steel

Martensitic steels have been successfully employed in resource-based industries where components must endure aggressive conditions. In industrial practice, many parts of these components are joined by welding techniques. The aim of this work was to understand the influence of welding on the wear resistance of quenched and tempered carbon martensitic steel subjected to dry linear reciprocating sliding micro-wear tests. Weld-joints were produced using autogenous Gas Tungsten Arc Welding process (GTAW). Micro-wear tests were performed at base metal (BM), weld metal (WM), coarse grained heat affected zone (CG-HAZ) and lowest hardness region of heat affected zone (LHR-HAZ). LHR-HAZ was softened during welding process so plastic deformation was facilitated, and consequently adhesion, material displacement and micro-ploughing. WM and CG-HAZ presented a similar martensitic structure, which explain the similarities found on wear behavior. These regions presented the lowest worn volume average values (w). It was interesting to note that despite its highest microhardness value, the highest w was observed for BM. For some BM samples, debris had a key role promoting material loss by micro-cutting which causes great extent of material removal compared to other micro-wear mechanisms as micro-ploughing and adhesion. Due to debris action BM also presented a great dispersion in w results. The results suggest that material loss of welded joint and BM was strongly controlled by micro-wear mechanisms.

Study of the effect of pulse plating parameters on the electrodeposition of NiP and NiP/SiC coatings and their microhardness values

ABSTRACT This study is focused on finding optimised conditions for electrodeposition of NiP and NiP/SiC coatings, which enhance the coatings' microhardness. Both the effect of particles and the effect of heat treatment at 400°C for 1 h on the microhardness of the coating were studied. The effects of pulse electrodeposition parameters including duty cycle, frequency, and peak current density on the composition of NiP and NiP/SiC composite coatings were examined, and the results were compared with those from direct current plating. Pulse plating increased the current efficiency of NiP deposition while decreasing the phosphorus content of these coatings in comparison to direct plating, resulting in higher microhardness values. It was also shown that wt.%P in NiP coating depends not only on peak current density but also on bath charge of pulse plating. Pulse plating parameters (duty cycle and frequency) and the low incorporation of SiC particles did not affect microstructure or the microhardness of the coatings, while heat treatment was the main factor that increased microhardness.

Effect of nano-hydroxyapatite with biomimetic analogues on the characteristics of partially demineralised dentin: An in-vitro study.

Research on dentin remineralisation protocols in particular 'biomimetic remineralisation' has gained huge momentum. Aim of this study was to evaluate if biomimetic analogs, incorporated in n-HAp, as an experimental formulation could aid in remineralization of artificial caries-like dentin and have anti-microbial effect on cariogenic bacteria, S mutans. An experimental paste was formulated using nano-hydroxyapatite (nHAp) with Non-Collagenous Protein analogs- polyacrylic acid (PAA), sodium tri-poly phosphate (STPP) with Simulated Body Fluid. Partially demineralised dentin specimens were divided into three groups (n=10) based on the remineralisation treatment as, Group A- n-HAp paste, Group B- n-HAp and NCP analogues and Group C (Control) - no treatment. At the end of the experimental period, the specimens were assessed using SEM-EDS analysis and Vickers microhardness testing. Further, the antimicrobial efficacy of the paste was assessed. The results were statistically analyzed using ANOVA with post-hoc Bonferroni test. Dentin specimens treated with the experimental paste revealed greater tubular occlusion, with intra tubular deposits and increased mineral content. Specimens treated with n-HAp alone had higher microhardness values and inhibitory effect on the cariogenic bacteria. Non-Collagenous Protein analogs incorporated in n-HAp could remineralize the demineralised dentin and had antibacterial efficacy against S mutans.

Protection of calcium silicate/sodium phosphate/fluoride toothpaste with serum on enamel and dentin erosive wear.

