bluuebunny/crossref_metadata_2025 huggingface dataset:
Ultrasonic Modulating Compound Discharge – Electrochemical Micro-Fine Machining Technology and its Applications
Authors: Zhu Yong Wei , Shao Jian , Chen Hong Zheng
Published: April 2014

A new micro-fine manufacturing method is proposed, that is the ultrasonic modulating compound synchronous pulse electro-discharged and electrochemical machining. By the micro-fine machining way, the μm-level precision may be acquired. The low voltage, the low electric conductivitys working fluid mixed with the nm powders is used, as the ultrasonic vibration effect and the nm powders' catalyst effect between the electrodes, the micro-spark electro-discharged and the micro-electrolysis machining can be realized, the micro electro-discharged sparks can remove the electrolytic passivation film on the workpiece surface, ultrasonic vibrating blast wave can remove the machining outcomes and renew the working fluid, the better micro-fine machining precision can be acquired. Micro-fine compound machining system is build, the processing parameters can be adjusted online within a certain range, the synchronous pulses can be developed by the cutting circuit, the synchronization of frequency and phase can be ensured between the ultrasonic vibration and the electronic power, the precision and the process stability can be improved effectively. The mechanism tests are carried about the ultrasonic modulating compound discharge-electrochemical machining, a few of micro-structures are machined in μm-level machining precision, the fine machining mean's feasibility and technical superiority are verified too.
A Solid-Core Photonic Crystal Fiber Nanosensor
Authors: Luo Ji , Ma Wen Ying , Yao Jun , Wang Wei Min , Lin Qiao
Published: April 2014

A novel evanescent field optical fiber sensor based on a solid-core photonic crystal fiber with large holes has been introduced and successfully fabricated. Experiments show that the ethanol solution of unit concentration causes 0.461dB attenuation of absorbance. The finite element numerical simulation of the grapefruit photonic crystal fiber has been performed. The energy overlap factor is 0.0039 when holes are filled with air, and that is 0.012 when holes are filled with water for the different effective refractive index of the holes. Besides, the relationship between the maximum power transmission and the refractive index is also studied and analyzed. This research provides helpful instructions to the study of evanescent field sensing based on the solid-core photonic crystal fiber with large holes especially for biochemical detection.
Miniature Stress Test of Miniature Components Based on Piezoresistive Stress Sensors Test Circuit
Authors: Wang Xiao Dong , Qin Yong Jian , Luo Yi
Published: April 2014

In this work, piezoresistive stress sensors test circuit fabricated into the sensitive structure as part of the normal processing procedure is used to measure the stresses difference distribution before and after the assembly. Sensor resistances were recorded before and after the adhesive bonding. Using the theoretical equations, the stresses on the die surface have been calculated from the data of sensor resistances. This technology not only provides a performance diagnostic tool for the sensitive structures and the miniature components, but also presents a design tool for low-stress micro-assemblies of miniature components.
Study on Measurement Method of Dynamic Linearity for High G Micro Accelerometer
Authors: Shi Yun Bo , Dong Sheng Fei , Zhou Zhi Jun
Published: April 2014

Linearity, dynamic linearity particularly, is an important parameter in measuring the performance of an accelerometer. The Hopkinson bar has been widely used in calibration of high g accelerometer and other high overloading conditions. Based on one-dimension stress wave theory and superposition theory of elastic waves, designed a Dual Warhead Hopkinson bar to demarcate the dynamic linear parameters of high g micro accelerometer accurately. A finite element model for Hopkinson bar calibration system was created, ANSYS/LS-DYNA was employed to simulate the operation process of Hopkinson bar, and the effects of the projectile's materials, adjustment pads materials and thickness on the acceleration waveform were found.
A MEMS-Based Electrostatic Field Sensor Using Out-of-Plane Thermal Actuation
Authors: Ye Chao , Chen Xian Xiang
Published: April 2014

In this paper, we report a MEMSbased electrostatic field sensor (EFS) using out-of-plane thermal actuation. The EFS mainly consists of shuttles, sensing electrodes, and clamp-clamp beams. The clamp-clamp beam with a hump is treated as thermal actuator to drive the shuttle, which is to modulate the external electrostatic field. The EFS was fabricated by a standard surface micromachining process and the area of the EFS is less than 2.5mm×2.5mm. The EFS has been tested and achieved a resolution of 60V/m.
Design and Deposition of Infrared Antireflection Protection Film on Magnesium Fluoride Substrate for 3~5 μm
Authors: Li Lin , Wang Da Xing , Fu Xiu Hua , Liu Dong Mei , Kou Yang
Published: April 2014

The infrared antireflection protection film is designed and deposited on magnesium fluoride substrate for 3~5 μm. The multilayer antireflection film is designed and prepared by ion beam assisted electron-beam deposition. After repeated experiments, the absorption peak of SiO2 is found at 3000nm,using MgF2 and SiO2 as the low-index materials to reduce the absorption. The coating structure is Sub|1.46H1.37L2.19H1.45L2.49M|Air. DLC (diamond-like carbon) protection coating is deposited by radio frequency plasma enhanced chemical vapor deposition (RF-PECVD). Through contrast tests, the best deposition process is obtained (the butane flow rate is 5sccm/s, deposition temperature is 80°C) by setting deposition time as invariant, the reaction gas flow rate and deposition temperature as variables. Meanwhile the problem of associativity between antireflection film and DLC protection coating is solved by adding a Si transition layer. The result shows that the average transmittance of this film in 3~5μm is 95.5%, and this film can withstands harsh environment tests. Key words: Magnesium fluoride substrate; Antireflection protection film; 3~5 μm infrared band Document Code: A Article ID: DIO
A New Readout System for LC Resonant Sensors
Authors: Ge Bing Er , Liang Ting , Hong Ying Ping , Li Chen , Wang Wei , Xiong Ji Jun
Published: April 2014

