Parametric Study of Abrasive Wear of Co CrC Based Flame Sprayed Coatings by Response Surface Methodology 2014 Tribology International

Parametric Study of Abrasive Wear of Co CrC Based Flame Sprayed Coatings by Response Surface Methodology 2014 Tribology International
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  Author's Accepted Manuscript Parametric study of abrasive wear of Co-CrCbased flame sprayed coatings by ResponseSurface MethodologySatpal SharmaPII: S0301-679X(14)00091-7DOI: JTRI3274 To appear in:  Tribology International  Received date: 14 January 2014Accepted date: 4 March 2014Cite this article as: Satpal Sharma, Parametric study of abrasive wear of Co-CrCbased flame sprayed coatings by Response Surface Methodology,  Tribology International, This is a PDF file of an unedited manuscript that has been accepted forpublication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, andreview of the resulting galley proof before it is published in its final citable form.Please note that during the production process errors may be discovered whichcould affect the content, and all legal disclaimers that apply to the journalpertain.  1 Parametric study of abrasive wear of Co-CrC based flame sprayed coatings by Response Surface Methodology Satpal Sharma School of Engineering, Gautam Buddha University, Greater Noida, U.P. (India)   Abstract Co base powder (EWAC1006 EE) was modified with the addition of 20%WC and the same was further modified by varying amounts of chromium carbide (0, 10 and 20wt.%) in order to develop three different coatings. Microstructure, elemental mapping XRD, porosity and hardness analysis of the three coatings was carried out. The effect of CrC concentration (C), load (L), abrasive size (A), sliding distance (S) and temperature (T) on abrasive wear of these flame sprayed coatings was investigated by response surface methodology and an abrasive wear model was developed. A comparison of modeled and experimental results showed 5-9 % error.  Keywords : Coating; Abrasive wear; Microhardness; Response Surface Methodology (RSM). 1. Introduction The progressive deterioration of metallic surfaces due to various types of wear (abrasive, erosive, adhesive, corrosive and chemical wear) in various industries (coal and hydro thermal power plants, cement, automotive, chemical and cement industry) leads to loss of plant operating efficiency and frequent breakdown of the components which in turn results in huge financial losses to the industry. The recognition of this fact has been the driving force behind the continuing development of the surface modification and surface coating technologies known as surface engineering. The properties of these surface layers may be different from those of the material as dictated by service requirements. The cobalt base alloys have found a wide variety of tribological applications for abrasive and adhesive wear resistance in many industries such as aerospace, automotive, hydro and gas turbines and cement industry. Some studies [1-6] report the effect of processing techniques, carbide additions and their  2 distribution and post spray heat treatment on the hardness and abrasive wear resistance of Co base coatings. The abrasive wear is influenced by a number of different factors such as the properties of the materials (microstructure and hardness), the service conditions (applied load and abrasive grit size) and environment (temperature and humidity). High hardness and good resistance to abrasion of cobalt based coatings are generally attributed to the presence of high volume fraction of carbides. Increase in hardness of these alloys with the addition of WC and TiC has been reported [7-8] . Maiti et al. [9] reported that with addition of WC upto 20% in WC-Co-Cr coatings the increases the hardness and abrasive wear résistance and further addition of WC increases hardness marginally. In the present study, the Co base alloy was modified with WC and varying amount of CrC   additions (0, 10 and 20%) to increase the hardness and abrasive wear resistance of coatings. In cement industry, various fans are used to transport alumina and silica particles of 5-50 micron size along with hot gases (temperature 393-423K). These solid particles travel along the fan blade surface at a very low angle (<10º). Abrasive wear has been reported to simulate the low angle solid particle erosion conditions [10-13]. Cement industry is trying many types of coating materials including cobalt  base alloy. Therefore, in this work a cobalt base alloy was selected for study and further developed for improved abrasion and erosion performance. It has also been found from the literature that most of the research on abrasive wear behavior of Co base alloys was carried out considering single dimensional aspect of applied wear conditions such as abrasive grit size and load only. Data generated using traditional method of research using single factor effect is valuable and detailed, but fails to indicate the effect of their interactions of various test parameters on abrasive wear. Therefore, a number of statistical methods have recently been implemented in wear studies. These methods share the advantage of facilitating research into the effects of different factors and their interactions (combined effect), by limiting the number of tests. Hence in this study an attempt has been made to study the independent as well as combined effect of the factors using fractional factorial design (Response Surface Methodology). Based on the experimental data obtained an abrasive wear model was developed to correlate the abrasive wear of the coatings in terms of applied factors and their interactions. The validity of the abrasive wear  3 model was evaluated under different abrasive wear conditions by comparing the experimental and modeled results. 2. Experimental procedure 2.1 Materials and methods The carbon steel substrate was used for deposition of modified Co base alloy coatings. The substrate was degreased and roughened to an average surface roughness of Ra 3.15 m (Rmax 18.2 m). Surface roughness was measured by Mahr – Perthometer (M 2  409). The nominal composition of substrate and commercially available Co base powder (EWAC 1006 EE) is shown in Table 1. This powder was modified by adding 20wt.% WC. Further addition of 0, 10 and 20wt.% CrC was carried out to develop three different compositions ((1006EE + 20wt.% WC+ 0wt.% CrC), (1006EE + 20wt.% WC+ 10wt.% CrC) and (1006EE + 20wt.% WC+ 20wt.% CrC)). In following sections these modified compositions are designated by 0, 10 and 20wt.% CrC coatings respectively. These compositions were deposited using flame spraying process by Super Jet spray torch (L & T India). The flame spraying was carried out using neutral flame of oxy-acetylene gas where the pressures of oxygen and acetylene were maintained at 0.3 MPa (3kgf/cm 2 ) and 0.12 MPa (1.2 kgf/cm 2 ) respectively. The substrate was preheated to 200±10 o C. The spraying parameters are shown in Table 2. 2.2 Characterization of coatings Coated samples were cut transversely for microstructural characterization (SEM, SEM- LEO – 435- VP, England), porosity and hardness. The samples were polished using standard metallographic  procedure and etched with a chemical mixture of 3 parts HCl + 1 part HNO 3 . SEM micrographs were used to study microstructure and worn surfaces. The porosity was measured by the point counting method [14-20]. The average of 25 areas of each coating has been used for porosity measurement. Vickers hardness of the coating was measured using a load of 5 kg and average of six readings of the coating was used for study purpose. Scanning electron microscopy of the worn surfaces of coatings was also carried out to identify the material removal mechanisms under abrasive wear conditions.
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