Fabrication And Cutting Performance Of New Ceramic Cutting Tool With Crack Self-Healing Function

Ceramic cutting tools offer the benefits of high hardness,good wear resistance,and heat resistance,implying a wide range of applications in the fields of high-speed cutting and cutting difficult-to-cut materials.However,the intrinsic brittleness of ceramic tool materials severely limits their further application and promotion.To address this problem,the typical approaches focus on toughening and strengthening ceramic tool materials to improve their resistance to crack propagation.In this paper,a novel kind of ceramic tool material with a crack self-healing function was created from the point of crack self-healing,with the goal of addressing the inherent crack sensitivity.The crack healing mechanism under heat treatment conditions was thoroughly investigated,as well as the crack healing behavior during the cutting process.The crack self-healing and strength recovery of ceramic tools in the cutting process are advantageous for delaying tool failure,extending tool life,and enhancing tool reliability.Based on the crack self-healing function,a new alumina-based ceramic tool material,Al₂O₃/SiCw/TiSi₂,was designed and fabricated.It was found that when 10 vol%TiSi₂ was added,the ceramic tool material had better overall mechanical properties under the sintering condition of 1600℃/30 min.Different sizes of cracks were prefabricated by the Vickers indentation method.The impacts of heat treatment temperature,holding time,and prefabricated crack size on the crack healing behavior of ceramic tool materials were studied by high temperature heat treatment,and the crack self-healing process was revealed.The results showed that the ceramic tool material had good crack healing ability.At 800℃,the crack with a maximum width of 0.68μm was healed,and the material’s bending strength was fully recovered.The high temperature oxidation reactions of Ti5Si₃ and SiCw were primarily responsible for crack healing in ceramic tool materials,whereas Ti5Si₃ was formed during the transformation of TiSi₂ during sintering and could be described by thermodynamically feasible reactions.The primary mechanism of the healing process was the local bridging of cracks caused by the in-situ growth of TiO₂ and the liquid phase filling of SiO₂ intermediate oxides（Si₂O3 and SiO）.The high temperature mechanical properties and evolution process of Al₂O₃/SiCw/TiSi₂ new ceramic tool materials were investigated.The results revealed that the bending strength of ceramic tool materials increased initially and subsequently reduced as temperature rose,while the Vickers hardness and fracture toughness assessed by the indentation method dropped as temperature increased.Under air conditions,the fracture toughness measured by the singleedged notch beam method showed obvious recovery.The changes in the high temperature mechanical properties of ceramic tool materials were connected to grain boundary softening,oxidized healing of microcracks and defects,and the viscosity of the glass phase.Among them,the viscosity of the glass phase and the oxidation healing of microcracks and defects are favorable for the improvement of tool materials’ strength.For dry turning the nickel-based alloy GH4169,the cutting performance of the new ceramic tool made of Al₂O₃/SiCw/TiSi₂ was investigated.The failure mode and crack healing behavior of the tool were analyzed.The machining process of the nickel-based alloy GH4169 utilizing the Al₂O₃/SiCw/TiSi₂ ceramic tool was simulated by AdvantEdge.Based on the temperature field distribution of the tool surface,the tool corner radius was determined to be 0.4 mm,and the rounded cutting edge radius was 0.04 mm.The orthogonal experiment was conducted within the cutting parameters range,which had been preliminarily specified.The optimum cutting parameters were established with the amount of material removed as the optimization objective and taking tool life into account:60 m/min of cutting speed,0.65 mm of cutting depth,and 0.08 mm/r of feed rate.Under the experimental conditions of this cutting amount,the cutting performances of the Al₂O₃/SiCw/TiSi₂（AST）ceramic tool,the Al₂O₃/SiCw（AS）ceramic tool,and the commercial ceramic tool LT55 were compared.The findings indicated that the newly created crack self-healing ceramic tool AST had a life that was 120%longer than the commercial ceramic tool LT55 and 20%longer than the AS ceramic tool without a healing agent.The main failure modes of the Al₂O₃/SiCw/TiSi₂ ceramic tool in dry cutting nickel-based alloy GH4169 are flank wear,tool material spalling caused by adhesive wear,and boundary wear.During the cutting process,the healing agent in the tool material could be oxidized to form molten oxide,filling the crack area.It contributed to the passivation of the crack tip and the slowing of crack propagation,both of which were advantageous for increasing tool life.