【作者】 王兵；

【导师】 李建功；

【作者基本信息】 兰州大学 ， 材料科学与工程·材料物理与化学， 2018， 硕士

【摘要】 Αl₂O₃陶瓷因其强度高、电绝缘性好、抗强酸强碱腐蚀、抗磨损等特点被广泛地应用于机械、电子电力、建筑工业、化学工业、医疗等领域。在地壳中,氧和铝分别是含量最高的非金属和金属元素,因此Αl₂O₃陶瓷的原材料来源丰富且价格低廉。但是,脆性这一致命缺陷限制了Αl₂O₃陶瓷更为广泛的应用。纳米晶微结构有望赋予Αl₂O₃纳米晶陶瓷良好的塑性和韧性。对于陶瓷材料来说,硬度和断裂韧性是最重要的两个性能参数,对于其在各个领域的应用有着极大的影响。因此致密（>99%）Αl₂O₃纳米晶陶瓷的硬度和断裂韧性研究具有重要意义。由于α-Αl₂O₃纳米颗粒制备的困难以及陶瓷烧结过程中晶粒的过度长大,导致难以获得晶粒细小的Αl₂O₃纳米晶陶瓷,因此关于Αl₂O₃纳米晶（<100 nm）陶瓷硬度和断裂韧性与其晶粒尺寸关系的研究还尚未被报导。本论文以硝酸铝煅烧-机械球磨-电解质聚沉分离得到的平均颗粒尺寸仅为4.2 nm（颗粒尺寸分布为2-8 nm）和7.2 nm（颗粒尺寸分布为2-15 nm）、完全分散的α-Αl₂O₃纳米颗粒为初始粉体,采用两步烧结法（即将陶瓷坯体以10?C/min的速率加热至较高温度T₁处不保温,随后以相同速率降温至较低温度T₂保温40 h,烧结完成后以5?C/min速率降到室温）制备了一系列致密（>99%）的平均晶粒尺寸小于100 nm的Αl₂O₃纳米晶陶瓷。利用维氏显微硬度计,对不同晶粒尺寸的Αl₂O₃纳米晶陶瓷的显微硬度进行了测量,并研究了显微硬度与晶粒尺寸之间的关系。研究发现,当Αl₂O₃纳米晶陶瓷的平均晶粒尺寸从96 nm减小到36 nm时,其显微硬度从17.70 GPa减小到11.00 GPa,即随着Αl₂O₃纳米晶陶瓷的晶粒尺寸减小,其显微硬度降低（反霍尔佩奇关系）。通过显微硬度测试的压痕裂纹长度计算Αl₂O₃纳米晶陶瓷的断裂韧性。分析断裂韧性数据发现,随着Αl₂O₃纳米晶陶瓷的平均晶粒尺寸从96 nm减小到36 nm,其断裂韧性从3.02±0.21 MPa?m^1/2增加到4.12±0.16 MPa?m^1/2,断裂韧性提高了36.42%。更多还原

【Abstract】 Alumina ceramic is widely used in machinery,electronic power,building industry,chemical industry and medical industry due to its high strength,good insulation,corrosion resistance against acids and bases,abrasion resistance.In the earth crust,Oxygen and Aluminum is the highest levels of the non-mental and mental elements,respectively,so alumina ceramic is easy to obtain and low in cost.However,the brittleness which is the fatal flaw of alumina ceramic limits its applications.Nanocrystalline microstructures are expected to giveΑl₂O₃ nanocrystalline ceramic with good plasticity and toughness.Hardness and fracture toughness are very important mechanical properties of ceramic materials,and these two properties parameters can affect the ceramic’s applications in various fields directly.Therefore,the preparation of dense ultrafine grained alumina ceramic and study of the hardness and fracture toughness ofΑl₂O₃ nanocrystalline ceramic with different grain sizes are of great significance.However,due to the difficulty of preparation of nano-powders and the over growth of grains,it is difficult to prepareΑl₂O₃ nanocrystalline ceramic samples.The relationship between the hardness and fracture toughness and grain size ofΑl₂O₃ nanocrystallline（<100 nm）ceramic have not been reported.In this paper,fully dispersedα-Αl₂O₃ nanoparticles with a mean particle size of 4.2 nm,a size distribution of 2-8 nm,an average particle size of 7.2 nm and a size distribution of 2-15 nm were obtained by ball milling and hydrochloric acid etching.Two-step sintering method（the ceramic green compacts is heated at a rate of 10?C/min to a higher temperature T₁ without hold,and then cooled at the same rate to a lower temperature T₂ holding for 40 h,and finally cooled down to room temperature at 5?C/min）was applied to prepare a series of denseΑl₂O₃ nanocrystalline ceramics with different grain sizes.Then,the microhardness ofΑl₂O₃ nanocrystalline ceramic with different grain sizes were measured by Vickers hardness tester,and the relationship between hardness and grain size was studied.The results showed that when the grain size ofΑl₂O₃ nanocrystalline ceramics decreased from 96 nm to 36 nm,its microhardness decreased from 17.70 GPa to 11.00GPa,which is known as inverse Hall-Petch relationship.Using indentation crack,hardness and modulus of elasticity the Fracture toughness ofΑl₂O₃ nanocrystalline ceramics with different grain sizes was calculated.Analysis of fracture toughness data showed that as the average grain size ofΑ1₂O₃ nanocrystalline ceramic decreases from 96 nm to 36 nm,its fracture toughness increases from 3.02±0.21 MPa?m^1/2 to 4.12±0.16 MPa?m^1/2,increases by 36.42%.更多还原