Search results for: SiGe alloys.

Authors: I. Kurashvili, G. Darsavelidze, T. Kimeridze, G. Chubinidze, I. Tabatadze

Abstract:

At present, a number of modern semiconductor devices based on SiGe alloys have been created in which the latest achievements of high technologies are used. These devices might cause significant changes to networking, computing, and space technology. In the nearest future new materials based on SiGe will be able to restrict the A³B⁵ and Si technologies and firmly establish themselves in medium frequency electronics. Effective realization of these prospects requires the solution of prediction and controlling of structural state and dynamical physical –mechanical properties of new SiGe materials. Based on these circumstances, a complex investigation of structural defects and structural-sensitive dynamic mechanical characteristics of SiGe alloys under different external impacts (deformation, radiation, thermal cycling) acquires great importance. Internal friction (IF) and shear modulus temperature and amplitude dependences of the monocrystalline boron-doped Si_1-xGe_x(x≤0.05) alloys grown by Czochralski technique is studied in initial and ⁶⁰Co gamma-irradiated states. In the initial samples, a set of dislocation origin relaxation processes and accompanying modulus defects are revealed in a temperature interval of 400-800 ⁰C. It is shown that after gamma-irradiation intensity of relaxation internal friction in the vicinity of 280 ⁰C increases and simultaneously activation parameters of high temperature relaxation processes reveal clear rising. It is proposed that these changes of dynamical mechanical characteristics might be caused by a decrease of the dislocation mobility in the Cottrell atmosphere enriched by the radiation defects.

Keywords: Gamma-irradiation, internal friction, shear modulus, SiGe alloys.

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Authors: Y. Li, K. Buddharaju, X. P. Wang

Abstract:

The mechanism of nickel (Ni) metallization in silicon-germanium (Si_0.5Ge_0.5) alloy nanowire (NW) was studied. Transmission electron microscope imaging with in-situ annealing was conducted at temperatures of 200^oC to 600°C. During rapid formation of Ni germanosilicide, loss of material from from the SiGe NW occurred which led to the formation of a thin Ni germanosilicide filament and eventual void. Energy dispersive X-ray spectroscopy analysis along the SiGe NW before and after annealing determined that Ge atoms tend to out-diffuse from the Ni germanosilicide towards the Ni source in the course of annealing. A model for the Ni germanosilicide formation in SiGe NW is proposed to explain this observation.

Keywords: SiGe, nanowires, germanosilicide.

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Authors: Guiheng Zhang, Wei Zhang, Jun Fu, Yudong Wang

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A 900 MHz three-stage SiGe power amplifier (PA) with high power gain is presented in this paper. Volterra Series is applied to analyze nonlinearity sources of SiGe HBT device model clearly. Meanwhile, the influence of operating current to IMD3 is discussed. Then a β-helper current mirror bias circuit is applied to improve linearity, since the β-helper current mirror bias circuit can offer stable base biasing voltage. Meanwhile, it can also work as predistortion circuit when biasing voltages of three bias circuits are fine-tuned, by this way, the power gain and operating current of PA are optimized for best linearity. The three power stages which fabricated by 0.18 μm SiGe technology are bonded to the printed circuit board (PCB) to obtain impedances by Load-Pull system, then matching networks are done for best linearity with discrete passive components on PCB. The final measured three-stage PA exhibits 21.1 dBm of output power at 1 dB compression point (OP1dB) with power added efficiency (PAE) of 20.6% and 33 dB power gain under 3.3 V power supply voltage.

Keywords: High gain power amplifier, linearization bias circuit, SiGe HBT model, Volterra Series.

