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

【摘要】：強(qiáng)度和硬度是材料的基本力學(xué)性能,而疲勞性能則是材料能否進(jìn)入實際工程應(yīng)用的最終判據(jù)。與傳統(tǒng)材料相比,超細(xì)晶材料表現(xiàn)出了良好的強(qiáng)度和硬度,然而傳統(tǒng)的嚴(yán)重塑性變形(SPD)工藝得到的超細(xì)晶在提高材料強(qiáng)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(dǎo)致疲勞裂紋過早地萌生和擴(kuò)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(shù)制備出的超細(xì)晶具有獨特的微觀組織特性使超細(xì)晶材料得到了良好的強(qiáng)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(shù)在輔助水冷卻的條件下成功制備出超細(xì)晶,對其常規(guī)力學(xué)性能和高周疲勞性能進(jìn)行了深入研究,主要研究結(jié)論如下:FSP超細(xì)晶Cu-Al合金呈等軸再結(jié)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(xì)晶Cu-Al合金的晶粒細(xì)化機(jī)制,從而減小了超細(xì)晶的晶粒尺寸;而且高角晶界和孿晶界的增加,有助于超細(xì)晶在提高強(qiáng)度的同時增大材料的均勻延伸率,使超細(xì)晶獲得良好的強(qiáng)塑性匹配。與等通道轉(zhuǎn)角擠壓(ECAP)超細(xì)晶銅相比,FSP超細(xì)晶銅具有更高的疲勞強(qiáng)度和疲勞比。ECAP超細(xì)晶銅的疲勞損傷表現(xiàn)為大尺度剪切帶和晶粒嚴(yán)重粗化,而FSP超細(xì)晶銅特有的均勻微觀組織結(jié)構(gòu)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(xì)晶Cu-Al合金中,降低層錯能可以提高超細(xì)晶材料的疲勞強(qiáng)度,抑制位錯的交滑移,從而抑制了疲勞過程中的再結(jié)晶和晶粒的長大,少量的剪切帶也在晶粒內(nèi)部產(chǎn)生。特別是在低應(yīng)力下,疲勞表面不會出現(xiàn)大尺度的擠出現(xiàn)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(xué)位授予單位】：沈陽工業(yè)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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