Surface Hardness Of Materials Research Articles

Experimental investigation on microstructure, mechanical and optical properties of RB-SiC ablated by nanosecond pulsed laser in nitrogen atmosphere

Reaction-bonded silicon carbide (RB-SiC) has gained significant attention owing to its exceptional physical and chemical properties. Improving the photovoltaic efficiency and mechanical properties of RB-SiC is conducive to further enhancing its applicability. Laser gas nitriding is an effective strategy to simultaneously reduce the surface reflectivity and enhance the surface hardness of materials. Accordingly, the evolution of microstructure, mechanical and optical properties of RB-SiC composite ablated by nanosecond pulsed laser in nitrogen atmosphere was comprehensively investigated. After laser gas nitriding, the surface hardness of RB-SiC composite was increased by 10.6–44.6 %. The chemical composition analysis indicated that Si-based nitride was formed on the laser-ablated surface, which was mainly responsible for the hardness enhancement. Additionally, the reflectivity of the laser-ablated surface was reduced by up to 95.2 % compared to the original RB-SiC composite. This study provides a straightforward and effective method to simultaneously improve the mechanical and optical properties of RB-SiC composites.

Floor impact sound reduction and impact absorption performance of floor mat

In Korea, the post evaluation system of floor impact sound performance was implemented in August 2022. Therefore, it is necessary to check the floor impact sound performance after the completion of the apartment. If a floor impact sound performance does not meet the regulation limit, compensationm and follow-up renovations are required. In this study, in order to develop a floor mat that can reduce heavy weight floor impact sound, the floor impact sound reduction performance and impact absorption performance of each condition of the sample were confirmed. Floor impact sound reduction performance was measured using the test methods of KS F 2865 and ISO 10140-3, and impact absorption performance was measured according to the test method of JIS A 6519. As a result of the measurement, the performance of reducing floor impact sound showed a clear difference in performance according to thickness rather than material type. Impact absorption performance was found to be affected by surface hardness and material thickness. In conclusion, it is considered that the selection, thickness, and surface hardness of materials are important design factors when developing floor mats.

Effect of roller burnishing on the mechanical behavior and surface quality of Ti6Al4V alloy

A low-cost and effective surface treatment technique that has gained popularity recently is roller burnishing. In this procedure, the rolling element is forced against the surface with a specified amount of force, which results in small plastic deformations that reduce surface roughness without removing chips from the surfaces. The method results in a considerable decrease in surface roughness while the material's surface hardness rises. The effects of roller burnishing process parameters (burnishing pressure, number of passes, and feed rate) on Ti6Al4V tensile strength and surface roughness were investigated experimentally in this study. In the study, the burnishing procedure was carried out via a specifically created disc-shaped equipment using the Taguchi L16 experimental design approach. The study's findings showed that the roller burnishing technique improved the Ti6Al4V alloy's surface quality, microhardness and ultimate tensile strength. It was shown that roller burnishing increased the surface roughness, microhardness and ultimate tensile strength by 64%, 16,25%, and 94%, respectively.

Failure of surface modification 3D printed polymer materials by UV/ozone irradiation

In today's technology, AM processes are widely adopted in the aerospace, energy, automotive, medicine, and agriculture industries. Fused Deposition Modeling (FDM) is one of the most remarkable methods in the AM family because of its superiorities. Besides the advantages provided, the mechanical strength of the printed parts is still not at a satisfactory level. Here, there are various secondary processes applied to polymer materials to improve both the mechanical properties and functionality of the printed part. Among these processes, the UV/O3 surface treatment method stands out as the most suitable one in terms of ease of application. In this study, two different infill orientation angles were applied to two standard test models. The fabrication process was initiated using suitable process parameters for filaments made of Polylactic Acid (PLA) and Thermoplastic Polyurethane (TPU) materials. The purpose of this investigation was to examine the mechanical strength of 3D printed polymer structures. For the same purpose, the UV/O3 (UV/Ozone) process was applied to the manufactured samples. The samples are then subjected to tensile and compression tests, Shore surface hardness measurements and Scanning Electron Microscopy (SEM) analyze for both the evaluation of mechanical properties and the examination of fracture surface structures. Consequently, significant increases of 28.33%, 25.21%, 27.90%, and 32.92% were observed in material surface hardness levels. This study is important in terms of presenting that the mechanical properties of 3D printed parts can be significantly improved with UV/O3 application, which is an effective and a practical process.

