热压烧结制备原位复合（TiB2+TiC）/Ti3SiC2复相陶瓷

采用热压烧结法制备了原位复合(TiB2+TiC)/Ti3SiC2复相陶瓷。采用X射线衍射、扫描电镜和透射电镜对材料的物相组成和显微结构进行了表征,研究了烧结温度对材料物相组成、烧结性能、显微结构与力学性能的影响。结果表明:烧结温度在1 350～1 500℃范围内,随着烧结温度的升高,合成反应进行逐渐完全,材料的密度、抗弯强度和断裂韧性显著提高。1 500℃烧结可得到致密的原位复合(TiB2+TiC)/Ti3SiC2复相陶瓷,材料晶粒发育较完善,层片状Ti3SiC2、柱状TiB2与等轴状TiC晶粒清晰可见,增强相晶粒细小,晶界干净,材料的抗弯强度、断裂韧性和Vickers硬度分别达到741 MPa,10.12 MPa.m1/2和9.65 GPa。烧结温度达到1 550℃时Ti3SiC2开始发生分解,材料的密度和力学性能又显著下降。     

Al2O3/Cr3C2/(W,Ti)C陶瓷材料的力学性能及微观结构

用热压烧结工艺在1 700℃,28 MPa保温保压30 min及N2气氛条件下,制备了添加不同含量Cr3C2和(W,Ti)C颗粒的Al2O3/CraC2/(W,Ti)C复合陶瓷材料.对复合陶瓷的力学性能进行测试.用环境扫描电镜、透射电镜和能谱分析仪对复合陶瓷的显微结构进行观察.结果表明与纯Al2O3相比,70Al2O3/10Cr3C2/20(W,Ti)C复合陶瓷材料的显微组织更均匀细化,具有良好的综合力学性能,其断裂韧性自纯Al2Oa陶瓷的4.0 MPa·m1/2提高到8.92 MPa·m1/2.分析发现其内部位错机制、纳米颗粒的淀析、裂纹扩展路径偏转、沿晶断裂、韧窝及解理撕裂等是材料断裂韧性提高的主要原因.     

Al2O3/Cu-Sn-Ti+B钎料/Ti-6Al-4V合金连接的微观结构及力学性能

在Cu-21Sn-12Ti钎料中添加不同质量分数的B粉制备Cu-Sn-Ti＋B复合钎料,然后在钎焊温度910℃保温10 min条件下钎焊Al2O3与Ti-6Al-4V合金。研究了原位生成TiB对Al2O3/Ti-6Al-4V合金接头微观结构及力学性能的影响。接头中原位生成的TiB呈晶须状均匀分布在Ti2Cu上,当采用TiB体积分数低于40%的钎料钎焊Al2O3与Ti-6Al-4V合金时,均可获得连接良好且界面致密的钎焊接头。随接头中TiB的体积分数增加,Ⅱ区中的Ti2（Cu,Al）含量增加,并逐渐变得连续,TiB的分布区Ⅲ范围增宽,Ti-6Al-4V合金向钎料中的溶解量增加。接头的室温抗剪强度随TiB的体积分数增加先上升后下降,当接头中TiB体积分数增至20%时,接头抗剪强度达最大,为70.1MPa。     

TiN含量对TiN-Al2O3复合材料力学性能及导电性能的影响

以纯度(质量分数)均为99%的微米级TiN和α-Al2O3粉体为原料,采用湿法球磨混合5h制备了TiN体积分数分别为0、10%、20%、30%和40%的TiN-Al2O3复合粉体。将复合粉体压制成型,在200℃干燥12h,通过热压炉在pN2=-0.098MPa条件下于1800℃保温3h烧结得到TiN-Al2O3复合材料,并研究了微米级TiN含量对TiN-Al2O3材料力学性能和导电性能的影响。结果表明:随着TiN含量的增加,复合材料的烧结性能和力学性能不断提高,电阻率不断下降。TiN含量为40%(体积分数)时,材料的抗弯强度498MPa,断裂韧性4.285MPa·m1/2,电阻率1.34×10-3Ω·cm;材料的导电性能符合渗流理论,其渗流阈值Vc=17.24%,这与试验结果一致。而显微结构分析表明:TiN颗粒主要分布在Al2O3晶界处,晶粒细小,它们相互交织在一起形成网络,起到了抑制Al2O3晶粒长大和增韧补强作用,提高了材料的力学性能。     