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Authors: Hyunwon Moon

Abstract:

It is necessary to realize new biomedical wireless communication systems which send the signals collected from various bio sensors located at human body in order to monitor our health. Also, it should seamlessly connect to the existing wireless communication systems. A 5.8 GHz ISM band low power RF front-end receiver for a biomedical wireless communication system is implemented using a 0.5 µm SiGe BiCMOS process. To achieve low power RF front-end, the current optimization technique for selecting device size is utilized. The implemented low noise amplifier (LNA) shows a power gain of 9.8 dB, a noise figure (NF) of below 1.75 dB, and an IIP3 of higher than 7.5 dBm while current consumption is only 6 mA at supply voltage of 2.5 V. Also, the performance of a down-conversion mixer is measured as a conversion gain of 11 dB and SSB NF of 10 dB.

Keywords: Biomedical, low noise amplifier, mixer, receiver, RF front-end, SiGe.

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Authors: Morteza Fathipour, Samira Omidbakhsh, Kimia Khodayari

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RF performance of SOI CMOS device has attracted significant amount of interest recently. In order to improve RF parameters, Strained Si/Relaxed Si0.8Ge0.2 investigated as a replacement for Si technology .Enhancement of carrier mobility associated with strain engineering makes Strained Si a promising candidate for improving RF performance of CMOS technology. From the simulation, the cut-off frequency is estimated to be 224 GHZ, whereas in SOI at similar bias is about 188 GHZ. Therefore, Strained Si exhibits 19% improvement in cut-off frequency over similar Si counterpart. In this paper, Ion/Ioff ratio is studied as one of the key parameters in logic and digital application. Strained Si/SiGe demonstrates better Ion/Ioff characteristic than SOI, in similar channel length of 100 nm.Another important key analog figures of merit such as Early Voltage (VEA) ,transconductance vs drain current (gm /Ids) are studied. They introduce the efficiency of the devices to convert dc power into ac frequency.

Keywords: cut-off frequency, RF application, Silicon oninsulator, Strained Si/SiGe on insulator.

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Authors: Y.J. Lai, H.Y. Peng, M.W. Wu, J. Shaw

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In this study, we used shape memory alloys as actuators to build a biomorphic robot which can imitate the motion of an earthworm. The robot can be used to explore in a narrow space. Therefore we chose shape memory alloys as actuators. Because of the small deformation of a wire shape memory alloy, spiral shape memory alloys are selected and installed both on the X axis and Y axis (each axis having two shape memory alloys) to enable the biomorphic robot to do reciprocating motion. By the mechanism we designed, the robot can increase the distance as it moves in a duty cycle. In addition, two shape memory alloys are added to the robot head for controlling right and left turns. By sending pulses through the I/O card from the controller, the signals are then amplified by a driver to heat the shape memory alloys in order to make the SMA shrink to pull the mechanism to move.

Keywords: Biomorphic Robot, Shape Memory Alloy.

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Authors: S. Kapoor, R. Liu, X. J. Wu, M. X. Yao

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A group of Stellite alloys are studied in consideration of temperature effects on their hardness and wear resistance. The hardness test is conducted on a micro-hardness tester with a hot stage equipped that allows heating the specimen up to 650°C. The wear resistance of each alloy is evaluated using a pin-on-disc tribometer with a heating furnace built-in that provides the temperature capacity up to 450°C. The experimental results demonstrate that the hardness and wear resistance of Stellite alloys behave differently at room temperature and at high temperatures. The wear resistance of Stellite alloys at room temperature mainly depends on their carbon content and also influenced by the tungsten content in the alloys. However, at high temperatures the wear mechanisms of Stellite alloys become more complex, involving multiple factors. The relationships between chemical composition, microstructure, hardness and wear resistance of these alloys are studied, with focus on temperature effect on these relations.

Keywords: Stellite alloy, temperature, hardness, wear resistance

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Authors: O. Khalaj, B. Mašek, H. Jirková, J. Svoboda

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By using a combination of new technologies together with an unconventional use of different types of materials, specific mechanical properties and structures of the material can be achieved. Some possibilities are enabled by a combination of powder metallurgy in the preparation of a metal matrix with dispersed stable particles achieved by mechanical alloying and hot consolidation. This paper explains the thermomechanical properties of new generation of Oxide Dispersion Strengthened alloys (ODS) within three ranges of temperature with specified deformation profiles. The results show that the mechanical properties of new ODS alloys are significantly affected by the thermomechanical treatment.

