成形压力对SiC/TiB2复合材料组织与性能的影响

基于熔融Si浸渗法制备出较致密的SiC/TiB₂复合材料, 并研究了坯体成形压力对SiC/TiB₂复合材料致密度、相组成、显微组织和力学性能的影响。实验结果表明, 复合材料由TiB₂、SiC和Si相组成。SiC/TiB₂复合材料的显微组织特征为: TiB₂相和SiC相均匀分布, 游离Si填充在TiB₂相和SiC相的空隙处, 且形成了连续相。随成形压力的增大, 复合材料中游离Si含量降低, TiB₂颗粒尺寸减小, 复合材料的力学性能先增加后降低。坯体最佳成形压力为200 MPa, 对应SiC/TiB₂复合材料的体积密度、开口气孔率、抗弯强度、断裂韧性和维氏硬度分别为3.63 g/cm³、0.90%、(354±16) MPa、(6.8±0.2) MPa·m^1/2和(21.0±1.1) GPa。     

原位合成TiB2/Fe复合材料的高温氧化行为

采用微波烧结技术原位生成TiB₂/Fe复合材料,研究其在500℃、600℃与700℃空气中的恒温氧化行为,并对氧化膜的表面、截面形貌及相组成进行了分析。结果表明:TiB₂/Fe复合材料由TiB₂、Fe₂B和α-Fe三种物相组成。随着氧化温度的升高,TiB₂/Fe复合材料的氧化增重明显增大,均呈现抛物线型规律,在500℃时,其氧化产物主要为Fe₂O₃和Fe₃O₄,而700℃时,其氧化物为Fe₂O₃、TiO₂、Fe₉TiO₁₅及少量Fe₃BO₆组成。相同温度下,随着TiB₂含量增加,TiB₂/Fe复合材料氧化物粒径、氧化增重和氧化层厚度均减小,氧化激活能增大,其抗氧化性能也越好。      

等离子加热反应合成TiB2-TiC-Fe2Ti复合材料

以Ti、B₄C和Fe粉为原料,采用等离子束加热反应合成TiB₂-TiC-Fe₂Ti复合材料,分析了其物相、组织结构、显微硬度和断口形貌等。结果表明：反应生成物中物相主要有TiB₂、TiC和Fe₂Ti,同时含有少量的Fe₃C。各物相以不同的形态均匀分布,TiB₂呈现六边形和长条形,TiC近似球形,Fe₂Ti作为粘结相存在于TiB₂和TiC相之间,促进了各相之间的结合。等离子束加热具有高加热及冷却速率,降低了晶粒生长时间,有利于获得细小的组织。随着电流增加,单位时间内输入坯体热量增多,TiB₂和TiC充分长大,各相之间结合更加紧密。     

TiB2/Cu复合材料的电弧侵蚀行为

采用放电等离子烧结法（SPS）制备TiB₂质量分数为1wt%~5wt%的TiB₂/Cu复合材料,测试其导电率和硬度。当TiB₂质量分数由0增至5wt%时,复合材料的导电率由96.9%（International Annealed Copper Standard,IACS）降至65.1%（IACS）,布氏硬度由42.8增至65.2。对所制备的不同TiB₂质量分数的TiB₂/Cu复合材料在直流24 V、不同电流条件下进行电接触实验,探究TiB₂添加量和电流对TiB₂/Cu复合材料耐电弧侵蚀性能的影响。结果表明,TiB₂/Cu复合材料的平均燃弧时间、平均燃弧能量和材料损耗量随着电流的增加而增加,TiB₂/Cu复合材料的阴极损耗量高于阳极,整体上TiB₂/Cu复合材料由阴极向阳极转移。在24 V和25 A条件下,不同TiB₂质量分数的TiB₂/Cu复合材料的燃弧时间和燃弧能量随操作次数增加不断波动,整体上呈逐渐增加的趋势,3wt% TiB₂/Cu复合材料的稳定性最高,平均燃弧时间和燃弧能量最低。随着TiB₂质量分数的增加,TiB₂/Cu复合材料损耗量降低,表面蚀坑变浅。     

