電偶合對鈦合金TC4表面化學(xué)轉(zhuǎn)化膜結(jié)構(gòu)和性能的影響
本文選題:鈦合金 + 電偶合; 參考:《山東大學(xué)》2017年碩士論文
【摘要】:金屬表面磷酸鹽化學(xué)轉(zhuǎn)化膜致密、晶粒細小、性能優(yōu)異,主要用于金屬的腐蝕防護、涂裝基底等方面。但目前,國內(nèi)外對于鈦合金表面磷酸鋅制備的研究較少。本文在常溫浸漬化學(xué)轉(zhuǎn)化的基礎(chǔ)上,重點研究了不同偶合材料、不同偶合面積比、不同接觸面積比及時間對鈦合金表面化學(xué)轉(zhuǎn)化膜的影響,利用X射線衍射儀、熱場發(fā)射掃描電鏡、劃痕儀及電化學(xué)工作站等技術(shù)手段系統(tǒng)的表征和分析化學(xué)轉(zhuǎn)化膜的結(jié)構(gòu)、形貌、結(jié)合強度、電化學(xué)性能,并對電偶合化學(xué)轉(zhuǎn)化機制進行了初步探討。結(jié)果表明未偶合條件下轉(zhuǎn)化,無論時間長短,鈦合金TC4表面沒有化學(xué)轉(zhuǎn)化膜形成,利用電偶合后基體表面均生成一層化學(xué)轉(zhuǎn)化膜。轉(zhuǎn)化膜的主要成分是磷酸鋅(Zn3(P04)2·4H20)。TC4-MZG(Mg-1.75Zn-0.55Ga 鎂合金)偶合體系得到的磷化膜層較致密,晶粒尺寸較小,無裸露基體現(xiàn)象。在所試驗范圍內(nèi),TC4-MZG面積比為1:1時,化學(xué)轉(zhuǎn)化膜晶粒細小、致密、孔隙率小,其結(jié)合強度、耐腐蝕性能也最好。TC4-MZG偶合體系完全接觸(接觸比為1)時,轉(zhuǎn)化膜晶粒尺寸明顯減小,結(jié)合力達到24 N。電偶合能夠開啟化學(xué)轉(zhuǎn)化反應(yīng),縮短轉(zhuǎn)化時間,加速成膜速率。轉(zhuǎn)化膜開始轉(zhuǎn)化的時間約在15 s~30 s之間。延長轉(zhuǎn)化時間能夠促進晶粒數(shù)量增多和晶粒長大,但并不是時間越長轉(zhuǎn)化效果越好。轉(zhuǎn)化20 min時,化學(xué)轉(zhuǎn)化膜均勻,致密,完全覆蓋基體,繼續(xù)增加轉(zhuǎn)化時間,晶粒處于不斷溶解和二次析出交替進行的狀態(tài)。TC4-AZ91D偶合體系對化學(xué)轉(zhuǎn)化膜物相、形貌影響明顯。TC4-AZ91D偶合體系形成的化學(xué)轉(zhuǎn)化膜是由Zn相和Zn3(PO4)2·4H20相構(gòu)成,且隨著偶合面積比的增大,Zn物相的含量越來越多。膜層由顆粒堆垛而成,這與其他偶合體系到的形貌不同。電偶合在化學(xué)轉(zhuǎn)化中的成膜作用不是一種偶然現(xiàn)象。常溫下利用電偶合在與鈦合金具有類似性質(zhì)的不銹鋼、銅合金表面均能制備出一層均勻致密的轉(zhuǎn)化膜。該轉(zhuǎn)化膜主要是由磷酸鋅(Zn3(PO4)2·4H2CO構(gòu)成。電偶合能夠縮短誘導(dǎo)時間,促進早期沉淀點的形成,制備出結(jié)構(gòu)、性能優(yōu)異的化學(xué)轉(zhuǎn)化膜。通過研究電偶合成膜過程中的電位-時間曲線可知,化學(xué)轉(zhuǎn)化膜的形成過程可以分為以下五個階段:陽極表面氧化層及基體的溶解過程,陰極早期形核階段,陰極晶核或新生晶粒的再溶解階段,陰極晶粒的快速長大階段,陰極轉(zhuǎn)化膜的穩(wěn)態(tài)生長階段。
[Abstract]:Phosphate chemical conversion film on metal surface is compact, fine grain, excellent performance, mainly used in metal corrosion protection, coating substrate and so on. However, the preparation of zinc phosphate on the surface of titanium alloy is seldom studied at home and abroad. On the basis of chemical transformation of impregnation at room temperature, the effects of different coupling materials, different ratio of coupling area, different ratio of contact area and time on the surface chemical conversion film of titanium alloy were studied by X-ray diffractometer. The structure, morphology, binding strength and electrochemical properties of the chemical conversion films were characterized and analyzed by means of thermal field emission scanning electron microscope, scratch tester and electrochemical workstation. The mechanism of electrocoupling chemical conversion was also discussed. The results showed that no chemical conversion film was formed on TC4 surface of titanium alloy under uncoupled conditions, and a layer of chemical conversion film was formed on the substrate surface after electrocoupling. The main composition of the conversion film is zinc phosphate (Zn3 (P04) 24H20). TC4-MZG (Mg-1.75Zn-0.55Ga magnesium alloy) coupling system. When the area ratio of TC4-MZG to TC4-MZG is 1:1, the grain size of TC4-MZG film decreases obviously when its grain size is fine, compactness, porosity is small, its bonding strength and corrosion resistance is the best. TC4-MZG coupling system is in complete contact (contact ratio is 1). The binding ability was 24 N. Electric coupling can open the chemical conversion reaction, shorten the conversion time and accelerate the film forming rate. The conversion time of the film was about 15 s ~ 30 s. Prolonging the transformation time can promote the increase of grain number and grain growth, but the longer the transformation time is, the better the transformation effect is. During 20 min conversion, the chemical conversion film was homogeneous, compact, completely covered with the matrix, and the transformation time was increased. The grain was in the state of continuous dissolution and secondary precipitation alternately. TC4-AZ91D coupling system had a good effect on the phase of the chemical conversion film. The chemical conversion film formed by the coupling system of .TC4-AZ91D is composed of Zn phase and Zn3 (PO4) 24H20 phase, and the content of Zn phase increases with the increase of coupling area ratio. The film is made of granular stacking, which is different from the morphology of other coupling systems. The film forming effect of electric coupling in chemical transformation is not an accidental phenomenon. A uniform and compact conversion film can be prepared on the surface of copper alloy by electric coupling at room temperature on stainless steel with similar properties to titanium alloy. The conversion film is mainly composed of zinc phosphate (Zn _ 3 (PO _ 4) _ (24) H _ 2CO). Electric coupling can shorten the induction time, promote the formation of early precipitation point, and prepare chemical conversion film with excellent structure and performance. By studying the potential-time curves of the electrocoupling-forming process, the formation process of the chemical conversion film can be divided into the following five stages: the dissolution of the oxidation layer on the anodic surface and the substrate, and the early nucleation stage of the cathode. The phase of redissolution of cathode nucleus or new grain, the rapid growth of cathode grain, and the steady state growth of cathode conversion film.
【學(xué)位授予單位】:山東大學(xué)
【學(xué)位級別】:碩士
【學(xué)位授予年份】:2017
【分類號】:TG174.4
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