The Ti-rich region of the Ge-Si-Ti ternary isotherm at 900 degrees C was determined by metallography, X-ray diffraction, and electron microprobe analysis. The sample alloys were prepared by arc-melting. It was confirmed that at 900 degrees C Ti5Si3 and Ti5Ge3 form a continuous solid solution Ti-5(Si1-xGex)(3) with the hP16 crystal structure. The lattice constants for Ti-5(Si1-xGex)(3) are linear functions of the composition variable x. This continuous solid solution also exists at 1100 degrees C. There is another solid solution Ti-3(Si1-yGey), that has the same crystal structure as Ti3Si (tP32), but this solid solution is stable only for y less than or equal to 0.44 at 900 degrees C. It was also shown that there is not any other binary or ternary phase within the Ti-Ti5Si3-Ti5Ge3 triangular region except Ti-5(Si1-xGex)(3) and Ti-3(Si1-yGey). In this region, there is one three-phase held Ti + Ti-5(Si1-xGex)(3) + Ti-3(Si1-yGey), and the compositions of these three phases are Ti0.96Si0.03Ge0.01, Ti0.63Si0.08Ge0.29, and Ti(0.75)Si(0.14)G(0.11) respectively. In addition, there are three two-phase fields within this region: Ti-5(Si1-xGex)(3) + Ti-3(Si1-yGey), Ti+Ti-3(Si1-yGey), and Ti+Ti-5(Si1-xGex)(3).
