【作者】 孙耀宁；

【导师】 樊丁；

【作者基本信息】 兰州理工大学 ， 材料加工工程， 2007， 博士

【摘要】 Ni₃Si金属间化合物具有优异的抗二氧化硫腐蚀性能以及良好的高温抗氧化性能,是一种潜在的高温结构材料,有望在石油化工、冶金、航空航天等要求耐高温耐腐蚀场合得到应用,也可取代部分正在使用的比强度较差的高温结构材料。本课题利用先进的激光技术,应用合金化、复合化的方法对Ni₃Si金属间化合物进行研究。以不同比例的Ni、Si、Ti、Nb、C、Cr合金粉末为原料,采用横流CO₂激光器,在高温合金表面利用激光熔覆技术成功制备Ni₃Si（或Ni₃（Si,Ti））金属间化合物及其复合材料涂层。分别采用XRD、OM、SEM、EPMA和DSC等手段分析了涂层的相组成,显微组织,测试了涂层在室温下的耐磨性能;测试了涂层在硫酸溶液、NaCl溶液中的耐蚀性能;对涂层在1100℃下的高温抗氧化性能进行了评定,探讨了涂层的氧化机理。激光熔覆Ni75Si25合金粉末的相组成为Ni₃Si和Ni（Si）固溶体。适量的Cr、Ti、Nb合金元素加入Ni75Si25后,涂层的基本组成相不变,随着合金元素加入量的增加,涂层组织得到明显细化。其中,含Cr熔覆层组织中出现了少量的Ni₅Si₂:含5%Nb熔覆层组织中出现了Nb₃Ni₂Si。激光熔覆Ni78Si13Ti9合金粉末的相组成为Ni₃（Si,Ti）和Ni（Si）固溶体。Ni75Si25、Ni78Sil3Ti9熔覆层和基体GH864的平均显微硬度分别为740HV、470HV和350HV。激光熔覆Ni78Si13Ti9+[Ti+C]合金粉末制备了TiC/Ni₃（Si,Ti）基复合涂层。Ti与C优先反应形成TiC,组织结构分析中没有发现剩余的C存在。TiC以球状、棒状或花瓣状等形貌出现。激光熔覆Ni78Si13Ti9-WC合金粉末制备了（Ti,W）C/Ni₃（Si,Ti）基复合涂层。原位合成（Ti,W）C复相陶瓷的形成过程为:激光辐照下,部分熔融的WC与液态Ti反应生成TiC,在随后的冷却中,TiC析出长大时W替代Ti。（Ti,W）C保持TiC晶体结构类型。（Ti,W）C的形成与WC溶解于液Ti中的量有关。随WC添加量的提高,涂层中碳化物增多,硬度增加。激光熔覆Ni78Si19Nb3+[Nb+C]合金粉末制备了NbC/Ni₃Si基复合涂层。NbC以八面体、树枝晶、花瓣状的形态出现。Nb在涂层中有两方面的作用,一是Nb与C反应NbC;二是Nb固溶于组织中起到细化作用。当[Nb+C]的加入量大于30wt.%,组织中NbC分布不均匀,出现团聚,涂层开裂倾向性大。室温磨损试验表明,激光熔覆原位自生TiC（或NbC）陶瓷增强金属间化合物基复合涂层的磨损表现为显微切削、轻微粘着和碳化物局部破碎导致的磨粒磨损等。磨损过程中,陶瓷颗粒相可有效的承担载荷,颗粒相“原位”形成,与基体结合良好,耐磨性随熔覆层中增强相体积分数的增加而增加。在1100℃高温条件下,原位自生TiC（或NbC）/金属间化合物基复合涂层具有良好的抗氧化性能。氧化动力学曲线基本遵循抛物线规律。两种涂层在氧化初期的氧化产物均为NiO,但NiO不稳定;随着氧化时间的增加,NiO出现疏松、剥落;循环氧化100小时后TiC/Ni₃（Si,Ti）涂层的氧化物为TiO₂和少量的SiO₂,NbC/Ni₃Si涂层的氧化物SiO₂和极少量的Nb₂O₅。结合氧化产物和氧化层形貌初步提出了TiC（或NbC）/金属间化合物基复合涂层的氧化机理。更多还原

