【摘要】：Cu-Cr系合金是一類擁有良好綜合性能的結(jié)構(gòu)功能一體化材料,當(dāng)?shù)诙鄰浬⒎植加诨w中時,可使銅合金在獲得高強度的同時保持了較好的導(dǎo)電性能。由于合金凝固時存在液-固相變過程,液相Cu易富集于底部,而密度較低的Cr相易于上浮揮發(fā),極易產(chǎn)生偏析現(xiàn)象,惡化其功能特性。本文基于歐拉數(shù)值模擬和流體技術(shù),通過數(shù)值模擬研究了Cu-Cr系合金中第二相在凝固過程中的偏析行為、溫度場以及第三相對合金偏析模式產(chǎn)生的影響,取得如下研究結(jié)果。(1)研究了Cu-Cr6.5%合金凝固過程中Cr在基體中的擴散分布面積隨時間和位置的變化規(guī)律,結(jié)果表明:凝固初期Cr相比較均勻的分散在合金基體中,Cr相熔點較高,先發(fā)生側(cè)向凝固,形成糊狀區(qū);凝固后期基體頂部的Cr會大量聚集,形成頂部偏析,側(cè)向凝固Cr相的形成壁面偏析,對壁面溫度場的分布產(chǎn)生影響。(2)分析了合金凝固過程中壁面溶質(zhì)濃度的變化和柱狀晶生長形態(tài),結(jié)果表明:液相合金向下流動方向與柱狀晶生長方向基本一致,這種流動模式也影響了熔體的組成;隨著柱狀晶體生長,溶質(zhì)逐漸向內(nèi)部富集;凝固后期,當(dāng)糊狀區(qū)溶質(zhì)濃度達到一定程度時,在紊流和重力作用下,柱狀晶尖端斷裂,成為等軸晶的形核中心。(3)研究了通道偏析的形成規(guī)律,結(jié)果表明:Cu-Cr通道偏析模型的形成,受到Mo相尺寸和數(shù)量的影響。當(dāng)粒子的大小范圍5~25μm形成粒子聚集成團,最終形成通道偏析;當(dāng)粒子尺寸小于5μm或大于25μm時,顆粒在糊狀區(qū)之間的相互作用并不會持續(xù)太長時間,因此并不能引起通道偏析。(4)研究了Mo相顆粒對Cr相偏析的作用機制,結(jié)果表明:顆粒的浮選對通道偏析的形成影響分為兩個階段,即偏析啟動階段和偏析成長階段。在糊狀區(qū)附近的局部流速增加將改變Cr相的移動及隨后的凝固,從而導(dǎo)致局部Cr相分離和抑制局部凝固,糊狀區(qū)的凝固速率也將發(fā)生變化。通道偏析的形成取決于Mo相顆粒大小和數(shù)量,當(dāng)Mo相顆粒直徑逐漸變大時,偏析帶逐漸減小。同時Mo相初始粒子的數(shù)量增加也增大糊狀區(qū)的不穩(wěn)定性,進而引起更多偏析帶。
[Abstract]:Cu-Cr alloy is a kind of structure-functional integrative material with good comprehensive properties. When the second phase is dispersed in the matrix, the copper alloy can obtain high strength and good electrical conductivity. Due to the liquid-solid transformation process during solidification, liquid Cu is easy to be enriched at the bottom, while the low density Cr phase is easy to float and volatilize, which is easy to produce segregation phenomenon and deteriorate its functional properties. Based on Euler numerical simulation and fluid technology, the segregation behavior of the second phase in Cu-Cr alloy during solidification, the effect of temperature field and the third relative alloy segregation mode are studied by numerical simulation. The results are as follows. (1) the variation of Cr diffusion area in the matrix during solidification of Cu-Cr6.5% alloy is studied. The results show that the Cr phase is uniformly dispersed in the alloy matrix at the beginning of solidification, and the melting point of Cr phase is higher. In the later stage of solidification, the Cr at the top of the matrix will accumulate in large quantities, forming the top segregation, and forming wall segregation of the Cr phase in the lateral solidification. (2) the variation of solute concentration and the growth morphology of columnar crystals during solidification are analyzed. The results show that the downward flow direction of liquid alloy is basically consistent with that of columnar crystal growth. This flow pattern also affects the composition of the melt; with the growth of columnar crystals, solute gradually enriches internally; at the end of solidification, when the concentration of solute in the paste region reaches a certain level, the columnar crystal tip breaks under the action of turbulence and gravity. (3) the formation of channel segregation is studied. The results show that the formation of Cu-Cr channel segregation model is affected by the size and quantity of Mo phase. When the particle size ranges from 5 渭 m to 25 渭 m, the particle aggregates and forms channel segregation, and when the particle size is less than 5 渭 m or more than 25 渭 m, the interaction between the particles in the paste region does not last for too long. Therefore, channel segregation can not be induced. (4) the mechanism of Mo phase particles acting on Cr phase segregation is studied. The results show that the effect of particle flotation on channel segregation formation is divided into two stages, namely, segregation start-up stage and segregation growth stage. The increase of local velocity near the paste region will change the movement of Cr phase and the subsequent solidification, resulting in local Cr phase separation and inhibition of local solidification, and the solidification rate of the paste region will also change. The formation of channel segregation depends on the size and number of Mo phase particles. When the diameter of Mo phase particles becomes larger, the segregation band gradually decreases. At the same time, the increase of the number of initial particles in Mo phase also increases the instability of the paste region, which leads to more segregation bands.
【學(xué)位授予單位】：西安建筑科技大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2017
【分類號】：TG146.11

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