Microstructural evolution during self-propagating high-temperature synthesis of Ti-Al system

In order to investigate the microstructural evolution during self-propagating high-temperature synthesis （SHS） of Ti-Al powder mixture with an atomic ratio of Ti： Al=1：1, a combustion front quenching method （CFQM） was used for extinguishing the propagating combustion wave, and the microstructures on the quenched sample were observed with scanning electron microscope （SEM） and analyzed with energy dispersive spectrometry （EDS）. In addition, the combustion temperature of the reaction was measured, and the phase constituent of the synthesized product was inspected by X-ray diffraction （XRD）. The results showed that the combustion reaction started from melting of the Al particles, and the melting resulted in dissolving of the Ti particles and forming of Al3Ti grains. As the Al liquid was depleted, the combustion reaction proceeded through solid-state diffusion between the solid Al3Ti and the solid Ti. This led to the forming of TiAl and Ti3Al diffusing layers. In addition, the combustion reaction is incomplete besides TiAl, there are a large amount of Ti3Al and TiAl3 and a small amount of Ti in the final product. This incompleteness chiefly results from the using of coarser Ti powder.     

外加Al2O3颗粒对Ti-Al-TiO2系合成产物微观结构的影响

Ti-Al-TiO2体系外加不同含量的Al2O3颗粒获得了Al2O3／TiAl基复合材料,研究了产物的相组成及微观组织。结果表明：Al2O3颗粒多分布在基体晶界处。随外加Al2O3含量的增大,晶粒变小,但增强相颗粒团聚严重。外加Al2O3量存在一个临界值。含量过高,易造成结构疏松,不致密,形成大的气孔,且由于TiO2的活化作用,会造成外加的Al2O3颗粒烧结呈板状联结分布;含量较低,颗粒与界面的结合不够紧凑,但颗粒的结晶度较好。     

掺杂对Al_2O_3/TiAl复合材料性能的影响

本研究采用Ti-Al-TiO2-La2O3体系,通过热压烧结工艺原位合成了Al2O3/TiAl复合材料.借助X射线衍射(XRD)、扫描电镜(SEM)等分析研究了材料的物相组成和微观组织结构,同时分别将掺杂La2O3和掺杂Fe2O3对合成Al2O3/TiAl复合材料微观结构和力学性能的影响进行了对比.结果表明:掺杂La2O3合成的Al2O3/TiAl复合材料基体尺寸相对掺杂Fe2O3合成产物较小,分散更加均匀,致密度更高.当La2O3掺杂量为3.93wt%时,Al2O3/TiAl复合材料的抗弯强度和断裂韧性达到最大值,分别为701.95MPa和7.79MPa·m1/2.由于稀土氧化物具有对基体和增强颗粒的净化,细化晶粒等作用,因此提高了TiAl基体与Al2O3增强颗粒结合强度,所以掺杂La2O3合成材料的力学性能相比掺杂Fe2O3合成的产物较高.     

Ti-C-Al-Fe_2O_3反应体系的热力学及形成产物的分析

针对Ti-C-Al-Fe2O3体系进行了热力学计算,并结合DSC及XRD分析,为研究该体系反应合成TiC,Al2O3提供了理论依据.计算结果表明：该体系在发生SHS反应时,可以生成TiC,Al2O3,Fe2Ti,TiAl3,Fe3C和Al4C3等产物,但TiC,Al2O3的热力学稳定性要远远大于Fe2Ti,TiAl3,Fe3C和Al4C3等相,因此,在1600℃的钢液引燃的SHS反应过程中,只能生成TiC,Al2O3两种产物.通过XRD分析也证明了在反应产物中只有TiC,Al2O3两种物质形成.     

Instability of TiC and TiAl3 compounds in Al-10Mg and Al-5Cu alloys by addition of Al-Ti-C master alloy

The performance of Al-Ti-C master alloy in refining Al-10Mg and Al-5Cu alloys was studied by using electron probe micro-analyzer （EPMA） and X-ray diffractometer （XRD） analysis. The results indicate that there are obvious fading phenomena in both Al-10Mg and Al-5Cu alloys with the addition of Al-5Ti-0.4C refiner which contains TiC and TiAl3 compounds. Mg element has no influence on the stability of TiC and TiAl3, while TiC particles in Al-10Mg alloy react with Al to form Al4C3 particles, resulting in the refinement fading. However, TiC particles are relatively stable in Al-5Cu alloy, while TiAl3 phase reacts with Al2Cu to produce a new phase Ti（Al, Cu）2, which is responsible for the refinement fading in Al-5Cu alloy. These indicate that the refinement fading will not occur only when both the TiC particles and TiAl3 compound of Al-Ti-C refiner are stable in Al alloys.     

