| High speed machining(HSM)is one of the main development directions in the field of modern manufacturing.As one of the main tool systems,ceramic tools have important applications in high-speed finishing and semi-finishing.In the process of practical machining,the tool-workpiece contact zone is an inhomogeneous thermal-force-chemical multi-field interaction.At this time,the high temperature mechanical properties of ceramic tools will change with different laws.This evolution will influence the failure of ceramic tools,tool life and the quality of the machined surface.At present,there is little research on the influence of the evolution of tool high-temperature mechanical properties on the quality of machined surface.Therefore,the mechanical properties and evolution mechanisms of ceramic cutting tools at high temperature and their affects on the surface quality are studied,and then the cutting performance of ceramic tools with different high temperature mechanical properties are evaluated.It is beneficial to the selection of ceramic tools and guide the further research of new ceramic cutting tools.Firstly,two different Al2O3/(W,Ti)C ceramic tool materials were prepared,one was Al2O3/(W,Ti)C ceramic tool material without metal phase Ni(marked as AWT),the other was Al2O3/(W,Ti)C/Ni ceramic tool material with metal Ni added(marked as AWTN).After optimized sintering process,the fracture toughness,bending strength and Vickers hardness of AWT at room temperature were 5.5±0.2 MPa·m1/2,750±25 MPa and 19.5±0.5 GPa,respectively.The fracture toughness,bending strength and Vickers hardness of AWTN at room temperature were 6.5±0.3 MPa·m1/2,850±30 MPa and 18.5±0.5 GPa,respectively.The evolution laws and mechanisms of high temperature fracture toughness,bending strength and hardness of AWT and AWTN with different room temperature mechanical properties were studied.The results showed that the fracture toughness of AWTN was higher than that of AWT ceramic material within the test temperature(200-1000 ?)range.The fracture toughness of AWTN ceramic tool material generally showed a downward trend,while AWT material increased slightly at 700 and 1000 ?.The bending strength of the two ceramic tool materials decreased with the increase of temperature(20?1000 ?).The hardness of AWT and AWTN decreased approximately linearly with the increase of temperature(20?1000 ?),and the hardness of the two materials at 1000 ? were very close.The evolution mechanisms of mechanical properties of ceramic tool materials at high temperature showed that,microcracks generated by WO3 transformation phenomenon occurred at about 700 °C could increase the toughness of the AWT.At 1000 ?,more strain energy was consumed due to plastic deformation and the rod-like and plate-like WO3 grains could cause pull-out and bridging effects,then the fracture toughness was improved.The low melting point metal phase decreased the interfacial bonding strength that changed the fracture mode at high temperature.The decrease of bending strength of ceramic tool material was also caused by the decrease of elastic modulus and materials oxidation at high temperature.The decrease of hardness at high temperature was mainly related to the softening rate of Al2O3 and(W,Ti)C.Due to the low melting point of metal phase Ni,the hardness of AWTN was slightly lower than that of AWT.The friction and wear characteristics of AWT/H13 steel and AWTN/H13 steel at the same temperature(600 ?)were studied.The experimental results showed that as the speed increased,the average friction coefficient decreased at the same load.The friction coefficient of AWT was lower than that of AWTN.The friction and wear characteristics of AWT ceramic tool material at different temperatures(ambient?600 ??700? and 800 ?)were investigated.The results showed that the friction coefficient of AWT material increased with the increase of temperature.The wear mechanism of ceramic materials from room temperature to 600 0C were adhesive and abrasive wear.Above 600 ? wear mechanisms were adhesive,oxidation and abrasive wear.The cutting performance of AWT and AWTN ceramic tools in high speed dry machining hardened H13 were studied.The results showed that,when the cutting speed increased,the cutting temperature increased.The roughness of machined surface decreased with the increase of cutting speed.The residual compressive stress of machined surface decreased.As the cutting speed increased,the work hardening of the workpiece surface gradually decreased.The cutting temperature increased with the increase of tool flank wear.The surface roughness decreased first and then increased with the increase of ceramic tool flank wear.The residual stress changed from compressive stress to tensile stress with the increase of ceramic tool flank wear.The microhardness of machined surface and the depth of hardened layer increased with the increase of tool surface wear.The variation of surface quality under the same cutting conditions of four ceramic too?s such as ATT5.?AT55.?AWTN and AWT were studied.The cutting temperature of ATT5 rises the fastest with the process of cutting,the high temperature mechanical properties of ATT5 drop seriously,and the surface quality changes obviously.The next was the AWTN.The temperature changes in the cutting zone of the AT55 and AWT tools were small,making the surface quality relatively stable.The cutting performance of four ceramic tools with different high temperature mechanical behaviors were studied.The fuzzy evaluation between them was established.The evaluation results showed that the cutting performance of the cutting tool was directly related to the mechanical behavior of the tool at high temperature.Weight vector could be obtained by entropy method.The high temperature hardness of ceramic tools had the greatest influence on cutting performance,followed by bending strength and fracture toughness at high temperature.Under the experimental conditions,the expressions of the relationship between high temperature mechanical properties and cutting performance(surface quality,flank wear and tool life)were obtained.At the same time,the ratio vector of cutting performance of four kinds of cutting tools was obtained by fuzzy evaluation analysis.The evaluation results were AT55>AWT>ATT5>AWTN,implied that AT55 had the best comprehensive cutting performance,followed by AWT cutting tool,and the cutting performance of ATT5 and AWTN ceramic tool were slightly worse than the previous two.It proved that the cutting performance of ceramic cutting tools with good mechanical properties at room temperature was not always optimal,and the mechanical behavior of ceramic cutters at high temperature had highly correlated with the cutting properties.This had important guiding significance for the selection of tools and the development of new tools. |
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