Understanding the behaviour of silver as a low friction coating in aerospace fasteners

Abstract

Nuts and bolts used in aero-engines are manufactured from heat-resistant super-alloys. When used in a like on like couple, these materials have a high coefficient of friction, and frequently seizure occurs. In order to prevent this, a silver coating is applied to the nut threads, providing a low friction boundary at the interface. Additionally, a radial crimp is applied to the nut, in order to provide a self-locking feature preventing vibration self-loosening. In this study, the coefficient of friction of the thread contact will be investigated both during initial joint assembly, and after thermal ageing. Additionally, a finite element model will be employed to investigate the contact mechanics as a consequence of the crimp. The low coefficient of friction observed during initial assembly was found to be a consequence of shear flow of the silver coating, with an approximate doubling of this value once the coating aged. Areas of silver removal were found to be coincident with areas of high contact pressure in the joint, attributable to the crimp feature.

Coordinating influence of multilayer graphene and spherical SnAgCu for improving tribological properties of a 20CrMnTi material

“…An effective method of improving the friction and wear behavior of 20CrMnTi is to prepare 20CrMnTi-based selflubricating composites containing solid lubricants, such as graphene, [12][13][14] carbon nanotubes (CNTs), 15,16 and silver. 17,18 Zhai et al 12 explored the mechanical and tribological behaviors of a Ni 3 Al-multilayer graphene composite. Their results indicated that multilayer graphene enhanced the mechanical properties of a Ni 3 Al-based composite.…”

Preparation of a Self‐Lubricating Cu/h‐BN Coating on Cemented Carbide

“…Solid self-lubricating coatings are mainly employed to control friction and wear, especially under harsh application conditions, such as aerospace, high vacuum, high speeds, high pressure, and very low or high temperatures [10,11]. Under extreme conditions, conventional lubricants cannot provide the desired performance or durability, and in some cases, they cannot be used.…”

Evaluation of environmental friendly Ag-PTFE composite coating for use in threaded compression fittings

“…5 The use of Ag within the aerospace industry has been primarily in fasteners, where low-friction Ag-coated self-locking nuts are used in the demanding conditions within aerospace engines. 6 Furthermore, as a relatively noble metal, it is corrosion resistant, a desirable material property for applications in highly corrosive environments.…”