退火及表面纳米化对冷喷涂Zn-Al涂层与IF钢基体结合性能的影响研究

发布时间：2018-03-22 21:19

  本文选题：无间隙原子钢　切入点：梯度纳米结构　出处：《中国科学技术大学》2017年博士论文　论文类型：学位论文

【摘要】：无间隙原子(IF)钢具有优良的深冲成形性能,广泛应用于汽车、家电等外板制造,是最重要的结构材料之一。但是,IF钢的耐蚀性较差,服役过程中很容易受到环境侵蚀而失效。Zn-Al合金防护涂层具有优良的耐蚀和耐磨性能,是最常用的延长钢铁结构件服役寿命的涂层材料之一。作为一种新型的涂层制备技术,冷喷涂可以在低温下实现涂层的沉积,在金属涂层制备领域具有广阔的应用前景。如何制备致密稳定的保护性涂层、以及如何提高涂层与基体之间的结合强度,是冷喷涂技术发展中的关键问题。本文利用冷喷涂技术在IF钢表面成功制备出致密的Zn-Al涂层,研究了后续退火处理和IF钢基体表面纳米化对涂层/基体界面结合强度的影响。利用金相显微镜、扫描电子显微镜、透射电子显微镜、能谱仪和X射线衍射表征了涂层、基体及界面化合物的微观组织、成分分布和相组成;利用显微硬度计、纳米压痕仪、摩擦磨损试验机和三电极系统评价了退火前后Zn-Al涂层的力学性能和耐蚀性能;利用三点弯曲和“拔钉法” (Studpull-offtest)研究了涂层/基体之间的结合强度。得出以下主要结论:1.利用冷喷涂技术在IF钢基体上制备出孔隙率0.5%的Zn-Al合金涂层,制备过程中未发生明显的氧化和相变。200-350 ℃温度范围内,涂层硬度随退火温度的升高逐渐增大;而涂层的摩擦磨损性能随退火温度的升高呈现下降趋势;退火后涂层的耐腐蚀性能变化不大。2.冷喷涂Zn-Al层的IF钢原始样品(Zn-Al/IF-CG)在400 ℃保温60 min退火后,涂层与基体之间的抗剥离能力略有提高;保温时间大于60 min后,涂层与基体界面形成Fe11Zn40、FeZn10和Fe2Al5-xZnx组成的混合化合物相,导致其抗剥离能力随退火时间的延长快速降低。3. SMAT处理能够在IF钢基体表面制备出梯度纳米结构组织,最表层平均晶粒尺寸～10 nm,硬度较粗晶基体提高～33%。表层梯度纳米结构组织在400℃以下具有良好的热稳定性。4. IF钢基体SMAT能够显著改善涂层/基体的界面结合性能,冷喷状态下Zn-Al层与SMAT样品(Zn-Al/IF-SMAT)的界面结合强度达到58.1MPa,较Zn-Al/IF-CG 样品提高了～30%。5.冷喷涂Zn-Al/IF-SMAT样品的界面结合强度不能通过后续扩散退火处理进一步提高。在400 ℃退火时,保温时间小于30 min时涂层/基体界面结合强度有所降低;随着保温时间的延长,界面结合强度开始升高并达到一个相对稳定值(～50.2 MPa);当保温时间大于90 min后,涂层-基体界面结合强度再次降低。6.相同条件退火处理后,冷喷涂Zn-Al层在表面纳米化IF钢基体上的结合强度均不低于在粗晶IF钢基体上的结合强度。
[Abstract]:The interstitial free if) steel is one of the most important structural materials for its excellent deep drawing formability and widely used in the manufacture of automobile, home appliances and other outer plates, but the corrosion resistance of if steel is poor. Zn-Al alloy protective coating is one of the most commonly used coating materials for prolonging the service life of iron and steel structural parts because of its excellent corrosion resistance and wear resistance due to environmental erosion during service. As a new coating preparation technology, Zn-Al alloy protective coating is a new kind of coating material. Cold spraying can achieve coating deposition at low temperature, which has a broad application prospect in the field of metal coating preparation. How to prepare dense and stable protective coating, and how to improve the bonding strength between coating and substrate, It is a key problem in the development of cold spraying technology. In this paper, a compact Zn-Al coating was successfully prepared on the surface of if steel by cold spraying. The effect of subsequent annealing and nanocrystalline on the interface strength of the coating / substrate was studied. The coating was characterized by metallographic microscope, scanning electron microscope, transmission electron microscope, energy spectrometer and X-ray diffraction. The microstructure, composition distribution and phase composition of matrix and interface compounds, the mechanical properties and corrosion resistance of Zn-Al coatings before and after annealing were evaluated by microhardness tester, nano-indentation tester, friction and wear tester and three-electrode system. The bonding strength between coating and substrate was studied by means of three-point bending and studpull-off test. The following main conclusions were drawn: 1.The Zn-Al alloy coating with 0.5% porosity was prepared on if steel substrate by cold spraying. The hardness of the coating increases gradually with the increase of annealing temperature, while the friction and wear properties of the coating decrease with the increase of annealing temperature. After annealing, the corrosion resistance of the coating changed little. 2. After annealing at 400 鈩，

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