In Situ Al_2O_3-TiB_2/Al-Cu Composite Fabricated by Reaction Pressing of TiO_2-Al-B-CuO System

The in situ formed Al2O3 and TiB2 particulates reinforced Al-3.3 wt pct Cu alloy composite hasbeen successfully fabricated by reaction pressing of TiO2, Al, B and CuO powders. The in situformed Al2O3 and TiB2 particulates with a size from 10 nm to 2 μm are unifOrmly distributedin the matrix. The composite has a tensiIe Strength of 482 MPa and an elastic modulus of103.3 GPa.     

共沉淀法制备Al_2O_3-YAG复相陶瓷及其显微结构研究

用共沉淀法制备了Ａｌ２Ｏ３－ＹＡＧ复合粉体,ＹＡＧ的结晶温度在１０００℃左右．共沉淀法 制备的Ａｌ２Ｏ３－ＹＡＧ复合粉体经１５５０℃热压烧结,获得致密烧结体,ＹＡＧ的加入量对烧结温度 的影响不大． Ａｌ２Ｏ３－５ｖｏｌ％ＹＡＧ复合材料的抗弯强度为６０４ＭＰａ,断裂韧性为５．０ＭＰａｍ１／２; Ａｌ２Ｏ３－２５ｖｏｌ％ＹＡＧ复合材料的抗弯强度为６１１ＭＰａ,断裂韧性为４５ＭＰａｍ１／２．所有这些数据 都高于单相Ａｌ２Ｏ３陶瓷的力学性能,说明ＹＡＧ的加入有利于Ａ１２Ｏ３陶瓷力学性能的提高． 通过显微结构观察发现：大的ＹＡＧ颗粒位于Ａｌ２Ｏ３晶界上,小的ＹＡＧ颗粒位于Ａｌ２Ｏ３晶粒 内．在 Ａｌ２Ｏ３－５ｖｏｌ％ＹＡＧ复合材料中,许多小的白色区域存在于 Ａｌ２Ｏ３晶粒内,这可能和较低 的Ｙ２Ｏ３含量有关．     

氧化铝-氧化钛纳米粉末的形貌、微结构和晶型转变

用溶胶-凝胶法合成了含氧化钛质量分数为10wt.%、30wt.%和50wt.%的氧化铝-氧化钛纳米复合粉末和单纯氧化铝纳米粉末,用溶胶-凝胶法合成的氢氧化物前驱体在700-1200℃锻烧2h转变为相应的氧化物,用XRD和TEM对氧化铝-氧化钛纳米复合粉末的形貌、微结构和晶相进行表征,结果表明,二氧化钛质量含量每增加约20wt.%,复合氧化物中氧化铝的α相转变温度就降低100℃,随着氧化钛加入量的增加,复合氧化物的晶粒迅速减小。第二相的加入有效地抑制了氧化铝基体晶粒的快速长大。添加质量分数为30wt.%氧化钛且在1000℃下煅烧的样品拥有25-32nm的最小晶粒。     

In-situ Synthesis and Formation Mechanism ofTiN-Al_2O_3/Al Composite

The synthesis of TiN and Al2O3 by in situ injection of reactive nitrogen gas into molten Al alloys has been evaluated over the temperature range from 1000 to 1600℃. It is shown that TiN and Al2O3 can be formed in melt with nitrogen and surplus oxygen (in vacuum room of the induction furnace) as the reactive gases over 1000℃. Up to 2.1 wt pct Al2O3 and 5.2 wt pct of TiN in situ phases in an Al alloy has been formed in a range of size from 0.8 to 5 μm. The formation mechanism of TiN and Al2O3 is discussed in this paper.     

Optical Absorption Characterizations of Porous Al_2O_3Host/NiO Nanocomposites

Porous Al2O3 host/NiO nanocomposites have been prepared by pyrolysis of Ni2(OH)2CO3 inthe nanostructured Al2O3 hosts. Diffuse reflection spectra in the wavelength range of 200 to800 nm were measured. Results show that (1) in each spectrum exist several absorption bandsof nano-NiO. With increasing the pyrolysis temperature from 550 to 1000℃, the numbers ofabsorption bands of NiO increase from 2 to 6 (P1-P6), (2) comparing with optical absorptionbands of single crystal NiO, for porous nanocomposites the P1, P2 and P4 present "blue shift"and the P3, P5 and P6 exhibit "red shift"; (3) when the pyrolysis temperature, Tp, is 550℃, theabsorption bands become so weak that only two bands (P1 and P6) can be observed and inverselywhen Tp=1000℃ all six absorption bands of NiO are strong, (4) for porous Al2O3/NiOnanocomposites prepared by pyrolysis at 1000℃ the PF+ caused by the F+ centers in theAl2O3 host moves towards the short wavelength at first with increasing the doping amount ofNiO from 5 to 50 wt pct and then shifts to the long wavelength with further increasing NiO. Inthis paper, the above phenomena and mechanism of the absorption bands of NiO are discussedin detail.     