Surface layer characterization of 2205 duplex stainless steel subjected to abrasive water jet descaling

Abrasive water jet (AWJ) is an environmentally friendly and acid-free descaling technology, that has the added benefit of strengthening the material surface. However, the effects of AWJ descaling on the surface layer of heterostructured (HS) materials and the application of deformable abrasives involving high cycle times for AWJ descaling have not been extensively reported. In this study, martensitic stainless steel particles with high cycle times were subjected to AWJ descaling to investigate the effect of AWJ on the surface layer characterization of 2205 duplex stainless steel (DSS). The properties of the 2205 DSS surface layer were characterized by the surface morphology, surface roughness, microstructure, and microhardness. When exposed to an AWJ intensity of 0.245 mmA, the surface of 2205 DSS exhibited the formation of extrusion craters and flat debris. Additionally, the surface roughness Ra was measured at 3.778 µm. The gradient hardening layer was formed on the surface of the AWJ specimen, and the depth of the hardening layer was 550 µm. The maximum microhardness was 395 HV, which is approximately 30% higher than that of the original specimen. Within the AWJ specimens, dislocation networks were observed in the ferrite, while the austenite exhibited dislocation cells, deformation twins, and strain-induced martensite. Furthermore, the experimental results indicate that plastic deformation was unevenly distributed between the two phases, with the majority of deformation occurring within the austenite phase. Owing to the requirement of deformation compatibility, several of geometrically necessary dislocations (GNDs) accumulated near the austenitic phase boundary to regulate the plastic strain gradient, and the hetero-deformation induced (HDI) stress generated by these dislocations strengthens the austenite. The AWJ refines the surface material structure; increases the density of dislocations, phase boundaries, and stacking faults; forms strain-induced martensite; and introduces a residual compressive stress field, which improves the material surface hardness.

Synthesis of Hard Layer by Titanium Addition During Welding Process and Quenched Directly

Enhance the surface hardness of materials usually conducted through a hardfacing technique. Hardfacing is popular, whereby materials with better properties are deposited over cheaper bulk material. This work fabricated hard layers by adding titanium (Ti) wire during the welding process. This research used low-carbon steel as the base material, wire optime Ti grade 1 for Ti addition, and an HV 600 electrode with a diameter of 3.2 mm for filler metal. A single-layer weld was conducted with SMAW (positive polarity and 90 A). The samples were directly quenched in a different solution after welding. The properties of the weld layer were examined phase, structure, microstructure, macrostructure, and hardness using optical emission spectroscopy (OES), x-ray diffraction (XRD), an optical microscope, a digital camera, and a hardness device, respectively. Adding titanium (Ti) to the weld layer and quenching the samples after welding in the solution enhances the hardness. This phenomenon is attributed to different phase compositions, oxides, and microstructures. A fine dispersion of small particles and oxide amount is important in increasing hardness. There is no cracking in the weld and base metal. In conclusion, samples BNTiO and BNTiM are recommended for lathe-cutting tools.

Effects of Litsea cubeba Essential Oil Incorporated into Denture Soft Lining Materials.

The antimicrobial properties, cell cytotoxicity and surface hardness of soft lining materials (GC soft liner, Viscogel and Coe comfort) incorporated with various concentrations of Litsea cubeba essential oil (LCEO) were evaluated. The minimum inhibitory concentrations of LCEO against Candida albicans and Streptococcus mutans were 1.25% v/v and 10% v/v, respectively. However, when LCEO was incorporated into the three soft lining materials (GC soft liner, Viscogel and Coe comfort), 10% v/v and 30% v/v of LCEO could inhibit the growth of C. albicans and S. mutans, respectively. The extracts of soft lining materials with 10% and 30% v/v LCEO, 2% chlorhexidine, 30% v/v nystatin and no additive were used for cytotoxicity tests on a human gingival fibroblast cell line. There was no significant difference in cell viability in all groups with additives compared to the no additive group (p > 0.05). Surface hardness increased significantly between 2 h and 7 day incubation times in all groups, including the controls (p < 0.05). A higher LCEO concentration had a dose-dependent effect on the surface hardness of all soft lining materials (p < 0.05). However, the surface hardness of materials with additive remained in accordance with ISO 10139-1. LCEO could be used as a natural product against oral pathogens, without having a negative impact on soft lining materials.

