Abstract
This study reports the fabrication of Nd:YAG (i.e., Neodymium-doped Yttrium Aluminum Garnet: Y3-xNdxAl5O12) transparent ceramics of a large size by the pressure slip-casting forming technique. Colloidal suspensions of primary oxides (i.e., Y2O3, Al2O3, Nd2O3, and SiO2 used as sintering aid) were cast under pressure through a porous membrane. Cakes with a good microstructural homogeneity and mean pore diameter of 90 nm were obtained. Modeling of the pressure slip-casting process at the millimetric to centimetric scale based on a computational fluid dynamics simulation showed good agreement with experimental results in terms of the casting kinetics (i.e., cake thickness and fluid flow as a function of time) and cake permeability. As a result, it was possible to better manage pressure casting parameters in order to obtain large size and homogeneous green parts. Finally, transparent Nd:YAG ceramics sintered by vacuum sintering, followed by post-sintering treatment by Hot Isostatic Pressing (HIP), demonstrated laser slope efficiency (51.7%) and optical-to-optical efficiency (44%) with 130 mJ of output laser energy at 1064 nm equivalent to commercial single crystals.
Highlights
Ceramic processes usually use a liquid approach, i.e., involve the shaping of colloidal suspensions.Many different methods are used for shaping, such as slip-casting, pressure slip-casting, tape-casting, gel casting, centrifugal casting, etc. [1]
We focused on the use of pressure slip-casting for the manufacturing of transparent ceramics based on Nd:YAG
A high concentration and low viscosity are required for the casting of ceramic slurry in the pressure slip-casting process
Summary
Ceramic processes usually use a liquid approach, i.e., involve the shaping of colloidal suspensions. The manufacturing of a segmented bar, with a gradual concentration of doping, makes it possible to minimize the longitudinal temperature differences and the stress gradients, according to the pumping direction in the laser cavity during the operation [5] This type of architecture and others are achievable by the use of suitable ceramic shaping processes, followed by co-sintering of the elaborated composite parts [6,7,8,9,10]. Stevenson et al [23] compared dry shaping (uniaxial pressing followed by CIP) and liquid shaping (tape-casting followed by CIP) Their results showed that the pressed samples had a larger pore size, leading to a longer and higher sintering temperature being required to reach full transparency. This study demonstrates that pressure casting is a shaping technique suitable for the manufacturing of transparent ceramics with a large size and laser quality equivalent to that of single crystals of the same composition
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