Surface plasmon induced enhancement in selective laser melting processes

Purpose Selective laser melting (SLM) is an advanced rapid prototyping or additive manufacturing technology that uses high power density laser to fabricate metal/alloy components with minimal geometric constraints. The SLM process is multi-physics in nature and its study requires development of complex simulation tools. The purpose of this paper is to study – for the first time, to the best of the authors’ knowledge – the electromagnetic wave interactions and thermal processes in SLM based dense powder beds under the full-wave formalism and identify prospective metal powder bed particle distributions that can substantially improve the absorption rate, SLM volumetric deposition rate and thereby the overall build time. Design/methodology/approach We present a self-consistent thermo-optical model of the laser-matter interactions pertaining to SLM. The complex electromagnetic interactions and thermal effects in the dense metal powder beds are investigated by means of full-wave finite difference simulations. The model allows for accurate simulations of the excitation of gap, bulk and surface electromagnetic resonance modes, the energy transport across the particles, time dependent local permittivity variations under the incident laser intensity, and the thermal effects (joule heating) due to electromagnetic energy dissipation. Findings Localized gap and surface plasmon polariton resonance effects are identified as possible mechanisms toward improved absorption in small and medium size titanium powder beds. Furthermore, the observed near homogeneous temperature distributions across the metal powders indicates fast thermalization processes and allows for development of simple analytical models to describe the dynamics of the SLM process. Originality/value To the best of the authors’ knowledge, for the first time the electromagnetic interactions and thermal processes with dense powder beds pertaining to SLM processes are investigated under full-wave formalism. Explicit description is provided for important SLM process parameters such as critical laser power density, saturation temperature and time to melt. Specific guidelines are presented for improved energy efficiency and optimization of the SLM process deposition rates.

Effect of Powder Size on Microstructure and Mechanical Properties of 2A12Al Compacts Fabricated by Hot Isostatic Pressing

This paper studied the effects of powder size on densification, microstructure, and mechanical properties of the hot isostatic-pressed 2A12 aluminum alloy powder compact. The results show that the near-fully dense powder compact can be successfully achieved and the smaller the powder is, the higher the relative density is. In addition, as the powder size decreases, the precipitated phases in the powder compact change from continuously point-like distribution at the junctions among powder particles to the concentrated distribution at the three-way intersections. Compared with the large powder, the tensile strength, yield strength, and elongation of the compact with the small powder were improved by 14%, 30.8%, and 48.6%, respectively.

Microstructure and Mechanical Properties of Powder Metallurgy Ti-22Al-24Nb-0.5Mo Alloys Joints with Electron Beam Welding

In this work, a Ti2AlNb based intermetallic alloy with the composition of Ti–22Al–24Nb–0.5Mo (at. %) pre-alloyed powder was firstly produced by gas atomization, and then fully dense powder metallurgy (PM) Ti2AlNb alloy was prepared by a hot isostatic pressing (HIPing) procedure. The HIPed alloy shows uniform microstructure with low number of porosities. In order to broaden the application field of PM Ti2AlNb alloys, electron beam welding (EBW) was proposed to join the intermetallics. The joint quality, microstructure and microhardness of PM Ti2AlNb alloy processed by EBW were characterized, and the results showed that the both base alloy and EBW joints have high metallurgy quality.