發(fā)布時間：2018-02-11 05:27

  本文關鍵詞： 攪拌摩擦加工 超細晶 層錯能 高周疲勞 疲勞損傷　出處：《沈陽工業(yè)大學》2017年碩士論文　論文類型：學位論文

【摘要】：強度和硬度是材料的基本力學性能,而疲勞性能則是材料能否進入實際工程應用的最終判據。與傳統(tǒng)材料相比,超細晶材料表現出了良好的強度和硬度,然而傳統(tǒng)的嚴重塑性變形(SPD)工藝得到的超細晶在提高材料強度的同時大大降低了材料的塑性,而且在疲勞變形過程中極易發(fā)生局部變形從而導致疲勞裂紋過早地萌生和擴展,大大降低了其疲勞性能,限制了這種新型材料的使用范圍。而新型的攪拌摩擦加工(FSP)技術制備出的超細晶具有獨特的微觀組織特性使超細晶材料得到了良好的強塑性匹配。層錯能是面心立方金屬的一個重要參量,決定了位錯滑移的方式,從而對疲勞變形有重要影響。因此,本文選取具有不同層錯能的Cu-Al合金為研究對象,利用FSP技術在輔助水冷卻的條件下成功制備出超細晶,對其常規(guī)力學性能和高周疲勞性能進行了深入研究,主要研究結論如下:FSP超細晶Cu-Al合金呈等軸再結晶狀態(tài),位錯密度比較低,高角晶界比例較高并引入大量的孿晶界。降低層錯能,改變了超細晶Cu-Al合金的晶粒細化機制,從而減小了超細晶的晶粒尺寸;而且高角晶界和孿晶界的增加,有助于超細晶在提高強度的同時增大材料的均勻延伸率,使超細晶獲得良好的強塑性匹配。與等通道轉角擠壓(ECAP)超細晶銅相比,FSP超細晶銅具有更高的疲勞強度和疲勞比。ECAP超細晶銅的疲勞損傷表現為大尺度剪切帶和晶粒嚴重粗化,而FSP超細晶銅特有的均勻微觀組織結構抑制了大尺度剪切帶的形成和晶粒的長大,其疲勞損傷以擠出為主。在超細晶Cu-Al合金中,降低層錯能可以提高超細晶材料的疲勞強度,抑制位錯的交滑移,從而抑制了疲勞過程中的再結晶和晶粒的長大,少量的剪切帶也在晶粒內部產生。特別是在低應力下,疲勞表面不會出現大尺度的擠出現象,疲勞裂紋主要沿晶界萌生。
[Abstract]:The strength and hardness are the basic mechanical properties of the material, while the fatigue property is the final criterion of whether the material can be applied in practical engineering. Compared with the traditional material, the ultrafine grained material shows good strength and hardness. However, the superfine grains obtained by the traditional severe plastic deformation (SPD) process not only increase the strength of the material, but also greatly reduce the plasticity of the material. Moreover, local deformation is easy to occur in the process of fatigue deformation, which leads to the premature initiation and propagation of fatigue cracks. The fatigue performance is greatly reduced. The application range of the new material is limited, and the ultrafine crystal prepared by the new friction stir processing (FSPs) technology has unique microstructure characteristics, which makes the ultrafine crystal material get a good strong plastic match. The stacking fault energy is the surface center. An important parameter of cubic metals, Therefore, the Cu-Al alloy with different stacking fault energy was selected as the research object, and the ultrafine grain was successfully prepared by FSP technology under the condition of auxiliary water cooling. The conventional mechanical properties and high cycle fatigue properties of the superfine Cu-Al alloy were studied. The main conclusions are as follows: the superfine Cu-Al alloy exhibits equiaxed recrystallization state and low dislocation density. The high angle grain boundary ratio is higher and a large number of twin boundaries are introduced. The reduction of stacking fault energy changes the grain refinement mechanism of ultrafine grain Cu-Al alloy, thereby reducing the grain size of ultrafine grain, and the increase of high angle grain boundary and twin grain boundary, It helps to increase the strength of the ultrafine crystal and increase the uniform elongation of the material. Compared with ECAP ultrafine crystal copper, FSP ultrafine crystal copper has higher fatigue strength and fatigue ratio. The fatigue damage of ECAP ultrafine crystal copper shows large scale shear band and serious grain coarsening. The uniform microstructure of FSP ultrafine crystal copper inhibits the formation of large scale shear band and grain growth, and its fatigue damage is dominated by extrusion. In ultrafine grained Cu-Al alloy, reducing stacking fault energy can improve the fatigue strength of ultrafine grained material. The intersecting slip of dislocation is restrained, thus the recrystallization and grain growth in fatigue process are restrained, and a small amount of shear band is also produced in the grain. Especially under low stress, there is no large-scale extrusion phenomenon on the fatigue surface. Fatigue cracks mainly occur along grain boundaries.
【學位授予單位】：沈陽工業(yè)大學
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：TG146.11

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本文編號：1502306