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Željko Alar - One of the best experts on this subject based on the ideXlab platform.
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DEVELOPEMENT OF REFERENCE Vickers Hardness BLOCKS BY THE POWDER METALLURGY PROCESS
2020Co-Authors: Tamara Aleksandrov Fabijanić, Željko Alar, Mladen FranzAbstract:Development of reference Hardness blocks for the high Hardness range by the powder metallurgy process will be presented in this paper. Development would start with the selection of powder, matrix and grain growth inhibitors as well as parameters related to the technological process of obtaining which are related to milling, compacting and sintering. Mentioned would be realized in order to ensure the measurement traceability of the Vickers Hardness for the Republic of Croatia for the high Hardness range and to contribute to the spectrum of materials and processes of manufacturing reference blocks for the Vickers Hardness on the global level.
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Influential factors on Hardness uniformity of Vickers Hardness blocks for high Hardness range
Measurement, 2015Co-Authors: Tamara Aleksandrov Fabijanić, Mladen Franz, Željko AlarAbstract:Abstract Reference Vickers Hardness blocks for high Hardness range were developed from WC 9–Co and WC 6–Co mixtures by two different processes of powder metallurgy, conventional liquid phase sintering in hydrogen and vacuum-sintering with subsequent hot isostatic pressing in one cycle, sinter-HIP, in order to analyse the appropriateness of the manufacturing process and the influence of starting characteristics of the mixtures on Hardness uniformity and overall metrological characteristics. WC powder of 150 nm grain size and 2.5 m 2 /g specific surface area with the addition of grain grow inhibitors was used as starting material. The emphasis of the research was placed on Hardness uniformity of the test surface as it is the most important property placed on Hardness blocks. For that purpose the surface of the blocks was divided into radial and circumferential divisions, forming different sections on the block surface. Hardness measurements were performed in each section with HV1 measuring method. A total of 40 indentations were performed, based on which the conclusions about Hardness uniformity of Vickers Hardness blocks were drawn. Hardness measurements and uniformity were tested by analysis of variance, ANOVA, for single factor in order to determine if significant Hardness variations across the block surface were present. From the research conducted it was concluded that Hardness distribution across test surfaces of Vickers Hardness blocks had a trend according to a process of manufacturing and the amount of binder in the WC–Co mixture. The best material and metrological characteristics were obtained on the block manufactured by sinter-HIP with 9 wt.% Co.
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potentials of nanostructured wc co hardmetal as reference material for Vickers Hardness
International Journal of Refractory Metals & Hard Materials, 2015Co-Authors: Tamara Aleksandrov Fabijanic, Željko Alar, Johannes PotschkeAbstract:Abstract The potential of nanostructured WC–Co hardmetal as reference material for Vickers Hardness was researched in this paper. Preliminary reference Vickers Hardness blocks were developed from a WC 9–Co mixture. The WC powder used was nanoscaled and had a grain size of 150 nm and a specific surface area of 2.5 m2/g. Hardness blocks were consolidated using the Sinter-HIP process. Properties of the sintered material were obtained by using standard measurement techniques like magnetic properties or the SEM analysis of microstructure. Special emphasis was placed on Hardness uniformity of the test surface as it is the most important property placed on reference Hardness blocks. Hardness uniformity was tested by analysis of variance, ANOVA, for single factor in order to determine if significant Hardness variations across the block surface were present. From the conducted research it was concluded that Hardness distribution over the whole test surface was uniform. The achieved superior properties of the material, such as full densification, nanosized homogeneous microstructure, high Hardness and good fracture toughness, influenced the metrological characteristics of the reference Vickers Hardness block. Hardness non-uniformity is nearly two times lower when compared to commercially available standard reference material made of ultra-fine WC–Co. Material response does not involve chipping, cracking or any other imperfections. The research opens a new area of application for nanostructured WC–Co hardmetals as reference material for Vickers Hardness for high Hardness range.
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Hardness UNIFORMITY OF Vickers Hardness BLOCKS FOR THE HIGH Hardness RANGE
2014Co-Authors: Tamara Aleksandrov Fabijanić, Mladen Franz, Željko AlarAbstract:Hardness uniformity is the most important property of Hardness block and depends on the quality of the starting material, process of obtaining, heat and surface treatment. All parameters must be selected very carefully to achieve homogenous microstructure with no defects. Vickers Hardness blocks for the high Hardness range were produced by two different processes of powder metallurgy ; conventional liquid phase sintering in hydrogen and sinter HIP. Nano powder of WC with a grain size of 150 nm with specific surface area of 2, 5 m2/g and addition of grain grow inhibitors was used as staring powder. Hardness uniformity of the produced blocks was investigated in this paper. Surface of the blocks was divided into radial and circumferential divisions forming different sections on the block surface. Hardness measurements were performed in each section with one level of the test force. Applied force was 9.807 N what corresponds to measuring method HV1. For reliable Hardness measurement five indentations were measured in each section. Overall 40 indentations were performed based on which conclusions about the Hardness uniformity of the Vickers Hardness blocks were brought. Hardness uniformity was tested by analysis of variance, ANOVA, for single factor in to order to determine if significant Hardness variations across the block surface are present. From carried research was concluded that Hardness distribution on test surfaces of Vickers Hardness blocks has a trend according to a process of obtaining.
Dominguez A Rodriguez - One of the best experts on this subject based on the ideXlab platform.
