TiB2-Cu基复合材料的燃烧合成研究

通过燃烧合成工艺制备了TiB2-40%Cu(质量分数）基复合材料，对复合材料的反应热力学、相组成以及微观组织进行了研究。热力学计算结果表明TiB是最稳定的相，中间相Ti-Cu化合物最终转变为TiB2相；XRD结果显示复合材料的相组成为TiB2相和Cu相，没有生成其他中间相；微观组织观察表明，合成产物组织致密，增强体TiB2陶瓷颗粒尺寸细小，形貌主要呈近等轴状和块状，Cu作为金属粘结剂将TiB2陶瓷颗粒相互连接在一起，Cu的存在促进了燃烧合成过程中材料的致密化行为。Cu的加入使TiB2-Cu基复合材料的致密度、弯曲强度和断裂韧性较TiB2纯陶瓷均有大幅度提高，材料的韧化机制为裂纹尖端塑性钝化机制。     

Ni的添加对TiB2-CU基复合材料微观组织的影响

利用燃烧合成工艺原位合成了TiB2-Cu基复合材料，为了改善TiB2陶瓷和Cu基体的润湿性，将金属Ni作为合金化元素加入到TiB2-Cu复合材料。通过XRD，SEM，EPMA和TEM等检测手段对金属Ni的添加对TiB2-Cu基复合材料微观组织的影响进行了研究。结果表明，含Ni复合材料的金属粘结相的面间距比不含Ni时Cu的面间距均有不同程度的减小；Ni加入后，TiB2-Cu-Ni复合材料的组织较TiB2-Cu复合材料更加致密，但陶瓷颗粒尺寸却大于TiB2-Cu复合材料的颗粒尺寸；Ni的加入降低了复合材料的导热率和冷却速度，使得部分TiB2陶瓷颗粒有足够的时间长成棒状，同时造成TiB2陶瓷颗粒间形成更多的烧结颈；Ni的加入也改善了陶瓷与金属粘结相之间的润湿性，使陶瓷相与金属粘结相的界面结合牢固，看不到TiB2-Cu复合材料中界面脱开的现象。金属Ni的添加有利于改善TiB2-Cu基复合材料的微观组织，进而利于复合材料的致密化。     

TiB2-Cu基金属陶瓷高温烧蚀行为研究

为研究TiB2-Cu基金属陶瓷材料的高温烧蚀行为,采用燃烧合成与同时致密化技术(SHS/PH IP)制备了TiB2-40Cu及TiB2-40Cu-8N i金属陶瓷复合材料.利用电弧风洞试验考察了材料的抗热震和抗烧蚀性能,利用扫描电镜、电子探针及X射线衍射等方法对材料烧蚀前后的微观组织形貌及成分进行了检测.结果表明,试验模型表面均有烧蚀冲刷痕迹,TiB2-40Cu模型由于抗热震性较差,其表面有裂纹出现,TiB2-40Cu-8N i的质量烧蚀率较TiB2-40Cu的质量烧蚀率低.微观组织分析表明,TiB2-40Cu模型烧蚀面中心区域剖面附近存在沿厚度方向100μm左右的烧蚀区.TiB2-40Cu复合材料的烧蚀机理为金属相的熔化、化学烧蚀和机械剥蚀.     

TiB/Ti基金属陶瓷燃烧合成反应热力学

为了解Ti-B二元体系的自蔓延合成反应进行的方向和最终产物的相组成，对Ti-B二元体系燃烧合成反应生成TiB的自由焓变、自由能、反应绝热温度和燃烧温度进行了理论分析和实验研究。结果表明，Ti含量过量的情况下TiB的反应生成自由焓比TiB2的反应生成自由焓高，反应生成自由能比TiB2的更低，TiB在生成热力学上比TiB2更稳定，Ti与B的SHS反应更易生成TiB相，Ti-B二元体系的反应绝热温度和燃烧温度随着Ti含量的提高而呈下降趋势。     

铝电解用NiFe2O4基金属陶瓷的制备

以铝电解惰性阳极为应用目标，制备了不同金属相(Cu—Ni)含量的Ni-Cu／NiFe2O4金属陶瓷，研究了烧结气氛、温度和保温时间对其性能的影响，解决了烧结过程中氧化物陶瓷的离解和金属相被氧化的问题，比较了不同烧结条件下所得试样的基本物理参数，找到了较优的Ni—Cu／NiFe2O4金属陶瓷制备工艺。结果表明：Cu／NiFe2O4金属陶瓷的金属相中添加15wt％ Ni后，可以提高金属相的液相线温度，改善金属相对NiFe2O4陶瓷相的润湿性能，从而可在保证金属相不溢出且分布均匀的前提下，大大提高金属陶瓷的烧结温度和保温时间，显著提高金属陶瓷的致密度，进而改善金属陶瓷惰性阳极的耐腐蚀性能和导电性能。     

