APPARATUS AND METHOD FOR JOINING OF CARBIDE CERAMICS

Abstract

A bonding tape for joining carbide ceramic structures, wherein the bonding tape comprises: a mixture comprising carbide ceramic particles, preceramic polymer liquid, fine carbon particles and metal nanoparticles that form a eutectic liquid at temperatures below 1400° C.

Claims

1. A bonding tape for joining carbide ceramic structures, wherein the bonding tape comprises: a mixture comprising carbide ceramic particles, preceramic polymer liquid, fine carbon particles and metal nanoparticles that form a eutectic liquid at temperatures below 1400° C.

2. The bonding tape of claim 1 wherein the carbide ceramic particles comprise one or more porous preforms and wherein the preceramic polymer liquid, fine carbon particles and metal nanoparticles that form a eutectic liquid at temperatures below 1400° C. infiltrate pores in the one or more porous preforms.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0031] For the present disclosure to be easily understood and readily practiced, the present disclosure will now be described for purposes of illustration and not limitation in connection with the following figures, wherein:

[0032] FIG. 1 schematically illustrates a preferred method of the present disclosure for ceramic to ceramic joining, particularly for carbide ceramics;

[0033] FIG. 2 comprises SEM micrographs of SiC ceramics preforms (a) before infiltration, (b) infiltrated with only polymer precursor and annealed at 1200° C., (c) infiltrated according to the present disclosure with metal nanoparticle infused precursor and sintered at 1200° C.;

[0034] FIG. 3 is an x-ray diffraction pattern of SiC ceramics using Ni nanoparticles added carbide formation illustrating that highly crystalline SiC ceramics (with residual metal carbide, in the case of FIG. 3, NiC) can be produced according to the method of the present disclosure;

[0035] FIG. 4 is a schematic representation of the method of the present disclosure employed to improve additive manufacturing processes using carbides; and

[0036] FIG. 5 shows a schematic example of the process of the present disclosure in joining two carbide ceramic structures.

DETAILED DESCRIPTION

[0037] In the following detailed description, reference is made to the accompanying examples and figures that form a part hereof, and in which is shown by way of illustration specific embodiments in which the inventive subject matter may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice them, and it is to be understood that other embodiments may be utilized and that structural, logical, and electrical changes may be made without departing from the scope of the inventive subject matter. Such embodiments of the inventive subject matter may be referred to, individually and/or collectively, herein by the term “disclosure” merely for convenience and without intending to voluntarily limit the scope of this application to any single disclosure or inventive concept if more than one is in fact disclosed.

[0038] The following description is, therefore, not to be taken in a limited sense, and the scope of this disclosure is defined by the appended claims.

[0039] The present disclosure seeks to overcome these challenges through an innovative processing approach which can decrease the shrinkage of the ceramics and lower sintering temperatures in ceramic to ceramic joining, particularly for carbide ceramics. A major breakthrough according to the present disclosure is to use a mixture of pre-ceramic polymer (slurry) and metal nanoparticles. Since this mixture fills pores between larger carbide particles, shrinkage of the green body during the densification is suppressed. Moreover, a eutectic reaction between metal nanoparticles and the carbide particles forms the transient liquid phase that decreases the densification temperature. This innovation involves new carbide formulations for low temperature and/or pressureless sintering that allows for manufacturing of 1) high density carbide ceramics “as-designed” (i.e., without shrinkage and shape deformation) and 2) joining of two different ceramics parts.

[0040] New carbide formulations according to the present disclosure preferably comprise a mixture (“Precursor Mixture”) of carbide particles (such as SiC, WC, Mo2C), preceramic polymer (such as polycarbosilane), fine carbon particles and metal nanoparticles (such as Ni, Mo, Nb) that form a eutectic liquid at low temperatures.

[0041] The basic science underlying the low temperature sintering of carbide ceramics according to the present disclosure is infiltration of metal nanoparticles which create transient liquid phases that accelerate the densification of ceramics. FIG. 1 schematically illustrates a preferred method of the present disclosure for ceramic to ceramic joining, particularly for carbide ceramics. When the nanoparticle-containing ceramic Precursor Mixture liquid 15 (described above) is impregnated into the voids 13 between large carbide grains 12 in a preform 10, metal nanoparticles 14 decorate the surface of large particles 12 in the preform 10 and react with carbide pre-ceramic polymer (or slurry) 15 to form a eutectic liquid 18 at low temperature. This transient liquid 18 accelerates material diffusion and thereby promotes densification and the crystallization of the carbide ceramics 19 much below normal sintering temperature of normal carbide powder formulations. A detailed reaction mechanism within this mixture is as follows. Metal nanoparticles react to form eutectic with Si, W, or Mo in the carbide formulations to form a eutectic silicide liquid below 1400° C. The eutectic liquid provides a transport path for the coarsening of primary carbide crystals and increasing the crystallinity. The eutectic liquid equilibrates with the carbon content in the precursor 16 to form stable nickel carbide, niobium carbide or molybdenum carbide phases to remove the liquid phase. Preferably, this infiltration method of the present disclosure can be adapted to powder bed additive manufacturing processes and the processing of a bonding tape for joining of carbide ceramics.

