Synthesis of iron aluminides from elemental powders: Reaction mechanisms and densification behavior
Synthesis of iron aluminides from elemental powders: Reaction mechanisms and densification behavior
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DOI：
10.1007/bf02656797
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发表时间：
1991-02
期刊：
影响因子：
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通讯作者：
B. Rabin;R. Wright
中科院分区：
文献类型：
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作者：
B. Rabin;R. Wright
对 Fe-15.8 wt pct Al 和 Fe-32 wt pct Al 元素粉末压块进行无压烧结和热压实验，分别大致对应于化学计量的 Fe3Al 和 FeAl 的组成。当加热到铝熔点附近时，压块中引发放热反应，从而合成所需化合物，反应时间为秒级。热分析和微观结构观察表明在快速放热致密加热过程中形成了瞬态液相。所显示的微观结构发展的机制包括固态的初始化合物形成、在铝颗粒位点处出现富铝液体、伴随液体向外扩散的铁溶解以及随后富铁化合物的沉淀。根据反应温度测量估计，Fe3Al 和 FeAl 的表观形成焓 ΔHf°(298) 分别为 -18 和 -31.8 kJ/mol。研究了真空常压反应烧结的加热速率、生坯密度和铝颗粒尺寸对烧结密度的影响。加工变量对致密化的影响被解释为加热过程中膨胀和随后由于瞬态液相而收缩的最终结果。通过在热压反应过程中施加接近 70 MPa 的外部压力，获得了接近全密度的 Fe3Al 和 FeAl 化合物。这些合金是部分有序的、化学均匀的，并且呈现出平均晶粒尺寸低于10μm的等轴晶结构。 Fe3Al 材料比相同成分的粗晶变形材料表现出明显更高的断裂强度和稍低的延展性。
Pressureless sintering and hot pressing experiments were conducted on elemental powder compacts of Fe-15.8 wt pct Al and Fe-32 wt pct Al, corresponding approximately to the compositions of stoichiometric Fe3Al and FeAl, respectively. Upon heating near the melting point of aluminum, an exothermic reaction was initiated in the compacts, resulting in synthesis of the desired compounds with reaction times on the order of seconds. Thermal analysis and microstructural observations indicate the formation of a transient liquid phase during rapid exothermic compact heating. The mechanisms shown to be responsible for microstructural development include initial compound formation in the solid state, appearance of an aluminum-rich liquid at the aluminum particle sites, iron dissolution accompanied by outward spreading of the liquid, and subsequent precipitation of the iron-rich compounds. Apparent enthalpies of formation,ΔHf°(298), estimated from reaction temperature measurements were −18 and −31.8 kJ/mol for Fe3Al and FeAl, respectively. The influences of heating rate, green density, and aluminum particle size on sintered density were studied for pressureless reaction sintering in vacuum. The effects of processing variables on densification were explained as the net result of swelling during heating and subsequent shrinkage due to the transient liquid phase. Near full density Fe3Al and FeAl compounds were obtained through the application of external pressures near 70 MPa during reaction in a hot press. These alloys were partially ordered, chemically homogeneous, and exhibited an equiaxed grain structure with an average grain size below 10μm. The Fe3Al material exhibited significantly higher fracture strength and somewhat lower ductility than coarse-grained wrought material of the same composition.