Effects of Al Additions on Microstructure and Mechanical Properties of MoSi2

The effects of Al additions on the microstructure and mechanical properties of MoSi2 have been studied. With the Al additions from 2.5 wt pct to 5 wt pct, the siliceous grain boundary phase in hot pressed samples was eliminated because of the formation of Al2O3 particles. It was shown that Al and SiO2 reacted at 860℃. During the reaction, Al atoms were mainly transferred to Al2O3 particles, and to some extent, diffused into MoSi2 grains. Both the toughness and strength of Al containing composites exceeded those of pure MoSi2 material. Bending strength and fracture toughness reach the highest value of 350 MPa, 4.05 MPa•m1/2, respectively, at ambient temperature when Al addition was of 3.5 wt pct.     

Effect of Wetting and NiAl_2O_4 Spinel Formation on the Bonding between Al_2O_3 and Ni

Al2O3-Ni interface formed under vacuum condition is non-wetting and weak. Severe instantaneous intedecial reaction (i.e. wetting) at the Al2O3-Ni interface promoted by oxygen can create a strengthened interface. The NiAl2O4 spinel-Ni intedece is weak and growth of the spinel interphase is detrimental to the Al2O3-Ni intedecial bonding. A proper control of the oxygen partial pressure can achieve wetting while avoiding the existence of spinel at the interface, producing stronger interfaces by both mechanical interlocking and more intimate chemical bonding in an Al2O3-20 vol pct Ni composite.     

Effects of Al2O3—Particulate—Contained Composite Filler Materials on the Shear Strength of Slumina Joints

Al2O3/Al2O3 joints were brazed with a new kind of filler materials,which were formed by adding Al2O3 particulates into Ag-Cu-Ti active filler metal.The results showed that the material parameters (the Ti content,Al2O3 particulate volume fraction) of the composite filler materials affected the shear strength of brazed joints.When the Ti content was 2 wt pct in the filler metal, the shear strength of brazing joints decreased with the increasing the volume ratio of Al2O3 particulate .When the Ti content was 3 wt pct in the filler metal, the shear strength of joints increased from 93.75 MPa(Al2O3 pOvol pct) to 135.32 MPa(Al2O3 p15 vol.pct).     

Welding TiB2 Ceramics and Metal Mo with Combustion Reaction Technology

Combustion reaction welding, one promising method to weld ceramics and metals, was used to weld TiB2 and Mo. The results showed that the reacted products through combustion reaction were TiB2 and MoB when the Mo contents in reactants were 20 wt pct and 40 wt pct while there was Mo besides MoB and TiB2 when there were 60 wt pct and 80 wt pct Mo in reactants. Diffusion of elements occurred at the interfaces of the two substrates. The interfaces between the reacted and the two substrates were indistinct after being welded. The welding temperature strongly affected properties of the samples. The value of bending strength of the sample with 80 wt pct Mo in reactant welded at 1500℃ was the highest, 368.52 MPa. The highest value of shear strength among all the samples was that of the one with 40 wt pct Mo in reactant welded at 1500℃, 50.97 MPa.     

Mechanical Properties and Microstructure of Si3N4-TiC Nanocomposites

1. IntroductionSilicon nitride is one of the promising structural ma-terials for high-temperature applications because of itshigh resistance to thermal shock, as well as high strength,high fracture toughness, and high resistance to chemicalattack[1~3]. However, wider application has been lim-ited mainly due to its inherent brittleness. Many effortshave been made to improve its properties by control-ling the microstructure or by fabricating various typesof composites[4~7].The silicon nitride wi…     

烧结助剂对反应热压烧结B4C基复合材料性能的影响

以微米级B₄C粉体为原料,通过与TiO₂葡萄糖原位反应制备TiB₂颗粒增韧B₄C复合材料。研究了烧结温度和烧结助剂对材料烧结行为及力学性能的影响。在1950℃反应热压下获得了相对密度为97.7%的TiB₂/B₄C复合材料,断裂韧性达到5.3 MPa·m1/2。添加Al₂O₃和Si烧结助剂后,分别在1950℃和1900℃ 获得了接近致密的(TiB_2,Al₂O₃)/B₄C和(TiB_2,SiC)/B₄C复合材料,断裂韧性分别提高到7.09和6.35 MPa·m1/2。显微组织分析表明,增韧作用主要来自残余应力引起的裂纹偏转。     

