【作者】 谷美林；

【导师】 黄传真；

【作者基本信息】 山东大学 ， 机械制造及其自动化， 2007， 博士

【摘要】 本文针对TiB₂陶瓷材料的缺点，根据复合陶瓷刀具材料物理、化学和烧结相容性原则，选择TiN和Al₂O₃颗粒为添加相，Ni和Mo为粘结相，采用液相热压烧结工艺，研制成功了高性能新型TiB₂基复合陶瓷刀具TiB₂-TiN（BT）、TiB₂-Al₂O₃（BA）和TiB₂-TiN-Al₂O₃（BTA），并对其液相热压烧结机理、常温力学性能及增韧机理、高温抗氧化性能及氧化机理、抗热震性能、切削性能及刀具失效机理进行了系统的研究。在优化的烧结工艺下，制备了TiB₂-TiN、TiB₂-Al₂O₃和TiB₂-TiN-Al₂O₃复合陶瓷刀具材料，并研究了添加相含量对TiB₂基陶瓷刀具材料致密化的影响。结果表明：添加相颗粒TiN和Al₂O₃对基体的致密化有明显促进作用。随TiN添加量的增加，TiB₂-TiN复合陶瓷刀具材料的致密度逐渐提高，且当TiN含量为30vol％时，TiB₂-TiN复合陶瓷刀具材料的相对密度达到了98.87％；少量的Al₂O₃添加相可以提高TiB₂-Al₂O₃的致密度，但当Al₂O₃添加相含量超过30vol％时，复合陶瓷刀具材料的致密度会随之下降。研究了TiB₂基复合陶瓷刀具材料液相热压烧结致密化过程，并建立了液相热压烧结初期和中后期致密化方程。结果表明，烧结初期的致密化机理是颗粒重排，影响复合陶瓷刀具材料致密化速度的因素有液相性质、外加压力、颗粒尺寸以及液相对添加相的润湿性；当液相对添加相的润湿角小于对基体的润湿角时，添加相会促进基体的烧结，并且添加相含量越高，复合陶瓷刀具材料的致密化速度越快；当液相对添加相的润湿角和对基体的润湿角相同时，添加相的含量对复合陶瓷刀具材料的致密化没有影响。烧结中后期的致密化机理是液相流动和晶界扩散控制的蠕变；添加相的晶界扩散系数D、晶界宽度W、扩散空位的原子体积a³和表面能γ对复合陶瓷刀具材料的致密化有影响；随烧结时间延长，TiB₂基复合陶瓷刀具材料的致密度（ρ）逐渐增加，且-1n（1-ρ）与烧结时间呈线性关系，复合陶瓷刀具材料的-1n（1-ρ）与添加相含量呈抛物线关系，即随添加相含量的增加，TiB₂基复合陶瓷刀具材料的致密度（ρ）逐渐增加大。系统研究了TiB₂基复合陶瓷刀具材料的力学性能、显微结构和增韧机理。研制成功了具有优良综合力学性能的TiB₂基复合陶瓷刀具材料BT30、BA30和BT30A10，其平均抗弯强度分别为：1240MPa、915MPa和1036MPa；其平均断裂韧度分别为：7.43MPa·m^1╱2、7.00MPa·m^1╱2和7.8MPa·m^1╱2；其平均维氏硬度分别为：20.47GPa、21.42GPa和20.33GPa。金属相和位错导致的解理及位错对裂纹的屏蔽作用是复合陶瓷刀具材料的主要增韧机理。建立了环形状金属和颗粒状金属桥联增韧力学模型，结果表明，同样体积的颗粒状金属裂纹桥联增韧值是环形状金属的5.09倍。研究了新型TiB₂基复合陶瓷刀具材料TiB₂-TiN、TiB₂-Al₂O₃和TiB₂-TiN-Al₂O₃在700℃、800℃和1000℃条件下的抗氧化性能及其氧化机理。结果表明，TiB₂-TiN复合陶瓷刀具材料的氧化增重随TiN含量的增加而逐渐增加，TiB₂-Al₂O₃和TiB₂-TiN-Al₂O₃复合陶瓷刀具材料的氧化增重随Al₂O₃含量的增加而逐渐减小。BT30和BT30A10在700℃开始氧化，BA30在800℃开始氧化；在800-1000℃范围内，BT30的氧化活化能最小，氧化最快，BT30A10次之，而BA30的氧化活化能最大，氧化最慢。经过800℃，50h氧化后，BT30和BT30A10的表面生成了TiO₂，TiO₂在材料表面形成了连续的覆盖层，并在TiB₂颗粒表面形成了包裹层，覆盖层和包裹层降低了材料进一步氧化的速度，并使材料表面的TiB₂颗粒很难被完全氧化；BA30表面仅有少量TiB₂被氧化，但是在TiB₂颗粒周围没有发现包裹层；氧化后BT30、BA30和BT30A10的抗弯强度均大于750MPa，能够满足连续切削的要求。经过1000℃，50h氧化后，BT30和BT30A10表面的TiN被完全氧化，TiB₂没有被完全氧化，而BA30表面的TiB2被完全氧化；氧化后BT30、BA30和BT30A10复合陶瓷刀具材料的抗弯强度都低于500MPa，不能正常切削。研究了BT30、BA30和BT30A10三种新型TiB₂基复合陶瓷刀具材料的抗热震性能和R-曲线行为，提出了热震裂纹扩展参数R_c，建立了考虑R-曲线特性的热震残余抗弯强度预测模型。结果表明，BT30、BA30和BT30A10复合陶瓷刀具材料的临界热震温差分别为750℃、800℃和750℃，在临界热震温差下单次热震后的抗弯强度保持率分别为26.37％、50.17％和33.78％。BT30、BA30和BT30A10复合陶瓷刀具材料的R-曲线参数（n）分别为0.038、0.139和0.087。单次热震后复合陶瓷刀具材料的残余抗弯强度与R-曲线有关，抗弯强度保持率是一个与R-曲线参数（n）有关的常数，R-曲线参数（n）越大，热震后抗弯强度保持率越高，材料的抗热震性能越好。研究了BT30、BA30和BT30A10三种新型TiB₂基复合陶瓷刀具连续或断续切削淬火40Cr合金钢、淬火45^#钢和奥氏体不锈钢1Cr18Ni9Ti时的切削性能及刀具失效机理，并部分与SG4刀具的切削性能进行对比。结果表明，在连续切削淬火40Cr合金钢时，BA30与SG4刀具的切削性能相当，且始终表现出比BT30更好的切削性能，BA30和BT30刀具的主要磨损形式为前后刀面磨损，磨损机理为磨粒磨损和BT30刀具前刀面粘着磨损。在连续切削淬火45^#钢时，三种新型TiB₂基复合陶瓷刀具抗磨损能力由强到弱的顺序为BA30＞BT30A10＞BT30，刀具的主要磨损形式是前后刀面磨损，低速下的磨损机理为磨粒磨损，高速下BA30和BT30A10刀具的磨损机理为磨粒磨损，BT30刀具后刀面磨损机理为磨粒磨损，前刀面磨损机理为氧化磨损。在连续切削奥氏体不锈钢1Cr18Ni9Ti时，BA30和BT30A10刀具切削性能很差，不能实现切削，而BT30刀具表现出良好的切削性能，采用0°前角的刀具比-5°前角的刀具表现出更好的耐磨性；刀具磨损形式为前后刀面磨损，后刀面磨损机理为磨粒磨损，前刀面磨损机理为扩散磨损。在断续切削淬火45^#钢时，BT30刀具表现出良好的抗破损性能，而BA30和SG4刀具的抗破损能力很差；在低速大切深条件下，BT30刀具的破损机理为机械破损，在高速小切深条件下，BT30刀具的破损机理为热破损，在中速中切深条件下，BT30刀具的破损机理为机械破损和热破损的综合作用。更多还原

【Abstract】 Aiming at the disadvantages of titanium diboride matrix composite ceramic materials, a new kind of titanium diboride matrix composite ceramic tool materials with high mechanical properties has been successfully developed according to the chemical, physical and sintering compatibility. Under the liquid-phase hot-pressing technology, the titanium diboride matrix composite ceramic tool materials, TiB₂-TiN, TiB₂-Al₂O₃ and TiB₂-TiN-Al₂O₃, were fabricated by adding the particles TiN and Al₂O₃ into TiB₂ with Ni and Mo as sintering aids. The hot-pressing technology