Wear 249 (2002) 1004–1013 Surface feature variations observed in 52100 steel sliding against a thin boron carbide coating Stephen J. Harris a , Gordon Krauss a , Matthew T. Siniawski b,∗ , Qian Wang b , Shuangbiao Liu b , Yong Ao b a Ford Motor Company, Dearborn, MI 48121, USA b Department of Mechanical Engineering, Northwestern University, Evanston, IL 60208, USA Received 2 February 2001; received in revised form 8 August 2001; accepted 15 August 2001 Abstract Boron carbide (B 4 C) is well known for its high hardness and wear resistance and has been used as a wear-resistant coating. If one of a pair of contact surfaces is coated by B 4 C, it may polish its mating surface and act as a run-in coating. Developing such run-in coatings demands a thorough understanding of the mating surface evolution in wear. This paper reports a study on the characteristics of the surface feature variations of 52100 steel balls run against B 4 C coated disks. The contact conditions, asperity contact temperature, pressure and deformation are analyzed. Changes in the surface statistical properties, asperity height autocorrelations and power density spectra are monitored for the 52100 steel as the sliding distance increases. The results indicate that under the conditions used in this research, the B 4 C coating can accomplish polishing in a sliding distance of less than 2 m. Based on these observations we suggest a new paradigm for an ideal run-in coating. © 2001 Published by Elsevier Science B.V. Keywords: Boron carbide coating; Finite-life coating; 52100 steel; Sliding wear; Surface features; Autocorrelation; Fast Fourier transform 1. Introduction Boron carbide (B 4 C) is well known for its high hardness and wear resistance. In addition, B 4 C offers such properties as high elastic modulus, high melting point, and low density. It has been used to provide resistance to fatigue for auto- motive gears [1], although poor oxidation resistance and low fracture toughness may limit its application. It is im- portant to conduct wear tests to investigate proper means of utilizing B 4 C as a surface coating. Larsson et al. [2] studied B 4 C coatings in self-mated sliding tests designed to reduce wear and found that B 4 C forms tribofilms of oxides that contribute to the decreasing of wear rates and the smoothing of tribosurfaces as the sliding distance increases. Another method of using B 4 C is to coat only one of the contacting surfaces, expecting B 4 C to polish its mating surface and act as a run-in coating by removing asperities on the uncoated part which would otherwise have caused high stresses in the coated part. In order for this run-in process to be con- trolled, it is necessary to have an in-depth understanding of the mating surface evolution in such a polishing process. ∗ Corresponding author. Tel.: +1-847-467-6961. E-mail address: m-siniawski@northwestern.edu (M.T. Siniawski). The current study aims at observing the characteristics of the surface feature variations of a 52100 steel ball sliding against a B 4 C coating. Changes in the surface statistical properties, asperity height autocorrelations, and power den- sity spectra are monitored for the 52100 steel as sliding distance increases. The autocorrelation function (ACF) is an effective means to correlate the asperity height at differ- ent locations on the surface. The Fourier transform (FT) of the ACF reveals the roughness components and is widely applied to study the structures of surface geometry [3]. Wieland et al. [4] demonstrated a relationship between sur- face roughness and the FT power spectrum amplitude. Wu [5] utilized FT for the simulation of rough surface, while Ao et al. [6] combined FT with neural networking for worn surface simulation. The work reported in this paper utilizes ACF and fast Fourier transformation (FFT) to unfold the nature of surface evolution and to examine the relationship among wear, surface features and the structure of worn surfaces. The contact conditions, asperity contact temper- ature, pressure and deformation are also analyzed, using a three-dimensional thermoelastic asperity contact model de- veloped by Liu and Wang [7]. Finally, the length of a run-in period for 52100 steel sliding against a B 4 C coating and a new paradigm for run-in coating design are suggested. 0043-1648/01/$ – see front matter © 2001 Published by Elsevier Science B.V. PII:S0043-1648(01)00840-7