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采用第一原理赝势平面波方法计算了D0_19结构的α_2-Ti-25Al-xNb(x=O—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(c_(12)-C_(44))与G/B比值表征和评判了不同浓度Nb合金化时α_2一Ti-25Al- xNb合金的韧脆化倾向.结果表明:在x=2—12时,α_2-Ti-25Al-xNb晶体的抗拉强度(σ_b)与σ_2相合金的弹性模量(B, E和G)随x增加而增大;在x=0—6时,α_2-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α_2-Ti_3Al,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,α_2-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.
The elastic modulus (B, G and E) and tensile strength (σ_b) of the crystal of α_2-Ti-25Al-xNb (x = O-12, atomic fraction,%) in D0_19 structure were calculated by the first principle pseudopotential plane wave method. ), And the tendency of ductile-brittleness of α_2-Ti-25Al-xNb alloy was characterized and evaluated by Cauchy pressure (c_ (12) -C_ (44)) and G / B ratio.The results show that in the When x = 2-12, the elastic modulus (B, E and G) of the tensile strength (σ_b) and σ_2 phase alloys of α_2-Ti-25Al-xNb crystal increase with increasing x; , The brittleness of α_2-Ti-25Al-xNb alloy is improved, and the larger the value of x is, the better the toughening effect is. However, at x = 7-9, the alloy brittleness is not weakened compared with α_2-Ti_3Al, x increases and then aggravates. When x is further increased, the brittleness of the alloy improves again with the increase of x, and the toughening effect of α_2-Ti-25Al-xNb alloy is the best at x = 12. The electron density of state DOS) and electronic structure density (PDOS), the preliminary explanation for the strengthening and toughening effect of Nb is given.