The TNM-alloy is an intermetallic titanium aluminide alloy of the third generation with a nominal composition of Ti-43.5Al-4Nb-1Mo-0.1B (in at%). At room temperature the microstructure consists of the three phases γ-TiAl, α2-Ti3Al and βo-TiAl. In the course of this diploma thesis a testing standard for a quantitative phase analysis by optical-light microscopy was developed. With this an efficient method for a quality check of billets and forged parts was established. Thermal, immersion and electrolytic etching methods were tested and the results obtained by optical-light microscopy were compared to micrographs taken by scanning electron microscopy and phase analysis by X-ray diffraction. An optimum method for a quantitative phase analyses is to use an electrolytically etched specimen and to employ imaging enhancing tools. With this method the microstructures of a so-called „high-β“-composition, at which the amount of Nb and Mo are on the higher specification limit, and a „low-β“-composition, with the amount on the lower limit, were characterized and phase fraction diagrams were established. Finally, materials exhibiting „high-β“- and „low-β“-composition were forged with different die-speeds, then analyzed to evaluate the influence of strain rate and chemical composition on the microstructure.