A new readout system based on LC resonant sensor is presented. The readout system consists of a reader coil inductively coupled to the LC resonant sensor, a measurement unit, and a PC post processing unit. The measurement unit generates an output voltage representing the sensor resonance, converts the output voltage to numerical form, and saves the converted digital data. The PC post processing unit processes the digital data and calculates the sensor's resonance frequency. The readout system enables wireless interrogation and its accuracy is exemplified by an experimental system. The experimental system can detect the resonant frequency of sensor automatically and effectively. The experimental results are presented for different sensor resonance frequencies with various sensor capacitance values and show good agreement with the theoretical results. The entire design is simple, easy to use, and widely applicable for applications where the coupling distance between sensor and reader coil is variable.
A High-Resolution Lowpass Sigma-Delta Modulator Applied in Micro-Gyroscope
Authors: Zhou Jia Jun , Wang Di , Zhao Ying Kai , Xu Hong Lin , Liu Xiao Wei
Published: April 2014

In this paper, in order to enhance resolution and guarantee the stability of the micro-gyroscope, a high-resolution lowpass sigma-delta modulator is proposed. It employs single-loop fourth-order and full differential structure. The simulated result on the Simulink platform shows that the SNDR is 105.4dB and the effective number of bits (ENOB) is 17.22bits. The entire circuits are implemented with 0.5μm CMOS process. The simulated result on Cadence shows that the SNDR is 99.7dB. The modulator operates at a sampling frequency of 25.6MHz and the signal bandwidth is 100kHz with 128 oversampling ratio (OSR). The dynamic range (DR) is 120 dB approximately and the SNDR changes linearly with the input level.
A Readout System Design for LTCC-Based Piezoresistive Accelerometer
Authors: Zhou Bao Xing , Zhang Yue Xia , Fang Ru Niu
Published: April 2014

This paper reports a readout system for a piezoresistive accelerometer which is fabricated by LTCC thick-film process technology. The authors first introduce a LTCC compatible design of this new kind of accelerometer, which is based on piezoresistive phenomenon. As the performance of the accelerometer circuitry is affected by temperature, a readout system is introduced for compensating the temperature drift and the non-linearity of this piezoresistive accelerometer by using the MAX1452 processor. The authors give the principles of the temperature compensation and the executive processes. The readout system also includes a ZigBee wireless transmission system and a real-time curve display window. Some tests on the system are carried out and the results manifest that the readout system designed in this paper is workable.
Effect of Annealing on the Microstructure Evolution and Mechanical Properties of Dual Phase Steel
Authors: Šebek Martin , Horňak Peter , Zimovčák Peter
Published: April 2014

The aim of present article was to consider the influence of annealing parameters on evolution of microstructure and mechanical properties of dual phase steel. Dual phase steel was annealed according to the three chosen cycles of annealing: into intercritical region (780°C), into austenite region (920°C) and into austenite region (920°C) by subsequently cooling into intercritical region (780°C) with the hold at the temperature of 495°C. Tensile tests of the heat-treated specimens were carried out. The obtained microstructure consists from three phases: ferritic matrix, austenite and martensite. Nanoindentation experiments were performed with the peak load of 19.62 mN for ferrite grains and 0.981 mN for austenite and martensite grains, using a Berkovich tip as an indenter. The nanohardness for ferrite and martensite was 2.5 ±1 GPa and 7.1 ±1 GPa and for austenite the nanohardness varied from 4.1 to 4.5 GPa.
Differential Scanning Calorimetry and Metallographic Analysis of Fe-Si Electrical Steel
Authors: Sopko Martin , Kováč František , Petryshynets Ivan , Molnárová Mária , Gavendová Petra
Published: April 2014

The microstructure development in cold rolled electrical steel under dynamic heat treatments was subjected to investigation. Significantly distinguish types of microstructures were obtained in the investigated steels confirming the different character of grain boundary motion. Application of annealing temperature within two phase region (austenite+ferrite) leads to abnormal grain growth in silicon steels. Moreover, in the optimum temperature range, there was a particular temperature leading to the most optimal microstructure and texture[1]. The effect of Si content on the phase transition temperature of the electrical steel (0.6, 1, 2.5, 2.9 % Si) was studied by using differential scanning calorimetry (DSC) analysis. The result indicated that DSC analysis could be used to detect the shift temperature of phase transformation in the electrical steel with different Si addition. DSC have been used in thermochemical studies and as complementary to the study of phase transformation. It can be used as a compliment to optical and electron microscopy.
Minor Phase Evolution in Homogeneous T24 Welds
Authors: Vodárek Vlastimil , Rožnovská Gabriela , Holešinský Jan , Maslova Anastasia , Kuboň Zdeněk
Published: April 2014

