定向凝固Al-Mn-Be合金初生金屬間化合物相生長行為及力學(xué)性能

定向凝固Al-Mn-Be合金初生金屬間化合物相生長行為及力學(xué)性能GROWTH BEHAVIOR OF PRIMARY INTERMETALLIC PHASES AND MECHANICAL PROPERTIES FOR DIRECTIONALLY SOLIDIFIED AI-MN-BE ALLOY

對Al-3Mn-7Be合金（原子分數(shù)，%）在1~1500 μm/s的抽拉速率下進行定向凝固實驗，研究了抽拉速率對合金組織演化、金屬間化合物形貌演變和合金力學(xué)性能等的影響規(guī)律。結(jié)果表明，Be元素的加入使二元相圖向高Mn區(qū)移動，引入了金屬間化合物λ相、T相、Be4AlMn和準晶I相，而且Be的加入明顯細化了合金的組織。隨著抽拉速率的增加，固/液界面過冷度和溶質(zhì)過飽和度增加，引起初生金屬間化合物相的競爭生長，初生相先由λ相轉(zhuǎn)變?yōu)門相，后轉(zhuǎn)變?yōu)闇示相，伴隨著形成初生Be4AlMn相。同時，初生相的形貌、尺寸和生長方式也隨抽拉速率的增加而發(fā)生改變。隨著抽拉速率的增加，定向凝固合金的強度先下降后提高，在抽拉速率較低和較高時，定向凝固合金均呈現(xiàn)了較大延伸率，這主要由其定向凝固組織、強化相的種類、形貌以及與基體構(gòu)成的界面結(jié)構(gòu)決定。

Intermetallic compounds (including quasicrystals) have been widely employed as reinforced phases in many alloys due to their high strength, high hardness and good thermal stability. The growth behavior and growth pattern of these intermetallic compounds affect the mechanical properties of materials significantly. However, the intermetallic compound, which exhibits complex crystal structures and directional bonding usually shows a faceted growth pattern with strong anisotropy and forms crystals with a wide range of morphologies and coarse grains during solidification. The inappropriate morphology and size of the intermetallic compound will destroy the integrity of the matrix and thus deteriorate the mechanical properties of materials. In this work, the microstructural evolution, morphology evolution of intermetallic compounds and mechanical properties have been investigated in directionally solidified Al-3Mn-7Be (at.%) alloy with a wide pulling rates of 1~1500 μm/s. The addition of Be results in the shift of Al-Mn binary phase diagram toward the Mn-rich side, the appearance of intermetallic compounds, namely λ-phase, T-phase, Be4AlMn, and icosahedral quasicrystal (I-phase) and significantly refines the microstructures of the as-cast and directionally solidified samples. With increasing pulling rates, a transition of primary phase is observed from λ-phase to T-phase, and then I-phase, accompanied by the formation of the primary Be4AlMn phase, which can be attributed to the increase of supersaturation and supercooling near the solid/liquid interface. Meanwhile, the morphology, size and growth pattern of primary phases vary with the increase of pulling rates. The mechanical properties of directionally solidified Al-3Mn-7Be (at.%) alloy have been investigated. It is indicated that the room-temperature strength of this alloy decreases first and then increases as the pulling rates increase, and a larger elongation is presented at the lowest and highest pulling rates, which can be attributed to the microstructures of alloys, properties of strengthening phases and the interfaces between matrix and strengthening phase.

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