Mean Hardness Values Research Articles

Evolution of microstructure, mechanical properties and phase stability of CoCrFeMnNi high entropy alloys

In the present study, the microstructure and mechanical properties of various CoCrFeMnNi high-entropy alloys were investigated. Analytical studies were conducted to determine the optimal chemical composition, mixing entropy, mixing enthalpy, atomic radii, valence electron concentration (VEC), dimensionless parameter, and melting point on the Co-Cr-Fe-Mn-Ni system. The microstructure of the alloys was analyzed using FESEM, XRD, and TEM. The results showed that the microstructure of all HEAs had dendritic and interdendritic regions, with secondary precipitations detected along the grain boundaries of the alloy, mainly composed of Mn and Ni. High-density dislocation structures and nano-precipitates were predominantly present in the alloy. The mechanical characteristics such as microhardness and tensile properties are conducted at room temperature. The HEA Co25Cr25Fe10Mn30Ni10 exhibited the highest average microhardness, while the Co20Cr20Fe30Mn10Ni20 HEA had the lowest mean hardness value. This significant difference of 7.2 % may be attributed to the hard phases composed of Mn and Ni. The results of the tensile experiments indicate that the Co20Cr20Fe20Mn20Ni20 alloy has the most favorable overall properties, with an ultimate tensile strength of 441 MPa. This represents a significant increase of 37.8 % compared to 20Cr20Fe20Mn20Ni20. Furthermore, the study examines the instability of the solid-solution state caused by differences in the valence electron concentrations of the constituent elements and phase stability.

The Effect of Different Coating Agents on the Microhardness, Water Sorption, and Solubility of EQUIA Forte® HT

Objective: This study aimed to assess the effect of four different surface-coating agents on the microhardness, water sorption, and solubility of the highly viscous glass ionomer cement EQUIA Forte® HT. Materials and methods: A total of 100 cylindrical EQUIA Forte® HT samples were examined, with 50 tested for Vickers hardness and the other 50 for water sorption and solubility. For each test, the specimens were divided into five groups (10 specimens/group) according to coating method: Group 1—no coating (control), Group 2—EQUIA Forte® Coat, Group 3—Single Bond™ Universal Adhesive, Group 4—ExciTE®F adhesive, and Group 5—petroleum jelly. Data were analyzed using the paired t-test, one-way analysis of variance, and Tukey’s post hoc test for multiple comparisons. Statistical significance was set at p < 0.05. Results: The mean microhardness of the coated groups was significantly higher than that of the uncoated group. Moreover, a significant difference in the microhardness value was detected between the coated groups. Furthermore, EQUIA Forte® Coat had the highest mean hardness value. The mean water sorption at 7 days showed that EQUIA Forte® Coat had the lowest values. In terms of water solubility, a statistically significant difference was found between no coating and all groups except EQUIA Forte®, between Single Bond Universal Adhesive and petroleum jelly, between petroleum jelly and EQUIA Forte Coat, and between EQUIA Forte® Coat and ExciTE®F. Conclusions: The study revealed that all coating agents significantly increased the microhardness of EQUIA Forte® HT, with EQUIA Forte® Coat showing the highest hardness and the lowest water sorption values.

An Assessment of Some Mechanical Properties of Harvested Potato Tubers cv. Spunta

