稀土氧化物在氮化硅陶瓷中应用的研究进展

简要论述了稀土氧化物在氮化硅陶瓷材料中的应用研究概况,介绍了单一稀土氧化物以及复合掺杂稀土氧化物在氮化硅陶瓷材料中的应用进展,并比较了它们对氮化硅陶瓷材料性能的影响;最后对稀土氧化物在氮化硅陶瓷材料中的应用前景作了简单分析和展望.     

添加氮化硅的橡胶油封

氮化硅是一种新的工程陶瓷材料，橡胶油封添加氮化硅后，能提高其耐磨性。     

发明专利

名称：一种多孔氮硅陶瓷材料的制备方法 申请号：CN201310386114.X 公开（公告）日：2014.01.01申请日：2013.08.30 申请（专利权）人：航天特种材料及工艺技术研究所 发明（设计）人：张辉;吕毅;张天翔;王涛;郭世峰;裴雨辰;赵英民;武建强 本发明提出一种多孔氮化硅陶瓷材料的制备方法,经配料、注浆成型、烧结而成。本发明具有工艺简单、不需发生化学反应、不需添加有机造孔剂、不需加压,能制备形状复杂的制品,素坯强度较高,均匀性好、内在缺陷少,最终陶瓷密度、强度均高于其它方法制备的氮化硅基多孔陶瓷材料。     

Si3N4陶瓷材料的高温氧化理论及其抗氧化研究现状

从热力学、动力学和整体控速过程探讨了氮化硅陶瓷材料高温氧化理论和氧化性质，阐述了表面改性技术对氮化硅抗氧化性能的影响．并对表面改性提高氮化硅抗氧化性能进行了展望。     

(TiB2,TiN)-Si3N4基复合材料的性能及显微结构

研究第二相粒子的引入对氮化硅陶瓷材料性能和显微结构的影响,结果发现：ＴｉＮ粒子的引入;对材料能起到协同增韧的作用,而ＴｉＢ２粒子由于与氮化硅颗粒表面的ＳｉＯ２发生反应,导致复合材料不致密,引起力学性能下降。     

陶瓷材料Knoop硬度测试中的能量平衡关系

借助于弹／塑性压痕模型，导出了一个用于描述陶瓷材料Ｋｎｏｏｐ压痕过程中能量平衡关系的表达式，并对由这一表达式所预测的压痕参数（Ｐ／ｄ）－ｄ之间存在的线性关系进行了实验验证，根据这一表达式，对陶瓷材料表现Ｋｎｏｏｐ硬度随荷载的变化关系进行了研究，指出：压痕过程中荷载所做功的额外消耗是导致表观硬度随荷载增大而降低的主要原因。     

Si3N4/Si3N4扩散连接的力学性能研究

采用热压法进行氮化硅陶瓷材料的扩散连接.结果表明:在1520℃,15MPa,60min条件下,氮化硅连接体的最高强度为448.6MPa,超过母材强度;平均连接强度为401.5MPa,为母材强度的96%.     

多孔氮化硅陶瓷的研究进展

综述了多孔氮化硅陶瓷材料的国内外研究现状和进展,介绍了多孔氮化硅陶瓷的主要制备方法,分析了微观组织对多孔氮化硅陶瓷力学性能的影响,并与其他多孔陶瓷进行了性能比较,最后展望了多孔氮化硅陶瓷的发展前景.     

烧结温度对不同Yb_2O_3含量的氮化硅陶瓷结构和性能的影响

在不同烧结温度、30 MPa压力下保温1h制备了不同Yb_2O_3含量的氮化硅陶瓷,通过XRD、SEM、阿基米德排水法、三点抗弯强度法、Vickers压痕法等手段测定了氮化硅陶瓷的物相组成、显微结构、致密度、抗弯强度、断裂韧性和硬度。研究了烧结温度对不同Yb_2O_3含量的氮化硅陶瓷的相变、显微结构和力学性能的影响。研究表明,Yb_2O_3含量的变化导致了Yb_2O_3和氮化硅表面SiO_2反应配比的变化,从而在Yb_2O_3-SiO_2二元体系和Yb_2O_3-SiO_2-Si3_N_4三元体系中,晶界第二相生成物也发生了变化。这些第二相生成物种类与烧结温度共同影响氮化硅陶瓷材料的显微结构和力学性能。5 wt%Yb_2O_3含量的Si_3N_4陶瓷在1850℃获得所有9个样品中最大的抗弯强度和断裂韧性,分别为874 MPa和5.83 MPa·m1/2;15 wt%Yb_2O_3含量Si_3N_4陶瓷中出现的第二相Yb_4Si_2O_7N_2,抑制了氮化硅晶粒在高温下的异常长大。     