【Abstract】 Intermetallic compounds based on Ni₃Si have been considered as the basis of high-temperature structural materials and chemical parts because the Ni₃Si displays an increasing strength with temperature increasing and shows excellent oxidation resistance and corrosion resistance in sulfur dioxide environments.In the present wok,Ni₃Si based intermetallic composites were investigated using metheds of alloying and of composite by laser cladding.The Ni₃Si based intermetallic composite coating was fabricated by laser cladding using the raw material of Ni,Si,Ti,Nb,C,Cr alloy powder at different ratio.The mierostructure of the laser clad intermetallic composite coating was characterized by XRD,OM,SEM,EPMA and DSC.The room temperature wear resistance of the coatings was evaluated under the sliding wear test condition,the high temperature isothermal oxidation resistance was tested at 1100℃in air.The wear and oxidation mechanisms were discussed.The laser clad Ni75Si25 coating which the microstructure consists of Ni₃Si/Ni₅Si₂ and Ni（Si）.The microhardness of Ni75Si25 coating shows 740HV; while the substrate shows 350HV.With the addition of Cr the microstrueture of the coating is mainly composed of Ni（Si）,Ni₃Si/Ni₅Si₂ and the Ni75Si25-5at.%Nb coating consist of Ni₃Si,Ni（Si）,Nb₃Ni₂Si and Ni₅Si₂,Ni75Si25-5at.%Ti coating consist of Ni（Si）and Ni₃（Si,Ti）.With the Cr,Ti and Nb addition,the microhardness of coatings was 700HV, 640HV,and 765HV respectively.The Ni78Si13Ti9+（Ti+C）clad layers were mainly composed of the Ni solid solution,Ni₃（Si,Ti）intermetallic compound and TiC carbide,the TiC was in-situ formed.TiC carbide was dispersed with global shape,clubbed shape,and flower-like shape.The crystal structure of TiC,the ratio of Ti/C,and the energy of laser beam play an important role in controlling the growth morphology of carbide. The volume fraction and the size of TiC carbide gradually increased from the bottom to the top of the clad layer.With the 20wt.%[Ti+C]addition,the microhardness of clad layer was 747HV.Phases of laser cladding Ni78Si13Ti9+WC were composed of Ni solid solution,Ni₃（Si,Ti）intermetallic compound and（Ti,W）C carbide.With increasing the percentage of WC,content of carbides formed in the coatings increased,the microhardness of clad layers was also enhanced.The NbC particle reinforced Ni₃Si composite coating was prepared by in situ contact reaction with preplaced powder mixtures of NioSi-Nb-C.It was found that compound material cladding coating mainly consists of NbC particles,Ni₃Si intermetallic and Ni solid solution.The NbC particle was about 2-4μm in size and dispersivly distributed in the coating with different morphologies.The microhardness of the clad layer showed a gradient increased with the increasing of[Nb+C]content.The wear mechanism of the particle reinforced Ni₃Si composite coatings were micro-cutting,slight adhesion and abrasive.During the wear process,carbide reinforcement serve as load-carring particles,carbide in-situ formed which have a good bonding with base.The friction coefficient decrease with the increasing of the carbide reinforcement.The carbide reinforced intermetallic matrix coatings exhibit excellent corrosion resistance.The coatings have an outstanding isothermal elevated temperature oxidation resistance in the high temperature addition.The oxidation kinetic curves mainly followed line-parabola rate law.In the initial course of the oxidation,the oxide scales mainly consisted of NiO,exposures up to 100h,the oxides which foemed in Ni-Si-Ti-C coatings consisted of TiO₂ and SiO₂,while the oxides which foemed in Ni-Si-Nb-C coatings consisted of SiO₂,the formation of SiO₂ under the NiO layer caused the NiO peeled.更多还原