Laser solid-state gas nitriding of NiTi for enhancing wear resistance

Abstract

NiTi and Ti alloys have been widely used in many applications that demand high specific strength property. However, the wear resistance of these alloys is poor. Various surface coating methods can be applied to enhance the wear resistance. Techniques to produce a nitrided surface such as PVD and CVD have been applied but these techniques have limitations such as poor interfacial adhesion and high temperature distortion, respectively. Laser gas nitriding has been widely studied but its application is still not accepted by the industry. The major problem of laser gas nitriding is that the process involves surface melting which would increase the surface roughness of surface finished components. This paper will report the results achieved by laser gas nitriding without the surface being melted. Laser processing parameters were optimized so that the surface could be nitrided without surface melting and thus the surface finish of the component could be maintained. The microstructure of the nitride surface was studied and X-ray analysis was carried out to examine the nitride structure. Hardness was measured by nanoindentation. The wear resistance of the surfaces with difference grid sizes of nitride tracks was studied. Significant improvement in wear resistance was observed. The process can be used to surface-harden Ti components with finished surface.NiTi and Ti alloys have been widely used in many applications that demand high specific strength property. However, the wear resistance of these alloys is poor. Various surface coating methods can be applied to enhance the wear resistance. Techniques to produce a nitrided surface such as PVD and CVD have been applied but these techniques have limitations such as poor interfacial adhesion and high temperature distortion, respectively. Laser gas nitriding has been widely studied but its application is still not accepted by the industry. The major problem of laser gas nitriding is that the process involves surface melting which would increase the surface roughness of surface finished components. This paper will report the results achieved by laser gas nitriding without the surface being melted. Laser processing parameters were optimized so that the surface could be nitrided without surface melting and thus the surface finish of the component could be maintained. The microstructure of the nitride surface was ...