Design Of Fe-based Cemented Carbides With Enhanced Toughness

Abstract:

Fe-based cemented carbides are characterised by their inferior toughness compared to Co-based cemented carbides. Co-based materials can undergo FCC to HCP martensitic transformation in the binder. This phase transition consumes crack energy, providing high values of combined toughness and hardness, which are unreachable for other binders without such transformation. In this work a strategy to overcome this problem by proper alloy design is presented. We propose Fe-based binders with controlled martensitic transformation (FCC to BCT/BCC), providing hardness and fracture toughness combinations superior to traditional Co-based cemented carbides. These new compositions, based on the Fe-Ni-Cr system, are potential candidates for cutting tool or wear part materials.

Comparison Of The Sintering Behavior Of Different WC-10 Wt.%Co Recycled Powders: Zinc Reclaim (ZR) Vs. Oxidation-reduction-carburization (ORC) Processes

Abstract:

Sintering shrinkage in recycled WC–Co hardmetal alloys has been investigated for two recycling routes: zinc reclaim and oxidation–reduction–carburization (ORC), and compared with virgin reference materials. Recycled powders are strongly agglomerated and exhibit significantly lower specific surface areas, making milling essential to enhance sinterability. Two stages are identified during solid-state sintering: up to 1000 ºC, densification is controlled by oxide content and specific surface area, while lattice strain plays a minor role. At higher temperatures, solid-state shrinkage kinetics become similar for virgin and recycled materials due to defect annealing and reduced surface area. Liquid-phase formation accelerates densification in virgin alloys, whereas an opposite trend is observed in recycled powders—especially ORC—due to a shift of solid-state diffusion to higher temperatures, which promotes overlap with liquid-phase rearrangement and solution–reprecipitation processes.

Processing Of Plasma Facing Components For Fusion Power Plants By Field Assisted Sintering Technologies

Abstract:

Self-passivating Metal Alloys with Reduced Thermo-oxidation (SMART) alloys are novel materials for fusion power plants due to their superior oxidation resistance in the case of a Loss of Coolant Accident (LOCA). Mechanical alloying of tungsten (W)-Chromium (Cr)-Yttrium (Y)-Zirconium (Zr) SMART materials with subsequent field assisted sintering (FAST/SPS) is a standard route for processing they alloys. For manufacturing of plasma-facing components, joining SMART alloys with a structural material of Eurofer 97 steel containing cooling channels is a promising approach. However, making stable joints from these two materials is challenging due to their large difference in the coefficient of thermal expansion and high thermal stress. In the present work, an experimental study of direct joining SMART and Eurofer 97 is presented. Parameter optimization shows the trade-off between the formation of an intermetallic phase at the interface and the thickness of SMART-Eurofer 97 diffusion zone with varying thickness. As expected, the thickness of the intermetallic phase and diffusion zone increases as the joining temperature increases from 800 °C to 1000 °C. Ongoing studies aim at qualifying the joints using heat-flux tests and mechanical testing. In addition, temporary spacer materials were used to integrate cooling channels in the steel backbone directly.

Alloy Development Of Sinter-based Iron-cobalt Electrical Steel Sheets

Abstract:

FeCo alloys exhibit the highest saturation polarization among industrial soft magnetic materials, enabling compact, high-flux components for aerospace and robotics. Conventionally, FeCo electrical steel sheets containing about 2 wt.% V are produced by rolling and punching. V reduces brittleness, improves machinability, and increases electrical resistivity to lower eddy-current losses, but at the expense of higher coercivity. Here, we present metal powder screen printing for near-net-shape fabrication of thin FeCo sheets from elementary powder mixtures combined with a master alloy. This approach enables resistivity tailoring by targeted alloying while keeping the V content low to further improve soft-magnetic performance. The influence of different powder types and compositions on densification, and the resulting magnetic and electrical properties is demonstrated, identifying critical challenges and pathways toward thin FeCo sheets with reduced high-frequency losses.

The 2-Powder Method For Producing Resource-saving And More Sustainable NdFeB Magnets

Abstract:

The 2-powder method (2PM) for manufacturing NdFeB magnets, patented by TU Darmstadt and further developed by Fraunhofer IWKS, offers the possibility of significantly reducing the criticality of rare earth-based magnets. Heavy rare earths (HREs) such as Dy or Tb are used in particular for applications in electromobility to ensure temperature stability of the magnets. In powder metallurgical production using the 2PM, a specific microstructure is set, whereby the HREs are only located in the outer areas of the magnetic grains. Further, the 2PM allows the utilization of the less-critical light rare earth Ce. In contrast to the conventional grain boundary diffusion process, the 2PM enables the production of much larger magnets (>10 mm). In our study, the magnetic properties of magnets with different RE contents were analyzed and their microstructure was investigated using high-resolution secondary electron microscopy. Finally, the improved sustainability of the 2PM was demonstrated due to life-cycle- assessment.

Low-temperature deposition of magnetite Fe3O4 passivation layers as an alternative to steam treatment to prevent stress corrosion cracking

Abstract:

Stress Corrosion Cracking (SCC) and Hydrogen Embrittlement (HE) are serious concerns for high-strength materials, e.g. martensitic (porous and fully dense) sintered steels, when a critical combination of a sensitive material, a corrosive electrolyte and a static load-induced tensile stress s occurs simultaneously. Atomic hydrogen H is emitted from the electrolyte. Due to its high diffusivity D and the exclusive existence of the Gorsky-effect, atomic hydrogen H diffuses particularly into dilatated metal lattice domains, especially into domains having a step stress gradient Ds/Dx and a high stress triaxiality T. The resulting loss of the cohesive strength s_th and the reduction of the yield limit s_y lead to time-delayed and spontaneous brittle failure. It is known that passivation layers, e.g. a magnetite Fe₃O₄ passivation layer generated during a steam treatment, affect the dissociation of molecular hydrogen H₂ into atomic hydrogen H and its adsorption and absorption. Unfortunately, the high processing temperature during the steam treatment J_st is not compatible with a martensitic microstructure. Therefore, a low-temperature deposition process was developed (hot browning).