氧化物-非氧化物复合材料的显微结构特征

利用SEM、TEM及HREM研究了氧化物-非氧化物复合材料的显微结构特征。结果表明(1)在氧化物基体中引入非氧化物,非氧化物颗粒将穿插于氧化物颗粒构成的骨架中;在非氧化物基体中引入氧化物,氧化物颗粒将弥散于非氧化物颗粒构成的编织状结构的空隙处。(2)氧化物与非氧化物之间的结合方式可分为(a)直接结合(在没有助烧剂、直接烧结的情况下);(b)通过晶界非晶质薄膜相结合(在有助烧剂奉与的直接烧结和反应烧结的情况下)。(3)所研究的试祥中普遍存在有微裂纹,这些微裂纹将有助于材料抗热震性的改善。     

氧化铝-莫来石高温复合陶瓷改性研究

以氧化铝、莫来石、氧化锆粉体为原料制备了氧化铝-莫来石-氧化锆复合陶瓷.使用密度测试仪、抗折强度测试仪、XRD和SEM等手段对材料的密度、力学性能进行了综合分析,尝试对影响复合陶瓷热震性能的因素及作用机理进行了讨论.研究结果表明:氧化锆弥散分布于基体晶界处,填充了基体颗粒间隙,抑制了基体晶粒长大,阻碍了裂纹扩展,提高了复合陶瓷的致密性和力学性能;ZrO2的t-m转变使基体内部产生一定的压应力区域,诱发显微裂纹的产生,分散主裂纹尖端应力,增强复合陶瓷的强度.     

Fe-(9~11)Cr-Y2O3作为ITER结构材料的制备与表征

采用传统的机械合金(MA)和放电等离子体烧结(SPS)工艺成功制备了Fe-(9~11)Cr二元合金及纳米氧化物弥散强化(ODS)合金，利用扫描电子显微镜(SEM)、X射线衍射仪(XRD)对MA粉末的形貌和物相进行分析，用能量色散谱(EDS)、显微维氏硬度仪、光学显微镜、透射电子显微镜(TEM)对合金样品进行表征。结果表明，在转速为300 r/min，球料比为10:1的条件下，MA粉末受到磨球与罐子内壁的撞击，晶粒尺寸不断细化，在40 h粉末晶粒尺寸减小至约16.1 nm趋于稳定。SPS烧结后晶粒尺寸无明显增大，各微量元素均匀分布在基体中。二元合金样品的维氏硬度随Cr含量增加而增大。10CrY合金样品经腐蚀液侵蚀后可粗略看到晶界呈均匀分布。ODS合金样品存在大量的纳米析出相，平均颗粒尺寸约30 nm。     

添加Gd元素对Mg-5Li-3Zn合金微观组织和力学性能的影响

在Mg-Li-Zn合金中添加了稀土元素Gd,对比研究了Mg-5Li-3Zn(LZ53,质量分数)和Mg-5Li-3Zn-2Gd(LZG532,质量分数)合金的微观组织和力学性能。研究发现,铸态LZ53合金由α-Mg基体和Mg-Li-Zn第二相组成。Gd元素的添加促使铸态LZG532合金中形成了W相。挤压过程中,两种合金中均发生不完全再结晶。LZ53合金的再结晶比例高于LZG532合金,但LZG532合金中再结晶晶粒尺寸更小。W相在挤压过程中被破碎成颗粒并沿挤压方向呈条带状分布。Gd元素的添加不能强化铸态LZG532合金,反而引起塑性降低。挤压变形显著提高了LZ53和LZG532合金的力学性能。挤压态LZG532合金的屈服强度和抗拉强度高于挤压态LZ53合金,强化来自于细晶强化、织构强化和W相颗粒的第二相强化。     

硅酸锆弥散强化日用陶瓷

以福建龙岩高岭土、安徽钾长石、江西星子石英为陶瓷主要原料,添加适量的硅酸锆为增强相,研究了硅酸锆引入量、烧成温度、保温时间等因素对日用陶瓷性能的影响,探究了硅酸锆颗粒弥散分布对日用陶瓷的强化机理。结果表明：当引入硅酸锆含量为6%(质量分数),烧成温度为1 300℃、保温时间为30 min时,强化效果最好,抗弯强度从基础配方的(58±6) MPa提升至(106±11) MPa,提升幅度为83%。硅酸锆颗粒弥散分布在基体内部,由于其与基体热膨胀系数的差异,冷却过程中在基体内部产生径向压应力与切向张应力,使裂纹在颗粒处钉扎,从而提高了陶瓷强度。     

