On the improvement of the ductile removal ability of brittle KDP crystal via temperature effect

Brittle KH2PO4 (KDP) crystal is difficult-to-machine because of its low fracture resistance whereby brittle cracks can be easily introduced in machining processes. To achieve ductile machining without any cracks, this type of materials is generally processed by some ultra-precision machining techniques at ambient temperature with nanoscale material removal, yielding low machining efficiency and high processing cost. Recently, thermal assisted techniques have been used to successfully facilitate the machining of some difficult-to-machine materials, like superalloys, but little effort has been made to explore whether the temperature effect can contribute to the ductile machinability of brittle materials yet. Thus, the aim of this study is to figure out the specific role of temperature in the deformation behaviours of brittle KDP crystal by nano indentation/scratch methods. It is found that compared with those at ambient temperature (AT, i.e. 23 degrees C), the hardness and Elastic modulus of KDP crystal at elevated temperature (ET, i.e. 160 degrees C) decrease substantially by 21.4% and 32.5%, respectively, while the fracture toughness increases greatly by 15.5%, implying a higher ability of ductile deformation at ET. Meanwhile, the scratch length within ductile removal has been identified to be extended more than 4 times by increasing temperature from AT to ET. Both the quantity and size of brittle features (e.g., cracks and chunk removal) show a reducing trend with the increase of temperature. To uncover the underlying mechanism of this phenomenon, an updated stress field model is proposed to analyze the scratch-induced stress distribution by considering the evolution of material property at various temperature. These presented results are significant for the future design of specific thermal-assisted processing techniques for machining brittle materials efficiently.

Automated summary

This study investigates the specific impact of temperature on the deformation behaviors of brittle KDP crystal through nano indentation/scratch methods. The results show that increasing the temperature significantly decreases the hardness and Elastic modulus of KDP crystal, while greatly increasing the fracture toughness, indicating a higher ability of ductile deformation at elevated temperature. Additionally, the scratch length in ductile removal process is extended more than 4 times by increasing temperature, and the quantity and size of brittle features show a reducing trend with temperature increase.