本文選題：攪拌摩擦加工　切入點(diǎn)：Mg-Y-Nd合金　出處：《華南理工大學(xué)》2016年博士論文　論文類型：學(xué)位論文

【摘要】：作為析出強(qiáng)化型鎂合金,Mg-Y-Nd合金具有優(yōu)異的室溫強(qiáng)度,高溫耐熱性和良好的生物相容性,在航空航天、陸上交通工具、生物醫(yī)用材料等領(lǐng)域都得到了一定程度的應(yīng)用。然而,Mg-Y-Nd合金為密排六方結(jié)構(gòu),導(dǎo)致其在室溫的塑性變形能力較差,所以Mg-Y-Nd合金的加工成形和工業(yè)應(yīng)用均受到了一定程度的限制。攪拌摩擦加工(Friction stir processing,FSP)是一種新型的劇塑性變形加工技術(shù),在制備具有較好塑性變形能力的細(xì)晶金屬材料方面具有較大潛力。尤其是在循環(huán)水的輔助冷卻作用下,再結(jié)晶晶粒的長(zhǎng)大受到限制,從而能獲得更為細(xì)小的晶粒組織。因此,本研究選取了鑄造Mg-Y-Nd合金作為研究對(duì)象,空氣中/水下攪拌摩擦加工(NFSP/SFSP)為制備手段,研究了材料在FSP過(guò)程中的微觀組織演變、后續(xù)時(shí)效熱處理對(duì)加工試樣微觀組織變化及室溫力學(xué)性能的影響、加工試樣的高溫超塑性及在模擬體液(Simulated body fluid,SBF)中的腐蝕行為,為鑄造Mg-Y-Nd合金力學(xué)性能的提升和加工成形性能的改善提供技術(shù)參考,為FSP技術(shù)在生物醫(yī)用材料制備領(lǐng)域的應(yīng)用提供實(shí)驗(yàn)依據(jù)。首先,選取了不同的加工參數(shù),分別對(duì)鑄造Mg-Y-Nd合金進(jìn)行NFSP和SFSP。研究了不同加工條件下,攪拌區(qū)的組織演變和力學(xué)性能對(duì)比。兩種不同加工條件下的FSP后,材料的微觀組織均得到了顯著細(xì)化,力學(xué)性能也均得到了大幅提高。相比較而言,由于NFSP過(guò)程中產(chǎn)生更大的熱積累,NFSP試樣攪拌區(qū)的中心寬度和平均晶粒尺寸均大于SFSP試樣,而且NFSP試樣中具有部分再結(jié)晶晶粒長(zhǎng)大而形成的粗晶帶狀結(jié)構(gòu)。得益于循環(huán)水的冷卻作用,SFSP可以制備出晶粒尺寸更為細(xì)小的Mg-Y-Nd合金,綜合力學(xué)性能也更為優(yōu)異,其中相對(duì)最優(yōu)的加工參數(shù)為600 rpm的旋轉(zhuǎn)速度和60 mm/min的行進(jìn)速度。其次,結(jié)合NFSP過(guò)程中的熱歷史變化,對(duì)鑄造Mg-Y-Nd合金在NFSP過(guò)程中,第二相的固溶與析出行為進(jìn)行了研究與探討。后續(xù)時(shí)效熱處理后,NFSP試樣的伸長(zhǎng)率略微降低,強(qiáng)度則得到了進(jìn)一步提高。在150℃的峰值時(shí)效條件下,增強(qiáng)相主要為β′′,而在180℃的峰值時(shí)效條件下,增強(qiáng)相主要為β1。時(shí)效處理后,大量的析出相為裂紋的萌生提供了更多的形核位置,同時(shí)也為裂紋的延伸提供了更為復(fù)雜的擴(kuò)展路徑。斷口形貌表明,組織內(nèi)部的第二相顆粒帶狀結(jié)構(gòu)是造成NFSP及峰值時(shí)效試樣的伸長(zhǎng)率較低的主要原因。再次,選取了晶粒組織更為細(xì)小的SFSP試樣,在不同的測(cè)試溫度和應(yīng)變速率下,進(jìn)行了高溫拉伸測(cè)試。得益于細(xì)小的α-Mg晶粒和良好的組織穩(wěn)定性,SFSP制備的細(xì)晶Mg-Y-Nd合金在733 K和3×10~(-3) s~(-1)的測(cè)試條件下獲得了最大的伸長(zhǎng)率(967%);在758 K和2×10-2 s~(-1)的測(cè)試條件下獲得了最優(yōu)的高應(yīng)變速率超塑性(900%);在應(yīng)變速率為1×10~(-1) s~(-1)和708-758 K的溫度范圍內(nèi),伸長(zhǎng)率都超過(guò)了500%。由于與基體之間存在良好的變形協(xié)調(diào)性,第二相顆粒并未導(dǎo)致變形過(guò)程中明顯的應(yīng)力集中,裂紋也主要形成于晶界位置。超塑性變形過(guò)程中的主要變形機(jī)制為晶格擴(kuò)散協(xié)調(diào)的晶界滑移,斷裂機(jī)制為微孔聚集。最后,研究了微觀組織的細(xì)化及均勻化對(duì)Mg-Y-Nd合金腐蝕行為的影響。電化學(xué)測(cè)試結(jié)果和體外浸泡試驗(yàn)結(jié)果共同表明,NFSP和SFSP試樣的耐腐蝕性能明顯優(yōu)于鑄態(tài)試樣。三者的主要腐蝕機(jī)理均為電偶腐蝕。不同的是,由于微觀組織中含有粗大的α-Mg晶粒和第二相,電偶腐蝕導(dǎo)致的粗大第二相脫落或整個(gè)晶粒的剝離,讓鑄態(tài)試樣的內(nèi)部基體組織在模擬體液中大面積的裸露,出現(xiàn)嚴(yán)重的局部腐蝕行為。得益于晶粒的細(xì)化和第二相的破碎,在同樣的腐蝕情況下,NFSP和SFSP試樣裸露的內(nèi)部基體組織相對(duì)較少,二者均呈現(xiàn)出了較為均勻的腐蝕形貌。此外,力學(xué)性能測(cè)試表明,鑄態(tài)試樣在SBF中浸泡5天后,最大拉伸載荷急劇下降為原始值的20%。通過(guò)FSP制備的細(xì)晶Mg-Y-Nd合金,在模擬體液中浸泡12天后仍能保持一定的機(jī)械完整性,仍能具備一定的承載能力。
[Abstract]:As the precipitation hardened magnesium alloy, Mg-Y-Nd alloy has excellent room temperature strength, high temperature resistance and good compatibility in biological, aerospace, land transport, the field of biomedical materials have been applied to a certain extent. However, Mg-Y-Nd alloy is close packed six party structure, resulting in plastic deformation poor at room temperature, so the processing and application of Mg-Y-Nd alloy are subject to certain restrictions. The friction stir processing (Friction stir, processing, FSP) is a new kind of severe plastic deformation processing technology has great potential in fine grain metal materials good plastic deformation ability in the preparation of the particular. In the auxiliary cooling water circulation under the grain is restricted, so as to obtain more fine grain structure. Therefore, this study selected the casting Mg-Y-Nd alloy as the research object Friction stir processing, water / air (NFSP/SFSP) for the preparation method, microstructure of materials in FSP in the process of evolution, affected the subsequent aging heat treatment on the mechanical properties at room temperature change and the microstructure of the specimen processing, processing and superplastic specimens in simulated body fluid (Simulated body, fluid, SBF) corrosion behavior the provided technical reference for the mechanical properties of Mg-Y-Nd alloy casting lifting and shaping performance improvement, to provide the experimental basis for the application of FSP technology in biomedical material preparation field. First, select the different processing