Investigation On Wear Behaviour And Fractal Of SiC_p/Al Composites

In this paper, a powder metallurgy method called "cold-press sintering +hot extrusion" is used to prepare Al/SiCp (130nm), Al/SiCp composite material. Also, its preparation process and mechanical properties are studied. We used optical microscope (Leica MEF4M) to observe the distribution of reinforced phase and tissue compactness; used JXA-840A scanning electron microscope with AN10000 X-ray spectrometer to observe and analyze the tensile specimen fracture surface, frictional wear surface and frictional wear sub-surface, etc.; studied the frictional wear performance characteristics, mechanism of SiCp/Al composite, as well as influence rules of SiCp size and content; and studied enhancement effects of sub-micron SiCp ultrafine particles.In this paper, WYKO NT1100 non-contact Optical Profiler is used to observe and analyze three-dimensional specimen wear surface morphology, and Perthometer S3P specimen surface analyzer made in Germany is used to measure the surface roughness of speciemen. Moreover, collected data is used as the the raw data for fractal study. On the basis of in-depth analysis of existing fractal dimension measuring methods, we applied WM function model as a fractal model to simulate worn surface profile; with the structure function method for calculating fractal dimension method, we studied the fractal characteristics of measured sample blocks'worn surface profile, as well as the relationship between fractal dimension D and traditional roughness parameters.Performance test of SiCp/Al Composites showed that their tensile strength increases with the rise of the content of SiCp volume, and their elongation rate decreases with the increasing of SiCp volume content and size. SiCp/Al Composites have good plasticity, and sub-micron SiCp/Al's tensile strength, compressive strength and elongation rate are superior to micron SiCP/Al; when SiCp content is low, the compressive strength increases with the increase of SiCp size; when SiCp volume content is high, the compressive strength of micron SiCp/Al composite begins to decline, but the compressive strength of sub-micron SiCp/A 1 composite is still increasing. According to the test results of mechanics performance testing, an obvious ultrafine particle enhancement can be seen in sub-micron SiCp.According to the tensile fracture surface of SiCp/Al composite, we can conclude that the fracture shows characteristics of toughening. The dimple size increases with the augment of SiCp content and size. SiCp/Al composite fracture mechanism, on one hand, is that the decohesion of SiCp /Al interface causes the initiation of the cavity, and then the cavity grows up, gets together and breaks up, leading to the formation of dimples, and then unites and develops to result in the matrix alloy tearing, which is the main manner of fracturing; on the other hand, the brittle fracture of SiC particles can also cause stress concentration, resulting in cavity generation, and growing up and aggregation of the cavity can induce cracks and cause fracture. Also, with the increase in SiC particle size, the second fracture tends to increase.Studies of tribological properties have shown that the wear mechanism of composite materials is the combined actions of adhesive wearing, micro-cutting and peeling layers. SiCp has some inhibitory effect on the adhesion wear of materials. As the size and content of SiCp increase, adhesive wear weakens, SiCp/Al matrix composites'wear resistance increases; 5% vol SiCp (130nm)/Al causes little wear loss of wear coupling parts, only 1/2～1/8 that of SiCp (14μm)/Al composite under the same load, which is an ideal wear-resistant material under medium or low load; 5 vol% SiCp (14μm)/Al is an ideal wear-resistant material under high load.Both pure Al and SiCp/Al composites has Fe-rich mechanical mixed layer on their friction surface. Mechanical mixed layer is beneficial to the reduction of SiCp shedding and adhesion phenomenon, but there is delamination phenomenon in layers, and they have great brittleness, and can easily crack or spall.Under a load of 150N, the friction coefficient of five kinds of materials containing SiCp/Al and pure Alincreases tends to decrease when time increases, and tends to stabilize. The initial friction coefficient and stable friction coefficient of pure Al are the smallest, and its running-in period is also the shortest. As time increases, the stable value of friction coefficient increases with the increase of SiCp content and particle size, and the friction coefficient of SiCp (14μm)/Al is larger than SiCp(130nm)/Al and pure Al. The wear loss of SiCp/Al and pure Al increases with time. After 12 hours, the increase rate of wear loss of 5% vol SiCp (130nm)/Al and 5% vol SiCp (14μm)/Al is significantly less than other materials. Up to 24 hours, the wear loss of 5% vol SiCP (130nm)/Al is less than that of 1.5% vol SiCp (14μm)/Al. Thus, we can infer that, under a condition of less load, the ultrafine particles have a certain enhancement effect on anti-fatigue wearing, and the anti-fatigue wearing performance of 5% vol SiCp (130nm)/Al tends to be better than that of 1.5% vol SiCP (14μm)/Al.Studies of fractal have shown that the wear surfaces of composite materials have fractal characteristics. The larger fractal dimension D is, the more complex those contours are. Simultaneously, there is a certain correlation between D and the contour arithmetic mean deviation as well as contour maximum height of traditional roughness evaluating parameters, but their linear relationship is not significant, and therefore they can not replace each other. By analyzing the test results of SiCP/Al composite worn surface topography fractal characteristics, it shows that, the worn surface profile has statistically self-affine fractal properties; there is a certain relationship between SiCp/Al composite surface profile fractal dimension and wear loss; and when D is within a certain extent, the wear loss increases as the fractal dimension increases. According to the SEM morphology of worn surfaces of Al, SiCp(130nm)/Al and SiCp (14μm)/Al composites, we can also conclude that the more sophisticated SEM morphology of composites' worn surface is, the greater the fractal dimension becomes. Therefore, surface profile fractal dimension can serve as a surface quality evaluation criterion of particle-reinforced metal-matrix composites.Studies have shown that structure function method is an effective approach to calculate fractal dimension; the fractal study of composite worn surface is an effective supplementary method for tribology research; and with the help of measurement of material wear surface fractal dimension, there is a certain feasibility to predict the wear loss of materials.