No abstract

Thermoplastics combine high freedom of design with economical mass production. Metallic coatings on thermoplastics enable power and signal transmission, shield sensitive parts inside of housings and can reduce the temperature in critical areas by functioning as a heat sink. The most used technical thermoplastics are polyamides (PA), while the described use cases are often realized using Cu. Consequently, several studies tried to apply copper coatings on PA substrates via thermal spraying; so far, this combination is only feasible using an interlayer. In this study, a new approach to metallize thermoplastics via thermal spraying based on validated state-of-the-art predictions of the thermoplastics’ material response at relevant temperatures and strain rates is presented. Using these predictions, high velocity wire-arc spraying was selected as coating process. Furthermore, the process parameters were adapted to realize a continuous coating while also roughening the substrate during coating deposition. The resulting Cu coating on PA6 had a sufficiently high coating adhesion for post-treatment by grinding. The adhesion is achieved by in situ roughening during the coating application. The results indicate that different process parameters for initial layer deposition and further coating buildup are required due to the low thermal stability of PA6.

The level of residual stresses is of great importance for many applications. In this work, the two established residual stress analysis methods x-ray stress analysis and incremental hole-drilling combined with electronic speckle pattern interferometry are compared. Each stress analysis method has its specific limitations. Furthermore, the residual stress state of a material is influenced by its processing history. To compare both methods, aluminum-based specimens (AlCu6Mn, AlZn5.5MgCu) with different processing histories were investigated. Measurements with both methods were conducted on the same specimens and on the same measurement spots. Highest stress levels were found in the mechanically machined specimen, while heat treatment via tempering or deposition welding shows reduced stress levels inside of the specimens. In case of cold spraying, the stresses in the feedstock material are considered negligible. In contrast, cold-spray coatings deposited on construction steel substrate exhibited tensile stresses, which relax over time at room temperature.

Thermal spraying processes include complex nonlinear interdependencies among process parameters, in-flight particle properties and coating structure. Therefore, employing computer-aided methods is essential to quantify these complex relationships and subsequently enhance the process reproducibility. Typically, classic modeling approaches are pursued to understand these interactions. While these approaches are able to capture very complex systems, the increasingly sophisticated models have the drawback of requiring considerable calculation time. In this study, two different Machine Learning (ML) methods, Residual Neural Network (ResNet) and Support Vector Machine (SVM), were used to estimate the in-flight particle properties in plasma spraying in a much faster manner. To this end, data sets comprising the process parameters such as electrical current and gas flow as well as the in-flight particle velocities, temperatures and positions have been extracted from a CFD simulation of the plasma jet. Furthermore, two Design of Experiments (DOE) methods, Central Composite Design (CCD) and Latin Hypercube Sampling (LHS), have been employed to cover a set of representative process parameters for training the ML models. The results show that the developed ML models are able to estimate the trends of particle properties precisely and dramatically faster than the computation-intensive CFD simulations.

Various feedstocks are available for the thermal spraying of metallic glasses, which are often alloyed with high amounts of cost-intensive elements. In previous steps, a novel, economic Fe-based metallic glass alloy with a high Si content has been developed using melt spinning. The aim of this work is to investigate the application of the alloy using the high-velocity arc spraying (HVAS) process. On this basis, four cored wires are manufactured with the aim of maximizing in situ intermixing and amorphous phase formation during the spraying process. The cross sections of the resulting coatings are analyzed by light microscopy, scanning electron microscopy and Vickers hardness testing. Phase analysis on the coatings is conducted with regards to the formation of amorphous phases using x-ray diffractometry (XRD) and differential scanning calorimetry. The XRD patterns indicate a mixture of (nano-) crystalline ferrite and amorphous phases. In particular, the coating manufactured with wire No. 1, a Fe-B-Si-C-Nb composition, exhibited good intermixing and a highly amorphous structure. This work demonstrates that glassy metallic coatings can be produced by means of HVAS using Fe-based cored wires comprising of conventional filler materials. A successful intermixing, in situ alloying and the subsequent formation of amorphous phases is achieved.