An Investigation on Temperature Distribution Within the Substrate and Nozzle Wall in Cold Spraying by Numerical and Experimental Methods Wen-Ya Li, Shuo Yin, Xueping Guo, Hanlin Liao, Xiao-Fang Wang, and Christian Coddet (Submitted April 20, 2011; in revised form August 6, 2011) During cold spraying (CS), heat exchange between the hot driving gas and the solid bodies, e.g., spray nozzle and substrate, results in the temperature redistribution within the solid bodies. In this study, numerical and experimental investigations on the heating behavior of the substrate and nozzle wall were conducted to clarify the temperature distribution within the solid bodies in CS. The results show that after heating by the hot gas, the highest temperature presents at the center point of the substrate and decreases toward the substrate back surface and edge. With increasing standoff distance or decreasing inlet temperature, the substrate temperature decreases gradually, but the temperature gradient within the substrate changes little. The numerical results are consistent with the experimental measurements. Besides, it is also found that increasing the substrate size (diameter) can lead to the gradual increment in the substrate temperature. Moreover, the numerical study on the temperature distribution within the nozzle wall reveals that the highest temperature presents at the throat section of the nozzle and that the nozzle material significantly affects the temperature distribution within the nozzle wall. Keywords cold spraying, heat exchange, numerical simulation, temperature distribution 1. Introduction Cold spraying (CS) is a new coating technique based on aerodynamics and high-speed impact dynamics. Differing from the conventional thermal spraying, the deposition process of CS particles relies purely on the kinetic energy rather than the combination of thermal and kinetic ener- gies of spray particles. In this process, spray particles (typically <50 lm) are accelerated to a high velocity ranging from 300 to 1200 m/s by the high-speed gas flow from a De Laval type nozzle (Ref 1). It has been widely accepted that there exists a material-dependent critical velocity, beyond which particles can adhere to the sub- strate through the intensive plastic deformation at a temperature well below the melting point of spray mate- rial, and thus a coating can be formed (Ref 2, 3). The relatively low particle temperature makes it possible to retain the original properties of the powder feedstock in the coating. As for the bonding mechanism of CS, the most prevailing hypothesis is that the occurrence of adi- abatic shear instability at the local contact zone crushes and excludes the oxide film from the interface, allowing the intimate conformal contact and thus the bonding to occur (Ref 2, 3). Besides, adhesion is considered to be an alternative mechanism for the bonding in CS, which also requires clean interface and high contact pressure (Ref 4). During the last decade, there has been growing interest in the gas flow and particle acceleration in CS. The existing studies on this field mainly focused on two aspects including the optimal design of the CS nozzle (Ref 5-12) and the investigation on the parameters influencing the gas flow and particle acceleration (Ref 12-17). Notwith- standing these findings, several important problems still need to be further studied, such as the heat exchange between the hot gas and the adjacent solid bodies, e.g., spray nozzle and substrate, in CS. The recent experimental investigation conducted by Fukumoto et al. (Ref 18) showed that the substrate temperature takes an important role in deposition efficiency, and higher substrate tem- perature can result in higher deposition efficiency in CS. Legoux et al. (Ref 19) investigated the heat transfer behavior between the hot gas and the substrate in CS experimentally. The results demonstrated that the inlet gas temperature, pressure, standoff distance, and nozzle traverse speed significantly affect the heat-transfer Wen-Ya Li, State Key Laboratory of Solidification Processing, Shaanxi Key Laboratory of Friction Welding Technologies, Northwestern Polytechnical University, XiÕan 710072, Shaanxi, PeopleÕs Republic of China; Shuo Yin and Xiao-Fang Wang, School of Energy and Power Engineering, Dalian University of Technology, Dalian 116024, Liaoning, PeopleÕs Republic of China; Xueping Guo, Marine Engineering College, Jimei University, Xiamen 361021, Fujian, PeopleÕs Republic of China; and Hanlin Liao and Christian Coddet, LERMPS (Laboratoire dÕEtudes et de Recherches sur les Mate ´ riaux, les Proce ´de ´s et les Surfaces), Universite ´ de Technologie de Belfort-Montbe ´ liard, Site de Se ´ venans, 90010 Belfort Cedex, France. Contact e-mail: liwy@nwpu.edu.cn. JTTEE5 21:41–48 DOI: 10.1007/s11666-011-9685-2 1059-9630/$19.00 Ó ASM International Journal of Thermal Spray Technology Volume 21(1) January 2012—41 Peer Reviewed