本文關鍵詞： 納米晶 鈷 力學性能 變形機制　出處：《吉林大學》2017年碩士論文　論文類型：學位論文

【摘要】：對納米晶材料的研究已經(jīng)有幾十年了,普遍認知是納米晶材料擁有優(yōu)越的力學性能,如高強度。粗晶材料在晶粒尺寸不斷減小過程中強度不斷增大,人們認為是位錯堆積的結果。在一定的納米尺度范圍這個規(guī)律依然適用,但到達某個臨界值時,強度隨著尺寸減小而減小,人們認為這是晶界滑移造成的。密排與面心相比擁有更少的滑移系,更少的位錯運動,這差異會對上面的力學行為產(chǎn)生怎樣的影響呢?基于上面的疑問,本文采用磁控濺射的方法制備了三種不同相結構的納米晶鈷(NC Co),然后都用XRD、SEM、TEM等手段進行微觀結構表征,采用納米壓痕儀進行力學性能研究。解釋面心納米晶金屬的尺寸依賴的力學性能,從位錯弓出模型角度。(1)通過控制磁控濺射過程中的工藝參數(shù)制備出了三種不同結構的納米晶鈷,然后運用XRD、SEM、TEM等手段對三種結構納米晶鈷進行表征,發(fā)現(xiàn)占空比越大有助于面心立方相的形成。密排相納米晶鈷的晶粒尺寸為37 nm,混合相納米晶鈷的晶粒尺寸為38 nm,面心相納米晶鈷的晶粒尺寸為25 nm。(2)基于單根位錯弓出模型發(fā)展的FCC金屬的V(d)(或L(d),m(d,T)和?y(d)函數(shù),本建�？蚣軐⒒谖诲e的力學描述將FCC金屬的尺寸依賴性特性和響應擴展到納米級體系中,該模型還成功預測速率依賴性力學行為作為H-P失效和相關的臨界晶粒尺寸的FCC NC金屬,該模型顯示與UFG和NC材料的許多實驗研究完全一致,然而模型的兩個局限性是T?RT和準靜態(tài)應變速率范圍發(fā)生與模型的偏差,這種統(tǒng)一的模型表明,依賴的力學函數(shù)具有從位錯角度的內在關系,這預期在本構規(guī)律發(fā)展中具有進一步的應用。(3)本次實驗納米壓痕硬度結果結合Ma等人的實驗成果可以得出,納米晶鈷強度與晶粒尺寸關系曲線出現(xiàn)負斜率(反H-P關系),晶粒尺寸的臨界值約為25nm。三種相結構的NC Co都表現(xiàn)出可觀的應變速率敏感性。NC Co的應變速率敏感性m值明顯要比NC Ni的m值要高,位錯活動不僅僅發(fā)生在晶界,孿晶界面上也有一些,這可能是納米晶鈷高m值的原因。雙相中存在大量的相界面,相界面與孿晶界面相似都有位錯活動,這導致雙相的m值顯著增大。雙相納米晶鈷的相界面與孿晶界面相似的效果,導致雙相納米晶鈷在低載荷下仍然有較高的蠕變量。
[Abstract]:Study of nanocrystalline materials has been for decades, the general cognitive has superior mechanical properties of nanocrystalline materials, such as high strength. Coarse grained material in the grain size decreases the strength increasing process, considered the dislocation accumulation results. Still applies at nanometer scale of the law, but to a certain a critical value, the strength decreases with the decrease in size, it is believed to be caused by grain boundary sliding. Compared with the close packed face centered slip system has less and less the difference of dislocation movement, what kind of impact on the mechanical behavior of the above? The above questions based on the three different phase structure the cobalt nanocrystals were prepared by RF magnetron sputtering (NC Co), and then use XRD, SEM, TEM and other means of characterization of microstructure and mechanical properties were studied by nanoindentation. Explain the surface nanocrystalline metal heart 鐨勫昂瀵鎬緷璧栫殑鍔涘鎬ц兘,浠庝綅閿欏紦鍑烘ā鍨嬭搴，

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