BaNb_2O_6/Al_2O_3复相陶瓷的制备及力学性能

为研究功能材料对结构陶瓷微观结构和力学性能的影响,将铁电相BaNb2O6引入到Al2O3陶瓷中,分别采用无压和热压烧结技术于1350℃制备BaNb2O6/Al2O3复相陶瓷,对其物相组成、微观结构和力学性能进行了研究。结果表明:BaNb2O6与Al2O3经过高温烧结能够稳定共存,BaNb2O6的加入促进了Al2O3陶瓷的烧结。BaNb2O6加入量为10%(体积分数)时,1350℃无压烧结和热压烧结制备的BaNb2O6/Al2O3复相陶瓷的致密度、抗弯强度和断裂韧性分别为94.6%、214MPa、2.28 MPa m1/2和99.3%、332 MPa、3.55MPa m1/2。当裂纹扩展遇到BaNb2O6晶粒时发生穿晶断裂,但在晶粒内部出现裂纹偏转,说明铁电相BaNb2O6晶粒内部的微观结构有助于陶瓷的强韧化。     

Al2O3/Fe纳米复合粉体的制备及其陶瓷的性能研究

以纳米α-Al2O3和Fe(NO3)3·9H2O为原料,采用非均相沉淀法制备了Fe包裹Al2O3的纳米复合粉体.经XRD、SEM分析发现:复合粉体前驱体经500 ℃焙烧,在H2中700 ℃还原可以得到纳米Fe包裹Al2O3的纳米复合粉体.粉体分散良好,Al2O3表面的纳米Fe粒子呈非连续状态,颗粒为球形,尺寸为30 nm左右,分布均匀.将复合粉体在热压下(30 MPa)烧结获得Al2O3/Fe复合陶瓷,当加入5mol%Fe时,陶瓷的热压烧结温度比单相Al2O3陶瓷降低将近100 ℃.含量为10mol%Fe的陶瓷样品在1500 ℃热压烧结后,断裂韧性可达到5.62 MPa,与相同条件下烧结的单相Al2O3陶瓷(KIc=3.57 MPa)相比提高了近57%.     

纳米TiN-Al_2O_3基复相陶瓷的电学及力学性能

以纳米Al2O3和TiN为原料,以SiO2为助烧剂,热压烧结后获得TiN-Al2O3复相陶瓷。TiN-Al2O3复相陶瓷具有较优异的力学性能:三点弯曲强度最高达到565.8MPa,断裂韧性在4～6MPa·m1/2之间。复相陶瓷中立方TiN均匀地分布在Al2O3基体中,TiN颗粒主要分布在Al2O3晶界处。当TiN颗粒的体积含量为5%时,TiN-Al2O3复相陶瓷的电阻率在1012～104Ω·cm范围内,其加载电压可达0.75kV/mm。     

TiB2-BN-AlN复相陶瓷的结构与性能研究

采用不同TiB2、BN、AlN体积配比制备TiB2-BN-AlN复相陶瓷,研究了TiB2、BN、AlN含量的变化对复相陶瓷烧结致密度、组织结构和性能的影响.结果表明:随着BN含量的增加,TiB2-BN-AlN复相陶瓷的致密度和抗弯强度降低,电阻率升高.另一方面,在空气中AlN颗粒表面易水解产生AlOOH和NH3,在热压烧结过程中,AlOOH会分解成Al2O3,同时Al2O3与AlN发生反应生成AlON,使得物质在AlN 晶粒之间扩散,从而提高复相陶瓷的致密度.     

