Evaluation of Vickers Hardness Number of Al-Si Alloy Under Heat Treated Conditions

The paper deal with the hardness property assessment of various Al-Si alloys under heat treated conditions. The tested specimens have the compositions of Si with percentages such as 12 18 and 24. The fabrication of the selected composition is carried out by melting the material to the melting temperature of around 800°C. The material is subjected to solutionised heat treatment for 3 hours at 500°C, 520°C and 535°C and quenched in water. Further aging is carried out at 155°C for 2 hours, 5 hours and 8 hours respectively for 500°C, 520°C and 535°C of solution heat treatment condition. The hardness property is evaluated using Vickers Hardness tester as per the standards of ASTM- E92. Thorough comparison of Vickers hardness number is performed among the as- cast and various heat treated environment. Desirable properties of alloy are observed at 520°C solutionised heat treatment & 5 hours of precipitation hardening at 155°C for 18% of Silicon composition. The hardness value decreases due to the increase in percentage of silicon and the values are observed.

Experimental investigation and performance enhancements characteristics of gaseous assisted powder mixed near dry electric discharge machining

Gaseous assisted powder mixed near dry EDM (GAPMND-EDM) is one of the recent hybrid technologies, which not only enhance the machining performance, but at the same time, high quality products with better surface quality characteristics can also be achieved. In this study, the response parameters were material removal rate, surface finish, micro hardness and residual stress. It was found that the maximum material removal rate (MRR 3.379 mg/min) was achieved with combination of (dielectric) oxygen gas with graphite powder while lowest surface roughness (SR 1.11 μm) was found to be with dielectric argon gas with graphite additives. Highest micro hardness (MH) and lowest residual stress (RS) was 820.30 Vickers hardness number (VHN) and 229 MPa found with dielectric combination of zinc additives with argon gas.

Effect of Resin Infiltration on Bleached Enamel: An In Vitro Evaluation of Micromorphology, Resin Penetration and Microhardness

Background: Tooth bleaching is a promising aesthetic treatment for shaded teeth; however, demineralized lesions also occur after bleaching, and Icon resin can infiltrate into the demineralized lesions and then improve the color of teeth. This study aims to evaluate the effectiveness of resin infiltration on bleached teeth that are managed with different protocols by assessing the micromorphology of enamel surfaces, the depth of resin penetration and the microhardness of enamel after bleaching and Icon resin infiltration.Methods: A total of 150 noncarious premolars with sound coronal structure, which were extracted for orthodontic purposes, were obtained in this study in three parts: part Ⅰ“micromorphology of enamel surfaces”（n=60）；part II“observation the depth of the resin penetration”（n=30)；part III “Vickers hardness number values”（n=60). Both part Ⅰ and part III were divided into six subgroups. Part II was divided into three subgroups. 10 samples per subgroup. Data were analyzed using SPSS 22.0, Mann-Whitney test.Results: The surface roughness of the teeth increased after bleaching. When etched with 15 % HCl before the resin infiltration, it would result in further increase in roughness, but the surface of the bleached teeth could be as smooth as that of normal teeth after resin infiltration. There was a statistically significant increase in the mean resin penetration depth of the bleached teeth with 5-day delay of resin infiltration over the bleached teeth with resin infiltration immediately (Mann-Whitney test, P<0.05). Otherwise，the VHN values of delayed ones were similar to the normal one.Conclusions: It suggested that Icon resin infiltration treatment should be delayed after tooth bleaching but not performed right after tooth bleaching.

Influences of Successive Exposure to Bleaching and Fluoride Preparations on the Surface Hardness and Roughness of the Aged Resin Composite Restoratives

Background and Objectives: Surfaces of composite restorations are adversely affected upon bleaching and topical fluoride application. Such a procedure is normally carried out in the presence of restorations already serving in a different oral environment, although previous in vitro studies only considered the freshly-prepared composite specimens for assessment. The current study accordingly aimed to evaluate both the surface hardness and roughness of aged composite restoratives following their successive exposure to bleaching and topical fluoride preparations. Materials and Methods: Disc specimens were prepared from micro-hybrid, nano-filled, flowable and bulk-fill resin composites (groups 1–4, n = 60 each). All specimens were subjected to artificial aging before their intermittent exposure to surface treatment with: none (control), bleach or topical fluoride (subgroups 1–3, n = 20). All surface treatments were interrupted with two periods of 5000 thermal cycles. Specimens’ surfaces were then tested for both surface hardness (Vickers hardness number (VHN), n = 10) and roughness (Ra, n = 10). The collected VHNs and Ras were statistically analyzed using two-way ANOVA and Tukey’s comparisons at α = 0.05 to confirm the significance of differences between subgroups. Results: None of the tested composites showed differences in surface hardness and roughness between the bleached and the non-treated specimens (p > 0.05), but the bleached flowable composite specimens only were rougher than their control (p < 0.000126). In comparison to the control, fluoride treatment not only reduced the surface hardness of both micro-hybrid (p = 0.000129) and flowable (p = 0.0029) composites, but also increased the surface roughness of all tested composites (p < 0.05). Conclusion: Aged composite restoratives provide minimal surface alterations on successive bleaching and fluoride applications. Flowable resin composite is the most affected by such procedures. Although bleaching seems safe for other types of composites, the successive fluoride application could deteriorate the aged surfaces of the tested resin composites.

