Cu 及 Cu-1.25 wt% Fe 單晶塑性變形後之微結構與析出物研究

The evolution of microstructure and precipitates in plastic deformed Cu and Cu-1.25 wt% Fe alloy single crystals

陳俊霖

指導教授 ： 張士欽

國立清華大學/工學院/材料科學工程學系/碩士(2013年)

摘要

高純度無氧銅與純銅以電弧熔煉法熔煉成為一個合金，接著將此合金以及一高純度無氧銅以Bridgman法分別成長成各別之單晶棒，接著施以不同的應變量以及退火溫度並比較它們之間的微結構與硬度的差異，並且用穿透式電子顯微鏡來研究銅鐵合金內部鐵顆粒析出物的大小以及形貌。
當銅與銅鐵合金壓縮變型量為25%並以300℃退火時，沒有任何的再結晶新晶粒被觀察到。對銅含有1.25%鐵合金進行25%壓縮變型並在700℃退火2小時僅僅只有少量的再結晶新晶粒在一些孤立區域被發現到，因此在本實驗中採用較大的壓縮變型應變量75%來研究整個塊材試片的再結晶現象以及晶粒尺寸之改變。
一般來說，在較高溫熱處理之材料其晶粒尺寸應該較大而且其硬度應該降低，然而在再結晶的過程中由於鐵顆粒析出物的形成以及成長的影響下，再結晶會受到阻礙並且硬度值下降的效應也會受到析出物的影響。而再結晶之後的晶粒成長部份也不會完全完成即使在800℃退火512小時，此溫度略低於鐵顆粒的固溶溫度820℃。
因為所使用的試片一開始為單晶，因此沒有任何的晶界以及只有極低的差排密度，相信析出物在冷加工處理時只會在差排周圍成核而析出。在75%壓縮變形時，由於差排密度變得相當高因此鐵顆粒得以析出更加均勻，利用穿透式電子顯微鏡的觀察與分析可以得知隨著退火溫度的的增加，析出物可以成長並解便隨著相變化之發生。

關鍵字

單晶 ； 銅鐵合金 ； 析出物 ； 相變化

並列摘要

High purity copper and pure iron were melted to form an alloy by arc melting. Cu-Fe alloy and pure copper single crystal bars were grown with the Bridgman method. Their difference in microstructures and hardness after different strain and annealing was compared. TEM samples were used to study the size and morphology of precipitates in the alloy.
With 25% compression and 300 oC annealing, there is no recrystallized new grain observed. For the copper/1.25% iron alloy with 25% compression and 700 oC /2 hours annealing, only small new grains were found in isolate narrow strips in the specimen. Therefore, a large strain of 75% compression is selected in this work to study the recrystallization phenomenon and the grain size in whole bulk specimens.
Generally, higher heat treatment temperature results in an increase in the grain size and a reduction of the hardness in a material. However, due to the influence of iron precipitate particles that formed and grew along with the recrystallization process, the recrystallization was impeded and the decrease in hardness was also counter affected by the iron precipitate particles. The recrystallization was not completed even after 512 hours annealing at a temperature as high as 800 oC that is lower than but very close to the solid solution temperature (about 820 oC).
Because the starting specimens are single crystal with no grain boundary and very low dislocation densities, the precipitates are believed to nucleate at dislocations formed in cold work. At 75% strain, the dislocation density is very high and the precipitates can nucleate more evenly. TEM observations indicate that with increasing annealing temperature the precipitates can grow with accompanying phase transformation.

並列關鍵字

single crystal ； Cu/ Fe alloy ； precipitate particles ； phase transformation

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