Fabrication of in situ Ti2AlN/TiAl composites by reaction hot pressing and their properties

Ti2AIN/TiAI composites with different volume fractions of reinforcement were successfully fabricated by hot-pressing sintering method （reaction hot pressing） using Ti, Al and TiN powders as starting materials. The synthesis process includes four stages： first, the reactions between Al and Ti powers and between Al and TiN powders respectively occur and result in TiAl3 phase; secondly, AI powders in the sample are exhausted; the remaining Ti cores react with TiAl3 layer to form Ti-Al intermetallics; moreover, a few Ti2AlN particles precipitate from the TiAl3 phase; thirdly, Ti-Al intermetallics react with the remaining Ti cores to form Ti3Al and TiAl phases. TiAl phase and original TiN powers are in direct contact each other; finally, the residual TiN powers react with TiAl phase and result in a plenty of TizAIN phase. Compared with TiAl matrix, the hardness, elastic modulus and high-temperature compressive strength of Ti2AlN/TiAl composite are improved obviously and they are all enhanced with increasing the volume fraction of Ti2AlN phase.     

Oxidation behavior of in-situ Al2O3/TiAl composites at 900℃ in static air

In-situ Al2O3/TiAl composites were successfully synthesized from the starting powders of Ti, Al, TiO2 and Nb2O5. The oxidation behavior of the composites at 900℃ in static air was investigated. The results indicate that the composite samples present a much lower oxidation mass gain. Under long-time intensive oxidation exposure, the formed oxide scale is multi-layer. The formation of the outer TiO2 layer is fine and dense, the internal Al2O3 scale has good adhesiveness with the outer TiO2 scale, and the TiO2+Al2O3 mixed layer forming the protective oxide scale is favorable for the improvement of oxidation resistance. It is believed that the incorporation of Al2O3 particulates into the metal matrix decreases the coefficient of thermal expansion of the substrate, and forms a local three-dimensional network structure that can hold the oxide scale. The formation of the oxide scale with fmer particle size, stronger adherence, less micro-defects and slower growth rate can contribute to the improvement of oxidation resistance. Nb element plays an important role in reducing the internal oxidation action of the materials, restraining the growth of TiO2 crystals andpromoting thc stable formation of the Al 2O3-riched layer,which is benfeicial to improve the oxidation properties.     

Self-Propagating High-Temperature Reductive Synthesis of TiB_2-Al_2O_3 Composite Powders

TiB2-Al2O3 composite powders were produced by self-propagating high-temperature synthesis(SHS) method with reductive process from B2O3-TiO2-Al system. X-ray diffraction(XRD) and scanning electron microscopy(SEM) analyses show the presence of TiB2 and Al2O3 only in the composite powders produced by SHS. The powders are uniform and free-agglomerate. Transmission electron microscopy (TEM) and high resolution electron microscopy (HREM) observation of microstructure of the composite powders indicate that the interfaces of the TiB2-Al2O3 bond well, without any interfacial reaction products. It is proposed that the good interfacial bonding of the composite powders can be resulted from the TiB2 particles crystallizing and growing on the Al2O3 particles surface with surface defects acting as nucleation centers.     

Al2O3-NbAl／TiAl基高温复合材料的研究

以Ti-Al-TiO2-Nb2O5为反应体系,利用热压烧结工艺原位合成了Al2O5／TiAl复合材料．通过Mo元素掺杂对体系进行增强,借助X射线衍射（XRD）、扫描电镜（SEM）等分析研究了掺入不同含量Mo时,Ti-Al-TiO2-Nb2O5体系的热压反应过程及其对体系微观组织结构、力学性能等的影响．结果表明：放热反应加速了系统的反应,从而降低了该体系的反应温度;产物体积密度随着Mo掺杂量的增大而增大;抗弯强度和断裂韧性呈峰值变化．     

Reaction dynamics in the combustion synthesis system of Al-CrO3-Al2O3-NaF-N2-O2

A new material with heat-resistant and adiabatic characteristics and high strength was prepared using the combustion synthesis method by mixed powders of CrO3, Al, Al2O3, and NaF in atmospheric gas. The reaction dynamic process of the Al-CrO3-NaF-Al2O3-N2-O2 new material system by the combustion synthesis method was discussed based on the observation results by SEM, EDS, and XRD in combination with the combustion front quenching method （CFQM） and the relation curves between reaction free enthalpies and the corresponding temperatures. The combustion synthesis mechanism and the formation reasons of the phase in the combustion product were analyzed.     