Objective To evaluate the effect of a toothpaste containing calcium silicate/sodium phosphate/fluoride associated or not to the boost serum (BS) against erosive tooth wear (ETW) on enamel and dentin.Methodology Bovine enamel and dentin specimens were subjected to an erosion-abrasion cycling model (1% citric acid - pH 3.6 -2 min / artificial saliva – 60 min, 4×/day, 5 days). Toothbrushing was performed for 15 s (2 min exposed to slurry), 2×/day, with the toothpastes (n=10): control without fluoride (Weleda), Arg/Ca/MFP (Colgate Pro-Relief), Si/PO4/MFP (Regenerate-Unilever), and Si/PO4/MFP/BS (Si/PO4/MFP with dual BS – Advanced Enamel Serum-Unilever). The effect of treatments on the eroded tissues was assessed by surface microhardness in the first day, and surface loss (SL) resulting from ETW was evaluated by profilometry (μm) after three and five days. Additional dentin specimens (n=5/group) were subjected to 20,000 brushing cycles to verify the abrasivity of the toothpastes. Data were subjected to ANOVA and correlation tests (5%).Results For enamel, no difference in microhardness was observed among the treated groups, and similar SL was obtained after 5 days. For dentin, Si/PO4/MFP/BS resulted in higher microhardness values, but none of the groups presented significantly lower SL than the control. There was no significant correlation between SL and abrasiveness.Conclusion The calcium silicate/sodium phosphate toothpaste and serum increased microhardness of eroded dentin, but they did not significantly reduce enamel and dentin loss compared to the non-fluoride control toothpaste. The abrasiveness of the toothpastes could not predict their effect on ETW.

Effect of titanium alloy powder reinforcement on the mechanical properties and microstructural evolution of GMAW mild steel butt joints

Despite its well-reported application in a few welding processes, the use of reinforcing powders in weld joints to improve weld integrity has not garnered ample research attention for Gas Metal Arc Welding (GMAW) process. In this study, the adoption of Titanium alloy powders as metallic reinforcement for mild steel butt welds was investigated. By adopting Taguchi’s L4 orthogonal array, process optimisation for titanium-reinforced mild steel butt welds were first carried out. In the second phase of welding, the optimum parameters were used to create and compare two sets of weldments; one set was reinforced with titanium alloy powder and the other set left unreinforced. It was observed that in the Weld Metal (WM) region, the titanium-reinforced samples had higher micro-hardness values than their unreinforced counterparts with an average of 285.62 HV and 211.6 HV respectively. However, there was no substantial improvement in the ultimate tensile strength of the mild steel butt welds due to titanium powder reinforcements. Interestingly, the formation of acicular ferrite microstructure was more prevalent in the titanium-reinforced weldments and this was attributed to the presence of titanium inclusions in the weld metal. This prevalence of acicular ferrite suggests improved toughness properties in the weld joint region. While the higher hardness values in the Weld Metal of the reinforced sample indicates improved wear resistance.

Effect of primer on the polymerization of dual cure resin cements

Objectives: The primer (G-Cem One Adhesive Enhancing Primer), which promote self-polymerization more in the absence of polymerization light is developed. To date, many studies on the mechanical properties and prognosis of various self-adhesive resin cements have been published. Since there is almost no comparison of the degree of polymerization depending on the application of primers, this study was attempted. Materials and Methods: A total of three types of dual cure self-adhesive resin cements (G-Cem One, G-Cem LinkAce, Rely-X U200) and one type of dual cure resin cement (Rely-X Ultimate) were evaluated. G-Cem One Primer was used as a primer enhancing of auto-polymerization. A mold 5 mm in diameter and 2 mm thick was made from aluminum, primers were applied on a glass slit, and each material was filled in the mold, and self-polymerization was induced. The microhardness was measured with a Vickers microhardness machine after 10 minutes, 1 hour,3 hours,6 hours and 24 hours. All dates were statistically analyzed. Results: G-Cem One, G-Cem LinkAce and Rely-X U200 showed high microhardness values when primers were applied at the beginning of cement mixing. Primer application did not show significantly different in Rely-X Ultimate. Conclusion: The application of a new primer has a dual cure self-adhesive resin cement which promotes the polymerization at the beginning of the mixing.

Ability of plasma nitriding to improve tribological behavior of medium and high boron electroless nickel coatings

The effect of heat treatment and plasma nitriding post-processes on the properties of medium and high boron electroless nickel coatings were investigated. Chemical Composition, microstructure, roughness, microhardness and tribological behavior of the coatings were evaluated. Results indicated that the highest microhardness value was achieved for the plasma nitrided high boron coating being equal 1459 HV0.1. Furthermore, it was found that the provision of denser structure along with formation of lubricant h-BN phase significantly improve the tribological behavior of the plasma nitrided coatings. According to the sliding wear test results, mean wear rate and Coefficient of friction values of the plasma nitrided coatings were more than 14 and 2 times lower than that of the heat treated ones, respectively.