Si3N4原料对形成长颗粒 Ca-α-Sialon晶粒形貌的影响

针对固定组份的Ｃａ－α－Ｓｉａｌｏｎ系统Ｃａ１.８Ｓｉ６.６Ａl５．４Ｏ１．８Ｎ1４．２）,选用不同α／β比值的Ｓｉ３Ｎ４原料考察了无压烧结所得材料的致密化、反应过程及显微结构的异同．结果表明,由两种不同α／β比值的Ｓｉ３Ｎ４原料制备的材料,其α－Ｓｉａｌｏｎ晶粒均具有长颗粒的形貌．但高β相含量的Ｓｉ３Ｎ４原料会阻碍Ｃａ－α－Ｓｉａｌｏｎ材料的致密化,β－Ｓｉ３Ｎ４相完全消失的温度也比α－Ｓｉ３Ｎ４提高了１００℃．原料中β相含量废越高,提供给α－Ｓｉａｌｏｎ生长的核心数越少,α－Ｓｉａｌｏｎ晶粒越粗大,而且高β相Ｓｉ３Ｎ４原料中宽的粒径分布导致所得α－Ｓｉａｌｏｎ晶粒尺寸的不均匀．     

液相法制备碳—碳复合材料Si—W防氧化涂层中的晶粒长大

研究了液相法制备Ｃ／Ｃ复合材料的Ｓｉ－Ｗ涂层及其在氧化试验中晶粒长大的过程，实验结果表明：在涂层制备过程中，有液态Ｓｉ参与的Ｓｉ和Ｗ的液－固反应在生成ＷＳｉ２的同时，在液－固界面张力的作用下，ＷＳｉ２晶粒迅速靠近；在涂层氧化过程中，在ＷＳｉ２晶体界面能和液－固界面张力的联合作用下，ＷＳｉ２晶粒通过溶解－沉淀的方式发生异常生长，进一步的观察表明，涂层中的晶粒长大能提高涂层的防氧化性能。     

Dy α-β Sialon 陶瓷的制备与相变研究

在Ｄｙ－Ｓｉ－Ａｌ－Ｏ－Ｎ系统相关系的研究基础上，设计了以ＤｙＡＧ和Ｍ’相作为晶界相的单相α－Ｓｉａｌｏｎ和β－Ｓｉａｌｏｎ以及复相α－β－Ｓｉａｌｏｎ材料。研究了它们的致密化行为，热处理过程中的α′→β′相变机制以及力学性能。结果表明：可以制备出以ＤｙＡＧ和Ｍ’本作为晶界相的单相α－Ｓｉａｌｏｎ和β－Ｓｉａｌｏｎ以及复相α－β－Ｓｉａｌｏｎ材料。作为绕结助剂，ＤｙＡＧ比Ｍ’更能有效地促进致密化。     

机械球磨法制备纳米晶Fe_（73．5）Cu_1Nb_3Si_（13．5）B_9的

对Ｆｅ_（７３．５）Ｃｕ_１Ｎｂ_３Ｓｉ_（１３．５）Ｂ_９成分的母合金进行了机械球磨，并对不同时间的球磨样品进行了Ｘ射线衍射（ＸＲＤ）和Ｍｏｓｓｂａｕｅｒ谱（ＭＳ）的测量，结果表明样品难以完全非晶化，形成了无序的αＦｅ－Ｓｉ固溶体纳米晶，晶粒尺寸在５ｎｍ左右，同时共有一部分富集Ｎｂ，Ｂ元素的界面非晶相。在各种球磨条件下对αＦｅ－Ｓｉ固溶体中的Ｓｉ含量进行了计算。纳米晶Ｆｅ_（７３．５）Ｃｕ_１Ｎｂ_３Ｓｉ_（１３．５）Ｂ_９软磁合金近年来受到了广泛的重视~［１］。这种材料通常是由熔融金属急冷制成非晶薄带，然后在晶化温度以上退火制成，晶化以后在非晶基体上均匀析出１０－２０ｎｍ尺寸的αＦｅ－Ｓｉ固溶体。机械球磨或机械合金化是近些年来发展起来的一种制备亚稳态材料如非晶，纳米晶，准晶等的有效手段，有一定优越性。本文利用机械球磨探讨一种制备纳米晶Ｆｅ_（７３．５）Ｃｕ_１Ｎｂ_３Ｓｉ_（１３．５）Ｂ_９合金粉末的新途径。     

