David Ulrich Furrer

Ni-based superalloys for turbine discs

Superalloys have been developed for specific, specialized properties and applications. One of the main applications for nickel-based superalloys is gas-turbine-engine disc components for land-based power generation and aircraft propulsion. Turbine engines create harsh environments for materials due to the high operating temperatures and stress levels. Hence, as described in this article, many alloys used in the high-temperature turbine sections of these engines are very complex and highly optimized.

Processing of nickel-base superalloys for turbine engine disc applications

Nickel-base superalloys used for critical rotating disc components have evolved into advanced, high performance, application-specific materials. The designs of modern turbine machinery applications have dictated a shift in material performance requirements from an emphasis solely on burst and creep strength to the addition of minimized fatigue crack growth rates and component residual stresses. Increased component performance has often resulted in material and process changes that are accompanied by subsequent manufacturing difficulties. For example, increased alloy content has pushed the primary processing route from ingot metallurgy toward powder metallurgy methods. The processing routes required in the manufacture of these materials are equally as complex as the alloys themselves and have a strong influence on the resultant properties of turbine engine discs. Challenges still lie ahead for material and process engineers working on these materials. Both turbine engine design changes and market pressures will mandate novel materials and processes that allow for cost effective solutions for the harsh environment applications these nickel-based superalloys have evolved to fill.

Combined Hydrophobicity and Mechanical Durability through Surface Nanoengineering

This paper reports combined hydrophobicity and mechanical durability through the nanoscale engineering of surfaces in the form of nanorod-polymer composites. Specifically, the hydrophobicity derives from nanoscale features of mechanically hard ZnO nanorods and the mechanical durability derives from the composite structure of a hard ZnO nanorod core and soft polymer shell. Experimental characterization correlates the morphology of the nanoengineered surfaces with the combined hydrophobicity and mechanical durability, and reveals the responsible mechanisms. Such surfaces may find use in applications, such as boat hulls, that benefit from hydrophobicity and require mechanical durability.

Making the Case for a Model-Based Definition of Engineering Materials

For over 100 years, designers of aerospace components have used simple requirement-based material and process specifications. The associated standards, product control documents, and testing data provided a certifiable material definition, so as to minimize risk and simplify procurement of materials during the design, manufacture, and operation of engineered systems, such as aerospace platforms. These material definition tools have been assembled to ensure components meet design definitions and design intent. They must ensure the material used meets “equivalency” to that used in the design process. Although remarkably effective, such traditional materials definitions are increasingly becoming the limiting challenge for materials, design, and manufacturing engineers supporting modern, model-based engineering. Demands for cost-effective, higher performance aerospace systems are driving new approaches for multi-disciplinary design optimization methods that are not easily supportable via traditional representations of materials information. Furthermore, property design values having the definitions based on statistical distributions from testing results can leave substantial margin or material capability underutilized, depending on component complexity and the application. Those historical statistical approaches based on macroscopic testing inhibit innovative approaches for enhancing materials definitions for greater performance in design. This can include location-specific properties, hybrid materials, and additively manufactured components. Development and adoption of digital and model-based means of representing engineering materials, within a design environment, is essential to span the widening gap between materials engineering and design. We believe that the traditional approach to defining materials by chemistry ranges, manufacturing process ranges, and static mechanical property minima will migrate to model-based material definitions (MBMDs), due to the many benefits that result from this new capability. This paper reviews aspects of the challenges and opportunities of model-based engineering and model-based definitions.

Role of Microstructure in Predicting Fatigue Performance

In this paper a methodology for prediction of fatigue crack initiation based on a representative scan of the material’s microstructure is presented. The model utilizes local energy barriers against slip at the atomistic and continuum levels to construct an energy balance for the stability of a persistent slip band, which is a precursor to crack initiation. Scatter in the fatigue results is predicted based on various realizations of the material’s measured microstructure and crystallographic texture.