Friction and wear performance of diamond-like carbon and Cr-doped diamond-like carbon coatings in contact with steel surfaces

Abstract

The development of modern engines involves the use of new materials such as diamond-like carbon (DLC) coatings. As these coatings possess different mechanical and physical characteristics to steel, investigation of their friction and wear properties when rubbing against a steel counterpart in a lubricated environment is needed. Specific tests were used to assess the tribological behaviour of these new surfaces (specifically an undoped DLC and a chromium-doped DLC coating). Chemical analyses were also performed in order to evaluate the reactivity of the formulated oil on the various surfaces. The results of the present work clearly show that there was no evidence of tribochemical reaction on DLC coatings. Anti-wear additives were still reacting on the steel counterpart for the undoped DLC case, resulting in better wear properties for the coating. The addition of a metal to the amorphous carbon matrix led to an improvement in wear but inhibited/removed the anti-wear film on the steel counterpart.

The influence of anti‐wear additive ZDDP on doped and undoped diamond‐like carbon coatings

“…It is proposed that the phosphate present in the additive has reacted with the Fe 2 O 3 in the cast iron counter body as described earlier. It is then seen to transfer to the DLC surface during sliding, because this surface is inert and does not react with the ZDDP . The XPS results of the quantified chemical species shown after tribotesting for 6 and 20 h in Tables and , respectively, show that the phosphate present after 6 h is mostly long‐chained metaphosphate (59%), after 20 h of testing, the shorter pyrophosphate chains dominate at a concentration of 67%.…”

Tribological Behaviour of Diamond‐Like Carbon Films used in Automotive Application: A Comparison

“…It is admitted that cam/follower system operates in boundary lubrication. [1] In this regime, the lubricant film is not thick enough to totally separate the two surfaces in contact. Hence, this system is governed by both unlubricated and lubricated contact rules.…”

“…As described by the Stribeck curve, lubrication regime depends mostly on the lubricant viscosity and the sliding speed. [1][2][3] Due to this reason tests are performed at different engine speeds. Figure 4 shows the friction measurement for each cycle and for each DLC coating.…”

“…Stribeck curve allows describing different lubrication regimes. [1][2][3] Some components as valve train parts operate under boundary lubrication where oil film is not enough thick to totally separate the surfaces. Cam/ follower pair represents the most critical interface of valve train that is the reason why this contact will be studied in this work.…”

“…Diamond-like carbon (DLC) coatings can be used in automotive applications due to excellent tribological behaviour such as a high wear resistance and very low friction coefficient. [1,2,4,5] But the mechanical properties of these films depend mostly on the proportion of sp 2 to sp 3 carbon bonds and hydrogen content. [6] The aim of this work is to obtain an overall characterization of properties and structure of two DLC coatings.…”