The indentation toughness of Mo₅Si₃-based phases was studied with regard to different alloying elements, amount of alloying addition as well as the presence of secondary phases. Cr, Ti, Nb, Ni and Co were added as alloying elements. The results show that the indentation fracture toughness of Mo₅Si₃ increases with the alloying additions, from 2.4MPa·m^1/2 for monolithic to just over 3MPa·m^1/2 for highly alloyed Mo₅Si₃. Small volume fractions of brittle secondary phases may have a positive impact on the indentation toughness; while larger fractions seems to lower the toughness.

Mechanical milling behavior of Mo-Si-Fe powders was investigated using XRD, SEM and TEM techniques. The mixtures of elemental molybdenum (>99%), silicon (>99%) and iron (>98%) powders with a stoichiometry of Mo_5-xFe_xSi₃(x=0.5, 1, 2) were milled in a planetary mill for up to 195h. For all three powder mixtures, high-energy milling of 60h led to formation of the Mo(Fe, Si) supersaturated solid solution (Mo_ss); and to a remarkable expansion of the solubility of Fe, Si in molybdenum. The transformation of Mo_ss to an amorphous phase was identified after longer time milling. In the milling process, the grain size of Mo (Fe, Si) decreased gradually and the internal stress increased linearly. After 40?h milling, the grain size was reduced to about 11nm. SEM analysis of mil l ed powders showed that the particle size increased initially with milling time. After 195h milling, particles exhibited a spherical morphology and the particle size were reduced to about 100nm.

The compressive creep behavior at 1200～1400℃ of an in-situ synthesized MoSi₂-30%SiC (volume fraction) composite and a traditional PM MoSi₂-30%SiC (volume fraction) composite is investigated. The creep rate of the in-situ synthesized MoSi₂-30%SiC (volume fraction) composite is about 10^-7s^-1 under stress of 60～120MPa, and significantly lower than that made by PM method above 1300℃. The reason is that the interface between SiC particle and MoSi₂ matrix in in-situ synthesized SiC_p/MoSi₂ is of direct atomic bonding without any amorphous glassy phase, such as SiO₂ structure. Creep deformation occurs primarily by dislocation motion and the dislocations have Burgers vectors of the type of 〈110〉 and 〈100〉.

The Nb-10Si (mole fraction, %) alloy was fabricated using the vacuum arc-melting method and heat-treated at 1850℃ and 1550℃ for 2～100h in Ar atmosphere. The microstructure of the alloy has been investigated using X-ray diffract ometry(XRD), scanning electron microscopy (SEM) equipped with X-ray energy dispersive spectrometry (EDS) and transmission electron microscopy (TEM). The results show that 1550℃, 100h is an optimum heat-treatment condition to acquire the equilibrium Nb+Nb₅Si₃ two-phase microstructure. The microstructure of Nb-10Si alloy in the as-cast condition consists of continuous Nb₃Si matrix and dispersed Nb particles, which implies that the alloy is in the metastable equilibrium state. In the case of 1850℃, 2h heat-treatment the Nb particles are coarsened evidently. How ever, in the heat-treatment condition of 1550℃ for 25～100h the growth of Nb particles is unconspicuous. After heat-treated at 1550℃, Nb₃Si phase transforms into the equilibrium Nb₅Si₃ and Nb phase with the increase of heat-treatment time gradually. TEM observations reveal that the interface of Nb phase and Nb₅Si₃ phase is clean and some twins with about 10nm in width are found.