Microstructural analysis and high-temperature strength of a directionally solidified Er 2Mo 3Si 4-MoSi 2 eutectic

Abstract

Recent investigations have shown that Er[sub 2]Mo[sub 3]Si[sub 4] is an effective reinforcement for strengthening MoSi[sub 2]. When present in hot-pressed MoSi[sub 2] compacts, the Er[sub 2]Mo[sub 3]Si[sub 4] improved both hot hardness and creep resistance of the MoSi[sub 2]. The crystal structure of Er[sub 2]Mo[sub 3]Si[sub 4], as reported by Bodak et al., is monoclinic with lattice parameters of 0.667 nm, 0.689 nm, and 0.681 nm. The point group and space group of this phase have been identified as 2/m and P2[sub 1]/c, respectively. A theoretical density for Er[sub 2]Mo[sub 3]Si[sub 4] was calculated to be 8.25 g/cm[sup 3] and this compares favorably with other refractory silicide compounds (e.g., Mo[sub 5]Si[sub 3] = 8.25 g/cm[sup 3]). Because of the low crystal symmetry, this intermetallic compound is expected to exhibit limited plasticity, but may possess good high temperature mechanical properties. Mechanical property data on Er[sub 2]Mo[sub 3]Si[sub 4] is still quite limited; however, preliminary creep results from a decremental step-strain rate test show that the directionally solidified (DS) Er[sub 2]Mo[sub 3]Si[sub 4]-MoSi[sub 2] eutectic has excellent creep resistance at 1,300 C. At this temperature a flow stress of 625 MPa was observed for a strain rate of 5 [times] 10[supmore » [minus]5]s[sup [minus]1], but failure occurred as the strain rate was reduced to 10[sup [minus]5]s[sup [minus]1]. In this paper the authors present further results obtained from constant engineering strain rate compression tests on the same DS eutectic bar.« less