This paper deals with the characterization of hardness, microstructure and precipitation processes in homogeneous T24 welds in the as-welded state and after laboratory PWHT at 745°C for 1 and 6 hours, respectively. Tempering of a T24 steel during quality heat treatment is accompanied by intensive precipitation of MX, M7C3 and M23C6 particles in the bainitic matrix. It was found that SAW welding resulted in a pronounced dissolution of minor phases in the base materials close to the joined faces. In the as-welded state microstructure of the CGHAZ was bainitic and the HV10 level in this part of the HAZ reached nearly 400 units. The dominant strengthening mechanism in the CGHAZ was attributed to transformation strengthening due to decomposition of austenite to bainite. Also the HV10 level in the bainitic filler metal (ca 320 HV10) was very close to the maximum acceptable hardness. PWHT at 740°C for 1 hour resulted in a significant decrease of hardness in the weld metal and especially in the CGHAZ. TEM studies revealed that recovery of bainite in the CGHAZ and the weld metal was accompanied by intensive precipitation of MX, M7C3 and M23C6 minor phases. The hardness level in the CGHAZ dropped to approximately 255 HV10. Prolonging of tempering at 740°C to 6 hours resulted in a modest softening in all parts of the weldments due to more pronounced both precipitation processes and recovery of bainite.
Mechanical and Phase Analysis of Bonding Area Explosively Welded Ti-Cr/Ni Steel in as-Received State and after Heat Treatment Using Synchrotron (BW-5)
Authors: Ostroushko Dmytro , Mazancová Eva , Saksl Karel , Halgaš Radoslav
Published: April 2014

Surface coatings protection is one of the most important processes ensuring efficient and economic use of basic materials, mostly of lower-quality. At interface of clad and basic material intermetallic phases are formed, representing quite different matrix with dissimilar properties unlike the welded materials. One type of surface coating is explosive bonding which belongs to group of pressure welding. The work is focused on some mechanical properties, micro-and nanohardness controlled by AFM and interface shape line, in homogeneities in vicinity of the wave joint both in basic material and in vicinity of the Ti and Cr/Ni stainless steel matrix weld line. Investigated weld was both in as-received state and after heat treatment carried out at 600°C/90 minutes/air. Phases has been identified X-ray diffraction performed BW-5 beamline applying synchrotron radiation, and Tiα, Fe-fcc and Fe-bcc were detected at interface area, whereas intermetallic phases were not revealed.
Hydrogen Response of 304 SS and Ti Weld Realised by Explosion
Authors: Mazancová Eva , Ostroushko Dmytro
Published: April 2014

Welds of thick plates (304 SS) cladded with Ti of commercial purity both in as received state and subsequently heat treated (HT, 600°C/1.5 h/air), charged by hydrogen, were investigated after fatigue tests (tension-pressure) with amplitude of 20 Hz. Simultaneously, samples of above mentioned welds were also exposed in H2S in accord with NACE Standard TM0284-2011 to find hydrogen induced cracking (HIC) response. Charged welds after the HT showed by 15 MPa higher threshold level than the welds without the HT. The HIC tests generally demonstrated favourable results both after as weld state and after subsequent HT. Short and thin cracks were observed, exclusively located in intermetallic phase areas, where approx. 16-20 wt. % of Ti was revealed. Fracture surfaces of fatigue bars showed maximal failure in areas with 42-97 wt. % of Ti.
Columnar Grain Growth with Enhanced Rotation Texture in Temper Rolled NO Silicon Steels
Authors: Petryshynets Ivan , Kováč František , Molnárová Mária , Gavendová Petra , Sopko Martin , Petrov Branislav
Published: April 2014

The present work investigates texture evolution stages in vacuum-degassed non-oriented electrical steels. The main idea behind the improvement of soft magnetic properties relies on deformation induced grain growth phenomena and heat transport phenomena promoting the preferable formation of columnar grains with so called cube crystallographic orientation {100}<0vw>. In order to achieve the desired orientation with appropriate microstructure state from magnetic properties point of view, we have used an adjusted temper rolling process at elevated temperature and subsequent dynamical annealing in laboratory conditions.
Failure Analysis of the Rail
Authors: Šmátralová Magdalena , Kosňovská Jana , Rožnovská Gabriela , Kurek Václav
Published: April 2014

The paper describes the rail failures occurring repeatedly in the same distance from the rail butt weldment. The results of this investigation, especially fractographic analysis of the fracture surface of rail, evaluation of its macrostructure and microstructure, EDS analysis and hardness measurements revealed that transverse crack initiated in the foot of rail gauge and propagated by fatigue mechanism until the final cleavage fracture.
Investigations on a Defect Sewer Pipe, Attacked by Microbiologically Produced Acid
Authors: Haubner Roland , Strobl Susanne , Linhardt Paul , Halwax Erich
Published: April 2014

A nodular cast iron (German designation GGG) sewer pipe leaked within a short time of use (13 years). The pipe was destroyed by sulphuric acid induced corrosion. Microbes form hydrogen sulphide and further oxidation leads to H2SO4. Sewer pipes are coated inside with a protective alumina cement layer, which was attacked firstly, followed by a corrosion of cast iron. Spongiose is a corrosion of cast iron, thereby ferrite is destroyed and graphite and cementite are remaining unattacked. Spongiose is observed commonly in grey cast iron, but is unusual for nodular cast iron. The alumina cement coated GGG tube, the corrosion products and their different graduations were investigated. In the corroded spongiose-layer the crystalline phases graphite, cementite, hematite and magnetite were identified. In the rust-layer deposits of lepodocrocite and goethite are the main phases but also sulphur, gypsum and other sulphuric compounds were observed.
Influence of Charge Composition on the Structure and Fatigue Properties of Nodular Cast Irons
Authors: Vaško Alan , Trško Libor , Chalupová Mária
Published: April 2014