Investigation on Electrical, Thermal, and Mechanical Properties of Silicone Rubber ATH Nanocomposites

In the present study, investigations have been carried out by choosing the nano-sized ATH (30 – 50 nm) particles as filler content in silicone rubber to acquire a deep insight to understand the use of nano ATH fillers in silicone rubber on its performance, to use it as insulation structure as an outdoor insulator. Variation in the surface condition of silicone rubber nanocomposites due to corona aging and the recovery characteristics analysis carried out through contact angle measurement. Nano ATH added in silicone rubber, up to 3 wt% of filler, shows increased dielectric constant with less loss factor. Water droplet-initiated discharges on silicone rubber nano ATH composites under DC voltage measured using UHF technique and the damage caused zone analyzed through AFM studies and by surface potential measurement, which indicates higher surface roughness and increased charge trap depth. It is observed that negative DC voltage has higher CIV followed by positive DC and AC voltage. Laser Induced breakdown studies (LIBS) show a direct correlation between plasma temperature and material surface hardness. Also, on laser shining on the surface of the specimen, its temperature was measured on the backside of the specimen through thermal imaging confirming increased diffusivity of temperature. Laser flash analysis shows a direct correlation between filler content in base polymer and thermal conductivity and diffusivity. Higher storage modulus and activation energies measured from the dynamic mechanical analysis indicate the significance of prepared composites as an excellent mechanical support structure for the power system network.

Development of hard and tough tool steel through precipitation of ultrafine carbides from super saturated solid solution

This study was inspired by the short life of the pins used in cotton seed separating machines in textile industries. The tip has been flame hardened to increase its hardness, and multiple heat treatment processes have been performed to distribute the hard carbide particles uniformly in the slightly soft ferrite matrix. The high carbon steel chosen as a base metal contains enough carbide-forming elements to supply the matrix with fine carbides. When the as-received sample was examined, needle-like martensitic structures with previous austenite grain boundaries were apparent. A carbide deposit forms both at the main and sub-boundary grain boundaries during grain boundary formation. A few spots of retained austenite are visible as white spots at some locations. The percentage of retained austenite is around 1%. With increased tempering time, the carbide was observed to shrink in size until it achieved its smallest size. Within the ferrite/martensitic phase, carbide grew in a specific direction after eight hours of tempering. The XRD results confirmed that these are Fe3C (cementite). SEM study at high magnification reveals the size and distribution of carbides. The existence of Fe3C is confirmed by EDS analysis of white spots, which exhibits iron and carbon peaks. There is also evidence of chromium, silicon, and magnesium in other locations. The Vickers hardness of the sample as obtained was 416 HV however it was reduced to 240 HV after precipitation. Following with flame hardening, the material's surface hardness is increased to 600 HV. Consequently, the material has a hard surface and a tough core. As a result, the material has a ductile fracture rather than brittle fracture.

Laser nitriding of Zr-based metallic glass: An investigation by orthogonal experiments

Laser nitriding is a useful method to improve the surface hardness of materials, and it has been newly introduced to harden the surface of Zr-based metallic glass (MG). However, the currently achieved improvement in surface hardness is only 15.7%. To explore the potential of laser nitriding of Zr-based MG, orthogonal experiments were designed and performed in this study. By nanosecond pulsed laser irradiation in nitrogen atmosphere, the effects of laser parameters (average laser power, scanning speed, overlap rate and number of irradiation cycle) on the surface hardness of Zr-based MG were systematically investigated. The experimental results showed the highest surface hardness reached 18.21 GPa (Meyer's hardness) by orthogonal design, which is about 2 times higher than that of the as-cast MG. Furthermore, the laser affecting layer consisting of nitride phase reached tens of microns. The obtained results demonstrated that significant improvement in surface hardness could be achieved by selecting appropriate laser irradiation parameters, which would be beneficial to the engineering applications of MGs as surface contact materials. • The potential of laser nitriding on improving the hardness of Zr-based MG was investigated by orthogonal experiments. • The achieved highest hardness was almost three times of the hardness of the as-cast MG surface. • The effects of laser parameters on the surface hardness were comparatively studied. • The characteristics of shear bands and serrated flows of the laser nitrided MG surfaces were changed.

