Composite materials based on titanium nitride for high-speed friction units

Abstract

621.762Tribological properties are examined for composite materials based on titanium nitride under conditions of dry friction for a wide range of speeds (1-25 m/sec). It is shown that the composites have a high level of tribological properties, which may be better (by up to an order of magnitude) than the properties of known materials. These results are used in guidelines for prospective materials for high-speed friction units. It has been found that there is a necessary condition for the materials to be used in high-speed friction units in that there should be high adhesion strength for the films of oxidation products together with low tendency to adhesion interaction with the counterbody.The reliability and operating economy of machines and mechanisms are dependent to a substantial extent on the tribological properties of the materials. Antifriction materials can now be divided conditionally into two groups: metals and ceramics. The first are unable to withstand high contact loads and speeds. For such conditions, ceramics are better. However, their high brittleness makes them unsuitable for use under conditions of sign-varying loading and impacts. In our view, an alternative may be metal-ceramic materials of matrix and framework types. The ceramic component substantially reduces the probability of adhesion, while the metallic component provides strength and reliability of composite material.Our preliminary tests have shown that such composites, which have the advantages of both groups, to a considerable extent overcome the shortcomings of each. For example, experimental metal-ceramic bearings of framework type based on (Ti, Cr)B 2 have been used in the turbocompressors of standard internal combustion engines ( Fig. 1) have provided up to 20-30% decrease in power in friction and at the same time have reduced the amount of oil pumped through them for cooling by factors of 2-4 [1-4].However, as the speed in the friction zone and thus the temperature there increase, there is a sharp increase in the adhesion component of the frictional force. Under these conditions, the tribological properties are dependent primarily on the capacity of the material to form protective oxide films during tribooxidation, which hinder seizure. Titanium nitride has that property. Oxide films on titanium nitride have high heat resistance and strength, since titanium oxynitride is formed, Ti − N − O [5]. Our studies also indicate that titanium nitride is highly effective as an antiseizure additive [2]. When titanium nitride is used as the basis of a composite material, one thus expects a significant improvement in the tribological properties and stable operation under dry friction conditions. The purpose of this study was to examine the tribological properties of new composites based on titanium nitride for use under conditions of dry friction in air in pairs with steels.The materials were formed by sintering from components in the presence of liquid phase (matrix type) or by impregnation with a binder of refractory frameworks (framework ...

Wear mechanism of composites based on titanium nitride

“…This may be accomplished by selecting the friction couples with low adhesion activity, developing special structure of material, and ensuring the formation of dense separating films with high adhesion strength. We showed previously [3][4][5] that titanium nitride and materials on its basis with a steel counterface most fully complied with these requirements. However, the nature of high wear resistance and wear mechanism of these materials still have to be examined.…”

“…Note, however, that the wear resistance of the composites based on titanium nitride is almost one order of magnitude higher than that of well-known composites [6,7]. This is due to two factors: (i) the low activity of adhesive interaction between titanium nitride and iron and its alloys and (ii) the capability of materials based on titanium nitride to form oxide films in the tribooxidation process, which are strongly bonded to the base and prevent seizure in friction units [4,5]. These factors make titanium nitride an effective antiseizure additive for other wear-resistant materials.…”