FEATURES OF MICROSTRUCTURE FORMATION IN NI–AL–W SYSTEM DURING SHS

Abstract

New generation superalloys based on Ni intermetallics exhibit high thermomechanical stability at high temperatures and are widely used in modern industry. The production of such materials by self-propagating high-temperature synthesis (SHS) has an advantage over traditional metallurgical production methods due to reaction heat utilization. The creation of coatings and surfacing based on NiAl intermetallic on the surface of W products in the SHS process is of great practical interest. This paper describes experiments on the interaction of a W substrate and a Ni–Al-based melt in the SHS regime. When connecting the W substrate to the NiAl intermetallic during the SHS process, a gradient welded joint with a thickness of 200–400 μm with a complex structure is formed. During the SHS reaction, the formation of a Ni and Al melt occurs, in which surface layers of the W substrate are diffused. During cooling, the tungsten-based phase dendrites (84–86 at% W and 16–14 at% Ni) and the NiAl-based pseudobinary eutectic dendrites (β-phase) which include W-containing phase precipitates of less than 50 nm in size and needlelike Ni3Al inclusions (γ′-phase) crystallize in the subsurface layer. A structured ternary eutectic W + Ni + Ni3Al (α + γ + γ′) containing particles of a solid solution based on Ni3Al intermetallic of about 100 nm in size was found in the transition layer. The paper demonstrates a modification of the W substrate surface with the formation of globular W precipitates (α-phase), which significantly increases the surface area.