The contribution deals with comparison of microstructure and fatigue properties of synthetic nodular cast irons with a different ratio of steel scrap in a charge. Chemical composition of individual meltages was regulated alternatively by ferrosilicon (FeSi) and carburizer or metallurgical silicon carbide (SiC). The fatigue tests were run at high-frequency sinusoidal cyclic push-pull loading (frequency f 20 kHz, load ratio R = 1, temperature T = 20 ± 5 °C) using the ultrasonic testing equipment KAUP-ZU. The paper shows the influence of charge composition on microstructure, fatigue properties and micromechanisms of failure.
In Situ Observation Method for Quantitative Evaluation of Solidification Phenomena and Solidification Cracks during Welding
Authors: Shinozaki Kenji , Yamamoto Motomichi , Kadoi Kohta , Wen Peng
Published: April 2014

Solidification cracking during welding is very serious problem for practical use. Therefore, there are so many reports concerning solidification cracking. Normally, solidification cracking susceptibility of material is quantitatively evaluated using Trans-Varestraint test. On the other hand, local solidification cracking strain was tried to measure precisely using in-situ observation method, called MISO method about 30 years ago. Recently, digital high-speed video camera develops very fast and its image quality is very high. Therefore, we have started to observe solidification crack using in site observation method. In this paper, the local critical strain of a solidification crack was measured and the high temperature ductility curves of weld metals having different dilution ratios and different grain sizes to evaluate quantitatively the effects of dilution ratio and grain size on solidification cracking susceptibility by using an improved in situ observation method.
Influence of Microstructure and Defect Population on the Fatigue Performance of Cast A356-T6 Automotive Components
Authors: Konečná Radomila , Nicoletto Gianni , Riva Enrica
Published: April 2014

In the paper fatigue specimens are extracted from different regions of cast aluminum cylinder heads produced by two foundries. A high strength region and a low strength region were identified within the cylinder head and the A356-T6 material locally characterized in terms of microstructure and defect population. High cycle fatigue testing according to a reduced staircase method was performed to determine the local fatigue strength at 107 cycles in the cylinder heads of the two foundries. The implications of the experimental observations are discussed.
Laser Hardening Parameters Influencing Component Lifetime and Residual Stresses
Authors: Němeček Stanislav , Míšek Michal , Černý Ivo , Sís Jiří , Ganev Nikolaj , Kolařík Kamil
Published: April 2014

Laser surface hardening is an advanced method of surface treatment of structural steels with a great potential for wide industrial applications. The technology is quite new and so, investigations have to be performed in order to gain a comprehensive knowledge about effects on microstructure, hardness, surface properties of treated materials, but also mechanical an particularly fatigue properties. Concerning fatigue resistance of material treated with this technology, results and knowledge recently published in the literature indicate that fatigue resistance can be either reduced or increased, even considerably, depending on numerous parameters of basic material, laser hardening parameters etc. This contribution contains results of a partial study of effect of laser hardening of relatively small specimens on fatigue resistance of 42CrMo4 steel. Two different parameters of the treatment were used, namely two speeds of laser beam on the material surface at constant beam energy. Unlike the lower speed, when fatigue resistance was slightly reduced, higher speed of laser beam resulted in a slight increase of fatigue resistance and fatigue limit. The results are discussed considering an occurrence of residuals stresses. Key words: Laser hardening, residual stress, lifetime, fatigue, fracture, microstructure, surface
Modern Self-Lubricating Coatings for Automotive, Aviation and Spacecraft Industry
Authors: Wendler Bogdan , Moskalewicz Tomasz , Kot Marcin , Zimowski Slawomir , Czyrska-Filemonowicz Aleksandra , Pawlak Wojciech , Rylski Adam , Wlodarczyk-Kowalska Katarzyna , Nolbrzak Piotr , Makowska Marcin
Published: April 2014

A series of nanocomposite, self-lubricating coatings designed for dry friction at different temperatures based on amorphous carbon or amorphous MoS2 or amorphous MoO3 matrix was deposited by magnetron sputtering onto high-speed (HS) steel or Ti6Al4V alloy substrates and characterized with use of LM, SEM, TEM and HRTEM microscopy as well as with use of several other techniques. The nanocomposite nc-MeC/a-C(:H) carbon-based coatings (where Me=Cr or Ti or W) were composed of different nanocrystalline phases of a given transition metal of a size of several nanometers embedded in an amorphous hydrogenated or hydrogen-free carbon matrix. The nanocomposite MoS2(Ti,W) coatings were composed of Tiα or Wα or TiS2 nanocrystallites of 3 nm ÷ 10 nm diam. embedded in a semi-crystalline MoS2 matrix with MoS2 clusters of 3 nm÷8 nm diam. The magnetron sputtered MoO3 based coatings after deposition were composed of Ag nanocrystallites of 50 nm÷100 nm diam. embedded in an amorphous fractal-type matrix composed of MoO3 clusters of different size from very small to relatively great ones (not exceeding, however, 400 nm diam.). These amorphous clusters after 3 hours annealing in the ambient atmosphere under normal pressure at 300 °C transform into nanocrystalline MoO3 ones or after same annealing at 450 °C into crystalline silver molybdate Ag2MoO4 ones. The coatings preserve their resistance to wear and their low friction coefficient to approximately 250 °C in case of carbon-based coatings or to 350 °C in case of MoS2-based ones or to 550 °C in case of MoO3-based coatings. Several mechanical and tribological chracteristics of the coatings are given in the paper as well.
Microstructure of CB2 Steel before and after Long-Term Creep Tests
Authors: Jandová Dagmar , Kasl Josef , Chvostová Eva
Published: April 2014