Mechanical properties of vegetables or crop materials play a noteworthy part in designing new related implements. These properties can be extracted from force–deformation curves. Several factors, such as soil preparation, irrigation, and pre- and post-harvest treatments influence them. The core objective of this investigation work was to analyze force–deformation curves obtained from compression, penetration, and shear tests of potatoes (Spunta cv.) produced with three tillage implements. The potatoes cv. Spunta were cultivated in loamy sand soil under the center-pivot irrigation system. The tillage implements used were a disc harrow plow, chisel plow, and moldboard plow. The trials were performed at a constant planting depth (15 cm) below the soil and a single plowing speed of 5.4 km/h. All data were expressed as an average of five replicates ± standard deviation. The force–deformation curves analysis showed that the modulus of elasticity for potatoes cv. Spunta ranged from 4.32 to 5.8 N/mm, the bioyield force ranged from 84.25 to 114.12 N, and rupture forces ranged from 100.90 to 139.78 N. Furthermore, the results showed that the average values of the elastic and plastic ranges were 3.0 and 2.1 mm, respectively. The mean value of hardness was 1671.53 N·mm. No significant differences were observed with respect to the two planting seasons, but tillage implements had a significant impact on the characteristics extracted from the compression tests. The mean of the maximum forces required to penetrate the potato during the penetration stage were 41.24 N, 44.86 N, and 47.16 N for potatoes produced with the disc harrow plow, chisel plow, and moldboard plow, respectively. Similarly, the means of the maximum forces required to cut the potato in the shear stage were 724.38 N, 761 N, and 773.43 N for the disc harrow plow, chisel plow, and moldboard plow, respectively. The force–deformation curves showed that additional information might be required to obtain a complete description of the potato quality necessary to harvest potatoes cv. Spunta using harvesting and handling equipment with reduced economic loss. An extensive study of the soil characteristics and the above-mentioned properties is also recommended. The results obtained about the mechanical characteristics of potatoes cv. Spunta can be useful in providing information that aids in designing potato harvesting machines and in potato products factories.

Microstructure Characterization and Mechanical Properties of Polymer‐Derived (HfxTa1−x)C/SiC Ceramic Prepared upon Field‐Assisted Sintering Technique/Spark Plasma Sintering

The high‐temperature microstructural evolution and mechanical properties of two SiC‐based polymer‐derived ceramics with different Hf:Ta molar ratios are investigated using electron microscopy techniques and manipulated by nanoindentation. The as‐pyrolyzed ceramic powder consists of an amorphous Si(HfxTa1−x)C(N,O) structure (where x = 0.2, 0.7) with localized nanocrystalline transition metal carbides (TMCs). Subsequent application of the field‐assisted sintering technique (FAST) for high‐temperature consolidation results in a crystalline (HfxTa1−x)C/SiC ultra‐high temperature ceramic nanocomposite. The microstructure contains powder particle‐sized grains and sinter necks between the former powder particles. The powder particles consist of a β‐SiC matrix and small TMCs. Large TMCs are observed on the internal surfaces of former powder particles. This is due to the pulsed direct current and the resulting Joule heating that facilitates diffusion as well as oxygen impurities. Sinter necks of large β‐SiC grains form during the FAST process. The microstructural regions are assessed using high‐throughput nanoindentation. The hardness for SiC/(Hf0.7Ta0.3)C is measured on the formed grains and the sinter necks giving mean hardness values of about 27 and 37 GPa, respectively.

Effect of Process Parameters on the Hardness of 3D-printed Thermoplastic Polyurethane that Includes Foaming Agent

Recent progress in Material Extrusion-based Additive Manufacturing (MEX) has introduced active foaming agents in filaments composition, thus allowing for the tuning, by various process parameters, the hardness and the mechanical behavior of 3D-printed parts. In case of thermoplastic polyurethane (TPU) filaments, these advances significantly broaden the range of applications, particularly in the domains of comfort and orthotics (wrist-hand orthoses, insoles), offering the dual benefits of design flexibility inherent in MEX and the comfort of lightweight and customizable structures. However, the field is still in its early stages, with only a limited number of research efforts dedicated to characterizing these novel materials. In this context, this study is focused on determining the influence of printing temperature (190�C, 220�C, 240�C), infill density (25%, 35%, 45%) and infill pattern (honeycomb, gyroid) over the hardness of cylindrical specimens made of Colorfabb varioShore TPU. A comprehensive methodology of calibration is also presented as mandatory for obtaining good quality and accurate products by establishing correlations between flow rate and printing temperatures. The findings showed that the printing temperature is the most relevant factor impacting the hardness of varioShore TPU prints. At a printing temperature of 190�C, which corresponds to less foamed prints, the honeycomb infill yielded higher hardness compared to the gyroid infill, but the difference was not significant. Also, at 220�C and 240�C, the mean values of hardness remain relatively consistent, regardless of infill density and pattern.

Comparison of fracture strength, surface hardness, and color stain of conventionally fabricated, 3D printed, and CAD-CAM milled interim prosthodontic materials after thermocycling.

