Study on the Mechanism of Enhanced Reactivity by Mechanical Alloying

1.反应体系：机械合金化反应活性与M (Zr, Ti, Nb, Ni, Al) -庚烷和Ti-陶瓷（Si_3N_4, SiC）体系的铣削过程中储存的能量有关。揭示了贮存能量与反应量之间的关系。观察到潜伏期和阈值蓄能的存在。反应过程：对反应产物进行x射线衍射和DSC分析。对于ti和zr -庚烷体系，在反应初期，反应相是亚稳态的，随温度的变化是可逆的。中间相可能是由庚烷分解产物H和C原子稳定的层错。用热解吸光谱研究了H原子的晶格位置，揭示了hcp Zr和bcc Nb的差异。研磨后粉末的烧结性能和烧结材料的微观结构：与传统的陶瓷或金属间化合物粉末相比，通过反应使研磨后的粒度细化了约一个数量级，从而提高了烧结性能。制备了晶粒尺寸约为100nm的ti - ti_4al_2c_2和TiN-Ti硅化物复合材料。烧结材料的力学性能：高温拉伸试验表明，在1000℃和1500℃下，ti - ti_4al_2c_2和TiN-Ti硅化物复合材料的伸长率分别高达400%和100%。从流变应力的应变速率依赖性出发，确定了合金的超塑性行为。

1.Reaction Systems : Reactivity at mechanical alloying has been related with the energy stored during milling for M (Zr, Ti, Nb, Ni, Al) -heptane and Ti-ceramics (Si_3N_4, SiC) systems. Correlation between the stored energy and the reacted quantity was revealed. Existence of the incubation period and threshold stored energy was observed.2.Reaction Process : The reaction products were examined by X-ray diffraction and DSC analyzes. For Ti-and Zr-heptane systems, at the early stage of reaction, the reaction phases are metastable that endure reversible change with temperature. The intermediate phases are likely the stacking faults stabilized by H and C atoms which are decomposition products of heptane. The lattice site of H atoms was investigated with thermal desorption spectroscopy and the difference between hcp Zr and bcc Nb was revealed.3.Sinterbility of the Milled Powders and Microstructures of the Sintered Materials : The particle size after milling was found to be refined about one order by the reaction resulting in improved sinterbility compared with conventional powders of ceramics or intermetallic compounds. Fine composites of TiAl-Ti_4Al_2C_2 and TiN-Ti silicides with the grain size of about 100nm were obtained.4.Mechanical Properties of the Sintered Materials : Tensile tests at elevated temperatures demonstrated elongation up to 400% at 1000C and 100% at 1500C for TiAl-Ti_4Al_2C_2 and TiN-Ti silicide composites, respectively. From the strain rate dependence of the flow stress, superplastic behaviors were confirmed.