Effect of different curing times and distances on the microhardness of nanofilled resin-based composite restoration polymerized with high-intensity LED light curing units

PurposeThis study examined the effect of different distances and curing times on the microhardness (VHN) of nanofilled resin-based composite (RBC) restorations polymerized with high-intensity LED LCUs. Materials and methodsSeventy-five RBC specimens (2 mm thickness and 5 mm diameter) were fabricated from Tetric-N-Ceram (Ivoclar Vivadent). Each of the 25 specimens was polymerized by means of one of three types of high-intensity LED LCUs: (B) Blue-Phase-G2 (polywave LED, Ivoclar Vivadent), (E) Elipar S10 TM (single-peak, 3 M ESPE), and (P) Planmica Lumion (single-peak, Mectron) at three different distances (0 mm, 2 mm, and 4 mm) at 20 sec, 40 s, and 60 sec. A microhardness tester (NOVA, Innovatest, The Netherlands) was used to measure the VHN from the top and bottom surfaces. Data for VHN were analyzed using mixed ANOVA, followed by post hoc analyses with p-values < 0.05. ResultsA significant difference was found in VHN between all three LED LCUs, where (B) specimens had the highest means, followed by (E) and (P). Bottom surface VHN values were reduced significantly (p < 0.05) compared to top surface values in all LCU types. With increasing distances up to 2 mm and 4 mm, VHN values with (E) and (P) were significantly reduced on the top and bottom surfaces (p < 0.05). When the curing times were increased for 40 and 60 sec, the VHN values were significantly improved (p < 0.05). Meanwhile, increasing the distance with (B) did not significantly reduce the VHN. Moreover, increasing the curing times did not significantly improve the VHN of the bottom surfaces. ConclusionHigh-intensity LCUs have variable effects on the surface (top/bottom) hardness of Tetric-N-Ceram nanofilled RBC restoration. With increasing distance, VHN was reduced; therefore, compensation with more curing time (2 mm/40 sec and 4 mm/60 sec) is highly recommended with Elipar S10 and Planmica Lumion LCUs to improve the material surface hardness.

Enhanced Polymerization and Surface Hardness of Colloidal Siloxane Films via Electron Beam Irradiation.

Electron beam (EB) curing is a foldable hard coating process and has attracted significant research attention in the field of flexible electronic devices. In this study, we report a method for enhancing material surface hardness with low-energy EB curing in a short time. The low-energy EB improved the coating hardness of films by inducing cross-linking polymerization of the silicon-containing monomer. The hardness of the cured coating layer was measured as 3 H using a pencil hardness tester, and the transparency of the coating was higher than 90%. Owing to a series of cross-linking reactions between Si–O–C and Si–OH groups under EB curing and the formation of Si–Si bonds, the cured layer exhibited remarkable durability in the 100000-flexible cycle test. Additionally, the natural oxidation of the C–O groups on the surface of the coating formed carboxyl groups that improved the hydrophilic properties of the coating layer. To the best of our knowledge, this is the first study to propose that the hardness of polyethylene terephthalate films can be improved using low-energy EBs to rapidly cure silicon-containing coatings. Our results provide a novel and commercially viable approach for improving the hardness of touch screens and foldable displays.

