【摘要】：硼(B)、鈮(Nb)元素在合金材料晶界的偏聚行為,直接影響合金材料的機(jī)械性能。澄清B、Nb元素在晶界的偏聚機(jī)制,有助于精準(zhǔn)控制其在晶界的偏聚行為,進(jìn)而提高材料的性能。本論文綜合運(yùn)用飛行時(shí)間二次離子質(zhì)譜、俄歇電子能譜、透射電子顯微鏡和電子背散射衍射等技術(shù)研究了高溫變形高純鎳和連續(xù)冷卻淬火的微合金鋼中B、Nb元素在晶界的偏聚,并采用正電子湮沒壽命技術(shù)分析了冷卻過程中微合金鋼中空位和位錯(cuò)等缺陷的行為。最后采用基于密度泛函理論的第一性原理研究了 B在bcc-Fe和fcc-Fe中的固溶方式和擴(kuò)散機(jī)制。利用飛行時(shí)間二次離子質(zhì)譜技術(shù),在高溫變形高純鎳中直接觀察到B在一般晶界和退火孿晶界上均形成顯著的偏聚,且偏聚區(qū)域的寬度隨著變形溫度的降低而增大。相同熱處理工藝下,B在孿晶界上的偏聚明顯比一般晶界上的偏聚弱。在一般晶界上觀察到兩種形態(tài)的偏聚:在1100℃變形(發(fā)生明顯的再結(jié)晶行為)的樣品中,B偏聚區(qū)域局限于晶界附近約1 μm范圍內(nèi),偏聚程度較強(qiáng);在700℃變形(未發(fā)生明顯的再結(jié)晶行為)的樣品中,B偏聚區(qū)域分布在晶界兩側(cè)約6 μm的范圍內(nèi),偏聚程度較弱。在部分樣品中的一般晶界上可以同時(shí)觀察到這兩種形態(tài)的偏聚。在微合金鋼連續(xù)冷卻過程中,隨著溫度的降低,Nb在原奧氏體晶界上的偏聚逐漸增強(qiáng),同時(shí)利用正電子湮沒壽命技術(shù)發(fā)現(xiàn)這一過程中伴隨著材料內(nèi)部空位型缺陷濃度的降低。分析認(rèn)為冷卻過程中空位向晶界的擴(kuò)散和位錯(cuò)向晶界的移動(dòng)可能均會(huì)促進(jìn)Nb向晶界的偏聚。借助于飛行時(shí)間二次離子質(zhì)譜技術(shù),在連續(xù)冷卻微合金鋼的原奧氏體晶界上直接觀察到了沿著原奧氏體晶界分布的Nb、Cu富集區(qū)。通過對(duì)原奧氏體晶界附近約40 μm范圍內(nèi)的所有富集區(qū)進(jìn)行分析,發(fā)現(xiàn)Nb只在Cu富集區(qū)內(nèi)出現(xiàn)富集,表明在微合金鋼連續(xù)冷卻過程中Cu元素促進(jìn)了 Nb在奧氏體晶界的富集。利用透射電子顯微鏡在原奧氏體晶界上觀察到了含Nb和Cu的析出物。根據(jù)第一性原理計(jì)算結(jié)果,在bcc-Fe中B既可以占據(jù)置換位置,又可以占據(jù)八面體中心位置,但以間隙機(jī)制進(jìn)行擴(kuò)散。所得擴(kuò)散系數(shù)為,D_0=1.05×10~(-7)×exp(-0.75eV/kBT)m~2·s~(-1)與實(shí)驗(yàn)結(jié)果基本吻合。在fcc-Fe中B傾向于占據(jù)置換位置,計(jì)算所得B以B-單空位復(fù)合體機(jī)制擴(kuò)散的擴(kuò)散系數(shù)約為D_0=6.30× 10~6×exp(-2.01 eV/kBT)m~2·s~(-1)。
[Abstract]:The segregation behavior of boron (B), niobium (Nb) at the grain boundary of the alloy directly affects the mechanical properties of the alloy. Clarifying the segregation mechanism of BNb at grain boundary is helpful to accurately control the segregation behavior of Bnb at grain boundary and improve the properties of the material. In this paper, the time of flight secondary ion mass spectrometry, Auger electron spectroscopy, transmission electron microscope and electron backscattering diffraction were used to study the high temperature deformed high purity nickel and continuous cooling quenched microalloyed steel. The segregation of Nb elements at grain boundaries and the behavior of defects such as vacancies and dislocations in microalloyed steels during cooling were analyzed by positron annihilation lifetime technique. Finally, the solution mode and diffusion mechanism of B in bcc-Fe and fcc-Fe were studied by using the first principle based on density functional theory (DFT). By means of time of flight secondary ion mass spectrometry, it was observed that the segregation of B was observed at both general grain boundary and annealing twin boundary directly in high-purity nickel deformed at high temperature, and the width of segregation region increased with the decrease of deformation temperature. Under the same heat treatment process, the segregation of B on twin boundary is obviously weaker than that on general grain boundary. Two kinds of segregation were observed at general grain boundaries: in the samples deformed at 1100 鈩，

本文編號(hào)：2390229