Alloy Design for Advanced Processes
- Simulation-based development/optimization and microstructure design of struc-tural alloys and MMCs for beam-based additive manufacturing and joining processes
Additive manufacturing (AM) techniques such as Selective Laser Melting (SLM) or Direct Metal Deposition (DMD) have been identified as an attractive option for the manufacture of novel functional components in comparison with conventional manufacturing techniques. They allow building components with complex 3D geometries layer by layer. The very rapid consolidation of the base material in a small material volume and the achieved high solidification rates allow for the manufacture of components containing meta-stable materials which tend to decompose in conventional casting or sintering processes. At the same time, these conditions may lead to complex out-of-equilibrium microstructures, pronounced element segregation and crack formation in the bulk alloy. Despite AM of metallic materials is a commonly established processing technology, the materials science in AM is only at its infancy. We therefore try to obtain fundamental knowledge of reactions and phase transformations in rapidly solidified multi-component alloys and metal-matrix composites (MMCs) by combining sophisticated experiments with modeling and simulation approaches (Calphad/Dictra/FEM). A major research goal is to understand the material behavior during SLM and to optimize the materials with regard to the very special process conditions rather than only trying to optimize the processing parameters for a given material.
- Experimental characterization of the influence of advanced processing technologies (e.g. AM, laser welding, shape forming etc.) on the microstructure and (thermo-)mechanical properties of complex structural materials
Advanced materials processing technologies like beam-based additive manufacturing inducing repeated heating and cooling of the matrix during the layer-by-layer build-up of the specimens, or high-performance subtractive manufacturing (grinding, milling) can lead to multiple solid state and solid-liquid phase transformations of metallic alloys. By using sophisticated in-situ technologies in combination with advanced characterization methods we study the complex interplay between the materials processing technologies, their influence on the microstructures and the material properties with regard to high-performance components.
Materials of interest
- High temperature/high performance structural materials (e.g. ODS-TiAl and Ni al-loys, γ’-hardening Ni alloys)
Titanium aluminides are promising candidates for high temperature capable light-weight materials to increase efficiency and performance in aerospace and automotive applications. Oxide Dispersion Strengthened (ODS) alloys are a class of materials that offer exceptional high temperature strength, oxidation and corrosion resistance at temperatures exceeding 1,000°C, along with outstanding resistance to radiation damage. Hence, these alloys are envisioned to be used in a number of aerospace, future fossil energy and nuclear power applications. However, while the fundamental material properties are exceptionally well suited to power generation, the manufacture of components using ODS alloys are currently subject to a number of economic and technical barriers. The aim is to develop novel high temperature/high performance structural alloys that are suitable for suitable for additive manufacturing techniques.
- FeMnSi-based shape memory alloys
Low cost Fe-Mn-Si based shape memory alloys have drawn much attention during the last two decades, as a cost-effective alternative to the expensive Ni-Ti based shape memory alloys. In particular, the alloy Fe-17Mn-5Si-10Cr-4Ni-1VC (mass%), which has been developed at Empa, Switzerland, shows very promising properties with regard to potential commercial applications. This alloy has higher reverse transformation temperature and larger thermal hysteresis in comparison to the Ni-Ti based alloys, which is adequate for producing stable recovery stresses at room temperature. Furthermore, very high recovery stresses of up to 400 MPa after heating to only 160°C can be achieved without so-called ‘training’ treatment, and the alloy can be easily and cost effectively produced under standard air melting and casting condition. Because of these advantages, the alloy is expected to be applied primarily in civil and mechanical engineering, e.g. prestressing elements in civil engineering structures or coupling/clamping devices. We study the correlation between the alloy composition, the processing route, the resulting microstructure and the thermos-mechanical properties.
- Novel composite materials (e.g. Metal-diamond/cBN composites)
The general aim of the project is to systematically develop novel metal-diamond composites which are optimized with regard to the special processing conditions during SLM (rapid solidification and subsequent multiple re-heating and cooling) and to characterize them with regard to their microstructures and mechanical properties. This requires a deep understanding of the phase formation, microstructure evolution and interface reactions in the composite material during the process and the influence on the material properties.