Study On Failure Mechanisms Of Ceramic Cutting Tool Based On The Evolution Of Mechanical Behaviors At Elevated Temperature

Ceramic cutting tool material is one of the most important cutting tool materials in the twenty-first Century because of its high heat resistance,high hardness,excellent wear resistance and chemical stability.At present,most of the research focuses on improving the comprehensive mechanical properties of ceramic cutting tool materials at room temperature.In high speed machining,the tool serve at the high temperature environment.So the mechanical properties at elevated temperature of ceramic materials seriously affect the cutting performance.If the mechanical behavior of ceramic cutting tool materials in service conditions can be investigated,then it will be helpful to reveal the failure mechanism of ceramic cutting tools in essence.In this paper,the mechanism of the mechanical behavior evolution of the ceramic cutting tool and the relationship between the tool failure mechanism and the mechanism of the tool failure are studied.The research results will be of great guiding significance for the selection of tool materials and the optimization of the cutting parameters.In this paper,two kinds of Al2O3/TiC ceramic cutting tool materials with the same component content but different particle size were compared to eliminate the effect of the difference of physical and chemical compatibility on the tool failure.First,two kinds of tool materials were prepared,one was TiC microparticle composite Al2O3 based ceramic cutting tool material(AT55),the other was microscale and nanoscale TiC particle composite Al2O3 based ceramic cutting tool material(ATT5).By optimizing the sintering process,the flexural strength,fracture toughness and hardness of AT55 cutting tool material at room temperature were obtained as 842 MPa,6.88 MPa m1/2 and 17.46 GPa respectively The flexural strength,fracture toughness and hardness at room temperature of ATT5 cutting tool material at room temperature were 880 MPa,7.00 MPa m1/2 and 18.2 GPa respectively.The evolutions of mechanical properties of two kinds of ceramic cutting tool materials,AT55 and ATT5,with different mechanical properties at room temperature were compared.It was found that the flexural strength of two kinds of ceramic cutting tool materials decreased with the increase of temperature(20?1000 ?),and decreased sharply after 800 ?.Although the flexural strength of ATT5 cutting tool material with TiC nanoparticles was higher than that of AT5 5,the flexural strength at elevated temperature was lower.The fracture toughness of the two tool materials decreased first and then increased with the increase of temperature(20-1100 ?).At 1000 ?,the fracture toughness of ATT5 ceramic tool material increased and peaked.The hardness of two kinds of ceramic cutting tool materials decreased approximately linearly with the increase of temperature(20-1000 ?).The analysis of the evolution mechanism of mechanical properties showed that the addition of TiC nanoparticles refined the grain of the ceramic tool material at room temperature.At the same time,the presence of TiC nanoparticles in the crystal played a role in increasing the ratio of transgranular fracture and preventing the crack growth,thus improving the flexural strength and fracture toughness at room temperature.At elevated temperature,TiC nanoparticles were oxidized more easily.At the same time,TiC nanoparticles refined the grains,increased the grain boundary ratio,and softened the material more easily,which resulted in the decrease of the mechanical properties of the materials at high temperature.The friction and wear characteristics of ceramic cutting tool materials at different temperatures were studied.At room temperature,the friction coefficient decreased linearly with the increase of sliding speed in the range of 50?150 m/min.With the increase of sliding speed,the metal adhered at the friction interface was more and more smooth and uniform,so the friction coefficient decreased with the increase of sliding speed.In the range of 600?800 ?,the friction coefficient decreased with the increase of temperature,and the trend gradually slowed down.Compared with room temperature,the friction coefficient at high temperature is smaller.The main wear mechanisms of AT55 ceramic tool material at room temperature were adhesion wear and abrasive wear,and the main wear mechanisms of the tool material at elevated temperature were abrasive wear and oxidation wear.The cutting performance of two kinds of AT55 and ATT5 ceramic tools with different high temperature performance in dry machining of H13 steel was compared.First,the AdvantEdge software was used to analyze the effect of cutting speed on the surface temperature distribution and cutting force of the ceramic cutting tool.The cutting parameters range of the AT55 cutting tool machining H13 steel was drawn up according to the evolution of the mechanical properties at elevated temperature,the cutting speed was 50?150 m/min,cutting depth was 0.5mm,feed was 0.1 mm/r.The machining experiment results showed that the life of the two kinds of ceramic cutting tools increased first and then decreased with the increase of the cutting speed.and the tool life was the longest at the cutting speed of 100 m/min,and the cutting performance of the AT55 cutting tool with higher mechanical properties at elevated temperature was superior to the ATT5 cutting tool with higher mechanical properties at room temperature.It could be seen that cutting performance of cutting tools was directly related to the mechanical properties at elevated temperature of tool materials,but had little relationship with the mechanical properties at room temperature.Based on the evolutions of the mechanical behavior at elevated temperature of cutting tools,the failure mechanisms of tool were analyzed.At low speed,the cutting temperature was relatively low,the hardness of the work piece was high,the cutting force was large,and the main failure mode of the tool was breakage and the main wear mechanisms were adhesive wear and abrasive wear before the breakage.At medium speed,the material softened and the cutting force decreased due to the increase of cutting temperature.The ceramic tool material was oxidized slightly at this temperature and the mechanical properties at elevated temperature decreased,but still remained at a high level.The main failure mode of the tool included flank wear,crater wear and notch wear.The wear mechanisms were adhesive wear,abrasive wear and slight oxidation wear.At high speed,the cutting temperature reached 900 ?.Because of the grain boundary softening at this temperature,the flexural strength of the ceramic tool material decreased seriously and the tool failure mode was mainly breakage,accompanied by flank wear and crater wear caused by oxidation at elevated temperature.