氮化硅结合氮化硅铁在氮气气氛下的高温稳定性

Stability of Si_3N_4 Bonded Fe_3Si–Si_3N_4 at High Temperature in N_2 Atmosphere

以硅粉和氮化硅铁颗粒为原料,经高纯氮气气氛下烧结,制备出氮化硅/氮化硅铁复合材料。将氮化硅/氮化硅铁复合材料试样分别在1 500、1 600、1 700℃氮气气氛下重烧,探究其高温稳定性。结果表明:当重烧温度为1 500℃时试样中存在的物相有β-Si_3N_4、α-Si_3N_4、Si_2N_2O、SiC以及Fe3Si;当重烧温度达到1 600℃时,β-Si_3N_4含量增加,Fe_3Si、Fe_5Si_3、FeSi_3种硅铁合金共存,α-Si_3N_4、Si_2N_2O消失;当重烧温度上升到1 700℃时,β-Si_3N_4含量显著下降并重新出现α-Si_3N_4,Fe_5Si_3和FeSi相共存,Fe_3Si相消失。结合热力学计算推断反应机理为:当重烧温度从1 500℃上升到1 600℃时,α-Si_3N_4、Fe–Si熔体中的Si以及Si_2N_2O均向β-Si_3N_4转变,导致β-Si_3N_4含量增加。当重烧温度上升到1 700℃过程中,熔融硅铁的存在加速了Si_3N_4的分解,导致β-Si_3N_4含量减少;试样冷却过程中,Si(l)、Si(g)将重新氮化形成氮化硅,使α-Si_3N_4重新出现。SiC在较高的温度下比Si_3N_4稳定,其反应的C源为结合剂中的残C,以及气氛中的CO。随温度升高,复合材料中Fe–Si合金的稳定顺序依次为:Fe3Si→Fe_5Si_3→FeSi。

Si3N4 reaction-boned Fe3 Si–Si3N4 composites were prepared in nitrogen atmosphere using Si and Fe3Si–Si3N4 powders as raw materials. The samples were re-sintered in N2 atmosphere at 1 500, 1 600, and 1 700 ℃, respectively, to explore the high-temperature stability of the material. The phase compositions and microstructures were characterized by X-ray diffraction and scanning electron microscopy. The results show that the main phases are β-Si3N4, α-Si3N4, Si2N2O, SiC and Fe3Si for the specimen re-sintered at 1 500 ℃. The content of β-Si3N4 increases, three kinds of antacirons（Fe3Si,Fe5Si3 and FeSi） coexist, α-Si3N4 and Si2N2O disappear when the re-sintered temperature increases to 1 600 ℃. As the re-sintered temperature increases to 1 700 ℃, the content of β-Si3N4 decreases significantly, the α-Si3N4 reappear, and the antacirons contain only Fe5Si3 and Fe Si. The reaction mechanism can be deduced. As the re-sintered temperature increases from 1 500 to 1 600 ℃, α-Si3N4, Si in the liquid Fe–Si alloy and Si2N2O transform to β-Si3N4. As the re-sintered temperature increases to 1 700 ℃, the melted antacirons accelerate the decomposion of Si3N4, leading to the decrease of β-Si3N4. α-Si3N4 is formed during the cooling process due to the reactions between Si（l,g） and N2. SiC is more stable than Si3N4 at elevated temperatures. The carbon source for SiC is residual carbon from dextrin. The stable phase of Fe–Si alloy in the composite is Fe3Si→Fe5Si3→Fe Si when with the temperature increases.