稀土氧化物弥散强化铁基粉末材料中 La_2O_3、CeO_2、Pr_6O_(11)、Nd_2O_3和 Sm_2O_3的光谱分析

为扩大稀土元素应用范围,湿法冶金工作者探索通过粉末冶金途径,把稀土氧化物作为弥散强化相加入铁基粉末制品中,以期改善材料的强度、硬度和耐磨性能,从而取代某些稀缺合金元素。为此,本文通过方法试验,建立了交流电弧粉末光谱法直接测定稀土氧化物弥散强化铁基粉末材料中 La_2O_3、CeO_2、Pr_6O_(11)、Nd_2O_3、Sm_2O_3轻稀上元素分量。以△S     

弥散增强铂

在铂基体中,均匀分布有在高温下稳定的第二相颗粒,这些非常细小通常呈扁平状的颗粒可以阻止铂晶体间的滑移,从而使铂合金高温强度和抗蠕变性能显著提高,称为弥散增强铂。常用的分散物质有氧化锆、氧化钍、碳化钛等。弥散增强铂为玻纤工业发展多排多孔大     

钛酸铝基复合陶瓷的研究

提出了钛酸铝陶瓷研究中存在的问题．论述了颗粒弥散强化陶瓷基复合陶瓷的机理，叙述了第二相颗粒补强钛酸铝基复合陶瓷的国内外研究状况．认为钛酸铝基复合陶瓷是一种很有前途的抗热震冲击且耐高温的材料，并指出了今后的研究方向。     

贵金属被复镍阴极在碱水溶液中的特性

在镍基体上通过热分解相应的氧化物制备(i)Pt、(ii)Pt-Rh2O3(50)、(iii)Pt-RuO2(50)和（Ⅳ）Pt-IrO2（50）被复镍阴极，与不锈钢（SUS304）阴极相比，该阴极的氢过电压纸300mv。Pt与另一些Pt族金属氧化物（ii-Ⅳ）组合后的被复层氢过电压又降低20－40mv。这些结果认为是由于微小理解纹密度和大的表面积所致。在含6ppmFe^ 的30％NaOH溶液中快速劣化试验，氢过电压增加为：（i)140mv；(ii)110mv；(iii)50mv；（Ⅳ）50mv；Ni／等离子喷镀雷尼镍（50μm）／Pt－IrO2(50)0mv。在离子交换膜电槽中Ni／喷镀镍（50μm）／Pt电极稳定运行120天。     

AlN陶瓷中的晶界第二相

晶界第二相是ＡＩＮ陶瓷显微结构的重要组成部分，对ＡＩＮ陶瓷的热导率有重大的影响。本工作研究了以Ｙ＿２Ｏ＿３为烧结助剂的无压烧结ＡＩＮ陶瓷中，晶界第二相的组成、含量及其分布，结果表明：晶界第二相的组成主要取决于配料中的Ｙ＿２Ｏ＿３／Ａｌ＿２Ｏ＿３比值，同时也受工艺因素影响；随着Ｙ＿２Ｏ＿３加入量增多，晶界第二相含量呈线性增加，其分布也变成从三个晶粒连接处延伸到所有晶界。还讨论了晶界第二相对热导率的影响。认为只要ＡＩＮ晶格完整无缺，ＡＩＮ相保持连通，即使存在少量的Ｙ＿４Ａｌ＿２Ｏ＿９和／或Ｙ＿２Ｏ＿３第二相材料，预期仍可获得高的热导率。     

莫来石陶瓷中的位错及其对力学性能的影响

利用透射电镜对莫来石陶瓷中位错的组态进行观察，结果表明，莫来石陶瓷中的位错易被第二相钉扎，两列位错遇易发生反应，全位错易分解成偏位错，并扩展形成层错。这说明，即使是脆性材料，其位错在一定条件下仍然是可动的。本文认为，位错在常温和高温条件下莫来石陶瓷力学性能影响不同，并从位错的角度解释了莫来石陶瓷力学性能的特点，提出改进材料制备工艺的途径。     