不同TiB2颗粒粒径的TiB2/Cu复合材料耐电弧侵蚀行为

采用放电等离子烧结法（SPS）制备了不同TiB₂颗粒粒径的3wt% TiB₂/Cu复合材料,研究了3wt% TiB₂/Cu复合材料致密度、导电率、硬度和耐电弧侵蚀性能随TiB₂颗粒粒径的变化规律,重点分析了不同TiB₂颗粒粒径的3wt% TiB₂/Cu复合材料耐电弧侵蚀行为。结果表明:3wt% TiB₂/Cu复合材料致密度和硬度随TiB₂颗粒粒径的增大而略有降低;TiB₂颗粒粒径越小,TiB₂/Cu复合材料的综合性能越好。随着TiB₂颗粒粒径的增大,3wt% TiB₂/Cu复合材料耐蚀稳定性降低,3wt% TiB₂/Cu阴极材料的损耗量明显增加;当TiB₂颗粒粒径为10 μm时,3wt% TiB₂/Cu复合材料的耐电弧侵蚀性能最佳。电弧蚀形貌观察表明:不同TiB₂颗粒粒径的3wt% TiB₂/Cu复合材料经电弧侵蚀后,3wt% TiB₂/Cu复合材料均由阴极向阳极发生转移;随着TiB₂颗粒粒径的增大,阴极质量损耗逐渐增加,触头表面电弧侵蚀面积增加;而在Cu基体中引入较小的TiB₂颗粒,有利于减弱电接触实验过程中TiB₂/Cu复合材料的喷溅现象。      

多粒径TiB2颗粒增强铜基复合材料的制备与载流摩擦磨损性能

采用粉末冶金工艺分别制备了单一粒径TiB₂颗粒和多粒径TiB₂颗粒增强铜基复合材料,对比研究了非载流和载流条件下多粒径（2 μm+50 μm）TiB₂/Cu复合材料的摩擦磨损行为。微观组织观察表明:不同粒径的TiB₂颗粒在Cu基体中分布均匀。与单一粒径TiB₂/Cu复合材料相比,多粒径TiB₂/Cu复合材料具有更高的相对密度、硬度和导电率。摩擦磨损实验结果表明:多粒径TiB₂/Cu复合材料抗摩擦磨损性能明显高于单一粒径TiB₂/Cu复合材料,当2 μm与50 μmTiB₂颗粒配比为1:2时,多粒径TiB₂/Cu复合材料的抗摩擦磨损性能最佳。相对于2 μm单一粒径TiB₂/Cu复合材料,电流为0 A时,（2 μm+50 μm）TiB₂/Cu复合材料的摩擦系数和磨损率分别降低了17.3%和62.5%;电流为25 A时,（2 μm+50 μm）TiB₂/Cu复合材料的摩擦系数和磨损率分别降低了6%和45.8%,同时载流效率和载流稳定性得到明显提高,磨损表面更加平整。磨损机制分析表明:多粒径TiB₂颗粒合理配比有利于提高复合材料载流质量,同时摩擦过程中大粒径的TiB₂颗粒起到支撑作用,小粒径的TiB₂颗粒弥散强化Cu基体,二者的协同作用使TiB₂/Cu复合材料具有更好的抗载流摩擦磨损性能。      

激光选区熔化成形原位自生TiB2/Al-Si复合材料的微观组织和力学性能

利用激光选区熔化（SLM）技术制备了原位自生TiB₂纳米陶瓷颗粒增强Al-Si基复合材料,并对成形后的TiB₂/Al-Si复合材料进行不同的热处理。通过XRD物相分析、SEM微观组织观察、电子背散射衍射（EBSD）、EDS元素扫描分析和力学拉伸试验等对TiB₂/Al-Si复合材料的微观组织进行观察和力学性能测试。研究表明,在原位自生TiB₂纳米陶瓷颗粒和SLM快速凝固特性的共同作用下,SLM成形的原位自生TiB₂/Al-Si复合材料具有超细晶结构,平均晶粒尺寸为1.1 μm;TiB₂/Al-Si复合材料的力学性能优异,屈服强度为262 MPa,抗拉强度为435 MPa,延伸率为11.88%。对比经不同热处理的TiB₂/Al-Si复合材料,直接时效处理（150℃/12 h）的TiB₂/Al-Si复合材料性能最优,抗拉强度达到488 MPa,提高了53 MPa,延伸率降低至7.2%。     

