位錯對Ti-6Al-4V合金α相形核及微織構(gòu)形成的影響

位錯對Ti-6Al-4V合金α相形核及微織構(gòu)形成的影響INFLUENCES OF DISLOCATIONS ON NUCLEATION AND MICRO-TEXTURE FORMATION OF α PHASE IN Ti-6Al-4V ALLOY

借助 Willis-Steeds-Lothe 方法計算了單根長直刃型與螺型位錯應力場, 并采用相場動力學方法模擬了含位錯 Ti-6Al-4V 合金中 β→α 轉(zhuǎn)變過程, 探索長直位錯應力場下共格 α 相的形核及對微織構(gòu)形成的影響.研究表明, 刃型位錯應力場與擇優(yōu) α 變體間相互作用能中, 正應力分量 S33起主要作用; 螺型位錯時切應力分量 S23作用最大.刃型位錯應力場對 α 變體選擇的作用要強于螺型位錯.刃型位錯下?lián)駜?yōu)變體以 V1 與 V7 為主, 螺型位錯時以變體 V7, V10 及 V12 為主, 且 V1/V7, V1/V4/V6 是刃型位錯下主要出現(xiàn)的變體組合類型, 而螺型位錯時則以 V7/V10/V12 組合為主.含位錯體系的微觀組織由位錯應力場與 α 變體之間相互作用能, 以及 α 變體之間彈性相互作用能共同決定.位錯周圍的應力場可導致界面能較高的界面類型出現(xiàn).

Titanium alloys are widely applied in aerospace, chemical and other related industries. The α+β alloys may obtain various microstructures and mechanical properties simply by varying their thermomechanical processing. Ti-6Al-4V alloy is the most common α+β titanium alloy. Its strength, ductility, fracture toughness and fatigue properties depend strongly on the microstructure especially texture. The understanding of the formation mechanisms of α micro-texture during processing is necessary for the optimization of the mechanical properties. In this work, the nucleation of α precipitates and micro-texture formation process under the influence of dislocations during the β→α transformation in Ti-6Al-4V alloy was simulated by phase field method. The stress field of an infinite straight dislocation was calculated by Willis-Steeds-Lothe method and used as input of the phase field model. It was shown that the normal stress component S33 plays a dominant role in α variants nucleation in the presence of edge dislocation, while the shear stress component S23 is the most important one for screw dislocation. The effect of edge dislocation on α variant selection is generally stronger than that of screw. V1 and V7 are the main variants selected by the edge dislocation while V7, V10 and V12 dominate around the screw dislocation, with V1/V7, V1/V4/V6 being the main variant cluster types around the edge dislocation, and V7/V10/V12 being the primary one for the screw dislocation. In a system with the presence of dislocations in the parent phase, the precipitate microstructure is determined by the combined effect of elastic interactions between the dislocation and different variants of a low symmetry precipitate phase, and elastic interactions among different variants. Variants with interfaces of relatively high energy may appear because of variants selection by dislocations.

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