(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。     

莫来石结合Al2O3-SiC浇注料的显微结构特征

借助SEM和EDAX研究了莫来石结合Al2O3 -SiC浇注料的显微结构特征。结果表明 :在莫来石结合Al2 O3 -SiC浇注料中 ,莫来石相与填充在其间隙的玻璃相形成连续基质 ;刚玉颗粒与基质中SiO2 反应生成的二次莫来石与基质中的原生莫来石交错存在 ,构成网状结构 ;SiC颗粒表面高温氧化生成的SiO2 膜 ,改善了SiC颗粒与基质的润湿性 ,是其与基质直接结合的媒介。     

Effect of compatibilizer on the dispersion of untreated silica in a polypropylene matrix

BACKGROUND: A new processing method for polypropylene–untreated precipitated silica (PP/SiO₂) composites based on the incorporation of a second polymer phase of polyamide 6 (PA6) is presented and compared with a more classic one making use of compatibilizers: glycerol monostearate (GMS), ethylene acrylic acid ionomer (IAAZE) and maleic anhydride grafted polypropylene (MA‐graft‐PP). The effects of processing methods and conditions on the microstructure and properties of PP/SiO₂ composites prepared by melt compounding are investigated with a view to reduce the size of aggregates of silica from the micrometre to the nanometre scale and to improve the link between filler and matrix. RESULTS: On the one hand, the presence of GMS and IAAZE compatibilizers significantly improves the dispersion of the silica particles. On the other hand, when using a PA6 second phase, the SiO₂ particles are dispersed in PA6 nodules. Within these nodules, SiO₂ appears dispersed at the nanoscale but with larger particles (‘aggregates’) of about 200 nm. Significant improvements in tensile strength and modulus are obtained using MA‐graft‐PP compatibilizer. An increase in impact strength is observed in the case of GMS compatibilizer. Thermal parameters indicate also that silica plays the role of nucleation agent for PP matrix. All improvements (tensile strength, modulus and impact strength) increase with the addition of compatibilized PA6 second phase. CONCLUSION: By the incorporation of masterbatch of silica in PA6 as a second polymer polar phase, a successful new production method for PP/SiO₂ nanocomposites has been developed. Interestingly, this method does not require any (expensive) pre‐treatment of the silica. Copyright © 2007 Society of Chemical Industry     

Stress distribution around Fe5Si3 and its effect on interface status and mechanical properties of Si3N4 ceramics

Si₃N₄ ceramics with different amount of Fe₅Si₃ were prepared by adding FeSi₂. Residual thermal stress distribution and elastic energy around Fe₅Si₃ particles in various depths were calculated. The interface status between second phase particles and matrix was analyzed in terms of stress and energy. High tangential compressive stresses and low radial tensile stresses were generated along the surface of the ceramics. Elastic strain energy caused by unit interface was high around big particles in deep area of the ceramics. Microcracks are observed around the big Fe₅Si₃ particles. Furthermore, accord to our calculation, microcracks are easily generated around particles in superficial layer of matrix when second phase particles have lower thermal expansion coefficient than the matrix, while microcracks tend to be generated in deep layer of matrix preferentially when the thermal expansion coefficient of second phase particles is higher than matrix. Residual stresses and microcracks around Fe₅Si₃ particles greatly influenced mechanical properties. Fracture toughness of Si₃N₄ ceramics with similar Si₃N₄ particle size distribution increased with the amount of Fe₅Si₃, and fine Fe₅Si₃ particles could enhance the strength of Si₃N₄ ceramics. Si₃N₄ ceramics exceeding 1.2 GPa strength were prepared.     

A new model for the influence of particle arrangement and interphase on the stiffness of particulate composites

In this work, the stiffness of a composite containing spherical particles surrounded by an inhomogeneous interphase embedded in an isotropic matrix is evaluated. The elastic constants of the interphase are modeled as continuous radial functions. It is assumed that this third phase developed between the polymeric matrix and the filler particles contains both areas of absorption interaction in polymer surface layers onto filler particles and areas of mechanical imperfections.It can be said that the concept of boundary interphase is a useful tool to describe quantitatively the adhesion quality between matrix and particles and that there is an effect of this phase on the thermomechanical properties of the composite. The thickness and volume fraction of this phase were determined from heat capacity measurements for various filler contents.On the other hand, it is assumed that the particle arrangement (distribution) and their interactions should affect the thermomechanical constants of the composite.The theoretical predictions were compared with experimental results as well as with other theoretical values derived from expressions given in the literature and in some cases, they were found to be in a reasonable agreement.     

