Pressureless Reactive Sintering of MoSi2 with a Ti–Si–TiC Precursor: Phase Evolution, Hardness, and Dimensional Response

MoSi2 composites containing 5–50 wt.% nominal Ti–Si–TiC precursor (Ti:Si:TiC = 1:1.2:2; TSC) were pressurelessly sintered under an Ar-protected atmosphere at 1300–1500 °C for 120 min. Phase evolution, surface morphology, Raman features, Vickers microhardness, dimensional response, and geometric bulk-density trends were evaluated as functions of precursor fraction and temperature, with auxiliary TG–DSC of unsintered powder mixtures. MoSi2 remained the dominant crystalline phase across the investigated conditions. Ti3SiC2-related reflections were most evident at 1425–1450 °C, whereas Mo5Si3-related features became more apparent in selected 5–15 wt.% specimens at 1500 °C. Compared with the 50 wt.% specimens, lower-TSC specimens generally retained more continuous Mo–Si-rich surface regions, while the 50 wt.% specimens exhibited coarse Ti-rich domains, open pores, and pronounced compositional heterogeneity. Raman spectra revealed localized crystalline-Si-rich regions, consistent with a spatially nonuniform Si distribution. TG–DSC of the unsintered mixtures showed apparent net mass increases of 2.36–4.44% at 1300 °C under nominal Ar. The highest Vickers microhardness, 1114.6 ± 98.8 HV0.2, was obtained for the 50 wt.% specimen at 1400 °C. The maximum direction-averaged linear shrinkage was 15.52% for the 10 wt.% specimen at 1500 °C, whereas the 50 wt.% specimens expanded at 1300–1450 °C. Considering phase constitution, surface continuity, Vickers microhardness, dimensional response, and geometric bulk-density trends, 10–25 wt.% nominal TSC at 1400–1450 °C was identified as a qualitative candidate processing region for subsequent validation rather than as a fully optimized condition.