热压TiC／Ti／Si／Al合成Ti3SiC2材料的研究

研究了向原料粉中掺加Al粉对合成高纯致密Ti3SiC2材料的影响。实验表明以2TiC／1Ti／1Si／0．2Al为起始原料组成，采用热压工艺在1200℃～1400℃的温度范围内，可以制备得到密度达到理论密度98％以上的高纯致密Ti3SiC2块体材料。由XRD数据计算得到的晶格参数与文献中的值接近。通过SEM和EPMA分析得知Ti3SiC2晶粒呈板状结晶形貌，且发育良好，晶粒在平面内的尺寸分别为3μm～8μm和4μm～10μm。     

原位热压合成Ti3 AlC2 陶瓷

分别用3Ti-Al-2C和2TiC-Ti-Al粉用原位热压技术制备Ti3AlC2陶瓷.采用XRD、DTA、SEM等测试手段研究其物相组成、反应过程及显微结构.结果表明:1300 ℃下3Ti-Al-2C体系的合成产物为层状Ti3AlC2、TiC和Al2O3相,1500 ℃下2TiC-Ti-Al体系的合成产物基本为层状Ti3AlC2相,纯度较高.在Ti-Al-C体系中,首先发生Ti与C反应生成TiC,接着发生Ti与Al反应相继生成TiAl3和TiAl,随后发生TiAl和TiC反应生成Ti2AlC,最后Ti2AlC和TiC反应生成Ti3AlC2.同时,分析了TiC掺杂对TiC-Ti-Al体系原位合成Ti3AlC2的影响.     

热压烧结燃烧合成Ti3AlC2粉体的研究

以燃烧合成Ti3AlC2粉体为原料，研究了不同热压温度下Ti3AlC2粉体的热压烧结过程。实验结果表明，热压烧结Ti3AlC2粉体可得到Ti3AlC2致密块体陶瓷，Ti3AlC2粉体的热压烧结活性比直接使用Ti、Al（或Al4C3）和C为原料热压烧结的活性高，热压烧结温度以1400-1500℃之间为佳：烧结温度为1450℃，压力25MPa，Ar保护，保温2h的条件下，烧结Ti3AlC2粉体可得理论相对密度为99．05％，维氏硬度2．8GPa，抗弯强度426．02MPa，断裂韧性10．08MPa·m^1/2的烧结块体；烧结样品的密度和断裂韧性随烧结温度升高而增大，抗弯强度在高于1400℃时随热压温度升高而降低。     

原位热压合成Ti3AlC2/Al2O3复合材料的研究

以Ti,Al,TiC,TiO2粉末为原料,采用原位热压合成法制备了Ti3AlC2/Al2O3复合材料。主要考察不同Al2O3含量对复合材料性能的影响。在1400℃,30MPa压力,保温2h条件下烧结制得致密的Ti3AlC2/Al2O3块体材料。采用XRD分析了不同Al2O3含量的复合材料的相组成。用SEM观察组织结构特征。测量了维氏硬度和电导率同Al2O3含量的关系曲线。研究结果表明,Al2O3的加入可大幅度提高复合材的硬度。Ti3AlC2/25%Al2O3的维氏硬度可达8.7GPa。虽然添加Al2O3后复合材料的电导率有所下降,但Al2O3对复合材料强度和硬度的增加有显著的贡献。Ti3Al2C2/Al2O3乃不失为一种性能良好的高温结材材料。     

热压亚微米Al2O3＋TiC陶瓷复合材料的反应

用X－射线衍射仪（XRD）、示差扫描量热法（DSC）和示差热分析法（DTA）研究了3TiO3 3C 4Al→3TiC 2Al2O3的燃烧反应。这个放热燃烧反应是在大约1000℃时进行。在直接燃烧热压时液态Al和TiO2（或石墨）固体颗粒之间的低润湿性会产生一种不希望的不均匀的显微结构。在目前的研究工作中,3TiO2 3C 4Al→非晶体相（还没证实）＋Ti,（2）热压反应,非晶体相（还没证实）＋Ti→3TiC＋2Al2O3。在热压反应中约1000℃时,也可观察到突然收缩,因为在热压反应过程中,无液态的出现,就能生产出具有亚微米蛳粒和均匀显微结构的高性能的Al2O3 TiC陶瓷复合材料。     

热压烧结Ti3AlC2材料的制备、结构与性能研究

采用热压工艺研究了不同工艺制度和原料中不同的Si含量对Ti3AlC2合成的影响.研究表明在1 300℃～1 500℃,30MPa压力和Ar气氛中热压摩尔比为n(TiC)n(Ti)n(Al)n(Si)=2110.2的混合粉末,可以得到纯度达98%(质量分数)以上的致密块体Ti3AlC2材料;添加的Si均匀分布在基体中,形成固溶体,当添加Si的摩尔比为0.2时,固溶体的化学式为Ti2 76Al0 78Si0.22C2.烧结试样的晶体为层片状结构,1 300℃和1 400℃时,烧结试样的晶粒尺寸分别为10μm～15μm和20μm～30μm.材料的维氏硬度为3.3 GPa～5.0 GPa,弹性模量为289 GPa,抗压强度为785 MPa,抗弯强度为375 MPa,断裂韧性为7.0 MPa·m1/2;25℃时,电导率为3.1×106 S·m-1,热容为125.4 J/mol·K,热导率为27.5 W/m·K;热膨胀系数为8.8×10-6 K-1.     