The purpose of this in vitro study was to investigate the fracture resistance, surface hardness, and color stain of 3D printed, CAD-CAM milled, and conventional interim materials. A total of 80 specimens were fabricated from auto polymerizing polymethyl methacrylate (PMMA), bis-acryl composite resin, CAD-CAM polymethyl methacrylate resin (milled), and 3D printed composite resin (printed) (n = 20). Forty of them were crown-shaped, on which fracture strength test was performed (n = 10). The others were disc-shaped specimens (10 mm × 2 mm) and divided into two groups for surface hardness and color stainability tests before and after thermal cycling in coffee solution (n = 10). Color parameters were measured with a spectrophotometer before and after each storage period, and color differences (CIEDE2000 [DE00]) were calculated. The distribution of variables was measured with the Kolmogorov Smirnov test, and one-way analysis of variance (ANOVA), Tukey HSD, Kruskal-Wallis, Mann-Whitney U tests were used in the analysis of quantitative independent data. Paired sample t-test was used in the analysis of dependent quantitative data (P < .05). The highest crown fracture resistance values were determined for the 3D printed composite resin (P < .05), and the lowest were observed in the bis-acryl composite resin (P < .05). Before and after thermal cycling, increase in mean hardness values were observed only in 3D printed composite resin (P < .05) and the highest ΔE00 value were observed in PMMA resin for all materials (P < .05). 3D printing and CAD-CAM milled interim materials showed better fracture strength. After the coffee thermal cycle, the highest surface hardness value was again found in 3D printing and CAD-CAM milled interim samples and the color change of the bis-acryl resin-based samples and the additive production technique was higher than the PMMA resin and CAD-CAM milled resin samples.

A novel in-situ synthesized bioactive TaZrTi alloy by high energy laser beam for total knee arthroplasty application

Total knee arthroplasty is the gold standard treatment for end-stage knee osteoarthritis, which could significantly improve function and relieve pain for patients. However, the present materials and manufacturing approaches are dissatisfactory for knee implants. In the present work, a Ta60-Zr20-Ti20 (in wt%) coating was in-situ synthesized onto Ti6Al4V alloy via a high energy laser beam. The microstructure analysis indicated that α-Ta/ZrTi solid solution generated into body-centered cubic (bcc) grains in dimensions of several to hundred micrometers. The Ta-riched dendrites nucleated, grew, and expanded in the ZrTi matrix. The mechanical and biological properties of the in-situ synthesized TaZrTi sample are compared with the conventionally rolled Ti6Al4V, which is also the substrate alloy. The mean values of hardness and elastic modulus of in-situ synthesized TaZrTi tested by the nanoindenter, are 10.31 and 134.84 GPa, respectively. These results are harder than the Ti6Al4V counterpart (5.14 GPa) with a preferred slightly low elastic modulus (152.95 GPa of Ti6Al4V). Subsequently, the in-situ synthesized TaZrTi exhibits an excellent wear resistance demonstrated by nano-scratch experiments. In addition, the osteoblastic and endothelial cells were cultured in vitro to evaluate the biocompatibility of in-situ synthesized TaZrTi. The results show a comparable bioactivity and surface affinity compared with the rolled Ti6Al4V in 7 days. Briefly, this in-situ synthesized TaZrTi alloy is expected to shed light on load-bearing orthopedic applications to relieve the pain of patients, and the findings in this study provide an insightful understanding of laser additive manufactured TaZrTi alloy.

COMPARATIVE ASSESSMENT OF HARDNESS OF TWO NANO-HYBRID RESIN-BASED DENTAL COMPOSITES

Objectives: To compare the hardness of two nano-hybrid resin-based dental composites. Materials and Methods: Two nano-hybrid composites i.e., Nexcomp by Meta Biomed, Korea, and Tetaric N Ceram by Ivoclar Vivadent, AG, Liechtenstein were selected, and hardness was evaluated according to ASTM E384-11e. T-test was used to statistically analyze the data. Results: The mean hardness value (VHN) of Tetaric N Ceram (78.4±3.14) was high when compared with Nexcomp (50±4.12). The statistical analysis showed a signifi cant diff erence with p-value of 0.00. Conclusion: Both composites had adequate hardness values and dental practitioners may select the material subject to the clinical situation and patient’s aff ordability.

