Si对K325铸造高温合金的凝固行为和拉伸性能的影响

Influence of Si on solidification behaviors and tensile properties of K325 alloy

采用扫描电镜、电子探针和差热分析等方法研究Si含量对铸造高温合金K325凝固行为、组织特征和拉伸性能的影响。结果表明:Si添加粗化枝晶、加重Nb元素偏析且偏析程度随Si含量增加呈增大趋势。不含Si合金的凝固路径为L→L+γ→L+γ+MC→γ+MC,铸态相组成为γ+MC。含Si合金的凝固路径为L→L+γ→L+γ+MC→L+γ+MC+γ/Laves→γ+MC+γ/Laves,铸态相组成为γ+MC+γ/Laves。此外,随着Si含量的升高,γ/Laves共晶相的尺寸明显增大且量明显增加,形貌由半连续状向连续致密筛网状和花瓣状转变。固溶处理后含Si合金中的γ/Laves共晶消失,相组成为γ+MC+Laves相,Laves相为具有尖锐棱角的块状。随Si含量增加,块状Laves相含量明显增多,Si含量为1.5%(质量分数)时,形成Laves相团簇区。Si对拉伸强度的影响与Si含量密切相关,小于1.0%的Si对合金抗拉强度无明显影响,然而Si含量为1.5%,抗拉强度明显降低。

The solidification behaviors, microstructure and tensile properties of K325 superalloy were investigated by means of SEM, EPMA, DTA, and so on. The results show that the addition of Si promotes the dendrite coarsening and aggravates the elements segregation of Nb, besides elements segregation increased along with increasing the Si content. The solidification sequence of K325 alloy without Si addition is as follows： L→L＋γ→L＋γ＋MC→γ＋MC, and the as-cast microstructure is γ＋MC. The solidification sequence of alloys containing silicon is as follows： L→L＋γ→L＋γ＋MC→ L＋γ＋MC＋γ/Laves→γ＋MC＋γ/Laves, and the as-cast microstructure is γ＋MC＋γ/Laves. Furthermore, the size and amount of γ/Laves eutectic phase significantly increases with increasing Si content, and the eutectic morphology changes from semi-continuous to continuous dense sieve pattern and petal-like. The γ/Laves eutectic phase disappears after the solution treatment of silicon-containing alloy. The phase composition is γ＋MC＋Laves phase, and Laves phase is blocky with sharp edges. The amount of Laves phase increases with increasing Si content, and Laves phase comes together into being clusters when Si content is 1.5%（mass fraction）. The influence of Si element on tensile strength is closely related to Si content. When Si content is less than 1.0%, Si has no obvious effect on the tensile strength of the alloy, while tensile strength decreases obviously when Si content is 1.5%.