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The influence of additions of molybdenum disilicide (MoSi2) on the microstructure and the mechanical properties of a silicon nitride (Si3N4) material, with neodymium oxide (Nd2O3) and aluminum nitride (AIN) as sintering aids, was studied. The composites, containing 5, 10, and 17.6 wt% MoSi2, were fabricated by hot pressing. All materials exhibited a similar phase composition, detected by X‐ray diffractometry. Up to MoSi2 additions of 10 wt%, mechanical properties such as strength, fracture toughness, or creep at 1400°C were not affected significantly, in comparison to that of monolithic Si3N4. The oxidation resistance of the composites, in terms of weight gain, degraded. After 1000 h of oxidation at 1400° and 1450°C in air, a greater weight gain (by a factor of approximately three) was obtained, in comparison to that of the material without MoSi2. Nevertheless, after 1000 h of oxidation, the degradation in strength of the composites was considerably less severe than that of the material without MoSi2. An additional layer was formed, caused by processes at the surface of the Si3N4 material, preventing the formation of pores, cracks, or glassy‐phase‐rich areas, which are common features of oxidation damage in Si3N4 materials. This surface layer, containing Mo5Si3 and silicon oxynitride (Si2ON2), was the result of reactions between MoSi2, Si3N4, and the oxygen penetrating by diffusion into the material during the hightemperature treatment.

The connection of such key technologies as laser and sensor technology opens a broad field of applications especially in medicine. The development of sensor-controlled medical laser systems represents a quantum leap in precision and safety in medical practice. This makes the treatment or surgery more gentle and safer for both physician and patient. This paper presents the possibilities and the potential of sensor-based laser procedures in medical practice. It starts with medical laser technology and sensor systems that are already used in medical diagnostics and therapy. A concrete example from laser surgery illustrates the advantages of laser ablation for an osteotomy of the mandible and a sensor and control concept for tissue-specific bone ablation. An Er:YAG laser system was combined with a process control and qualified for layer-specific ablation of hard tissue. Layer-specific ablation of tissue is especially important when, as in the laser osteotomy of the mandible (lower jaw), vulnerable structures, as e.g. nerves (mandibular nerve), run underneath the to-beablated tissue that may not be damaged. The closed loop control system developed for laser osteotomy is based on the evaluation of process emissions that occur during the laser ablation and are recorded with several sensors. Thereby optical and acoustic process emissions are used for achieving switching-off criteria for the laser system before damaging the nerve. Tests were performed on dissected bone specimens from the rabbit's femur and minipig's jaw. After laser application the bone specimens were evaluated macroscopically, radiologically, histologically and by micro computed tomography.