Papers by Keyword: Vickers Hardness

Abstract: Hardness measurements can simple, but very useful provide materials mechanical properties. This is atest that is extremely localized in volume and does not affect significantly the structural properties. Theaim of this article is to highlight on influence of the applied load forces to the hardness measurementresults. In engineering practice it is generally the most widely used method of measuring the Vickershardness. This method has a variability of the loading forces in a wide range from nano/micro up tohigh loads in hundreds N. There is a well-known plastic material response, therefore, were taken intoaccount several steels commonly used in technical practice S355 NL+N, 316LVM, 34CrMo-4. Wheninterpreting the results should always point out to the value of the load. In common engineering practiceleads to confusion, or to comparing the hardness of the material obtained at different loads. Thisproblem is quite often occurs at nowadays and needs to be solved. Focus should be not only in termsof results depending on the load, but also from a statistical perspective of scattering measurements atvarious loads. Generally, in the technical practice is discussed independence measurement results ofVickers hardness on applied load, due geometric similarity of indents. When is used different forcesthere is a changed of the hardness results. This phenomenon is known as a size effect. This effect isgenerally related to each mechanical testing of materials. However, engineering practice getting intoconflict with this effect.

Abstract: The objective of this study is to investigate the microstructure and effect of annealing to the hardness properties of oxide dispersion strengthened (ODS) Fe-15Cr-0.3Y₂O₃ alloy. This type of alloy was prepared by mechanical alloying (MA) method followed by compacting and sintering. The microstructure of milled Fe-15Cr-0.3Y₂O₃ alloy powders and pellet was examined by using field emission scanning electron microscope (FESEM). The milled alloy powders consist of nearly spherical shape of powder particles with average size of 10 µm. For the alloy pellet microstructure, the formations of Y₂O₃ nanoparticles with average size of 5 nm were observed indicating the dispersion and incorporation of this nano-scale dispersoids into the alloy matrix. Fe-15Cr-0.3Y₂O₃ alloy pellet was annealed at temperature of 600°C, 800°C and 1000°C, respectively for the Vickers hardness test. The Vickers hardness test was performed by using a micro-Vickers hardness tester with a load of 200 gf. The hardness value (HV) of this alloy pellet started to decrease at temperature of 600°C indicating the grain growth of this material at high temperature

Abstract: A composite surface layer was fabricated on a high-vanadium alloy steel (HVAS) plate by means of a surface gas nitriding at 550°C for 70h. The microstructural charaterization and phase analysis of resultant nitride layers were performed using optical, scanning electron microscopy, electron probe microanalyzer, X-ray diffraction methods and hardness measurements. The results of the investigation showed that a composite layer consisting of ε-Fe_2–3N and γ'-Fe₄N phases is feasible on the surface of HVAS. Vickers hardness test indicate that the hardness value of the nitrided sample is about 1100 HV at the top surface, and decreases gradually to about 700 HV in the matrix. The depth of hardened layer after surface gas nitriding was about 200 μm.

Abstract: The objective of this study is to investigate the effect of adding some alloying elements (including iron, aluminum, chromium, cobalt, and titanium) to 90 wt. % copper – 10 wt. % nickel alloy on the hardness property. Copper-nickel synthetic alloys were prepared in an induction furnace, in an argon/7% vol. hydrogen atmosphere in cylindrical boron nitride crucibles. They were then homogenized at 950°C for 10 hours in the same protective atmosphere. Vickers hardness measurements, microstructure examination, and Energy Dispersive Spectrometry (EDS) mapping analysis were performed for all synthetic alloys. Hardness measurements results show that the addition of all the alloying elements used in this investigation improve the hardness of the 90 wt. % copper – 10 wt. % nickel alloy. It was concluded that the aluminum was the most effective alloying element on the hardness value for 90 wt. % copper – 10 wt.% nickel alloy.

Abstract: A four-layer functionally gradient material (FGM) of Cu/Ti₃SiC₂ was fabricated by hot pressing (HP) in vacuum. Oxidation behavior of Cu/Ti₃SiC₂ FGM was also investigated. The results show that the oxidation dynamics of Cu/Ti₃SiC₂ FGM at 600~800 °C for 30 h in air followed parabolic rate law. The hardness was increased with increasing content of Ti₃SiC₂. Thermal shock resistance was well owing to the effect of thermal stresses mitigated with FGM.