A pilot 4t valve made of CB2 steel was produced in the frame of COST Action 522. Specimens for long-term creep tests were taken from positions with a wall thickness of 130 mm and 85 mm. Creep testing was carried out at 650°C and a stress range from 50 MPa to 120 MPa. The longest times to rupture of specimens in individual positions were 67,857 h and 82,649 h respectively. Ruptured samples underwent fractographic and microstructural analyses. Quantitative evaluation of substructure was performed using SEM and TEM. Microstructure consisted of tempered martensite with primary boron and niobium nitrides and secondary particles of M23C6 carbide, Laves phase and vanadium nitride. During creep tests coarsening of Laves phase occurred and new particles nucleated on the site of M23C6 carbides, NbN or BN nitrides. Significant increase in volume fraction of Laves phase was detected in specimens ruptured up to 20,000 hours in comparison to as received conditions; any further increase was found out after longer creep exposures. Concerning to M23C6 carbides any important changes were found out in their size and distribution. Density of fine MX nitride was higher after creep tests than in as received conditions with the exception of two longest creep exposures. Several Z-phase particles were also identified after these two exposures.
Microstructure and Mechanical Properties of Ultrafine-Grained Magnesium AZ91 Alloy
Authors: Fintová Stanislava , Pantělejev Libor , Kunz Ludvík
Published: April 2014

Microstructure, mechanical properties, cyclic plastic deformation behavior and fatigue strength of ultrafine-grained (UFG) magnesium alloy AZ91 processed by equal channel angular pressing (ECAP) were investigated. ECAP of originally cast alloy results in development of bimodal structure, improved yield stress, tensile strength and ductility when compared to the as-cast state. Endurance limit based on 107cycles is also improved, however exhibits large scatter. Initiation of fatigue cracks takes place in regions of large grains in the bimodal structure, where the content of Mg17Al12particles is low.
Homogenization of AlSi7MgCu0.5 Alloy as-Cast Structure by ECAP Processing
Authors: Matvija Miloš , Fujda Martin , Vojtko Marek , Kočiško Robert
Published: April 2014

The homogenization of AlSi7MgCu0.5 alloy as-cast structure by using an equal channel angular pressing (ECAP) was investigated. The heat treatment of as-cast alloy applied before ECAP processing was required to increase alloy plasticity. Therefore, the samples of analyzed alloy were solution annealed at temperature of 550 °C for 4 hours and subsequently water quenched. Quenched samples were artificially aged at temperature of 300 °C for 5 hours to obtain an over-aged alloy state. The solution annealing of as-cast alloy state caused a partial spheroidization and coarsening of eutectic Si-particles. During artificial aging of analyzed alloy, the incoherent particles precipitated uniformly from α-solid solution. The ECAP technique at room temperature homogenized its heterogeneous dendritic microstructure and formed the ultra-fine grains of solid solution. A redistribution and fragmentation of the eutectic Si-particles and precipitated particles was occurred.
Structural Stability of Welded Joints of Magnesium Alloy EZ33A-T5
Authors: Kocurek Robert , Adamiec Janusz
Published: April 2014

Magnesium alloys of Mg-Zn-RE-Zr group are characterized by creep resistance up to 250°C, good castability, absence of the microporosity and gas corrosion resistance. Defect of these alloys are low mechanical properties at ambient temperature. Magnesium alloys are used in the automotive, aerospace and defense industries, mainly as gravitational casts to sand moulds or die-casting. Casting defects often appear in these casts (misruns, micro-shrinkage, cracks), especially for large-size castings. The welding technologies are most often applicable to repair of casts, mainly non-consumable electrode welding in the inert-gas cover. Welded joints made of magnesium alloys should have properties at least the same as the ready cast, in particular it should ensure stability of the structure and properties of all welded joint in working temperature. In the literature there is a lack of information about stability and properties of welded joints of Mg-4E-3Zn (EZ33A-T5 acc. to ASTM B80) alloy castings. In research work determined the structure of welded joints of Mg-4RE-3Zn alloy casting after stress-relief annealing and defined changes of structure and properties during long-term annealing at the temperature of 250°C. It was found that the structure of welded joint of casting alloy Mg-4RE-3Zn is stable at the temperature of 250°C through at least 1000 hours. The hardness of tested joints equal 80 HV. Therefore welding technologies can be used for repair of magnesium alloy casts with addition of zinc and rare earth elements.
Use of Decomposition of Non-Thermoelastic Martensite for Structural Changes of CuZnAl Shape Memory Alloys
Authors: Vojtko Marek , Zubko Pavol , Ďurišin Martin
Published: April 2014

