Computer simulation of γ＇ and θ phase precipitation of Ni-Al-V alloy using microscopic phase-field method

The precipitation processes of γ‘ and θ phases in Ni75Al6.5 V18.5 alloy were simulated at different temperatures and the precipitation sequence of two phases and morphological evolution were investigated. The simulation demonstrates that the two phases precipitate simultaneously at high temperature and γ‘ phase precipitates earlier than θ phase at 1000 K and 1120 K. With the temperature decreasing, the velocity of precipitation quickens, the quantity of θ phase increases and the size reduces; but the volume fraction increases, the quantity of phase increases and the size reduces as well. The two phases nucleate and grow independently at high temperature and the θ phase precipitates from the boundaries of γ‘ phase at 1000 K and 1120 K. We also find that there are many kinds of domain boundaries between the same and different phases. The results of average deviation of composition and average absolute long range order parameter show that the ordering and compositional clustering of γ‘ phase happen simultaneously at high temperature, the congruent ordering occurs prior to spinodal decomposition at 1 000 K and 1 120 K and the ordering advances and quickens as the temperature decreases. Ordering and compositional clustering of θ phase occur simultaneously at each temperature and are quickened with temperature decreasing.     

Ni75Al5.5V19.5合金沉淀行为的微观相场模拟

利用微观相场方法模拟了Ni75Al5.5V19.5合金两种有序相D022和L12随温度变化时的不同沉淀过程.发现过冷度在相变驱动力中处于主导地位.高温下D022相首先析出,之后L1 2相在D022相和无序相的界面以及D022相形成的界面处析出,L1 2相长大时同时向无序基体和D022相推移;低温下L1 2相先析出,D022相在L1 2相的界面处形核长大,同时L1 2相通过失稳分解由非化学计量相向平衡相转变,其尺寸减小.该合金最终两相体积分数同时达到平衡并基本相等.随温度降低,L1 2相由高温时的非经典形核与失稳分解的混合机制向低温时的失稳分解转变;D022相的沉淀机制由非经典形核与失稳分解的混合机制向低温时的非经典形核转变.     

四近邻对势对Ni75Al5V20合金沉淀机制影响的微观相场模拟

利用微观相场动力学模型,研究了4近邻对势对Ni75Al5V20合金沉淀机制的影响.结果表明,不改变4近邻对势,DO22相和Ll2相沉淀机制均为失稳分解与非经典形核混合型机制.随Ni-Al4近邻对势V4Ni-Al向负值方向绝对值增大,Ll2相沉淀机制转变为失稳分解.随Ni-V4近邻对势V4Ni-V增大,DO22相沉淀机制转变为失稳分解,Ll2相转变为非经典形核机制,Ll2相中的Al浓度平衡值增大.随Al-V 4近邻对势V4Al-V向负值方向绝对值增大,对沉淀机制的影响趋势与V4Al-V增大类似;随V4Al-V向正值方向增大,与V4Al-V减小的影响类似.     

Effect of high temperature aging on microstructure and mechanical properties of a directionally solidified Ni3Al base alloy IC6A

1　ＩＮＴＲＯＤＵＣＴＩＯＮＴｈｅｄｉｒｅｃｔｉｏｎａｌｌｙｓｏｌｉｄｉｆｉｅｄＮｉ3ＡｌｂａｓｅａｌｌｏｙＩＣ6ＡｗｉｔｈｔｈｅｃｈｅｍｉｃａｌｃｏｍｐｏｓｉｔｉｏｎｏｆＮｉ (7.5～8.5 )Ａｌ (13.0～ 15 .0 )Ｍｏ (0 .0 2～ 0 .1)Ｂ (0 .0 0 5～0 .0 5 )Ｙ (ｍａｓｓｆｒａｃｔｉｏｎ ,% )ｈａｓｂｅｅｎｒｅｃｅｎｔｌｙｄｅｖｅｌ ｏｐｅｄｂａｓｅｄｏｎａｌｌｏｙＩＣ6ａｓａｈｉｇｈ ｔｅｍｐｅｒａｔｕｒｅｓｔｒｕｃ ｔｕｒａｌｍａｔｅｒｉａｌｕｓｅｄｆｏｒａｄｖａｎｃｅｄｊｅｔ ｅｎｇｉｎｅｖａｎｅｓｏｐ ｅｒ…     

Surface diffusivity of atomic deuterium on Ni3（Al,Ti）（110）surface with and without boron

1　ＩＮＴＲＯＤＵＣＴＩＯＮＩｔｉｓｗｅｌｌａｃｃｅｐｔｅｄｔｈａｔｍｏｉｓｔｕｒｅ ｉｎｄｕｃｅｄｅｍｂｒｉｔ ｔｌｅｍｅｎｔｉｓｔｈｅｍａｊｏｒｃａｕｓｅｏｆｔｈｅｌｏｗｄｕｃｔｉｌｉｔｙａｎｄｉｎ ｔｅｒｇｒａｎｕｌａｒｆａｉｌｕｒｅｏｆＮｉ3Ａｌａｎｄ     

MICROSCOPIC PHASE-FIELD SIMULATION COUPLED WITH ELASTIC STRAIN ENERGY FOR γ′(Ni3Al) PRICIPITATION IN Ni-Al ALLOY

基于微观相场动力学模型和微观弹性能理论,对Ni-Al合金中沉淀相Ni3Al(γ′)形貌演化、早期沉淀机制和后期粗化过程进行了原子层面的计算机模拟.结果表明:沉淀过程中γ′相形貌由早期随机分布的圆形或不规则状逐渐向方形转变,其排列的取向性也越来越明显,最后形成周边圆滑的长方块状颗粒,沿[10]和[01]弹性\"软\"方向规则排列.弹性应变能作用下的粗化过程遵循优先选择的原则,位于弹性\"软\"方向上的颗粒不断长大和粗化,位于弹性\"软\"方向外的颗粒逐渐消失,沉淀后期在基体中形成高度择优取向的微观组织.低浓度Ni-Al合金中γ′相的早期沉淀机制为非经典形核长大机制,其演化序列为:过饱和固溶体→非化学计量比有序相→化学计量比平衡γ′相→长大.