The Effect of Three Desensitizing Toothpastes on Dentinal Tubules Occlusion and on Dentin Hardness.

There are two main methods used for dentin hypersensitivity (DH) treatment: dentinal tubule occlusion and blockage of nerve activity. Dentifrices are the most common vehicles for active ingredients used for DH treatment. The aim of this study was to evaluate the efficacy of three toothpastes on dentinal tubule occlusion, mineral acquisition, and dentin hardness. Forty human dentin disks were submerged in 40% citric acid for 30 s and then exposed to tooth brushing for 2 min twice a day for 14 days using three toothpastes: Dontodent Sensitive (group 1), Dr. Wolff's Biorepair (group 2), and Sensodyne Repair and Protect (group 3). In the control group (group 4), the samples were brushed with water. All of the samples were evaluated using scanning electron microscopy (SEM), energy-dispersive X-ray (EDX), and Vickers dentin hardness determination. On SEM images, the degree of dentinal tubule occlusion was assessed using a five-grade scale. The mean score values in groups 1-4 were 3.60 ± 0.69, 2.20 ± 0.91, 2.30 ± 1.16, and 5.00 ± 0.00, significantly higher in study groups when compared to the control group (Kruskal Wallis test p < 0.05). EDX evaluation showed significantly higher calcium and phosphorus concentrations in groups 1 and 3 when compared to control group d. The mean values of Vickers dentin hardness numbers in groups 1-4 were 243.03 ± 10.014, 327.38 ± 56.65, 260.29 ± 37.69, and 225.83 ± 29.93, respectively. No statistically significant results were obtained when comparing the hardness mean values in groups (Kruskal-Wallis statistical test, p = 0.372 > 0.05). All three toothpastes tested demonstrated significant occlusion of dentinal tubules. Dontodent Sensitive and Sensodyne Repair and Protect toothpastes enhanced the calcium and phosphorus content of the dentin surface. None of the toothpastes increased dentin hardness as a result of mineral acquisition.

Variation in enamel mechanical properties throughout the crown in catarrhine primates

Enamel mechanical properties vary across molar crowns, but the relationship among mechanical properties, tooth function, and phylogeny are not well understood. Fifteen primate lower molars representing fourteen taxa (catarrhine, n = 13; platyrrhine, n = 1) were sectioned in the lingual–buccal plane through the mesial cusps. Gradients of enamel mechanical properties, specifically hardness and elastic modulus, were quantified using nanoindentation from inner (near the enamel-dentine junction), through middle, to outer enamel (near the outer enamel surface) at five positions (buccal lateral, buccal cuspal, occlusal middle, lingual cuspal, lingual lateral). Cuspal positions had higher mechanical property values than lateral positions. Middle enamel had higher mean hardness and elastic modulus values than inner and outer locations in all five crown positions. Functionally, the thicker-enameled buccal cusps of lower molars did not show evidence of increased resistance to failure; instead, lingual cusps—which show higher rates of fracture—had higher average mechanical property values, with no significant differences observed between sides. Preliminary phylogenetic results suggest there is relatively little phylogenetic signal in gradients of mechanical properties through the enamel or across the crown. There appears to be common mechanical property patterns across molar crowns in Catarrhini and potentially among primates more broadly. These results may allow more precise interpretations of dental biomechanics and processes resulting in mechanical failure of enamel in primates, such as wear and fracture.

Influence of Combined Heat Treatment and Hot Isostatic Pressure (HT-HIP) on Titanium Aluminide Processed by L-PBF.

