Vikram Jayaram

Indian Institute of Science, Department of Materials Engineering, Bangalore 560012, India

Small scale test methods are now available to probe mechanical behaviour in uniaxial loading, bending and fracture for the determination of location-specific mechanical properties. This talk focuses on materials and length scales that are relevant to industrial applications in coatings, weldments and residual life assessment of samples extracted from high temperature components. The first example is one of bond coats on superalloys where we demonstrate the use of micro scale tests to study the ductile-brittle transition as a function of platinum content and the variation in fracture toughness across a 0.1 mm graded Pt-Ni-Al diffusion aluminide. A new method is presented using a clamped beam under central loading that leads to stable crack propagation under load control and allows the determination of R-curves and fatigue crack growth with sub-micrometre spatial resolution. The second example describes our efforts to adapt the age-old technique of bending creep to small size cantilever testing for creep evaluation of steam turbine components from which extracted specimens need to be as small as possible. It transpires that the assumption of steady state creep characterized by a single stress exponent allows a good match to be established between bending and uniaxial creep parameters, while length scale effects start to appear below a critical size of ~ 1 mm in coarse grained aluminium. Challenges in using such creep data under non-steady state conditions for predictions based on uniaxial parameters will be discussed.