Effects of Nb Content on the Mechanical Alloying Behavior and Sintered Microstructure of Mo-Nb-Si-B Alloys

Different from conventional Mo-Si-B-based alloys consisting of Moss, Mo3Si, and Mo5SiB2, Mo3Si-free Mo-Si-B-based alloys (Moss+Mo5Si3+Mo5SiB2 or Moss+Mo5SiB2) show great potentials for more excellent oxidation resistance and elevated temperature strength. In the present work, alloying element Nb was added to Mo-12Si-10B (at.%)-based alloy to suppress the formation of the Mo3Si phase. Mo-12Si-10B-xNb (x = 10, 20, 22, 24, 26, 28, 30, and 40) bulk alloys were fabricated using mechanical alloying followed by cold pressing and then sintering at 1773 K for 2 h. Effects of Nb content on the mechanical alloying behavior and then sintered microstructure were studied. The addition of Nb with an amount less than 30 at.% accelerated the mechanical alloying process, but 40 at.% Nb addition decreased the process due to excessive cold welding and high powder volume. For the sintered bulk alloy prepared from the mechanically alloyed powders milled for 30 h, a critical Nb content between 24 and 26 at.% was found to suppress Mo3Si production and γNb5Si3 phase formed in the alloys with the addition of Nb content more than 26 at.%. Prolongation of a prior milling process could facilitate the suppression of Mo3Si and delay the formation of niobium silicides.

Synthesis of Cast Composite Materials by SHS Metallurgy Methods

The review of the results obtained by the authors in synthesis of cast composite materials by the methods of SHS metallurgy is made. The main attention is paid to synthesis of heat-resistant materials based on intermetallic compounds of nickel and titanium and niobium silicides as well as tungsten-free hard alloys based on titanium and chromium carbides. The parameters allowing one to govern the process, material structure and composition were determined. Practical application was specified.

Deformation Behavior of Niobium Silicides during High Temperature Compression

Deformation behavior of (Nb)/α-Nb5Si3 two-phase alloys is examined by high temperature compression tests. The alloys exhibit brittle fracture behavior at temperatures up to 1473 K, while reasonable compressive deformability at 1673 K. Upon high temperature compression of the alloys, the flow stress gradually decreases after the peak stress due to the recrystallization/recovery in the (Nb) phase, as well as the increase in the density of mobile dislocations within the α-Nb5Si3 phase. Two types of slip systems that operate in α-Nb5Si3 have been identified as {011)<11-1] and {001)<100] in the present study.