Keywords: Hot forming, ODS, alloys, thermomechanical, Fe-Al, Al2O3.

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Authors: Mohsin Talib Mohammed, Zahid A. Khan, Arshad N. Siddiquee

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Biometallic materials are the most important materials for use in biomedical applications especially in manufacturing a variety of biological artificial replacements in a modern worlds, e.g. hip, knee or shoulder joints, due to their advanced characteristics. Titanium (Ti) and its alloys are used extensively in biomedical applications based on their high specific strength and excellent corrosion resistance. Beta-Ti alloys containing completely biocompatible elements are exceptionally prospective materials for manufacturing of bioimplants. They have superior mechanical, chemical and electrochemical properties for use as biomaterials. These biomaterials have the ability to introduce the most important property of biochemical compatibility which is low elastic modulus. This review examines current information on the recent developments in alloying elements leading to improvements of beta Ti alloys for use as biomaterials. Moreover, this paper focuses mainly on the evolution, evaluation and development of the modulus of elasticity as an effective factor on the performance of beta alloys.

Keywords: Beta Alloys, Biomedical Applications, Titanium Alloys, Young's Modulus.

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Authors: Pin-Hsu Kao, Wen-Shou Tseng, Hung-Ming Tai, Yuan-Ming Chang, Jenh-Yih Juang

Abstract:

We report a lithography-free approach to fabricate the biomimetics, quasi-beehive Si nanostructures (QBSNs), on Si-substrates. The self-assembled SiGe nanoislands via the strain induced surface roughening (Asaro-Tiller-Grinfeld instability) during in-situ annealing play a key role as patterned sacrifice regions for subsequent reactive ion etching (RIE) process performed for fabricating quasi-beehive nanostructures on Si-substrates. As the measurements of field emission, the bare QBSNs show poor field emission performance, resulted from the existence of the native oxide layer which forms an insurmountable barrier for electron emission. In order to dramatically improve the field emission characteristics, the platinum nanopillars (Pt-NPs) were deposited on QBSNs to form Pt-NPs/QBSNs heterostructures. The turn-on field of Pt-NPs/QBSNs is as low as 2.29 V/μm (corresponding current density of 1 μA/cm2), and the field enhancement factor (β-value) is significantly increased to 6067. More importantly, the uniform and continuous electrons excite light emission, due to the surrounding filed emitters from Pt-NPs/QBSNs, can be easily obtained. This approach does not require an expensive photolithographic process and possesses great potential for applications.

Keywords: Biomimetics, quasi-beehive Si, SiGe nanoislands, platinum nanopillars, field emission.

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Authors: A. Hossain, A. S. W. Kurny

Abstract:

The factors necessary to obtain an optimal heat treatment that influence the hardness and resistivity of Al-6Si-0.5Mg casting alloys with Cu or/and Ni additions were investigated. The alloys were homogenised (24hr at 500^oC), solutionized (2hr at 540^oC) and artificially ageing at various times and temperatures. The alloys were aged isochronally for 60 minutes at temperatures up to 400^oC and isothermally at 150, 175, 200, 225, 250 & 300^oC for different periods in the range 15 to 360 minutes. The hardness and electrical resistivity of the alloys were measured for various artificial ageing times and temperatures. From the isochronal ageing treatment, hardness found maximum ageing at 225^oC. And from the isothermal ageing treatment, hardness found maximum for 60 minutes at 225^oC. So the optimal heat treatment consists of 60 minutes ageing at 225^oC.

Keywords: Ageing, Al-Si-Mg alloy, hardness, resistivity.