In Vitro Re-Hardening of Bleached Enamel Using Mineralizing Pastes: Toward Preventing Bacterial Colonization

The search for materials able to remineralize human hard tissues is a modern medical challenge. In this study, the protective effect on the enamel microhardness by a paste based on hydroxyapatite and sodium fluoride (Remin Pro) was evaluated after two different enamel bleaching procedures. Forty sound human incisors were randomly assigned to different treatments: bleaching with an in-office agent (Perfect Bleach Office+); bleaching with an at-home agent (Perfect Bleach); bleaching with the in-office agent followed by the prophylaxis paste; bleaching with the at-home agent followed by the prophylaxis paste; no treatment (control). Bleaching was performed at 0, 8, 24 and 32 h, followed by a 3-min re-mineralizing treatment in the subgroups designed to receive it. Specimens underwent a micro-hardness tester and a mean Vickers Hardness number was considered for each specimen. ANOVA exhibited significant differences among groups. Post-hoc Tukey testing showed significant micro-hardness decrease after the application of both the two bleaching agents. The treatment with prophylaxis paste significantly increased the micro-hardness values of bleached enamel.

Nöggerathite-(Ce), (Ce,Ca)2Zr2(Nb,Ti)(Ti,Nb)2Fe2+O14, a New Zirconolite-Related Mineral from the Eifel Volcanic Region, Germany

The new mineral nöggerathite-(Ce) was discovered in a sanidinite volcanic ejectum from the Laach Lake (Laacher See) paleovolcano in the Eifel region, Rhineland-Palatinate, Germany. Associated minerals are sanidine, dark mica, magnetite, baddeleyite, nosean, and a chevkinite-group mineral. Nöggerathite-(Ce) has a color that ranges from brown to deep brownish red, with adamantine luster; the streak is brownish red. It occurs in cavities of sanidinite and forms long prismatic crystals measuring up to 0.02 × 0.03 × 1.0 mm, with twins and random intergrowths. Its density calculated using the empirical formula is 5.332 g/cm3. The Vickers hardness number (VHN) is 615 kgf/mm2, which corresponds to a Mohs’ hardness of 5½. The mean refractive index calculated using the Gladstone–Dale equation is 2.267. The Raman spectrum shows the absence of hydrogen-bearing groups. The chemical composition (electron microprobe holotype/cotype in wt %) is as follows: CaO 5.45/5.29, MnO 4.19/4.16, FeO 7.63/6.62, Al2O3 0.27/0.59, Y2O3 0.00/0.90, La2O3 3.17/3.64, Ce2O3 11.48/11.22, Pr2O3 1.04/0.92, Nd2O3 2.18/2.46, ThO2 2.32/1.98, TiO2 17.78/18.69, ZrO2 27.01/27.69, Nb2O5 17.04/15.77, total 99.59/99.82, respectively. The empirical formulae based on 14 O atoms per formula unit (apfu) are: (Ce0.59La0.165Nd0.11Pr0.05)Σ0.915Ca0.82Th0.07Mn0.50Fe0.90Al0.045Zr1.86Ti1.88Nb1.07O14 (holotype), and (Ce0.57La0.19Nd0.12Pr0.05Y0.06)Σ0.99Ca0.79Th0.06Mn0.49Fe0.77Al0.10Zr1.89Ti1.96Nb1.00O14 (cotype). The simplified formula is (Ce,Ca)2Zr2(Nb,Ti)(Ti,Nb)2Fe2+O14. Nöggerathite-(Ce) is orthorhombic, of the space group Cmca. The unit cell parameters are: a = 7.2985(3), b = 14.1454(4), c = 10.1607(4) Å, and V = 1048.99(7) Å3. The crystal structure was solved using single-crystal X-ray diffraction data. Nöggerathite-(Ce) is an analogue of zirconolite-3O, ideally CaZrTi2O7, with Nb dominant over Ti in one of two octahedral sites and REE dominant over Ca in the eight-fold coordinated site. The strongest lines of the powder X-ray diffraction pattern (d, Å (I, %) (hkl)) are: 2.963 (91) (202), 2.903 (100) (042), 2.540 (39) (004), 1.823 (15) (400), 1.796 (51) (244), 1.543 (20) (442), and 1.519 (16) (282), respectively. The type material is deposited in the collections of the Fersman Mineralogical Museum of the Russian Academy of Sciences, Moscow, Russia (registration number 5123/1).

