【作者】 郭训忠；

【导师】 陶杰；

【作者基本信息】 南京航空航天大学 ， 材料加工工程， 2011， 博士

【摘要】 核聚变工程包层的管路对电绝缘、抗腐蚀等性能方面具有特殊要求，所以需要在管路内表面制备高质量的氧化铝陶瓷层。但是由于管路连接件如三通、弯头形状相对复杂，采用常规方法难以实现在其内表面制备氧化铝陶瓷涂层的目的。另外，在航空、航天、石化等工程领域中常使用钛合金管道，而钛合金由于自身抗冲刷、耐磨损性能较差，亦需要在复杂的管道内表面制备氧化铝涂层。基于上述问题，本文提出了新的技术路线：首先采用内爆法将铝管与钢管（或钛管）进行爆炸复合，使纯铝覆层与基管之间实现冶金结合；其次采用冷推弯及液压胀形的先进成形工艺对带有铝层的双金属管坯进行塑性变形，制备双金属复合弯头及三通管件；后采用微弧氧化工艺将铝层实施陶瓷化处理。通过本工艺路线，最终在弯头或三通管件内表面原位生成氧化铝陶瓷层。本文的三项关键技术分别为：制备带有铝层且界面具有冶金结合的高质量双金属复合管；双金属复合弯头及三通的塑性成形规律及变形机理；纯铝层的陶瓷化以获得致密的α-Al₂O₃。采用爆炸复合工艺制备了尺寸精度高、内表面质量好、界面结合强度高的双金属复合管。对铝-316L不锈钢体系、铝-纯铁体系、铝-CLAM钢体系的双金属复合管起爆端、中部及尾部结合质量进行了评价。采用压剪试验、径向压扁及弯曲试验对双金属复合管的结合性能进行了测试，铝-纯铁、铝-316L不锈钢、铝-CLAM钢的界面剪切强度分别为76.0、75.6、73.8MPa；三种体系的复合管弯曲试样内弯及外弯角度超出138°时、径向压扁率为33%时，界面无任何开裂。结果表明，纯铝覆层与基管的界面结合性能优良，可以经受大的塑性变形。在铝-316L不锈钢双金属复合管的冷推弯成形中，采用有限元方法系统研究了不同的相对旋转半径、不同的芯棒材料及摩擦系数对推弯成形效果的影响。研究结果表明，在相同的管坯直径条件下，随着弯曲段相对旋转弯曲半径的增大，复合管坯材料的贴模效果、圆截面畸变及壁厚均匀性得以明显改善；芯棒材料对于成形效果具有重要影响，使用刚性芯棒和低熔点合金芯棒对于减小圆截面椭圆度效果最佳，但刚性芯棒的界面剪切应力明显大于低熔点合金；摩擦系数越低，界面最大剪切应力越小，壁厚均匀性越好。在铝-纯铁双金属复合弯头的冷推弯成形中，研究了推弯后的界面结合情况、等效应力场及应变场。另外，研究了两端带有直段且具有矩形截面的铝-CLAM钢双金属特殊弯管冷推弯成形，提出了不同于圆形截面管材的推弯塑性变形机理：材料的流动沿轴向进行，难以越过刚性棱边进行径向补料，故最终造成弯曲段外侧减薄难以快速补料，减薄更加严重；弯曲段内侧则由于刚性区的作用，增厚现象得以抑制。在铝-316L不锈钢双金属复合三通的内高压成形中，采用有限元模拟方法研究了支管顶部位置及过渡圆角区域的钢层节点、铝层节点随时间变化的历史曲线；其次研究了各金属层在典型截面线上的厚度分布规律，并与单层不锈钢三通壁厚规律进行了对比分析。另外，对复合三通成形中的内压力、摩擦系数以及推进距离对于支管高度以及壁厚减薄率的影响规律进行了系统研究。结果表明，复合三通的成形内压不宜过高；应选择具有较小摩擦系数的润滑剂；轴向推进距离对于复合三通的壁厚均匀性无明显影响，但对支管高度影响较大。在铝-CLAM钢体系的双金属复合三通的内高压成形中，研究了内压及摩擦系数对铝-CLAM钢铁双金属壁厚分布及支管高度影响。根据模拟结果，对铝-316L不锈钢、铝-纯铁及铝-CLAM体系的双金属复合三通进行了实际的内高压成形试验，最终获得了高质量的复合三通管件。通过上述工艺，可实现在纯钛管件内表面制备氧化铝层。首先对铝-纯钛进行爆炸复合，对复合后的界面形貌、元素分布及物相进行了表征；对内、外层的界面结合强度以及压扁、压缩等性能进行了测试。采用冷推弯及液压胀形工艺成功制备了铝-纯钛双金属复合弯头及三通管件。采用微弧氧化工艺对铝-316L不锈钢、铝-纯铁、铝-CLAM钢及铝-纯钛体系的双金属复合管件纯铝层进行陶瓷化处理。首先研究了基于硅酸盐体系的电解液配方、电流密度及氧化时间对氧化铝层厚度、显微硬度、表面粗糙度及氧化铝晶型的影响规律并分析了微弧氧化成膜机理。研究结果表明，采用2g/L的氢氧化钾、3g/L硅酸钠、5g/L六偏磷酸钠、10g/L酒石酸钠的电解液，通过20A/dm²的电流密度90min氧化处理可获得致密的、厚度约为145μm，且α-Al₂O₃含量超出67.2%的高质量陶瓷层。通过使用含有氧化铬粒子的电解液，可以制备出Al₂O₃+Cr₂O₃复合陶瓷层。对制备的陶瓷层分别进行了结合性能、摩擦磨损性能、耐腐蚀性能及抗冲刷性能、电绝缘性能的测试。结果表明，氧化铝层、复合陶瓷层与基体的结合性能不低于55N及60N；Al₂O₃+Cr₂O₃复合陶瓷层的磨损量最小，Al₂O₃层次之；带有氧化铝陶瓷层试样的自腐蚀电位Ecoor约为-0.26V，腐蚀电流Icorr约为1.1E-7，Al₂O₃+Cr₂O₃复合陶瓷层的自腐蚀电位约为-0.23V，腐蚀电流约为7.56E-8；氧化铝陶瓷层的抗冲刷性能优良；氧化铝陶瓷层的体积电阻率约为1.73×10¹² cm，远超出设计值10⁴Ω m。更多还原

【Abstract】 The stainless steel pipe-fittings in the test blanket module of fusion engineering aredemanded to possess high properties in electrical isolation and anti-corrosion. Ceramic coatinglike Al₂O₃on the inner surface of the pipe-fittings is needed to attain this goal. However, it isdifficult to prepare Al₂O₃layer on the inner surface of the pipe joints, such as T-shapes and elbows,owing to their complex profile and irregular surface. In addition, in the fields of aeronautics,astronautics, and petrochemical industry, Al₂O₃coating in the irregular titanium pipe joints is alsoa feasible method to overcome the defects of titanium alloys products, including erosion andscouring abrasion.A new technical route was proposed to solve these problems in this study. The steps of thenew method were as follows: