本文選題：鎂合金 + 孿生��； 參考：《重慶大學》2016年博士論文

【摘要】：本文以研究鎂合金中形變孿晶間的應變協調效應及其變體選擇機制為主要目的。以商業(yè)AZ31熱軋板為初始材料,通過壓縮、拉伸、軋制等多種變形方式對其進行一定量的塑性變形。變形組織中觀察到晶內多孿晶、孿晶對、孿晶鏈、長孿晶帶等多種孿晶圖案以及不同類型的二次孿晶。重點利用(原位)電子背散射衍射(EBSD)技術表征了孿晶圖案的形貌和取向關系,結合(廣義)Schmid定律和局部應變協調效應(m￠判據)研究了孿晶發(fā)生與變體選擇機制。跡線分析是取向旋轉法鑒定孿晶變體的重要補充,但對觀察面依賴。研究發(fā)現,AZ31板壓縮中Schmid factor(SF)最大相對變體的跡線角在平行c軸和壓縮方向的觀察面上分布在高角度(79-86°),利于從中區(qū)分實際變體,因此鎂合金壓縮中跡線分析變體的最佳觀察面總平行c軸和壓縮方向。軋制中孿晶活度對晶粒取向高度依賴,通過分析軋制中的側向應力,發(fā)現文獻中應用于孿晶的修正Schmid判據對應相同的應力狀態(tài),具有一致性�？紤]側向應力的廣義Schmid定律不僅能解釋孿晶的變體選擇,而且能預測孿晶活度隨織構的變化規(guī)律。AZ31板沿橫向(TD)壓縮中出現了多種{101_2}拉伸孿晶圖案,如晶內多孿晶、晶間孿晶對和孿晶鏈。沿接近晶粒101_0壓縮時,晶內六個孿晶變體中一對相對變體的SF非常大,因此這兩個變體都容易激活。當接近112_0壓縮時,晶內四個變體的SF比較大且接近,此時相鄰變體因為應變相容性最好(m￠最高)而經常激活。晶界處的孿晶傳遞形成孿晶對或孿晶鏈,孿晶對通常有較高的m￠和SF,其中被誘導孿晶也可能有較低的SF。統計結果顯示,孿晶間的應變協調效應在孿晶對中普遍存在,可以激活一定量的non-Schmid孿晶;高m￠不是Schmid定律主導變體選擇的結果。細晶強織構軋制中孿晶傳遞能力進一步增強,形成了長孿晶帶。長孿晶帶中的孿晶都有較高的SF且相連孿晶間有高m￠(通常0.8),說明應變協調效應與Schmid定律協同決定孿晶變體選擇且促進長孿晶帶形成。原位EBSD獲得的圖像質量圖顯示,孿晶應變在拉伸過程中穿過晶界傳遞到相鄰晶粒,證實了晶間孿晶傳遞現象和孿晶間的應變協調效應。另外,原位觀察到孿晶獨立在孿晶界和晶內成核等現象。AZ31板沿法向(ND)拉伸中超大晶粒的初級{101_2}孿晶交割處出現了大量{101_2}-{101_2}二次孿晶。統計發(fā)現,(交割孿晶-二次孿晶)晶界取向關系擇優(yōu)分布在49°9_094,這與初級和二次孿晶變體選擇有關。相互交割的初級孿晶通常來自晶內應變相容性最好的相鄰變體;二次孿晶經常在與其母體孿生面相鄰的兩個孿生系統上激活,其中與交割孿晶應變不相容性較低的孿生系統激活頻率更高。{101_1}-{101_2}二次孿晶變體與初始母體有四種不同的取向關系,對應四個二次變體,它們的擇優(yōu)出現依賴具體的變形方式。單獨利用Schmid定律或局部應變協調效應(m￠判據)都無法解釋這種依賴性。本文基于初級和二次孿晶變體間的應變相容性和Schmid定律提出一種復合Schmid因子mc,能夠統一解釋三種變形方式下二次孿晶變體的激活規(guī)律及擇優(yōu)差異。
[Abstract]:In this paper, the main purpose of this study is to study the strain coordination effect and the selection mechanism of the deformation twins in the magnesium alloy. The commercial AZ31 hot rolled plate is used as the initial material, and a certain amount of plastic deformation is carried out by compression, tensile, rolling and other deformation modes. The intragranular twins, twin pairs, twin chains and long twin bands are observed in the deformation structure. With a variety of twin patterns and different types of two twins, the relationship between the morphology and orientation of the twin patterns is characterized by (in situ) electron backscatter diffraction (EBSD), and the mechanism of twin generation and variation selection is studied with the (generalized) Schmid law and the local strain coordination effect (M criterion). The trace analysis is the identification of the orientation rotation method. It is an important supplement for the twins, but it is dependent on the observation surface. It is found that the trace angle of the largest relative variation of the Schmid factor (SF) in the AZ31 plate compression is distributed at the high angle (79-86 degrees) in the parallel C axis and the compression direction, which is beneficial to distinguish the actual variant from it, so the best observation surface of the optimal observation surface of the trace analysis variant in the compression of the magnesium alloy is the total parallel C. The twinning activity in rolling is highly dependent on the grain orientation in rolling. By analyzing the lateral stress in the rolling, it is found that the revised Schmid criterion applied to twins in the literature is consistent with the same stress state. The generalized