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Authors: S. K. Tiwari, Dinesh Kumar Shukla, R. Chandra

Abstract:

Friction stir welding is a solid state joining process. High strength aluminum alloys are widely used in aircraft and marine industries. Generally, the mechanical properties of fusion welded aluminum joints are poor. As friction stir welding occurs in solid state, no solidification structures are created thereby eliminating the brittle and eutectic phases common in fusion welding of high strength aluminum alloys. In this review the process parameters, microstructural evolution, and effect of friction stir welding on the properties of weld specific to aluminum alloys have been discussed.

Keywords: Aluminum alloys, Friction stir welding (FSW), Microstructure, Properties.

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Authors: Kleiner Marques Marra, Tércio Pedrosa

Abstract:

This paper reports the production of uranium-molybdenum alloys, which have been considered promising fuel for test and research nuclear reactors. U-Mo alloys were produced in three molybdenum contents: 5 wt.%, 7 wt.%, and 10 wt.%, using an electric vacuum induction furnace. A boron nitride-coated graphite crucible was employed in the production of the alloys and, after melting, the material was immediately poured into a boron nitride-coated graphite mold. The incorporation of carbon was observed, but it happened in a lower intensity than in the case of the non-coated crucible/mold. It is observed that the carbon incorporation increased and alloys density decreased with Mo addition. It was also noticed that the increase in the carbon or molybdenum content did not seem to change the as-cast structure in terms of granulation. The three alloys presented body-centered cubic crystal structure (g phase), after solidification, besides a seeming negative microsegregation of molybdenum, from the center to the periphery of the grains. There were signs of macrosegregation, from the base to the top of the ingots.

Keywords: Incorporation of carbon, macrosegregation and microsegregation, solidification, uranium-molybdenum alloys.

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Authors: N. Kazantseva, P. Krakhmalev, I. Yadroitsev, A. Fefelov, N. Vinogradova, I. Ezhov, T. Kurennykh

Abstract:

Martensitic texture-phase transition in Selective Laser Melting (SLM) Ti-6Al-4V (ELI) alloys was found. Electron Backscatter Diffraction (EBSD) analysis showed the initial cubic beta < 100 > (001) BCC texture. Such kind of texture is observed in BCC metals with flat rolling texture when axis is in the direction of rolling and the texture plane coincides with the plane of rolling. It was found that the texture of the parent BCC beta-phase determined the texture of low-temperature HCP alpha-phase limited the choice of its orientation variants. The {10-12} < -1011 > twinning system in titanium alloys after SLM was determined. Analysis of the oxygen contamination in SLM alloys was done. Comparison of the obtained results with the conventional titanium alloys is also provided.

Keywords: Additive technology, texture, Ti-6Al-4V, twins, oxygen content.

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Authors: Porojan S., Sandu L., Topală F.

Abstract:

Minor problems arising from optimizations by welding of fixed prostheses frameworks can be identified by macroscopic and microscopic visual inspection. The purpose of this study was to highlight the visible discontinuities present in the laser welds of dental Ni-Cr alloys. Ni-Cr base metal alloys designated for fixed prostheses manufacture were selected for the experiments. Using cast plates, preliminary tests were conducted by laser welding. Macroscopic visual inspection was done carefully to assess the defects of the welding rib. Electron microscopy images allowed visualization of small discontinuities, which escapes visual inspection. Making comparison to Ni-Cr alloys taken in the experiment and laser welded, after visual analysis, the best welds appear for Heraenium NA alloy.

Keywords: macroscopic visual inspection, electron microscopyimages, Ni-Cr dental alloys, laser welding.