Fe_(72.5)Cu_1Nb_(1.5)Mo_(1.5)V_1Si_(13.5)B_9合金的磁性和晶化过程

本文研究了Ｆｅ７２．５Ｃｕ１Ｎｂ１．５Ｍｏ１．５Ｖ１Ｓｉ１３．５Ｂ９合金在不同热处理温度下磁性能的变化及其晶化过程。在ＦｅＣｕＮｂＳｉＢ合金中用Ｍｏ,Ｖ部分替代Ｎｂ仍能获得软磁性能良好的纳米微晶。其最合适的热处理退火条件为５３５℃,保温１小时。与用机械合金法合成纳米晶相比较,佐证了非晶晶化法形成纳米微晶,其优异的磁性能是由于微晶中同时存在晶粒和晶界两种磁相,晶粒与晶界之间有交换相互作用。     

机械球磨法制备纳米晶Fe73.5Cu1Nb3Si13.5B95的结构研究

对Ｆｅ７３．５Ｃｕ１ｎｂ３Ｓｉ１３．５Ｂ９成分的母合金进行了机械球磨，并对不同时间的球磨样品进行了Ｘ射线衍射（ＸＲＤ）和Ｍｏｓｓｂａｕｅｒ谱（ＭＳ）的测量，结果表明样品难以完全非晶化，形成了无序的αＦｅ－Ｓｉ固溶体的纳米晶，晶粒尺寸在５ｎｍ左右，同时共存一部分富集Ｎｂ，Ｂ元素的界面非晶相。在各种球磨条件下对αＦｅ－Ｓｉ固溶体中的Ｓｉ含量进行了计算。     

Ca-α-Sialon的反应致密化

本文通过反应热压制备了单相Ca－α-Sialon材料,研究了Ca－α－Sialon形成的反应致密化过程．不同温度下产物的XRD结果表明,1250℃样品开始软化,1300℃时体系中反应形成了钙铝黄长石相,1500℃时钙铝黄长石重新溶解于液相中,同时形成了Ca－α－Sialon,1600℃时反应完全,原料中各相完全消失,形成了单相Ca－α－Sialon．不同温度下产物的密度表明,伴随着上述反应形成过程,材料经过颗粒重排、溶解-反应-沉淀过程和晶粒生长三个阶段,通过液相烧结达到了致密化．     

Sm-Fe-Si-C非晶合金的晶化动力学

用差热分析（ＤＴＡ）,结合Ｘ射线衍射（ＸＲＤ）研究了Ｓｍ－Ｆｅ－Ｓｉ－Ｃ非晶态合金的晶化动力学。结果表明：温度低于９００℃时,该合金晶化相为α－Ｆｅ（Ｓｉ）固溶体和Ｓｍ２（Ｆｅ,Ｓｉ）１７Ｃｘ。α－Ｆｅ（Ｓｉ）相的晶化表观激活能为４３１．５１ｋＪ／ｍｏｌ,Ｓｍ２（Ｆｅ,Ｓｉ）１７Ｃｘ相的晶化表观激活能为５１４．４３ｋＪ／ｍｏｌ。上在晶化初期活能变化不大,当α－Ｆｅ（Ｓｉ）相的体积分数大于７０％,Ｓ     

预退火对Fe73.5Cu1Mo3Si13.5B9纳米晶合金形成的影响

采用Ｘ射线衍射，电子衍射及透射电子显微技术研究了Ｆｅ７３．５Ｃｕ１－ｘＭｏ３Ｓｉ１３．５Ｂ９非晶合金４１０℃预退火对随后４８０℃退火所形成的纳米晶结构的影响。结果表明，预退火对Ｆｅ７３。０５，Ｃｕ１Ｍｏ３Ｓｉ１３．５Ｂ９合金纳米晶结构的形成有重要影响。当预退火时间从０小时增加到３小时，合金在４８０℃，小时退火形成的晶相化α－Ｆｅ（Ｓｉ）的晶粒尺寸从１５ｎｍ减小到８ｎｍ。预退火使α－Ｆｅ（Ｓｉ）相的     

液相法制备联碳－碳复合材料Si－W防氧化涂层中的晶粒长大

研究了液相法制备Ｃ／Ｃ复合材料的Ｓｉ－Ｗ涂层及其在氧化试验中晶粒长大的过程实验结果表明：在涂层制备过程中，有液态Ｓｉ参与的Ｓｉ和Ｗ的液－固反应在生成ＷＳｉ２的同时，在被－固界面张力的作用下，ＷＳｉ２晶粒迅速靠近；在涂层氧化过程中，在ＷＳｉ２晶体界面能和液－固界面张力的联合作用下，ＷＳｉ２晶粒通过溶解－沉淀的方式发生异常长大．进一步的观察表明，涂层中的晶粒长大能提高涂层的防氧化性能．     