Postprocessing is essential for improving titanium aluminide (TiAl) microstructure and part quality after using the laser powder bed fusion (L-PBF) method. It has been reported that Ti-48Al-2Cr-2Nb (%at) processed by L-PBF has internal defects and low fracture toughness. Microstructure control by heat treatment (HT) showed a significant improvement in the ductility of the material. Alternatively, hot isostatic pressing (HIPing) could be applied to reduce the residual stresses and internal defects formed during the L-PBF. Combining the benefits of these two subsequent processes into a single predetermined process is appealing for Ti-48Al-2Cr-2Nb (%at) to minimize cost. This work presents a novel strategy to postprocess L-PBF TiAl by applying combined heat treatment and hot isostatic pressing in one process, namely HT-HIP. The process includes three cycles with different conditions (i.e., temperature, time, and pressure). These conditions were determined to achieve improved part quality and microstructure. The results show that the tensile residual stresses decreased from a peak of 249 MPa in the as-built sample to compressive stresses that peaked at -90 MPa after the HT-HIP process. The number and size of internal defects could be greatly reduced. The defects were transformed into a regular spherical shape, which is good in terms of fatigue strength. Additionally, a duplex microstructure with lamellar α2/γ colonies could be introduced for better ductility. Different levels of duplex microstructure could be achieved along with the process cycles. The grain structure using EBSD analysis showed refined equiaxed grains, which demonstrate better strength after the HT-HIP process. Twinning boundaries were also observed in the HT-HIP sample. The grain orientation tendency to the build direction significantly reduced after the HT-HIP process. The nanoindentation test was applied to evaluate the nanohardness of the as-built and HT-HIP samples. It could be demonstrated that the nanohardness is dependent on the formed phases and lamellar density inside the grains. The mean hardness value was 8.19 GPa for the as-built sample, while it was 5.48 GPa for the HT-HIP sample.

The Effect of Additional Finishing and Polishing Sequences on Hardness and Roughness of Two Different Dental Composites: An In Vitro Study

Aim: The aim of this study was to evaluate the effect of additional finishing and polishing sequences on a new structural colored (Omnichroma) and a conventional dental composite (Estelite Sigma Quick). Materials and Method: Forty disk-shaped dental composite specimens were prepared from each dental composite and assigned to four groups in terms of additional finishing polishing sequences. Group 1: Mylar strip (control). Group 2: Abrasive disks. Group 3: After abrasive disks, application of a felt brush with abrasive paste. Group 4: After abrasive disks, application of a felt brush with abrasive paste. Then, a single-bottle adhesive was applied as a surface sealer. Hardness and surface roughness were measured using the Vickers hardness test and a profilometer, respectively. SEM images of one of each group were captured at 500x, 1500x, and 3500x magnifications. Two-way analysis of variance, Tukey HSD, and Shapiro–Wilk tests were used for the statistical analysis. Results: Mean hardness values differ in terms of finishing-polishing sequences ( P &lt; .001), dental composites ( P &lt; .001), and interaction of finishing-polishing sequences-dental composites ( P &lt; .001). Mean roughness values differ in terms of finishing-polishing ( P = .002). The main effect of composites on roughness values was not found statistically significant ( P = .990). Also, there is no difference between the mean roughness values in terms of the interactions of finishing-polishing and composites ( P = .967). Conclusion: Finishing-polishing with abrasive disks and abrasive paste are important steps for these dental composites. However, the application of a single-bottle adhesive as a surface sealant on these composites decreases the hardness of the materials.

THERMO-MECHANICAL AND MICROSTRUCTURAL INVESTIGATIONS OF AA 6061/GNPS WELDED JOINTS DEVELOPED BY CONTINUOUS DRIVE FRICTION WELDING

The paper provides a novel technique for merging graphene nanoplatelets (GNPs) within aluminium matrix (AA 6061) by continuous drive friction welding (CDFW). The welding processes were done at 1400 rpm and 2000 rpm rotational speeds with two different frictional loads 2000 N and 2500 N for 5 sec and 7 sec welding times. The welded joints were subjected to tensile and hardness tests. The heating-cooling cycles through the welding process were monitored. The microstructure investigation was performed using optical and scanning electron microscopes (SEM). The effect of welding conditions on the ultimate tensile strength (UTS) results of AA 6061 and AA 6061/GNPs were completely studied in details. There is no big detectable variation in the mean hardness values due to the GNPs addition. The best welding conditions for achieving the highest mechanical properties were defined. The presence of GNPs in the welded joints results in lower heating at the welded joint at the same welding conditions. Finer grain structure and homogeneous distribution for the GNPs within the welding zone were observed.

Comparative evaluation of microleakage and hardness of newer posterior restorative materials.