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Authors: M. Nazmunnahar, J. J. Del Val, A. Vimmrova, J. González

Abstract:

We report the microstructural and magnetic properties of Ni50Mn39Sn11 and Ni50Mn36Sn14 ribbon Heusler alloys. Experimental results were obtained by differential scanning calorymetry, X-ray diffraction and vibrating sample magnetometry techniques. The Ni-Mn-Sn system undergoes a martensitic structural transformation in a wide temperature range. For example, for Ni50Mn39Sn11 the start and finish temperatures of the martensitic and austenite phase transformation for ribbon alloy were Ms=336K, Mf=328K, As=335K and Af=343K whereas no structural transformation is observed for Ni50Mn36Sn14 alloys. Magnetic measurements show the typical ferromagnetic behavior with Curie temperature 207 K at low applied field of 50 Oe. The complex behavior exhibited by these Heusler alloys should be ascribed to the strong coupling between magnetism and structure, being their magnetic behavior determined by the distance between Mn atoms.

Keywords: Structural transformation, as-cast ribbon, Heusler alloys, Magnetic properties.

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Authors: M. Ertas, A. C. Onel, G. Ekinci, B. Toydemir, S. Durdu, M. Usta, L. Colakerol Arslan

Abstract:

To develop AZ91D magnesium alloys with improved properties, we have applied TiN and VN/TiN multilayer coatings using DC magnetron sputter technique. Coating structure, surface morphology, chemical bonding and corrosion resistance of coatings were analyzed by x-ray diffraction (XRD), scanning electron microscope (SEM), x-ray photoelectron spectroscopy (XPS), and tafel extrapolation method, respectively. XPS analysis reveal that VN overlayer reacts with oxygen at the VN/TiN interface and forms more stable TiN layer. Morphological investigations and the corrosion results show that VN/TiN multilayer thin film coatings are quite effective to optimize the corrosion resistance of Mg alloys.

Keywords: AZ91D Mg alloys, High corrosion resistance, Transition metal nitride coatings, Magnetron sputter.

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Authors: T. Ahmed, Z. Butt, M. Ali, S. Attiq, M. Ali

Abstract:

A series of Ti based shape memory alloys with composition of Ti50Ni49Cr1, Ti50Ni47Cr3 and Ti50Ni45Cr5 were developed by vacuum arc-melting under a purified argon atmosphere. The histometric and corrosion evaluation of Ti-Ni-Cr shape memory alloys have been considered in this research work. The alloys were developed by vacuum arc melting and implanted subcutaneously in rabbits for 4, 8 and 12 weeks. Metallic implants were embedded in order to determine the outcome of implantation on histometric and corrosion evaluation of Ti-Ni-Cr metallic strips. Encapsulating membrane formation around the alloys was minimal in the case of all materials. After histomorphometric analyses it was possible to demonstrate that there were no statistically significant differences between the materials. Corrosion rate was also determined in this study which is within acceptable range. The results showed the Ti- Ni-Cr alloy was neither cytotoxic, nor have any systemic reaction on living system in any of the test performed. Implantation shows good compatibility and a potential of being used directly in vivo system.

Keywords: Shape memory alloy, Ti-Ni-Fe, histomorphometric, corrosion.

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Authors: Mahmoud M. Tash, S. Alkahtani

Abstract:

The present study was undertaken to investigate the effect of pre-aging and aging parameters (time and temperature) on the mechanical properties of Al-Mg-Zn (7075) alloys. Ultimate tensile strength, 0.5% offset yield strength and % elongation measurements were carried out on specimens prepared from cast and heat treated 7075 alloys. Aging treatments were carried out for the as solution treated (SHT) specimens (after quenching in warm water). The specimens were aged at different conditions; Natural aging was carried out at room temperature for different periods of time. Double aging was performed for SHT conditions (pre-aged at different time and temperature followed by high temperature aging). Ultimate tensile strength, yield strength and % elongation as a function of different pre-aging and aging parameters are analyzed to acquire an understanding of the effects of these variables and their interactions on the mechanical properties of Be-treated 7075 alloys.

Keywords: Duplex Aging Treatment, Mechanical Properties, Al-Mg-Zn (7075) alloys.

