Sliding Friction Behavior of Sintered Ni-Cr Composites with Solid Lubricants

Abstract

High temperature applications of self-lubricated sliding surfaces have gained industrial importance during the recent years. One popular system is based on sintered Ni-Cr composites with addition of solid lubricants. In the present work these composites were prepared under controlled sintering conditions with different combinations of solid lubricants (MoS₂, Ag and CaF₂) at 1200 °C under flowing argon. The physical properties such as sintered density, relative density and porosity were studied. The microstructures and phase studies of the Ni-Cr based composites were conducted using SEM analysis while the hardness of the composites was measured by Vickers Micro Hardness Tester. The friction tests were conducted with ball on disc configuration following ASTM G-99-95a standard. The MoS₂ solid lubricant provides best lubrication at room temperature which is demonstrated by a low friction coefficient compared to pure Ni-Cr composites. The SEM pictures of worn out tracks show solid debris distribution, and filling of pores with solid lubricant phases. The time taken for stabilization of friction coefficient also varies with the type of solid lubricant. Dual and multiple additions of solid lubricants are also able to reduce the friction of coefficient compared to pure Ni-Cr composite.