Improvement of Mechanical and Operational Properties of PcBN Utilizing TiN Coated Powders: Experimental Evaluation and Theoretical Basement

The paper discusses the results of the experimental investigation of the structure, mechanical properties and the performance of the new PcBN composites, obtained from cBN powders with TiN coating in comparison with standard BL-PcBN composites with TiN binder. As demonstrated, the proposed method for optimizing the structure and properties of composites results in a significant increase in their strength and overall performance. As well as this, the results of FE modeling allowed a theoretical explanation to be given for these experimental data. It was shown that using composites obtained from cBN powders with a coating containing 3%–8% Ti in a cutting tool allows for a 20% reduction in tool wear rate during high-speed (220 m/min) cutting of hardened steel compared to a tool equipped with a standard composite PcBN, and the tool wear rate reaches the level of the BL group composite with 40% (vol.) TiN content. Under conditions of mainly abrasive mechanical wear at a speed of 110 m/min, the efficiency of the tool with the new composite is relatively low. During high-speed processing under dynamic impact loads, the experimental composites, unlike the BL-PcBN composites, retain their workability. In this case, tools with cBN-3%Ti composite are most effective. Using the developed special algorithm and based on the statistical theory of extreme values and estimation of the probable level of microdamage in the ceramic phases using the FEM method, a study of the influence of the microstructure on the stress state and brittle strength of BL-PcBN and experimental composites was conducted. The parameters calculated on the basis of modeling demonstrate that, other things being equal, the strength of the composite made from coated powders is 1.1–1.3 times higher than that of PcBN of the same phase composition, but with a structure that occurs during sintering of powders made according to the traditional technology of mechanical mixing of components.