Microstructural Characterization and Properties of Sn-Ag-Cu (SAC) Compound Induced by Zn Alloying

The microstructural properties and intermetallic (IMC) formation of Sn-Ag-Cu (SAC) through varying amounts of zinc were examined in this study while having tin held at constant composition. Samples were prepared and heated in a furnace for 168 hours to achieve complete solidification and homogenization. Results showed relatively fine microstructure primarily containing Sn dendrites, eutectic, and pro-eutectic phases. Microstructures for each alloy was similar for which majority of them formed copper-based IMCs and Sn dendrites. The alloy (0.7Sn-0.15Ag-0.1Cu-0.05Zn) containing minimal amount of zinc with high amount of Ag resulted to high Vickers hardness number. Structural analysis showed that these group of alloys composed mainly of β-Sn, Cu6Sn5, and Ag3Sn.

Investigations on growth and property of mid-infrared lithium selenoindate single crystals

Lithium selenoindate (LiInSe2) crystals with high optical quality are successfully grown by small-angle inclined horizontal temperature gradient condensation. In order to evaluate the various characteristics, the powder X-ray diffraction (XRD) spectrum, optical damage resistance ability and Vickers hardness in lithium selenoindate crystals were studied. The growth crystals have orthorhombic nature, a = 6.184 Å, b = 7.092 Å and c = 8.207 Å. The damage thresholds of LiInSe2 crystal with the front face and back face were 224 mW/cm2 and 165 mW/cm2. Also the Vickers hardness number of LiInSe2 crystal was found to be 342.4 kg/mm2.

Vickers Microhardness Dependence Load and Determining of Tensile Strength of HQ 705 Steel from Microhardness Curves

Vickers microindentation hardness test has been applied for a long time to determine the mechanical properties of a small volume of samples. The procedure of this hardness test consists of using a constant load on a rigid indenter and measuring the dimensions of the indenter residual impression (indentation imprint) on the surface of the sample tested after loading and unloading. The objective of this research is to characterize the mechanical properties and material constants of HQ (High Quality) 705 alloy steel mainly its VHN (Vickers Hardness Number) and tensile strength before and after quenching and tempering heat treatments. The characterization is based on Vickers microhardness dependence load curves.Quenching treatment was performed in a furnace by heating the samples at austenite temperature of 850 o C with holding time of two hours and then the samples were rapidly cooled in oil bath. Tempering processes were conducted by heating again the quenching samples to temperatures of 150, 200, 250, 300, 350, 400, 450, 500, 550 and 600 o C with holding time of two hours for each sample. Finally, all samples were slowly cooled in atmospheric temperature. The mechanical properties of samples were characterized by using Vickers microhardness dependence load curves.The results show that VHN (Vickers Hardness Number) depends on indentation load and VHN increases with increment of load for indentation load lower than 5 N. VHN is almost constant for indentation load greater than 5 N. The raw material (without heat treatment) has the VHN and tensile strength of 3413 MPa and 1050.61 MPa respectively and the quenched samples have the VHN and tensile strength of 5407 and 1861 MPa respectively. The Vickers hardness and tensile strength decrease with the increment of tempering temperatures. The higher tempering temperature produces lower hardness and tensile strength. The raw material tensile strength of 1058.8 MPa obtained by tensile test is comparable to its tensile strength of 1050.61 MPa obtained by Vickers indentation. This result indicates that Vickers microindentation is valid to use for evaluating the tensile strength of HQ 705 alloy steel.

Influence of Al2O3 sol concentration on the microstructure and mechanical properties of Cu–Al2O3 composite coatings

Copper ( Cu ) is widely used as electrical conducting and contacting material. However, Cu is soft and does not have good mechanical properties. In order to improve the hardness and wear resistance of Cu , sol-enhanced Cu – Al 2 O 3 nanocomposite coatings were electroplated by adding a transparent Al oxide ( Al 2 O 3) sol into the traditional electroplating Cu solution. It was found that the microstructure and mechanical properties of the nanocomposite coatings were largely influenced by the Al 2 O 3 sol concentration. The results show that the Al 2 O 3 nanoparticle reinforced the composite coatings, resulting in significantly improved hardness and wear resistance in comparison with the pure Cu coatings. The coating prepared at the sol concentration of 3.93 mol/L had the best microhardness and wear resistance. The microhardness has been improved by ~20% from 145.5 HV (Vickers hardness number) of pure Cu coating to 173.3 HV of Cu – Al 2 O 3 composite coatings. The wear resistance was also improved by ~84%, with the wear volume loss dropped from 3.2 × 10-3 mm3 of Cu coating to 0.52 × 10-3 mm3 of composite coatings. Adding excessive sol to the electrolyte deteriorated the properties.