[0042] The results from a preferred method of the present disclosure for joining ceramic particles are shown in FIG. 2. FIG. 2 comprises SEM micrographs of SiC ceramics preforms (a) before infiltration, (b) infiltrated with only polymer precursor and annealed at 1200° C., (c) infiltrated according to the present disclosure with metal nanoparticle infused precursor and sintered at 1200° C.

[0043] The reaction between metal nanoparticles and SiC precursor promotes the crystallization of the amorphous SiC matrix and the relative density of polymer derived SiC ceramics can be increased up to 96%. FIG. 2 (a) shows the microstructure of a porous SiC preform consisting of crystalline SiC grains approximately 10 μm in size, before the liquid precursor was infiltrated. SiC particles were first dry pressed and partially sintered without any sintering agent. After the pores were filled with the precursor and thermally treated at 1200° C., very different microstructures were found and an effect of metal nanoparticles was clearly observed. Without the metal nanoparticles in the liquid ceramic precursor, rounded SiC grains evolved from the precursor matrix and the porous region became occupied by amorphous SiC as shown in FIG. 2(b). In contrast, FIG. 2(c) shows that SiC ceramics from the metal-nanoparticle infused precursor are composed of faceted SiC grains and the intergranular phase almost disappears. A mechanism for the metal nanoparticle assisted crystallization and densification of SiC ceramic is schematically shown in FIG. 1. Metal nanoparticles deposited on the surface of SiC preform reacts with SiC precursor 16 and forms the transient liquid 18. Then, Si and C diffuse through the liquid phase and attach on the surface of SiC grains 12, which thereby removes the intergranular amorphous phase at low temperature.

[0044] FIG. 3 is an x-ray diffraction pattern of SiC ceramics using Ni nanoparticles added carbide formation illustrating that highly crystalline SiC ceramics (with residual metal carbide, in the case of FIG. 3, NiC) can be produced according to the method of the present disclosure.

[0045] As shown in FIG. 4, the method of the present disclosure preferably may be employed to improve additive manufacturing processes using carbides. As shown in FIG. 4, an SiC Precursor Mixture 40 containing metal nanoparticles (not shown) and fine carbon particles 42 is applied to a dry bed or structure 41 comprised of large SiC particles 43. Another layer of large SiC particles 43 is applied over SiC Precursor Mixture 40 and the whole structure is heated to around 1200° C. to 1400° C. which causes rapid formation of liquid silicides, liquid sintering and then the formation of more stable and refractory carbides and crystalline SiC 45. One advantage of such process is that complex shapes may be processed via low temperature sintering of SiC (or other carbide ceramics) without shape change or shrinkage.

[0046] FIG. 5 shows an example of the process of the present disclosure in joining two carbide ceramic structures. Here, the method of the present disclosure preferably may be employed to fabricate a new flexible silicon carbide bonding tape 54 which can be placed between silicon carbide surfaces 52 to be joined together via heating at temperatures below 1400° C. and achieve densification and bonding without shrinkage. First, a slip will be made from a preferred carbide formulation such as the Precursor Mixture described above. The slip is formed into a thin tape 54 by tape casting and drying. Then the tape 54 with a preferred thickness of 0.1 mm-5 mm will be infiltrated with additional carbon-rich SiC Precursor Mixture and placed between two bulk carbide ceramic structures 52. Heating of this whole structure 58 leads to the joining of the two parts 52 according to the above described mechanism of the present disclosure to achieve good densification and bonding without shrinkage.

[0047] It will be readily understood to those skilled in the art that various other changes in the details, components, material, and arrangements of the parts and methods which have been described and illustrated in order to explain the nature of this disclosure may be made without departing from the principles and scope of the disclosure as expressed in the subjoined claims.

[0048] In the foregoing description of preferred embodiments of the present disclosure, various features are grouped together in a single embodiment to streamline the disclosure. This method of disclosure is not to be interpreted as reflecting an intention that the claimed embodiments of the disclosure require more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive subject matter lies in less than all features of a single disclosed embodiment. Thus, the following claims are hereby incorporated into the foregoing description, with each claim standing on its own as a separate embodiment.