| 其他摘要 | In contrast to conventional polycrystalline metals, metallic glasses (MG) have the unique atomic strustrue with short-range order and no long-range order，which leads to their high strength, hardness, elastic limitation, specific strength as well as good corrosition resitance. However, the glass-forming ability (GFA) and macroscopic plasticity of bulk metallic glasses (BMGs) are two main issues to inhibit their largely application. Among the BMG family, Cu-based BMGs exhibit higher strength while lower cost. In this work, the GFA, compressive property and toughness for Cu–Hf–Al ternary metallic glasses were systematically studied. The alloy with higher GFA as well as higher toughness was developed. The major contents and conclusions are shown as following:
1. In the Cu-Hf binary system, Cu100-xHfx (44≤x≤46) compositions near the (L→Cu10Hf7+CuHf2) eutectic exhibit BMG formability with a critical diameter of 1 mm, together with a wide supercooled liquid region (DTx) of about 55 K. By incorporating the third element Al in the binary base system, the relevant eutectic translates from binary to ternary (L→Cu10Hf7+CuHf2+CuHfAl), resulting in significant stabilization of the liquid as indicated by a drop of 47 K for the eutectic temperature with respect to the Al-free binary. The GFA of the Cu-Hf-Al ternary alloy dramatically increases and the formation of centimeter-scale BMG at an optimized composition Cu49Hf42Al9 (DTx=83 K).
2. Improvement of the GFA from Cu-Hf binary to the Al-incorporated ternary is also consistent with the observation that the liquid becomes “stronger”, as evidenced by an increase of the fragility parameter, D*, from 8.6 for Cu55Hf45 up to 16.8 for Cu49Hf42Al9. The combination of the thermodynamic stabilization and slowing down of kinetics leads to a pronounced increase of the F1 parameter, from 0.35 for Cu55Hf45 to 0.5 for Cu49Hf42Al9, respectively. In comparison to the reduced glass transition temperature (Trg) or fragility parameter (D*), F1 can effectively reflect the GFA of BMGs.
3. Along Cu91-xHfxAl9 (40≤x≤46) series alloys, the glass transition temperature (Tg) and shear modulus (μ) decrease linearly with Hf content increasing, from 782 K to 774 K, 43.0 GPa to 41.3 GPa, respectively. While the Poisson’s ratios (v) keep constant within the test error, from 0.351 to 0.355. Contribute to its lower μ and Tg, the BMG Cu49Hf42Al9 (C1) with high Hf content shows higher malleability than Cu45Hf46Al9 (C2) under compression test. While n does not play an important role on the higher malleability of BMG C2.
4. BMG C1 and C2 show similar yield stress and strength scatter within the range of 2210~2470 MPa and 2200~2440 MPa, respectively. Weibull statistics is employed to describe their strength distribution. BMG C2 shows higher Weibull modulus (m=53) compared to BMG C1 (m=40) implying more uniform strength distribution.
5. In terms of the notch toughness, Cu-based BMGs with relatively higher GFA are classified into two groups, with KQ=60 MPam1/2 and KQ=38 MPam1/2, respectively, within the range of the brittle Fe-based BMGs and the tougher Zr-based BMGs. The Y/Ag incorporation into the ternary Cu-Zr-Ti(Al) based alloys enhances the GFA, while the toughness is significantly degraded. Among these BMGs, Cu49Hf42Al9 exhibits the best combination of higher GFA and toughness.
6. In contrast to the v criterion proposed before, the toughness of Cu-based BMGs does not show obvious dependence onn, which are within the range of 0.351~0.377 and 0.364~0.373, for “brittle”and “ductile” BMGs, respectively. The critical n value from britlle to ductile BMGs does not exihit here. However, the toughness increases with the increasement of Tg or μ: the BMGs with μ<34 GPa or Tg<700 K exhibit britlle behavior. Different with the polycrystalline metals, the toughness of Cu-based BMGs increases acomponying with the increasement of strength. |
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