添加剂对稻草灰熔融特性影响的实验研究

为了给生物质热化学转化中灰结渣和聚团问题的解决提供参考和依据,在小型实验装置上对稻草、稻草与添加剂混合物进行了燃烧试验.通过热力平衡计算软件选出合适的添加剂,添加剂包括Al粉、Si粉、Al2O3、SiO2、Ca3(PO4)2、CaSiO3、CaCO3、Al2(SO4)318H2O、CaSO4、CaO、(NH4)H2PO4等,通过对样品燃烧生成的底灰进行观测分析,选择较理想的添加剂(NH4)H2PO4,Al2(SO4)318H2O,CaSO4,CaO,CaCO3.理想添加剂样品底灰的XRD测试结果表明,(NH4)H2PO4可将稻草中钾转化为高熔点的K2CaP2O7;CaSO4和Al2(SO4)318H2O则可将碱金属钾以K2SO4形式固定在底灰中;CaO,CaCO3不直接与碱金属反应,但可与系统中的其它元素进行反应,促进稻草中熔融态钾的转化析出.实验结果表明,添加剂是解决由碱金属引起的秸秆灰熔融问题的有效途径之一.     

Al_2O_3-TiC复合材料放电等离子烧结(SPS)致密化研究

用燃烧合成及放电等离子烧结法制备出致密Al_2O_3-TiC复合材料;分析了烧结温度与材料致密度、显微结构及力学性能的关系;真空气氛、1650℃、保温5min烧结试样的相对密度达99.8％,断裂韧性为4.61 MPa·m~(1/2);更高温度下烧结,气相反应加剧,不利于致密度进一步提高,力学性能也有所下降。沿晶断裂是其主要断裂方式。     

Fabrication and mechanical properties of Al<Subscript>2</Subscript>O<Subscript>3</Subscript>/TiAl composites

Al₂O₃/TiAl composites were successfully fabricated by hot-press-assisted exothermic dispersion method with elemental powder mixtures of Ti, Al TiO₂ and Nb₂O₅, and the microstructure and mechanical properties were investigated. The results indicate the fine Al₂O₃ particles tend to disperse on the grain boundaries. The grain size of TiAl matrix decreases and the hardness increases with increasing Nb₂O₅ content. The bending strength and fracture toughness reach to a maximum when Nb₂O₅ content is 6 wt%, under 642 MPa and 6.69 MPa·m^1/2, respectively. Based on the fractography and the observation of crack propagation path, it is concluded that the strengthening and toughening of such composites at room temperature can be attributed to the refinement of the TiAl matrix, the deflection behavior in the crack propagation and the dispersion of Al₂O₃ particles.     

纳米Ni_3Al/Al_2O_3复合陶瓷的制备及性能

利用氢电弧等离子体法制备了纳米Ni3Al金属间化合物,并以此为弥散相,以氧化铝为基体,采用热压烧结工艺在1 450℃下制得纳米Ni3Al/Al2O3复合陶瓷,并研究其力学性能和微观结构。结果表明:加入纳米Ni3Al的复合陶瓷断裂韧性比纯氧化铝陶瓷有了明显提高,当加入质量分数5%纳米Ni3Al时,断裂韧性最高达12.1 MPa.m1/2。利用扫描电子显微镜观察试样的断口形貌,分析陶瓷的微观结构发现:随着纳米Ni3Al含量的增加,片状晶数量逐渐降低,说明纳米Ni3Al质量分数的加入抑制了片晶的生长。     

