Features of Microstructure Formation in the Ni–Al–W System during SHS

Abstract

New-generation superalloys based on Ni intermetallics possess high thermomechanical stability at high temperatures and are widely used in modern industry. The fabrication of such materials by self-propagating high-temperature synthesis (SHS) is advantageous over traditional metallurgical technologies due to the use of the chemical-reaction energy. The development of coatings and pads based on the NiAl intermetallic on the surface of tungsten articles during SHS is of great practical interest. In this work, experiments on the interaction of the W substrate and the Ni–Al-based melt are performed in the SHS mode. When the W substrate connects with the NiAl intermetallic during SHS, the gradient welded joint 200–400 μm in thickness having a complex structure occurs. The Ni and Al melt is formed during the SHS reaction, and surface layers of the W substrate diffuse into it. The crystallization of the dendrites of the tungsten-based phase (84‒86 at % W and 16–14 at % Ni) and dendrites of the pseudobinary NiAl-based eutectic (β phase), in which precipitates of W-containing phase smaller than 50 nm in size and needle Ni₃Al inclusions (γ') are present, occurs during cooling in the near-surface layer. The W + Ni + Ni₃Al (α + γ + γ') containing the solid solution particles based on Ni₃Al intermetallics of about 100 nm in size is revealed in the transient layer. The modification of the W substrate is modified with the formation of globular precipitations of W (α phase) in it, which considerably increases the surface area.