Microstructure and mechanical properties of commercial, bronze-bond, diamond-abrasive tool materials

Bronze-matrix, diamond-particle composites are commonly employed as tool materials in grinding applications, in particular for precision grinding of optical materials. However, while tool selection and performance is often rationalized in terms of changes in tool “modulus/stiffness” or “hardness,” neither the range and variability of the mechanical properties nor the fundamental microstructural parameters controlling them are well understood. This has hindered quality control and prevented the accumulation of the industrial property-performance data essential to the development of improved tool materials and processes. In this study, bronze-bond diamond-abrasive composite tool materials, with systematic differences in their diamond sizes and concentrations, were obtained from different commercial vendors, characterized mechanically and microstructurally, and the results statistically analyzed. Microstructurally, a size dependent diamond distribution and relatively high levels of porosity (~10 vol%) were observed. The mechanical properties exhibited a high degree of variability, with statistically significant differences occurring based on the vendor and diamond concentration, but not diamond size. Porosity was shown to be the key microstructural parameter controlling mechanical properties. Porosity depended on vendor, diamond size, and diamond concentration, but large, nonsystematic variations were also observed, indicating that it is not consistently controlled in current commercial materials. Finally, the porosity and mechanical properties were shown to correlate strongly with ultrasonic wave speed over a wide range of tool materials, demonstrating a practical nondestructive method for tool characterization.