Effect of surface texturing on friction properties of WC/Co cemented carbide

Abstract

An experimental study was carried out to investigate the tribological properties of different surface textured WC/Co cemented carbide. The influence of applied load, sliding speed and area density of textures on frictional performance of surface textured patterns was investigated by Taguchi method. Results show that the textured surfaces filled with molybdenum disulfide solid lubricants can reduce the average friction coefficient, wear rates of Ti–6Al–4V alloy balls and adhesion of Ti–6Al–4V alloy materials on the worn track of cemented carbide compared with un-textured ones. Variance analysis of the experimental data indicates that the area density of textures plays major contribution of both average friction coefficient and wear rate of Ti–6Al–4V alloy balls. Higher area density of textures is beneficial to improve tribological performance of the cemented carbide samples. Sliding speed seems to have no effect on the tribological performance of textured surfaces within the reliability interval of 90%. Applied load has effect on both average friction coefficient and wear rate of Ti–6Al–4V alloy balls at the reliability interval of 95%.

Introduction

Cemented carbide is sintered material consisting of refractory metal carbide and bonding phase. It is known that cemented carbide is widely used as cutting tool material. Moreover, cemented carbide is used on fabrication of mechanical seal rings [1], [2] for its excellent properties, i.e. high hardness, wear resistance, excellent strength and toughness. For mechanical seal rings, wear is the major failure mode [3]. In other words, the working life of mechanical seal rings depends to a large extent on the tribological properties of component material. Therefore, improving the friction and wear properties of cemented carbide has important significance in increasing the working life of mechanical seal rings.

In recent years, surface texturing [4] which involves flat and smooth lands interrupted by local depressions has attracted more and more attention. It has been pointed out that the depressions can trap wear debris [5], store lubricant [6], [7] and also contribute to increase the load carrying capacity of sliding surface under fluid lubrication [8], [9], [10], [11], hence improve tribological behavior of the frictional interface. Pettersson and Jacobson [4] produced surface textures on silicon wafers and they were subsequently PVD coated with TiN or DLC coatings. The results of friction experiments indicated that it was very beneficial to produce certain textures on surface of silicon wafers sliding with steel balls under boundary lubricated conditions. Xiong et al. [7] fabricated surface textures with different dimple densities on nickel-based composites and filled the dimples with molybdenum disulfide powder. The friction and wear experiment was conducted with the surface textured composites and un-textured ones sliding against alumina balls. They reported that the textured composites reduced friction coefficients and raised the effective lubricating temperature of molybdenum disulfide to about 500 °C, meanwhile, textured composites had lower wear rates and longer wear life compared to un-textured ones. Wakuda et al. [12] conducted a friction experiment with surface textured silicon nitride ceramic sliding against steel pin. It was found that the textured samples successfully realized reduction in friction coefficient compared with smooth samples, and the tribological characteristics depended greatly on the size and density of the micro-textures. Mishra and Polycarpou [13] investigated the viability of textured gray cast iron surface for improved tribological performance under aggressive starved lubrication compressor conditions. It was reported that the tribological performance of textured patterns was driven by geometric parameters of textured dimples, sliding speed, as well as the type of lubricant and refrigerant.

Taguchi method [14], [15] is a low cost and high benefit technology for optimizing design parameters, it enables the design objectives to be satisfied by carrying out the least number of tests. The Taguchi method has been widely used in experimental study on tribological properties of various materials. Davim et al. [16] investigated the influence of sliding speed, normal load and sliding speed on dry sliding wear of aluminum metal matrix composites based on Taguchi method. The results indicated that the sliding distance had the highest physical and statistical influence on the wear of the metal matrix composites. Davim et al. [17], [18], [19] also reported their research on the friction and wear behavior of sialon ceramics and silicon nitride ceramics under dry conditions. It was indicated that both sialon ceramics and silicon nitride ceramics presented high wear resistance and the wear forms for ceramic composite were adhesion and microabrasion. They [20], [21], [22], [23] still used orthogonal design to investigate the influence of cutting parameters on tool wear. The tool species including polycrystalline diamond tool, ceramic tool and coated carbide tool were selected for turning (drilling) metal–matrix composites, cold work tool steel and glass fiber reinforced plastic composites, respectively. The results indicated that, for all turning operations, cutting speed had the most significant influence on the tool wear, however, cutting time was the most important factor of tool wear in drilling of metal–matrix composites with polycrystalline diamond drills. Siddhartha et al. [24] investigated the influence of operational parameters and material parameters on dry sliding wear characteristics of titania reinforced homogeneous and graded epoxy composites by Taguchi method. It was indicated that the normal load played major contribution of the wear rate for homogeneous composites, while the sliding distance showed significant percentage contribution of the wear rate for graded composites. Sahoo [25] used Taguchi orthogonal design of experiments to investigation the influence of coating process parameters on the wear behavior of electroless Ni–P coatings sliding against steel. The results indicated that bath temperature and annealing temperature had the most important influence on wear characteristics of this coating. Rashmi et al. [26] investigated the dry sliding wear behavior of epoxy with organo-modified montmorillonite using Taguchi techniques. It was indicated that the sliding distance was the most important factor affecting wear rate of epoxy nanocomposites.

Literature review shows the lack of study on the tribological performance of surface textured cemented carbide, and, investigation on the influence of the geometrical parameters of surface textures on friction and wear behavior using Taguchi method is seldom. In the present study, laser surface texturing was performed on the cemented carbide, and the textured depressions were subsequently filled with molybdenum disulfide solid lubricants. The effect of surface texturing on the tribological properties of cemented carbide was investigated by carrying out dry sliding tests against titanium alloy balls. Taguchi method was also applied to investigate the influence of applied load, sliding speed and area density of textures on frictional performance.