Al2O3/LiTaO3陶瓷复合材料的制备与力学性能

采用氮气保护热压烧结工艺制备Al2O3/LiTaO3(简称ALT)陶瓷复合材料，系统研究了其微观组织和力学性能。ALT陶瓷复合材料的相对密度比烧结纯LiTaO3陶瓷的高得多，表明Al2O3起到烧结助剂的作用。TEM观察表明，Al2O3p分布均匀，两者结合紧密，界面上有非常微量的分解物。ALT陶瓷复合材料的力学性能均随Al2O3p含量的增加而提高，Al2O3p的体积分数为40％时，其各项力学性能都是最高。     

热压烧结Al2O3-ZrB2-SiC复相陶瓷的高温力学性能研究

为提高Al2O3陶瓷的高温力学性能,采用热压烧结工艺(烧结温度1 800℃,烧结压力20 MPa,保温1 h)制备了Al2O3-ZrB2-SiC复相陶瓷(简称AZS),并研究了ZrB2含量对Al2O3基陶瓷高温抗折强度和抗热震性的影响。结果表明:1)在Al2O3基陶瓷中加入第二相ZrB2能有效改善材料的高温抗折强度和高温强度保持率,在1 000和1 200℃时,加入20%体积分数ZrB2的AZS陶瓷试样具有最高的高温抗折强度,而加入24%体积分数ZrB2的AZS陶瓷试样具有最高的高温强度保持率。2)AZS陶瓷的抗热震性能优于纯Al2O3陶瓷。经100℃温差急冷后,加入20%体积分数ZrB2的AZS陶瓷具有最高的残余强度,比纯Al2O3陶瓷提高了17.2%;经300和500℃温差急冷后,加入24%体积分数ZrB2的AZS陶瓷都具有最高的残余强度,比Al2O3陶瓷分别提高了35.3%和20.9%。     

Addition of Al–Ti–B master alloys to improve the performances of alumina matrix ceramic materials

In the present work, a new technique to improve the performances of alumina matrix ceramic materials is presented, in which Al, Al₃Ti and TiB₂ are incorporated into alumina matrix ceramic materials in the form of Al–Ti–B master alloys. Composites of Al₂O₃/TiB₂/AlN/TiN are fabricated by the technology of transient liquid phase sintering, during which new phases such as AlN and TiN are produced by the chemical reactions taking place among Al, Ti and N₂ (the protective atmosphere). The densification rate of the composites as a function of Al–Ti–B volume content is discussed. The fundamental properties of the composites such as hardness, fracture toughness and bending strength are examined. The relations of volume content of Al–Ti–B master alloys and mechanical properties of alumina matrix ceramic materials are analyzed. The effects of fracture mechanism on mechanical properties of the composites are researched together with the refining performances of Al–Ti–B master alloys.     

The Emergence for Multilamellar Ti–Al–N Solid Solution in Ti/AlN Composites Sintered at Various Temperatures

Nowadays, a variety of coatings such as Ti–Al–N and TiN have been proposed in titanium machining, but few results on fabrication of bulk Ti/AlN composites were reported. Here, we prepared bulk Ti‐60 wt%AlN composites via vacuum hot‐press sintering at 1250°C–1450°C under an applied pressure of 30 MPa for 1 h. With sintering temperature increasing, the mechanical properties of Ti/AlN composites improved and achieved the maximum values when the sintering temperature is 1450°C. SEM detected the multilamellar grains which are confirmed as Ti–Al–N solid solution by XRD and EDS. Finally, microstructure evolution and phase transformation of Ti/AlN composites were illustrated that Al and N atoms diffuse across the grain boundary and react with Ti atoms to form TiN phase and multilamellar Ti–Al–N solid solution. This work is interesting for producing high strength and toughens metal/ceramic composites.     

Pressureless sintering of alumina matrix ceramic materials improved by Al–Ti–B master alloys and diopside

Al–Ti–B master alloys and diopside are simultaneously introduced in alumina matrix ceramic materials as sintering aids. Fine structural alumina matrix ceramic materials are fabricated by pressureless sintering during which liquid phase, leading to interface reactions between alumina matrix and additives, is formed. Hardness, fracture toughness and bending strength of the composites are measured. The effects of diopside on mechanical properties and fracture mechanism of fine structural alumina matrix ceramic materials are analyzed together with the microstructure observations on fracture surfaces, the polished surfaces and the indentation cracks.     

