Higher Surface Hardness Values Research Articles

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.

ANALISIS SURFACE HARDNESS ALUMINUM 6061 HASIL GAS NITRIDING DENGAN VARIASI HOLDING TIME

The nitriding coating process is widely applied in the industry. Gas nitriding is a technique used to improve the mechanical properties of a metal. This study aims to determine the influence of holding time variations on surface hardness and diffusion depth in aluminum alloy 6061 (Al-Mg-Si) that undergoes gas nitriding. The independent variable used in this study was holding time, namely, initial specimen (without holding time treatment), and specimens that experienced holding ranging from 1 hour, 2 hours, 3 hours, 4 hours, and 5 hours. The cooling medium used after gas nitriding was air. The highest surface hardness value was obtained in aluminum alloy 6061 specimens without holding time treatment, namely with a hardness value of 141 VHN while the lowest surface hardness value was produced by the specimen with a holding time of 5 hours. The lowest surface hardness value was 55.4 VHN. Based on the results of the EDAX composition test known that the specimen of aluminum alloy 6061 with a holding time of 5 hours diffused nitrogen element of 1.57% and oxygen element of 5.27%.

Characteristics of ASTM A36 steel mechanical properties in pack carburizing with carburizing agent coconut shell charcoal and goat bone powder mixed

In the study the specimens were ASTM A36 low carbon steel pack carburizing at 950℃, soaking time variations of 1, 2 and 3 hours. The carburizing agent is a mixture of coconut shell charcoal and goat bone powder (Capra aegagrus hircus). The size of the powder is 100 mesh, with variations in weight percentage between goat bone powder and coconut shell charcoal: 10%:90%, 20% : 80%, and 30% : 70%. Furthermore, the impact test, hardness, microstructure test and composition test were carried out, to determine the mechanical properties of the specimens. The results of the study show, soaking time and the composition of the carburizing agent affect the mechanical properties of the specimen The lowest impact toughness of 0,0576 joules/mm2 was obtained by the specimen at a soaking time of 1 hour, the composition of the carburizing agent (% wt goat bone powder: coconut shell charcoal) 20% : 80%. The highest surface hardness value was 854.734 Kg/mm2 at 3 hours soaking time with 10%:90% carburizing media composition. The results of microstructure observations showed that in specimens treated with pack carburizing ferrite structure, pearlite turned into martensite.

Taze ve Doğal Yaşlanmış Ağaç Malzemeye Uygulanan Üç Çeşit Verniğin Yüzey Sertliği

Aim of study: This study was carried out to determine the surface hardness values of some varnishes applied to the surface of naturally aged wood material.&#x0D; Material and methods: Acrylic, polyurethane and water-based varnish was applied to the surface of the experimental samples prepared from naturally aged and fresh Scots pine (Pinus sylvestris L.), sessile oak (Quercus petrea L.) and chestnut (Castanea sativa M.) wood materials. A total of 360 test samples, 10 for each wood type, cutting direction, age period, and varnish type were prepared then the surface hardness values of these samples were determined.&#x0D; Main results: As a result of the experiments, the effect of the age period on the surface hardness of the varnish layer was found to be insignificant. The highest surface hardness value in wood material was obtained in the tangential section of oak wood and the difference between oak wood and chestnut wood was statistically insignificant. As a varnish type, the highest surface hardness value was obtained in polyurethane varnish, followed by acrylic varnish and water-based varnish, respectively. In addition, the surface hardness of the varnish layer in the tangential section of the wood material was found to be higher than that of the radial section.&#x0D; Highlights: In cases where high surface hardness is required in the varnish layer, polyurethane varnish can be preferred. As a result of the experiments, water-based varnish with a low surface hardness value will be able to give a working performance compatible with wood material with a hygroscopic structure, thanks to its high elasticity. For this reason, wood with a high amount of dimensional change can be used to protect the material against external influences.

The evaluation of the efficiency of different waxes on some physical and surface properties of fiberboard

