在直接式能量沉積(Direct Energy Deposition, DED)中，固液化條件和異質粉末材料將導致熔池內部擁有複雜的物理現象。熱力行為及質量傳遞過程皆會影響熔覆層之成形尺寸與微觀結構。在本研究中，建立異質材料直接式能量沉積之三維暫態數值模擬，其中包含粉末流以及雷射照射於金屬基板之燒熔情形，多相流使用流體體積法(Volume of fluid, VOF)計算空氣與金屬兩相，粉末流考慮以四軸噴嘴形式呈現之粉末高斯分布建立粉末沉積函數，以及粉末熱與雷射遮蔽率，熔池動態行為則考慮表面張力(Surface tension)、馬倫格尼力(Marangoni force)及固液化模型，其中固液化模型中利用粉末及基板材料之各別熔點，以質量分率將兩者進行混和。將上述考慮之動態行為除固液化模型外，以源項形式作用於自由液面表面上。
除異質模擬外，亦建立同質模擬與實驗數據比對成形尺寸及第二枝晶臂間距(SDAS)，由模擬結果得知，成形尺寸之異質與同質平均誤差分別為4.4 %及7.2 %， SDAS之平均誤差則分別為13.7 %與38.3 %，由此可見以異質模擬較同質模擬更為準確。分析馬倫格尼力對於表面切線速度之影響，發現雷射能量大小將影響馬倫格尼力，間接使得表面切線速度大小改變，導致熔池後方內部漩渦之渦度，隨著雷射能量增加而變大。針對濃度場之分析，由於熔池後方之漩渦將粉末濃度向後帶動，並在熔池邊緣速度減慢，使得較多的粉末質量沉澱於後方，因此在熔池初期，接合度(dilution)較大處，可以觀察到較明顯之擴散行為。利用溫度梯度G與凝固速度R隨高度變化之關係，發現當雷射能量越小，會得到溫度梯度越小且凝固速度越大之趨勢。另外在本研究中之dilution較小，故會得到較為平滑之固液化線。

In Direct Energy Deposition (DED), solidification conditions and dissimilar powder materials lead to complex physical phenomena inside the melt pool. Both the heat and mass transfer processes affect the molding size and microstructure of the cladding layer. This study establishes a three-dimensional transient numerical simulation of dissimilar material direct energy deposition, including the powder flow and the cladding model. The multiphase flow is calculated by the Volume of Fluid (VOF) method. The powder flow is considered to be a Gaussian distribution to establish the powder deposition function, as well as the powder heat and the laser shielding rate. In the dynamic behavior of the melt pool, the solidification model uses melting points which are mixed by the mass fraction of the powder and substrate material. Besides the solidification model, the dynamic behavior also considers the surface tension and Marangoni force.
In addition to the dissimilar material simulation, this study also establishes the homogenous material simulation to compare with the experimental measurement's geometry and the second dendrite arm spacing (SDAS). According to the dissimilar and similar simulation results, the average errors of the modeling size are 4.4 % and 7.2 %, and the average errors of dendrite are 13.7 % and 38.3 %, respectively, which shows that the dissimilar material simulation is more accurate than the similar material simulation. By analyzing the influence of the Marangoni force on the surface tangential velocity, we ascertained that the magnitude of the laser power will affect the Marangoni force, which will indirectly change the magnitude of the surface tangential velocity. This phenomenon result in a greater strength of the vortex behind the melt pool. For the analysis of the concentration field, the powder concentration is driven backward by the vortex behind the melt pool at locations with higher dilution. The velocity slows down at the edge of the melt pool, and hence that more powder mass is deposited in the rear. Using the relationship between the temperature gradient G and the solidification rate R with height, it is found out that the temperature gradient become weaker as the laser power decrease, and vice versa for the solidification rate become stronger. In addition, the dilution in this study is small such that a smoother solidus line can be obtained.

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