本文選題：單相合金　切入點：過冷度　出處：《西北工業(yè)大學(xué)》2016年博士論文　論文類型：學(xué)位論文

【摘要】：采用熔融玻璃包覆與循環(huán)過熱相結(jié)合的方法,在預(yù)抽真空及氬氣保護(hù)條件下,通過高頻感應(yīng)熔煉使大體積Co-20at.%Pd合金和Ni-20at.%Cu合金獲得了深過冷。討論了影響合金凈化效果的因素及獲得穩(wěn)定深過冷的控制條件。結(jié)合理論模型分析,系統(tǒng)研究了Co-20at.%Pd合金和Ni-20at.%Cu合金的組織演化和晶粒細(xì)化現(xiàn)象。探討了深過冷合金熔體快速凝固組織中的應(yīng)力累積規(guī)律�；诳齑阊b置設(shè)計,系統(tǒng)研究了大過冷度條件下實驗合金系晶粒細(xì)化的再結(jié)晶機制,實現(xiàn)了大過冷大體積Ni-20at.%Cu合金快速凝固組織的再結(jié)晶。本文主要研究內(nèi)容和結(jié)果如下:1.采用熔融玻璃凈化與循環(huán)過熱相結(jié)合的深過冷技術(shù),在預(yù)抽真空和惰性氣體保護(hù)條件下,使大體積Co-20at.%Pd合金獲得了340K的超過冷度,并且在過冷度?T約265K時,合金熔體已達(dá)到實際的超過冷狀態(tài)。在獲得的過冷度范圍0-340K,Co-20at.%Pd合金的凝固組織發(fā)生了兩次晶粒細(xì)化。在50 K(27)(35)T(27)265K時,合金的晶粒細(xì)化歸因于枝晶重熔。在265 K(27)(35)T(27)280K時,合金的晶粒細(xì)化機制由枝晶重熔機制向應(yīng)力誘導(dǎo)再結(jié)晶機制過渡。利用透射電鏡分析技術(shù),發(fā)現(xiàn)超過冷快淬合金具有大量位錯,層錯及小角度亞晶界。這些亞結(jié)構(gòu)說明超過冷快淬合金發(fā)生了部分再結(jié)晶,但再結(jié)晶不充分。在(35)T(29)280 K時,Co-20at.%Pd合金的晶粒細(xì)化完全由再結(jié)晶機制主導(dǎo)。2.隨初始過冷度的提高,Ni-20at.%Cu單相合金凝固組織經(jīng)歷了“粗大樹枝晶—粒狀晶—定向細(xì)枝晶—粒狀晶”的轉(zhuǎn)變過程。第一類晶粒細(xì)化來源于枝晶重熔。通過再結(jié)晶過程中的形核、生長和應(yīng)力累積理論計算,并結(jié)合深過冷Ni-20at.%Cu合金第二類細(xì)化組織中位錯形貌的透射電鏡觀察結(jié)果,間接證明了導(dǎo)致第二類晶粒細(xì)化現(xiàn)象的應(yīng)力誘導(dǎo)再結(jié)晶機制。3.基于兩相模型和應(yīng)力累積模型建立了快速凝固過程應(yīng)力累積模型,該模型可以半定量地估計深過冷熔體快速凝固過程中初生組織內(nèi)部的應(yīng)力累積。當(dāng)初始過冷度超過臨界過冷度值時,凝固收縮和熱應(yīng)變誘導(dǎo)的枝晶間液相流動將導(dǎo)致初生枝晶骨架內(nèi)產(chǎn)生應(yīng)力累積,應(yīng)力將促使初生枝晶骨架發(fā)生碎斷和塑性變形,同時以應(yīng)變能的形式存儲于枝晶碎片中,并進(jìn)一步作為后續(xù)回復(fù)和再結(jié)晶過程的熱力學(xué)驅(qū)動力。4.利用Ga-In合金液對深過冷Ni-20at.%Cu合金熔體在再輝之前進(jìn)行快淬,結(jié)果發(fā)現(xiàn),快淬微觀組織含有大量顯著塑性變形亞結(jié)構(gòu),例如密集位錯網(wǎng)絡(luò)等。進(jìn)一步對快淬組織進(jìn)行等溫退火,首次在深過冷快速凝固組織中發(fā)現(xiàn)了再結(jié)晶現(xiàn)象。而對自然冷卻合金進(jìn)行相同條件下的等溫退火,微觀組織幾乎沒有發(fā)生變化,這說明自然冷卻合金內(nèi)部儲存的塑性應(yīng)變能遠(yuǎn)遠(yuǎn)小于快淬合金組織內(nèi)的塑性應(yīng)變能。顯然,這些實驗研究結(jié)果揭示了過冷單相合金在大過冷度區(qū)間內(nèi)發(fā)生晶粒細(xì)化現(xiàn)象的潛在物理機理之一,即再結(jié)晶機制。5.研究了不同過冷度快淬Ni-20at.%Cu合金的微觀組織,發(fā)現(xiàn)合金試樣具有沿其軸線方向的晶粒尺寸梯度,且隨初始過冷度的增加,試樣頂部近表面微觀組織晶粒尺寸逐漸減小。在沿晶粒尺寸梯度方向上,隨試樣的深度增加,快淬Ni-20at.%Cu合金微觀組織內(nèi)的小角度晶界分?jǐn)?shù)逐漸減小,而孿晶分?jǐn)?shù)逐漸增大,這些是再結(jié)晶轉(zhuǎn)變的典型特征,從而說明快淬合金在等溫退火過程中發(fā)生了再結(jié)晶。
[Abstract]:By using molten glass coating method combined with thermal cycle, in vacuum and under argon, by induction melting of the massive Co-20at.%Pd alloy and Ni-20at.%Cu alloy were obtained. The influence factors of purification effect of Undercooled Alloy are discussed and obtain stable control conditions of deep cold. Combined with the analysis of the theoretical model, the microstructure evolution and grain refinement of Co-20at.%Pd alloy system and Ni-20at.