Research on the Influence of the Manufacturing Process Conditions of Iron Sintered with the Addition of Layered Lubricating Materials on its Selected Properties

Abstract

The purpose of the conducted experiments was to test the selected properties of materials intended for porous sintered bearings containing layered materials in the form of powders with an average particle size of 0.5–1.5 μm, with very good tribological properties. The subject of the research was a sinter based on iron powder with the addition of layered materials; molybdenum disulfide MoS2 (average particle size 1.5 μm), tungsten disulfide WS2 (average particle size 0.6 μm), hexagonal boron nitride, h-BN (average particle size 0.5 and 1.5 μm) with two different porosities. The article presents the results of density and porosity tests, compressive strength, metallographic and tribological tests and the assessment of changes in the surface condition occurring during the long storage period. The use of layered additives allows for an approximately 20% lower coefficient of friction. In the case of sulfides, the technological process of pressing 250 MPa, 350 MPa, and sintering at a temperature of 1120 °C allows us to obtain a material with good strength and tribological properties, better than in the case of h-BN. However, the main problem is the appearance of elements from the decomposition of sulfide compounds in the material matrix, which results in rapid material degradation. In hexagonal boron nitride, such disintegration under these conditions does not occur; the material as observed does not degrade. In this case, the material is characterized by lower hardness, resulting from a different behavior of hexagonal boron nitride in the pressing and sintering process; in this case, pressing at a pressure of 350 MPa seems to be too low. However, taking into account that even with these technological parameters, the obtained material containing 2.5% h-BN with an average grain size of 1.5 μm allowed obtaining a coefficient of friction at the level of 0.41, which, with very good material durability, seems to be very positive news before further tests.

Study of Nano h-BN Impact on Lubricating Properties of Selected Oil Mixtures

“…At the same time, the conducted research presented in work [ 10 ] and the present one confirm the validity of the previously proposed lamellar model and, at the same time, indicate further directions of research.…”

“…At the same time, as reported by Gupta et al [ 28 ], the use of layered materials of smaller-sized particles in base oils provides better anti-seizure properties [ 28 , 29 ]. A similar relation is observed when introducing layered materials directly during the preparation of friction subassemblies in the sintering process [ 10 ].…”

“…A characteristic quality of layered materials is that parallel layers, made up of individual atoms connected by strong covalent bonds, are connected by weak Van der Waals forces. These layers can easily move relative to each other, granting the materials low friction coefficients [ 8 , 9 , 10 ]. This group of materials includes, for example, molybdenum disulfide (MoS 2 ), tungsten disulfide (WS 2 ) [ 11 ], hexagonal boron nitride (h-BN) [ 12 , 13 , 14 ], and graphite (C), etc.…”

“…Technical solutions for placing layered materials, e.g., boron nitride, in a friction node on several methods [ 7 , 10 , 22 , 23 , 24 ]. The material can be inserted when producing of the elements that work together, e.g., manufacturing products made of sintered powders.…”

“…The material can be inserted when producing of the elements that work together, e.g., manufacturing products made of sintered powders. Technical solutions for placing layered materials, e.g., boron nitride, in a friction node are based on several methods [ 7 , 10 , 22 , 23 , 24 ]. The material can be inserted when producing the elements that work together, e.g., manufacturing products made of sintered powders.…”