Figure 3 Representative true stress-true strain curves for both [100] and [110] Mo in (a), Mo-5Re in (b), Mo-14Re in (c) and Mo-42Re in (d).
True stress-true strain curves of [110] and [100] Mo-5Re coincide in elastic region, as shown in Figure 3(b). [110] Mo-5Re and [100] Mo-5Re both yield at true stress ~300MPa that lower than Mo, suggesting softening effect happens in Mo-5Re. After yield, true stress in [100] Mo-5Re gradually rises from 300MPa to ~600MPa as true strain reaches 2.5%. Then, stress drops from ~600MPa to ~300MPa at strain 5%. Whereas, [110] Mo-5Re maintains flow stress at ~400MPa from yield point to 7.5% strain. As strain higher than 10%, stress fluctuations emerge strongly in both [100] and [110] Mo-5Re.
Figure 3c shows mechanical responses of [100] and [110] Mo-14Re. The yield stress in [110] Mo-14Re is higher than in [100] Mo-14Re, which is differ with Mo and Mo-5Re. The true stress in [110] Mo-14Re is always higher than in [100] Mo-14Re from yield point to 25%. It is noted that stress drop behaviors are much less distinct in Mo-14Re than in Mo and Mo-5Re, showing the plastic deformation in Mo-14Re is more stable than in Mo-5Re and Mo. What is more, true stress gradually increases from strain 2.5% to 25% in both [110] and [100] Mo-14Re, expect for a slight stress drop from 600MPa to 500MPa. The final stress reaches 1200MPa in [110] Mo-14Re, and 800MPa in [100] Mo-14Re at strain ~25%.
The true stress-true strain curves of [100] and [110] Mo-42Re are shown in Figure 3d. The stress in [110] Mo-42Re is higher than in [100] Mo-42Re at yield point. The stress in [110] Mo-42Re maintains at steady level from 1% to 5%. While in this region, the stress in [100] Mo-42Re rises from 450MPa to 750MPa. Two curves overlap within 7.5% to 15%, as shown in the white dotted square in Figure 3d. As strain continually increases, the stress in [110] Mo-42Re rapidly enhances to 2000MPa from 15% to 25%. The stress in [100] Mo-42Re, however, steadily rises to 1200MPa. The stress drops behaviors in Mo-42Re is much smoother than in Mo-14Re.
Figure 4a shows the results for Mo, Mo-14Re and Mo-42Re with [100] orientation. Yield strength enhances with Re content rises. Besides, the stress at 25% strain is effectively improved in [100] Mo-42Re, which means strong hardening effect. An outstanding feature is that stress drop behaviors weaken as Re content increases, both in samples with [100] orientation (Figure 4a) and with [110] orientation (Figure 4b). The stresses are adjacent in [110] Mo-14Re and Mo-42Re in the stain region between 2% to 10%. As strain higher than 15% in [110] samples, stresses in Mo and Mo-42Re begin to rapidly increases. Such a behavior may be induced via large changing shape of samples.
Figure 4 The true stress-true strain curves of Mo, Mo-14Re and Mo-42Re with [100] orientation in (a) and with [110] orientation in (b). (c) is the summary of yield stresses.
Figure 5 shows the surface micrographs of samples after compression with true strain 25%. Only one group of parallel slip bands emerge in [100] Mo and Mo-14Re, as shown in Figure 5a and 5c. [110] Mo still behaviors strong slips along a single slip plane. Two groups of slips bands tangles in [100] Mo-42Re, which may lead to strengthening effect. Plastic deformation in [110] Mo-14Re and Mo-42Re are dominated by multi-slip bands. Asymmetric deformation leads inclination in [100] Mo-42Re, as seen in Figure 5e.