PSI - Issue 56

Balichakra Mallikarjuna et al. / Procedia Structural Integrity 56 (2024) 184–189 Mallikarjuna / Structural Integrity Procedia 00 (2019) 000 – 000

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unlike traditional manufacturing processes. MAM is based on depositing the parts by layer-by-layer of material addition. The component or part is created layer-by-layer; the next layer is deposited over the previously deposited under the heat or chemicals (Bandyopadhyay, 2016). MAM technologies such as Directed energy deposition (LENS, DMD, DM3D, Beam, etc.) and Powder Bed Fusion (SLM, DMLS, Renishaw, SLS, Trumpf etc.,) processes have revolutionised the manufacturing business in recent times (Diepold et al., 2020). However, MAM technologies face several technological problems, such as limited choice of materials, slow process speed, lack of available industrial standards, accuracy and reliability (Bhavar et al., 2017). MAM uses a laser or electron beam or plasma as a heat source to melt the powders during material layer-upon-layer deposition. DED techniques such as Laser Engineered Net Shaping (LENS) use a laser to melt the powders coming from the nozzles. Where a focused laser beam creates the melt pool on the substrate. Then the powders are injected into the melt pool (powder size is between 40 to 150 µm) via nozzles (Liu Weiping and John DuPont, n.d.). The series of beads (solidified melt pools) result in a layer. A successive layer is deposited by incrementing the laser head in the z-axis by a layer thickness. DED processes involve complex thermal behaviour in each melting pool and in the layers. The melt pool and thermal history significantly affect the microstructure, mechanical properties, residual stress, and distortion of the end part. To understand all these intrinsic variables, researchers have carried out a thermomechanical analysis of the DED process on the deposited parts (Balichakra et al., 2016; Hazarika et al., 2016; Kamara et al., 2011; Marimuthu et al., 2013; Roberts et al., 2009, 2012). Thereby eliminating the number of experiments required for the deposition of the TiAl parts (Balichakra et al., 2019; Bandyopadhyay & Traxel, 2018; Manvatkar et al., 2011). The LENS processes various materials such as titanium alloy, H13 tool steel, stainless steel, composites etc.(Murr et al., 2009; J. Wang et al., 2019; L. Wang et al., 2008). Neela et al. (2009), carried out process modelling of the LENS process. They study the influence of process parameters on thermal behaviour, mechanical properties, and build quality. This study concluded that overheating of the top layers can be avoided by reducing the heat input during the deposition of these layers. Manvatkar et al. (2011), carried out a 3D transient thermal finite element analysis to predict cooling rates, thermal cycling during deposition, and melt pool dimensions. The predicted temperatures were used to correlate with the hardness of the sample. Pratt et al. (2008) investigated the residual stress development in LENS-deposited samples both numerically and experimentally. The specimens were deposited at different laser powers, scan speeds and powder feed rates. Their investigation showed that laser velocity does not contribute significantly to residual stress development, while laser power strongly influences residual stress development. The melt pool and temperature prediction in the DED process were reported. The melt pool size at the edges is more significant than inside the wall (Mallikarjuna et al., 2021). Several researchers reported predicting the melt pool, thermal cycles, residual stress, and distortion in the directed energy deposited parts (Abdullah & Anwar, 2020; Hajializadeh & Ince, 2020; Mallikarjuna & Reutzel, 2022; Shen & Chou, 2012; Zhang et al., 2016). Towards this end, the current work presents result of the thermomechanical modelling of directed energy deposited γ -TiAl plate geometries. This work attempted to predict the melt pool, thermal history and residual stress in γ -TiAl

plate geometries. 2. Methodology 2.1 Thermomechanical analysis

This work uses a sequencing method to simulate the thermomechanical analysis. First, the transient thermal analysis is carried out to predict the temperatures. Secondly, mechanical analysis is carried out by importing body temperatures (through LDREAD) from thermal analysis. For both the analysis, necessary initial conditions, material properties and boundary conditions were used. To perform the thermomechanical analysis, ANSYS macros are created, which consist of necessary elements, boundary conditions and properties. Finally, results are extracted from thermal and mechanical analyses such as temperature history, melt pool and stresses, respectively. The Coupled field scheme of thermo-mechanical analysis is represented in Fig 1. The material properties, boundary conditions, and governing equations are found elsewhere (Balichakra et al., 2019) . The thermomechanical analysis was carried out for the plate geometry. The details of the process parameters used are presented in Table 1.