Abstract: Zirconia toughened alumina (ZTA) has good mechanical properties and widely used in cutting insert application. Although the ZTA is well known of its good mechanical properties, its still can be improved in order to produce better properties. It can be done by adding additives as reinforcement such as magnesium oxide (MgO), cerium oxide (CeO), titania (TiO₂) and chromia (Cr₂O₃). The effect of TiO₂-Cr₂O₃ addition on the physical properties of ZTA were investigated in this study. The composition of TiO₂ was varied from 0 wt% to 3.5 wt% while Cr₂O₃ was fixed at 5 wt%. The starting powder materials were mixed by wet mixing for 30 minutes in acetone. Then the powder mixtures were hydraulically pressed at 260 MPa. The green pellets were sintered at 1600°C for 1 hour using an electrical furnace in presureless condition. The results were characterized by XRD, density, and also Vickers hardness. The ZTA-Cr₂O₃-TiO₂ ceramic composite achieved the highest density of 4.1 g/cm³ and Vickers hardness of 1919 HV prior to the addition of 2.0 wt% TiO₂. Therefore, it can be decisively concluded that the addition of Cr₂O₃-TiO₂ does affected the properties of ZTA.

Abstract: ZTA based ceramic composite system is widely accepted as cutting tools for many of these harder and wear resistant workpiece materials. This is due to their beneficial mechanical properties i.e. high temperature strength, high hardness and ability to maintain its cutting edge shape at higher temperatures. Although a lot of works have focused on the effect of various sintering additives on the ZTA ceramic system, the effect of Magnesia (MgO) and Titania (TiO₂) on ZTA has not yet been studied. In this work, the physical properties of Zirconia Toughened Alumina (ZTA) ceramic composite with MgO and TiO₂ as additives was investigated. The composition of TiO₂ varied from 0 wt% to 3.5 wt% whereby other materials such as Al₂O₃, Yttria Stabilized Zirconia (YSZ) and MgO were kept at constant weight percentage. Sintered samples were then tested and analyzed by XRD, Vickers hardness and high precision densimeter to investigate phase content, hardness value and densification respectively. Results showed that the solubility limit of TiO₂ in ZTA-MgO ceramic composites is at 2.0 wt%. Further addition of TiO₂ resulted in the formation of secondary phase known as Zirconium titanium oxide (Zr_0.35TiO_0.65O₂) which deteriorate the properties exhibited by ZTA-MgO-TiO₂ ceramic composites.

Abstract: In this investigation, the optimization of the multiple responses of Vickers hardness, Impact strength with notched and Un-notched conditions of the process parameters of rotational speed, tool tilt angle and feed rate with the straight cam profiled tool is considered. The three factors, five level rotatable central composite design are selected to optimize the responses of friction stir welded AA 8011 aluminium alloys. The highest relative efficiency is found using the data envelopment analysis to predict the optimum parameters. It reveals that at the rotational speed of 680 RPM, the tool tilt angle of 85 degrees and the feed rate of 24 mm/min the good weld quality can be achieved.

Abstract: In this investigation, an attempt using data envelopment analysis based Taguchi method, is involved in solving the multi-response optimization of the process parameters of rotational speed, transverse speed, tool tilt angle with different tool pin profiles on the stir zone evolution in AA8011 Aluminium alloys. Three different tool pin profiles (hexagonal, pentagonal pin profiles of High Carbon High Chromium steel and Hexagonal tool pin profile of H13 steel) have been used to make the joints at the different combination of process parameters using L₉ orthogonal array. The Vickers hardness and Impact strength are measured to optimize the process parameters using DEA based Taguchi method. It is found that the optimum conditions of rotational speed 660 RPM, transverse speed of 30 mm per minute and tilt angle of 2 degrees with the hexagonal tool pin profile of High Carbon High Chromium steel yielded a good quality weld.

Abstract: The aim of the study was to compare the surface microhardness of composite resins polymerized in different mode of light unit. Three commercial composite resins: Charisma (Heraeus Kulzer Co.), Filtek Z 250 (3M ESPE Co.) and G-aenial Anterior (GC Company Co.), were used in this study. Fifteen samples of each material were obtained by placing the composite resin in plastic rings having 2 mm high and 6 mm inner diameter. All composite samples were cured using blue light-emitted diode G 0010 (SKI, China). Five samples were cured using ramp mode of the light unit, five samples were cured using single light: high intensity (constant) mode and five samples were cured using pulse mode. The samples were finished and polished and then stored in distilled water, at room temperature for 48 hours. The samples were subjected to microhardness evaluation using microhardness tester (Micro-Vickers Hardness System CV-400DM^TM, CV Instruments Namicon). A 50 g load was applied through a Vickers indenter. For each sample three indentations were made in different areas of the sample and the value of Vickers hardness was calculated as a mean result of the three recordings. Statistical Mann-Whitney U test and Kruskal-Wallis test were used to compare the values of surface hardness. Polymerization of all three composite resins using pulse mode leaded to significantly lowest mean hardness values and single light high intensity mode to the highest values. Filtek Z250 composite resin showed the highest microhardness mean values in all three polymerization mode and Charisma the lowest values. Surface microhardness of composite resins is influenced by different modes of light unit. Single light high intensity mode of polymerization leaded to the highest values of microhardness, followed in descending order by ramp and pulse mode. The best results regarding the surface microhardness was recorded for Filtek Z250composite resin, followed in descending order by G-aenial Anterior and Charisma.