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Authors: Ahmed. S. Alasmari, M. S. Soliman, Magdy M. El-Rayes

Abstract:

This study focuses on the effect of the addition of magnesium (Mg) and silver (Ag) on the mechanical properties of aluminum based alloys. The alloying elements will be added at different levels using the factorial design of experiments of 2²; the two factors are Mg and Ag at two levels of concentration. The superior mechanical properties of the produced Al-Cu-Mg-Ag alloys after aging will be resulted from a unique type of precipitation named as Ω-phase. The formed precipitate enhanced the tensile strength and thermal stability. This paper further investigated the microstructure and mechanical properties of as cast Al–Cu–Mg–Ag alloys after being complete homogenized treatment at 520 °C for 8 hours followed by isothermally age hardening process at 190 °C for different periods of time. The homogenization at 520 °C for 8 hours was selected based on homogenization study at various temperatures and times. The alloys’ microstructures were studied by using optical microscopy (OM). In addition to that, the fracture surface investigation was performed using a scanning electronic microscope (SEM). Studying the microstructure of aged Al-Cu-Mg-Ag alloys reveal that the grains are equiaxed with an average grain size of about 50 µm. A detailed fractography study for fractured surface of the aged alloys exhibited a mixed fracture whereby the random fracture suggested crack propagation along the grain boundaries while the dimples indicated that the fracture was ductile. The present result has shown that alloy 5 has the highest hardness values and the best mechanical behaviors.

Keywords: Precipitation hardening, aluminum alloys, aging, design of experiments, analysis of variance, heat treatments.

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Authors: H. Harada, S. Nishida, T. Nagumo, M. Endo, H. Watari

Abstract:

This study was aimed for investigating of manufacturing high aluminum content Mg alloys using a horizontal twin roll caster. Recently, weight saving has been key issues for lighter transport equipments as well as electronic component parts. As alternative materials to aluminum alloys, developing magnesium alloy with higher strength has been expected. Normally high Aluminum content Mg alloy has poor ductility and is difficult to be rolled because of its high strength. However, twin roll casting process is suitable for manufacturing wrought Mg alloys because materials can be cast directly from molten metal. In this study, manufacturing of high aluminum content magnesium alloy sheet using the roll casting process has been carried out. Effects of manufacturing parameter, such as roll velocity, pouring temperature and roll gap, on casting was investigated. A microscopic observation of the crystals of cross section of as cast strip as well as rolled strip was conducted.

Keywords: AZ91, AZ111, AZ121, Magnesium alloys, Twin roll casting

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Authors: Joon Ho Kim, Tae Kwon Ha

Abstract:

Single crystals of Magnesium alloys such as Mg-1Al, Mg-1Zn-0.5Y, Mg-3Li, and AZ31 alloys were successfully fabricated in this study by employing the modified Bridgman method. Single crystals of pure Mg were also made in this study. To determine the exact orientation of crystals, Laue back-reflection method and pole figure measurement were carried out on each single crystal. Dimensions of single crystals were 10 mm in diameter and 120 mm in length. Hardness and compression tests were conducted and the results revealed that hardness and the strength strongly depended on the orientation. The closer to basal one the orientation was, the higher hardness and compressive strength were. The effect of alloying was not higher than that of orientation. After compressive deformation of single crystals, the orientation of the crystals was found to rotate and to be parallel to the basal orientation.

Keywords: Compressive strength, Hardness, Mg alloys, Modified Bridgman method, Orientation, Pole figure, Single crystal.

