Numerical Simulation of Transport Phenomena for a Double-Layer Laser Powder Deposition of Single-Crystal Superalloy
Numerical Simulation of Transport Phenomena for a Double-Layer Laser Powder Deposition of Single-Crystal Superalloy
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DOI：
10.1007/s11661-013-2178-9
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发表时间：
2014-04-01
影响因子：
2.8
通讯作者：
Qi, Huan
中科院分区：
文献类型：
--
作者：
Liu, Zhaoyang;Qi, Huan
单晶高温合金涡轮叶片已广泛应用于燃气轮机和航空发动机中。作为一种有效的修复技术，激光粉末沉积修复涡轮叶片磨损叶片尖端具有近净成形能力和高度可控的凝固组织。成功的单晶合金叶片修复技术需要沿衬底材料的晶体取向与新沉积的层相同的方向连续外延生长晶粒。本文提出了一个三维数值模型来模拟多层同轴激光粉末沉积过程中的输运现象。为了验证模拟结果，在镍基定向凝固合金GTD 111的定向凝固衬底上沉积了镍基单晶高温合金Rene N5粉末。研究了激光功率、扫描速度和送粉速度等工艺参数对熔池温度场、速度场、熔池几何尺寸和连续层重熔比的影响。数值模拟结果表明，由于熔敷几何形状的散热能力降低，熔池的最高温度逐层升高，从而增加了熔池尺寸和后续熔敷层处的流体流动速度。模拟结果与实验结果吻合较好。在第二层的沉积过程中，第一沉积层的大部分可重熔到珠子高度的85%。扫描速度的提高降低了温度梯度/凝固速度的比值，导致前一层熔覆层顶面附近的非定向晶的高度比增大。结果表明，模拟和实验中所采用的工艺参数可以产生比S取向不均的晶高比R大的重熔比，从而使所有取向不均的晶得以重熔，并保证了单晶合金多层沉积过程中衬底定向凝固晶体取向的连续生长。
A turbine blade made of single-crystal superalloys has been commonly used in gas turbine and aero engines. As an effective repair technology, laser powder deposition has been implemented to restore the worn turbine blade tips with a near-net shape capability and highly controllable solidified microstructure. Successful blade repair technology for single-crystal alloys requires a continuous epitaxial grain growth in the same direction of the crystalline orientation of the substrate material to the newly deposited layers. This work presents a three-dimensional numerical model to simulate the transport phenomena for a multilayer coaxial laser powder deposition process. Nickel-based single-crystal superalloy Rene N5 powder is deposited on a directional solidified substrate made of nickel-based directional-solidified alloy GTD 111 to verify the simulation results. The effects of processing parameters including laser power, scanning speed, and powder feeding rate on the resultant temperature field, fluid velocity field, molten pool geometric sizes, and the successive layer remelting ratios are studied. Numerical simulation results show that the maximum temperature of molten pool increases over layers due to the reduced heat dissipation capacity of the deposited geometry, which results in an increased molten pool size and fluid flow velocity at the successive deposited layer. The deposited bead geometry agrees well between the simulation and the experimental results. A large part of the first deposition layer, up to 85 pct of bead height, can be remelted during the deposition of the second layer. The increase of scanning speed decreases the ratio of G/V (temperature gradient/solidification velocity), leading to an increased height ratio of the misoriented grain near the top surface of the previous deposited layer. It is shown that the processing parameters used in the simulation and experiment can produce a remelting ratio R larger than the misoriented grain height ratio S, which enables remelting of all the misoriented grains and guarantees a continuous growth of the substrate directional-solidified crystalline orientation during the multilayer deposition of single-crystal alloys.