The physical properties of restorative materials are critical when restoring posterior teeth. Restorative materials are continuously evolving in the quest for creating long lasting restorations. To compare and evaluate microleakage and hardness of three different posterior restorative materials: Cention N, Zirconomer Improved and Solare Sculpt. For micro leakage evaluation, 40 extracted human third molars were randomly divided into three experimental groups of 10 teeth each and two control group of 5 teeth each. Standardized box shaped class II cavity preparation was done in Group I, II, III and V. In Group V, cavity was prepared but left unrestored. No cavities were prepared in Group IV. Cavities in Group I, II, and III were restored with Cention N, Zirconomer Improved, Solare Sculpt respectively. Teeth were thermocycled together for 500 cycles. All the samples were placed in 2% methylene blue for 24h. Microleakage evaluation was done using stereomicroscope. For hardness evaluation ten standardized discs of each material were prepared and evaluated using vicker's hardness test. All the groups showed some amount of microleakage. The mean micro-leakage score was significantly more among Group II compared to Group I. There was no significant difference in mean micro-leakage score between Groups I and III. The mean hardness value was significantly more among Groups I and II compared to Group III. No material was able to completely eliminate microleakage. Cention N showed high hardness among the materials tested.

A high strength and conductivity bulk Magnéli phase Ti4O7 with superior electrochemical performance

Here we report for the first time that Magnéli phase Ti 4 O 7 electrode with super performance is successfully prepared by hot-pressed sintering of single-phase submicron Ti 4 O 7 powders. The microstructure, mechanical properties, electrical conductivity and electrochemical performance of the Ti 4 O 7 electrodes were also investigated. Results show that the compact and homogeneous bulk Ti 4 O 7 without evident defects such as pores and cracks is achieved when the submicron Ti 4 O 7 powder was sintered at 1200 °C for 0.5 h. As a result, the bulk density of the Ti 4 O 7 reaches its theoretical value (4.323 g cm −3 ). Additionally, it has excellent physical and chemical properties, including the mean values of hardness and Young's modulus of 15.20 ± 0.42 and 247.40 ± 6.70 GPa, respectively, the Vickers-hardness of 1165.5 ± 9.5 HV, the highest known conductivity of 1252.5 S cm −1 , and the widest known electrochemical stability window of 4.19 V in 1 M NaCl solution.

Synthesis, characterization, and evaluation of the antifungal properties of tissue conditioner incorporated with essential oils-loaded chitosan nanoparticles.

PurposeThis study aims to investigate new tissue conditioner (TC) formulations involving chitosan nanoparticles (CSNPs) and essential oils (EO) for their antifungal potential, release kinetics, and hardness.Materials and methodsCSNPs were synthesized, and the separate solutions of CSNP were prepared with two types of EO, i.e., Oregano oil and Lemongrass. The EO was loaded separately in two concentrations (200 μL and 250 μL). The blank and EO-loaded CSNPs were screened against Candida albicans (C. albicans), and their minimum inhibitory concentration was established. GC Reline™ (GC corporation, USA) TC was considered a control group, whereby the four experimental groups were prepared by mixing CSNPs/EO solutions with TC powder. The antifungal effectiveness (C. albicans) and release kinetics behavior (1–6 h, 24 h, 48 h, and 72 h) was investigated. The Shore A hardness of control and experimental groups was evaluated in dry and wet modes (deionized water and artificial saliva). For statistical analysis, SPSS version 22 was used to do a one-way ANOVA post-hoc Tukey’s test.ResultsCompared to the control group, TCs containing blank CSNPs and CSNPs loaded with EO showed 3 and 5 log reductions in C. albicans growth, respectively. A significantly high antifungal effect was observed with TC containing lemongrass essential oil (200 μL). The continuous release of EO was detected for the first 6 hours, whereas completely stopped after 48 hours. Mean hardness values were highest for dry samples and lowest for samples stored in artificial saliva. The statistically significant difference within and between the study groups was observed in mean and cumulative essential oils release and hardness values of TCs over observed time intervals irrespective of storage media.ConclusionTCs containing essential-oil-loaded CSNPs seem a promising alternative treatment of denture-induced stomatitis, however, a further biological analysis should be taken.

