TITLE: Joining Technology for Advanced Ceramics. Perspectives, Problems and Opportunities

Technical Review, 96 pages, PATRIA, Inc., 1994.

By W.A. Zdaniewski

State of the art of joining structural ceramics has been critically assessed both from scientific and technological viewpoint. Commonly used, unconventional and emerging joining techniques and concepts have been identified, and potential opportunities for further development outlined. Pressure-assisted diffusion bonding, glass and eutectic joining, in situ joining by ceramic processing (nitridation), vapor-deposition, molecular adhesion, etc., are some of the joining concepts discussed. In broad terms, joining of structural ceramics can be accomplished by processes utilizing temperatures in excess of melting temperature, down to those relying on room temperature processing. Solid, liquid or vapor phases can serve as adhesive donors. Special attention to surface adhesion is given. A unified theory of molecular adhesion and mechanical strength is as yet lacking, but recent theoretical developments suggest that adhesion of solids might be regarded as the inverse of fracture phenomena. It is suggested that concerted efforts of scientific and engineering communities are required to achieve technological breakthroughs.

TITLE: Effect of Joint Thickness and Residual Stresses on the Properties of Ceramic Adhesive Joints, Part I & Part II Experimental

J. Amer. Ceram. Soc. 70 [2] 110-118, 1987.

By W.A. Zdaniewski, H.P. Kirchner, A. Segall and J.C. Conway.

The finite element analysis was used to determine the stress distribution in adhesive joints prepared using alumina adhesives and silicate glass adhesives with varying thicknesses and thermal expansion coefficients. These analyses, together with the results of literature analyses for joints subjected to externally applied loads, aided in interpreting the experimental observations which are descibed in Part II of the paper.

TITLE: Joining of Alumina Ceramics by Inducing Localized Reducing Conditions

J. Amer. Ceram. Soc. 70 [1] C4-6, 1987.

By W.A. Zdaniewski and H.P. Kirchner.

Alumina ceramics were joined by hot-pressing with polystyrene or mica sheets at temperatures of 1250º or 1350º C. The polystyrene decomposed during hot pressing, creating reducing conditions in the joints which enhanced interfacial diffusion and bonding. Measured fracture toughness and flexural strength of such joints approached values for monolithic alumina. Joints prepared under similar conditions but without polystyrene showed much lower K_IC and strength values.

TITLE: Toughening of Ceramic Adhesives for Structural Ceramics

Final Report, Ceramic Finishing Company, State College, PA. November, 1984.

By H.P. Kirchner, W.A. Zdaniewski, J.C. Conway and A. Segall.

TITLE: Crystallization Toughening of Alumina Joints

Advanced Ceram. Mater. 2 [3A] 204-208, 1987.

By W.A. Zdanniewski, H.P. Kirchner and P.M. Shah.

Alumina ceramics were joined at high temperatures using powdered glasses or gels as adhesives capable of crystallization. The fracture toughness of the joints was improved by subsequent heat treatment leading to precipitation of crystalline phasees. Measured K_Ic values increased from values typical of glasses to between 1.1 and 2.3 MPam^1/2. The increases were limited by only partially controlled interfacial reactions with the alumina, and by residual porosity in the joints.

TITLE: Toughening of a Sintered Alumina by Crystallization of the Grain Boundary Phase

Advanced Ceram. Mater. 1 [1] 99-103, 1986.

By W.A. Zdaniewski and H.P. Kirchner .

An alumina ceramic with an amorphous grain-boundary phase was heat-treated to crystallize the grain-boundary material. The fracture toughness of the as-received and heat-treated materials, which was measured by the indentation method, showed that fracture toughness is increased by heat-treatment. X-ray diffraction analysis showed the presence of a new crystalline phase or phases after heat treatment and increased strain in the alumina. Fractographic investigations indicated increased crack deflection during intergranular fracture in the surface of the heat-treated alumina and increased surface roughness (waviness) in the interior. The toughening mechanism may involve crystallization of grain boundary material and formation of fracture-resistant agglomerates.

TITLE: Effect of Grain Boundary Oxidation of SiC on Fracture Toughness

J. Amer. Ceram. Soc. 70 [8] 548-552, 1987.

By W.A. Zdaniewski and H.P. Kirchner.

Hot-pressed SiC was oxidized at temperatures from 900º C to 1300º C, and the fracture toughness was determined by the indentation method. The apparent fracture toughness of the surface layers increased with the oxidation T and then decreased. The observed variations in apparent fracture toughness were consistent with earlier observations of strength variations in oxidized SiC. Some specimens were fractured, and the fracture surfaces were characterized. Based on these observations, the variations in fracture toughness were attributed to variations in residual compressive stresses induced by oxidation.