氮化硅陶瓷抗裂性的研究

讨论了工艺因素对氮化硅陶瓷结构、物理机械性能及其抗裂性的影响。查明，Al2O3 Y2O3复合烧结助剂及与其相配合的硅酸乙酯结合剂对氮化硅陶瓷强受和抗裂性变化有影响。证明用压痕法可以评定陶瓷的抗裂性。     

R-Curve Behavior and Strength for In-Situ Reinforced Silicon Nitrides with Different Microstructures

R -curves for two in-situ reinforced silicon nitrides A and B of nominally the same composition are characterized using the Griffith equation and indentation fracture mechanics. These R -curves are calibrated against fine-grained silicon nitrides which have a known chevron-notch (long-crack) toughness and with a nearly flat R -curve behavior. Silicon nitride A, with its coarser microstructure and higher chevron-notch toughness, shows lower resitance to crack growth than silicon nitride B if the crack size is less than ∼200 μm. These results are consistent with the indentation–Strength measurements which show a crossover of strength between the two materials at an indentation load between 49 and 98 N, and below the crossover A has a lower strength. The toughening behavior is explained using an elastic-bridging model for the short crack, and a pullout model for the long crack. The effects of R -curve properties on design are discussed.     

Multi‐Scale Effects in the Strength of Ceramics

Multiple length‐scale effects are demonstrated in indentation‐strength measurements of a range of ceramic materials under inert and reactive conditions. Meso‐scale effects associated with flaw disruption by lateral cracking at large indentation loads are shown to increase strengths above the ideal indentation response. Micro‐scale effects associated with toughening by microstructural restraints at small indentation loads are shown to decrease strengths below the ideal response. A combined meso‐micro‐scale analysis is developed that describes ceramic inert strength behaviors over the complete indentation flaw size range. Nano‐scale effects associated with chemical equilibria and crack velocity thresholds are shown to lead to invariant minimum strengths at slow applied stressing rates under reactive conditions. A combined meso‐micro‐nano‐scale analysis is developed that describes the full range of reactive and inert strength behaviors as a function of indentation load and applied stressing rate. Applications of the multi‐scale analysis are demonstrated for materials design, materials selection, toughness determination, crack velocity determination, bond rupture parameter determination, and prediction of reactive strengths. The measurements and analysis provide strong support for the existence of sharp crack tips in ceramics such that the nano‐scale mechanisms of discrete bond rupture are separate from the larger scale crack driving force mechanics characterized by continuum‐based stress‐intensity factors.     

Short-Crack Toughness and Abrasive Machining of Silicon Nitride

Hardness and toughness are often used to analyze the abrasive machining behavior of ceramic materials. However, toughness values of silicon nitride ceramics with microstructures containing elongated grains increase with crack extension. The present study investigates the effect of toughness on the process of abrasive machining to determine which value of toughness should be used in the analysis. The toughness curves (i.e., toughness as a function of crack length) of ten different silicon nitride materials are characterized by an indentation-strength technique and an indentation technique. The forces in surface grinding are measured as a function of the depth of cut. Examination of ground surfaces by scanning electron microscopy indicates that the material-removal processes in grinding follows the formation of short cracks (i.e., microcracks) and grain-scale material dislodgement. An indentation fracture model for material removal in abrasive machining is used to correlate the grinding forces with toughness and hardness of the materials. An agreement is obtained between the experimental results and the indentation model only when the toughness associated with short cracks is used. This study shows the importance of using appropriate toughness values corresponding to the microfracture processes in analyzing abrasive machining results for materials possessing rising toughness curves.     

Mechanical properties of structural ceramic materials based on silicon nitride

The creation of structural ceramic materials based on silicon nitride is considered. The results of a study of the properties of these materials in a wide temperature range are presented, including data on the short-term strength, elastic characteristics, and parameters of fracture mechanics and results of long-term static and dynamic tests of some silicon nitride materials.Translated from Ogneupory i Tekhnicheskaya Keramika, No. 11, pp. 14–17, November, 1996.     

Mechanical reliability evaluation of silicon nitride ceramic components after exposure in industrial gas turbines

Several studies have recently been undertaken to examine the mechanical reliability and thermal stability of silicon nitride ceramic components that are currently being considered for structural application in industrial gas turbines. Specifically, ceramic components evaluated included a bow-shaped silicon nitride nozzle evaluated in an engine test rig, silicon nitride vanes exposed in an engine field test, and an air-cooled silicon nitride vane that is currently under development. Despite the differences in field test conditions all of the exposed silicon nitride ceramic components exhibited a significant material recession arising from the oxidation of silicon nitride and subsequent volatilization of the oxide (i.e., silica). The fracture strength of exposed airfoils was also decreased due to the formation of a subsurface damage zone induced by the turbine environments. In addition, studies indicated that the properties of as-processed ceramic components, especially in airfoil regions, were not always comparable to those generated from the standard specimens with machined surface extracted from production billets. The component characterization efforts provided an important insight into the effect of gas turbine environments on the material recession and mechanical reliability of materials as functions of exposure time and conditions, which were very difficult to obtain from a laboratory scale test.     