(Ti,V)_3AlC_2/Al_2O_3复合材料的制备及力学性能

为了提高Ti_3Al C_2陶瓷的力学性能,本研究以Ti C粉、Ti粉、Al粉和V2O5粉为起始反应原料,采用原位热压技术在1350°C下反应烧结合成出了(Ti,V)_3AlC_2/Al_2O_3复合材料。利用X-射线衍射和扫描电子显微技术对合成产物的物相和微观结构进行了表征,并分析了复合材料的合成机制。最后,对(Ti,V)_3AlC_2/Al_2O_3复合材料的力学性能进行了研究。测试结果表明:(Ti_(0.92),V_(0.08))_3Al C_2/10wt%Al_2O_3复合材料具有最佳的力学性能,其硬度、断裂韧性及抗弯强度分别为5.56 GPa、12.93 MPa·m~(1/2)和435 MPa,相比于单相Ti_3Al C_2材料分别提升了60%、108%和31%。     

Toughening mechanism of alumina-matrix ceramic composites with the addition of AlTiC master alloys and ZrO2

Titanium carbide and aluminium are introduced in alumina matrix in the form of AlTiC, which is a kind of master alloy. Alumina-matrix ceramic composites are prepared by using transient liquid phase and hot-press sintering. Significant improvements in mechanical properties have been attained due to the good toughening effect of AlTiC master alloys and ZrO₂. The microstructures and toughening mechanisms of the fabricated alumina-matrix ceramic materials are analysed using a scanning electron microscope, a transmission electron microscopy and an electron probe microanalysis, respectively. Results show that the microstructures of “intracrystalline shape” and “intercrystalline shape” are formed and “sublattice” exists in the composites, which may extend crack path and restrain intracrystalline failure, thus improving the fracture toughness of the composites.     

自蔓延高温合成TiB2+Al2O3/NiAl复合材料

Al2O3 TiB2复相陶瓷材料具有金属材料无法比拟的高硬度、高熔点、高导热、低膨胀系数、高耐磨性、高温化学稳定性等优良的性能,但由于两种材料都属于硬而脆的材料,复合后仍然存在脆性大、裂纹敏感性强、抗机械冲击性和温度急变形差等缺点。为了克服这些缺点,本文探索了在陶瓷相中添加金属间化合物(NiAl或FeAl)。X射线衍射结果表明合成产物的主要组成相分别为Al2O3 TiB2、Al2O3 TiB2 NiAl及Al2O3 TiB2 FeAl,反应按预期进行,且燃烧合成反应进行的较为彻底。通过对不同成分反应产物的致密度、强度、断裂韧性对比,可知产物的致密度在FeAl含量为15%时达到最高99.5%,Al2O3 TiB2 NiAl体系中NiAl含量为20%达到最高98.5%。随金属间化合物含量的增加,合成复合材料的硬度下降,而断裂韧性提高。     

