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

✍ Scribed by Prashant Potnis; Jennifer Holtzinger; Dipak Das; Vikram Jayaram; S K Biswas

• Book ID: 104094628
• Publisher: Elsevier Science
• Year: 2009
• Tongue: English
• Weight: 750 KB
• Volume: 204
• Category: Article
• ISSN: 0257-8972
• DOI: 10.1016/j.surfcoat.2009.08.038

✦ Synopsis

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 3 Al leads to gross bending and crack bifurcation.