氮化硅陶瓷在四大领域的研究及应用进展

氮化硅陶瓷不仅具有较高的力学性能还具有良好的透波性能、导热性能以及生物相容性能,是公认的综合性能最优的陶瓷材料。作为轴承球的致密氮化硅陶瓷广泛应用在机械领域;作为透波材料的多孔氮化硅陶瓷广泛应用在航空航天领域;随着对氮化硅陶瓷材料的深入研究,其在导热性和生物相容性方面的优异特性逐渐被科研工作者认识并得到开发和应用。本文详细阐述了氮化硅粉体的制备方法,并综述了氮化硅陶瓷作为结构陶瓷在机械领域和航空航天领域的研究进展,此外还介绍了其作为功能陶瓷在半导体领域、生物制药领域的研究和应用现状,最后对其未来发展进行了展望。     

氮化硅陶瓷的烧结

氮化硅陶瓷广泛用作高温结构材料,是很有前途的陶瓷材料之一。本文研究了氮化硅陶瓷烧结动力学,分析了影响氮化硅陶瓷烧结的因素,为氮化硅陶瓷烧结提供了依据     

Fatigue Threshold R‐curves Predict Fatigue Endurance Strength for Self‐Reinforced Silicon Nitride

There is a need for methods that can help predict and avoid fatigue failures of silicon nitride ceramic components. The fatigue threshold R‐curve has been proposed as potential solution to this problem. In this study, the fatigue threshold R‐curve for small, semielliptical surface cracks was calculated for a silicon nitride ceramic using the published bridging stress distribution developed from fatigue threshold tests on macroscopic crack specimens. To test the accuracy of the endurance strengths predicted using the fatigue threshold R‐curve, fatigue tests were conducted using four‐point bend beams of silicon nitride containing semielliptical surface cracks introduced by Knoop indentation. The effectiveness of the methodology was verified; indeed, 77% of the beams tested at stress levels above the predicted endurance strength failed within 10⁷ cycles and 0% of the beams tested below the predicted endurance strength failed within 10⁷ cycles. Furthermore, using the bridging stress distribution, which is thought to be a material property, the need for prohibitively difficult fatigue threshold experiments on small surface cracks is avoided. Accordingly, this methodology is potentially quite practical for use in the engineering design of ceramic mechanical components.     

Effect of temperature on the pre-creep mechanical properties of silicon nitride

The elasto-plastic properties and contact damage evolution of a commercial polycrystalline silicon nitride are evaluated as a function of temperature up to 1000 °C, using a recently developed method combining Hertzian indentation and FEM simulation. The results of the study are compared to existing data for other ceramic materials such as alumina and zirconia. Silicon nitride is found to exhibit an excellent combination of elasto-plastic properties in the pre-creep temperature range and good contact damage resistance. These qualities make this material ideal for high temperature applications in general, and in particular to be used in spherical indenters for the evaluation of mechanical properties of other materials at elevated temperature using the procedure applied in this work.     

High temperature ceramic radomes (HTCR) – A review

An electromagnetically transparent, structurally robust and environmentally resistant enclosure of radar antenna for ground based systems to modern avionics in military aircraft and missiles is called as radome. Radome materials are classified based on: (i) type of function - surface-based or flight-mode and (ii) speed of operation - subsonic, supersonic to hypersonic. The desired properties of these materials are low dielectric constant and low loss factor in addition to its capacity to withstand the high temperature of operation. Composite laminates of glass or aramid fibre reinforced polymeric resins are radome material candidates for applications in subsonic range. However, ceramics are the only viable option for military aerospace applications such as a fighter jet travelling at Mach 3 or an advanced hypersonic missile speeding up to Mach 5. This review outlines the hand-full of ceramic materials already in application as radome materials like high-purity-alumina, pyroceram, slip-cast-fused-silica, their processing technology, electromagnetic and mechanical properties, advantages and disadvantages with respect to advanced military vehicles. Use of silicon nitride based radome materials, that has exceptional mechanical strength and thermal stability up to 1400 °C is illustrated with respect to reaction bonded silicon nitride, hot pressed silicon nitride, silicon oxynitride, sialon and their composites. Design of new generation radome materials was conceptualized and discussed as applicable to silicon nitride and related ceramics, wherein incorporation of varied degree of porosity improves electromagnetic properties, simultaneously, maintaining the required mechanical strength. Multilayer and graded porosity and its influence on electromagnetic properties were briefly discussed. Si₃N₄ ceramics having controlled porosity leading to optimum electromagnetic and mechanical properties produced through systematic processing is proposed as the futuristic high temperature radome material for supersonic applications.