Research On Preparation And Performance Of α-Sialon-Based Ceramic Tool Material

Sialon ceramic tools are one of the important candidates for cutting nickel-based superalloys due to the high hardness,high strength,high toughness,good wear resistance,and excellent mechanical stability at high temperatures.However,the current research is mainly focused onβ-Sialon and its multiphase ceramics,and there is a lack of systematic research onα-Sialon ceramic tools.In this paper,α-Sialon single-phase ceramics andα-Sialon composite ceramics were prepared by spark plasma sintering（SPS）technology,and the effects of sintering temperature,holding time,sintering aidditive content and second phase type on phase composition,relative density,microstructure and mechanical properties were,systematically studied.Based on the standard tools made of these materials,dry cutting tests were carried out on Inconel 718 alloy to explore the cutting performance and wear mechanism of the tools.The main research contents and results of this paper are as follows:Firstly,α-Sialon single-phase ceramics were prepwered by spark plasma sintering technology,and the effects of different sintering processes（sintering temperature,holding time）and sintering aidditive Y₂O₃content on the phase composition,relative density,microstructure and mechanical properties ofα-Sialon ceramics were studied.The results showed that as the sintering temperature increased from 1650℃to 1750℃,the main composition withα-Sialon phase had no change,the relative density increased,α-Sialon equiaxed grain content was reduced and rod-shaped grain content was increased,the hardness was slightly decreased,and the toughness was obviously improved.With the holding time from 5 min to 10 min,α-Sialon phase composition was unchanged,the relative density was slightly increased,the rod-like crystals increases,and the toughness was further improved.With the introduction of the sintering aidditive content（2 wt.%）,the phase composition ofα-Sialon ceramics was stable,the relative density was increased,the rod-like grains content was increased,and the fracture toughness was increased.A brittle phase was formed when the sintering aid content was 4wt.%,which led to a decrease in fracture toughness.The Vickers hardness slightly decreases with the increase of the sintering aid content.The sample with a sintering aidditive amount of2 wt.%prepared at a sintering temperature of 1750℃for a holding time of 10 min,has the best mechanical properties with a Vickers hardness of 20.21±0.21 GPa and a fracture toughness of 6.23±0.23 MPa·m^1/2.Then,the second phase Ti N,Mo Si₂ and Hf B₂ were introduced intoα-Sialon ceramics,respectively,andα-Sialon composite ceramics were prepared by spark plasma sintering technology.The influence of the type and content of the second phase on the microstructure and mechanical properties ofα-Sialon-based composite ceramics was explored.The results show that adding a small amount of Ti N（2.5 vol%）would inhibit the growth ofα-Sialon rod-shaped grains.As the Ti N content was increased to 10 vol%,the inhibitory effect was weakened and rod-shaped grains are formed,the Vickers hardness ofα-Sialon composite ceramics was decreased to 19.77±0.40 GPa,and the fracture toughness was first decreased and was then increased to 4.29±0.14 MPa·m^1/2.With the increase of Mo Si₂ content,the aspect ratio of rod-shapedα-Sialon grains was increased,the microstructure presented a significant bimodal distribution,the hardness had small change（～21 GPa）and the fracture toughness was increased to 6.13±0.28 MPa·m^1/2.With the increase of Hf B₂ content,the solid solution of Si₃N₄ was inhibited to formα-Sialon phase,the Vickers hardness has no obvious change（～22GPa）,and the fracture toughness was increased to 4.80±0.25 MPa·m^1/2,due to residual stress toughening by a large difference in thermal expansion coefficient between Hf B₂ andα-Sialon,and residual stress toughening occurs.Finally,theα-Sialon single-phase ceramics with excellent mechanical properties and theα-Sialon composite ceramics containing 10 vol%Ti N,10 wt.%Mo Si₂ and 10 vol%Hf B₂ were processed into standard tools,and the cutting performance and wear morphology of the tool were studied by dry cutting of Inconel 718 alloy.The study showed that under the condition of fixed high-speed cutting parameters,when the wear standard was reached,α-Sialon single-phase ceramic tools with higher fracture toughness(greater than 6 MPa·m^1/2)andα-Sialon-based composite ceramic tools with Mo Si₂ had larger cutting lengths（646 m and 688 m）.Theα-Sialon composite ceramic tool with Ti N had higher cutting surface quality,and could still be used after reaching the wear standard in rough machining.The main wear forms ofα-Sialon-based ceramic tools were flank wear,groove wear and secondary flank wear,and secondary flank wear was negatively related to the surface quality of the workpiece.The wear mechanism was mainly abrasive wear,bond wear and chipping.Combining the cutting effect and the form of wear,α-Sialon-based ceramic tools are more suitable for rough machining of Inconel 718 alloy.