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

1.将粒度为-100目和-325目的氢化钛粉末和粒径为32微米和3微米的雾化铝粉按化学计量混合后，在800 MPa下单轴压制成10 mm大小的立方体。在DTA曲线上，烧结体中的合成反应在放热峰之前开始。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。在包括反应温度的873-1173K范围内，放热峰越低，密度越高，5K/min的反应速率越慢。在低于或高于873-1173K的范围内，通过将速率提高到20K/min，可以缩短总工艺时间。在1703K保温60min后，TiAl是压坯中的主要相，气孔更圆，数量更少。细粉的组合均匀速度最快，尺寸变化最小，密度最高，最适合于机械零件。2.在单轴压缩压坯中，铝颗粒变形并移动到形状较不变形的硬质氢化钛颗粒之间的间隙中。由于氢化物在压实方向上更接近，所以在压坯中每单位长度两个氢化物之间的压坯在同一方向上比在垂直方向上的压坯数量多。在钛颗粒中的氢化物分解后，铝熔化并流入钛颗粒的边界，然后扩散到颗粒的核心，导致压坯膨胀。随后的烧结使颗粒更紧密地聚集在一起。这些机制使压实方向的膨胀和收缩都变大。

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.