【作者】 宋金鹏；

【导师】 黄传真；

【作者基本信息】 山东大学 ， 机械制造及其自动化， 2012， 博士

【摘要】 本文针对TiB：陶瓷材料难以烧结致密化、抗弯强度、断裂韧度低等缺点,根据复合陶瓷刀具材料物理、化学相容性原则,采用热压烧结工艺,以Ni. Co、(Ni,Mo)、(Co,Mo)、(Ni,Ti)、(Co,Ti)作为金属相,以TiC、WC作为硬质相,研制成功了新型TiB2基复相陶瓷刀具TiB2-25wt.%TiC-WC(TTW7)、 TiB2-WC(BW3).TiB2-WC-TiC(TWTN3),并对金属相含量、金属相与硬质相的物理相容性、材料的液相烧结致密化机理、力学性能、微观组织、增韧机理、刀具切削性能及失效机理进行了系统研究。提出了新型TiB2基复相陶瓷刀具材料的设计目标和设计原则。确定了TiC和WC为TiB2基复相陶瓷刀具材料的添加相,确立了TiB2基复相陶瓷刀具材料体系。建立了金属相全包覆硬质相晶粒模型,推导了TiB：基复相陶瓷刀具材料中金属相含量的计算式,确定了实现金属相全包覆硬质相时的金属相体积分数为φ∈[3.5%,13%]。对金属相与硬质相间的物理相容性研究表明,硬质相颗粒越小,容许的硬质相与金属相热膨胀系数差越大。研究了TiB2基复相陶瓷刀具材料液相烧结时的致密化机理。烧结初期的致密化机理主要是增强相在液相中的溶解、气孔收缩、颗粒重排,在烧结初期气孔逐步形成球形。研究了TiB2基复相陶瓷刀具材料在烧结中后期致密化过程中相对密度与烧结工艺参数之间的关系,结果表明,随晶粒尺寸(b)、液相厚度(λl)、保温时间(t)和液相密度(pL)的增大,材料的相对密度不断增加；而随液相动力粘度(μ)和坯体高度(h)的增大,材料的相对密度不断减小；其中烧结压力(P)和烧结温度(T)对材料相对密度的影响不大。对烧结温度、保温时间、金属相含量和硬质相含量进行了优化。研究了金属相和硬质相含量对TiB2复相陶瓷刀具材料力学性能的影响,确定了制备TTW7、BW3和TWTN3刀具的工艺方案。研制成功了TiB2-25wt.%TiC-WC(TTW7)复相陶瓷刀具材料,其中TiB2-25wt.%TiC复合粉的含量为72wt.%,WC的含量为20wt.%,Ni的含量为8wt.%。在1650℃下烧结复相陶瓷材料时,基体和WC具有良好的化学相容性。随着WC含量的增加,微观组织中的粗大晶粒和气孔逐渐减少,TiB2复相陶瓷刀具材料的抗弯强度、断裂韧度、硬度逐渐增大；但是当WC含量超过20wt.%时,刀具材料的力学性能降低。当WC含量为20wt.%时,材料的抗弯强度为955.7MPa,断裂韧度为7.5MPa·m1/2,硬度为23.5GPa。研制成功了TiB2-WC(BW3)复相陶瓷刀具材料,其中TiB2的含量为72wt.%,WC的含量为20wt.%,(Ni, Mo)的含量为8wt.%。在1650℃下烧结复相陶瓷材料时,TiB2和WC具有良好的化学相容性。金属相为Co的复相陶瓷刀具材料中的气孔、粗大晶粒明显多于金属相为Ni、(Ni, Mo)的复相陶瓷刀具材料,且前者的力学性能低于后两者。金属相为(Ni, Mo)的复相陶瓷刀具材料的缺陷最少,力学性能最好,其抗弯强度为1307.0MPa,断裂韧度为8.2MPa·m1/2,硬度为22.7GPa。研制成功了TiB2-TiC-WC(TWTN3)复相陶瓷刀具材料,其中TiB2的含量为42wt.%,WC的含量为20wt.%,Ni的含量为8wt.%,TiC的含量为30wt.%。在1650-C下烧结复相陶瓷刀具材料时,TiB2、WC和TiC具有良好的化学相容性。对微观组织的研究表明,当TiC含量为10wt.%时,复相陶瓷刀具材料中存在许多气孔和粗大晶粒；随TiC含量的增加,气孔及粗大晶粒逐渐减少；当TiC含量为30wt.%时,TWTN3及TWTNM3复相陶瓷刀具材料微观组织中的缺陷逐渐消失。材料的抗弯强度为996.6MPa,断裂韧度为7.6MPa.m1/2,硬度为23.6GPa。研究了刀具材料TTW7、BW3和TWTN3的增韧机理。结果表明,金属相均以环状兼颗粒状分布在硬质相形成的晶界上,具有弥散强化作用,其增韧机理是裂纹桥联和偏转、WC晶粒拔出和固溶强化；材料的断裂模式是沿晶断裂和穿晶断裂同时存在。研究了TTW7、BW3、TWTN3和SG4刀具连续切削淬硬Crl2MoV模具钢、哈氏合金C-276和奥氏体不锈钢1Cr18Ni9Ti时的切削性能及刀具失效机理。结果表明,干切削淬硬Cr12MoV模具钢和哈氏合金C-276时,加工表面会发生粘屑现象；加入冷却液后粘屑现象消逝。干切削奥氏体不锈钢1Cr18Ni9Ti时,当切削速度选择合适时,加工表面质量良好。四种刀具在湿切削状态下,以切削速度为60m/min、进给量为0.1mm/r、切削深度为0.3mm连续切削淬硬Cr12MoV模具钢时,刀具的抗磨损能力由强到弱的顺序为B W3>SG4>TTW7>TWTN3;刀具的主要失效形式是后刀面沟槽磨损、刀尖破损、主切削刃微崩、前刀面剥落,其主要磨损机理是磨粒磨损及粘着磨损。四种刀具在湿切削状态下,以切削速度为60m/min、进给量为0.1mm/r、切削深度为0.2mm连续切削哈氏合金C-276时,刀具的抗磨损能力由强到弱的顺序为B W3>SG4>TTW7>TWTN3;刀具的主要磨损形式是后刀面沟槽磨损、刀尖破损、主切削刃微崩,其主要磨损机理是磨粒磨损和粘着磨损。四种刀具在干切削状态下,以切削速度为80m/min、进给量为0.1mm/r、切削深度为0.1mm连续切削奥氏体不锈钢1Cr18Ni9Ti时,刀具的抗磨损能力由强到弱的顺序为TTW7>SG4>TWTN3>BW3;刀具的主要磨损形式是是后刀面沟槽磨损、刀尖破损、主切削刃微崩、前刀面剥落,其主要磨损机理是磨粒磨损、扩散磨损和粘着磨损。更多还原

【Abstract】 Titanium diboride matrix composite materials are difficult to be sintered. The flexural strength and fracture toughness of the materials are very low. Aiming at the disadvantages of the materials, the materials with high performance have been successfully developed according to the chemical and physical compatibility. Under the liquid-phase hot-pressing technology, the high-performance titanium diboride matrix ceramic tool materials such as TiB2-25wt.