反应硼化烧结WCoB基金属陶瓷的组织与性能

采用单质钨粉、钴粉和硼粉结合反应硼化烧结法制备了WCoB基金属陶瓷,研究了WCoB基金属陶瓷在烧结过程中的物相转变和尺寸变化,烧结温度对其力学性能和显微组织的影响。结果发现:随着烧结温度的升高,材料物相逐渐由单质相变为二元硼化物相和三元硼化物相,并且材料的尺寸先发生细微收缩,再在硼化反应过程中逐渐增加,最后在液相烧结过程中逐渐减小;随着烧结温度的升高,WCoB基金属陶瓷的抗弯强度和硬度先增加后减小,在1420℃达到最大,分别为1470 MPa和84.6HRA,显著提高了WCoB基金属陶瓷的抗弯强度。     

碳含量对(Ti,W) (C,N)-Co金属陶瓷的显微结构与力学性能的影响

采用纳米TiN、亚微米TiC等陶瓷粉体原材料,以金属Co作为粘结剂,制备了Ti(C,N)-Co金属陶瓷材料,研究了不同碳含量的掺加对金属陶瓷材料的显微结构和力学性能的影响.结果表明:金属陶瓷的组织中有黑芯-灰壳结构和白芯-灰壳结构,随着碳含量的增加,金属陶瓷的组织中白芯的陶瓷相稍有增多,硬质陶瓷相颗粒粒径有所长大;金属陶瓷的抗弯强度和硬度有相似的趋势,高碳含量可以得到较高的断裂韧性.     

TiB2基金属陶瓷的显微结构与力学性能

以Fe-Ni-Ti-Al 为助烧剂, 用热压的方法制备了TiB2 基金属陶瓷。研究了烧结温度、烧结时间、助烧剂对材料显微结构和力学性能的影响, 初步分析了TiB2 基金属陶瓷的增韧机理。结果表明, 随着烧结温度的提高, 材料弯曲强度降低, 洛氏硬度升高;随着烧结时间延长, 弯曲强度出现峰值。SEM、EDS 观察表明, 助烧剂中的Ti 避免了Fe₂B、Ni₂₃B₆ 等脆性相的生成, Al 有除氧的作用。裂纹偏转和裂纹桥联是TiB2 金属陶瓷重要的增韧方式。     

燃烧合成Co（Ti）-Al2O3金属陶瓷的组织与性能

利用低放热Al-TiO2反应体系部分取代高放热Al-CoO反应体系,并加入适量的稀释剂Al2O3吸收反应热量,通过热爆燃烧合成结合致密化工艺制备了铁磁性Co(Ti)-Al2O3金属陶瓷。研究表明,Co(Ti)-Al2O3金属陶瓷中随着Al-TiO2体系的增加,燃烧反应温度降低,金属相尺寸减小,分布更均匀,同时在金属相与基体之间形成过渡区域,提高了界面结合。Co(Ti)-Al2O3复合材料的饱和磁化强度随着金属Co含量增加而增加,最高可达到37.2849Am2/kg,而矫顽力在3997.6～5615.4A/m范围内变化,介于软磁体和硬磁体之间。     

放电等离子烧结制备Ti(C,N)-Co金属陶瓷的组织和性能

采用放电等离子烧结方法制备了Ti(C,N)-Co金属陶瓷,研究了烧结温度和Co含量对TiCN基金属陶瓷力学性能的影响。结果表明:烧结温度在1400℃~1700℃范围内,当Co含量为1%时,随着温度的升高,样品的密度、弯曲强度和硬度不断增大;当Co含量为5%时,随着温度的升高,样品的密度、弯曲强度、硬度呈现先上升后下降的趋势。随着Co含量的增加,TiCN-Co金属陶瓷烧结致密化所需温度降低。烧结温度为1600℃、Co含量为5%时,金属陶瓷试样具有较高的综合力学性能,分别为弯曲强度815MPa和硬度HV101505。     

Self-propagating High-temperature Synthesis, Microstructureand Mechanical Properties of TiC-TiB2-Cu Composites

TiC-TiB2-Cu composites were produced by self-propagating high-temperature synthesis combined with pseudo hot isostatic pressing using Ti, B4C and Cu powders. The microstructure and mechanical properties of the composites were investigated. The X-ray diffraction （XRD） and scanning electron microscopy （SEM） results showed that the final products were only TiC, TiB2 and Cu phases. The clubbed TiB2 grains and spheroidal or irregular TiC grains were found in the microstructure of synthesized products. The reaction temperature and grain size of TiB2 and TiC particles decreased with increasing Cu content. The introduction of Cu into the composites resulted in a drastic increase in the relative density and flexual strength, and the maximum values were obtained with the addition of 20 wt pct, while the fracture toughness was the best when Cu content was 40 wt pct.     

