Concentration Heterogeneity in Structure of Ni3Al Intermetallic Synthesized under Compression

By X-ray analysis,TEM and SEM methods the phase composition,microstructure,and deviation from stoichiometric composition were investigated for the Ni3Al intermetallic compound obtained by cast and self-propagation high-temperature synthesis under compression with followed homogenization anneal,with the Al concentration being 24.0 and 25.0 at.pct with and without B(0.5 at.pct).It was discovered that in SHS intermetallic alloys an average local deviation from stoichiometric composition is significantly more than in the cast alloy.Dependence of the local deviation from the stoichiometric composition on the distance has a zig zag nature at the level of the grain groups.Deviation from the stoichiometric composition at the boundaries of the general type is less than at the boundaries of the special type.When the intensity of boundary migrations of the general type decreases,the degree of deviation from the stoichiometric composition increases.There in correlation between the solubility of B in the crystalline lattice of the Ni3Al phase and the value of the deviation from the stoichiometric composition in the grains.When the B concentration in a solid solution increases,the deviation from stoichiometric composition decreases.     

自蔓延高温合成TiC—Al2O3—Fe系金属陶瓷的致密化研究

采用ＳＨＳ／ＰＨＩＰ工艺制备了致密的ＴｉＣ－Ａｌ２Ｏ３－Ｆｅ系金属陶瓷，研究了延迟时间，高压特续时间，压力及Ｆｅ含量对合成ＴｉＣ－Ａｌ２Ｏ３－Ｆｅ金属陶瓷实度的影响，结果表明，采用ＳＨＳ／ＰＨＩＰ技术制备了ＴｉＣ－Ａｌ２Ｏ３－Ｆｅ系金属陶瓷时，合成产物中气体的排放，液相的存在及组成相之间的润湿性是制备密实材料的关键。     

INVESTIGATION ON SELF-PROPAGATING HIGH-TEMPERATURE SYNTHESIS OF TiAl INTERMETALLIC COMPOUND

The self-propagating high-temperature syn-thesis method was used to synthesize the TiAl intermetalliccompound,and two kinds of synthesis modes were studied inthis paper.The results show that the thermal explosion modeis suitable for the synthesis of TiAI,the pre-heating tempera-ture has a great influence on the synthesis.Microstructurestudy show that the density of the sample fabricated by thermal explosion mode is higher than that fabricated by propa-gating mode.     

SHS quenching as a route to bulk glassy Fe<Subscript>34</Subscript>Co<Subscript>34</Subscript>B<Subscript>10</Subscript>Si<Subscript>14</Subscript>Nb<Subscript>8</Subscript> alloys

The method of SHS quenching combined with dynamic annealing was used to prepare bulk amorphous metallic glass alloys Fe₃₄Co₃₄B₁₀Si₁₄Nb₈ in a two-stage process. The structural properties and microstructure of thus prepared materials were found to be close to those produced by other methods, such as melting-injection-molding and melt spinning.      

Al含量对热爆反应合成Al／TiC复合材料的影响

本文利用热爆反应合成法制备了Ａｌ／ＴｉＣ复合材料，研究了反应合成过程中，温度特性以及Ａｌ含量对其的影响，结果表现：在反应合成过程中的Ａｌ的熔化，然后是陶瓷相的合成反应，并且随着Ａｌ含量的增加，反应最高温度降低，而反应起始温度和反应持续时间基本不变。此外，研究了Ａｌ含量对反应生成 影响。     

毛坯生产新技术－近终成形

微电弧熔炼成形、电渣转注成形、喷射沉积成形、金属泥成形、电磁铸造成形及自蔓延成形等冶金新技术相继发展，形成材料制备科学的新分支──近终成形技术。目前近终成形正处于发展阶段，其领域的边界尚不分明，但毫无疑问它将是２１世纪金属毛坯生产的新方向。     

自蔓延高温合成技术新进展

介绍了自蔓延高温合成（SHS）技术的发展和国内外研究概况，包括制备工艺、应用领域等。分析了自蔓延高温合成技术的最新研究动向。     

Synthesis of β-SiAlON: A combined method using sol–gel and SHS processes

β-SiAlON has been prepared by a SHS reaction performed under high nitrogen pressure on a compacted mixture of silicon and mullite. In order to optimise this reaction, the solid mixture was prepared from a liquid solution in which the mullite (2SiO₂-3Al₂O₃) was formed by a sol–gel process. The SHS samples were characterized by using Scanning Electron Microscopy (SEM) and X-ray diffraction. A Rietveld refinement performed on the recorded diffractograms revealed a very high formation rate of β-SiAlON (more than 80 wt%) when the reaction was carried out under low nitrogen pressure. From the whole of our results, a mechanism of β-SiAlON formation has been suggested.     

Combustion synthesis of SOFC materials in a continuous reactor

La_0.8Sr_0.2CrO₃ and LaMg_0.2Cr_0.8O₃ materials for use in solid oxide fuel cells (SOFCs) were synthesized in a continuous SHS reactor from powder mixtures of La₂O₃, MgO, SrCO₃, Cr₂O₃, and Cr. Based on XRD data, the degree of conversion was found to grow with increasing combustion temperature and burning velocity. SHS-produced powders were reground in a vibratory mill, pressed into cylindrical pellets (3–4 mm in height and 10 mm in diameter), and sintered. The required level of properties was attained for sintering temperatures above 1600°C. The article is published in the original.     

Thermal explosion in mechanoactivated 3Ni + Al mixtures

Explored was thermal explosion in mechanoactivated 3Ni + Al mixtures. Mechanoactivation was found to result in an abnormal decrease in the effective activation energy E and ignition temperature T_ign for thermal explosion. Analysis of reaction thermogram allowed us to find out the kinetic function. Mechanoactivation conditions for synthesis of Ni₃Al in thermal explosion mode have been optimized. SHS reaction in 3Ni + Al mixtures mechanoactivated for 180 s was found to obey the first-order kinetics.