Transient printing characteristics with wavy build profiles for laser additive manufacturing of small size structures

Laser directed energy deposition(DED)is a multi-physics process that accompanies mass flow,energy transfer,and complex phase transitions.The printing characteristics of small size parts are significantly affected by the progressive variations of the temperature fields and the fluid flow within the molten pool.In this work,the deposition characteristics during multi-layer and multi-track laser DED were explored through a well-tested phenomenological model and corresponding experimental results.The variations of the build profiles and the decoupled track and layer profiles were systematically examined.Moreover,the printing characteristics of the builds with different scanning lengths were compared.Results showed that the multi-layer and multi-track transient deposition processes generated a significantly wavy surface profile.Compared with the long scanning length part,the beginning region of the short build produced an obvious bulge followed by sharply decreased height along the scanning direction.The transverse section of the short build varied significantly at different positions.Two adjacent columns of tracks were extracted from the overall build,demonstrating that the tracks tilted outwards and the angle increases along the scanning direction.The 3D numerical model was validated with corresponding experiments for builds with various layers.The scientific findings from this work can provide useful insights for the understanding of the additive mechanisms during laser DED for the precise shape control of small size parts.

Tunable band gap and optical properties of surface functionalized Sc2C monolayer

Using the density functional theory, we have investigated the electronic and optical properties of two-dimensional Sc2C monolayer with OH, F, or O chemical groups. The electronic structures reveal that the functionalized Sc2C monolayers are semiconductors with a band gap of 0.44–1.55 eV. The band gap dependent optical parameters, like dielectric function, absorption coefficients, reflectivity, loss function, and refraction index were also calculated for photon energy up to 20 eV. At the low-energy region, each optical parameter shifts to red, and the peak increases obviously with the increase of the energy gap. Consequently, Sc2C monolayer with a tunable band gap by changing the type of surface chemical groups is a promising 2D material for optoelectronic devices.

In Situ Elimination of Pores During Laser Powder Bed Fusion of Ti–6.5Al–3.5Mo–l.5Zr–0.3Si Titanium Alloy

The printing quality of components manufactured using laser powder bed fusion(LPBF)generally depends on the presence of various defects such as massive porosity.Thus,the efficient elimination of pores is an important factor in the production of a sound LPBF product.In this study,the efficacy of two in situ laser remelting approaches to eliminating pores during the LPBF of a titanium alloy Ti–6.5 Al–3.5 Mo–l.5 Zr–0.3 Si(TC11)was assessed both experimentally and computationally.These two remelting methods are surface remelting and layer-by-layer printing and remelting.A multi-track multi-layer phenomenological model was established to analyze the variation of pores with the temperature and velocity fields.The results showed that surface remelting with a high laser power,such as 180 W,can eff ectively eliminate pores within three deposited layers.However,such remelting could not reach defects in deeper regions.Layer-by-layer remelting with a 180 W laser could eff ectively eliminate the pores formed in the previous layer in real time.The results obtained in this study can provide useful guidance for the in situ control of printing defects supported by real-time monitoring,feedback,and operating systems of an intelligent LPBF equipment.