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Freeform Fabrication of Titanium Aluminide via Electron Beam Melting Using Prealloyed and Blended Powders  [PDF]
Denis Cormier,Ola Harrysson,Tushar Mahale,Harvey West
Advances in Materials Science and Engineering , 2007, DOI: 10.1155/2007/34737
Abstract: Titanium aluminide (TiAl) is an intermetallic compound possessing excellent high-temperature performance while having significantly lower density than nickel-based superalloys. This paper presents preliminary results of experiments aimed at processing TiAl via the electron beam melting (EBM) process. Two processing routes are explored. The first uses prealloyed powder, whereas the second explores controlled reaction synthesis. Issues such as processing parameters, vaporization of alloying elements, microstructure, and properties are discussed.
Effect of Bio Field Treatment on the Physical and Thermal Characteristics of Vanadium Pentoxide Powders
Mahendra Kumar Trivedi, Shrikant Patil, Rama Mohan Tallapragad
Material Science & Engineering , 2013, DOI: 10.4172/2169-0022.S11-001
Abstract: Vanadium pentoxide powders are very useful in producing ferrous as well as aluminium alloys, in removing carbon and sulphur and as catalysts in synthesizing ammonia and sulphuric acid. It is also used as corrosion inhibitor petroleum and chemical processing. In the present investigation V2O5 powders are exposed to biofield. Both the exposed and unexposed powders are later characterized by various techniques. The average particle size is found to decrease with increase in number of days after treatment up to a maximum of 15.9% in 110 days indicating severe fracture at agglomerate/ crystallite boundaries. The BET surface area showed a surprising decrease (it should increase as particle size is decreased) of 7.22% in 109 days indicating the surface densification/ removal of sharp surface corners/ formation of large particles. SEM photographs indeed showed that samples exposed to biofield after 20 days showed increase in size as well as rounded corners. Thermal analysis indicated an increase in melting temperature by 9.9% in samples treated after 57 days along with a much reduced change in weight. X-ray diffraction of the powder samples indicated both increase and decrease in crystallite size, unit cell volume and molecular weight of samples exposed to biofield after 28, 104, 124 and 139 days. These results indicate that the catalytic nature of vanadium pentoxide can be controlled by exposing to bio field and using after a specific number of days after exposure.
Fabrication of Single-Phase NiTi by Combustion Synthesis of Mechanically Activated Powders  [PDF]
S. Mousavi Nasab,M. Aboutalebi,S. H. Seyedein,A. Molavi Kakhki,J. Vahdati Khaki
Journal of Metallurgy , 2012, DOI: 10.1155/2012/153841
Abstract: Single-phase NiTi was fabricated through the thermal explosion mode of combustion synthesis of mechanically activated powders. Combustion and ignition temperatures of combustion synthesis were investigated in different milling times. In this process, equiatomic powder mixtures of nickel and titanium were activated by planetary ball mill and pressed into disk-shaped pellets then heated in a tube furnace, while temperature-time profile was recorded. X-ray diffraction analysis (XRD) was performed on milled powders as well as synthesized samples. Scanning electron microscopy (SEM) was also used to study the microstructural evolution during milling. The results showed that there was a threshold milling time to obtain single-phase NiTi. It was also seen that the ignition temperature and combustion temperature were reduced significantly by increasing milling time. 1. Introduction NiTi alloy combines the characteristics of shape memory effect and superelasticity with excellent corrosion resistance, wear resistance, mechanical properties, and good biocompatibility [1]. They have been practically used for couplings, actuators, and smart materials, as well as external and internal biomedical applications, for example, orthodontic arch wires, catheters, and orthopaedic implants, and in cardiovascular surgery, and so forth [2]. The extent of the shape memory effect and the temperature range over which it is exhibited depend strongly on the composition of the alloy, and in order to realize the maximum benefits of this effect, it is essential to have an alloy of exact stoichiometry and very good homogeneity [3]. Conventionally, NiTi intermetallics are produced by arc or induction melting followed by hot working and forming [2]. Arc melting requires multiple remelts to achieve sufficient homogeneity, while induction melting has the drawback of oxygen contamination [4]. The powder metallurgy technique has also been used for the NiTi fabrication and offers the ability to avoid the problems of casting defects due to segregation and to produce a variety of component shapes while minimizing subsequent machining operations [5]. Among the mentioned techniques, combustion synthesis (CS) has advantages of time and energy savings that make it an attractive alternative to the conventional methods for the production of various classes of materials [6]. Very homogeneous alloys of desirable stoichiometry also can be synthesized by this route, thus eliminating the subsequent thermomechanical processing for homogenization [7]. Moreover the reacted products are purer and have better
Characteristics of Biometallic Alloy to Additive Manufacturing Using Selective Laser Melting Technology  [PDF]
Marcello Vertamatti Mergulh?o, Maurício David Martins Das Neves
Journal of Biomaterials and Nanobiotechnology (JBNB) , 2018, DOI: 10.4236/jbnb.2018.91008
Abstract: Biomaterial powders are in high development due to expansion of additive manufacturing (AM) processes. Selective laser melting (SLM) is a particular AM technology, which completely melts a powder bed layer by laser beam. Investigations of appropriated physical properties of feedstock (powder alloy) were the aim of this study. Cobalt-chromium-molybdenum (Co-Cr-Mo) alloy was used to overview of gas-atomized powder properties in different granulometric ranges (D1 12 - 19 μm, D2 20 - 46 μm and D3 76 - 106 μm), as their: physical, chemical properties and thermal analysis. SLM manufactured standard tensile specimens of usually granulometric range powder size provided mechanical, chemical and thermal properties of biocompatible Co-Cr-Mo alloy. The physical properties showed that powders in the range of 20 to 50 μm provide a better flow ability and packed density, which are relevant characteristics to SLM processing. Manufacturing by SLM process provided suitable mechanical properties in the health area, as well as, maintained the biocompatible properties of the Co-Cr-Mo alloy.