Pressureless sintering of in-situ toughened Yb α-SiAlON ceramics by adding seed crystals prepared by combustion synthesis

Single-phase Yb α-SiAlON ceramics in-situ toughened by elongated grains were prepared by pressureless sintering, with the crystalline powder prepared by combustion synthesis used as seed crystals. The effects of seed addition on the densification, phase transformation, microstructure development, and mechanical properties of the samples were investigated in detail. From the experimental results, it was found that the added seed crystals could promote the phase transformation and facilitate the growth of elongated grains. By adding seed crystals the fracture toughness of the sintered α-SiAlON ceramics was considerably improved, with no obvious degradation in the bulk density and hardness at the same time.     

Fabrication,characterization and mechanical properties of SiC-whisker-reinforced Y-TZP composites

The microstructure and mechanical properties of hot-pressed yttria-stablized tetragonal zirconia polycrystals (Y-TZP) reinforced with up to 30 vol % SiC whiskers were investigated. The homogeneously dispersed and fully dense SiC whisker/Y-TZP composites were fabricated by wet-mixing the constitutents and uniaxially hot-pressing the resulting powder. The grain size of the matrix depended on the whisker volume fraction and the hot-pressing temperature. The significant increase of fracture toughness of about MPa m^1/2 at 10 Vol % SiC and a small increase in strength were achieved by uniformly dispersing the whiskers in the Y-TZP matrix. Fracture surfaces revealed evidence of toughening by the mechanisms of crack deflection, pullout, and crack bridging by the whiskers and also a phase transformation of ZrO₂. The observed increase in the fracture toughness of Y-TZP due to the addition of SiC whiskers was correlated with existing models of toughening mechanisms. Good agreement was achieved between the theoretical predictions and the experimental toughness values, obtained from the Y-TZP/SiC_w composites.     

Strength and fracture toughness of in situ-toughened silicon carbide

Fine β-SiC powders either pure or with the addition of 1 wt % of α-SiC particles acting as a seeding medium, were hot-pressed at 1800 °C for 1 h using Y₂O₃ and Al₂O₃ as sintering aids and were subsequently annealed at 1900 °C for 2, 4 and 8 h. During the subsequent heat treatment, the β → α phase transformation of SiC produced a microstructure of “in situ composites” as a result of the growth of elongated large α-SiC grains. The introduction of α-SiC seeds into the β-SiC accelerated the grain growth of elongated large grains during annealing which led to a coarser microstructure. The sample strength values decreased as the grain size and fracture toughness continued to increase beyond the level where clusters of grains act as fracture origins. The average strength of the in situ-toughened SiC materials was in the range of 468–667 MPa at room temperature and 476–592 MPa at 900 °C. Typical fracture toughness values of 8 h annealed materials were 6.0 MPa m^1/2 for materials containing α-SiC seeds and 5.8 MPa m^1/2 for pure β-SiC samples. This revised version was published online in November 2006 with corrections to the Cover Date.     

原位生成TiC/Ti5Si3纳米复合材料的显微结构研究

研究了原位生成ＴｉＣ／Ｔｉ_５Ｓｉ_３纳米复合材料的显微结构．实验结果表明,以ＳｉＣ和Ｔｉ 为原料,通过反应热压工艺可以原位合成ＴｉＣ／Ｔｉ_５Ｓｉ_３复合材料,其中的大部分ＴｉＣ粒子为纳 米粒子．ＴｉＣ晶粒与Ｔｉ_５Ｓｉ_３晶粒的晶界上存在原子台阶．复合材料还含有少量Ｔｉ_３ＳｉＣ_２相．这 些Ｔｉ_３ＳｉＣ_２相主要呈棒状分布在Ｔｉ_５Ｓｉ_３基体中,另有少量Ｔｉ_３ＳｉＣ_２相位于大的ＴｉＣ晶粒内．     

Densification and Microstructure of β-sialon/Nano-size SiC Composites

β-sialon/nano-size SiC composite ceramic with DyAG(Dy3Al5O12) as grain boundary phase was fabricated through hot-pressing. The effect of nano-size SiC on densification, phase composition, microstructure and mechanical properties of the materials was studied     

