Vickers Microhardness Of Samples Research Articles

Investigation of a Ti–30Zr binary alloy fabricated through spark plasma sintering

A series of Ti–30Zr alloys have been synthesized by the spark plasma sintering (SPS) process using a mixture of elemental powders processed by mechanical alloying. A sintering temperature of 900°C was used during SPS with heating rates of 140, 200 and 350°Cmin−1 with a constant load of 50MPa. The effect of the heating rate on the densification, microstructure, phase transformation and microhardness is discussed. The sintering kinetics and the in situ densification were performed by the analysis of the punch displacement during SPS processing. Structural details of consolidated materials were evaluated by the combination of X-ray diffraction, field emission scanning electron microscopy and differential scanning calorimetry tests. Vickers microhardness of samples was also evaluated. The results show that samples reached high densification values up to 99.7% of the relative density by using lower sintering temperatures in comparison to conventional sintering techniques. Phase transformation analysis demonstrates the formation of αʹʹ and ω metastable phases without using any post-treatment. Microhardness values between 950 and 1040HV were obtained as an effect of the SPS parameters and metastable phase precipitations.

Densification behavior of 316L-NiB stainless steel powder and surface morphology during selective laser melting process using pulsed Nd:YAG laser

Purpose This paper aims to report the production of 316L-1 Wt.% NiB cubes by using the selective laser melting (SLM) process. The laser used was pulsed, millisecond Nd:YAG system with maximum average power 100 W. Design/methodology/approach Densification under different processing conditions (pulse energy, average laser power, laser scan speed, powder layer thickness, pulse frequency) was investigated. Morphology, macro and microstructure of laser melted samples were characterized by digital camera images and by scanning electron microscope. Density of the cubes was determined by Archimedes method in water. Vickers microhardness of samples was determined under the load of 25 g. Corrosion behavior of 316L and 316L-NiB samples was conducted in 5 per cent HCl solution at the testing temperature of 20°C during 240 h. Findings Using laser power of ∼60-70 W, lower beam overlap and powder layer thickness of 200 µm, 3D cubical samples were obtained with significant balling in individual layers and an overall porosity being around 30 per cent. By increasing laser power to ∼80 W, with higher beam overlap and lower powder layer thickness of 100 µm, SLM parts with no balling and the presence of small pores of up to 4 per cent (20 Hz) and 9 per cent (40 Hz) were obtained. With further increase of laser power to 90 W, overall porosity rose to around 12 per cent. The addition of 1 Wt.% NiB to stainless steel negligibly lowered its corrosion resistance in 5 per cent HCl solution. Originality/value A part from 316L stainless steel with balling-free structure and good density was successfully obtained through pulsed-SLM process with the aid of 1 Wt.% of NiB addition. Aside from significant influence on the improved structure of cubes, NiB had a favorable effect on microhardness values while practically not affecting the corrosion resistivity of the base material in an aggressive surrounding.

The effect of protocol for disinfection of extracted teeth recommended by center for disease control (CDC) on microhardness of enamel and dentin

Background According to the guideline of the United States center for disease control (CDC), the extracted teeth should be sterilized by autoclaving or storage in 10% formalin before using for educational or research purposes. The objective of this study was to evaluate the effect of this protocol on microhardness of dentin and enamel. Material and Methods Thirty extracted single-root teeth were used in this study. The crowns were resected, and the roots were longitudinally sectioned into two halves. The Vickers microhardness (VHN) of specimens was measured on polished canal dentin and buccal enamel surfaces. The crowns were randomly divided into three groups (n=10). Group 1 and 2 were sterilized using autoclave and formalin, respectively while group 3 (control) was stored in synthetic tissue fluid. The root halves were also randomly divided into 3 groups (n=20) which were treated as mentioned above for crown samples. Following sterilization, VHN of samples was measured again. ANOVA and paired samples t-tests were used to analyze the data. Results Autoclaving caused a significant reduction in microhardness of dentin (P <0.001, 12.04% decreases in VHN). However, there were no significant differences for before and after sterilization within other groups. Conclusions Based on the results of this study, the CDC protocol is recommended in studies related to enamel microhardness. However, Autoclaving is not an appropriate sterilization method in studies related to dentin microhardness. In these studies, two-week immersion in 10% formalin is recommended. Key words:Autoclave, CDC, extracted teeth, formalin, microhardness, sterilization.