Bilindiği üzere odun esaslı levha ürünlerinin özellikle kullanım yerlerinde suya ve rutubete maruz kaldıklarında dayanımlarının az olması bu ürünlerin dezavantajlı olarak kabul edilen ve iyileştirilmesi gereken özelliklerinden biridir. Bu nedenle odun esaslı levhaların suya, rutubete karşı dayanımlarını artırabilmek adına üretimleri esnasında su itici maddeler kullanılmaktadır. Bu çalışmada, levha üretiminde yaygın olarak kullanılan su itici maddelerden biri olan parafine alternatif olarak iki farklı vaks-mum türü seçilmiş ve etkinlikleri değerlendirilmiştir. Levha örneklerinin 2-24 saat süre için kalınlığına şişme (KŞ) ve su alma (SA) değerleri, yüzey pürüzlülük parametreleri ile yüzey sertlik değerleri belirlenmiştir. Ölçümler sonucunda, kontrol grubuna kıyasla diğer grupların KŞ ve SA oranlarında belirgin derecede iyileşme olduğu belirlenmiştir. Özellikle sadece parafin, parafin-balmumu ve parafin-soya vaksı karışımlarının tutkala ilave edildiği grupların oldukça düşük SA ve KŞ değerleri verdiği görülmüştür. Yüzey pürüzlülük parametreleri ise vaks türüne, uygulama yöntemine bağlı olarak değişim göstermiştir. En yüksek yüzey sertlik değeri balmumu ve parafinin karışım halinde yüzeye uygulandığı grupta elde edilmiştir. Buna göre, kullanılan bitkisel ve hayvansal vaks türlerinin de su itici etki gösterebilecekleri, özellikle uygun yöntem ve farklı kombinasyonlarla uygulanmaları durumunda etkinliklerinin artırılabileceği düşünülmektedir.

Comparison of Flexural Strength and Surface Hardness of Polymethyl Methacrylate Resin Reinforced with Silanised Aluminium Oxide Nanoparticles- An In-vitro Study

Introduction: In complete denture fabrication, the common denture base material used is heat activated Polymethyl Methacrylate (PMMA). Considering various advantages, still there are some disadvantages like poor flexural strength and poor wear resistance. The flexural strength of any material reflects its potential to resist catastrophic fracture under a flexural load. Another property that influences the surface characteristics of acrylic resins is the surface hardness, which indicates the ease of finishing a material and its resistance to in-service scratching during cleaning procedures and exposure to various oral fluids. Thus an ideal denture base material should exhibit greater flexural strength and high surface hardness for the longevity of the dentures. Aim: To evaluate the effects of adding different percentages of silanised aluminium oxide (Al2O3) nanoparticles on the flexural strength and surface hardness of a conventional heat-polymerised acrylic resin. Materials and Methods: The in-vitro experimental study was conducted between October 2020 to Janaury 2021 at Drs. Sudha and Nageswara Rao Siddhartha Institute of Dental Sciences, Vijayawada, Andhra Pradesh, India. A total of 120 samples were fabricated and were grouped into four groups coded A to D (n=30). Group A was the control group (without adding Al2O3). Specimens in the other three groups (B to D) were reinforced with silanised Al2O3 at loadings of 1%, 2.5% and 5% w/w. Flexural strength was assessed with a three-point bending test using a universal testing machine. Surface hardness test was conducted using a Vickers Hardness (VH) tester. Data was analysed using Analysis of Variance (ANOVA) and Tukey’s post-hoc test. Results: Among all the reinforced groups highest flexural strength value was seen in Group C- PMMA+2.5% w/w silanised aluminium oxide nanoparticles reinforced group (88.33 Mpa) and highest surface hardness value was seen in the Group D- PMMA+5% w/w silanised Aluminium oxide nanoparticles reinforced group (29.44 VH). Conclusion: Reinforcement of the conventional heat cured acrylic resin with 2.5% w/w silanised Al2O3 nanoparticles significantly increased its flexural strength and hardness.

Comparison of Mechanical Properties of 3D-Printed, CAD/CAM, and Conventional Denture Base Materials.

To evaluate and compare the mechanical properties (flexural strength and surface hardness) of different materials and technologies for denture base fabrication. The study emphasized the digital technologies of computer-aided design/computer-aided manufacturing (CAD/CAM) and three-dimensional (3D) printing. A total of 160 rectangular specimens were fabricated from three conventional heat-polymerized (ProBase Hot, Paladon 65, and Interacryl Hot), three CAD/CAM produced (IvoBase CAD, Interdent CC disc PMMA, and Polident CAD/CAM disc), one 3D-printed (NextDent Base), and one polyamide material (Vertex ThermoSens) for denture base fabrication. The flexural strength test was the three-point flexure test, while hardness testing was conducted using the Brinell method. The data were analyzed using descriptive and analytical statistics (α = 0.05). During flexural testing, the IvoBase CAD and Vertex ThermoSens specimens did not fracture during loading. The flexural strength values of the other groups ranged from 71.7 ± 7.4 MPa to 111.9 ± 4.3 MPa. The surface hardness values ranged from 67.13 ± 10.64 MPa to 145.66 ± 2.22 MPa. There were significant differences between the tested materials for both flexural strength and surface hardness. There were also differences between some materials with the same polymerization type. CAD/CAM and polyamide materials had the highest flexural strength values. Two groups of CAD/CAM materials had the highest surface hardness values, while a third, along with the polyamide material, had the lowest. The 3D-printed materials had the lowest flexural strength values. Generally, CAD/CAM materials show better mechanical properties than heat-polymerized and 3D-printed acrylics do. Nevertheless, a material's polymerization type is no guarantee of its optimal mechanical properties.

