Deformation behavior of a two-phase Mo–Si–B alloy

Abstract: Mo–Si–B alloys are being considered as possible candidates for high-temperature applications beyond the capabilities of Ni-based superalloys. In this paper, the high-temperature (1000–1400°C) compression response over a range of quasi-static strain rates, as well as the monotonic and cyclic crack growth behaviors (as a function of temperature from 20°C to 1400°C) of a two-phase Mo–Si–B alloy containing a Mo solid solution matrix (Mo(Si,B)) with ∼38vol% of the T2 phase (Mo5SiB2) is discussed. Analysis of the compression results confirmed that deformation in the temperature–strain-rate space evaluated is matrix-dominated, yielding an activation energy of ∼415–445kJ/mol. Fracture toughness of the Mo–Si–B alloy varies from ∼8MPa√m at room temperature to ∼25MPa√m at 1400°C, the increase in toughness with temperature being steepest between 1200°C and 1400°C. S–N response at room temperature is shallow whereas at 1200°C, a definitive fatigue response is observed. Fatigue crack growth studies using R =0.1 confirm the Paris slope for the two alloys to be high at room temperature (∼20–30) but decreases with increasing temperature to ∼3 at 1400°C. The crack growth rate (da/dN) for a fixed value of ΔK in the Paris regime in the 900–1400°C range, increases with increasing temperature. [Copyright &y& Elsevier]