HIGH TEMPERATURE STRENGTH OF COMPOSITE MATERIAL WITH CELL STRUCTURE ON THE BASIS OF Ni<sub>3</sub>Al INTERMETALLIDIDE

Abstract

The powder metallurgy method was used to obtain materials in the form of a single-phase alloy based on Ni3Al and in the form of composite material (Ni3Al + W) with cell structure based on it. The structural unit of the composite material was a round granule (grain) with average size of 25 μm from nickel alloy, on which the continuous tungsten coating with thickness of ~0.4 μm was deposited by chemical vapor deposition. Compression tests at room temperature have shown that the yield stress of composite material (Ni3Al + W) with cell structure at temperatures of 20 – 1000 °C is higher than of single-phase Ni3Al-based alloy (up to 1.7 times), but at higher test temperature the yield strength of the composite is compared with the yield strength of the nickel alloy. The specific yield strength (that is, normalized for the density of 7.8 g/cm3 for the alloy and of 9.5 g/cm3 for the compo site) behaves similarly. At the temperature of 1300 °C, single-phase Ni3Al-based alloy exhibits solid-liquid behavior under compression. Creep tests were carried out for compression under vacuum at temperatures of 1000 – 1200 °C. Using the pair and parametric methods of mathematical analysis of creep processes according to Hollomon, regression equations of creep rate, stress and temperature of the test were obtained. The ultimate strength of creep for the given tolerances for steady-state creep rate and inverse values were calculated. It is shown that at all test temperatures the composite material has lower creep rate (up to 7 times) and higher ultimate strength of creep (up to 2.5 times) than the nickel alloy on which it is based. Creep activation energies of the materials studied are determined using the exponential law of coupling of experimental values. The creep activation energy for the nickel alloy found is close to the activation energy of nickel self-diffusion in Ni3Al and materials based on it (230 ÷ 310 kJ/mol), and for the composite – to self-diffusion activation energy of tungsten (503 kJ/mol).