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1. Thermophysical Properties of Laser Powder Bed Fused Ti-6Al-4V and AlSi10Mg Alloys Made with Varying Laser Parameters

   https://doi.org/10.3390/ma16144920  

   Akwaboa, Stephen; Zeng, Congyuan; Amoafo-Yeboah, Nigel; Ibekwe, Samuel; Mensah, Patrick (July 2023, Materials)

   This study investigated the influence of diverse laser processing parameters on the thermophysical properties of Ti-6Al-4V and AlSi10Mg alloys manufactured via laser powder bed fusion. During fabrication, the laser power (50 W, 75 W, 100 W) and laser scanning speed (0.2 m/s, 0.4 m/s, 0.6 m/s) were adjusted while keeping other processing parameters constant. Besides laser processing parameters, this study also explored the impact of test temperatures on the thermophysical properties of the alloys. It was found that the thermophysical properties of L-PBF Ti-6Al-4V alloy samples were sensitive to laser processing parameters, while L-PBF AlSi10Mg alloy showed less sensitivity. In general, for the L-PBF Ti-6Al-4V alloy, as the laser power increased and laser scan speed decreased, both thermal diffusivity and conductivity increased. Both L-PBF Ti-6Al-4V and L-PBF AlSi10Mg alloys demonstrated similar dependence on test temperatures, with thermal diffusivity and conductivity increasing as the test temperature rose. The CALPHAD software Thermo-Calc (2023b), applied in Scheil Solidification Mode, was utilized to calculate the quantity of solution atoms, thus enhancing our understanding of observed thermal conductivity variations. A detailed analysis revealed how variations in laser processing parameters and test temperatures significantly influence the alloy’s resulting density, specific heat, thermal diffusivity, and thermal conductivity. This research not only highlights the importance of processing parameters but also enriches comprehension of the mechanisms influencing these effects in the domain of laser powder bed fusion. 

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2. Tailoring the coefficient of thermal expansion in a functionally graded material: Al alloyed with Ti-6Al-4V using additive manufacturing

   https://doi.org/10.1016/j.jallcom.2024.176971  

   Tonyali, Beril; Sun, Hui; Liu, Zi-Kui; Keist, Jayme; Beese, Allison M (December 2024, Journal of Alloys and Compounds)

   Functionally graded materials enable the spatial tailoring of properties through controlling compositions and phases that appear as a function of position within a component. The present study investigates the ability to reduce the coefficient of thermal expansion (CTE) of an aluminum alloy, Al 2219, through additions of Ti-6Al-4V. Thermodynamic simulations were used for phase predictions, and homogenization methods were used for CTE predictions of the bulk CTE of samples spanning compositions between 100 wt% Al 2219 and 70 wt% Al 2219 (balance Ti-6Al-4V) in 10 wt% increments. The samples were fabricated using directed energy deposition (DED) additive manufacturing (AM). Al2Cu and fcc phases were experimentally identified in all samples, and aluminides were shown to form in the samples containing Ti-6Al-4V. Thermomechanical analysis was used to measure the CTE of the samples, which agreed with the predicted CTE values from homogenization methods. The present study demonstrates the ability to tailor the CTEs of samples through compositional modification, thermodynamic calculations, and homogenization methods for property predictions. 

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3. Effects of Build Orientation on Fatigue Performance of Ti-6Al-4V Parts Fabricated via Laser-Based Powder Bed Fusion

   Torries, Brian; Shamsaei, Nima; Thompson, Scott M (August 2017, 28th International Solid Freeform Fabrication Symposium - An Additive Manufacturing Conference)

   The effects of build orientation on the fatigue behavior of additively-manufactured Ti-6Al- 4V using a Laser-Based Power Bed Fusion (L-PBF) process is investigated. Ti-6Al-4V rods were manufactured in vertical, horizontal, and 45º angle orientations. The specimens were then machined and polished along the gage section in order to reduce the effects of surface roughness on fatigue behavior. Fully-reversed strain-controlled uniaxial fatigue tests were performed at various strain amplitudes with frequencies adjusted to maintain an average constant strain rate throughout testing. Results indicate slight variation in fatigue behavior of specimens fabricated in the different orientations investigated. Fractography was conducted using scanning electron microscopy after mechanical testing in order to investigate the crack initiation sites and determine the defect responsible for the failure. The experimental program utilized and results obtained will be presented and discussed. 

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4. Effects of Inter-Layer Time Interval on Temperature Gradients in Direct Laser Deposited Ti-6Al-4V

   Masoomi, M.; Thompson, S.M.; Shamsaei, N.; Bian, L. (August 2016, Annual International Solid Freeform Fabrication Symposium)

   Parts fabricated via additive manufacturing (AM) methods are prone to experiencing high temperature gradients during manufacture resulting in internal residual stress formation. In the current study, a numerical model for predicting the temperature distribution and residual stress in Directed Energy Deposited (DED) Ti–6Al–4V parts is utilized for determining a relationship between local part temperature gradients with generated residual stress. Effects of time interval between successive layer deposits, as well as layer deposition itself, on the temperature gradient vector for the first and each layer is investigated. The numerical model is validated using thermographic measurements of Ti-6Al-4V specimens fabricated via Laser Engineered Net Shaping® (LENS), a blown-powder/laser-based DED method. Results demonstrate the heterogeneity in the part’s spatiotemporal temperature field, and support the fact that as the part number, or single part size or geometry, vary, the resultant residual stress due to temperature gradients will be impacted. As the time inter-layer time interval increases from 0 to 10 second, the temperature gradient magnitude in vicinity of the melt pool will increase slightly. 

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5. Effect of Specimen Surface Area Size on Fatigue Strength of Additively Manufactured Ti-Al-4V Parts

   Pegues, Jonathan; Roach, Michael; Williamson, R. Scott; Shamsaei, Nima (August 2017, 28th International Solid Freeform Fabrication Symposium - An Additive Manufacturing Conference)

   As additive manufacturing becomes an increasingly popular method for advanced manufacturing of components, there are many questions that need to be answered before these parts can be implemented for structural purposes. One of the most common concerns with additively manufactured parts is the reliability when subjected to cyclic loadings which has been shown to be highly sensitive to defects such as pores and lack of fusion between layers. It stands to reason that larger parts will inherently have more defects than smaller parts which may result in some sensitivity to surface area differences between these parts. In this research, Ti-6Al-4V specimens with various sizes were produced via a laser-based powder bed fusion method. Uniaxial fatigue tests based on ASTM standards were conducted to generate fatigue-life curves for comparison. Fractography on the fractured specimens was performed to distinguish failure mechanisms between specimen sets with different sizes. 

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