Study On TiCN-based Ceramic Tool With A Core-rim And Particle Dispersion Microstructure And Tool Cutting Performance

The flexture strength,fracture toughness and hardness of TiCN-based ceramic tools were difficult to improve simultaneously.And at present,types of high-performance domestic TiCN ceramic tools were fewer.Aiming to overcoming these disadvantages,TiCN-based ceramic tools,which had high-performance,low metal addition and a core-rim and particle dispersion microstructure,were developed successfully.According to the principle of physical and chemical compatibility,Ni,Co,（Ni,Co）and（Ni,Mo）were employed as the metal additives,and Hf C,WC and Ti B₂ were employed as the additives.TiCN-Hf C（THNM）,TiCN-Hf C-WC（THNMW）and TiCN-Hf C-Ti B₂（THNMT）ceramic tool materials were fabricated successfully by hot-pressed sintering.Then microstructure,mechanical properties,hardening and toughening mechanism,high temperature oxidation resistance and mechanism,cutting performance and failure mechanism were investigated.Based on the design principle of composite materials,a new type of TiCN-based ceramic tool material was established by adding new additives and designing a core-rim and particle dispersion microsturcture.Effects of Hf C content,metal,sintering temperature,holding time,WC content and Ti B₂content on mechanical properties and microstrcure of TiCN-based ceramic materials were investigated.Results showed that these factors had significant impacts on mechanical properties and microstrcure.When the TiCN-based ceramics had good comprehensive mechanical properties and microstrcure,the Hf C content was 20wt.%,WC content was 32wt.%,Ti B₂ content was 32wt.%,metal was（Ni,Mo）,sintering temperature was 1450℃or 1600℃and holding time was 30min.Under this condition,Hf C was uniformly dispersed in the matrix,and the core-rim structure with TiCN as the core and（Ti,Hf,Mo）（C,N）or（Ti,Hf,W,Mo）（C,N）as the rim was formed.Meanwhile,the synergistic hardening and toughening mechanism of the core-rim and particle dispersion was studied,which included densification hardening,chemical bond hardening,strong grain boundary hardening,particle dispersion toughening,and strong grain boundary toughening.Finally,three novel TiCN-based ceramic tool materials were successfully developed:THNM ceramic tool had a hardness of22.91GPa,flexural strength of 1346.41MPa,fracture toughness of 8.46MPa·m^1/2;that of THNMW ceramic tool were 21.06GPa,1270.56MPa and 9.47MPa·m^1/2;that of THNMT ceramic tool were 21.49GPa,964.05MPa and 6.65MPa·m^1/2.Oxidation behaviors of THNM,THNMW,THNMT tool materials at 800,900,1000,1100℃for 1,2,4,7,10h were studied.Results showed that at1100℃,the relationship between oxidation weight of THNMW and THNMT tool materials and oxidation time was basically parabolic;while the relationship between oxidation weight of THNM tool materials and oxidation time was linear.When the temperature was below 1100℃,the order of these three tools was THNMT,THNM and THNMW sorted by their oxidation resistance from strong to weak,and at 1100℃,the order was THNMT,THNMW and THNM.Simultaneously,a high-temperature oxidation model of these TiCN-based tool materials was established.The oxidation can be divided into four stages:in the first stage,a complete and dense oxide layer was formed and the oxidation was dominated by interface reactions;in the second stage,the complete-dense oxide layer and the matrix were further oxidated,and the oxidation was dominated by mass transfer;in the third stage,liquid B₂O₃ generated in the oxidation of THNMT which can fill some pores and a dense oxide layer formd,and the oxidation was dominated by mass transfer;a secondary oxide layer is formed between the outer oxide layer and the transition layer in THNM and THNMW and oxidation was dominated by mass transfer and interface reaction;in the fourth stage,oxide layer was fractured and the oxidation was dominated by interface reactions and mass transfer.In addition,the ideal cross-section model of the sample after oxidation was established,and the formulas of radial stress difference,circumferential stress difference,and axial stress difference at any point between the oxide layers were deduced based on the heat conduction and thermal stress formulas,and the crack formation mechanism in oxidation layers was revealed.The cutting performance of THNM,THNMW,THNMT,AN5 ceramic tools in continuously dry machining hardened 0Cr18Ni9,hardened H13 and hardened GCr15 was investigated.The results showed that when these tools continuously machined the hardened 0Cr18Ni9 with the parameters of 180m/min,0.1mm/r and 0.2mm,the order of these tools was THNM,THNMW,AN5 and THNMT sorted by their wear resistance from strong to weak.Meanwhile,the tool failure was tool flank wear and crater wear,and the wear mechanism of flank was mainly adhesive wear,abrasive wear and oxidation wear.When these tools continuously machined the hardened H13 with the parameters of 110m/min,0.1mm/r and 0.15mm,the order of these tools was AN5,THNM,THNMW and THNMT sorted by their wear resistance from strong to weak.Meanwhile,the tool failure was tool flank and rake wear,and the wear mechanism of flank was mainly abrasive wear,adhesive wear and oxidation wear.When these tools continuously machined the hardened GCr15 with the parameters of 70m/min,0.1mm/r and 0.15mm,the order of these tools was THNMT,AN5,THNMW and THNM sorted by their wear resistance from strong to weak.Meanwhile,the tool failure was tool flank and rake wear,and the wear mechanism of flank was mainly adhesive wear and oxidation wear.