Wear Properties of Ilmenite/sillimanite Reinforced Hyper Eutectic Al-Si Alloy Matrix Composites

Abstract

The prime objective of the present work is to develop light weight, low cost Aluminium metal matrix composite (AMCs) for break rotor application exhibiting good wear property. AMCs were fabricated by using automobile grade LM30 Al-Si alloy as a matrix and ilmenite and sillimanite as reinforcement. The effect of various sizes and concentrations of reinforced particles on the microstructural and wear properties of LM30 alloy based composites was investigated. The effect of solid lubricants (graphite and tin) on the microstructural and wear properties of the developed composites was also studied. The work done in present investigation is divided into eight chapters which are as follows: Chapter 1: This chapter presents an introductory discussion about tribology and its applications. It also describes various postulates of tribology, such as wear, friction, and lubrication. The need to develop materials to minimize tribological energy losses has also been discussed. The different types of composites and reinforcements along with their advantages, have been discussed. At the end, the superior properties of ceramic particles reinforced AMCs have been described. Chapter 2: This chapter presents available literature pertaining to the development of particle reinforced hypereutectic Al-Si alloy composites. The current work is based on the stir casting process. Thus, the main focus of this chapter is to cover the literature on the processing of AMCs using stir casting process and study their physical properties especially wear resistance. In the last of this, the gaps in literature is presented. Based on the literature gap the objectives of the current work has been finalized and presented. Chapter 3: This chapter describes the procedure followed for fabrication, testing, and characterization of the base alloy and the developed composites. The different parameters used during the processing of AMCs through stir casting are discussed. This section covers the discussion on various testing equipments and the different characterization techniques to analysis the samples. This include microhardness, density measurement, dry sliding wear (pin-on-disc arrangement), optical microscopy, scanning electron microscopy (SEM), and X-ray diffraction techniques. The flow chart of the methodology is also presented. Chapter 4: The chapter deals with results and discussions on as developed AMCs with single size range ilmenite reinforcement. The effect of different size range fine; 32-50 µm, medium; 50-75 µm and coarse; 75-106 µm ilmenite incorporated inside the Al-alloy matrix with variation in their concentration in between 5-20 wt. % is discussed. In this chapter, the surface morphology of the AMCs was studied with the help of optical microscope to observe the distribution of the particles in the Al-matrix. It is observed that bulk hardness and micro hardness measured at Rockwell, and Vickers hardness tester of 15 wt.% fine size (32-50 µm) ilmenite reinforced composites was higher as compared to other composites due to increased number of particles in metallic matrix. All AMCs were tested on pin-ondisc setup for dry sliding wear test at various loading conditions. It revealed that 15 wt.% fine size (32-50 µm) ilmenite reinforced composites shows the superior wear resistance. Wear tracks and wear debris were analyzed by using SEM. Chapter 5: In this chapter the results obtained from the AMCs reinforced with a combination of fine and coarse ilmenite particles i.e., dual size (F: C=1:4, 2:3, 3:2 and 4:1) were used to prepare dual sized ilmenite reinforced composite samples are presented. The selection of two different-size range particles helps to avoid the agglomeration of fine-sized particles, which deteriorates the matrix properties. The role of different ratios of the fine and coarse size of ilmenite particles in the Al-matrix on the wear behavior and coefficient of friction have been studied at different loads. On the basis of obtained results, wear track and debris of AMCs samples collected after the wear test at different conditions were analyzed under SEM-EDS to categorize the wear mode of the composites. Chapter 6: This chapter describes the results of the developed AMCs using a 10 wt.% and 15 wt.% wide size range (32-106 µm) of ilmenite reinforcement with 1 wt.% solid lubricant(s) Gr/Sn. The wear behavior of the developed composites has been studied for their end application. Since the combination of dual solid lubricants improves the wear resistance of prepared AMCs, dual solid lubricants (0.5 wt.% Sn+ 0.5wt.% Gr) have been added in single and dual size range ilmenite reinforced composite to obtain better wear resistance. The optical micrographs obtained for different composite formulations show different structural features. Finally, SEM-EDS and XRD analysis of wear tracks and wear debris are discussed, which provide evidence regarding wear mechanisms involved during the material removal process at different applied load conditions during wear testing. A theoretical study of frictional heat generated during dry sliding and its dissipation has been done to establish the operative wear mechanism in the composites. Chapter 7: The chapter represents the results and discussions on the as developed AMCs reinforced with two different minerals ilmenite and sillimanite. The effect of Gr/Sn as a solid lubricant and reinforcement of two different minerals ilmenite, and sillimanite in the LM30 alloy, to develop aluminum metal matrix composite is also done. The microstructural analysis to observe the distribution of the reinforcement has been done for all the developed composites. The hardness of the composite was measured to see the effect of reinforcement. The wear and friction tests were performed for the end application of composite in the industries. The SEM-EDS analysis was done to analyze the wear mechanism. A comparison of wear properties of the developed composite has been done with grey cast iron specimen used in the brake rotor in the automobile industries. Chapter 8 summarizes the entire work done in the present thesis to understand the influence of reinforcement and solid lubricants. The present work shows a uniform distribution of the reinforced particles in the LM30 (Al-Si alloy) matrix developed by the stir casting process. XRD data shows the presence of ilmenite particles as well as a new phase developed during the casting process. It was found that hardness of the LM30 alloy improved with incorporation of ilmenite particles in the Al-matrix. With decreasing the particle size, hardness of the composites also increased significantly. The present research showed superior wear and friction results for 15 wt.% dual size range reinforced ilmenite particles having dual solid lubrication (0.5 wt.% Sn + 0.5wt.% Gr) for the AMCs containing fine particles in larger proportion (F:C=4:1). Wear rate and COF values of single range ilmenite particles reinforced AMCs at a given reinforcement amount decreased with decrease in particle size. However, it was observed that the wear rate and COF values further reduced for (F:C=4:1) dual size range ilmenite reinforced composite. The fine particles provide large interfacial sites for effective load transfer and reduce wear rate and COF values. In contrast, the coarse particles support a major proportion of applied load and shield the finer particles from ploughing action. It is observed that the wear rate values of 15 wt.% dual size range ilmenite with dual solid lubrication (0.5 wt.% Sn+ 0.5wt.% Gr) with a higher concentration of fine particles i.e. F:C=4:1 was almost comparable with grey cast iron specimen. Also, the brake rotors fabricated using composites provide a weight reduction of nearly 60% as compared to cast iron brake rotors. Considering these facts, 15 wt.% dual size range ilmenite with dual solid lubrication (0.5 wt.% Sn+ 0.5wt.% Gr) reinforced composites with higher portion of finer particles can be better substitute for brake rotor materials in light motor vehicles.