Nucleation and precipitation strengthening in dilute Al-Ti and Al-Zr alloys
Nucleation and precipitation strengthening in dilute Al-Ti and Al-Zr alloys
复制标题
DOI：
10.1007/s11661-007-9283-6
复制
发表时间：
2007-10-01
影响因子：
2.8
通讯作者：
Seidman, David N.
中科院分区：
文献类型：
--
作者：
Knipling, Keith E.;Dunand, David C.;Seidman, David N.
两种常规凝固的Al-0.2Ti合金（0.18和0.22 at）。pct Ti)在375℃或425℃下时效3200小时后没有硬化，这是由于没有Al3Ti析出，正如电子显微镜和电导率测量所证实的那样。Al-0.2Zr合金(0.19 at。由于Al3Zr （L1(2)）在富含Zr的枝晶区析出，pct Zr在两种温度下均表现出强烈的时效硬化。这两种合金之间的差异可以用平衡相图来解释：(1)Ti在α - al中的固溶度和液相溶解度的差异远大于Zr在α - al中的溶解度；(2) Ti在α - al中的溶解度较小，限制了凝固过程中固溶体中溶质的保留量，而较高的固溶度减少了凝固后时效过程中影响析出的过饱和度。Al3Ti （L1(2)）与α - al的晶格参数失配也大于Al3Zr (L1(2))，进一步阻碍了Al3Ti的成核。经典的成核理论表明，在Al-Ti合金的常规凝固过程中（与Al-Zr合金不同），无法获得克服Al3Ti核弹性应变能所需的最小溶质过饱和，从而解释了没有Al3Ti析出和存在Al3Zr析出。
Two conventionally solidified Al-0.2Ti alloys (with 0.18 and 0.22 at. pct Ti) exhibit no hardening after aging up to 3200 hours at 375 degrees C or 425 degrees C. This is due to the absence of Al3Ti precipitation, as confirmed by electron microscopy and electrical conductivity measurements. By contrast, an Al-0.2Zr alloy (with 0.19 at. pct Zr) displays strong age hardening at both temperatures due to precipitation of Al3Zr (L1(2)) within Zr-enriched dendritic regions. This discrepancy between the two alloys is explained within the context of the equilibrium phase diagrams: (1) the disparity in solid and liquid solubilities of Ti in alpha-Al is much greater than that of Zr in alpha-Al; and (2) the relatively small liquid solubility of Ti in alpha-Al limits the amount of solute retained in solid solution during solidification, while the comparatively high solid solubility reduces the supersaturation effecting precipitation during post-solidification aging. The lattice parameter mismatch of Al3Ti (L1(2)) with alpha-Al is also larger than that of Al3Zr (L1(2)), further hindering nucleation of Al3Ti. Classical nucleation theory indicates that the minimum solute supersaturation required to overcome the elastic strain energy of Al3Ti nuclei cannot be obtained during conventional solidification of Al-Ti alloys (unlike for Al-Zr alloys), thus explaining the absence of Al3Ti precipitation and the presence of Al3Zr precipitation.