Thermal and mechanical properties of CNT-Se90−xTe10Agx (x=0, 5 and 10) glassy composites

Abstract Carbon nanotubes (CNT)-Se 90− x Te 10 Ag x ( x = 0, 5 and 10) glassy composites have been synthesized by melt quenched technique. The XRD pattern confirms the amorphous nature of CNT-glassy composites under investigation. The crystallization kinetics of CNT- Se 90− x Te 10 Ag x ( x = 0, 5 and 10) glassy composites have been studied by using differential scanning calorimeter (DSC) with different heating (5, 10, 15 and 20 K/min) rates under non-isothermal conditions. The glass transition temperature T g , crystallization temperature T c and overall activation energy for crystallization E c have been determined. Also, order parameters n , m have been determined to study dimensionality of growth and nucleation during crystallization. The Vickers micro-hardness of samples under investigation is measured to see the effect of CNT incorporation in glassy systems. The results indicate that glass transition temperature and micro-hardness are enhanced for all investigated glassy systems after incorporation of CNT. The enhancement of these parameters with CNT content could be explained on the basis of increase in cross-link density due to modification of chemical bond formation in glassy system with CNT content, which is also confirmed from Raman spectra of investigated glassy composites.

HARDNESS OF SINTERED PM MATERIALS WITH MICROGRADIENTS IN COMPOSITION

Particles of iron powder were electrolytically coated with a copper and subsequently with a hydrocarbon. Coated powder was compressed into cylindrical samples at 600 MPa and sintered at 1120°C. Using Microhardness Tester LECO LM-700AT, Vickers microhardness of samples has been investigated by indenting the unetched metallographic polished section. Test loadings were 10g, 25g, 50g, 100g, 200g, 300g, 500g and 1000g. Loading time was set on 10 seconds. It was found that there are different values of microhardness within a grain. Microhardness measurements taken at different points in the specimen enabled us to map the occurrence of various hardness values, which reflects a variety of the local microstructure of the examined material. At large loading, effective properties of a large volume of material are measured and the range of measured hardness narrows. ISE was observed.

Sintering behavior and mechanical properties of the mica–diopside machinable glass-ceramics

The machinability of fluor-mica glass-ceramics is an attractive characteristic of these materials. However, the poor mechanical strength and hardness has limited their applications. In this research, to overcome this problem, a glass frit in the system CaO–SiO 2–P 2O 5–MgO was gradually added to a mica-based frit. After sintering of compacted mixtures, simultaneous crystallization of diopside and mica occurred that led to improved mechanical properties. The sinterability of various samples was investigated and their microstructure and crystallinity were evaluated by electron microscopy (SEM) and X-ray diffraction (XRD). The presence of plate-like crystals of mica, spherical particles of apatite and fibrous inclusions of diopside was the microstructural specification of the optimum composition. The four-point bending strength and the Vickers microhardness of samples were also determined.

Effect of hydrolysis time and type of catalyst on the stability of tetragonal zirconia-silica composites synthesized from alkoxides

ZrO2-transformation-toughened glass-ceramics have been prepared by the sol-gel process from either colloidal gels (CG) or polymeric gels from alkoxides (PG), using, in the latest method, a different catalyst (acid, basic and without catalyst), and different compositions in the ZrO2·SiO2 system (free ZrO2 included). The different methods of synthesis of tetragonal zirconia in SiO2 matrix were compared in order to obtain thermal stability, and a high amount of stabilized tetragonal zirconia. The effect of catalyst, hydrolysis time, chemical composition, critical particle size in ZrO2(t)→ZrO2(m) transformation, the doping with vanadium on the ZrO2(t) stability in SiO2 matrix and Vickers microhardness of samples have also been studied.