Effect of V content on the microstructure and mechanical properties of Mo2FeB2 based cermets

Four series of cermets with V content between 0 and 7.5 wt.% in 2.5 wt.% increments were studied by scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX) and X-ray diffractometry (XRD). The transverse rupture strength (TRS), hardness (HRA) and fracture toughness (K_IC) were also measured. It was found that the grain size was affected by the V content. The cermets with 2.5 wt.% V addition exhibited the smallest grain size. An increasing V content decreased the wettability of the binder on the Mo₂FeB₂ hard phase, and accordingly resulted in the increase of porosity and aggregation of ceramic grains. EDS results showed that V addition occurred primarily in the hard phase, with a little amount in the Fe alloy binder. In addition, the content of Mo element in the binder decreased with increasing V content. The cermets with 2.5 wt.% V addition showed the highest TRS, hardness and fracture toughness of 2350 MPa, HRA 90.6 and 15.1 MPa m^1/2, respectively.     

Effect of TaC addition on the microstructures and mechanical properties of Ti(C, N)-based cermets

The microstructures of the prepared Ti(C, N)-based cermets with various TaC additions were studied using X-ray diffractometry (XRD) and scanning electron microscopy (SEM). Mechanical properties such as transverse rupture strength (TRS), fracture toughness (K_1C) and hardness (HRA) were also measured. The results showed that the grain size of the cermets decreased with increasing TaC addition, but too high TaC addition resulted in agglomeration of the grains. An increasing TaC addition increased the dissolution of tungsten, titanium, molybdenum and tantalum in the binder phase. The hardness of the cermets decreased slightly with increasing TaC addition. The transverse rupture strength was the highest for the cermets with 5 wt.% TaC addition, which was characterized by fine grains, homogeneous microstructure and the moderate thickness of rim phase in the binder. The fracture toughness of the cermets with TaC addition from 0 to 5 wt.% decreased obviously, which resulting from decreased grain size. The further decreasing of fracture toughness for the cermets with 7 wt.% TaC addition was due to increased porosity and interfacial tensile stress.     

Sintering properties of submicron TiC powders from carbon coated titania precursor

The sintering behavior of submicron titanium carbide (TiC) synthesized from carbon coated titania (TiO₂) precursor was investigated in TiC-Ni system. The densification was examined as functions of initial carbon content (30.95–34 wt.%) and Ni content (3–20 wt.%). The sintered density of TiC-Ni was markedly decreased with increased carbon content in the precursor. The amount of Ni had a relatively small influence on the densification of submicron TiC-Ni cermet compared with TiC (commercially available HCS)-Ni cermets. The results show that submicron TiC with only 3 wt.% Ni can be sintered to densities above 95% TD in flowing Ar+10H₂ at 1500°C and below. The improvements in densification result from the capillary force increase since it is inversely dependent on the particle size. With decreased Ni content, the Vickers hardness increased and the fracture toughness decreased, as expected. However, the sufficient densification cannot be achieved for commercial HCS TiC powder sintered with Ni (<10 wt.%) under the same conditions. Therefore, both the Vickers hardness and fracture toughness decreased as the Ni content decreased. This was due to the increase of porosity in the sintered samples containing commercial TiC powder.     

Effect of SiC whisker addition on the microstructures and mechanical properties of Ti(C,N)-based cermets

Ti(C, N)-based cermets with addition of SiC whisker (SiC_w) were prepared by vacuum sintering. The microstructures of the prepared cermets were investigated by using X-ray diffractometry (XRD) and scanning electron microscopy (SEM). Mechanical properties such as transverse rupture strength (TRS), fracture toughness (K_IC) and hardness (HRA) were also measured. It was found that the grain size of the cermets was affected by the SiC whisker addition. The cermets with 1.0 wt.% SiC whisker addition exhibited the smallest grain size. The porosities of the cermets increased with increasing SiC whisker additions. The addition of the SiC whisker had no influence on the phase constituents of the cermets. Compared with the cermets with no whisker addition, the highest TRS and fracture toughness for cermets with 1.0 wt.% SiC whisker addition increased by about 24% and 29%, respectively. The strengthening mechanisms were attributed to finer grain size, homogeneous microstructure and moderate thickness of rim phase. The toughening mechanisms were characterized by crack deflection, whisker bridging and whisker pulling-out.     