and sintering theory, the mechanical properties and toughening mechanisms, the oxdiation behavior and theory at high temperature, the thermal-shock resistance and the cutting performance of the titanium diboride matrix composite ceramic tool materials were studied.The composite ceramic tool materials, TiB₂-TiN, TiB₂-Al₂O₃ and TiB₂-TiN-Al₂O₃, were fabricated by the optimized hot-pressing technology, and effect of additives on the density was studied. It is shown that the TiN and Al₂O₃ particles can promote the sintering process of the TiB₂ ceramic tool materials. The relative density of TiB₂-TiN increases consistently with an increase in the content of TiN and gets up to 98.87% when the addition content of TiN is 30vol%. A small amount of Al₂O₃ can distinctly improve the density of the TiB₂ ceramic tool materials, but more content of Al₂O₃, exceeding 30vol%, is not beneficial to improving the density of the TiB₂ ceramic tool materials. The densification process was studied, and the densification equations of the initial and final sintering stages were established. It is shown that the densification during the initial stage of sintering is determined by the grain accommodation, 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. When the wetting angle between liquid-phase and particle is smaller than that between liquid-phase and matrix, particle can promote the sintering process of the TiB₂ ceramic tool materials, and the more amounts and the faster of the densification rate. Whereas, particle is not beneficial to the sintering of the TiB₂ ceramic tool materials when the wetting angle between liquid-phase and particle is equal to that between liquid-phase and matrix. The process of densification during the final sintering stage is determined by liquid flow and solid diffusion, and the densification rate has been affected by grain-boundary diffusion coefficient （D）, grain-boundary width （W）, atom volume （α³） and surface tension of the particle. The density increases consistently with the increase in sintering time, and the -ln（1-ρ） is linear with the sintering time. The relationship between the -ln（1-ρ） and the particle amounts is a parabola, that is to say, the densification of TiB₂ matrix composite ceramic tool materials first slightly and then sharply increases with an increase in the content of the additives.The mechanical properties, microstructure and toughening mechanisms of the TiB₂ matrix composite ceramic tool materials were studied. The TiB₂ matrix composite ceramic tool materials, BT30, BA30 and BT30A10, were fabricated successfully. Their average flexural strength are 1240MPa, 915MPa and 1036MPa, the average fracture toughness are 7.43MPa·m^1/2, 7.00MPa·m^1/2 and 7.8MPa·m^1/2, the average Vickers hardness are 20.47GPa, 21.42GPa and20.33GPa, respectively. The main toughening mechanisms are metal bridging, cleavage vein in the fracture surface and crack shielding caused by dislocations. The mechanics model of bridging by metal particle and metal ring was established. The model indicates that the toughening value by metal particle is 5.09 times higher than that by metal ring at the same amount of metal.The oxidation behavior of the TiB₂ matrix composite ceramic tool materials, TiB₂-TiN, TiB₂-Al₂O₃ and TiB₂-TiN-Al₂O₃, at the temperature of 700℃, 800℃and 1000℃was investigated systematically. It is shown that the oxidation gain of TiB₂-TiN increases with an