Evaluation of surface hardness of NiCr coating using Finite Elements Analysis

Introduction: To enhance resistance to surface damage of materials due to mechanical actions, there have been created many procedures that allow its modification for different needs. This leads to researches conducted to determine the changes achieved in the properties due to said procedures. One method commonly applied is, for example, physical means of vapor deposition of thin films on a surface. In recent years, many rational and empirical models have been proposed for the study of said properties. One of these models is computational analysis, which allows determining a great number of properties while avoiding applying destructive tests, achieving to reduce experimental time spent and costs of manufacture of test tubes as well as the test itself. In this research, the hardness of a surface coating of Nichrome (NiCr 80-20) was determined with an indentation test modeled in Ansys, based on the finite elements' method. Objective: To design a computational model that allows determining the surface hardness of material with coating Method: The realization of this project was made with the software for engineering analysis ANSYS, and the model was made based on the Vickers Indentation Test regulation given by the ASTM, which states that the test must be done with a pyramidal diamond indenter, applying forces greater than 1 kgf. Results: By running the respective numerical analysis for both the substrate and the coating, a surface hardness of 197.5073 VH was obtained for NiCr coating and surface hardness of 160.5809 VH for the S235 Steel (hardness of the interface). Conclusions: It was determined that the model proposed is correct seeing as the values obtained for the Vickers' Hardness is approximately the same as the experimental value with an error of 0.7501% for the coating layer and 0.2605% for the substrate. It was also concluded that it is possible to use this same procedure to obtain the surface hardness for different materials than those treated in this article by using this tool. In this research the hardness of a surface coating of Nichrome (NiCr 80-20) was determined with an indentation test modeled in Ansys, based on the finite elements’ method [1]. Objective: To design a computational model that allows to determine the surface hardness of a material with coating Method: The realization of this project was made with the software for engineering analysis ANSYS, and the model was made based on the Vickers Indentation Test regulation given by the ASTM [2], which states that the test must be done with a pyramidal diamond indenter, applying forces greater than 1 kgf. Results: By running the respective numerical analysis for both the substratum and the coating, a surface hardness of 197.5073 VH was obtained for the S235 Steel (hardness of the interface) and a surface hardness of 160.5809 VH for the NiCr coating. Conclusions: It was determined that the model proposed is correct seeing as the values obtained for the Vickers’ Hardness is approximately the same as the experimental value with an error or 0.7501% for the substratum and 0.2605% for the coating layer. It was also concluded that it is possible to use this same procedure to obtain the surface hardness for different materials than those treated in this article by using this tool.

The modification of surface of barrels by gas nitriding

Steels which are used for manufacturing of highly stressed parts of military equipments such as barrels of small arms weapons must be modified by heat treatment due to achieve required mechanical properties. Moreover, other important properties of functional parts, especially a friction coefficient and surface pa-rameters of bore of barrels, must be optimized due to obtain the best accuracy in target and to increase the life time of barrel [1, 2]. The technology chromium plating, very widespread in the past, has been gradually replacing by more ecological nethods. This article is devoted to find a technology as a replacement of tradi-tional chromium plating. Experiments are focused on using of optimized gas nitriding processes for surface treatment. As a result, a higher surface hardness with low influence on the dimensional accuracy is expected. Gas nitriding process was applied to steels 42CrMo4 and 32CrMoV12-10 used for barrel manufacturing. The most important parts of barrel were evaluated, especially surface parameters as a morphology than chemical composition and naturaly a microstructure of the material. The analysis of surface morphology were performed by scanning electron microscopy; chemical composition was evaluated by GDOES method and mechanical properties by using microhardness methods. The measurements of depth of diffusion layer were performed by destructive and non-destructive methods. The measurements showed the influences of chemical composition of alloying elements in core of material after chemical-heat treatment process on depth of diffusion and influence of technology on development of porosity. All fundamental mechanical prop-erties significant for requiring function of barrel were documented [1, 2]. Nevertheless, the main task was the description of the porosity development in compound layer after gas nitriding and the increasing of sur-face hardness and the depth of diffusion layer according to chemical composition. Nitriding process was ap-plied for increasing of surface hardness of material in depth and improving of mechanical properties. Me-chanical properties of tested material were significantly increased.

