A systematic computational design approach to develop ceramic-composites for dry cutting application

Machining of various high temperature and difficult-to-cut materials such as titanium and nickel alloys is a challenging task, especially at high cutting speeds. Hence proper tool materials need to be designed and manufactured for cutting such alloys under dry cutting conditions which are considered as an environmental-friendly and cost-effective machining technology. In recent years, there has been an increasing interest in ceramic-composite cutting inserts which consist of a single or hybrid reinforcement with various attributes in terms of volume fraction, size, interface of matrix-reinforcement, and self-lubricity to achieve excellent mechanical, thermal and tribological properties. The relatively high coefficient of friction at the tool-workpiece interface in the case of ceramic tools often generates excessive heat during dry machining, which eventually leads to significant wear and hence the reduction of the tool's life. Self-lubricating inclusions in the ceramic matrix can lead to a novel solution to improve the tribological properties of such composites by forming a lubricating film (tribo-film) during sliding. However, recent studies showed that adding solid lubricants could limit the mechanical properties of ceramic composites. Therefore, designing high-toughness ceramic-matrix self-lubricating composites for dry cutting of hard-to-cut materials is essential. Such a high-performance ceramic cutting material with improved performance can be reached through a suitable material design and processing technique. The focus of this research is to develop innovative ceramic composites cutting inserts using a comprehensive computational material design tool that could predict the most suitable combinations of solid lubricants in the ceramic matrix for enhancing structural, thermal and tribological properties. In the material design stage, various combinations of ceramic materials and inclusions with optimum attributes will be first selected based on predictions of mechanical properties (such as constitutive behavior and fracture toughness), thermal properties (such as thermal conductivity) and tribological properties (such as wear resistance). Optimum combination of various inclusions such as hexagonal boron nitride (hBN), nickel-coated cubic boron nitride, grapheme platelets, CNTs, Molybdenum disulfide (MoS2), metals (like Ag, Cr), metal oxides (like Ag2O, Cu2O, ZnO ), fluorides (like BaF2, CaF2) etc. in ceramic matrices (oxide and non-oxide nitrides and carbides) can give best combination of self-lubrication, toughness and thermal conductivity with proper computational design tools. A mean-field homogenization scheme will be developed to predict the constitutive behavior while J-integral based fracture toughness model will be used to predict the effective fracture toughness of the ceramic composites. An effective medium approximation will be used to predict the potential optimum thermal properties. A deterministic mechanical friction model will be developed for friction mechanism and tribological behavior of various tribosystem (ceramic tools and workpiece combinations) in order to identify the best self-lubricating inclusions in the ceramic matrix. After the material design stage, some basic-shaped inserts, as well as pin-shaped dies, will be designed and manufactured to be used in Spark Plasma Sintering (SPS). Sintering of the designed inserts will then be done using (SPS) with designed matrix and reinforcement(s). Mechanical and thermal properties will be measured experimentally and the computational designs will be validated. Sliding wear tests against various hard-to-cut workpieces under dry conditions will be performed on these ceramic composites (various tribosystems). The effect of the reinforcements as solid lubricants on the microstructure, mechanical properties, and self-lubricating behavior of ceramic composite will then be studied. It is expected that the outcomes of the proposed project will provide a useful guideline for the manufacturing of environmentally friendly and low-cost tool inserts.