Effects of Substrate Hardness and Spray Angle on the Deposition Behavior of Cold-Sprayed Ti Particles

In this study, finite element analysis combined with experimental observation was conducted to clarify the effects of substrate hardness and spray angle on the deposition behavior of cold-sprayed Ti particles. It is found that metallurgical bonding is highly possible to occur between the Ti particle and Cu substrate due to the intensive metal jet at the rim of the interface which helps to remove the cracked oxides. Because metallurgical bonding and large interfacial contact area can guarantee high adhesion strength, the thick Ti coating is achieved after deposition on the Cu substrate. As for the soft Al substrate, the first layer Ti particles are embedded in and then trapped by the soft substrate material, which results in the occurrence of mechanical interlock at the interface. As a consequence, the final coating thickness is also relatively large. When using hard stainless steel as the substrate, the essential conditions for forming the mechanical interlock are lacked due to the high hardness of the substrate material. In addition, the metal jet at rim of the interface is less prominent and also the interfacial contact area is smaller in comparison with the Ti-Cu case. Therefore, the particle-substrate bonding strength and the consequent coating thickness are relatively low. Besides, it is also found that the particle deformation and coating quality are significantly affected by the spray angle. The deformation of the particle localizes at only one side due to the additional tangential momentum. Also, such localized deformation becomes increasingly intensive with decreasing the spray angle. Moreover, the coating thickness is found to reduce with the decrease in spay angle, but the coating porosity shows a reverse trend.