%Cu alloy. The effect of the stress accumulation of microstructure of highly Undercooled Alloy Melts in rapid solidification. The design of quenching device based on recrystallization mechanism of grain refinement than the experimental condition of the alloy cold system, realize the recrystallization than the rapid solidification structure of cold mass Ni-20at.%Cu alloy. The main research contents and results are as follows: 1. using molten glass purification and superheating cycle, high undercooling technique In the vacuum, and under the protection of inert gas, the large volume of Co-20at.%Pd alloy was 340K more than cold, and in the degree of supercooling? T about 265K, more than the cold state alloy melt has reached the actual. In the undercooling range of 0-340K, occurred two times grain refinement of solidification structure of Co-20at.%Pd alloy. In 50 (27) K (35) T (27) 265K, grain refining alloy is attributed to the dendrite remelting. In the 265 K (27) (35) T (27) 280K, the grain refinement mechanism of the alloy is composed of dendrite remelting mechanism to stress induced recrystallization mechanism transition analysis. By using the technique of transmission electron microscope, found that more than cold quenched alloy has a large number of dislocations, stacking faults and small angle subgrain boundaries. These sub structure shows more than cold quenched alloy was recrystallized, but recrystallization is not sufficient. In (35) T (29) 280 K, fine crystal grain of Co-20at.%Pd alloy by the recrystallization mechanism leading.2. with early It had increase the cooling and solidification of Ni-20at.%Cu single-phase alloy experienced a transition from the process of coarse dendrite - granular crystal orientation - granular crystal crystal twigs ". The first kind of grain refinement from dendrite remelting. Through recrystallization in the process of nucleation, growth and stress accumulation and observe the results with the theoretical calculation, transmission electron microscope dislocation morphology of undercooled Ni-20at.%Cu alloy second kinds of refinement in the organization, leading to grain refinement phenomenon indirectly proved that the second types of stress induced recrystallization mechanism of.3. two-phase model and stress accumulation model is established for the rapid solidification process of stress accumulation based on the model, the model can semi quantitatively estimate the internal primary tissue during rapid solidification of undercooled melt in the stress accumulation. When the initial undercooling exceeds the critical undercooling, solidification shrinkage and thermal strain induced by the interdendritic liquid flow will cause the primary dendrite bone 鏋跺唴浜х敓搴斿姏绱Н,搴斿姏灝嗕績浣垮垵鐢熸灊鏅墮鏋跺彂鐢熺鏂拰濉戞，

本文編號：1600133