Performance evaluation of castor oil-ethanol blended coolant under minimum quantity lubrication turning of difficult-to-machine materials

Abstract A recent trend in the processing of difficult-to-machine materials is the replacement of traditional coolants with vegetable oil, which is environmentally friendly. In this study, a new type of blended coolant that is suitable for minimum quantity lubrication (MQL) was developed by leveraging the mutual solubility of castor oil and ethanol. The physicochemical properties of the blended coolant and its effects on cutting vibration, surface hardness, surface roughness and tool wear mechanism under different working conditions were studied. Turning experiments on AISI 304 steel under dry cutting, flood cutting, vegetable oil (castor oil) minimum quantity lubrication (VMQL), 95 % ethanol MQL (EMQL), and blended coolant MQL (BMQL) conditions were conducted using a coated carbide tool. Among all the cooling methods tested, the minimum vibration in the axial and radial axis directions occurred in the BMQL, with vibration intensity reductions of 2.46 % and 3.38 %, respectively. Furthermore, the tool wear and changes in the matrix material surface hardness were the smallest under the BMQL, and the surface roughness decreased by 4.50 % or more. The average wear, VB, of the flank face decreased by more than 7.72 %. The blended coolant proved to be more conducive to cooling for cutting processes under MQL.

Research on a different method to reach the saturate limit of titanium aluminide alloy surface mechanical and fatigue properties by laser shock process

Laser shock peening is one of the best method to enhance the mechanical and fatigue properties of titanium aluminide alloys. Most research depends on the pressure model produced by Professor Fabrro, based on Von-Mise stress yield standard, when the pressure is 2 Hugoniot elastic limit (HEL), the plastic deformation reaches the maximum limit and when the pressure is 2.5HEL The stress release from the edge of laser shock area, This research discussed the titanium aluminide alloys surface mechanical and fatigue properties after reducing the pressure of laser shock and inducing the repetitions of laser shock properly. When the pressure reached HEL the material began plastic deformation, in the experiment environment there are several factors affect the results, so the pressure should be more than 1HEL and less than 2HEL-2.5HEL. As the same repetitive times the effective of 2HEL-2.5HEL pressure is better than the less pressure but with the repetitive times rise the 2HEL-2.5HEL pressure specimens would be cracked and the less pressure specimens mechanical and fatigue properties still increase. The results show that with inducing the repetitions and reducing the pressure the material surface hardness improved nearly 25% and the fatigue life increase nearly 40% in high fatigue cycle, the microstructure is similar but the less pressure more repetitive times specimens contains dislocation cells. It indicates that with 2HEL-2.5HEL pressure (the maximum plastic deformation) the mechanical and fatigue properties reached to its peak after 3 times LSP and with 1.5 HEL pressure 8 times repetitive laser shock can reach to the saturate limit of the material itself, that means with less pressure and more repetitive laser shock is more accurately to get close to the saturate limit of the material.

Investigation of the influence of rail hardness on the wear of rail and wheel materials under dry conditions (ICRI wear mapping project)

Some railway managers and practitioners fear that introducing premium rail materials will have a detrimental effect on the wheels of trains that use the line. A review of relevant investigations across all scales in the laboratory, and in the field has been carried out. This showed that, as rail hardness increases, its wear, and overall system wear reduces. Wheel wear does increase with increasing rail hardness, but only for wheels running on rails that are softer than them. Similar trends were observed in all studies, so it seems that the fears were unfounded.While the wear trends appear well characterised some issues have been identified. One relates to the varying work hardening capability of wheel and rail materials. Often only bulk hardness is quoted, but work hardening can increase material surface hardness by up to 2.5 times and make materials that were initially softer, harder than the opposing material. Another related issue is test length. It is essential that enough cycles are applied such that the materials reach steady state wear, i.e., the point at which work hardening has reached its limit. In previous work it is not always clear that steady state wear has been reached. Some gaps have been identified in the current knowledge base, the largest of which is the failure to determine which mechanisms lead to the wear trends seen.Analysis of recent work on different clad layers on rail discs and premium rail materials allowed some of these gaps to be addressed. Results indicated that opposing wheel material hardened to the same level independent of rail hardness. Wheel wear is therefore stress driven under the conditions used, and dictated by the wheel material properties only. At higher slip levels relationships become less clear, but here temperature and therefore hot hardness is most influential and is as yet uncharacterised.

A laboratory study of Equotip surface hardness measurements on a range of sandstones: What influences the values and what do they mean?