Nearly dense Ti–6Al–4V/TiB composites manufactured via hydrogen assisted BEPM

Titanium matrix composites reinforced with in situ formed titanium boride whiskers have long aroused significant interest for advanced applications in fields such as aerospace, biomedicine, and armaments. However, processing approaches dedicated to fabricating these composites have usually been limited by the cost-performance dilemma, thereby limiting commercial success. Blended elemental powder metallurgy (BEPM) has historically been the most economical route to produce titanium-based composites. At the same time, the need to reduce undue sinter porosities has imposed complicated and expensive extra thermomechanical steps in BEPM manufacturing. In the present study, nearly dense Ti–6Al–4V-based composites reinforced with in situ synthesized titanium monoborides (TiB) are prepared by simple press-and-sinter hydrogen-assisted BEPM without hot deformation or hot pressing using TiH₂, TiB₂, and master alloy (Al–V) powder blends as starting material. Vacuum sintering of compacted powder blends results in the formation of a dehydrogenated Ti–6Al–4V matrix with excessive porosity and unevenly distributed partially reacted TiB₂ particles. Such an inappropriate pre-sintered microstructure can be completely transformed into low-porosity uniform Ti–6Al–4V/TiB composites with tailored grains by using hydrogenation and milling of pre-sintered material into hydrogenated pre-alloyed powders and, finally, by using these powders in a second press-and-sinter processing step. The useful influence of hydrogen as a temporary alloying element on microstructure formation is discussed. The densification of hydrogenated powder compacts upon vacuum heating, and the hydrogen emission from the material is studied via dilatometric tests. The evolution of microstructure and phase composition during processing steps was investigated by scanning electron microscopy and x-ray diffraction. Compressive tests were used to evaluate the mechanical properties of materials produced after the first and second sintering. The results show that hydrogen-assisted BEPM can be a cost-effective route for in situ fabrication of Ti–6Al–4V/TiB composites with reliable mechanical properties.     

Synthesis and microstructure of Ti2AlN ceramic by thermal explosion

Ti₂AlN ceramic with a small amount of TiN was rapidly synthesized by the thermal explosion (TE) technique using Ti, Al and TiN as starting materials. The effects of the starting composition, the particle size of TiN and the compacts’ height on the phase composition and microstructure of obtained Ti₂AlN ceramic were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results showed that high purity Ti₂AlN ceramic containing 4% TiN could be fabricated at 700 °C for 2 min with a molar ratio of 1.1:1.1:1(Ti: Al: TiN). It was further found that small particle size of TiN and compacts’ height of 2–8 mm were beneficial to obtain high purity Ti₂AlN. Finally, the formation mechanism of Ti₂AlN ceramic via thermal explosion was proposed.     

In-situ synthesis and low-temperature fabrication of B4C/TiB2-based multilayer graded composites with B4C and Ti–Al intermetallics mixtures through transient liquid phase sintering

The seven-layer B4C/TiB2-based graded composites was prepared with B4C and Ti–Al intermetallics through stepped laminating processing and transient liquid phase spark plasma sintering. The sintering strategy of the graded composites was proposed based on the sintering products of monolayer materials with different contents of Ti–Al intermetallics from 5 wt% to 60 wt%. The top three layers and bottom three layers were sintered respectively at 1650 °C and 1500 °C, and then the middle layer was used as the binder to joint the as-preserved two sections at 1550 °C. The apparent density of the as-prepared B4C/TiB2-based multilayer graded composites was 2.94 g/cm3, which was lower than that of most advanced ceramics. With the increase in the addition of Ti–Al intermetallics, the hardness of B4C/TiB2-based multilayer graded composites decreased from 31 GPa (B4C-riched) to 25 GPa (TiB2-riched), whereas the fracture toughness increased from 3.8 MPa·m0.5–6.02 MPa·m0.5. The compressive strength was up to 1100 MPa, displaying the jagged stress-strain curve. Crack propagation resistance mechanisms such as deflection and bridging enhanced the fracture toughness. The B4C/TiB2-based multilayer graded composites fabricated at low temperature possess high front hardness, high rear toughness, high overall strength and low density, and has promising applications in impact-resistant fields such as lightweight ceramic armor.     

导电Al2O3基陶瓷刀具材料的超声—放电复合加工技术研究

采用超声－放电复合加工技术对Ａｌ２Ｏ３／（Ｗ,Ｔｉ）Ｃ,Ａｌ２Ｏ３／ＴｉＢ２,Ａｌ２Ｏ３／ＴｉＢ２／ＳｉＣｗ三种Ａｌ２Ｏ３基陶瓷刀具材料表面定位方孔进行加工,研究了共加工机理和加工参数对不同陶瓷材料加工效率,加工表面粗糙度的影响,由于该复合加工技术有产地结合了超扬波加工和放电加工的特点,因而能高效,高质量地加工陶瓷材料。试验结果表明,在同样的加工条件下,材料去除率的大小顺序为Ａｌ２Ｏ３／（Ｗ,Ｔｉ