Effects of Al_2O_3-Particulate-Contained Composite Filler Materials on the Shear Strength Alumina Joints

Al2O3l2O3 joints were brazed with a new kind of filler materials, which were formed by adding AI203 particulates into Ag-Cu-Ti active filler metal. The results showed that the material parameters (the Ti content, Al2O3 particulate volume fraction) of the composite filler materials affected the shear strength of brazed joints. When the Ti content was 2 wt pct in the filler metal, the shear strength of brazing joints decreased with the increasing the volume ratio of Al2O3 particulate. When the Ti content was 3 wt pct in the filler metal, the shear strength of joints increased from 93.75 MPa(AI203p 0 vol. pct) to 135.32 MPa(AI203p 15 vol. pct).     

Properties of Dispersion Casting of Y2O3 Particles in Hypo, Hyper and Eutectic Binary Al-Cu Alloys

In the present work,the dispersion casting of Y-2O-3 particles in aluminum-copper alloy was investigated in terms of microstructural changes with respect to Cu contents of 20 （hypo）,33 （eutectic） and 40 （hyper） wt pct by scanning electron microscopy （SEM） and energy dispersive spectroscopy （EDS）.For the fabrication of Al-Cu alloy dispersed Y-2O-3 ceramic particles,stir casting method was employed.In case of Al-20 wt pct Cu alloy （hypoeutectic）,SEM images revealed that primary Al was grown up in the beginning.After that,eutectic phase with well dispersed ceramic particles was formed.In case of eutectic composition,Y-2O-3 particles were uniformly dispersed in the matrix.When the Cu is added into Al up to 40 wt pct （hypereutectic）,primary phase was grown up without any Y-2O-3 ceramic particles in the early stage of solidification.Thereafter, eutectic phase was formed with well dispersed ceramic particles.It can be concluded that Y-2O-3 ceramic particles is mostly dispersed in case of eutectic composition in Al-Cu alloy.     

(SiC,TiB2)/B4C复合材料的烧结机理

研究了在热压条件下制备 (SiC, TiB₂)/ B₄C复合材料的烧结机理。认为烧结助剂的加入使本体系成为液相烧结,同时粉料的微细颗粒对复合材料的烧结致密也有重要贡献。分析和测量了制取的复合材料的相组成、显微结构和力学性能。结果表明,采用B₄C与Si₃N₄和少量SiC、TiC为原料,Al₂O₃＋Y₂O₃为烧结助剂,在烧结温度1800~1880℃,压力30 MPa的热压条件下烧结反应生成了SiC、TiB₂和少量的BN,制取了(SiC, TiB₂)/B₄C复合材料。所形成的晶体显微结构为层片状。制得的试样的硬度、抗弯强度和断裂韧性分别可达HRA88.6、540 MPa和5.6 MPa·m1/2。      

Effect of Y2O3 and Total Oxide Addition on Mechanical Properties of Pressureless Sintered β-SiC

The effect of Y2O3 and the total oxide volume fraction (Y2O3 Al2O3) on density and mechanical properties of low temperature (1770～1940℃) pressureless sintered β-SiC ceramics were presented. The optimum temperature for pressureless sintering of β-SiC was found to be～1850℃ and the optimum content of Y2O3 in the oxides was found to be between 40 and 57 wt pct. The highest sintered density was achieved by adding oxides at 14 vol. pct. Both of the highest strength and fracture toughness were achieved at～14 vol. pct oxide addition and yttria concentrations between 40 and 57 wt pct in the oxides. Hardness, on the other hand, was found to be the highest for samples with 14 vol. pct oxide addition and ～64 wt pct Y2O3 in oxides.     