Effect of core-shell particles dispersed morphology on the toughening behavior of PBT/PC blends

Methyl methacrylate-co-styrene-co-glycidyl methacrylate grafted polybutadiene (PB-g-MSG) and styrene-co-glycidyl methacrylate grafted polybutadiene (PB-g-SG) core-shell particles were prepared to toughen poly (butylene terephthalate) (PBT) and polycarbonate (PC) blends. The compatibilization reaction between the epoxy groups of glycidyl methacrylate and the carboxyl groups of PBT induced the PB-g-SG particles dispersed in the PBT phase. On the other hand, the good miscibility between PMMA (the shell phase of PB-g-MSG) and PC induced the PB-g-MSG particles dispersed in the PC phase. The different phase morphology led to different toughening behavior. The PBT/PC/PB-g-MSG blends with the PC encapsulated morphology showed much lower brittle-ductile transition core-shell particles content (10-15 wt% or 15-20 wt%) compared with the PBT/PC/PB-g-SG blends (20-25 wt%). The difference between the toughening efficiency of the core-shell particles was due to the change of deformation mechanisms. In PBT/PC/PB-g-MSG blends, the cavitation of PB rubber phase led to the occurrence of shear yielding of the matrix. While in the PBT/PC/PB-g-SG blends, the debonding between PBT and PC interface induced the shear yielding of the matrix. The variation of the core-shell particles dispersed phase morphology also affected the crystallization properties and DMA results of the PBT/PC blends. Modification of the phase morphology provided an useful strategy to prepare PBT/PC blends with higher toughening efficiency.     

Volta potential of second phase particles in extruded AZ80 magnesium alloy

Magnesium alloys show strong susceptibility to localized corrosion when immersed in aggressive solutions (e.g. chlorides). The existence of second phase particles in the microstructure might represent initiation sites for localized corrosion. This is due to the formation of galvanic couples between the particles and the matrix. Extruded AZ80 magnesium alloy has been investigated by means of scanning Kelvin probe force microscopy (SKPFM) in order to measure the Volta potential of different phases relative to the matrix. The phases present in the alloy have been identified by optical microscopy and scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDXS). Three different phases were observed: Al₈Mn₅, Mg₂Si and Mg₁₇Al₁₂ (β phase). All phases exhibited positive Volta potentials relative to the matrix indicating a cathodic behaviour. The Volta potential depends on the composition of second phase particles. The Al₈Mn₅ intermetallics showed the strongest cathodic behaviour. Based on the SKPFM results, it is expected that the cathodic phases are effective sites for the initiation of localized corrosion in extruded AZ80 magnesium alloy.     

Toughening of Glasses by Metallic Particles

The role of elastic, thermoelastic, and interfacial properties in the toughening of a brittle matrix by metallic second-phase particles was studied. Two composites were studied: glass+partly oxidized Ni particles (thermal expansion coefficient of the glasses lower than, equal to, and higher than that of Ni) and glass+partly oxidized Al particles (thermal expansion and elastic moduli equal). Weak interfacial bonding between the nickel and its oxide and developed stress concentrations are the major toughness limitations found in the glass/Ni composites. When the thermal expansion coefficient and elastic modulus of the second phase are sufficiently greater than that of the glass matrix, a propagating crack will bypass the particles. When the thermal and elastic stresses are minimized and satisfactory bonding is achieved (glass/Al composites), a 60x toughness increase was realized.     

Morphology evolution during cooling of quiescent immiscible polymer blends: matrix crystallization effect on the dispersed phase coalescence

The influence of the matrix crystallization on the coalescence of the dispersed phase particles, in quiescent immiscible polymer blends, is a topic that is scientifically addressed scarcely. The coarsening of the phase structure that is induced by the matrix crystallizing domains was studied using the well-established system comprising a polypropylene and an ethylene–propylene rubber (PP/EPR blends). This subject is of great importance as the effectiveness in the toughening of PP is directly determined by the EPR particle size. Cooling experiments were commenced for resolving the correlation among the imposed cooling conditions, the formed matrix crystalline morphology, and the coalescence of the dispersed phase particles. A confirmation of the profound effect of the PP crystallization on the coalescence of EPR particles was undoubtedly obtained. The contribution of the crystallization to the coalescence of the dispersed phase particles is largest at a finite rate of cooling. A thorough discussion regarding the observed effects, encompassing a potential rejection or an engulfing of the dispersed phase particles by the growing crystallites, was undertaken.