Conference Agenda

The presentation describes the journey from exploring basic principles in cold spraying and arising obstacles to demands in structural applications and solutions to enable applications in repair and additive manufacturing. As a powder spray technique dealing with solid impacts, cold spraying results in coatings of high purity and unique properties, not attainable by other spray methods. When impact conditions exceed critical velocities, bonding of solid particles is enabled by high strain rate deformation and associated heating, which in consequence by thermal softening then leads to localized adiabatic shear instabilities at particle interfaces. As shown by modelling and experiments, properties of the deposit improve with increasing the ratio between individual particle impact velocity and critical velocity at attained impact temperature. By well-tuned impact conditions, electrical and thermal conductivities as well as mechanical strengths similar to those of respective bulk material could be achieved, enabling applications in serial production.

However, new applications in structural parts by cold spray additive manufacturing and repair demand for further developments. Cold sprayed deposits are highly work hardened and still contain non-bonded interfaces as microcracks, both contributing to rather limited ductility and possibly reduced strength. Apart from that, deposit quality decreases with deviation from orthogonal impact angle. These challenges are so far tackled by well-tuned powder properties, primary spray parameter sets as well as by post treatments. Moreover, tuning of surface deformability and common interface strain proof as additional tool for enhancing deposit properties. To certain extent, such is applicable by secondary parameters that govern the surface temperature by direct heating or adjusted robotics. Also externally caused deformation could offer benefits.

Optimized path planning then enables the transfer to 3D geometries in part repair. The presented concept demonstrates how to include all that into one common digital environment to enable structural part repair and additive manufacturing. By all-inclusive control, cold spraying should get ready for new applications.

Non-exhaust particulate emissions originating from braking and clutch operations are emerging as a major contributor to air pollution and are projected to account for up to 90% of road transport–related particles by 2050. In line with upcoming Euro 7 and Ambient Air Quality Directive (AAQD) regulations, there is an urgent need to develop industrial solutions capable of significantly reducing particulate matter (PM10 and PM2.5) emissions from automotive and industrial friction systems.

Advanced coating technologies, such as High Velocity Oxygen Fuel (HVOF) spraying and Gas Dynamic Cold Spraying (CS), offer significant potential for addressing this challenge through the application of wear-resistant coatings on brake discs, brake pads, and clutches. These coatings are designed to minimize wear, enhance corrosion resistance, and maintain stable frictional performance while reducing the generation of harmful ultrafine particles.

Although wear-resistant coatings have been the subject of intensive research for many years and a range of materials and technologies is already available on the market, their application to gray cast iron substrates—commonly used for key friction components—remains a significant challenge in industrial practice.

This challenge is addressed by an international EUREKA project, leveraging the expertise of research institutes and industrial partners across Portugal, Spain, and the Czech Republic to develop coating solutions, improve mechanical design, and deliver validated prototypes and scalable processes.

The presentation will introduce multiple coating variants applied to gray cast iron substrates using HVOF and CS technologies, and will provide an evaluation and comparison of selected relevant mechanical and wear properties.

In recent years Cold Spray has been getting hotter to enable the spraying of higher melting point materials. Whereas HVOF can be cooled with the addition of non-reactive auxiliary gases. This addition of non-reactive gases such as nitrogen or argon into HVOF processes is termed Warm Spray and hence the HVOF Warm Spray may replicate Cold spray in these high temperature applications. The presentation will review the benefits of Warm Spray as an innovative process for protective coatings or damage repair for both internal diameter and outer diameter applications.

In recent years, cold spraying has rapidly developed in fields of surface functionalization, repair and additive manufacturing. Micron-scale defects are one of the determining factors of deposit quality and lifetime in application. However, defect analysis often lacks a systematic characterization of defect feature, density and distribution. This study proposes a K-means based clustering method for the identification and statistical analysis of micron-scale defects in cold spray deposits based on microcopy or tomography cross sections. The method integrates image processing techniques with feature engineering to enable automatic classification of defect types through optimized feature vector selection. In addition, a binning-based statistical approach is used to quantify defect characteristics such as size distributions and proportions. A representative study was performed on cold sprayed deposits obtained using various powder materials, particle size ranges, spraying conditions, and post-treatments. The results reveal main differences and distribution patterns of micron-scale defects under various conditions, and further explore their potential impact on the performance of the deposited layers. In summary, this study provides new tools for the quantitative characterisation of micron-scale defects in cold spraying, which can help to improve the accuracy of quality assessment and provide support for material performance analysis and process optimization.

Keywords: Cold Spraying; Defect Clustering; Image Analysis; Microstructure; Porosity