Cu22Zn4.6Al shape memory alloy shows memory phenomenon after quenching from dual phase region. Amount of shape memory effect continuously decreases with raised quenching temperature. Decrease is caused by increasing of amount of non-thermoelastic martensite in structure [. Approximately above 700°C there is no effect and martensite is non-thermoleastic. Non-thermoelastic martesite decomposes to alpha and gamma/beta phases at heating at elevated temperatures.[ This effect can be used for modification of structure and thus mechanical and shape memory properties. Some various types of structures were obtained and mechanical and shape memory properties were evaluated. Using of decomposition of non-thermoelastic martensite allows to obtain fine structure with the same amount of alpha phase and martensite as in basic state. This type of structure has better shape memory properties and higher mechanical properties.
Mechanical Properties and Microstructure of IN738LC Nickel Superalloy Castings
Authors: Zýka Jiří , Andršová Irena , Podhorná Božena , Hrbáček Karel
Published: April 2014

IN738LC is a cast nickel-base superalloy developed for applications requiring high strength at elevated temperatures. Its balanced composition provides a good combination of tensile and creep-rupture properties as a result of gamma prime precipitate strengthening enhanced by solid solution and grain-boundary strengthening. Experimental castings are used in heat treated state. This alloy is used widely, for example, for manufacturing of gas turbine blades. Recently, customers demand different weight of castings hence different conditions during solidifying and cooling of the castings originate, resulting in different castings microstructure. When approving the castings, mechanical values are measured by tensile test on test bars made from the cast blade roots. This work investigates mechanical properties casting structure correlations, particularly grain, casting defects, carbides.
Nickel Alloys in Directionally Solidified State – Characterisation of Microstructure and Phase Composition of the Alloys
Authors: Malcharcziková Jitka , Kursa Miroslav , Pohludka Martin
Published: April 2014

The paper deals with the characterisation of the structure and phase composition of selected types of nickel alloys. Experimental alloys were prepared by vacuum induction casting. Castings were directionally solidified in corundum tubes with specified apex angle in the two-zone crystallisation furnace. Rate of directional solidification was 100 mm/h. Observation was carried out on the samples in the as-cast and directed state. Influencing of the structure by the process of directional solidification is evident. Porosity and micro-hardness were determined in transverse and longitudinal sections of individual samples and character of the formed structures was evaluated. Microstructural characterisation of materials was performed with use of scanning electron microscope. Distribution of individual elements was captured on X-ray maps, which documented significant chemical heterogeneity of investigated samples. Matrix composition corresponds approximately to the nominal composition of the alloys. The alloys contain moreover with variable content of primary and alloying elements. In the alloys with molybdenum and zirconium the phase enriched by these alloying elements were detected. On the other hand chromium is evenly dispersed in the basic matrix and it does not accumulate in the phases.
Zinc Alloys for Biodegradable Medical Implants
Authors: Pospíšilová Iva , Vojtěch Dalibor
Published: April 2014

Both magnesium and zinc are considered as suitable elements for preparation of biodegradable materials that can be gradually dissolved in human organism without the production of toxic compounds. Although many magnesium-based materials possess good mechanical properties and biocompatibility, corrosion rates accompanied by hydrogen release and pH increase are too high. On the contrary, Zn is characterized by much lower corrosion rate in physiological solution compared to magnesium and its alloys. Therefore, we study Zn-Mg binary alloys with 0-7 wt.% of Mg. In this case, magnesium was selected to improve mechanical properties and biocompatibility of pure Zn. The structures of alloys were studied by an optical metallographic microscope and SEM equipped with EDS analyzer. Mechanical properties were studied using Vickers hardness measurements. Our results showed that mechanical properties of binary Mg-Zn alloys improve with increasing content of Mg, achieving the maximum at eutectic composition. Higher Mg concentrations strongly deteriorate mechanical properties of binary Mg-Zn alloys.
Microstructure Development in Powder Metallurgy Steels: Effect of Alloying Elements and Process Variables
Authors: Hryha Eduard , Nyborg Lars
Published: April 2014

Microstructure of the powder metallurgy (PM) steels and especially mechanism of its formation differs significantly from the microstructure of the conventional steels even if composition will be exactly the same. The difference is not only connected to the presence of the pores, which are inalienable feature of the PM parts. Presence of the prior inter-particle boundaries, which can be contaminated by residual oxides, as well as microstructure heterogeneity are another characteristic features of the microstructure of PM steels. Microstructure heterogeneity is connected to the PM manufacturing process: powder mix, consisting of the base powder and additional alloying elements is compacted and then sintered. Fully prealloyed powder is not always possible to use in standard press & sintering route due to the solid solution strengthening of the ferrite resulting in bad powder compressibility. Hence, in order to provide good powder compressibility only pure iron or low-alloyed (typically <3 wt.%) powders are used. Required alloying elements and carbon (added as graphite) are further admixed in the powder form and are distributed during sintering by diffusion into iron particles at high temperatures. To assure satisfactory distribution of alloying elements, oxide layer, covering surface of the powder particles and hindering mass-transfer of the alloying elements, has to be removed first. This can be done by gaseous reducing agents as hydrogen and carbon monoxide. However, their cost and/or purity are of issue for modern alloyed PM steels. Admixed carbon, additionally to its function as alloying element, plays a role of effective reducing agent at higher temperatures. Paper summarizes the main features of microstructure formation during the whole sintering cycle (heating and isothermal sintering) and effect of alloying additives (different carbon sources, alloying elements) and processing parameters (sintering atmosphere composition, temperature profile) on the microstructure formation during conventional sintering process. Results indicate that for successful sintering of alloyed PM steels with homogeneous defect-free microstructure, hydrogen-rich atmospheres and high-temperature sintering are required.
Powder Metallurgically Produced Carbide Free Bainite
Authors: Vuorinen Esa , Vang Jesper , Carradot Malo , Johansson Pernilla , Navara Erik
Published: April 2014