Effect of Bench Time on Surface Hardness of Nanofiller Composite Resin

The purpose of this study was to evaluate the effect of different bench time on surface hardness of the composite resin after being stored in the refrigerator at 4°C. Before used in this study, the composite resin was refrigerated at 4°C for the test group and kept at 25°C for the control group. The specimens were divided into control group (I) and five experimental groups according to the bench time before polymerization, 0 (II); 15 (III); 30 (IV); 45(V); and 60 (VI) minutes. Sixty specimens with 10 mm diameter and 2 mm thickness were made by using nanofiller composite resin. The material was filled into stainless steel mold and curing for 20 s. After kept in a dark box for 24 hours, the surface hardness of all specimens were tested using Microhardness Tester. The data were analyzed with one-way ANOVA (p≤0.05) and LSD’s post hoct test. The results showed that the 60 minute bench time group presented the highest surface hardness value followed by 45, 30, 15 and 0 minutes bench time group. Moreover, the hardness value of 60 min group was almost similar with the control group. Statistical analysis showed no significant differences (p>0.05) between groups. It concluded, bench time has an effect on the surface hardness of composite resin but no significant differences statistically.

Effects of shot peening pre-treatment and plasma nitriding parameters on the structural, mechanical and tribological properties of AISI 4140 low-alloy steel

In recent years, hybrid surface treatments which include plasma nitriding combined with pre-shot peening operations have been proposed for the improvement of nitriding efficiency. The main objective of this study is to characterize the effects of dual process on the friction and wear behavior of metallic materials. For this purpose, AISI 4140 steel samples were shot peened at various densities of 16, 20 and 24 A. The pre-treated samples were plasma nitrided at a temperature of 500 °C for 1 and 4 h. The structural and mechanical properties of samples were analyzed by XRD, SEM and microhardness tester. Wear tests were performed under dry sliding conditions to determine the tribological properties of the samples. This study showed that the shot peening treatment formed finer grains, compressive residual stresses on the surface and increased the diffusion kinetics of the samples. The surface hardness and residual stresses increased with increasing shot peening density. It was evidence that the finer grains, increased dislocation density and surface defects increased the case depth obtained from plasma nitriding by enabling easier diffusion of nitrogen. The depth of the diffusion zones in shot peened plus plasma nitrided specimens was found almost two times thicker than that of the diffusion zones in specimens treated only by plasma nitriding. The highest surface hardness values were obtained from pre shot peened and plasma nitrided samples in consequence of the interactive effect from nitride phases/layers and increased surface compressive residual stress. As a result, pre-shot peened plus plasma nitrided samples exhibited higher wear resistance than specimens treated only by shoot peening and hybrid treating in glow a discharge atmosphere.

Modelling and optimisation of treatment parameters using response surface methodology: application to superficial hardening of 2017A alloy using the rods-balls device

This work was concerned with the study of the surface hardening process of 2017A alloy using the rods-balls device. The objective of this work was to define the optimal processing parameters relative to the surface hardness of 2017A alloy using the response surface methodology. The regression model proposed in this paper has been developed using the central composite design (CCD). Analysis of variance (ANOVA) was validated with a confidence level > 93%. The final model is established on the basis of additional statistical analysis using other statistical criteria such as Malows cp and Akaike's information criterion. The optimal point (d = 4 mm, t = 10 min and f = 50 Hz) was determined by the Hessian matrix, it corresponded to the highest surface hardness value Hs = 422.25 HB. Highest surface hardness is then characterised by a gain in hardness Hs of 35.68%.