Titanium diboride copper-matrix composites

Copper-matrix titanium diboride platelet (3–5 μm) composites containing 15–60 vol% TiB2, were fabricated by powder metallurgy, using copper-coated TiB2 (60 vol% TiB2) and various amounts of copper powder. The porosity was ≤0.5% when TiB2 was ≤48 vol%. Above 48 vol% TiB2, the porosity increased abruptly with increasing TiB2 content, reaching 6.7% at 60 vol% TiB2. As a result, the hardness and compressive yield strength dropped precipitously with increasing TiB2 volume fraction beyond 48%. At 48 vol% TiB2, the thermal conductivity was 176 W m-1°C-1, the electrical resistivity was 3.42× 10-6Ωcm, the coefficient of thermal expansion (CTE) was 10.2×10-6°C-1, the compressive yield strength was 659 MPa, and the Brinell hardness was 218. For composites made by conventional powder metallurgy, using a mixture of TiB2 platelets (not coated) and copper powder, the porosity was ≤1.8% when TiB2 was at ≤42 vol%; above 42 vol% TiB2, the porosity increased abruptly and the hardness and compressive yield strength decreased abruptly. The electrical resistivity and thermal conductivity were also affected by the porosity, but less so than the mechanical properties. Composites made using copper-coated TiB2 exhibited lower electrical resistivity, higher thermal conductivity, lower CTE, higher compressive yield strength, greater hardness, greater abrasive wear resistance, greater scratch resistance and lower porosity than the corresponding composites made from uncoated TiB2. This revised version was published online in November 2006 with corrections to the Cover Date.     

Mechanical properties of titanium diboride based cermets

Mechanical properties of titanium diboride (TiB₂) cermets critically depend on the composition of the binder phase. Both, fracture toughness and hardness are substantially increased by avoiding the formation of extremely brittle secondary borides which form during sintering by chemical reactions between TiB₂ and the metallic additives. Fractographic observations of TiB₂ cermets without secondary borides show the presence of ductile ligaments of the binder phase bridging the advancing crack tip. The powder metallurgy processing route applied to these materials allows modification of the binder phase structure from the ferritic iron-aluminium phase to Fe-Ni-Al austenite by changing the aluminium content of the powder mixtures. The highest toughness values have been obtained for the TiB₂ cermets with an austenitic binder phase. X-ray diffraction analyses of the fracture surfaces of such samples show that the binder phase is metastable exhibiting stress induced martensitic transformation during fracture. This new family of materials presents an outstanding combination of hardness and toughness, comparable to those obtained with commercial grades of tungsten carbide (WC) hardmetals.     

Properties of NbC-Co cermets obtained by spark plasma sintering

Sub-micrometer sized NbC-Co powder mixtures with 8, 12, 18 or 24.5 wt.% Co were consolidated by spark plasma sintering (SPS) for 2 min at 1200-1280 °C and 30-60 MPa. The optimum densification conditions were determined by analysing the dimensional change of the NbC-12 wt.% Co powder compact. SPS for 2 min at 1280 °C under a pressure of 60 MPa allowed full densification of the NbC-Co cermets with limited NbC grain growth. The microstructure is characterized as a highly interconnected NbC grain network with an inhomogeneously distributed Co binder. The Vickers hardness increased from 11.70 to 15.40 GPa whereas the fracture toughness decreased from 9.0 to 5.5 MPa m^1 / 2 with decreasing Co content from 24.5 to 8 wt.%.     

燃烧合成TiC-Ni材料的室温及高温力学性能

研究了燃烧合成新工艺制备的TiC-Ni金属陶瓷材料的力学性能。结果表明:TiC-Ni金属陶瓷硬度值和抗弯强度在Ni含量为20 wt%时达到最高值,断裂韧性在Ni含量为30 wt%时达到最大值,TiC-Ni材料在室温下具有无宏观塑性变形的脆性断裂特征。随着温度的升高,TiC-Ni材料弯曲强度下降,温度超过1000℃开始发生塑性变形。其强度与传统方法生产的相近成分材料相比比较接近。