Study of fracture behaviour of bond coats on nickel superalloy by three-point bending of microbeams

• Published in: Surface & coatings technology Vol. 204; no. 5; pp. 586 - 592
• Main Authors: Potnis, Prashant, Holtzinger, Jennifer, Das, Dipak, Jayaram, Vikram, Biswas, S K
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 15.12.2009; Elsevier
• Subjects: Applied sciences; Bond coat; Cross-disciplinary physics: materials science; rheology; Exact sciences and technology; Fracture toughness; Fractures; Materials science; Mechanical properties and methods of testing. Rheology. Fracture mechanics. Tribology; Metals. Metallurgy; Physics; Surface treatments; Three-point bending; Bond coat; Three-point bending; Fracture toughness; Ruptures; Mechanical properties; Surface treatments; Superalloys
• ISSN: 0257-8972; 1879-3347
• DOI: 10.1016/j.surfcoat.2009.08.038

A microbeam testing geometry is designed to study the variation in fracture toughness across a compositionally graded NiAl coating on a superalloy substrate. A bi-material analytical model of fracture is used to evaluate toughness by deconvoluting load–displacement data generated in a three-point bending test. It is shown that the surface layers of a diffusion bond coat can be much more brittle than the interior despite the fact that elastic modulus and hardness do not display significant variations. Such a gradient in toughness allows stable crack propagation in a test that would normally lead to unstable fracture in a homogeneous, brittle material. As the crack approaches the interface, plasticity due to the presence of Ni 3Al leads to gross bending and crack bifurcation.