parameters, respectively for casting Mg-Y-Nd alloy NFSP and SFSP. were studied under different processing conditions, contrast group evolution and mechanical properties of the stir zone. Two kinds of different processing conditions FSP, microstructure of materials have been significantly refined, the mechanical properties are greatly improved compared. By contrast, due to greater heat generated in the process of NFSP accumulation, NFSP sample mixing area of the center width and the average grain size is greater than SFSP samples, and NFSP samples with coarse grained banded structure part of recrystallized grains formed. Due to the cooling effect of circulating water, SFSP can produce more grain size Mg-Y-Nd alloy fine, comprehensive mechanical properties are more excellent, the rotation speed of the relative optimal processing parameters for 600 rpm and 60 mm/min speed. Secondly, combined with the thermal history changes of NFSP in the process of casting Mg-Y-Nd alloy in the NFSP process, the second phase of the solid solution and precipitation behavior with the subsequent discussion. After aging heat treatment, NFSP specimen elongation decreased slightly, the strength is improved further. In the peak aging condition of 150 DEG C, mainly for the reinforcement of B '', and in the peak of 180 DEG C when The effect under the condition of reinforcement is mainly beta 1. after aging treatment, a large number of precipitates provided more nucleation sites of crack initiation, crack extension also provides a more complex propagation path. The fracture morphology showed that the particle banded structure of the organization is a major cause of NFSP and peak aging specimens of lower elongation. Again, select the grain more fine SFSP specimen, in the test of different temperature and strain rate, the high temperature tensile test. A -Mg due to the small grain and good stability, SFSP preparation of fine grain Mg-Y-Nd alloy in 733 K and 3 * 10~ (-3) s~ (-1) under the conditions of the test to get the maximum elongation (967%); 758 in K and 2 * 10-2 s~ (-1) test conditions to obtain optimal high strain rate superplasticity (900%); the strain rate of 1 * 10~ (-1) s~ (-1 708-758) and K The temperature range of elongation is more than the existence of good distortion coordination between 500%. and the matrix, the second phase particles did not result in the process of deformation obvious stress concentration, cracks are mainly formed in the grain boundaries. For lattice diffusion of grain boundary sliding deformation of the main coordination mechanism in the process of superplastic deformation, the fracture mechanism is micropore aggregation. Finally, the refinement of microstructure and the effect of homogenization on the corrosion behavior of Mg-Y-Nd alloy. The results of electrochemical test and in vitro immersion test results show that NFSP and SFSP, the corrosion resistance of the sample was superior to the cast specimen. The main corrosion mechanism of the three are different. The galvanic corrosion is due to a -Mg grain the microstructure contains thick and the second phase, stripping the galvanic corrosion caused by the coarse second phase shedding or whole grain, make the internal microstructure of as cast samples in simulated body A large area of liquid in bare, local corrosion behavior serious. Due to the grain refinement and the second phase of the crushing, corrosion in the same conditions the NFSP and SFSP specimens exposed internal microstructure is relatively small, the two are showing a more uniform corrosion morphology. In addition, the mechanical properties tests show that the cast samples after soaked in SBF for 5 days, the maximum tensile load decreased sharply in fine grained Mg-Y-Nd alloy as the original value of the 20%. prepared by FSP, after 12 days of immersion in SBF can still maintain a certain mechanical integrity, can still have a certain carrying capacity.

【學(xué)位授予單位】：華南理工大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2016
【分類號(hào)】：TG146.22

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