Selective Laser Sintering of Al 2 O 3 -Al Powder Compacts
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Selective Laser Sintering of Al2O3-Al Powder Compacts Adalberto Castro Hernández, Marina Vlasova, Pedro A. Márquez Aguilar and Mykola Kakazey Center of Investigation in Engineering and Applied Sciences, Autonomous University of Morelos State (CIICAp-UAEM), Av. Universidad, No. 1001, Col. Chamilpa, C.P. 62209, Cuernavaca, Morelos, Mexico. ABSTRACT It was established that at selective laser sintering of Al2O3 - Al compacted mixtures oxidation of the Al particles took place due to diffusion of oxygen into the volume of the workpieces. Depending on the content of aluminum, composite ceramics of various types were formed. INTRODUCTION Selective laser sintering (SLS) is a modern method of sintering of α-Al2O3 ceramics with different types of additives [1, 2]. One of them is Al. This has a low melting temperature (660 °C), and thus, it can be assumed that the introduction of aluminum powder reduces the sintering temperature of such refractory ceramics. The objective of this work was to study the physical-chemical processes occurring in the laser-heated zone of α-Al2O3-Al mixtures. EXPERIMENTAL DETAILS In this work, α-Al2O3 and Al powders with purity of 99.9% and a particle size of a 40 nm were used. Mixtures with composition x wt.% Al2O3 + (100-x) wt.% Al were prepared from these powders, where x varied from 0 at 100 wt.%. The mixtures were homogenized and then compacted at pressures of 100 - 175 kg/cm2. The obtained workpieces were subjected to laser processing with λ ~ 10,600 nm, in a continuous regime. The irradiation power (P) was 20, 40, 50, 60 and 80 W. The laser beam was moved across the workpiece surfaces (v) with speeds of 0.05, 0.1, 0.5 and 1 mm/s. The width of the laser beam was 3 mm. The irradiation scheme is shown in Figure 1. The specimens were characterized by Optical Microscopy (OM), Scanning Electron Microscopy combined with microanalysis (SEM-EDS), and X-Ray Diffraction (XRD). The size of the α-Al2O3 and Al particles was estimated from XRD data, according to the Scherrer formula: ఒ
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(1) where k ~ 0.94; λ = 0.154184 nm; β =ξ ܤଶ ܾ ଶ ~ 0.11; B is the experimental full width at half maximum (FWHM) of a XRD reflection, and b is the FWHM of a standard.
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DISCUSSION Specimens obtained from Al2O3 powder A considerable densification of the samples occurred at the powder compaction stage (Figure 2). Since it was desirable to achieve a maximum density in the workpieces during the subsequent laser treatment, they were pressed at 175 kg/cm2. As a result of the laser treatment, tracks were formed on the surface of the specimens, where polycrystalline corundum (α-Al2O3) with different crystallite sizes was formed (Figure 3). Depending on the irradiation regime, the average crystallite size varied (Figure 4): the bigger the irradiation power, and the faster t
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