材料期刊网

采用第一原理赝势平面波方法计算了D0₁₉结构的α₂-Ti-25Al-xNb(x=0-12, 原子分数, %) 晶体的弹性模量(B, G和E) 和抗拉强度 (σ_b), 并利用Cauchy压力(c₁₂-c₄₄)与G/B比值表征和评判了不同浓度Nb合金化时α₂-Ti-25Al-xNb合金的韧脆化倾向. 结果表明: 在 x=2-12时, α₂-Ti-25Al-xNb晶体的抗拉强度 (σ_b)与α₂相合金的弹性模量(B, E和G)随$x$增加而增大; 在x=0-6时, α₂-Ti-25Al-xNb合金脆性有一定改善, 且x值越大韧化效果越好; 但在x=7-9 时, 相对于α₂-Ti₃Al, 合金脆性不但没有得到弱化, 反而随x增加而加剧; 随后, 当x进一步增大时, 合金脆性又随x增加再次得到改善, 至x=12时, α₂-Ti-25Al-xNb合金的韧化效果最好. 通过电子态密度 (DOS) 和投影电子态密度 (PDOS)等电子结构的分析, 初步解释了Nb的这种强化与韧化作用.

Intermetallic alloys based on Ti₃Al are potential high-temperature structural materials due to their low density, high specific strength, excellent creep behavior and good oxidation resistance, but their application has been hampered by the low room--temperature ductility and ambient brittleness. Numerous experiments have shown Nb is most effective additive to improve their ductility and toughness at low temperature, but the influence of Nb content on the mechanical properties of Ti₃Al-based alloys has not been understood. In this work, using the first-principles pseudo--potential plane wave method, ultimate tensile strength σ_b of α₂-Ti-25Al-xNb (x=0-12, atomic fraction, %) single crystal with D0₁₉ structure and bulk modulus B, Young's modulus E as well as shear modulus G of α₂-Ti-25Al-xNb polycrystalline alloys have been calculated, and their ductile/brittle behavior is characterized and assessed by the Cauchy pressure (c₁₂-c₄₄) and the G/B ratio. The results reveal the ultimate tensile strength σ_b of α₂-Ti-25Al-xNb crystals and the elastic moduli (B, E, G) of α₂-Ti-25Al-xNb alloys monotonously increase with the addition of Nb in the whole range of x=0-12. Meanwhile a very sensitive ductile/brittle behavior of α₂-Ti-25Al-xNb alloys to Nb content is also detected. The addition of Nb with low content is demonstrated to be profitable for weakening of the brittleness of α₂-Ti₃Al alloys, and the toughening tendency of α₂-Ti-25Al-xNb alloys increases as increasing Nb addition in the range of =0-6. Whereas in the range of x=7-9, relative to α₂-Ti₃Al alloys no toughening effect can be seen as Ti in Ti₃Al being partially substituted by Nb. As x≥10, the toughening effect of Nb addition is activated again, and an obvious improvement in the ductility and strength of α₂-Ti-25Al-12Nb alloy is observed as comparing with α₂-Ti-25Al-6Nb alloy. For this toughening and strengthening effect of Nb addition a reasonable explain was given by means of the analysis of the density of states (DOS) and the projective density of states (PDOS) of α₂-Ti-25Al-xNb (x=0, 6, 7, 12) crystals.