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Authors: M. Asato, C. Liu, N. Fujima, T. Hoshino, Y. Chen, T. Mohri

Abstract:

We study the temperature dependence of the interaction energies (IEs) of X (=Ru, Rh) impurities in Pd, due to the Fermi-Dirac (FD) distribution and the thermal vibration effect by the Debye-Grüneisen model. The n-body (n=2~4) IEs among X impurities in Pd, being used to calculate the internal energies in the free energies of the Pd-rich PdX alloys, are determined uniquely and successively from the lower-order to higher-order, by the full-potential Korringa-Kohn-Rostoker Green’s function method (FPKKR), combined with the generalized gradient approximation in the density functional theory. We found that the temperature dependence of IEs due to the FD distribution, being usually neglected, is very important to reproduce the X-concentration dependence of the observed solvus temperatures of the Pd-rich PdX (X=Ru, Rh) alloys.

Keywords: Full-potential KKR-Green’s function method, Fermi-Dirac distribution, GGA, phase diagram of Pd-rich PdX (X=Ru, Rh) alloys, thermal vibration effect.

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Authors: D. Adhikari, R. P. Koirala, B.P. Singh

Abstract:

A self-association model has been used to understand the concentration dependence of free energy of mixing (GM), heat of mixing (HM), entropy of mixing (SM), activity (a) and microscopic structures, such as concentration fluctuation in long wavelength limit (Scc(0)) and Warren-Cowley short range order parameter ( 1 α )for Cu- Tl molten alloys at 1573K. A comparative study of surface tension of the alloys in the liquid state at that temperature has also been carried out theoretically as function of composition in the light of Butler-s model, Prasad-s model and quasi-chemical approach. Most of the computed thermodynamic properties have been found in agreement with the experimental values. The analysis reveals that the Cu-Tl molten alloys at 1573K represent a segregating system at all concentrations with moderate interaction. Surface tensions computed from different approaches have been found to be comparable to each other showing increment with the composition of copper.

Keywords: Concentration fluctuations, surface tension, thermodynamic properties, Quasi-chemical approximation.

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Authors: A. Ismaeel, C. S. Wang, D. S. Xu

Abstract:

The γ-TiAl based Ti-Al-Mn-Nb alloys were fabricated by selective laser melting (SLM) on the TC4 substrate. The microstructures of the alloys were investigated in detail. The results reveal that the alloy without electromagnetic stirring (EMS) consists of γ-TiAl phase with tetragonal structure and α2-Ti3Al phase with hcp structure, while the alloy with applied EMS consists of γ-TiAl, α2-Ti3Al and α-Ti with hcp structure, and the morphological structure of the alloy without EMS which exhibits near lamellar structure and the alloy with EMS shows duplex structure, the alloy without EMS shows some microcracks and pores while they are not observed in the alloy without EMS. The microhardness and wear resistance values decrease with applied EMS.

Keywords: Selective laser melting, γ-TiAl based alloys, microstructure, properties, electromagnetic stirring.

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Authors: Gurmeet Singh Cheema, Navjotinder Singh, Gurjinder Singh, Amardeep Singh Kang

Abstract:

Aluminium and its alloys have excellent corrosion resistant properties, ease of fabrication and high specific strength to weight ratio. In this investigation an attempt has been made to study the effect of different post weld heat treatment methods on the mechanical and metallurgical properties of TIG welded joints of the commercial aluminium alloy. Three different methods of post weld heat treatments are solution heat treatment, artificial ageing and combination of solution heat treatment and artificial aging are given to TIG welded aluminium joints. Mechanical and metallurgical properties of As welded joints of the aluminium alloys and post weld heat treated joints of the aluminium alloys were examined.

Keywords: Aluminium Alloys, Post weld Heat Treatment, TIG welding.

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Authors: Hany R. Ammar, Khalil A. Khalil, El-Sayed M. Sherif

Abstract:

The current study investigated the influence of milling time and ball-to-powder (BPR) weight ratio on the microstructural constituents and mechanical properties of bulk nanocrystalline Al; Al-10%Cu; and Al-10%Cu-5%Ti alloys. Powder consolidation was carried out using a high frequency induction heat sintering where the processed metal powders were sintered into a dense and strong bulk material. The powders and the bulk samples were characterized using XRD and FEGSEM techniques. The mechanical properties were evaluated at various temperatures of 25°C, 100°C, 200°C, 300°C and 400°C to study the thermal stability of the processed alloys. The processed bulk nanocrystalline alloys displayed extremely high hardness values even at elevated temperatures. The Al-10%Cu-5%Ti alloy displayed the highest hardness values at room and elevated temperatures which are related to the presence of Ti-containing phases such as Al3Ti and AlCu2Ti. These phases are thermally stable and retain the high hardness values at elevated temperatures up to 400ºC.