firstly, stainless steel or titanium pipes were metallurgical bondedwith aluminum pipes through explosive welding. Then, the forming clad pipes were processedinto clad T-shapes and elbows by means of cold push-bending and hydroforming respectively.Finally, the aluminum layer of as-prepared pipe-fittings was oxidized into Al₂O₃by micro-arcoxidation. The complex pipe-fittings with ceramic layer of Al₂O₃were obtained through the newtechnical route. The key technology of the study was including preparation of clad pipe with highquality, plastic forming mechanism of clad elbow and clad T-shapes and the oxidation of thealuminum to obtain the dense α-Al₂O₃layer.Al-316L SS, Al-Fe and Al-CLAM steel clad pipes were prepared by explosive welding whichexhibited high dimensional accuracy, inner surface flatness and bonding strength. The bondingstrength of the clad pipes at the initial explosive end, middle part, and tail end was characterizedthrough pressure-shear test, radial flattening test, and bending test. The results showed thatAl-316L, Al-Fe and Al-CLAM samples displayed bonding strength of76.0,75.6and73.8MPa,respectively. And adhered interface could keep well-bonded when the pipes were bent at an angleexceeded138°and radial flattened by33%. Therefore, the pure aluminum layer was stronglybonded with matrix alloys and the clad pipe could undergo large deformation in the later plasticdeformation.The cold push-bending process of the Al-316L SS clad pipes was simulated by FE software.The effects of relative radius, mandrel material and friction coefficient on the quality ofpush-bended parts were investigated by the numerical simulation. For the tube blanks with thesame diameters, larger relative radius of gyration at the bended part led to lower distortion ofcircular section, better material filling quality and homogeneity of thickness distribution, indicating better quality of plastic formed pipes. Using rigid material and low melting point alloyas mandrel in the forming process could apparently reduce the distortion of circular section.Among them, low melting point alloy was more favorable than rigid mandrel due to its muchlower interfacial shear stress. In addition, lower friction coefficient resulted in smaller shear stressand better homogeneity of thickness distribution. For the Al-Fe clad pipes, the shear stress,equivalent stress and strain were analyzed during the cold push-bending process. Based on thecold push-bending results of Al-CLAM pipes with rectangular section and straight segment on theends, plastic formation mechanism differed from circular pipes was proposed. The material waseasy to flow along the axial direction but difficult to flow over the rigid ridge of tube blank.Therefore, extrados with large deformation exhibited severe thinning while intrados exhibitedsuppressed thickening.The hydroforming process of the Al-316L clad pipe was also simulated by FE software.Historical curves of nodes on both the stainless steel and aluminum layer at the area of