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生長速度對定向凝固Ti-46Al-8Nb合金微觀組織及其硬度的影響
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更新時間：2015-09-14
在一定的溫度梯度下，采用Bridgman定向凝固爐對Ti-46Al-8Nb合金進行不同抽拉速度(3~70 μm/s)的定向凝固實驗。研究定向凝固過程中的相變過程、微觀組織以及微觀偏析情況，并測量枝晶間距λ、層片間距λL和維氏硬度HV隨凝固條件的變化規(guī)律。
生長速度對定向凝固Ti-46Al-8Nb合金微觀組織及其硬度的影響Effect of growth rate on microstructures and hardness in directionally solidified Ti-46Al-8Nb alloy
在一定的溫度梯度下，采用Bridgman定向凝固爐對Ti-46Al-8Nb合金進行不同抽拉速度(3~70 μm/s)的定向凝固實驗。研究定向凝固過程中的相變過程、微觀組織以及微觀偏析情況，并測量枝晶間距λ、層片間距λL和維氏硬度HV隨凝固條件的變化規(guī)律。結(jié)果表明：在生長速度范圍內(nèi)，初生相為β相，凝固過程中發(fā)生包晶反應，最終得到α2/γ層片結(jié)構(gòu)和B2相的組織。包晶反應導致較大的偏析，其中Al在枝晶間富集而Nb在枝晶心部富集。另外，隨著生長速度的增加，枝晶間距以及層片間距逐漸減小，并且分別遵從λ=719.88v-0.21和λL=2.86v-0.25關(guān)系。而其維氏硬度隨著生長速度的增加而增加，這是由于高的生長速度對應較大的過冷度，使層片組織細化，硬度值升高，其線性擬合函數(shù)式為HV=300.2v0.08。并將所得數(shù)據(jù)與先前的實驗結(jié)果進行對比和分析。
Ti-46Al-8Nb alloy was studied in directional solidification experiments at different growth rates (3-70 μm/s) using a Bridgman type directional solidification furnace at a constant temperature gradient. The phase transition, microstructure and microsegregation were investigated during the directional solidification, and the evolution of cellular spacing (λ), lamellar spacing (λL) and Vickers hardness with the growth rate were measured. The results show that, at the selected growth rates the growth of primary β phase accompanied with the peritectic reaction is observed, and the final microstructure is composed of a2/g lamellar structure and B2 phase. The peritectic reaction leads to the distribution of solute inhomogeneous severely, in which Al is rich in the interdendritic region and Nb is rich in the core of the dendrite. Additionally it is obtained that the cellular spacing and the lamellar spacing decreased with the increase of the growth rate in the selected growth rates according to the relationship of λ=719.88v-0.21?and λL=2.86v-0.25, respectively. While the values of Vickers hardness HV?increase with the increase of the growth rate according to the relationship of HV=300.2v0.08, which could be attributed to the fined lamellar structure due to the high undercooling. The results obtained above were compared with the previous results in this work.
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