本文選題：微觀組織 + 微壓縮�。� 參考：《哈爾濱工業(yè)大學(xué)》2015年碩士論文

【摘要】：隨著微型產(chǎn)品需求日益增加,微成形技術(shù)得到迅猛的發(fā)展。塑性微成形技術(shù)具有生產(chǎn)成本低、成形件性能好等優(yōu)點(diǎn),非常適合微型零件的批量化生產(chǎn),在微機(jī)電系統(tǒng)以及微系統(tǒng)技術(shù)等領(lǐng)域具有廣闊的應(yīng)用前景。然而,一般金屬材料的平均晶粒尺寸與微成形制件的特征尺寸相當(dāng),極大地影響微型零件的填充質(zhì)量和尺寸精度。而利用劇烈塑性變形方法制備的具有超細(xì)晶粒度的材料能明顯改善常規(guī)材料的變形不均勻性,在塑性微成形技術(shù)領(lǐng)域中具有明顯的優(yōu)勢(shì)。本文通過高壓扭轉(zhuǎn)(HPT)工藝制備出不同圈數(shù)HPT純鈦試樣,并研究其在高壓扭轉(zhuǎn)過程中微觀組織演變規(guī)律以及顯微硬度分布規(guī)律。通過研究超細(xì)晶純鈦的存儲(chǔ)能、再結(jié)晶溫度以及超細(xì)晶純鈦退火過程中的靜態(tài)熱穩(wěn)定性,揭示超細(xì)晶純鈦熱穩(wěn)定性機(jī)理。最后研究了應(yīng)變速率和晶粒尺寸對(duì)純鈦在室溫微壓縮過程中的變形行為、表面形貌和微觀組織變化的影響。研究了純鈦在高壓扭轉(zhuǎn)過程中微觀組織演變規(guī)律以及顯微硬分布規(guī)律,結(jié)果表明:在高壓扭轉(zhuǎn)過程中發(fā)生α相(密排六方結(jié)構(gòu))到ω相(六方結(jié)構(gòu))轉(zhuǎn)變,且隨著高壓扭轉(zhuǎn)圈數(shù)的增加,ω相的體積分?jǐn)?shù)逐漸增加。在高壓扭轉(zhuǎn)過程中,試樣的顯微硬度值顯著增加,但在試樣中心存在低硬度區(qū)。試樣邊緣處顯微硬度隨著扭轉(zhuǎn)圈數(shù)的增加而逐漸增加,當(dāng)扭轉(zhuǎn)圈數(shù)大于5圈時(shí),試樣顯微硬度值達(dá)到飽和。扭轉(zhuǎn)圈數(shù)為1/4圈時(shí),晶粒受到環(huán)向的純剪切變形作用,在晶粒內(nèi)部有大量的位錯(cuò)和孿晶,晶粒尺寸依然較大。扭轉(zhuǎn)圈數(shù)為1圈時(shí),試樣中心處晶粒尺寸依然較大,而試樣半徑1/2處晶粒已細(xì)化到200nm。扭轉(zhuǎn)圈數(shù)大于5時(shí),組織內(nèi)部已無孿晶,試樣中心處同時(shí)存在已細(xì)化區(qū)和未細(xì)化區(qū),而試樣半徑1/2處晶粒已細(xì)化到150nm以下。表明高壓扭轉(zhuǎn)工藝具有較強(qiáng)的晶粒細(xì)化能力。研究了高壓扭轉(zhuǎn)不同圈數(shù)試樣的形變存儲(chǔ)能、再結(jié)晶溫度以及再結(jié)晶激活能。結(jié)果表明:高壓扭轉(zhuǎn)5圈試樣再結(jié)晶溫度在703.8℃到748.8℃之間,再結(jié)晶激活能在94.4KJ/mol到112.2KJ/mol之間,晶粒長大的激活能約為109KJ/mol。高壓扭轉(zhuǎn)變形超細(xì)晶純鈦在退火過程中微觀組織演變可分為幾個(gè)階段,各個(gè)階段可以相互重疊:第一階段存在于劇烈塑性變形材料的晶粒中的位錯(cuò)重新分布和其數(shù)量的減少;第二階段劇烈塑性變形時(shí)形成的不平衡晶界中位錯(cuò)重新分布,導(dǎo)致大角度晶界形成。晶界寬度較窄,約為幾個(gè)原子尺寸;第三階段不平衡晶界組織發(fā)生回復(fù)現(xiàn)象,導(dǎo)致內(nèi)應(yīng)力和晶格畸變同時(shí)減小。此時(shí)晶粒尺寸依然很小,無再結(jié)晶形核階段;第四階段發(fā)生再結(jié)晶過程,若回復(fù)后組織存在個(gè)別不平衡晶界,則在再結(jié)晶過程中出現(xiàn)晶粒異常長大;第五階段加熱過程中晶粒長大。純鈦室溫微壓縮實(shí)驗(yàn)表明:超細(xì)晶純鈦的應(yīng)變速率敏感性高于粗晶純鈦。當(dāng)晶粒尺寸低于200nm時(shí),材料的流動(dòng)應(yīng)力非常平穩(wěn),這與超細(xì)晶純鈦晶粒內(nèi)部較高的位錯(cuò)密度有關(guān)。隨著微壓縮試樣晶粒尺寸的增大,流動(dòng)應(yīng)力逐漸降低,但當(dāng)試樣晶粒數(shù)目非常少時(shí),材料的流動(dòng)應(yīng)力反而升高。通過SEM觀察其形貌,結(jié)果表明隨著晶粒尺寸的增大,微壓縮試樣側(cè)面的凹凸不平感越來越明顯,這是由于表面層晶粒所占的比重較大,使得單個(gè)晶粒變形對(duì)于試樣整體變形影響較大所致。當(dāng)晶粒尺寸處于超細(xì)晶范疇時(shí),試樣表面光滑、表面質(zhì)量較高。通過對(duì)微壓縮試樣中心處的微觀組織進(jìn)行觀察,結(jié)果表明:晶粒尺寸較大時(shí),出現(xiàn)一定數(shù)量的孿晶,晶粒呈長條狀并且晶粒內(nèi)部存在大量的小角度晶界,表明其變形機(jī)制為位錯(cuò)滑移以及孿生變形。晶粒尺寸較小時(shí),晶粒仍然近似于等軸狀,晶粒內(nèi)部小角度晶界數(shù)量較少。
[Abstract]:With the increasing demand for micro products, micro forming technology has developed rapidly. The plastic micro forming technology has the advantages of low production cost and good forming properties. It is very suitable for mass production of micro parts. It has a broad application prospect in microelectromechanical systems and micro system technology. However, the average metal material is average. The size of the grain is equivalent to the characteristic size of the micro forming part, which greatly affects the filling quality and the size accuracy of the micro parts. The material with superfine grain size prepared by the strenuous plastic deformation method can obviously improve the deformation nonuniformity of the conventional material, and has obvious advantages in the field of plastic micro forming. This paper is used in this paper. HPT pure titanium samples with different cycles were prepared by high pressure torsion (HPT) process, and the microstructure evolution and microhardness distribution in the process of high pressure torsion were studied. The thermal stability of ultrafine crystal pure titanium, the recrystallization temperature and the static thermal stability during the annealing process of ultrafine crystal pure titanium were studied, and the thermal stability of ultrafine crystal pure titanium was revealed. The effect of strain rate and grain size on the deformation behavior, surface morphology and microstructure changes of pure titanium in the process of chamber temperature microcompression was studied. The microstructure evolution and microhardness distribution of pure titanium during high pressure torsion were studied. The results showed that alpha phase (six square knot) occurred during the high pressure