放电等离子烧结Ni/TiB2-TiC复合材料微观组织及磨损性能

采用放电等离子烧结技术,以Ni、Ti、B₄C混合粉末为原料制备Ni/TiB₂-TiC复合材料,分析了Ni含量对复合材料的物相组成、组织结构、硬度和耐磨性的影响。结果表明：Ni/TiB₂-TiC复合材料主要物相为γ-Ni、TiB₂和TiC,其中TiB₂呈矩形条状和多边形状,TiC则呈现不规则块状;随着原始粉末中Ni含量的增加,TiB₂和TiC陶瓷相尺寸减小,其在Ni粘结相中的分布呈现出均匀化的趋势,复合材料更加致密。Ni含量显著影响Ni/TiB₂-TiC复合材料的耐磨性和磨损机制,Ni含量较低时（20wt%和30wt%）,复合材料摩擦系数（COF）较大且存在明显的波动,出现严重的疲劳磨损;随着Ni量的增加（40wt%）,材料的COF降低且趋于平稳,表现为微切削磨损;当Ni含量持续增加时（50wt%）,由于局部Ni的聚集导致粘着磨损产生,COF有所上升,耐磨性反而下降。     

多粒径TiB2/Cu复合材料耐电弧侵蚀行为

采用粉末冶金工艺制备了不同配比的多粒径(2 μm+10 μm+50 μm) TiB₂/Cu复合材料。通过JF04C触点材料测试系统对多粒径TiB₂/Cu复合材料进行耐电弧侵蚀性能试验,研究(2 μm+10 μm+50 μm) TiB₂颗粒质量比分别为1∶1∶1、1∶1∶3、1∶3∶1、3∶1∶1时,TiB₂/Cu复合材料的耐电弧侵蚀性能及电弧侵蚀形貌变化规律,探究多粒径配比对TiB₂/Cu复合材料表层耐电弧侵蚀行为的影响。结果表明:当(2 μm+10 μm+50 μm) TiB₂颗粒质量比为1∶1∶1时,TiB₂/Cu复合材料相对密度和导电率最高,分别为99.1%和87.1%IACS。当(2 μm+10 μm+50 μm) TiB₂颗粒质量比为1∶1∶1和1∶3∶1时,TiB₂/Cu复合材料的组织均匀性较好,电弧侵蚀后材料损失相同,材料转移量最少。其中,质量比为1∶3∶1时,TiB₂/Cu复合材料平均燃弧能量最低,且燃弧时间和燃弧能量最稳定。研究表明,这与复合材料的综合物理性能密切相关。在颗粒增强Cu基复合材料设计过程中,引入合适配比的多粒径TiB₂颗粒有助于提高TiB₂/Cu复合材料的密度、导电率等综合物理性能。电弧侵蚀过程中,不同粒径的TiB₂颗粒相互协同作用,有助于提高TiB₂/Cu复合材料的耐电弧侵蚀性能和服役稳定性。      

挤压铸造TiB2P/Al复合材料室温力学性能

采用挤压铸造法制备不同体积分数的TiB_2P/Al复合材料, 利用扫描电镜、 硬度计、 拉伸试验机等对复合材料的室温力学性能进行了研究, 系统地分析了体积分数和热处理工艺对材料力学性能的影响。结果表明: 挤压铸造TiB_2P/Al复合材料的布氏硬度、 抗弯强度和弹性模量随增强相TiB₂体积分数的增加而提高。45% TiB_2P/Al复合材料T6处理后硬度和抗弯强度分别比退火态时提高了23%和40%, 但热处理状态对弹性模量的影响不大。      

TiAl-B合金凝固过程中初生TiB2的固-液界面形态演变特征

用原位自生法制备了TiAl-B合金，并用XRD、SEM对材料的相组成、微观组织和初生TiB2晶体的界面结构特征进行了研究。结果表明：该合金主要由TiAl和TiB2两相组成；初生TiB2呈六面棱柱状，在其（0001）面存在清晰的生长台阶，凸台状或柱棒状分枝，它们的各晶面取向与母体的取向一致。分析表明，在TiAl-B合金凝固过程中初生TiB2晶体的固-液界面是不稳定的，使固-液界面由一完整光滑的界面逐渐演变为由多个相互独立的次级界面构成的复杂界面，次级界面亦为小面结构，具有相同的晶面取向关系。     

