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Al_2O_3/Al wrapped powder and nano gradient coating of metal substrates

Author: LiuBaoLan
Tutor: ZhongXiangChong；JiaXiaoLin
School: Zhengzhou University
Course: Materials Science
Keywords: gradient coating nanometer bonding strength thermal shock resistance microhardness
CLC: TG174.4
Type: Master's thesis
Year: 2009
Downloads: 59
Quote: 0
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Abstract


With the development of modern science and teehnology,there are higher requirements for the surficial performance of materials,and many methods of surface treatment come forth.The characteristics,the preparation methods,development, application of metal-based ceramic gradient coatings and nano-coatings were overviewed in the first part of this thesis.The advantages and disadvanges of the preparation methods and materials of the gradient coating were summarized.On this basis,it was proposed that metal-based Al2O3/Al gradient coating was prepared by using slurry method.In this coating,the Al powders was used for transitional material, and the nano-Al2O3/Al was used for reinforcement particles.In this paper,Al2O3 coated Al nanometer powders were synthesized by calcining the dry gel prepared from Al（NO3）3·9H2O,nanometer Al and ammonium acid carbonate through heterogeneous precipitation method.The optimal solution concentration of raw materials and ratio were determined by experiments.TG-DSC, XRD,SEM,TEM,infrared spectrum analysis and particle size analysis were used to characterize the coating nano-powders.The Al2O3/Al composite powders with good dispersibility and uniform spherical particles were obtained when Al（NO3）3 solution concentration was 0.2mol/L,and the ratio of Al（NO3）3/NH4HCO3 was 1/8.The metal-based Al2O3/Al gradient coating was obtained through heat treatment by using aluminium dihydrogen phosphate as binder,sodium molybdate as corrosion inhibitor,aluminum powders as transition material,alumina as surface coatting material.The adhesion,bond strength,the number of thermal shock resistance, microhardness of the gradient coatings were tested by using multi-techniques.The result show that the optimal ratio of binder/aggregate was 0.55,the proper amount ofγ-Al2O3 in the aggregate was 10%,the optimal temperature of heat treatment is 700℃.The microstructure、composition and phase distribution were characterized by using SEM,EDS,XRD.It can be seen that chemical composition changes continuously,there was no remarkable interface because that the aluminum in the transition layer reacted with the ferrum in the metal substrate forming ferroaluminium which make the bonding strength higher because of element’s interpenetration,it was found that the bond strength and thermal shok resistance of the gradient coating were better than single-Al2O3 ceramic coating.On the basis of Al2O3 coated Al nanometer powders and metal-based Al2O3/Al gradient coating,the gradient coating containing the Al2O3/Al nanometer panicles was prepared.It were found that the microhardness and thermal shock resistance of the gradient coating with 0.7wt%nanometer powder were better than those of the coating without nanometer podwer.

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CLC: > Industrial Technology > Metallurgy and Metal Craft > Metallurgy and Heat Treatment > Metal corrosion protection,metal surface treatment > Corrosion control and protection > Metal surface protection technology
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