Development of high toughness silicon nitride ceramics

氮化硅陶瓷由于具有高强度、断裂韧性和良好的高温强度等性能，已成为汽车、刀具、航空航天、装甲等行业的主导结构陶瓷。最近，氮化硅被确定用于另一种应用，例如用于制造人造骨骼和植入物的生物材料。在上述所有应用中，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.)和杨氏模数(高于300 GPa.)。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结构，并导致新一代氮化硅陶瓷，其机械性能优于现有材料，并可能接近一些韧性较低的金属和合金，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、显微组织发展和力学性能方面。这里的策略是鼓励细长的-Si3N3晶粒的生长，并改变界面以加强拔出和裂纹桥联。裂纹桥联已被认为是氮化硅陶瓷增韧的主要和最有效的机制。目前的研究计划是基于申请人的初步研究，其中已经证明，当使用选定的添加剂时，断裂韧性有可能大幅提高。在一个实例中，测量了&gt；14 MPa.m1/.2的断裂韧性。据申请人所知，这一断裂韧性值是公开文献中有记录以来最高的。这一计划的成功结果将导致创造一种新的陶瓷类别，其性能组合在过去是无与伦比的。它还将为在汽车、航空航天和能源领域这一快速增长的先进陶瓷领域培训研究生、PDF和研究助理提供机会。

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.