Temperature-Dependent Absorptances of Ceramics for Nd:YAG and CO2 Laser Processing Applications

Abstract

The absorptance of a material at the laser wavelength and as a function of temperature, ranging from room temperature to the removal point, significantly affects the efficiency of the laser machining process. A priori predictions of a laser machining process, using either simplistic or sophisticated models, requires knowledge of the material's absorptance behavior. An experimental apparatus for such measurements is described. The device consists of a specimen mounted inside an integrating sphere, heated rapidly by a CO 2 or a Nd:YAG laser. Reflectances are measured with a small focused probe laser (Nd:YAG or CO 2 ), while specimen surface temperatures are recorded by a high-speed pyrometer. Experimental results have been obtained for wavelengths of 1.06 m (Nd:YAG) and 10.6 m (CO 2 ) for graphite, alumina, hot-pressed silicon nitride, sintered -silicon carbide, as well as two continous-fiber ceramic matrix composites (SiC-based). Data are presented for temperatures between room temperature and the ablation/decomposition points.

Fiber Laser Cutting of Alumina Substrates for Electronic Applications Comparison of the Experimentally Determined and Simulated Influence on the Mechanical Strength

“…This is comparable to the reflectivity of 79% reported by Liu et al [16]. With respect to the laser cutting process using a near infrared fiber laser, please note that Zhang and Modest [17] published experimental results showing that the absorption of alumina at 1,064 nm significantly increases to more than 90% at temperatures exceeding the melting point of the material. The room temperature transmission is determined to 15% at 1,070 nm.…”

Mathematical modelling of the fibre laser surface processing of a zirconia engineering ceramic by means of three-dimensional finite-element analysis

“…The fibre laser with a given power density and a constant traverse speed (see section 3.2) is passed on the top surface of the ceramic. During this time, the laser energy is absorbed by the ceramic and to about 90 per cent as reported by Zhang and Modest [10]. The absorbed light in form of heat causes a degree of surface heating, which leads to a degree of melting, followed by some level of ablation through vaporization and finally solidifies during its cooling process to ambient temperatures.…”

“…This is the amount of or heat being passed on from one surface to another; in this case, the thermal energy radiated by the laser beam was only being passed onto one surface during the heat transfer as described by Cengel and Turner [45]. Absorption of 90 per cent was assigned to the model by taking in consideration of the absorption values found in a previous investigation by Zhang and Modest [10]. An emissivity of 0.40 was used as it is a typical value for all ceramics.…”

“…• C. From observing the temperature distribution obtained experimentally and from the FEA model (see Figs 8,10, and 12), it can be seen that the distribution of heat varies in different positions on the ZrO 2 ceramic as the fibre laser beam is frozen in one position in order to investigate the heat distribution for this study. From this, one can see that the rapid surface and the bulk heating occurs, which is followed by the rapid cooling effect which took place where the ZrO 2 is transformed from M → M + T → T → T + C during heating.…”

“…However, this method is ideal for measuring the temperature changes in the bulk; it is not suitable for measuring the surface temperatures so pyrometers or contactless devices are also employed, as demonstrated by Zhang and Modest [10], Hao and Lawrence [11],…”