%TiC-WC(TTW7), TiB2-WC(BW3) and TiB2-WC-TiC(TWTN3), were fabricated by adding metal phases and hard phases. The metal phases were Ni, Co,(Ni, Mo),(Co, Mo),(Ni, Ti), and (Co, Ti) respectively. The hard phases were TiC and WC. The content of metal, the physical compatibility between the metal phases and the hard phases, the densification mechanism during the sintering process, the mechanical properties, the micro structure, toughening mechanisms of the materials, the cutting performance and failure mechanisms of tools were investigated.Additives and compositions of the titanium diboride matrix ceramic tool materials were determined according to the design purpose and design principles. The additives were TiC and WC. According to the model for the metal phase coating the hard phases, the metal phase volume fractionφ∈[3.5%,13%] can be calculated. The smaller the size of the hard phase is, the bigger the difference of the thermal expansion coefficient between the metal phases and the hard phases is. The result is obtained by calculating the physical compatibility of the metal phases and the hard phases.The densification process was investigated, and the densification equations of the initial and final sintering stages were established. It is shown that the densification during the initial sintering stage is determined by the formation of the metal liquid, the dissolution of the ceramic particle, the shrinkage of pores, the grain recomposition, and the densification rate has been affected by the physical properties of liquid-phase, external compressive pressure, particle size and the wetting angle between liquid-phase and particle. The relative density during the final sintering stage increases with an increase in the size of grains(b), the content of the metal(λ1), sintering time(t) and the density of the liquid(ρL) and decreases with an increase in the dynamic viscosity coefficient of the liquid(μ) and the height of the samples(h). The effects of external compressive pressure(P) and sintering temperature(T) on the relative density during the final sintering stage were not obvious.Sintering temperatures, sintering times, the contents of the metals and the hard phases were optimized by the orthogonal test method. Titanium diboride matrix ceramic tool materials were frabricated according to the optimal sintering process. The effects of the metal phases and the contents of hard phases on the mechanical properties of the materials were investigated and the fabrication processes of the cutting tool such as TTW7, BW3and TWTN3were made.TiB2-25wt.%TiC-WC(TTW7) composite was fabricated successfully. The contents of TiB2-25wt.%TiC, WC and Ni were72wt.%,20wt.%and8wt.%, respectively. The matrix and WC grains had a good chemical compatibility in the composite that was sintered at1650℃. The mechanical properties increased with a decrease in the defects such as coarse grains and pores when the content of WC increases. The mechanical properties reduced when the content of WC was more than20wt.%. The optimal mechanical properties of TiB2-25wt.%TiC-20wt.%WC composite were955.7MPa of flexural strength,7.5MPa·m1/2of fracture toughness and23.5GPa of Vickers hardness.TiB2-WC(BW3) composite was fabricated successfully. The contents of TiB2, WC and (Ni, Mo) were72wt.%,20wt.%and8wt.%, respectively. TiB2and WC grains had a good chemical compatibility in the composite that was sintered at1650℃. The defects including coarse grains, pores and brittle phases had an important effect on the the mechanical properties. TiB2-WC-Co composites had more defects such as coarse grains and pores in the micro structure than TiB2-WC-Ni and TiB2-WC-(Ni, Mo) composites, so the mechanical properties of the composites were very low. TiB2-WC-(Ni, Mo) composite has a good micro structure, so the composite has optimal mechanical properties that were1307.OMPa of flexural strength,8.2MPa·m1/2of fracture toughness and22.7GPa of Vickers hardness.TiB2-TiC-WC(TWTN3) composite was fabricated successfully. The contents of TiB2, WC, Ni,(Ni, Mo) and TiC were42wt.