Development Of Crack Self-healing Ceramic Tool

The cutting heat can be effectively used to get liquid phase to fill cracks by crack self-healing ceramic tool material,and mechanical properties of materials can be recovered.A new kind of crack self-healing ceramic tool ATTM15 was successfully developed in the present research.The material composition was designed,the sintering process parameters were optimized,the effect of healing temperature,healing time and pre-crack length on flexural strength of ceramic tool materials after crack self-healing was studied,and the cutting performance of the crack self-healing ceramic tool when machining 321 austenitic stainless steel was studied experimentally.The material composition was designed by using Al₂O₃ as the matrix and TiB₂/TiSi₂ as the addition phase.Oxidation products of TiSi₂ could protect the phase of TiB₂ and fill in cracks.The chemical compatibility and physical compatibility of the crack self-healing ceramic tool materials were analyzed.The elastic modulus and thermal expansion coefficient of Al₂O₃ and TiB₂ were well matched.The effects of TiSi₂ content,sintering temperature and sintering time on mechanical properties and microstructure of ceramic tool materials were studied.The material phase of crack self-healing ceramic tool materials was analyzed,and the sintering temperature and the sintering time were optimized.The optimized sintering temperature was 1600?,sintering time was 30min,and sintering pressure was 32MPa.The research results showed that TiSi₂ could improve the fracture toughness of crack self-healing ceramic tool materials,the optimum content of TiSi₂ was 15wt%,and fracture modes were intergranular fracture and transgranular fracture.The flexural strength,Vickers hardness and fracture toughness increased firstly and then decreased with an increase in the sintering temperature.Changing trends of the flexural strength,Vickers hardness and fracture toughness were influenced by sintering time were consistent.They increased firstly and then decreased with an increase in the sintering temperature.The optimum comprehensive mechanical properties of ceramic tool material ATTM15 were measured with the flexural strength,Vickers hardness and the fracture toughness of 711.98±41.48MPa,16.89±0.27GPa and 4.82±0.10MPa·m1/2,respectively.The Vickers hardness indenter was used to generate the pre-cracks.Effects of healing temperature,healing time and pre-crack length on flexural strength were studied,the behavior of crack self-healing ceramic tool material Al₂O₃-TiB₂-TiSi₂ was also analyzed.The crack self-healing mechanism of Al₂O₃-TiB₂-TiSi₂ crack self-healing ceramic tool material was revealed.It is shown that the flexural strength increased firstly and then decreased with an increase in the healing temperature.At 800?,the strength of crack-healing specimen was recovered up to 92.66%,compared with the flexural strength of raw smooth specimen.The flexural strength of crack self-healing ceramic tool material increased with an increase in the healing time.At the healing temperature of 800 ? for 90 min,the flexural strength of crack self-healing specimen was recovered completely and the recovery percentage of flexural strength reached up to 107.25%.The flexural strength of crack-healing specimens with a crack length of 150?m and 300?m were fully recovered,but incomplete recovery appeared at the crack length of 500?m.The optimized healing temperature,healing time and pre-crack length for complete strength recovery were 800?,90 min,and less than 300mm,respectively.The crack-healing mechanism was attributed to the crack-filling with liquid phases of SiO2 and TiO2.The most important advantage of this mechanism was that the reaction products were filled with no gas produced during the crack healing process.It was beneficial to the recovery of the strength and surface quality of ceramic tool materials.The cutting performance of crack self-healing ceramic tool ATTM15 for machining 321 austenitic stainless steel was studied experimentally.The tool wear mechanism of crack self-healing ceramic tool ATTM15 was preliminarily analyzed.It is shown that the optimized cutting speed was 60 m/min,the optimized feed rate was 0.3 mm/r and the optimized depth of cut was 0.25 mm.The cutting speed was the most important factor affecting wear resistance of crack self-healing ceramic tool ATTM15,while the depth of cut and feed rate had less effect.The main tool wear modes of crack self-healing ceramic tool ATTM15 were rake wear,flank wear and boundary wear.The main tool wear mechanisms of crack self-healing ceramic tool ATTM15 were oxidation wear,diffusion wear,and adhesive wear.Oxidation wear was beneficial to crack healing.