increases in the content of TiN, and that of TiB₂-Al₂O₃ and TiB₂-TiN-Al₂O₃ decreases with an increase in the content of Al₂O₃. The oxidation of TiB₂-TiN and TiB₂-TiN-Al₂O₃ occurs at 700℃, and that of TiB₂-Al₂O₃ begins at 800℃. The oxidation energy of the BT30 is the least one among the BT30, BA30 and BT30A10, and that of BA30 is the highest one at the temperature range from 800℃to 1000℃. After an oxidation time of 50h at the temperature of 800℃, TiO₂ appears at the surface of the BT30 and BT30A10, it covers the materials surface and surrounds the TiB₂ particles, which prevents the oxidation from occurring still. Light oxidation of the BA30 occurs and the TiO₂ does not surround the TiB₂. The flexural strength of the BT30, BA30 and BT30A10 is more than 750MPa after the oxidation and can act as tool still. After an oxidation time of 50h at the temperature of 1000℃, the TiN of the BT30 and BT30A10 and the TiB₂ of BA30 have been reacted completely. The flexural strength of the BT30, BA30 and BT30A10 is too low to act as tool.The thermal-shock resistance and R-curve behavior of the BT30, BA30 and BT30A10 were investigated, and the prediction model of flexural strength was established. The parameter of crack propagation after thermal-shock was proposed. It is shown that the critical difference in temperature of the BT30, BA30 and BT30A10 is 750℃, 800℃and 750℃, the holding rate of flexural strength is 26.37%, 50.17% and 33.78%, the parameter of the R-curve is 0.038, 0.139 and 0.087, respectively. The holding rate of flexural strength after a single thermal-shock is a constant relating to the parameter of the R-curve, and the bigger of the parameter the bigger of flexural strength.Compared to the commercial SG4 ceramic tool partly, the cutting performance of the BT30, BA30 and BT30A10 in continuous machining hardened 40Cr alloy steel, hardened 45^# steel, stainless steel lCrl8Ni9Ti, and in intermittent machining hardened 45^# steel was studied. The wear mechanisms of the TiB₂ composite ceramic tool materials were analyzed. It is shown that the wear resistance ability is BA30>BT30 when continuous machining hardened 40Cr alloy steel, and the difference between BA30 and SG4 is not significant. The main wear patterns are tool flank and rake wear as well as the main wear mechanism is abrasive wear. The wear resistance ability is BA30>BT30A10>BT30 when continuous machining hardened 45^# steel. The main wear patterns are tool flank and rake wear as well as the main wear mechanism is abrasive wear in low speed, the main wear mechanism of the BA30 and BT30A10 is abrasive wear in high speed, the main wear mechanism of the BT30 is oxidation wear on rake face and abrasive wear on flank face in high speed. The BA30 and BT30A10 are not suitable to machining stainless steel lCrl8Ni9Ti, however the wear resistance of the BT30 is strong. The wear resistance of the tool with a rake angle of 0°is superior to that with a rake angle of -5°. The wear patters are tool flank and rake wear as well as the wear mechanism of tool flank is abrasive wear, and that of the tool rake is diffusing wear. The fracture resistance of the BT30 is superior to that of the BA30 and BT30A10 when intermittent machining hardened 45^# steel, and the fracture mechanism is mechanical fracture in low speed and high depth, thermal fracture in high speed and low depth, mechanical and thermal fracture in medial speed and depth.更多还原