| 12Cr-ODS Fe-based superalloy was a new type composite in which oxide dispersed strengthen (ODS) technology was used and was evolved from the convential refractory steel and Fe-based superalloy. It could be a considerable material applicated in fusion reator, astronavigation, aviation and gas tubine, etc. In this paper,12Cr-ODS alloyed powders was fabricated by Mechanical Alloying through elemental powders, and on this base 12Cr-ODS sintered body was obtained by mould die pressing, vaccum sintering and hot insostatic pressing. X-ray diffraction(XRD), scanning electron microscope(SEM), energy dispersed X-ray detectior(EDX), Transmission electron microscope(TEM) and other properties testers were used to study the effects of parameters of Mechanical Alloying on characteristics of alloyed powders and the effects of parameters of pressure and sintering on the properties and micstructure of sintered alloy. The oxidation behavior was observed and the dynamic equation and thermoldynamics mechanism were also analyzed.This paper firstly summarized the principle and characteristics of Oxide Dispersion Strengthened technology and mechanical alloying. Then a detailed overview about development and application of both iron based and oxides dispersion strengthened iron based superalloy were exhibited. In addition, oxidation mechanism of metal materials was also introduced. Based on all above, the objective, the significance, content and technical route of the research were proposed.Effects of Mechanical alloying parameters on characteristics of Nanocrystalline Fe-Cr-W-Ti-Y2O3 powders, including alloying degree, grain size, microhardness and morphology had been systematically investigated in this paper. The results showed the particles size was decreased and the distribution was more homogenenous with the elongation of milling duration. The shape of particle was transform to equiaxed from flakelike. The size of particle was less than 20μm after 48h milling. More milling duration also lead to higher alloying extent, finer grain size, increase of lattice distortion and O content. The value were 9.14nm,0.7059%,0.96%,612.5HV, respectively. Elevated milling rotation would decrease the average size of particles and higher alloying extent. The addition of 1 wt%～3wt%SA or 5vol% alcohol would decrease the particle size, while 5vol% have no obvious effect, but all Process control agents could inhibit the alloying process. The enhancement of Ball Powder Ration would lead the decrease of particle size, but increase the contamination and decrease the powder yield.A0, A2 and A50 powders, distingwished by the ways of adding SA were fabricated. A2 and A50 sintered body were obtained in this paper. The result showed it effeced the properties and microstructure of alloys obviously. A2 powders exhibited a relatively equiaxed particle morphology and more uniform distribution of particle size than A50 powders, from which flakelike particles were found. However, the surface of A50 powders particle were smoother than that of A2. A50 have not reached alloying completely, while the composition of A2 powder was close to the design one. The oxidation of A50 in the heating was obvious, while the mass of A2 was lessened in the heating, which indicated the SA was volatilized completely. The relatively density and bending strength of compact increased with the increase of pressing pressure. The value was 6.41g/cm3 and 137.5MPa, respectively.The main phase in A2 and A50 alloys were both Fe-Cr, and the microstructure was consist of ferritic and the second phase. The second phase in A50 appeared banding and the size could reach 25μm, while that of A2 was equaxied and the size was approximately 3μm. The grain size of A50 and A2 were approximately 20μm and 5～10μm, respectively. The strength of A2 was higher than that of A50 given the same temperature. The strength of A50 was increased with the elevation of sintering temperature and reached 352.1MPa when 1400℃, while that of A2 reached a peak at 1380℃according to the value 521.4MPa.A2 alloy sintered at 1380℃have been strengthened by HIP, after which the tensile strength reached 1054MPa. It was much higher than that of alloy before HIP, but the ductility was decreased. The tensile strength of AO alloy fabricated by HIP reached 1101MPa, and the elongation was only 3.7%, the way of crack appeared brittle fracture. Two kinds of phase were observed in the alloy, one was phase rich in Cr, Ti and O, and the other one was complicated nano-compound riched in Ti-Y-O.This paper investigated the oxidation behavior of A2 and A50 at high temperature, and the results showed that the oxidation extent was increased as the elongation of oxidation time and elevation of oxidation temperature. The oxidation dynamic equation of A50 at 600℃and 800℃was (ΔW)]1.84=7.13t and (ΔW)3.98=3.27t respectively. The oxidation dynamic equation of A2 at 800℃was (AW)1.67=4.04t. The oxide film of A2 oxidated after 24h was dense double structure. The inner one was consist of most Cr2O3 and less Fe2O3 and WO3, while the outer one was mainly consist of Fe2O3. |
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