Study On The Preparation And Cutting Performance Of TiB₂-based Ceramic Tools In Cutting Of Ti6Al4V

With the rapidly advanced development of aerospace,energy,and chemical industries,the use of titanium alloys has increased dramatically,which requires much higher demands on its high-speed and high-efficiency machining operations.For high-speed machining of titanium alloys,carbide tools and traditional ceramic tools currently used exhibit very low wear resistance with low tool lifetime,which leads to the critical need to develop tool materials that could withstand higher cutting speeds and cutting temperatures.Based on the cutting application background in machining titanium alloy?Ti6Al4V?with new Ti B₂-based ceramic tools,the methodology of"tool material preparation-tool material properties-tool cutting performance feedback optimization,"and the route of"sintering aid-microstructure-mechanical properties-cutting performance-wear mechanism"were employed in this research.The effects of sintering additives on sintering behavior,mechanical properties,and cutting performance of TiB₂-based ceramics were studied in the present study.The outputs of wear curve and wear mechanism were analyzed in detail in order to optimize the sintering additives to obtain high-performance Ti B₂-based cutting tool for titanium alloy machining.In this research,TiB₂-20vol%B₄C?TB2?and TiB₂-80vol%B₄C?TB8?ceramic cutting tools were prepared by hot-pressing at 2000°C in argon.The mechanical properties,friction and wear properties,and cutting performance of TB2 and TB8 were studied in comparison with commercially available tungsten carbide cutting tools?YD?evaluated in this study.The results showed that the addition of B₄C could improve the densification,hardness,and bending strength of Ti B₂-based ceramics,but reduced the fracture toughness.The friction coefficient of TB8 was the highest in sliding friction against to Ti6Al4V alloy at high temperature,followed by YD,and TB2 that has the lowest value?about 0.4?.Meanwhile,Ti B₂-B₄C ceramics held better resistance to high temperature oxidation than the commercial cemented carbide.Tool life decreased as cutting speed increased in cutting Ti6Al4V with various parameters.In addition,cutting temperature of the tools increased with the increase of wear content,and the cutting temperature of YD increased at a faster rate with the wear content than the TiB₂-B₄C ceramic tools.Results also showed that the tool life of TB2 was longer in roughing processes,but YD exhibited a longer tool life and a lower surface roughness in finishing.In addition,the crater wear and flank wear of different tools were apparent,and the crater wear of YD was more severe than the other TiB₂-based tools.The main wear mechanism of TB2 and TB8 was adhesive wear,while micro-tipping also occurred in TB8.The main wear mechanism of YD was adhesive wear.Due to the high temperature activity of Ti and B₄C,TiB₂-B₄C tools with lower B₄C content could have better cutting performance.On the other hand,TiB₂-B₄C-Ni/Al ceramic tool material was prepared by hot-pressing at 1800°C by doping the low-melting-point metallic additives;i.e.,Ni and Al.The effect of metallic phase content on the microstructure,mechanical properties,and cutting performance of the material were then characterized.The results showed that the Ni/Al additive could significantly reduce the sintering temperature of TiB₂-B₄C ceramic.The addition of Ni/Al also resulted in the decrease in the flexural strength and hardness of TiB₂-B₄C-Ni/Al ceramics,but slight change in the the fracture toughness,with the increased content of Ni/Al.Measurements showed that the flexural strength,fracture toughness,and hardness of TiB₂-20vol%B₄C-5vol%Ni/Al were 711MPa,4.6MPa·m^1/2,and 22.69GPa,respectively.The tool life decreased,and the wear rate of the crater increased with the increase of Ni/Al content under various cutting parameters employed in this study.The main wear mechanism of the tools was adhesive wear,while there was also micro-tipping in the finishing process.Since the low-melting-point metal grain boundary phase could reduce high temperature performance of the cutting tools,thus the tool life of TiB₂-B₄C-Ni/Al ceramics,in general,is lower than that of TiB₂-B₄C tools.Furthermore,in order to avoid the adverse effects of B₄C and low-melting-point metals on the cutting performance of the tools,and improve the sintering performance of TiB₂ based ceramics,TiB₂-Mo/Co and TiB₂-Mo/Co-C ceramic cutting tools were prepared by the introduction of carbon and high-melting-point metals?Mo/Co?as additives.Their microstructure,mechanical properties,and cutting performance were studied.The results showed that the combined Mo/Co-C as a composite additive could significantly improve the densification and mechanical properties of TiB₂-based ceramics,with relative density of 97%at 1900°C as compared with the single-phase additives?C or Mo/Co?.The flexural strength,fracture toughness,and hardness of Ti B₂-Mo/Co-C ceramic tool material were 574 MPa,4.27 MPa·m^1/2,and 19.34 GPa,respectively.However,due to the strong chemical affinity of C and Ti,cutting performance of the TiB₂-based ceramic tool with Mo/Co additive was better than that of TiB₂-based tool with Mo/Co-C as the sintering aid.The effective cutting length of TiB₂-Mo/Co cutting tool was about 2400m at v_c=150m/min,f=0.1mm/r,a_p=0.5mm,which was much higher?about 3 times?than that of TB2?850m?.TiB₂-Mo/Co and TiB₂-Mo/Co-C ceramic tools showed obvious crater wear,flank wear,and groove wear.The main wear mechanisms were adhesive wear and micro-tipping.Among all of the Ti B₂-based tools with different additives evaluated in this research,the TiB₂-Mo/Co tool exhibits a longer tool life due to the lower content and higher melting point of metal additives,as well as the absence of B₄C that has high affinity with Ti.