Ti-Al-B合金空心管状初生TiB的生长机制

采用原位自生法制备了Ti-17Al-1.5B复合材料,并用XRD、SEM对复合材料的相组成和微观组织进行了研究。结果表明:该合金由Ti₃Al和TiB两相组成。初生TiB多呈较粗长的空心管状,共晶TiB呈短纤维状。根据晶体生长的固-液界面稳定性理论分析认为:TiB的B27晶体结构和晶体生长过程中的棱边效应导致初生TiB容易生长成空心管状。这是因为,在初生TiB晶体的[010]方向的固-液界面生长至一临界尺寸以后,晶面中心处因扩散受阻(热扩散和溶质扩散)而存在非常大的扩散过冷使晶面中心的台阶停止生长,这时TiB优先在棱边处长大;另外,TiB [010]方向生长速度非常快。二者的共同作用使初生TiB易于长成与 方向一致的空心管状。而共晶TiB则由于径向尺寸很小(呈纤维状),不易于长成空心管状。      

TiO2和O-Al2O3晶体的生长习性

通过水热法制备粉体的实验观察到金红石、锐钛矿和α-Al2O3晶体的生长习性．采用配位多面体生长习性法则合理地解释了Ti O2和α-Al2O3的生长习性．其主要结果为α-Al2O3晶体的生长习性为平板{0001}，其各晶面的生长速度为：V｛0001 }＜V｛1123}；锐钛矿的生长习性为四面体，其各晶面的生长速度为V<010>=V<001>>V<010>>V<111>．而PBC理论很难合理地解释α-Al2 O3晶体的生长习性．     

TiB2超硬薄膜的合成及性能

采用离子束溅射方法制备了ＴｉＢ２硬质薄膜，ＡＦＭ观察表明薄膜表面非常光谱，ＡＥＳ、ＸＲＤ和ＸＰＳ分析证明薄膜中主要是Ｂ、Ｔｉ比为１．８，六方结构的ＴｉＢ２多晶体、且呈现强烈的（１０１）择优取向，由超显微压痕测量系统测得的加载、卸载曲线计算得到的薄膜的显微硬度比高达４８ＧＰａ     

硼含量对Ti-50Al-xB合金中TiB2微观形貌的影响

用XRD,SEM对原位自生法制备的Ti-50Al-xB（at%）合金的相组成和微观组织进行了研究。结果表明：该合金主要由TiAl和TiB2两相组成;TiB2主要以片状,极片状,细棒状和声状形式存在,TiB2微观形貌随着合金中B含量的变化而发生显著变化,当B含量由0.4at%增加至1.4at%时,TiB2的微观形貌由片状依次演变为板片状、细棒状直至块状,而基体形貌没有明显变化。根据TiB2晶体形核与生长条件对TiB形貌演变过程进行了分析。     

Morphology, Growth Process and Symmetry of {0001} Face on Yb：YAl3（BO3）4 Crystal

The {0001} face develops on the habit of self-frequency doubling laser crystal Yb: YAl3(BO3)4 (YbYAB) only under high growth rate condition, and its morphology is rough. To study the growth mechanism of {0001} face, we have observed the growth morphology on {0001} polishing section by atomic force microscopy (AFM). A series of AFM images captured in different growth durations on the {0001} polishing section reflect the crystal growth process. It is shown that the growth morphology on the {0001} polishing section was rough with many hillocks at the first growth stage, and it can become smooth finally, although the growth morphology on the {0001} face develoFed naturally on YbYAB crystal habit is always rough. On the smooth {0001} surface formed at the last growth stage, there aresome triangular pits. This fact is different from that of hillocks in most crystal growth morphologies. AFM can easilydistinguish the pits or hillocks on the surface, but differential interfere contrast microscopy (DIC) can not do. Theorientation of the triangular pits is just the opposite to the triangular {0001} faces. The chemical etching patternis also composed of this kind of triangular pits. These growth morphology and etching pattern of the {0001} facesshow 3m symmetry, but the point group of YbYAB crystal is 32. The symmetric contradiction between morphologyand point group does not exist for quartz, although whichsurface morphology we can distinguish the right form ormorphology we can not do. The reason for the symmetricand its point group is not known yet.has the same point group as YbYAB. From quartz {0001}left form of the crystal, but from YbYAB {0001} surfacecontradiction between YbYAB {0001} surface morphology and its point group is not known yet.     

