Simple model of interfacial bonding strength in detachment of reinforcing phase from clad layer during run-in process Y.C. Lin * , S.W. Wang, Y.H. Cho Department of Mechanical Engineering, National Taiwan University of Science and Technology, 43, Keelung Road, Section 4, Taipei 106, Taiwan, ROC article info Article history: Received 13 January 2009 Accepted 26 March 2009 Available online 31 March 2009 Keywords: Wear model Wear resistance Reinforcing phase abstract This study elucidates the relationship between the wear performance of a clad layer and the bonding strength of interface between the reinforcing phase and the matrix. A simple mathematical model is pro- posed to elucidate the differences among the wear performance of various clad layers with different rein- forcing particles. Analytical results indicate that, at the beginning of the run-in process, the wear resistance of a clad layer depends on the strength of the matrix, the hardness and geometric character- istics of the reinforcing phases and the bonding strength of the interface between the matrix and the rein- forcing phase. In some special cases, this simple mathematical model can be used to estimate the critical bonding strength of an interface between reinforcement and matrix for wear performance. According to the analysis, the reinforcing phase has complex geometric characteristics that enhance mechanical inter- locking. More complicated shape of reinforcement can prevent the reinforcing phase from being pulled out and enhance the wear performance of the clad layer. Moreover, wear tests of TiC-W and WC-Ti clad specimens are used to verify the qualitative correctness of the model. Ó 2009 Elsevier Ltd. All rights reserved. 1. Introduction Surface cladding has been extensively used to improve the wear resistance of metals [1–5]. This surface modification can be used to reinforce local surfaces in machine guideways and in various wear resistance applications. However, such materials normally include a matrix that embeds one or several reinforcing phases as a composite. The reinforcing phase may have the form of particles, whiskers, fibers or complex shapes [6–9]. In several engineering applications, reinforcing phases possess high hard- ness or modulus of elasticity while the matrix is a tough material. Numerous hard materials have been used to enhance the wear resistance of the clad layer, but sometimes the improvement of wear resistance is not evident, because the reinforcement is de- tached from the clad layer during rubbing. Under a heavy loading (>600 MPa) wear process, the detached fragment contains rein- forcing phases and are buried under the rubbing surface [10]. However, under regular loading, pulling out or breakage of the reinforcement is observed on the worn surface [11,12]. Although several kinds of ceramics particles have been used as reinforce- ments to improve the wear resistance of clad layers, the wear per- formances of such clad layers vary widely. Other studies have obtained valuable results that explain this finding of the different clad layers under abrasive wear conditions [13–15]. Hence, this study focuses on the wear behavior of a metal under the rubbing against a clad layer. A simple mathematical model is proposed to elucidate the differences among the wear performance of various clad layers with different reinforcing particles. Moreover, wear test results are used to check the qualitative validity of the pro- posed model. 2. Wear resistance and reinforcing phase detachment model Previous studies have found that if the reinforcement does not detach during wear, then the wear resistance of the clad layer can be attributed to the matrix and the reinforcement [1]. Accord- ingly, if the plastic deformation of matrix is minor and the rein- forcement does not break, then the wear resistance index (expressed as the reciprocal of the wear rate) of the clad layer can be expressed as follows [16]: k wc ¼ bk wp þ ak wm ð1Þ k wc : wear resistance index of clad layer (expressed as the reciprocal of wear rate); k wp : wear resistance index of reinforcement in clad layer; k wm : wear resistance index of matrix in clad layer; b ¼ Ap Ac : ra- tio of the reinforcement area to the apparent contact area in con- tacting region; a ¼ Am Ac : ratio of the matrix area to the apparent contact area in contacting region; A c : apparent contact area of clad layer (mm 2 ); A p : total area of contact with the reinforcement within the apparent contact area (mm 2 ); A m : total area of contact with the matrix within the apparent contact region (mm 2 ) and, 0261-3069/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.matdes.2009.03.032 * Corresponding author. E-mail address: yclin@mail.ntust.edu.tw (Y.C. Lin). Materials and Design 30 (2009) 3388–3394 Contents lists available at ScienceDirect Materials and Design journal homepage: www.elsevier.com/locate/matdes