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Adapting conventional sintering (CS) techniques of monolithic ceramics for the production of oxide ceramic matrix composites (Ox-CMCs) comes along with a few drawbacks, such as fiber degradation. Thus, the applicability of two-step sintering (TSS) for the production of Ox-CMCs based on Nextel™ 610 fibers and porous alumina matrix is investigated in this study for the first time. Uniaxial tensile tests were performed to evaluate the performance of mini-composites produced by TSS and compared with those produced by CS. Parameters known for influencing the mechanical behavior of the mini-composites, such as grain size, porosity, shrinkage, as well as matrix properties, were analyzed. Both sintering techniques resulted in similar grain size distributions, whereas TSS showed higher total porosity and lower amount of sintering-induced cracks. As a result, TSS samples showed a higher tensile strength of 230±27 MPa when compared to 133±8 MPa for CS. In general, it was observed that most of the densification happens during the first phase of TSS, while the matrix is slowly strengthened during the second step. Therefore, the reported TSS process is a very promising and easy-to-apply heat treatment for producing Ox-CMCs with controlled microstructure.

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The production of complex‐shaped all‐oxide ceramic matrix composites (Ox‐CMC) is somewhat restricted by their current processing methods, as well as by the lack of applicable joining techniques. Thus, we present a new method for joining Ox‐CMCs based on the gelation of slurries with the polysaccharide polymer alginate. For this investigation, Nextel 610/alumina‐zirconia composites were produced using alginate as binder and aluminum acetate as gelling agent. The joining capabilities of this technique were investigated with microstructural analyses and single‐lap compression shear tests. For that, a slurry‐containing alginate was used to join two composite plates at different stages of the processing: gel state, dried green body and after sintering. Joining composites plates in their gel or green state was successful as the joints showed shear strength values similar to the interlaminar shear strength of the composites plates. The quality of the joints was attributed to the interactions between the alginate chains of the composite plates and the joint. We also show that even the joining of already sintered Ox‐CMCs is feasible. However, densification cracks and lower shear strength are observed for such cases.

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