%,20wt.%,8wt.%,8wt.%and30wt.%, respectively. TiB2, WC and TiC grains had a good chemical compatibility in the composite that was sintered at1650℃. The micro structure and mechanical properties of the composite were investigated. There are many pores and coarse grains in the composite when the TiC content is10wt.%. The quantity of the pores and the coarse grains reduced gradually with an increase in the content of TiC. The defects of micro structure disappeared in TiB2-WC-TiC-Ni and TiB2-WC-TiC-(Ni, Mo) composite when the TiC content is30wt.%. The mechanical properties increased when the defcts reduced. The optimal mechanical properties of TiB2-WC-TiC-Ni composite were996.6MPa of flexural strength,7.6MPa·m1/2of fracture toughness and23.6GPa of Vickers hardness.Toughening mechanisms of TTW7, BW3and TWTN3composite cutting tool materials were studied. The metal phase dispersed at the interface of the ceramic phase, which formed rings and particles in the composite. The main toughening mechanisms are crack bridging and deflection, pulling out of WC grain, the change of fracture mode and solid solution.Compared to the commercial SG4ceramic tool, the cutting performance and failure mechanisms of the cutting tools such as TTW7, BW3and TWTN3in continuous machining hardened Cr12MoV mold steel, hastelloy alloy C-276and stainless steel1Cr18Ni9Ti were investigated. The wear mechanisms of the ceramic tools were analyzed. The wear resistance of the ceramic tools was very poor in high cutting speed. There were many small scraps that adhered to the finished surface when these tools were used to machine hardened Cr12MoV mold steel and hastelloy alloy C-276without cutting fluid, but there were no small scraps on the surface when they were used to machine the materials with cutting fluid. Under the proper cutting speed, the quality of the finished surface was very good when these tools were used to machine stainless steel1Cr18Ni9Ti without cutting fluid. The wear resistance is BW3>SG4>TTW7>TWTN3when continuous machining hardened Cr12MoV mold steel with cutting fluid under the cutting conditions that the cutting speed is60m/min, the feed rate is0.1mm/r and the cutting depth is0.3mm. The main wear patterns are tool flank and rake wear as well as the main wear mechanisms were adhesive wear and abrasive wear. The wear resistance is BW3>SG4>TTW7>TWTN3when continuous machining hastelloy alloy C-276with cutting fluid under the cutting conditions that the cutting speed is60m/min, the feed rate is0.1mm/r and the cutting depth is0.2mm. The main wear patterns are tool flank and rake wear as well as the main wear mechanisms were adhesive wear and abrasive wear. The wear resistance is TTW7>SG4>TWTN3>BW3when continuous machining stainless steel1Cr18Ni9Ti without cutting fluid under the cutting conditions that the cutting speed is80m/min, the feed rate is0.1mm/r and the cutting depth is0.1mm. The main wear patterns are tool flank and rake wear as well as the main wear mechanisms were adhesive wear, abrasive wear and diffusing wear.更多还原