protrusionand fillet were investigated during the hydroforming process. Also, the thickness distribution oflayers at crucial sections was studied and compared with that of single layer stainless-steelT-shapes. In addition, process parameters including inner pressure, friction coefficient and feeddistance were optimized based on the analysis of their influence on the protrusion height and wallthinning rate. It indicated that proper inner pressure and lubricant with lower friction coefficientshould be selected during the forming process. Feed distance at axial direction exhibited stronginfluence on the protrusion height, but poor relevance with the thickness homogeneity. Similarly,the effects of the inner pressure and friction coefficient on the protrusion height were alsoinvestigated for the Al-CLAM clad pipe. Finally, these clad pipes were practically hydroformedinto T-shapes according to the simulation results.Same technical route was performed to prepare Al₂O₃layer on the inner surface of TA1pipe-fittings. Aluminum pipe and TA1pipe were firstly cladded by explosive welding. Themicrostructure of the Al-TA1clad pipe was characterized including morphology, elementdistribution and phase structure. The interfacial bonding strengths between the layers, radialflattening and compression properties were measured to evaluate the quality of welded pipes. Theclad pipe-fittings were successfully fabricated by cold push-bending and hydroforming process.Micro-arc oxidation technology was employed to fabricate Al₂O₃layer on the inner surfaceof the prepared clad pipe-fittings based on Al-316L SS, Al-Fe, Al-CLAM steel and Al-TA1. Wesystematically studied the influence of the electrolyte component, current density, oxidizationduration on the Al₂O₃layer’s thickness, micro-hardness, surface roughness and crystal structure.Consequently, mechanism of micro-arc oxidation to obtain the high content of α-Al₂O₃was proposed. Al₂O₃layer with length of145μm and α-Al₂O₃phase proportion of67.2%wasprepared through micro-arc oxidation at current density of20A/dm²for90min in optimizedelectrolyte, containing2g/L potassium hydroxide,3g/L sodium silicate,5g/L sodiumhexametaphosphate and10g/L sodium tartrate. Al₂O₃/Cr₂O₃composite layer was fabricated usingthe electrolyte contained Cr₂O₃particles. The properties of the ceramic layer such as bondingstrength, wear resistance, erosion resistance and electrical isolation was evaluated. The resultsindicated that bonding strength between Al₂O₃and matrix, composite layer and matrix was largerthan55N and60N respectively, while the composite layer exhibited better wear resistance thansingle Al₂O₃layer. Samples with Al₂O₃layer displayed natural corrosion potential （Ecoor） of-0.26V and corrosion current （Icorr） of1.1E-7, while those with composite layer displayed Ecoorof-0.23V and Icorr of7.56E-8. Al₂O₃ceramic layer displayed good anti-erosion performance andexcellent volume resistivity of1.73×10¹² cm, much larger than the designed value of10⁴Ω m.更多还原