AbstractThe Equotip rebound tester is a simple, non‐destructive technique to measure the surface hardness of materials. Having a low impact energy gives the Equotip advantages over the commonly used Schmidt Hammer on weathered rock and stone. In this study we have investigated the influence of different parameters (sample size, moisture content and surface roughness) on the surface hardness values obtained from freshly cut blocks of four types of sandstone. In a series of laboratory experiments both Single Impacts (SIM) and Repeat Impacts (RIM) methods have been used with C and D probes (which have different impact energies). Our results show that whilst sample size is of great importance we find that smaller samples can be reliably evaluated than previously reported. Moisture contents are also found to exert a more important influence on both SIM and RIM results than previously thought, with up to 26% lower hardness values recorded on saturated vs dry sandstone. Conversely, we find that surface roughness (over Sz values of 100 to 800 microns) does not have a significant impact on SIM measurements collected using the D probe. Both SIM and RIM data are found to be good proxies for compressive strength and open porosity, with SIM data collected with the C probe showing the best fits. Data collected using 3D microscopy helps visualize and quantify the small impact marks created by the Equotip and confirms that these are much reduced when using the C vs D probe. The results highlight the benefits of the Equotip to studies of the nature and deterioration of sandstone, the need for careful evaluation of any confounding factors which might influence the values obtained, and illustrate the different advantages of C and D probes. © 2019 John Wiley &amp; Sons, Ltd.

SURFACE HARDENING OF POWDERED IRON-CARBON ALLOYS

There are many ways to improve the quality of iron-carbon alloys used as structural materials, one of which is surface heat treatment with highly concentrated energy streams. The effect of electron-beam heating on the structure and properties of powder-metal ceramic materials was studied in this work. In order to solve this problem, the following tasks were solved: the study of the influence of the technological parameters of electron-beam processing on the structure and phase composition of the sintered materials on the basis of iron powder with graphite additions, determination of the influence of the thickness of the surface layer on the temperature gradient under the electron beam treatment of the material surface and formation structure, investigation of the influence of the chemical composition and the thickness of the surface layer on the hardness and microhardness of materials after electron beam processing. The advantages of electron-beam processing are shown in comparison with other methods of hardening the surface of parts. The influence of electron-beam processing regimes on the structure and phase composition of layered iron-based powder materials is studied. In the work the process of surface heat treatment of powdered laminated iron-carbon alloys is investigated. It was established that doping of a surface layer with carbide chromium allows to increase the surface strength of materials after treatment with an electron beam twice. Distribution of structural components of iron-carbon alloy under surface heat treatment depending on the thickness of the surface layer is investigated. Research results can be used to create economically alloyed structural iron-carbon alloys, which must have high surface hardness and high bulk strength. It is shown that in the middle of the samples the microhardness is practically the same for all materials and is about 3-4 GPa. On the surface, with a thickness of the upper layer of 0.5-1.0 mm, the average values of microhardness are about 5.0-5.5 GPa. With an increase in the thickness of the layer to 1.5-2.0 mm, the average microhardness reaches about 7.5-9.0 GPa. Surface hardness of materials also increases to 68 HRC with hardness in the middle of about 35-40 HRC. Research results can be used to create economically alloyed structural iron-carbon alloys, which must have high surface hardness and high bulk strength .

Wear behavior of various dental restorative materials

The aim of this study was to compare the wear behavior of various dental restorative materials and effects of wear on the surface mechanical properties. For this purpose, a multi-purpose friction/wear tester and a mechanical indenter with a diamond probe were used. The dental ceramics showed the lowest amount of wear depth (64 ± 3·2 μm) at 15 min cycle. There was an insignificant increase (p > 0·05) in the wear of ceramic in 15 min time interval, however the difference was significant (p < 0·05) while comparing at 30 min interval reaching to (99 ± 4·4 μm) at 150 min. Wear resulted in increase in the surface hardness of materials; ceramics (from 6·06 ± 1·11 GPa to 6·65 ± 1·12 GPa) and resin composites (from 1·44 ± 0·31 GPa to 1·66 ± 0·34 GPa) and significantly increase for alloys. For example, the hardness of CoCr was increased from 5·38 ± 0·72 GPa to 7·18 ± 0·75 GPa after wear. Dental ceramic remains the most wear resistant among tested materials. Among direct restorative materials, amalgam alloy has better wear resistance. Wear of dental alloys resulted in greater surface hardening compared to the direct restorative materials.