Steels with carbide free bainitic (CFB) microstructures show excellent strength, toughness and wear resistance. Cast or wrought products produced by conventional metallurgy have become gradually introduced in manufacturing of numerous machine components. The required silicon addition of more than 1.5wt% in CFB-steels limits the possibilities to produce components of these steels by P/M methods. The aim of this work has been to investigate the possibilites to produce CFB-steels by pressing and sintering. Four different powder mixtures based on Distaloy DC powder have been pressed to a relative density of 90 % and sintered in a N2-H2 atmosphere at 1150 °C. The sintered components were then austenitized followed by austempering at a temperature above the martensite start temperature. Tensile and impact testing together with microhardness measurements have been performed. The microstructures were studied by optical microscopy as well as SEM and XRD-methods. The tensile strength values achieved varied from 313 to 737 MPa, the elongation after fracture were between 0.1 and 0.2%. The impact toughness values varied between 4 and 11 J. The hardness of the bainite after short sintering time varied between 630 and 710 HV and the hardness of the CFB was 350 HV after short sintering time but reached 573 after prolonged sintering. The microstructure consisted mainly of bainite, small amount of CFB mixed with austenite but also of ferrite and retained austenite after short sintering time. A longer sintering time created a structure consiting of mainly CFB with bainite and a small amount of ferrite. The most interesting applications for P/M produced CFB-containing steels should be components subjected to sliding or rolling-sliding wear loads, as gears. The hardness and strenght values achieved in the present work indicate that P/M produced CFB-steels can prove superior to conventional P/M steels in many applications.
Microstructure of Composites Based on Phosphated Iron Powder
Authors: Kabátová Margita , Dudrová Eva , Bruncková Helena
Published: April 2014

The commercial carbonyl iron powder coated with iron phosphate (20 wt.%) was dried (60°C for 2 h in air), calcinated at 400°C for 3 h in air, compacted at 600 MPa into cylindrical samples and subsequently sintered at 820, 900 and 1110°C for 30 min in N2-10%H2 atmosphere. By means of EDX and XRD analyses the phase composition of the coating and sintered microstructure was studied. Microstructure resulting from sintering at 820 and 900°C was formed by initial iron particles surrounded with the crystalline FePO4 and α-Fe2O3 phases. Due to liquid phase sintering at 1110°C a mixed microstructure containing spheroidized α-Fe phase surrounded by solidified liquid phase consisting of iron oxides and phosphorous compounds has been formed. In order to prepare a network composite microstructure the compacts based on spherical iron particles size of 100-160 µm coated with 2 wt.% of iron phosphate were dried, calcined at 400°C, compacted and liquid phase sintered at 980°C.
The Effect of Ni Interlayers on Compaction of Mo/Mo Silicide Composites
Authors: Senčeková Lucia , Iždinský Karol , Simančík František , Štefánik Pavol , Švec Pavol
Published: April 2014

Abstract: Reactions during compaction of Mo/Mo silicide wires with Ni interlayers are qualitatively assessed in this work. It appeared that due to extreme high temperature strength of MoSi2 hot pressing even at 1800°C/60 min/30 MPa in vacuum had not been sufficient to compact the Mo/Mo silicide wires in the absence of any additional interfacial layer. Therefore Ni had been chemically coated on the surface of Mo/Mo silicide wires that were subsequently compacted by hot pressing. Structural analysis revealed the reaction between Ni and MoSi2 resulting in the formation of ternary (MoNiSi) compounds. These established an interfacial bonding with minimal porosity.
Microstructure and Properties of Composites Prepared by Reactive Pressure Infiltration of Aluminium into Metal and Ceramic Powder Preforms
Authors: Opálek Andrej , Iždinský Karol , Nagy Štefan , Simančík František , Štefánik Pavol , Kúdela Jr. Stanislav
Published: April 2014

Nickel aluminides exhibit very attractive high temperature properties. However, due to high melting temperatures they are difficult to prepare. Gas pressure reactive infiltration is a relatively cheap technology that provides composites where nickel aluminides are formed due to mutual reaction between Ni powder and molten aluminium forced to penetrate into powder preform. The feasibility of this concept is demonstrated in this work. Ni powder and/or Ni+25 vol. % Al2O3 powder mixture, respectively, were mechanically pressed and then infiltrated with aluminium using 5 MPa argon gas pressure at the temperature of 750 °C for 120 s. Al/Al2O3 composite using loose alumina powder was prepared in similar manner for comparison. The microstructure of composites was observed by scanning electron microscopy and newly formed intermetallic phases were analysed by energy-dispersive X-ray spectroscopy. Relative elongations during additional thermal cycling up to 800 °C had been recorded. Composites were additionally characterized by hardness measurements.
Mixed and Vacuum/Pressure Impregnated Fe/SiO2/Shellac Composites
Authors: Kabátová Margita , Füzer Jan , Füzerova Jana , Dudrová Eva , Kollár Peter
Published: April 2014

