Si對(duì)K325鑄造高溫合金的凝固行為和拉伸性能的影響

Si對(duì)K325鑄造高溫合金的凝固行為和拉伸性能的影響Influence of Si on solidification behaviors and tensile properties of K325 alloy

采用掃描電鏡、電子探針和差熱分析等方法研究Si含量對(duì)鑄造高溫合金K325凝固行為、組織特征和拉伸性能的影響。結(jié)果表明：Si添加粗化枝晶、加重Nb元素偏析且偏析程度隨Si含量增加呈增大趨勢(shì)。不含Si合金的凝固路徑為L(zhǎng)→L+γ→L+γ+MC→γ+MC，鑄態(tài)相組成為γ+MC。含Si合金的凝固路徑為L(zhǎng)→L+γ→L+γ+MC→ L+γ+MC+γ/Laves→γ+MC+γ/Laves，鑄態(tài)相組成為γ+MC+γ/Laves。此外，隨著Si含量的升高，γ/Laves共晶相的尺寸明顯增大且量明顯增加，形貌由半連續(xù)狀向連續(xù)致密篩網(wǎng)狀和花瓣?duì)钷D(zhuǎn)變。固溶處理后含Si合金中的γ/Laves共晶消失，相組成為γ+MC+Laves相，Laves相為具有尖銳棱角的塊狀。隨Si含量增加，塊狀Laves相含量明顯增多，Si含量為1.5%(質(zhì)量分?jǐn)?shù))時(shí)，形成Laves相團(tuán)簇區(qū)。Si對(duì)拉伸強(qiáng)度的影響與Si含量密切相關(guān)，小于1.0%的Si對(duì)合金抗拉強(qiáng)度無(wú)明顯影響，然而Si含量為1.5%，抗拉強(qiáng)度明顯降低。

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%.

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