High-temperature tribology plays an important role in many engineering applications such as metal forming operations and aerospace industry. Several problems in hot-metal forming of high strength steels occur such as oxidation of tool and workpiece surfaces, increased wear of tools and scaling of workpiece. Moreover, operations at elevated temperatures can significantly influence frictional behavior of tool steels. Present research attempts to analyze experimentally and understand tribological behavior of AISI H11 and AISI H13 under dry conditions at room temperatures. High velocity oxy-fuel (HVOF) thermal spray NiCrBSi coating was developed on tool steels. The room-temperature wear performance of uncoated and coated tool steels was evaluated on pin-on-disc tribometer in the laboratory. In-depth analysis of exposed as-sprayed samples was examined with X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS).

Superplastic forming (SPF) is an advanced sheet manufacturing process typically used for low- volume, high-value products. SPF dies made from refractory castables have a lower production cost than metal dies, but their brittle nature is a limiting factor. This work investigates surface degradation mechanisms in ceramic dies and how they are affected by the application of thermal spray coatings. Among the more notable accomplishments of the study is the development of a test rig that simulates die-part interface conditions during superplastic forming and monitors die wear, making it possible to predict ceramic die lifetime for different coatings.

Deep-drawing is a widely used sheet metal forming process in the aircraft and automotive industry. The manufacturing of modern parts with complicated shapes and curvatures requires forming tools with highest shape accuracy even at complex surface geometries. However, the application of novel, high-strength sheet metals combined with a continuous increase in productivity impose high tribological demands on forming tools and finally lead to increasing wear. In order to minimize the high costs for the repair and maintenance of such tools it is crucial to enhance their service life by an appropriate surface modification, which is able to preserve the high shape accuracy. Conventional coatings obtained by thermal spraying of coarse grained feedstock materials are not suitable to achieve this aim. In this collaborative study, the feeding and HVOF spraying of WC-Co submicron powders (- 8 + 1 µm) have been investigated to manufacture superfine structured, wear resistant near-net-shape coatings with improved macroscopic properties and smooth surfaces. Special equipment for the powder feeding and a novel HVOF flame spraying system designed by Thermico (optimized for the processing of fine-scaled powder fractions) have been employed. Correlations related to the process dynamics at varying HVOF gas compositions, the thermokinetic particle behavior in-flight and corresponding coating properties have been analyzed.

The electromagnetic forming (EMF) is a process for forming sheet metals or thin metal tubes with a high electrical conductivity such as Al-alloys. Extremely high forming velocities can be achieved by employing this process based on pulsed electro-magnetic fields. To exploit the advantages of this process in forming sheet materials with a limited electrical conductivity thermal spraying methods have been applied. The essential requirement is based on the design and development of an electrically conductive layer system, which can act as a “driver“ for materials to be formed. Therefore, the layer has to fulfil high demands on its density as well as on the adhesion to the substrate. In this contribution a new coating concept for thin sheets to be electromagnetically formed is presented. The influences of pre-cleaning processes, coating parameters, layer properties and sheet thickness on the deformation are scrutinized. Accompanying metallographic, mechanical and microscopic investigations of the coated layers help to understand the mechanisms of materials behaviour during EMF processes.

This paper assesses the potential of thermal spraying in the context of rapid production tooling. The tooling described, which is intended for sheet metal forming, overcomes the limitations of rapid tooling techniques by leveraging the benefits of rapid prototyping and thermal spray technologies. Paper text in German.