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improvement of Vickers Hardness measurement on swnt al2o3 composites consolidated by spark plasma sintering
Journal of The European Ceramic Society, 2014Co-Authors: Morales A Rodriguez, Gallardo A Lopez, Fernandez A Serrano, Rosalia Poyato, A Munoz, Dominguez A RodriguezAbstract:Abstract Dense alumina composites with different carbon nanotube content were prepared by colloidal processing and consolidated by Spark Plasma Sintering (SPS). Single-wall carbon nanotubes (SWNTs) were distributed at grain boundaries and also into agglomerates homogeneously dispersed. Carrying out Vickers Hardness tests on the cross-section surfaces instead of top (or bottom) surfaces has shown a noticeable increase in the reliability of the Hardness measurements. This improvement has been mainly attributed to the different morphology of carbon nanotube agglomerates, which however does not seem to affect the Vickers Hardness value. Composites with lower SWNT content maintain the Vickers Hardness of monolithic alumina, whereas it significantly decreases for the rest of compositions. The decreasing trend with increasing SWNT content has been explained by the presence of higher SWNT quantities at grain boundaries. Based on the results obtained, a method for optimizing Vickers Hardness tests performance on SWNT/Al 2 O 3 composites sintered by SPS is proposed.
Johannes Potschke - One of the best experts on this subject based on the ideXlab platform.
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potentials of nanostructured wc co hardmetal as reference material for Vickers Hardness
International Journal of Refractory Metals & Hard Materials, 2015Co-Authors: Tamara Aleksandrov Fabijanic, Željko Alar, Johannes PotschkeAbstract:Abstract The potential of nanostructured WC–Co hardmetal as reference material for Vickers Hardness was researched in this paper. Preliminary reference Vickers Hardness blocks were developed from a WC 9–Co mixture. The WC powder used was nanoscaled and had a grain size of 150 nm and a specific surface area of 2.5 m2/g. Hardness blocks were consolidated using the Sinter-HIP process. Properties of the sintered material were obtained by using standard measurement techniques like magnetic properties or the SEM analysis of microstructure. Special emphasis was placed on Hardness uniformity of the test surface as it is the most important property placed on reference Hardness blocks. Hardness uniformity was tested by analysis of variance, ANOVA, for single factor in order to determine if significant Hardness variations across the block surface were present. From the conducted research it was concluded that Hardness distribution over the whole test surface was uniform. The achieved superior properties of the material, such as full densification, nanosized homogeneous microstructure, high Hardness and good fracture toughness, influenced the metrological characteristics of the reference Vickers Hardness block. Hardness non-uniformity is nearly two times lower when compared to commercially available standard reference material made of ultra-fine WC–Co. Material response does not involve chipping, cracking or any other imperfections. The research opens a new area of application for nanostructured WC–Co hardmetals as reference material for Vickers Hardness for high Hardness range.
Morales A Rodriguez - One of the best experts on this subject based on the ideXlab platform.
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improvement of Vickers Hardness measurement on swnt al2o3 composites consolidated by spark plasma sintering
Journal of The European Ceramic Society, 2014Co-Authors: Morales A Rodriguez, Gallardo A Lopez, Fernandez A Serrano, Rosalia Poyato, A Munoz, Dominguez A RodriguezAbstract:Abstract Dense alumina composites with different carbon nanotube content were prepared by colloidal processing and consolidated by Spark Plasma Sintering (SPS). Single-wall carbon nanotubes (SWNTs) were distributed at grain boundaries and also into agglomerates homogeneously dispersed. Carrying out Vickers Hardness tests on the cross-section surfaces instead of top (or bottom) surfaces has shown a noticeable increase in the reliability of the Hardness measurements. This improvement has been mainly attributed to the different morphology of carbon nanotube agglomerates, which however does not seem to affect the Vickers Hardness value. Composites with lower SWNT content maintain the Vickers Hardness of monolithic alumina, whereas it significantly decreases for the rest of compositions. The decreasing trend with increasing SWNT content has been explained by the presence of higher SWNT quantities at grain boundaries. Based on the results obtained, a method for optimizing Vickers Hardness tests performance on SWNT/Al 2 O 3 composites sintered by SPS is proposed.
Murat Tiryakioglu - One of the best experts on this subject based on the ideXlab platform.
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On the representative strain in Vickers Hardness testing of 7010 aluminum alloy
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2015Co-Authors: Murat Tiryakioglu, Jeremy S. RobinsonAbstract:Abstract A review of the concept of representative strain in Vickers Hardness testing is provided and different values reported in the literature are summarized. A new criterion for the proper selection of the representative strain is introduced. By using this criterion, the stress–strain curves of 63 specimens excised from a 7010 aluminum alloy rectilinear forging, cooled differently from the solution treatment temperature have been analyzed. Regression analyses have been conducted between the Vickers Hardness numbers and the true stress values corresponding to twenty eight true plastic strain levels. These results indicate that the representative strain associated with diamond indentation is between 0.0185 and 0.0301 with the most likely number of 0.0240. The value of the constraint factor changes with the assumed representative strain and is essentially equal to 3.00 when 0.0240 is chosen as the representative strain.
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on the relationship between Vickers Hardness and yield stress in al zn mg cu alloys
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2015Co-Authors: Murat TiryakiogluAbstract:Abstract The relationship between Vickers Hardness and yield stress was investigated by using data from nineteen datasets from sixteen independent studies, covering six commercial and four experimental alloys. In these datasets, six different product forms that ranged from single crystals to extrusions were used. All datasets showed a linear yield stress–Vickers Hardness behavior with the same slope, which was recently reported by the author and his colleagues for alloy 7010 [M. Tiryakioglu et al., Mater. Sci. Eng. A, 631 (2015) 196–200]. The y-intercept, which represents the increase in stress under the indenter during Vickers Hardness testing, was different for each dataset. The coefficient of determination, R2, values for the fits of combined data were 0.982 and 0.971 for commercial and experimental alloys, respectively.
