During the impact and solidification of thermal spray droplets on a substrate, the density increases when the droplet solidifies. Depending on the material, the changes in density could be significant. For example, aluminum oxide's density changes by 66%, while the changes are 12% and 19% for nickel and copper, respectively. For zirconia, this change is 24%. The effect of such densification on the dynamic of the droplet impact and the formation of porosity could be dramatic. In this study, the effect of shrinkage of a molten droplet during solidification on droplet impact is numerically investigated for several materials. Results for the impact of molten alumina, nickel, copper, and zirconia droplets on both smooth and rough surfaces are presented. The results of variable density cases are compared with those assuming constant density. The effect of thermal shrinkage is particularly vital in the interaction of two impacting droplets. The shrinkage promotes the formation of additional pores.

This paper presents an overview of the engineering and innovation behind BMW’s use of thermal spraying in the production of automotive engines at its light metal foundry in Landshut, Germany. It discusses the factors that drive engine development at BMW, the different approaches in play for improving the performance of cast aluminum crankcases, and the opportunities made possible by thermal spray technology. It describes the aluminum crankcase production process, from die casting to honing, with emphasis on BMW’s state-of-the-art implementation of twin wire arc spraying. It explains how the spraying process is controlled and how key process steps and parameters are monitored and optimized in real time along with coating properties and microstructures. If a coating defect is detected, it is documented on the fly and, in many cases, corrected in a subsequent process step. A few examples of defect detection at work are presented.

Low-pressure cold spraying (LPCS) is a coating technique, in which a portable cold spray system, e.g., DYMET 304K system is used to prepare technical coatings. Usually, compressed air is used as the process gas. The LPCS process is an appropriate method for spraying of metallic-ceramic composite powder materials, e.g., Cu, Ni, Zn, Al with additions of Al 2 O 3 particles in the powder blends. The main functions of the hard ceramic particles are cleaning the nozzle, activating the sprayed surface and peening the coating structure. This method has advantages for example in the field of repairing and restoration applications. For that, repairing casting defects and voids is one interesting application of the process. For these purposes, zinc-based composite materials are recommended for restoration and repairing of corrosion and mechanical damages. In this study, Zn+Al+Al 2 O 3 , Zn+Cu+Al 2 O 3 and Zn+Ni+Al 2 O 3 composite materials were investigated. Zinc and aluminum give corrosion resistance by cathodic protection whereas copper and nickel will provide also more mechanical resistance. Coating properties, such as microstructures, open-cell potential behavior and mechanical properties (hardness and adhesion strength) were investigated. The coatings have relatively dense coating structures and for corrosion resistance, zinc gives a cathodic protection for other materials in these composite coatings. Furthermore, mechanical properties are sufficient due to the relatively high hardness and adhesion to the Fe52 steel base material. These coatings have high potential in their use as repair materials for macroscopic casting defects.

This study investigates the effects of sintering on conventional and nanostructured plasma sprayed YSZ. In order to gain a better understanding of the differences in sintering behavior, the layers are sintered under constrained and non-constrained conditions over a temperature range of 800 to 1520 °C. The influence of particle size on sintering kinetics, microstructure development, electrical properties, and thickness is assessed for free-standing layers as well as deposits on rigid substrates.