torsion process. The volume fraction of Omega phase increases with the increase of the number of high pressure torsional rings. In the process of high pressure torsion, the microhardness value of the sample increases significantly, but there is a low hardness zone at the center of the sample. The microhardness at the sample center increases with the increase of the number of torsional rings, when the number of torsional rings is more than 5 circles. The microhardness value of the sample is saturated. When the number of torsional rings is 1/4 ring, the grain is subjected to the pure shear deformation of the ring direction. There are a large number of dislocation and twin crystals in the grain. The grain size of the sample center is still larger when the number of twisting rings is 1 rings, and the grain size of the specimen has been refined to the number of 200nm. torsional rings at 1/2. At 5, there is no twin in the tissue. At the same time, there are already refined and unrefined regions at the center of the sample, and the grain size of the specimen has been refined to less than 150nm at 1/2. It shows that the high pressure torsion process has a strong grain refinement ability. The results show that the recrystallization temperature of the high pressure torsion 5 ring specimens is between 703.8 and 748.8, and the activation energy of recrystallization is between 94.4KJ/mol and 112.2KJ/mol. The activation energy of grain growth is about 109KJ/mol. high pressure torsion deformation of ultrafine crystal titanium in the annealing process, the microstructure evolution can be divided into several stages, each stage can overlap each other: first order The dislocation redistribution and the decrease in the number of dislocation in the grain of the strenuous plastic deformation material; the dislocation redistribution in the unbalanced grain boundary formed in the second stage of severe plastic deformation, resulting in the formation of a large angle grain boundary. The width of the grain boundary is narrower, about several atomic sizes, and the third phase unbalance grain boundary tissue has a recovery phenomenon. The internal stress and lattice distortion decrease at the same time. At this time, the grain size is still very small and no recrystallization nucleation stage. The fourth stage of recrystallization process, if there is an individual unbalanced grain boundary after the recovery of the tissue, the abnormal grain growth in the recrystallization process; the grain growth during the fifth stage heating process. The pure titanium room temperature micro compression experiment shows that: The strain rate sensitivity of ultrafine pure titanium is higher than that of coarse-grained pure titanium. When the grain size is lower than 200nm, the flow stress of the material is very stable, which is related to the higher dislocation density inside the ultrafine crystal pure titanium grain. The flow stress is increased. The morphology of the surface is observed by SEM. The results show that with the increase of grain size, the concave and convex side of the microcompression specimen becomes more and more obvious, which is due to the larger proportion of the grain in the surface layer, which makes the deformation of the single grain larger to the whole deformation of the sample. The surface of the specimen is smooth and the surface quality is high. By observing the microstructure at the center of the microcompression specimen, the results show that when the grain size is larger, there are a certain number of twins, the grain is long and there is a large number of small angle grain boundaries in the grain, which indicates that the deformation mechanism is dislocation slip and twin deformation. Grain size is a grain ruler. The grain size is still approximately equal to the equiaxed shape, and the small angle grain boundaries in the grains are relatively small.
【學(xué)位授予單位】：哈爾濱工業(yè)大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2015
【分類號(hào)】：TG146.23

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本文編號(hào)：1933898