The Influencing Effect of Silver Nitrate Fillers on the hardness of Flexible Resin

The development of polymer chemically produces alternative materials to polymethyl methacrylate, such as nylon, and epoxy resin, these resins are modified by thermoplastic process, and This Received The disadvantage of acrylic resin is the colonization of microorganism growth of fungi and candida adhesion. This study is designed to evaluate and compared the consequence of silver nitrate fillers reinforcement Accepted flexible acrylic hardness as one of the mechanical properties to find the effect of various concentrations. A (0.1and 0. 2) ml of the filler (silver nitrate) additive to the flexible acrylic. Forty five (45) specimens were prepared for testing in this study. The hardness test was used in this study. The sample of this test was divided into (3) groups (control group) and experimental groups as follows: Group A= (15) specimens without silver nitrate (Control group 0% silver nitrate). Group B= (15) specimens with (0.1 ml) silver nitrate. Group C= (15) specimens with (0.2 ml) silver nitrate. All control and test groups were processed; curred then finished and polished the specimens ready for testing. Shore A test against the concentration of silver nitrate the result of this study showed a high significant increase in the mean value of hardness for control groups to the silver nitrate compared with experimental groups.

Wire-based electron beam additive manufacturing of tungsten

In present study, the feasibility of wire-based additive manufacturing of commercially pure tungsten using electron beam technique could be demonstrated. Three different representative volumetric AM structures were built and subsequently characterized. The parts show a sound visual appearance with the absence of macroscopic cracks or severe distortion. The fabricated parts exhibit high density and the value depends on the welding sequence applied; while the thin- and medium-walled structure has a relative density of ~100% and 99.875%, the measured relative density of the volumetric structure is slightly reduced to ~99.131% due to the smaller periodic bonding defects. However, a higher density could be achieved compared to powder-based processes on refractory metal. The mean hardness value of the fabricated AM structures is approx. 366–380 HV1 and is in the range of approx. 89–93% of the conventionally fabricated substrate of 410 ± 39 HV1. A coarsening of the grains from the bottom to the top and a change in morphology can be noted for all AM structures. While the coarsening is quite severe for the thin-walled structure, it is moderate for the volumetric AM structures due to the change of the thermal boundary conditions. Caused by the deposition process, the microstructure in the substrate also changes and exhibits a coarse-grained heat-affected zone. Nevertheless, the grain size is still smaller compared to the AM bulk material.

Precipitation of Fine Carbides, Transformation of the Retained Austenite and Corrosion Properties on EN-31 Steel by Cryogenic Treatment Process

Investigate of precipitation carbides transformation of the retained austenite and corrosion properties on EN-31 steel by cryogenic treatment method. In this work to identify the percentage of retained austenite and corrosion rate, was presented on EN 31 bearing steel by which cryogenic treatment process. Further, the hardness values of CHT and DCT were compared by using the microstructure view of the CHT and DCT samples. The optimized cryotreated samples were prepared for metallographic examination as per ASTM E3-01. Then the specimen was subjected to factor level setting like cooling rate, soaking period, soaking temperature and tempering temperature at various conditions. Moreover, the precipitation of fine carbides and the transformation of retained austenite to martensite showed considerable variations in the hardness of the optimized DCT samples compared to the CHT samples. The mean hardness value of this sample is 861HV and 19.20%, 847HV and 17.25%, 838HV and 17.10%, 857HV and 18.40%, 790HV and 13.45% improvement in the hardness compared to CHT.

Use of AFM topography images to determine microindentation hardness of cast tungsten carbide powders

Hardness is defined as the resistance of a material to localized plastic deformation. Owing to their non-destructive nature, static indentation hardness tests are widely used in industry. Hardness testing is particularly useful for the mechanical characterization of materials that cannot be tested otherwise, e.g. powdered materials. In this study, challenges related to Vickers microindentation hardness testing of hard brittle cast tungsten carbide (CTC) powders were extensively investigated. Test load was optimized to obtain sufficiently large crack-free indentations allowing for precise measurement of the diagonal lengths. The influence of the operator and imaging technique on the measured hardness value was evaluated. Topography of residual imprints was investigated using atomic force microscopy (AFM) and a systematic and operator bias-free method to locate the indentation vertexes was developed. Results suggested that measurement variability introduced by AFM scanning and post-processing was as low as 3.1% and 1.3% with respect to the mean hardness value, respectively. Since the variability due to the measuring system can be isolated, the homogeneity of powders can be reliably evaluated from the hardness measurements thus obtained.