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Purpose The purpose of this paper is to analyze and investigate heat accumulation caused by temperature changes and interface microstructure effected by element diffusion. Design/methodology/approach Al/Cu bimetallic structure is initially manufactured through laser powder bed fusion process. To minimize trial and error, finite element modeling is adopted to simulate temperature changes on the Al-based and Cu-based substrate. Findings The results show that forming pure copper on Al-based substrate can guarantee heat accumulation, providing enough energy for subsequent building. The instantaneous laser energy promotes increase of diffusion activation energy, resulting in the formation of transition zone derived from interdiffusion between Al and Cu atoms. The interface with a thickness of about 22 µm dominated by Kirkendall effect moves towards Al-rich side. The interface microstructure is mainly composed of a-Al, a-Cu and CuAl2 phase. Originality/value The bonding mechanism of Al/Cu interface is atom diffusion-induced chemical reaction. The theoretical basis provides guidance for structural design and production application.

Purpose This study aims to obtain the mechanistic insights for the fabrication of pure copper thin wall components by selective infrared (IR) laser melting (SLM) and correlated with microstructure development, microhardness, surface morphology and phase analysis. Experimental processes for single track and selection of substrate materials have been studied using a combination of different laser powers and scanning speeds. Design/methodology/approach SLM of pure copper was performed on a YONGNIAN Laser YLMS-120 SLM machine using an Nd: YAG fiber laser operating at 1,060 nm in the NIR region. Single-track experiments and processing parameters are investigated through different combinations of laser power and scanning speed. The microstructure of the fabricated pure copper samples by SLM technique was analyzed by means of X-ray diffraction, scanning electron microscope equipped with energy disperse spectrometer, optical microscope (OM) and micro-hardness tester. Findings Steel-based substrates were found suitable for pure copper manufacturing due to sufficient heat accumulation. The width of a single track was determined by liner energy density, showing discontinuities and irregular morphologies at low laser powers and high scanning speeds. As a result of instability of the molten pool induced by Marangoni convection, cracks and cavities were observed to appear along grain boundaries in the microstructure. The top surface morphology of SLM-processed component showed a streamflow structure and irregular shapes. However, the powder particles attached to side surface, which manifest copper powders, are even more sensitive to melt pool of contour track. The crystal phase characteristics of copper components indicated increasing crystallite size of a-Cu, and the decreasing intensity of diffraction peak was attributed to the presence of defects during SLM. The maximum relative density and microhardness were 82 per cent and 61.48 HV0.2, respectively. The minimum thickness of a pure copper thin wall component was 0.2 mm. Originality/value This paper demonstrated the forming mechanism and explored feasibility of pure copper thin wall parts by SLM technology in the NIR region. The surface morphology, microstructure and crystal structure were preliminary studied with laser processing parameters.

The mechanism of phase transformation and microstructure of yttria-stabilized zirconia (YSZ), prepared by selective laser melting (SLM) at a laser wavelength of 1 μm, has been investigated. Also, the effect of different working gases and heat treatment has been studied. Experimental results present that processing parameters can be optimized and determined by Liner Energy Density. X-ray diffraction analysis confirmed the absence of monoclinic phase under argon flow during SLM, with gray-color appearance due to the lack of oxygen, which impedes the transformation from tetragonal to monoclinic phase partially. Later, the color becomes white during heat treatment because samples are exposed to the air with sufficient amount of the oxygen and the diffraction peaks of monoclinic phase increased. When SLM and heat treatment was carried out in the air, the YSZ samples appeared in white-color, which indicates the presence of both monoclinic and tetragonal phase. The morphology and microstructure showed there occurred bonding phenomenons among particles, only surface partially melted between particles with weak bonding strength. The top surface morphology of air-prepared sample showed cracks, un-melting particles and cave-like pores because of uneven distribution of temperature variations. This paper also made a preliminary research and provided a feasibility method to melt zirconia ceramics completely, in which more energy input by multi-scanning in the air working gas.