(北京航空材料研究院 先進(jìn)高溫結(jié)構(gòu)材料重點(diǎn)實(shí)驗(yàn)室，北京 100095)
摘 要: 通過在高速凝固法(HRS)定向凝固過程中調(diào)整隔熱擋板與殼型之間的間隙，獲得了較低的定向凝固溫度梯度(~30？℃/cm)，制備了含有雀斑組織的單晶高溫合金試棒。結(jié)果表明：采用常規(guī)HRS工藝(溫度梯度~50？℃/cm)制備的合金一次枝晶間距為323？μm，含有1.70%鑄態(tài)共晶；而采用較低溫度梯度HRS工藝制備的合金一次枝晶間距達(dá)到了704？μm，是常規(guī)HRS工藝的2.2倍，并且合金的二次枝晶及三次枝晶較為發(fā)達(dá)；此外，雀斑組織區(qū)域包含較多平均晶粒尺寸為200？μm的等軸晶晶粒和4.64%的鑄態(tài)共晶，同時(shí)分布著富集Ta元素的MC碳化物。定向凝固過程中較低的溫度梯度增大了合金的一次枝晶間距并使合金元素的凝固偏析加重，導(dǎo)致糊狀區(qū)液相發(fā)生對流的傾向增大，從而促進(jìn)了雀斑組織的形成。
關(guān)鍵字: 高溫合金；低溫度梯度；定向凝固缺陷；雀斑；凝固偏析
（Science and Technology on Advanced High Temperature Structural Materials Laboratory, Beijing Institute of Aeronautical Materials, Beijing 100095, China）
Abstract:The low thermal gradient during directional solidification was obtained by adjusting the distance between the baffle and the shell mold during traditional Bridgman (HRS) directional solidification process, and the single crystal superalloy bars containing freckles were prepared. The results show that the primary dendrite arm spacing of the normal HRS process alloy is 323？μm, which contains 1.70% cast eutectic. The primary dendrite arm spacing of the alloy prepared by lower temperature gradient HRS process reaches 704？μm，which is 2.2 times of that prepared by the normal HRS process. In addition, the secondary dendrite arm and thirdly dendrite arm are extremely developed under the low temperature gradient HRS process. The region of the freckles contains a large amount of equiaxed grains with a grain size of about 200？μm and 4.64% eutectic, and there are MC carbides enriched in Ta. The coarsen primary dendrite arm spacing and aggravated solidification segregation, caused by low thermal gradient during directional solidification, increase the tendency of convection of the liquid phase in the mushy zone, and promote the formation of freckles.
Key words: superalloy; low thermal gradient; directional solidification defects; freckle; solidification segregation