铈对铝铜合金—Al_2O_3颗粒复合材料界面的影响

本文探讨了铈对铝铜合金—Al_2O_3颗粒复合材料界面的影响。结果表明,适量铈可以改善铝铜合金与Al_2O_3间的润湿性能,提高界面结合强度。但未发现界面反应相,界面仍属于直接结合类型。凝固过程中,颗粒与凝固相界面相互作用的结果,导致颗粒大多分布于胞晶或树枝晶间,未发现铈对Al_2O_3颗粒的这种分布状态产生显著影响     

Adsorption behavior of heavy metal ions by carbon nanotubes grown on microsized Al2O3 particles

Carbon nanotubes （CNTs） were grown on the surface of microsized Al2O3 particles in CH4 atmosphere at 700℃ under the catalysis of Fe-Ni nanoparticles. The CNTs on Al2O3 were used for adsorbing Pb^2＋, Cu^2＋, and Cd^2＋ from the solution and the results were compared with active carbon powders, commercial carbon nanotubes, and Al2O3 particles. The as-grown CNTs/Al2O3 have demonstrated extraordinary absorption capacity with further treatment or oxidation, as well as hydrophilic ability that other CNTs lacked. The adsorption capacity of CNTs on Al2O3 is superior to other adsorbents and the preference order of adsorption on composite Al2O3 is pb^2＋〉Cu^2＋〉Cd^2＋. It seemed that the adsorption of those Pb^2＋, Cu^2＋, and Cd^2＋ did not change the surface properties of composite particles. The adsorption behaviors of Pb^2＋, Cu^2＋, and Cd^2＋ by CNTs on Al2O3 match well with the Langmuir isothermal adsorption model and the second order kinetic model. The calculated saturation amount adsorbed by 1 g of CNTs on Al2O3 are 67.11, 26.59, and 8.89 mg/g for Pb^2＋, Cu^2＋, and Cd^2＋ in single adsorption test, respectively.     

Research on Surface Modification of 96 Al2O3 by Ni Ion Implantation

A matrix of 96 Al2O3 ceramics was implanted with Ni ion of different dosages and energies using a MEVVA implanter. Then metallic structures of copper were made on the implanted ceramics, by using selective electroless copper plating. In addition, the characteristics and microstructure of the implanted layer were studied by using the SEM, RBS and XPS. The results show that： 1） the implanted Ni exits as Ni^2, Ni^2＋, and Ni^3＋ in the surface of Al2O3 and metal Ni particles precipitate on ceramics during implantation; 2） the concentration of Ni submits to the Gauss distribution along the direction of implantation on the surface of Al2O3 and high Ni concentration on the surface can be obtained if the Ni is implanted with low energy and a high dosage and 3） Ni ion implantation can activate the surface of Al2O3 and induce electroless copper plating on the ceramics.     

铜基氧化铝弥散材料中氧化铝颗粒的控制试验

针对铜基氧化铝弥散材料的氧化铝粒度控制这个难题．通过硝酸铝的分解，对原位生成时氧化铝在不同生成条件下的粒度变化进行研究，发现颗粒综合情况较好的生成方法．     

低温燃烧法制备YAG透明陶瓷纳米粉体

透明YAG陶瓷具有较好的化学稳定性、光学性能和高温性能,是单晶激光材料的有力替代品,纳米YAG粉体的合成有利于制备性能优异的YAG透明陶瓷．采用低温燃烧法,以Y2O3、Al（NO3）3·9H2O、柠檬酸、乙二醇为原料,采用TG／DSC,XRD和SEM等测试手段对YAG前驱体进行表征,对YAG前驱体在不同温度下进行煅烧．结果发现,在900℃左右已完全转变成YAG相,最终获得单分散、无团聚、形状规则的YAG纳米粉体．     

颗粒增强纯铝基复合材料的磨损特性

研究了Ａｌ２Ｏ３及ＳｉＣ颗粒增强纯铝基复合材料的磨损特性，结果表明，Ａｌ２Ｏ３或ＳｉＣ颗粒的加入，提高了复合材料的耐磨粒磨损性能，随着颗粒含量的增加，复合材料的耐磨性增大；ＳｉＣ与Ａｌ２Ｏ３复合材料的耐磨性相近；复合材料孔隙率较大时耐磨性降低；复合材料的耐磨性不随硬度升高而增加；颗粒增强纯铝基复合材料干摩擦的磨损机理以磨粒磨损为主；润滑摩擦的磨损机理为氧化磨损．