Keywords: Nanocrystalline Aluminum Alloys, Mechanical Alloying, Sintering, Hardness, Thermal Stability.

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Authors: F. Brunke, L. Waalkes, C. Siemers

Abstract:

Due to reduced stiffness, research on second generation titanium alloys for implant applications, like the metastable β-titanium alloy Ti-15Mo, become more and more important in the recent years. The machinability of these alloys is generally poor leading to problems during implant production and comparably large production costs. Therefore, in the present study, Ti-15Mo was alloyed with 0.8 wt.-% of the rare earth metals lanthanum (Ti-15Mo+0.8La) and neodymium (Ti-15Mo+0.8Nd) to improve its machinability. Their microstructure consisted of a titanium matrix and micrometer-size particles of the rare earth metals and two of their oxides. The particles stabilized the microstructure as grain growth was minimized. As especially the ductility might be affected by the precipitates, the behavior of Ti-15Mo+0.8La and Ti- 15Mo+0.8Nd was investigated during static and dynamic deformation at elevated temperature to develop a processing route. The resulting mechanical properties (static strength and ductility) were similar in all investigated alloys.

Keywords: Ti-15Mo, Titanium alloys, Rare earth metals, Free-machining alloy.

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Authors: S. Porojan, L. Sandu, F. Topalâ

Abstract:

Microplasma welding is a less expensive alternative to laser welding in dental technology. The aim of the study was to highlight discontinuities present in the microplasma welded joints of dental base metal alloys by visual analysis. Five base metal alloys designated for fixed prostheses manufacture were selected for the experiments. Using these plates, preliminary tests were conducted by microplasma welding in butt joint configuration, without filler material, bilaterally and with filler material, proper for each base metal. Macroscopic visual inspection was performed to assess carefully the irregularities in the welds. Electron microscopy allowed detection of discontinuities that are not visible to the eye and revealing details regarding location, trajectory, morphology and size of discontinuities. Supplementing visual control with microscopic analysis allows to detect small discontinuities, which escapes the macroscopic control and to make a detailed study of the weld.

Keywords: base metal alloys, fixed prosthodontics, microplasmawelding, visual inspection

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Authors: Mahmoud M. Tash

Abstract:

The present study was undertaken to investigate the effect of aging parameters (time and temperature) on the mechanical properties of Be-and/or Zr- treated Al-Mg-Zn (7075) alloys. Ultimate tensile strength, 0.5% offset yield strength and % elongation measurements were carried out on specimens prepared from cast and heat treated 7075 alloys containing Be and/or Zr. Different aging treatment were carried out for the as solution treated (SHT) specimens (after quenching in warm water). The specimens were aged at different conditions; Natural and artificial aging was carried out at room temperature, 120C, 150C, 180C and 220C for different periods of time. Duplex aging was performed for SHT conditions (pre-aged at different time and temperature followed by high temperature aging). Ultimate tensile strength, yield strength and % elongation data results as a function of different aging parameters are analysed. A statistical design of experiments (DOE) approach using fractional factorial design is applied to acquire an understanding of the effects of these variables and their interactions on the mechanical properties of Be- and/or Zr- treated 7075 alloys. Mathematical models are developed to relate the alloy mechanical properties with the different aging parameters.

Keywords: Casting, Aging Treatment, Mechanical Properties, Al-Mg-Zn (7075) alloys, Be- and/or Zr-Treatment, Experimental Correlation.

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