A new method for fracture toughness determination of graded (Pt,Ni)Al bond coats by microbeam bend tests

Abstract

A novel method is proposed for fracture toughness determination of graded microstructurally complex (Pt,Ni)Al bond coats using edge-notched doubly clamped beams subjected to bending. Micron-scale beams are machined using the focused ion beam and loaded in bending under a nanoindenter. Failure loads gathered from the pop-ins in the load–displacement curves combined with XFEM analysis are used to calculate K _c at individual zones, free from substrate effects. The testing technique and sources of errors in measurement are described and possible micromechanisms of fracture in such heterogeneous coatings discussed.

Keywords:

• microbeam
• bond coat
• focused ion beam
• fracture toughness
• finite element modeling

Acknowledgements

We thank the Defense Research & Development Organization (DRDO), India, for funding this project. We also acknowledge Md. Zafir Alam, DMRL, Hyderabad for providing Pt-aluminide coatings for the tests and Dr A. Mahato (Mechanical Engineering, IISc) and T.S. Bhat (SUNY, Stonybrook, USA) for fruitful discussions on the FEM analysis.