Wear 274–275 (2012) 326–334 Contents lists available at SciVerse ScienceDirect Wear j o ur nal ho me p age: www.elsevier.com/locate/wear Optimization of surface treatment to enhance fiber–matrix interface and performance of composites S. Tiwari a , J. Bijwe a,∗ , S. Panier b a Industrial Tribology Machine Dynamics & Maintenance Engineering Centre (ITMMEC), Indian Institute of Technology Delhi, New Delhi 110016, India b Polymers and Composites Technology & Mechanical Engineering Department, Ecole des Mines de Douai, Douai Cedex 59504, France a r t i c l e i n f o Article history: Received 25 April 2011 Received in revised form 26 September 2011 Accepted 26 September 2011 Available online 1 October 2011 Keywords: Sliding wear Polyetherimide–carbon fabric composites Nitric acid treatment to fibers Surface analysis of carbon fibers a b s t r a c t Oxidation treatment with concentrated HNO 3 was employed to the carbon fabric (CF) for various time intervals (30–180 min) to observe the effect of treatment on two simultaneous processes involved viz. improvement in its adhesion with the matrix and reduction of fiber strength which in turn is responsi- ble for change in the performance properties of composites. Seven composites with untreated and acid treated CF were developed based on the polyetherimide (PEI) matrix and evaluated for adhesive wear properties under various loads (200–600 N) against mild steel disc. 90 min treated CF composite indi- cated the best tribological properties and showed 30% reduction in specific wear rate (K 0 ) and 23% in coefficient of friction () respectively at 600 N load. Treatment beyond this time proved detrimental for improvement in properties. Field emission scanning electron microscopy (FE-SEM) showed increase in roughness with treatment time, while atomic force microscopy (AFM) studies indicated substantial increase in roughness value. Scanning electron microscopy (SEM) of worn surfaces supported the wear mechanisms and improvement in adhesion between fiber and matrix. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Carbon fibers are one of the most favored reinforcements in tribological applications due to its very good strength, thermal con- ductivity, lubricating properties etc. [1–3]. However, carbon fibers are chemically inert in nature and hence have poor wettability and adsorption with most of the matrices. To ensure the expected enhancement in properties, it is necessary to have a very good fiber/matrix interface which would transfer the load from one fiber to another efficiently through the matrix [4,5]. Amongst various fiber surface treatments [6–10], nitric acid (HNO 3 ) treatment is rated as the most classical one to improve the interaction between fiber and matrix as a consequence of increase in surface area and surface energy [11–15]. Interestingly any such method when employed to the fiber, which etches its surface, also affects its strength adversely. First effect of etching leads to the enhancement in the fiber–matrix adhesion and hence improvement in strength of a composite. Simultaneously, strength of fibers gets reduced due to etching and subsequently contribut- ing to the deterioration in the strength of fibers and hence that of composite. The extent of this negative effect depends on the type, ∗ Corresponding author. Tel.: +91 11 26591280. E-mail address: jbijwe@gmail.com (J. Bijwe). duration and dose of treatment. In the case of HNO 3 treatment, many factors such as time of treatment, concentration of acid, and boiling or just dipping of fibers in acid are the influencing factors. It is extremely important to choose the right parameters for the treatment to achieve maximum possible benefits. Few researchers have reported on the effect of HNO 3 treatment on properties car- bon fibers [14,15], while others have focused on the influence of treatment on mechanical properties of composites for unidirec- tional (UD) composites [16], bi-directional (BD) composites [17,18] and short fiber reinforced composites [19]. Manocha [16] stud- ied the role of fiber–matrix interface in carbon fiber (treated with concentrated nitric acid) reinforced epoxy UD composites and reported a steep increase in flexural, tensile and inter-laminar shear strength (ILSS) of the composites. However, for prolonged treat- ment, the flexural and tensile strength decreased sharply whereas ILSS decreased gradually. Su et al. [17] compared various effect of treatments on fibers and reported that the composite of the CF etched with HNO 3 (immersed for 2 h) had the poorest tribological and mechanical properties as compared to the one with CF modified with anodic oxidation and plasma treatments. In view of tribological studies, Zhang et al. [19] showed improved friction and wear behavior of polyimide (PI) compos- ites with pitch-based short carbon fibers, oxidized with HNO 3 (at 90 ◦ C for 1.5 h). Though a lot is reported in the case of HNO 3 treat- ment of CF, there is no in depth studies reported which could reveal the complete picture of a fiber treated for various time intervals 0043-1648/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.wear.2011.09.014