A NOVEL METHOD FOR IMPROVING PLASMA NITRIDING EFFICIENCY: PRE-MAGNETIZATION BY DC MAGNETIC FIELD

In this study, a novel pre-magnetization process, which enables easy diffusion of nitrogen, was used to enhance plasma nitriding efficiency. Firstly, magnetic fields with intensities of 1500[Formula: see text]G and 2500[Formula: see text]G were applied to the untreated samples before nitriding. After the pre-magnetization, the untreated and pre-magnetized samples were plasma nitrided for 4[Formula: see text]h in a gas mixture of 50% N2–50% H2 at 500[Formula: see text]C and 600[Formula: see text]C. The structural, mechanical and morphological properties of samples were examined by X-ray diffraction (XRD), scanning electron microscopy (SEM), microhardness tester and surface tension meter. It was observed that pre-magnetization increased the surface energy of the samples. Therefore, both compound and diffusion layer thicknesses increased with pre-magnetization process before nitriding treatment. As modified layer thickness increased, higher surface hardness values were obtained.

Effect of gaseous ozone and light-activated disinfection on the surface hardness of resin-based root canal sealers.

Although root canal instruments remove most of the content from the main root canal space, disinfection or irrigation plays an indispensable role in all areas of the root canal system, especially in parts that are inaccessible by instruments. The originality of this study was to investigate the effect of two novel disinfection techniques on the surface hardness of resin-based endodontic sealers using atomic force microscopy (AFM). Forty extracted single-rooted maxillary central human teeth were prepared and divided into four groups according to treatment methods. The first group was irrigated with saline and served as a control, other groups irrigated with sodium hypochlorite (NaClO); gaseous ozone; and light-activated disinfection (LAD). The groups were divided into two subgroups, according to the obturation method used: subgroup A: gutta-percha and AH plus; and subgroup B: EndoREZ/resin-coated cones. After obturation, atomic force microscopy (AFM) measurement was performed to analyze the surface hardness of the sealers. There was a significant difference between group 1A and group 3A (p < 0.05). Group 3B had the highest surface hardness values that were statistically different (p < 0.05). When disregarding the sealers, the ozone possessed statistically higher surface hardness values than the other groups in all root thirds (p < 0.05). The use of ozone and LAD may alter the surface hardness of resin-based sealers. The use of AFM can be considered an alternative hardness test techonology for sealing material.

Effect of storage in water and thermocycling on hardness and roughness of resin materials for temporary restorations

PURPOSE: This study evaluated the effect of storage in water and thermocycling on hardness and roughness of resin materials for temporary restorations. MATERIAL AND METHODS: Three acrylic resins (Dencor-De, Duralay-Du, and Vipi Cor-VC) were selected and one composite resin (Opallis-Op) was used as a parameter for comparison. The materials were prepared according to the manufacturers' instructions and were placed in stainless steel moulds (20 mm in diameter and 5 mm thick). Thirty samples of each resin were made and divided into three groups (n = 10) according to the moment of Vickers hardness (VHN) and roughness (Ra) analyses: C (control group): immediately after specimen preparation; Sw: after storage in distilled water at 37 °C for 24 hours; Tc: after thermocycling (3000 cycles; 5-55 °C, 30 seconds dwell time). Data were submitted to 2-way ANOVA followed by Tukey's test (α = 0.05). RESULTS: Op resin had higher surface hardness values (p 0.05) in roughness among materials (De = 0.31 ± 0.07; Du = 0.51 ± 0.20; VC = 0.41 ± 0.15; Op = 0.42 ± 0.18). Storage in water did not change hardness and roughness of the tested materials (p > 0.05). There was a significant increase in roughness after thermocycling (p < 0.05), except for material Du, which showed no significant change in roughness in any evaluated period (p = 0.99). CONCLUSION: Thermocycling increased the roughness in most tested materials without affecting hardness, while storage in water had no significant effect in the evaluated properties.

Effects of Superplasticity in Boronizing of Duplex Stainless Steel

In this research, conventional boronizing process (CB) and a new method of boronizing process under compression load condition (LB) were conducted and compared in order to study the effect of superplasticity on boronized substrate. Both processes were conducted on duplex stainless steel (DSS) with two different microstructures; as-received DSS with coarse grain microstructure (CDSS); and thermo-mechanically treated DSS with fine grain microstructure (FDSS) which can show superplastic behavior at high temperatures. Both processes were conducted at duration of 6 hours and temperatures between 1123 and 1223 K. All of boronized specimens demonstrated thin, smooth and compact morphology of boride layer. For CDSS, both CB and LB processes produced about similar surface hardness values within the range of 1425 – 2330 HV. For FDSS, CB process produced surface hardness between 1522 and 2601 HV, while under LB, the highest surface hardness values in the range of 1659 - 2914 HV were obtained. The result shows that introduction of load during boronizing has initiated superplastic deformation on FDSS thus accelerated diffusion of boron atoms into surface which finally lead to significantly higher surface hardness.