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

Tao Yang,Xiping Guo

doi:10.3390/met9060653

Abstract

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.

Highlights

Mo-Si-B alloys, as promising ultrahigh temperature structural materials, have drawn much attention in the past few decades
A typical Mo-Si-B alloy is comprised of a Mo solid solution (Moss), and Mo3 Si (A15) and Mo5 SiB2 (T2) phases [1,2]
The much higher dislocation density in Mo3 Si than those in Mo5 Si3 (T1) and Mo5 SiB2 in elevated temperature compressive creep tests [7,8] indicates that the ultrahigh-temperature strength of Mo3 Si is not satisfactory

Summary

Introduction

Mo-Si-B alloys, as promising ultrahigh temperature structural materials, have drawn much attention in the past few decades. A typical Mo-Si-B alloy is comprised of a Mo solid solution (Moss), and Mo3 Si (A15) and Mo5 SiB2 (T2) phases [1,2]. As the most Mo-rich molybdenum silicide, the Mo3 Si phase shows poor oxidation resistance due to its low Si content and marginal B solubility [3,4,5,6]. The much higher dislocation density in Mo3 Si than those in Mo5 Si3 (T1) and Mo5 SiB2 in elevated temperature compressive creep tests [7,8] indicates that the ultrahigh-temperature strength of Mo3 Si is not satisfactory. Suppression of Mo3 Si product in a Moss-toughening Mo-Si-B-based alloy may result in better oxidation resistance and elevated temperature strength. As a lighter element compared with Mo, alloying with Nb can lower the density of a Mo-Si-B alloy, which shows greater attraction than

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Results

Conclusion