Fe/SiO2/shellac composites based on iron powder consisting of irregularly and/or spherical shaped particles coated with SiO2 layer or with admixed SiO2 powder were prepared either by mixing the Fe-SiO2 powder with shellac or by vacuum/pressure impregnation (VPI) of sintered Fe-SiO2 compacts with shellac dissolved in ethanol. The effect of iron particle shape, density of compacts and method of shellac application on electrical resistivity and magnetic coercivity was evaluated and correlated with microstructure and features of insulating layer. For VPI composites based on spherical particles a uniformly thick insulating layer was created. This resulted in the electrical resistivity and coercivity of 780-1120 μΩ.m and 177-290 A/m. For composites based on irregularly shaped particles the shellac admixing is more preferable.
Critical Weak Points of Atmospheric Plasma Sprayed Thermal Barrier Coatings
Authors: Jech David , Čelko Ladislav , Juliš Martin , Klakurková Lenka , Slámečka Karel , Obrtlík Karel , Švejcar Jiří
Published: April 2014

The 8 wt. % yttria stabilized zirconia top coat (TC) and the CoNiCrAlY bond coat (BC) were sprayed onto the surface of newly developed fine-grained cast polycrystalline nickel-based superalloy Inconel 713LC by means of atmospheric plasma spraying (APS). As-prepared samples were isothermally exposed at the temperature of 1050 °C for 200 hours in an ambient atmosphere. Structural changes in the thermal barrier coatings (TBC) system after thermal exposure were studied by means of scanning electron microscope equipped with an energy dispersive microanalyzer. Critical weak points were identified on both the substrate-bond coat and bond coat-top coat interfaces.
Properties of Ni-Co Alloy Coating Prepared from Sulphate Bath
Authors: Hagarová Mária , Dzedzina Rastislav , Gavendová Petra
Published: April 2014

The paper deals with nickel – cobalt coatings on the copper substrate prepared by electroplating process. The different Co content in the alloy coating depending on chemical composition of sulphate electrolyte and current density. The microstructure and composition of Ni-Co coating were observed with use of light and scanning electron microscopy. The mechanical properties were determined with use of the test according to EN ISO 6892-1:2009 standard and means of a Vickers microhardness tester. The results showed that under the same bath composition and technological parameters of process the Ni-Co alloy coating exhibited laminated structure. Their strength and hardness of the deposited coatings were higher than those for the Ni coatings.
Slag Investigation from Iron Smelting and Iron Processing Sites in Austria – From Hallstatt and Medieval Period and the 19th Century
Authors: Haubner Roland , Strobl Susanne
Published: April 2014

Slags from three iron smelting and processing sites were investigated. The composition of the slags is connected to the metallurgical processes and the investigation should provide an indication of the process conditions.A slag from a small bloomery furnace at the archaeological site Waschenberg (Hallstatt period) was investigated. Slags from the medieval period were found near Eisenerz and at this time iron was produced in developed bloomery furnaces (Stuckofen). These slags are termed fayalitic slags and they consist of wustite (FeO), fayalite (Fe2SiO4) and glass-phase (amorphous silicates) in various concentrations. Three solidification-types were described and correlated with the microstructures and the FeO-SiO2-CaO2 phase diagram.During the 19th century steel was produced in puddling furnaces by remelting iron products from Eisenerz. Such slags, from this process, found in the surroundings of Palfau, were investigated and contain FeO and Ca rich glass-phase, but no fayalite.Due to the different compositions of the slags the solidification and the microstructures are different.
Differences in Mouse and Human Nonmemory B Cell Pools
Authors: Benitez Abigail , Weldon Abby J. , Tatosyan Lynnette , Velkuru Vani , Lee Steve , Milford Terry-Ann , Francis Olivia L. , Hsu Sheri , Nazeri Kavoos , Casiano Carlos M. , Schneider Rebekah , Gonzalez Jennifer , Su Rui-Jun , Baez Ineavely , Colburn Keith , Moldovan Ioana , Payne Kimberly J.
Published: April 2014

Identifying cross-species similarities and differences in immune development and function is critical for maximizing the translational potential of animal models. Coexpression of CD21 and CD24 distinguishes transitional and mature B cell subsets in mice. In this study, we validate these markers for identifying analogous subsets in humans and use them to compare the nonmemory B cell pools in mice and humans, across tissues, and during fetal/neonatal and adult life. Among human CD19+IgM+ B cells, the CD21/CD24 schema identifies distinct populations that correspond to transitional 1 (T1), transitional 2 (T2), follicular mature, and marginal zone subsets identified in mice. Markers specific to human B cell development validate the identity of marginal zone cells and the maturation status of human CD21/CD24 nonmemory B cell subsets. A comparison of the nonmemory B cell pools in bone marrow, blood, and spleen in mice and humans shows that transitional B cells comprise a much smaller fraction in adult humans than mice. T1 cells are a major contributor to the nonmemory B cell pool in mouse bone marrow, in which their frequency is more than twice that in humans. Conversely, in spleen, the T1:T2 ratio shows that T2 cells are proportionally ∼8-fold higher in humans than in mice. Despite the relatively small contribution of transitional B cells to the human nonmemory pool, the number of naive follicular mature cells produced per transitional B cell is 3- to 6-fold higher across tissues than in mice. These data suggest differing dynamics or mechanisms produce the nonmemory B cell compartments in mice and humans.