Ti_2AlC-TiB_2对TiAl基复合材料组织及力学性能的影响

以Ti、Al和B4C为原料,采用真空电弧熔炼的方法制备了含Ti_2AlC-TiB_2增强相的TiAl基复合材料;分析了添加不同含量的Ti_2AlC-TiB_2对复合材料的物相组成、组织结构及力学性能的影响,并探讨了微观组织结构的形成机制。结果表明:Ti_2AlC-TiB_2/TiAl复合材料主要由TiAl、Ti3Al、TiB_2和Ti_2AlC等物相组成,TiB_2和Ti_2AlC分布在层片状的TiAl+Ti3Al基体中;随着原料中B4C含量的增多,复合材料组织中Ti_2AlC-TiB_2含量增多,且TiAl基体的晶粒被明显细化,TiB_2和Ti_2AlC分布于基体晶界或晶内。Ti_2AlC主要为层片状和板条状,尺寸5~15μm,而TiB_2颗粒形态与其含量有关,当Ti_2AlC-TiB_2含量小于20wt%时,TiB_2颗粒呈针棒状,尺寸为0.5~5μm,当Ti_2AlC-TiB_2含量增加到30wt%时,TiB_2颗粒主要呈块状,尺寸为5~20μm。Ti_2AlC由TiC与Ti-Al熔体发生包晶反应生成,Ti_2AlC和TiB_2的形成提高了Ti_2AlC-TiB_2/TiAl复合材料的硬度、塑性和抗压强度。当4Ti+Al+B4C的加入量为10wt%时,复合材料的变形量比纯TiAl提高14%,而抗压强度达到最高值1 591 MPa。Ti_2AlC和TiB_2通过裂纹偏转、颗粒钉扎、拔出等机制对Ti_2AlC-TiB_2/TiAl复合材料起到增强增塑的作用。     

Morphology of C60 Crystals Grown from the Vapor Phase

Abstract

The morphology of C₆₀ crystals grown from the vapor phase have been studied. In all observations, only hexagonal and rectangular shaped crystal faces were found. Very different morphology, highly faceted {111} faces and flat {100} faces were observed using scanning electron microscopy (SEM) and atomic force microscopy (AFM). the highly regular shape and similar distance between all neighboring macrosteps observed for the {111} faces can be explained by taking into account that edges of two adjacent {111} and {100} planes can act as step sources.     

Three-dimensional microstructural characterization of discontinuously reinforced Ti64–TiB composites produced via blended elemental powder metallurgy

Three-dimensional (3D) microstructures of TiB reinforcement in two discontinuously reinforced Ti–6Al–4V (Ti64) alloy composites produced via blended elemental (BE) powder metallurgy are reconstructed from large-area high-resolution optical montage serial sections. The TiB phase in both composites shows whisker morphology with roughly hexagonal cross-sections, a unimodal size distribution, and uniform random morphological orientations. The TiB whiskers in these composites are significantly coarser compared to similar materials produced via pre-alloyed powder metallurgy but did not contain coarse primary TiB particles.     

KDP crystal doped with L-arginine amino acid: growth,structure perfection,optical and strength characteristics

Potassium Dihydrogen Phosphate (KDP) crystal doped with L-arginine (L-arg) amino acid with 1.4 wt% concentration in the solution was grown onto a point seed by the method of temperature reduction. For the first time an attempt was made to grow large-size (7 × 6 × 8 cm³) optically transparent crystals, which allowed to analyze the effect of L-arg additive on the physical properties of the different growth sectors ({100} and {101}) of KDP. The incorporation of L-arg into both growth sectors of the crystal was confirmed by the methods of optical and IR spectroscopy and found to be caused by the ability of the amino acid to form hydrogen bonds with the face {100} and electrostatically interact with the positively charged face {101} of KDP crystal. A slight variation in the unit cell parameters was reported, the elementary cell volume of KDP:L-arg crystal increased in comparison with the one of pure KDP by 2·10⁻² and 2.07·10⁻² Å³ in the sectors {100} and {101}, respectively. It was found that the doping of L-arg enhanced the SHG efficiency of KDP and depended on the crystal growth sectors. The SHG efficiency of KDP:L-arg was by a factor 2.53 and 3.95 higher in comparison with those of pure KDP for {101} and {100} growth sector, respectively. The doping was found to lead to softening of both faces by ∼3–10% and ∼14–17% in the sectors {101} and {100}, respectively. Investigation of the influence of L-arg molecules on the bulk laser damage threshold of the crystals showed that the bulk laser damage threshold of the samples of KDP:L-arg crystal was higher than the one of the pure crystal in the sector {101} and lower in the sector {100}. The correlation between microhardness and laser damage threshold were discussed. The study is helpful for further searching, designing and simulation of hybrid NLO materials.