Schmid law considering the lateral stress can not only explain the selection of the twins but also predict the twins. A variety of {101_2} tensile twin patterns, such as intragranular twins, intercrystalline twins, and twin chains, are found in.AZ31 plates along the transverse (TD) compression. The SF of a pair of relative variants in the six twin variants in the crystal is very large, as these two variants are easily activated when they are close to 112_0 compression. The SF of the four variations in the crystal is large and close, and the adjacent variants are often activated because of the best strain compatibility (the highest m). The twins at the grain boundary form twin pairs or twin chains, and the twins are usually higher in M and SF, and the induced twins may also have lower SF. statistics showing the strain coordination effect between twins. It is common in twin pairs that a certain amount of non-Schmid twins can be activated; high m is not the result of the selection of the leading variant of Schmid's law. The twin transfer ability of the fine crystal strong textured rolling is further enhanced and the long twin crystal band is formed. The twins in the long twinning bands have high SF and high m (usually) between the twins (usually 0.8), indicating the strain covariance. The modulation effect and Schmid's law coordinate the selection of twins and promote the formation of the long twinning bands. The image quality map obtained by in situ EBSD shows that the twin strain passes through the grain boundary to the adjacent grain during the stretching process, which confirms the phenomenon of intergranular twins transfer and the strain coordination between twins. In addition, the twins are observed in situ that twins are independent in twins. A large number of {101_2}-{101_2} two twins appeared at the primary {101_2} twinning at the primary {101_2} twin in the normal direction (ND) stretching of the boundary and the intragranular nucleation. It was found that the grain boundary orientation of the two twin crystals (the intertwinning twins) was preferentially distributed at 49 degree 9_094, which was related to the selection of the primary and two twinning variants. The two twinning is often activated in two twin systems adjacent to the twin surface of the mother, and the twin system with the lower incompatibility of the twinning strain is higher in the activation frequency of the twin system, and there are four different orientation relationships between the.{101_1}-{101_2} two twin and the initial parent. Four two variations, their selection depends on the specific deformation mode. Using the Schmid's law or the local strain coordination effect (M criterion) can not explain this dependence. Based on the strain compatibility between the primary and two twin variants and the Schmid law, a compound Schmid factor MC is proposed, which can explain the three variations in a unified way. The activation pattern and the preferred difference of the two twinning variants under the shape.
【學位授予單位】：重慶大學
【學位級別】：博士
【學位授予年份】：2016
【分類號】：TG146.22

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