Molecular dynamics study of melting of a bcc metal-vanadium II : thermodynamic melting  [PDF]
V. Sorkin,E. Polturak,Joan Adler
Physics , 2003, DOI: 10.1103/PhysRevB.68.174103
Abstract: We present molecular dynamics simulations of the thermodynamic melting transition of a bcc metal, vanadium using the Finnis-Sinclair potential. We studied the structural, transport and energetic properties of slabs made of 27 atomic layers with a free surface. We investigated premelting phenomena at the low-index surfaces of vanadium; V(111), V(001), and V(011), finding that as the temperature increases, the V(111) surface disorders first, then the V(100) surface, while the V(110) surface remains stable up to the melting temperature. Also, as the temperature increases, the disorder spreads from the surface layer into the bulk, establishing a thin quasiliquid film in the surface region. We conclude that the hierarchy of premelting phenomena is inversely proportional to the surface atomic density, being most pronounced for the V(111) surface which has the lowest surface density.
Molecular dynamics study of melting of a bcc metal-vanadium I: mechanical melting  [PDF]
V. Sorkin,E. Polturak,Joan Adler
Physics , 2003, DOI: 10.1103/PhysRevB.68.174102
Abstract: We present molecular dynamics simulations of the homogeneous (mechanical) melting transition of a bcc metal, vanadium. We study both the nominally perfect crystal as well as one that includes point defects. According to the Born criterion, a solid cannot be expanded above a critical volume, at which a 'rigidity catastrophe' occurs. This catastrophe is caused by the vanishing of the elastic shear modulus. We found that this critical volume is independent of the route by which it is reached whether by heating the crystal, or by adding interstitials at a constant temperature which expand the lattice. Overall, these results are similar to what was found previously for an fcc metal, copper. The simulations establish a phase diagram of the mechanical melting temperature as a function of the concentration of interstitials. Our results show that the Born model of melting applies to bcc metals in both the nominally perfect state and in the case where point defects are present.
Effect of fabrication conditions on the properties of indium tin oxide powders

Xie Wei,

中国物理 B , 2008,
Abstract: This paper reports that indium tin oxide (ITO) crystalline powders are prepared by coprecipitation method. Fabrication conditions mainly as sintering temperature and Sn doping content are correlated with the phase, microstructure, infrared emissivity $\varepsilon $ and powder resistivity of indium tin oxides by means of x-ray diffraction, Fourier transform infrared, and transmission electron microscope. The optimum sintering temperature of 1350${^\circ}$C and Sn doping content 6$\sim $8wt{\%} are determined. The application of ITO in the military camouflage field is proposed.
Selective Laser Melting (SLM) of pure gold
Mushtaq Khan,Phill Dickens
Gold Bulletin , 2010, DOI: 10.1007/BF03214976
Abstract: This work presents an investigation into the Selective Laser Melting (SLM) of 24 carat gold (Au) powder with a mean particle size of 24μm. An SLM 100 system was used which is intended for production of highly detailed and intricate parts. Gold powder was tested for its properties such as tap density, Particle Size distribution (PSD) and reflectance etc. A suitable processing window was identified and gold cubes were produced using these parameters. Gold cubes were also checked for their internal porosity and mechanical properties.
Vanadium sacrificial layers as a novel approach for the fabrication of freestanding Heusler Shape Memory Alloys  [PDF]
Lars Helmich,Niclas Teichert,Walid Hetaba,Anna Behler,Anja Waske,Svetlana Klimova,Andreas Huetten
Physics , 2015,
Abstract: In this study we report a method for the preparation of freestanding magnetocaloric thin films. Non-stoichiometric Heusler alloys Ni-Mn-Sn, Ni-Co-Mn-Sn and Ni-Co-Mn-Al are prepared via sputter deposition. A sacrificial vanadium layer is added between the substrate and the Heusler film. By means of selective wet-chemical etching the vanadium layer can be removed. Conditions for the crystallization of Vanadium layers and epitaxial growth of the Heusler films are indicated. Magnetic and structural properties of freestanding and as-prepared films are compared in detail. The main focus of this study is on the influence of substrate constraints on the Martensitic transistion.
Sintering of low-melting glass powders and glass-abrasive composites  [PDF]
Shilo A.E.,Bondarev E.K.,Kukharenko S.A.
Science of Sintering , 2003, DOI: 10.2298/sos0303117s
Abstract: Sintering of glass powders in Na2O-B2O3-SiO2 and PbO-ZnO-B2O3-SiO2 systems as well as of their mixtures has been studied. The process of sintering is shown to change because of crystallization of the glass of the PbO-ZnO-B2O3-SiO2 system. Addition of diamond or cubic boron nitride to glass powders affects shrinkage in sintering composites. Sintering of powders of lead-containing glass proceeds by the mechanism of viscous flow.
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