Combustion Synthesis and Sintering of TiAl Intermetallic Compounds and Net Shape Manufacturing of Machine Parts.

1. 将粒径为-100目和-325目的氢化钛粉与粒径为32目和3微米的雾化铝粉进行化学计量混合，在800MPa下单轴压实成10mm大小的立方体。在DTA曲线上，烧结过程中的合成反应开始于放热峰之前。超过峰值温度后，铝颗粒的熔化在短时间内降低了烧结密度。当速率为5K/min时，放热峰较低，密度较高，例如在873-1173K范围内（包括反应温度）。在低于或高于873-1173K的范围内，通过将速率提高到20 K/min，可以缩短总工艺时间。在1703 K下保温60min后，TiAl相为致密物的主要相，气孔呈圆形，气孔数量较少。较细粉末的组合可实现最快的均质化，最小的尺寸变化和最高的密度，最适用于机械零件。在单轴压紧的压块中，铝颗粒变形并移动到坚硬的氢化钛颗粒之间的间隙中，而氢化钛颗粒具有相当不变形的形状。由于氢化物更趋向于紧化方向，同一方向上单位长度氢化物间的紧化数要大于垂直方向上的紧化数。钛颗粒中的氢化物分解后，铝熔化并流入钛颗粒边界，然后扩散到颗粒的核心，引起致密体的膨胀。随后的烧结使颗粒更紧密地聚集在一起。这些机制使膨胀和收缩在压实方向上都变大。

1. Titanium hydride powders with particle sizes-100 and -325 mesh and atomized aluminum powders with particle diameters of 32 and 3 micrometers are mixed stoichiometricly and compacted uniaxially under 800MPa into cubes 10mm in size. The synthesizing reaction in the compact during sintering starts prior to the exothermic peak in a DTA curve. Beyond the peak temperature, the melting of aluminum particles decreases the sintered density in a short time. The exothermic peak is lower and the density higher with the slower rate 5K/min for example in the range 873-1173K which includes reaction temperatures. Total process time is shortened by increasing the rate to 20 K/min in ranges lower or higher than the 873-1173K range. After holding at 1703 K for 60min, TiAl is the major phase in the compact, with pores more round-shaped and less in number. The combination of the finer powders results in the fastest homogenization, the least dimensional change and the highest density, and is most suitable for machine parts.2.In a uniaxially-pressed compact, aluminum particles deform and move into gaps between the hard titanium hydride particles which have rather non-deformed shapes. Since the hydrides approach more in the compacting direction, the number of the compacts between two of them per unit length in the compact is larger in the same direction than in the perpendicular ones. After the decomposition of the hydrides in the titanium particles, The aluminum melts and flows into the titanium particle boundaries, and then diffuses into the cores of the particles causing the expansion of the compact. The subsequent sintering brings the particles closer together. These mechanisms make both the expansion and the shrinkage larger in the compacting direction.