添加TiC对燃烧合成Ti2AlC粉体的影响

实验表明，以Ti,Al和碳黑单质粉末为反应物原料，按Ti2AlC化学计量比为原料摩尔配比，得到的燃烧产物主晶相为Ti3AlC2，而Ti2AlC的含量很少。当保持总原料各组分配比不变，加入TiC时，燃烧产物中的Ti2AlC相却变为主晶相，而Ti3AlC2和TiC相的含量急剧减少。燃烧产物Ti2AlC相的含量随添加的TiC质量分数（0－25％）的增加而增加。从动力学和热力学的角度探讨了TiC对燃烧合成Ti2AlC的影响机理。     

TiC及Ti2C在铝结晶过程中的核心作用

将工业纯铝（９９．７％）用亚包晶成分的Ｔｉ（＜０．１５％）实行变质处理，采用电子衍射等方法研究其结晶核心，证明α－Ａｌ核心除ＴｉＣ粒子外，还存在Ｔｉ_２Ｃ。ＴｉＣ为立方晶格，ａ＝０．４３８０ｎｍ；Ｔｉ_２Ｃ为正交晶格，ａ＝１．２０ｎｍ，ｂ＝１．０６ｎｍ，ｃ＝１．５０ｎｍ     

Si掺杂放电等离子合成Ti2AlC/Ti3AlC2材料及理论分析

以Ti粉、Al粉、活性炭和Si粉为原料,采用放电等离子工艺分别以摩尔比为2.0Ti/1.1Al/1.0C、2.0Ti/1.0Al/0.1Si/1.0C、2.0Ti/1.0Al/0.2Si/1.0C、2.0Ti/0.9Al/0.2Si/1.0C和2.0Ti/1.0Al/0.3Si/1.0C,在1 200 ℃合成了Ti2AlC/Ti3AlC2块体材料.通过合成试样的X射线衍射谱,确定了放电等离子合成试样的物相组成,并用扫描电镜结合能谱仪观察了合成试样的显微结构和微区成分.结果表明:以2.0Ti/1.1Al/1.0C为原料放电等离子合成了层状结构明显的Ti2AlC材料;掺Si后所有试样都由Ti2AlC、Ti3AlC2和Ti3SiC2 3种物相组成;当掺Si量逐渐增大,即Al与Si的量比减小时,试样中Ti3AlC2和Ti3SiC2的含量增加,而Ti2AlC的含量降低,同时颗粒得到细化.应用量子化学计算结果解释了掺Si后不利于Ti2AlC的生成,而有利于Ti3AlC2的生成机理,说明了掺Si后固溶体的产生过程.     

Fabrication of monolithic bulk Ti3AlC2 and impurity measurement by K-value method

Polycrystalline bulk Ti3AlC2 material with high purity and density was fabricated by hot pressing from the powder mixture with the starting stoichiometric mole ratios of 2.0TiC/1.0Ti/1.1Al/0.1Si at 1 300-1 500 ℃. X-ray diffraction patterns and scanning electron microscopy photographs of the fully dense samples indicate that the proper addition of silicon is favorable to the formation of Ti3AlC2, consequently results in high purity of the prepared samples. The Ti3AlC2 hot pressed at 1 300 ℃ and 1 400 ℃ is in plane-shape with sizes of 6-8 μm and 15-20 μm in the elongated dimension, respectively. The purities of samples are measured by the K-value method, and the contents of TiC are given by a linear equation.     

Synthesis of Ti2AlC by hot pressing and its mechanical and electrical properties

Ti2AlC bulk material was synthesized by hot pressing of mixture powders of TiC, Ti, Al and active carbon. The phase compositions of resultant product at different temperature were detected by X-ray diffractometer. The microstructures of the samples were observed by SEM. Finally, the mechanical properties and thermal properties of the sample at 1 400 ℃ were measured. The results show that high purity Ti2AlC material with little Ti3AlC2 can be synthesized by hot pressing 0.5TIC/1.5Ti/1.0A1/0.5C at 1 400 ℃. Ti2AlC exhibits high mechanical properties and metallic electrical properties. Its fractm＇e toughness is 7.0 MPa·m^1/2, its flexural strength is 384 MPa at room temperature, and its electrical conductivity is 2.56 × 10^6 Ω^-1·m^-1 at room temperature.     

Synthesis of high-purity Ti2AlN ceramic by hot pressing

High-purity Ti2AIN ceramic was prepared at 1300℃ by hot pressing（HP） of Ti/Ai/TiN powders in stoichiometric proportion. The sintered product was characterized using X-ray diffraction（XRD） and MDI Jade 5.0 software （Materials Data Inc, Liverpool, CA）. Scanning electron microscopy（SEM） and electron probe micro-analysis（EPMA） coupled with energy-dispersive spectroscopy（EDS） were utilized to investigate the morphology characteristics. The results show that Ti2AIN phase is well-developed with a close and lamellar structure. The grains are plate-like with the size of 3-5 μm, thickness of 8-10 μm and elongated dimension. The density of Ti2AlN is measured to be 4.22 g/cm^3, which reaches 97.9% of its theory value. The distribution of Ti2AlN grains is homogeneous.     

新型层状Ti_3AlC_2陶瓷的制备及性能研究

采用热压烧结工艺,以Ti、Al、C、TiC粉末为原料制备了高密度的Ti3AlC2块体材料.用Archimedes法测定不同成分条件下合成试样的密度,用X射线衍射分析仪及扫描电镜分析材料的相组成和形貌,用维氏硬度计测试材料的硬度.结果表明,以TiC代替全部C和部分Ti时,材料的力学性能有了明显改善.Ti3AlC2陶瓷的微观结构为片层状,层状晶粒长度约为20 μm,硬度为3～5.0 GPa,抗拉强度为454.7 MPa,断裂韧度为5.60 MPa·m1/2.