發(fā)布時間：2018-03-26 02:00

  本文選題：等離子體滲氮　切入點：熱力學(xué)　出處：《哈爾濱工業(yè)大學(xué)》2017年碩士論文

【摘要】：在過去十年時間,本課題組開展了對不同Cr當量淬火鋼進行低溫等離子體氮化或氮碳共滲處理實驗研究,如17-4PH、M50、2Cr13、304、316、M50NiL、38CrMoAl、40CrNi和30CrMnSi等,并且已經(jīng)成功實現(xiàn)了表面層的納米化,但是現(xiàn)有的納米化的機制無法解釋納米化后出現(xiàn)低氮化合物的原因。本文研究了 Fe-Cr-N體系的調(diào)幅分解反應(yīng),旨在揭示等離子體滲氮后鋼表面發(fā)生納米化的機制,基于“偽二元”和雙亞點陣兩種熱力學(xué)模型計算了 Fe-Cr-N體系的吉布斯自由能。在“偽二元”模型得到Fe-Cr-N體系的吉布斯自由能-成分曲線出現(xiàn)了雙勢阱,說明Fe-Cr-N體系在一定條件下可以發(fā)生調(diào)幅分解。雙亞點陣模型計算了不同Cr當量鋼中含氮馬氏體的吉布斯自由能與含氮量的關(guān)系,得到了不同Cr當量鋼滲氮調(diào)幅分解的溫度區(qū)間和最佳氮勢。結(jié)合多組實驗的TEM分析,本文提出了Cr當量鋼滲氮納米化的機制:在一定條件下,隨著N含量的增加,α'N發(fā)生調(diào)幅分解反應(yīng),生成納米尺寸的低氮化合物FeNz和高氮馬氏體α"N,從而使?jié)B層組織細化。通過第一性原理對不同Cr當量含氮馬氏體和低氮化合物的結(jié)構(gòu)進行了模擬,發(fā)現(xiàn)含氮馬氏體和低氮化合物結(jié)構(gòu)的總能都小于0,說明在O K下這些結(jié)構(gòu)都可以存在。并且Cr當量為1/11和1/7的含氮馬氏體結(jié)合能和形成能隨含氮量的變化出現(xiàn)了雙勢阱趨勢,進一步提出滲氮納米化組織可能是調(diào)幅分解導(dǎo)致的微觀機制。由于Fe-3d、Cr-3d和N-2p的雜化,在不同Cr當量含氮馬氏體的費米能級附近處,都出現(xiàn)了贗能隙,從電子結(jié)構(gòu)角度說明這些結(jié)構(gòu)在0K下都是相對穩(wěn)定的,為調(diào)幅分解在滲氮溫度下發(fā)生提供了條件。低氮化合物的第一性原理計算從能量和電子結(jié)構(gòu)兩個方面都說明低氮化合物面心立方比體心立方結(jié)構(gòu)更穩(wěn)定一些,解釋了在實驗過程中檢測到的低氮化合物都為面心立方結(jié)構(gòu)的原因。
[Abstract]:In the past ten years, our group has carried out experimental research on nitridation or nitrocarburizing treatment of different Cr-equivalent quenched steels at low temperature, such as 17-4PHM50 / 2Cr13304316M50 / NiL338CrMoAl4Cr40CrNi and 30CrMnSi, and has successfully realized the nanocrystallization of the surface layer. However, the existing mechanism of nanocrystalline can not explain the reason of the formation of low nitrogen compounds after nanocrystalline. In this paper, the amplitude modulation decomposition of Fe-Cr-N system is studied to reveal the mechanism of nanocrystalline formation of steel surface after plasma nitriding. The Gibbs free energy of Fe-Cr-N system is calculated based on the two thermodynamic models of "pseudo-binary" and double-sub-lattice. The Gibbs free energy-component curve of Fe-Cr-N system is obtained by using "pseudo-binary" model. The results show that amplitude modulation decomposition can occur in Fe-Cr-N system under certain conditions. The relation between Gibbs free energy and nitrogen content of nitrogenous martensite in different Cr equivalent steels is calculated by double sub-lattice model. The temperature range and optimum nitrogen potential for nitriding amplitude modulation decomposition of different Cr equivalent steels were obtained. The mechanism of nitriding nanocrystalline nitriding of Cr-equivalent steel was put forward by TEM analysis under certain conditions. With the increase of N content, the amplitude modulation decomposition reaction of 偽 -N occurs. Nano-sized low nitrogen compounds FeNz and high nitrogen martensite 偽 "N were formed to refine the microstructure of the layer. The structures of different Cr equivalent nitrogenous martensite and low nitrogen compounds were simulated by first principles. It is found that the total energy of both nitrogen-containing martensite and low-nitrogen compounds is less than 0, which indicates that these structures can exist at O K. and the binding energy and formation energy of nitrogen-containing martensite with Cr equivalent of 1 / 11 and 1 / 7 have a double potential well trend with the change of nitrogen content. It is further suggested that the nitriding nanocrystalline structure may be the microcosmic mechanism of amplitude modulation decomposition. Due to the hybrid of Fe-3d Cr-3d and N-2p, pseudo-energy gaps appear near the Fermi energy levels of different Cr equivalent nitrogenous martensite. From the point of view of electronic structure, these structures are relatively stable at 0K. The first principle calculation of low nitrogen compounds shows that low nitrogen compounds are more stable than bulk centered cubic structures in terms of energy and electronic structure. The reason why all the low nitrogen compounds detected in the experiment are face-centered cubic structures is explained.
【學(xué)位授予單位】：哈爾濱工業(yè)大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2017
【分類號】：TG156.82
，

本文編號：1665835