Abstract:
Silicone carbide sintered bodies comprising controlled porosity in the range of about 3 to 25 vol% are prepared from raw batches containing a multimodal distribution of silicon carbide particles. The silicon carbide particles are comprised of at least a first set of particles having one average grain size and a second set of particles having another average grain size larger than the first set of particles. The resulting pores in the sintered bodies are 3 to 5 microns in the largest dimension, with an aspect ratio between 1/1 and 3/1. The sintered porous bodies, when used in the form of mechanical seal members, exhibit good tribological properties.
Abstract:
Prepare hardened cermets by: forming a porous ceramic compact that contains a first, or metal component reactive, ceramic component, and a second, or substantially nonreactive, ceramic component; at least partially filling the pores with a metal component to form a metal-filled ceramic compact; exposing the metal-filled compact to an elevated temperature to form a cermet-hardening component; and cooling the resultant compact to form a hardened cermet. Laminates of hardened cermets having differing ratios of first to second ceramic components can also be formed.
Abstract:
Ceramic metal compositions are described that include a ceramic phase content of at least 60 percent by volume of said composition and a copper metal phase permeating the ceramic phase. The resulting composition is substantially fully densified, having a connected or isolated ceramic grain structure, preferably of fine B4C grains of less than 3 micrometers average diameter. The process of the invention includes, as a key element, contacting a porous article of ceramic phase with copper metal followed by heating to a temperature above that at which the copper metal melts and subjecting said article to pressure of at least 200 MPa, such that the porous body is filled with metal and the composition is substantially fully densified.
Abstract:
Metal carbides may be formed by mixing metal powder with a stoichiometric amount of graphite, compressing the same in a mould/die and then sintering. High temperatures (and may be a bonding agent) are required to effect the final step and finished product. These disadvantages are overcome by exploiting dry high energy milling to bring the starting materials into a very finely divided and reactive state, with regions of metal, carbon and metal based solid solution ranging from 3 to 100 nanometres in diameter. As an alternative source of carbon, cationic organic surfactants may be used instead of graphite in the appropriate proportion. Compacting the milled mixture, followed by sintering at lower temperatures by a margin of at least 400 DEG C, will produce very strong dense carbides at low cost. The method may be extended to include metal based composites, which also includes cermets, by incorporating an appropriate excess of metal powder(s) in the starting materials. The carbides and their metal based composites have applications in the field of abrasives, cutting tips for lathe tools, masonry drills and master alloys for steels.
Abstract:
Uniform, boron-containing ceramic powders are prepared by using an apparatus where boric oxide or a hydrate thereof and a carbon source are passed through a cooled reactant transport (6) at a temperature below the melt temperature of the reactants. The reactant transport (6) communicates with a reactor chamber (16) and includes a gas-flow space (20) along the perimeter of the transport (6). The reactants are passed to a reactor (16) having a heating means (40) where the reactants are reacted at a temperature above 1400°C. The resulting uniform, boron-containing ceramic powders are then cooled in cooling chamber (42).
Abstract:
A composite ceramic composition including a boron carbide phase and a method of forming the same. The composite ceramic composition includes a tungsten boride phase, a transition metal boride phase. The composite ceramic composition may also include a carbon disposed in solid solution with at least the tungsten boride phase and the transition metal boride phase. The transition metal boride phase may include a boride of at least one metal chosen from Cr, Nb, and Zr.
Abstract:
A fiber having an environmental barrier coating is provided that includes, in one illustrative form, a Hi Nicalon preform assembled in a tooling for chemical vapor infiltration and cleaned to remove sizing char from fibers of the Hi Nicalon preform; a ytterbium doped silicon carbide coat located over the Hi Nicalon preform; a boron nitride interface coat applied over the ytterbium doped silicon carbide coat; and a silicon carbide coat applied over the boron nitride interface coat. In another embodiment the fiber has an environmental barrier coating, comprising: a Hi Nicalon S fiber; wherein the Hi Nicalon S fiber is coated in tow form with yttrium doped silicon carbide; and a silicon doped boron nitride coat applied over the yttrium doped silicon carbide. In a third embodiment the fiber has an environmental barrier coating, comprising: a T-300 carbon fiber preform assembled in tooling for chemical vapor infiltration; alternating layers of silicon carbide and boron carbide are applied over the preform; and a silicon doped boron nitride interface coat applied over the silicon carbide coat.
Abstract:
A super-hard material is a late transition metal doped B4C ceramic. The lightweight ceramics can display Vickers Hardness in excess of 45 GPa. Transition metals, such as Ni, Co, Rh, and Pd can be doped into the boron carbide at levels up to about 2.5 %. A spark plasma sintering (SPS) of an evacuated powder of B4C and the transition metal at temperatures up to 2000 °C, and pressures of up to about 100 GPa forms a super-hard material as a body. The late transition metal doped B 4 C ceramic can be used for armor, grinding materials, thermoelectric materials, and catalysts.