New Grades of Hardmetals for a Rock Cutting Tools

A concept is developed for creating hardmetals for rock cutting tools. The concept pays particular attention to increasing energy absorption and the fatigue strength of hardmetals. In order to provide high rock cutting tool efficiency it should be fitted with hardmetal inserts which exhibit high bending strength, fracture toughness, total work of deformation, and energy absorption coefficient. This has been realized in the development of new grades of hardmetals for rock cutting tools. The efficiency of rock cutting tools fitted with inserts made from the new grades of hardmetal exceeds that of similar tools fitted with standard hardmetals inserts by a factor of 2.8     

Melting Diagram for the Cr ― Nb ― C System in the (Cr) ― (Nb) ― ― (NbC) Region

Powder Metallurgy and Metal Ceramics - It is shown from experimental tests on alloys in the Cr ― Nb ― C system in the region of the (Cr) ― (Nb) ― (NbC) subsystem at the...     

Procedure for Choosing Abrasive Composites for Grinding Materials that are Hard to Machine

A procedure is developed for choosing a composite abrasive for grinding alloys that are hard to machine based on considering the interaction of tool materials and the article being machined. The efficiency of the procedure is demonstrated using the composite created for machining titanium alloys.__________Translated from Poroshkovaya Metallurgiya, Nos. 1–2(441), pp. 31–38, January–February, 2005.     

Grain-Size Composition and Coercive Force of Nd2Fe14B Alloy Powder in a Finely Divided State

The change in grain-size composition and magnetic properties of powder prepared by grinding cast alloy Nd₂Fe₁₄B in a ball mill for different times is studied. It is shown that during grinding the coercive force of the powder increases uniformly at first reaching a maximum, and then it decreases. It is established that this phenomenon is not due to powder oxidation during grinding but a reduction in the level of particle uniaxial anisotropy caused by deformation of their surface layer during grinding. The change in coercive force of Nd ₂Fe₁₄B alloy powder on grinding obeys the same features that are observed with mechanical grinding of other uniaxial magnetic materials.     

An Experimental and Computational Modeling Study on Additively Manufactured Micro-Architectured Ti–24Nb–4Zr–8Sn Hollow-Strut Lattice Structures

Herein, the design, manufacturing, and mechanical testing of hollow-strut lattice structures of the metastable β-titanium alloy Ti–24Nb–4Zr–8Sn (Ti2448) are performed. Due to the absence of studies in the literature, this study focusses on two important aspects: 1) the designing of micro-architectured lattice structures and 2) metastable β-titanium alloy. Face-centered cubic (FCC) and body-centered cubic (BCC) hollow-strut lattices are designed by computer-aided design and manufactured by laser powder bed fusion. The microstructure of the hollow lattices shows plates of α″-martensite phase within the β phase. The FCC hollow lattice structure shows higher tensile strength compared to the BCC hollow lattice structure, while the load-bearing capability of the FCC hollow lattice structure is lower than that of the BCC hollow lattice structure. At lower strains, the tensile force-displacement curve of the hollow lattice structure matches the simulated tensile force-displacement curve. At higher strains, a large deviation in the force-displacement curve is observed in the hollow lattices.     

The Mechanism of HDS Catalysis

The mechanism of heterogeneous catalytic reactions is much more difficult to elucidate than that of homogeneous systems. Despite the facilities provided by physical methods for investigating the surface of solids, obtaining detailed information on the structure of the active component in real heterogeneous catalysts presents difficulties due to the nonuniform chemical composition of the surface species. Some of these surface species are totally inactive in catalysis, and others can catalyze the given chemical reaction by different pathways and according to different mechanisms. This results in a change of selectivity to the desired product and the appearance of intermediates and reaction by-products. Furthermore, the effect of the reaction medium on the catalyst gains importance during a catalytic process when, at high temperature and pressure, one type of surface species is transformed into another, thus changing the mechanism and direction of the catalyzed reaction.     

Effect of pulsed magnetic treatment on the corrosion of titanium

ABSTRACT

Results of corrosion tests of titanium in the initial state and after treatment using pulsed magnetic field are presented. It is shown that samples after treatment have better corrosion resistance due to the formation of denser and finer corrosion products with better adhesion to the substrate. Samples after treatment have more homogeneous microstructure due to a substantial increase of dislocations which are uniformly distributed. Mechanisms of dislocation multiplication and a model explaining the effect of the treatment on the corrosion are discussed.

This paper is part of a themed issue on Materials in External Fields.     

lectrical Conductivity of Permeable Sintered Materials Composed of Discrete Randomly Oriented Fibers

A theory of the electrical properties of individual contacts is used to calculate the electrical conductivity of porous materials composed of discrete fibers with imperfect interparticle contacts. It is shown that the conductivity of these materials may be substantial even if the contacts are small. The materials' conductivity is significantly affected by a change in the relative length of the fibers.     

Solid Solutions of Lindbergite–Glushinskite Series: Synthesis,Ionic Substitutions,Phase Transformation and Crystal Morphology

To clarify the crystal chemical features of natural and synthetic oxalates Me²⁺(C₂O₄)∙2H₂O (Me²⁺ = Fe, Mn, Mg, Zn), including minerals of the humboldtine group, solid solutions of lindbergite Mn(C₂O₄)∙2H₂O–glushinskite Mg(C₂O₄)∙2H₂O were precipitated under various conditions, close to those characteristic of mineralization in biofilms: at the stoichiometric ratios ((Mn + Mg)/C₂O₄ = 1) and non-stochiometric ratios ((Mn + Mg)/C₂O₄ < 1), in the presence and absence of citrate ions. Investigation of precipitates was carried out by powder X-ray diffraction, scanning electron microscopy and energy-dispersive X-ray spectroscopy. Thermodynamic modelling was performed in order to evaluate the lindbergite–glushinskite equilibrium. It was shown that glushinskite belongs to the orthorhombic β-modification (sp. Gr. Fddd), while lindbergite has a monoclinic α-modification (sp. gr. C2/c). Mg ions incorporate lindbergite in much higher quantities than Mn ions incorporate glushinskite; moreover, Mn glushinskites are characterized by violations of long-range order in their crystal structure. Lindbergite–glushinskite transition occurs abruptly and can be classified as a first-order isodimorphic transition. The Me²⁺/C₂O₄ ratio and the presence of citric acid in the solution affect the isomorphic capacity of lindbergite and glushinskite, the width of the transition and the equilibrium Mg/Mn ratio. The transition is accompanied by continuous morphological changes in crystals and crystal intergrowths. Given the obtained results, it is necessary to take into account in biotechnologies aimed at the bioremediation/bioleaching of metals from media containing mixtures of cations (Mg, Mn, Fe, Zn).