“…In CM Ti-6Al-4V, the critical above which acicular, long orthogonally oriented α ′ phase forms was determined to be 410°C/s (see Figure 13(d) [210]). The appearance of α + β phases in DED Ti-6Al-4V could be a result of direct phase transformation from prior β (wherein is low), or phase transformation from α ′ to β and finally to α + β phases upon subsequent consecutive thermal cycles [12,211]. Figure 13. Micrographs illustrating (a) the acicular martensitic α ′ [203], (b) basketweave Widmanstätten structure [201] and (c) colony structure [31] in DED Ti-6Al-4V alloy.…”
Section: Structures Of the Ded-processed Alloysmentioning
Amongst the many additive manufacturing (AM) techniques, directed energy deposition (DED) is a prominent one, which can also be used for the repair of damaged components. In this paper, we provide an overview on it, with emphasis on the typical microstructures of DED alloys and discuss the processing-microstructure-mechanical property correlations. Comparison is made with those manufactured using the conventional techniques and those obtained with laser beam powder bed fusion (LB-PBF). The characteristic solidification rates and thermal histories in DED result in distinct micro-and meso-structural features and mechanical performance, which are succinctly summarized. The potential of DED for manufacturing graded materials and for component repair is elaborated while highlighting the key-associated challenges and possible solutions. Modelling and simulation studies that facilitate an in-depth understanding of the DED technique are summarized. Finally, some critical issues and research directions that would help develop DED further and extend its application potential are identified.
“…In CM Ti-6Al-4V, the critical above which acicular, long orthogonally oriented α ′ phase forms was determined to be 410°C/s (see Figure 13(d) [210]). The appearance of α + β phases in DED Ti-6Al-4V could be a result of direct phase transformation from prior β (wherein is low), or phase transformation from α ′ to β and finally to α + β phases upon subsequent consecutive thermal cycles [12,211]. Figure 13. Micrographs illustrating (a) the acicular martensitic α ′ [203], (b) basketweave Widmanstätten structure [201] and (c) colony structure [31] in DED Ti-6Al-4V alloy.…”
Section: Structures Of the Ded-processed Alloysmentioning
Amongst the many additive manufacturing (AM) techniques, directed energy deposition (DED) is a prominent one, which can also be used for the repair of damaged components. In this paper, we provide an overview on it, with emphasis on the typical microstructures of DED alloys and discuss the processing-microstructure-mechanical property correlations. Comparison is made with those manufactured using the conventional techniques and those obtained with laser beam powder bed fusion (LB-PBF). The characteristic solidification rates and thermal histories in DED result in distinct micro-and meso-structural features and mechanical performance, which are succinctly summarized. The potential of DED for manufacturing graded materials and for component repair is elaborated while highlighting the key-associated challenges and possible solutions. Modelling and simulation studies that facilitate an in-depth understanding of the DED technique are summarized. Finally, some critical issues and research directions that would help develop DED further and extend its application potential are identified.
“…For instance, the temperature-sensitive yield strength and the flow properties have a very strong effect on the mechanical response of alloys [15], which can be correlated with the solid-state phase transformations (SSPTs)during manufacturing [3,13,16]. Within this context, several numerical works have been conducted to investigate SSPTs during the metal deposition process, especially for Ti–6Al–4V dual phase ( α and β phases) alloy [17–21]. Nevertheless, few studies have addressed the effect of SSPTs on the distortion and residual stress development in AM of Ti–6Al–4V [22].…”
A fully coupled thermal-microstructural-mechanical finite element modelling framework is developed to investigate the distortion and residual stresses during directed energy deposition (DED) of multi-phase Ti-6Al-4V alloy. The Johnson-Cook constitutive model is used to predict the yield strength of each phase as a function of strain, strain rate and temperature where the flow stress is calculated by a linear mixing rule based on the volumetric phase fractions. A thin-walled rectangular sample is chosen as the reference geometry and the results are compared with experimentally measured in situ thermal history and distortion data, where a reasonable agreement is achieved. The proposed modelling framework with physics-based material constitutive model provides useful information for a better understanding of process-microstructure-property relations in additive manufacturing by DED.
“…Driven by highly localized and moving energy input, microstructure of additively manufactured (AMed) Ti-6Al-4V products features with coarse β [5,6] and α [7][8][9], which are damage for the mechanical properties. β and α are two different topics.…”
Section: Introductionmentioning
confidence: 99%
“…β and α are two different topics. We mainly focus on the former here as details related with α has been discussed in our previous research [9]. The size of solidified β grains can be as large as several 100 micrometers or even several millimeters, which significantly lowers the performance of products.…”
The β grain of Ti–6Al–4V during wire laser additive manufacturing (WLAM) is notorious for its coarse grains and thus reducing the mechanical performance. In this research, to predict and further control the microstructure, three-dimensional (3D) β grain evolution is simulated by 3D cellular automaton method coupled with the transient thermal profile calculated from processing modeling. Simulations are validated by experiments. The competitive growth between grains shows that the grain growth rate is less than the isotherm moving velocity, leading to a flat S–L interface, which in turn makes the orientation plays a more important role than the undercooling. It interprets the phenomena that Ti–6Al–4V grains with ⟨001⟩ orientation along the building direction are preferred during WLAM. Effects of processing parameters on microstructure, such as the deposited layer, the laser power, the inter-layer time and the preheating temperature of substrate, are also investigated. Results show that the grain size at the horizon plane increases with the increase of the deposited layer, the laser power and the preheating temperature, while inter-layer time has few effects on the β grain evolution. 3D grain simulation of additive manufacturing shows promising prospect in predicting the microstructure, revealing underlying mechanisms and optimizing processing parameters.
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