Study On Development And Cutting Performance Of High Mechanical Property Cermet Tool Materials

Because cermet tool materials have higher hardness than cemented carbide tools and have higher flexural strength and fracture toughness than ceramic tools, they are suitable for cutting hardened steels and high-strength steels. Therefore, it is necessary to study the high mechanical property cermet tool materials and to promote their practical applications.Micro-scale and nano-scale modified cermet tool material is one of the most important research area of ceramic material. Nano-scale modified cermet tool materials have been successfully developed with the micro-scale Ti(C,N) as the matrix and nano-scale Al₂O₃ and nano-scale Ti(C,N) as the additives. The effect of the content of rare earth compounds (Cr₃C₂, VC, La₂O₃ and Y₂O₃) and fabrication technology on the microstructure and mechanical properties of material system Ti(C, N)-Ni-Co was investigated. The mechanical property, microstructure and cutting performance of the developed high mechanical property cermet tool materials were researched.According to the design principle for cermet tool materials, the basic material system of Ti(C,N) matrix cermet tool materials was proposed with the metal Ni, Co and Mo as the bonding phase and the phase VC, Cr₃C₂, La₂O₃, Y₂O₃, Al₂O₃ and MgO as the additives. The optimal fabrication technology is the fabrication temperature of 1450℃, the applied pressure of 25MPa and the fabrication time of 30min. The effect of additives such as Cr₃C₂, VC, La₂O₃ and Y₂O₃ on the microstructure and mechanical properties of material system Ti(C,N)-Ni-Co was researched. It is shown that the flexural strength of cermet tool material Ti(CN)-(Ni-Co)-Cr₃C₂-VC can decrease and the hardness and fracture toughness will increase with an increase in thecontent of VC. And the maximum flexural strength of 981MPa can be reached when content of VC is 0.8wt%, but the maximum hardness and fracture toughness can be reached when the content of VC is 16wt%. The addition of rare earth oxides (La2O3 and Y2O3) can result in toughening effect and increase the fracture toughness of the cermet tool materials at the fabrication conditions of 1450°C, 25MPa and 30min, but no strengthening effect is found.The microstructure and mechanical properties of Ti(C,N) matrix cermet tool materials modified by nano-scale A12O3 or nano-scale Ti(C,N) was systematically researched. It is shown that the addition of nano-scale AI2O3 can increase the hardness and the fracture toughness. The nano-scale A12O3 modified optimal material system is Ti(C0.7N03)- (Ni-Mo) -Cr2C3-Al2O3-MgO respectively modified by an amount of nano-scale A12O3 with the content of 10% or 12% in term of mass, the mechanical properties of which are the flexural strength of 925 and 900MPa, the hardness of 18.4 and 17.4Gpa, and the fracture toughness of 9.05 and 9.95MPa.m1/2. The nano-scale Ti(C, N) modified optimal material system is the tool material Ti(Co.7No.3)- (Ni-Mo) -VC-Cr2C3 modified by nano-scale Ti(C, N) with a content of 10% in term of mass. The mechanical properties of the modified cermet tool material n-VC8 with nano-scale Ti(C, N) are higher than those of the material VC8 without nano-scale Ti(C, N). The flexural strength, the hardness and the fracture toughness of the tool material n-VC8 are respectively improved from 623MPa to 808MPa, from 16.2Gpa to 17.7Gpa and from 8.78MPa.m1/2 to 9.79MPa.m1/2.The toughening mechanisms of Ti(C,N) matrix cermet tool materials modified by nano-scale A12O3 or nano-scale Ti(C, N) were systematically researched. The main toughening mechanisms are the transformation of fracture mode, microstructure change, microcracks, crack deflection and bridging, microcracks induced by residual stress, crack inflection and ductile grain toughening. The grain growth model for Ti (C,N) cermet tool material was established and primarily verified. The model is of important theoretical guidence for desinging the microstructure of cermet tool material.The cutting performance of the developed advanced Ti(C,N) cermet tools, cemented carbide tools (YG8 and YT14), and commercial ceramic tools (LT55 andSG-4) were researched when turning cast irons, annealed steel 45 , hardened steel 45# and high-hardness steel 40Cr respectively. It is shown that the developed cermet tools are not suitable for turning grey gast iron HT200. The wear resistance of the developed cermet tools such as n-Al2O36, n-Al2O312 and n-VC8 is stronger than that of YT14, LT55 and SG-4 when turning annealed steel 45#(12-16HRC). The cutting performance of the developed cermet tools such as n-Al2O312, n-VC8 and n-VC16 is better than that of YT14, and is the same as that of LT55 and SG-4 when turning hardened steel 45* at the cutting speed of v = 182m/min. The wear resistance of the nano-scale modified cermet tools is stronger than that of LT55 and SG-4 when turning 40Cr. And the wear resistance of the nano-scale modified cermet tool n-Al2O38 is the strongest one, and the optimal cutting conditions are the cutting speed v = 168/w/min, the feed rate / = O.lmm/r and the cutting depth ap = 0.2mm.The wear resistance of most nano-scale modified cermet tools is stronger than that of LT55 and SG-4 when turning conventional steel 45(25-30 HRC). And the wear resistance of the nano-scale modified cermet tool n-Al2O>8 and n-Al2O310 is thestrongest one at the cutting speed v=96-218m/min, the feed rate / = 0. \mm I r and the cutting depth ap = 0.2mm.The wear pattern and mechanisms were analyzed, and the main wear pattern is flank wear. The main wear mechanisms are abrasive, adhesion and dispersion wear.