Development of high toughness silicon nitride ceramics

由于氮化硅陶瓷具有高强度、断裂韧性和良好的高温强度等综合性能，已成为包括汽车、刀具、航空航天和装甲工业在内的许多行业的主导结构陶瓷。最近，氮化硅已被确定用于另一种应用，例如用于制造人造骨和植入物的生物材料。在所有上述应用中，关键要求是高断裂强度（远高于1000 MPa）、断裂韧性（远高于10MPa.m1/2）、硬度（远高于10 GPa）和杨氏模量（超过300 GPa）的组合。该计划的长期目标是开发一种能够提供更高抗裂纹扩展能力的微观结构，并产生新一代氮化硅基陶瓷，其机械性能上级现有材料，并可能接近一些低韧性金属和合金，如铝和铝合金。短期目标是研究氮化物（氮化硼、氮化锆等）等非氧化物添加剂的作用。在致密化、组织发展和力学性能方面。这里的策略是鼓励细长的Si 3 N3晶粒的生长，并修改界面，以加强拔出和裂纹桥接。裂纹桥联是氮化硅基陶瓷主要的增韧机制。目前的研究计划是基于申请人的初步研究，其中已经表明，当使用选定的添加剂时，断裂韧性的主要增加是可能的。在一种情况下，测量到> 14MPa.m1/.2的断裂韧性。据申请人所知，该断裂韧性值是公开文献中记录的最高值。该计划的成功结果将导致创造一种新的陶瓷类别，具有过去无法比拟的性能组合。它还将为研究生，PDF和研究人员提供在汽车，航空航天和能源领域快速发展的先进陶瓷领域的培训机会。

Due to the combination of properties such as high strength, fracture toughness and good high temperature strength, silicon nitride ceramics have become the leading structural ceramics in many industries including automotive, cutting tools, aerospace and armour industries. Recently, silicon nitride has been identified for yet another application such as biomaterials for the manufacture of artificial bones and implants. In all of the above noted applications, the key requirements are the combination of high fracture strength (well over 1000MPa), fracture toughness (well above 10 MPa.m1/2), hardness (well above 10 GPa) and Young's modulus (over 300 GPa). The long term objective in this program is the development of a microstructure capable of providing higher resistance to crack propagation and resulting in a new generation of silicon nitride based ceramics with mechanical properties superior to those of the existing material and possibly close to that of some lower toughness metals and alloys such as aluminum and aluminum alloys. The short term objective is to study the role of non-oxide additives such as nitrides (boron nitride, zirconium nitride, etc.) in the densification, microstructure development and mechanical properties. The strategy here is to encourage the growth of elongated ß-Si3N3 grains and to modify the interface in order to intensify the pull-out and crack bridging. Crack bridging has been identified as the major and most powerful mechanism of toughening in silicon nitride based ceramics. The present research program is based on the applicant's preliminary studies where it has been shown that major increases in fracture toughness are possible when selected additives are used. In one instance, fracture toughness of >14 MPa.m1/.2 was measured. To the applicant's knowledge this value for fracture toughness is the highest ever recorded in the open literature. Successful outcome of this program will lead to the creation of a new class of ceramics with a combination of properties unmatched in the past. It will also provide the opportunity for training of graduate students, PDFs and Research Associates in this rapidly growing area of advanced ceramics in automotive, aerospace and energy sectors.