Al_2O_3对全稳定ZrO_2显微组织的影响

本文利用ＳＥＭ、ＥＤＡＸ等测试手段，细致地研究了Ａｌ２Ｏ３对全稳定ＺｒＯ２显微组织的影响．研究的结果表明，Ａｌ２Ｏ３在全稳定ＺｒＯ２中主要分布于晶界及第二相粒子中，其在晶内的固溶度极低；Ａｌ２Ｏ３能显著地促进ＺｒＯ２晶粒的生长，从而使气孔难以消除，降低材料的密度．     

原位合成TiB_2/ZL205A复合材料的组织及流动性

采用原位合成法制备了TiB_2/ZL205A复合材料,对所合成复合材料的物相、TiB_2颗粒形貌及分布、流动性进行了研究。结果表明:TiB_2/ZL205A复合材料主要由α-Al、Al_2Cu和TiB_2组成,TiB_2颗粒呈多边形或卵圆形,平均颗粒尺寸500nm左右,大部分沿晶界分布,少量分布在晶粒内部。TiB_2/ZL205A复合材料的流动性与浇铸温度及TiB_2质量分数的关系均可用指数阻尼模型进行描述。当浇铸温度由710℃提高到750℃时,7wt%TiB_2/ZL205A复合材料的流动性提高了30.4%;当浇铸温度在750℃以上时,7wt%TiB_2/ZL205A复合材料的流动性随浇铸温度的提高而提高的速率降低。与基体合金相比,在730℃浇铸时,3wt%TiB_2/ZL205A复合材料的流动性降低了21.8%,7wt%TiB_2/ZL205A复合材料的流动性降低了36.4%。     

Processing of Ceramic Based Nanocomposite Using α-Al2O3 Powder and FeCl2 Solution as Starting Materials

Alumina-iron nanocomposite powders were prepared by a two-step process. In the first step, α-Al2O3-FeCl2 powder mixture was formed by mixing α-Al2O3 powders with FeCl2 solution followed by drying. In the second step, the FeCl2 in the dry power mixture was selectively reduced to iron particles. A reduction temperature of 750℃ for 15 min in dry H2 was chosen based on the thermodynamic calculations. The concentration of iron in FeCl2 solution was calculated to be 20 vol. pct in the final composite. Two techniques were used to produce composite bulk materials. The Al2O3 nanocomposite powders were divided to two batches. The first batch of the produced mixture was hot pressed at 1400℃ and 27 MPa for 30 min in a graphite die. To study the effect of oxygen on the Al2O3/Fe interface bonding and mechanical properties of the composite,the second batch was heat treated in air at 700℃ for 20 min to partially oxidize the iron particles before hot pressing. Characterization of the composites was undertaken by conventional density measurements, X-ray diffractometry (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and electron probe micro analysis (EPMA). The suggested processing route (mixing, reduction and hot pressing)produces ceramic-metal nanocomposite much tougher than the pure Al2O3. The fracture strength of the produced Al2O3/Fe nanocomposite is nearly twice that of the pure Al2O3. The presence of spinel phase,FeAl2O4, as thick layer around the Fe particles in the Al2O3 matrix has a detrimental effect on interfacial bonding between Fe and Al2O3 and the fracture properties of the composite.     

Al_2O_3/B_4C的致密化机制

初始晶粒尺寸为0.33μm和7.0μm的Al2O3/14%B4C粉末在不同温度烧结,并模拟计算陶瓷粉末烧结过程。通过对比实验结果和计算结果,找出影响材料致密化的机制,讨论晶粒尺寸对扩散机制的影响,并估算出致密化激活能。在实验烧结温度范围内,界面反应被认为是影响Al2O3/B4C粉末致密化过程的主要因素。Al2O3/14%B4C陶瓷的致密化激活能是1820±60KJ.mol-1,这结果很大程度上支持界面反应致密化机制。     

SiC晶须增韧Al_2O_3及ZrO_2（Y_2O_3）基陶瓷复合材料的抗热震行

采用三点弯曲及扫描电镜等方法研究了ＳｉＣｗ／Ａｌ２Ｏ３、ＳｉＣｗ／ＺｒＯ３（Ｙ２Ｏ３）及ＳｉＣｗ／Ａｌ２Ｏ３＋ＺｒＯ２（Ｙ２Ｏ３）陶瓷复合材料的抗热震性．结果表现ＳｉＣｗ的加入使Ａｌ２Ｏ３、ＺｒＯ２（Ｙ２Ｏ３）以及Ａｌ２Ｏ３＋ＺｒＯ２（Ｙ２Ｏ３）基体的抗热震性显著提高，Ａｌ２Ｏ３陶瓷基复合材料的抗热震性明显优于ＺｒＯ２（Ｙ２Ｏ３）陶瓷基复复合材料．同时发现在Ａｌ２Ｏ３十ＳｉＣｗ材料基础上再加入少量ＺｒＯ２（２Ｙ）颗粒（１０Ｖｏ１％），也可进一步提高Ａｌ２Ｏ３＋ＳｉＣｗ材料的抗热震性．