In this paper, we obtain samples of composite materials with a layered niobium-based matrix unidirectionally reinforced with single-crystal sapphire fibers using the solid-phase method of diffusion welding. Sapphire fibers are obtained by the Stepanov method (EFG). As a result of tests, the dependences of the strength of such fibers on the length are obtained for the first time. The strength values correspond to the global level. X-ray spectral microanalysis of the obtained materials is performed. The formation of solid solutions and intermetallic compounds of the Nb-Al system during composite-structure formation is established. Strength tests (500–700 MPa) are carried out and the effective surface energy of fracture of the composites is determined ((9–49) × 10³ J/m²), and their correlation with the fabrication modes is established. The features of the fracture structure of such materials and the processes inhibiting its fracturing under load are studied.

The internal crystallisation method (ICM) allows producing bundles containing hundreds and thousands of the fibres of a limited length. It is shown in the present paper that ICM can be used to produce fibres composed of a sapphire matrix and inclusions of calcium hexaaluminate. The fabrication of such composite fibres is described in the present paper. An effect of the calcium hexaaluminate inclusions in sapphire fibres is evaluated by testing model composites with brittle molybdenum matrices. The critical stress intensity factors of composite-fibre/molybdenum-matrix specimens are higher than those of specimens reinforced with sapphire fibres. The model specimens reveal non-linear stress/strain behaviour. The results of this work show the effectiveness of composite fibres as a reinforcement for brittle matrices.

Layered composite materials with alternating layers of a solid solution of aluminum in nickel and intermetallic Ni-Al compounds are obtained. The evolution of the composite structures depending on...

By the internal crystallization method oxide composite fibers containing high-strength sapphire and hexaaluminates of calcium, lanthanum or barium are obtained. The presence of “weak” planes in the layered structure of hexaaluminates provides cracks inhibition. The dependences of the ultimate strain (strength) of the fibers of these compositions on the length are obtained. The positive effect of such fibers was evaluated on composites with brittle matrices of recrystallized molybdenum and nickel-aluminum intermetallic. The fracture toughness of composite materials with such fibers significantly exceeds the fracture toughness of composites with sapphire fibers. The composites were tested in the temperature range of 20– 1400 °C and showed non-brittle behavior under load, and their strength and fracture toughness correspond to the requirements for structural materials of this kind. The structure of fibers and composites was also studied by electron microscopy.

Single-crystal sapphire fibers are obtained by the Stepanov/edge-defined film-fed growth (EFG) method. The procedure for obtaining them is described. Mechanical testing of the fibers is carried out according to the presented scheme, and the dependences of the limiting deformation and strength of the fibers on the length are determined. The dependences are of the power-law type and decrease with the length of the fibers. The strength of the obtained fibers corresponds to the international standard and meets the conditions for their use as reinforcing fibers for high-temperature composite materials. From blanks containing layer-by-layer unidirectionally arranged sapphire fibers, niobium powder, and metal foils of molybdenum and aluminum, layered-fibrous composites are obtained by solid-phase diffusion welding under load. Using scanning electron microscopy with X-ray analysis, the structure of the composites is studied. It is found that, in addition to the initial components, it includes intermetallic compounds of niobium, molybdenum, and aluminum, as well as solid solutions of these metals formed during the technological process. As a result of mechanical testing of the composite samples, deformation curves of load–deformation dependences are obtained, which, together with the developed fracture surfaces, indicate the nonbrittle nature of the fracture of composites containing brittle components. The dependences of the strength of the composites on temperature in the range of 20–1400°C are obtained, which meet the requirements for high-temperature structural materials of this kind.