颗粒级配对固相烧结碳化硅陶瓷的影响

通过粗细碳化硅粉体的颗粒级配实现了致密固相烧结碳化硅(S-SiC)陶瓷的增强增韧, 系统研究了粗粉(~4.6 µm)加入量对烧结试样的致密化、微结构与力学特性的影响。结果表明: 当粗粉加入量不超过75wt%时, 可制备出相对密度≥98.3%的致密S-SiC陶瓷, 烧结收缩率低至14.5%;引入的粗粉颗粒产生钉扎作用, 显著抑制了S-SiC陶瓷中异常晶粒生长, 形成细小的等轴晶粒, 进而提高了S-SiC陶瓷的抗弯强度。同时, 粗粉颗粒的引入导致S-SiC陶瓷的断裂方式由穿晶断裂转变为穿晶-沿晶复合断裂, 使得S-SiC陶瓷的断裂韧性增强。对于粗粉引入量为65wt%的S-SiC陶瓷, 抗弯强度与断裂韧性分别为(440±35) MPa与(4.92±0.24) MPa•m^1/2, 相比于未添加粗粉的S-SiC陶瓷, 分别提升了14.0%与17.1%。     

SiCxOy相分解方式对SiCO(Al)纤维烧结致密化的影响

研究了SiCO(Al)纤维向SiC(Al)纤维的高温转化过程, 并研究了纤维中SiC_xO_y相的分解特征及不同高温处理方式对纤维结构和烧结致密化的影响。结果表明: 纤维中SiC_xO_y相分解的温度范围为1430~1850℃, 当采用连续处理方式处理, 即使在1800℃下, 纤维芯部SiC_xO_y相未能彻底分解, 且快速分解速率导致纤维中形成粗大结晶颗粒和气孔, 无法得到致密的高结晶结构。而在静态条件下处理, 可以提高SiC_xO_y相分解程度。1650℃下保温处理1 h后可以完全脱除SiC_xO_y相, 同时保持晶粒均匀。再经过1900℃烧结, 即可制得呈致密高结晶结构SiC(Al)纤维。     

Rapid densification and reaction sequences in self-reinforced Y-α-SiAlON ceramics with barium aluminosilicate as an additive

Y-α-SiAlON (Y_1/3Si₁₀Al₂ON₁₅) ceramics with 5 wt.%BaAl₂Si₂O₈ (BAS) as an additive were synthesized by spark plasma sintering (SPS). The kinetic of densification, phase transformation sequences and grain growth during sintering process were investigated. Full densification could be achieved by 1600 °C without holding and using a heating rate of 100 °C min⁻¹, but the transformation from α-Si₃N₄ to α-SiAlON is not completed simultaneously with the densification process. The equilibrium phase assemblage could be reached after SPS at 1800 °C for 5 min and the resultant material possesses self-reinforced microstructure with high hardness of 19.2 GPa and fracture toughness of 6.8 MPa m^1/2. The complete crystallization of BAS is beneficial to the high temperature mechanical properties. The obtained could maintain the room strength up to 1300 °C.     

Investigation and characterization of densification,processing and mechanical properties of TiB2–SiC ceramics

In the present work, high-frequency induction heating was firstly used to densify TiB₂–SiC ceramic, and the microstructure analysis indicated that the average grain size of the sample, which was sintered through induction heating, was smaller than that of the sample sintered through hot-pressing. The flexural strength and fracture toughness were improved after refining the grains and increasing the relative density. In order to characterize the densification behavior of TiB₂–SiC ceramic sintered through induction heating, the typical curve of measured linear shrinkage of a sample was calculated and used. The tangential and normal grinding forces were substituted by the horizontal and vertical forces measured from the dynamometer in order to characterize intuitively the effect of grinding parameters on the microstructure and residual stress. The above-mentioned results revealed that the high-frequency induction heating has more advantages over hot-pressing. The results and way of these works can be applied to aid materials engineering design for the development of new materials, quality assurance, and characterization assessment of durability.     

Microstructure and mechanical properties of liquid phase sintered Mo2FeB2 based cermets

Mo₂FeB₂ based cermets were fabricated by liquid phase sintering at different sintering temperatures and soaking time. Almost full densification was achieved at 1080 °C without soaking time. However, a lower sintering temperature resulted in the aggregation of binder phase and a higher contiguity of hard phase. An increase of sintering temperature or soaking time promoted an in situ growth of elongated Mo₂FeB₂ grains in the intermediate state of sintering. Abnormally large and faceted Mo₂FeB₂ grains appeared at 1320 °C for 20 min. The growth of the abnormally large grains was associated with grain coalescence. The transverse rupture strength (TRS), hardness (HRA) and fracture toughness (K_IC) were also measured, and attempts were made to relate them to the microstructural development.