N18锆合金的单轴拉伸和应力松弛性能
Properties of Uniaxial Tension and Stress Relaxation of Zircaloy N18
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摘要: 本工作试验研究20~700 ℃、不同应变加载速率下N18锆合金的单轴拉伸和应力松弛性能。结果表明，N18合金的单轴拉伸应力-应变曲线出现明显的屈服拐点，且温度低于500 ℃时呈现后继屈服强化，高于500 ℃后又呈后继屈服软化。除横向试样的断面收缩率高于轧向试样外，试样取向对N18合金的单轴性能影响不大。温度低于300 ℃时，N18合金的应变速率敏感性受温度的影响不大；350 ℃时，N18合金的敏感系数达到最小值，其后，对应变速率的敏感性随着温度的升高逐渐增强。N18合金在不同温度和应变水平下均产生明显的应力松弛。在300 ℃以内，最大应力松弛程度受温度影响较小，且随应变水平的增大明显降低；在350~550 ℃范围内，应变水平越高，对应的最大应力松弛程度越大；N18合金的最大松弛程度在350 ℃附近出现最小值。在350~450 ℃范围内，N18合金表现出明显的动态应变时效特性。Abstract: A series of uniaxial tension and relaxation tests were completed at temperatures from 20 ℃ to 700 ℃. The results show that, the tensile constitutive curves of the alloy present obvious yield breaks, subsequent yield hardening in the temperature range from 20 ℃ to 500 ℃ and softening in the range from 500 ℃ to 700 ℃. The elastic modulus, strength and percentage elongation of the alloy in the rolling direction are closed to those of the alloy in the transverse direction, but percentage reduction of area of the uniaxial specimen in the transverse direction is somewhat large. With increase of temperature, elastic modulus and strength of the alloy decrease, and percentage elongation and percentage reduction of area increase. It is seen that the percentage elongation has a sudden reduction in the temperature range from 350 ℃ to 450 ℃. The elevated temperature makes properties of the alloy to have strong sensitivity of strain rate under strain loading. The sensitivity of strain rate is slightly affected by the variety of tempera-ture below 300 ℃ and the alloy behaves least sensitivity to strain rate at 350 ℃. Subsequently, the sensitivity of strain rate enhances with increase of temperature. The influence of temperature on stress relaxation effect of N18 alloy is outstanding. The influence of the variety of temperature on the maximum of stress relaxation is unobvious below 300 ℃, and with increase of strain level the maximum of stress relaxation reduces obviously. Conversely, the strain level is higher, the extent of the maximum of stress relaxation is larger in the temperature range from 350 ℃ to 550 ℃. About 350 ℃, the maximum of stress relaxation reaches minimum value. In the range from 350 ℃ to 450 ℃, N18 alloy presents characteristic of dynamic strain aging obviously.
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