为了提高旋耕刀、犁铧等农机触土刀具表面强度,以铝热剂的放热反应提供内在热源、等离子弧作为外在热源,采用摘反应等离子熔覆技术在 Q235钢表面原位合成了 Al2O3-Ti(C,N)复合材料涂层。利用扫描电镜、能谱仪、 X射线衍射仪、显微硬度计、金相显微镜等对复合涂层的微观结构及强质硬化相的成分、组织及性能进行了分析。结果表明:涂层与基体呈冶金结合,涂层主要由网状、嵌套、球状等 3种结构组成,硬质相 Al2O3、Ti(C,N)与粘结相 Fe-Ni之间相互包裹、互相嵌套,构形成空间网状骨架结构；涂层硬度最高可达 HV0.52160,平均硬度 HV0.51870,约为基体 Q235钢的 7.7倍；涂层摩擦系数约为0.372,其磨损量约为 65Mn钢及 Q235钢的 1/7和 1/17,与基体相比,复合涂层具有较高的硬度和较好的摩擦磨损性能,可以为农机材料表面强化提供参考。

In order to improve surface strength of agricultural machinery key parts such as rotary blade and plough underatmospheric conditions, the heat released from the exothermic reaction of termite as an internal heat source, and plasmaarc column as an external heat source, the in situ synthesis of Al2O3-Ti(C,N)(AT composite materials) composite coatingwas prepared on Q235A steel specimen surface by reactive plasma cladding technology.Firstly, raw materials were thecheap thermite (iron oxide and aluminum powder), titanium powder, graphite powder, TiN powder and Ni60A powder,which were mixed in a planetary type ball mill DQM according to the mass fraction ratio of Fe2O3∶Al∶Ti∶C∶TiN∶Ni60A= 36.5∶13.5∶8.4∶2.1∶4.5∶35, milled for 6 hours, was made a mixed powder paste with the self made glue which was theadhesive, and then was coated on the surface of pretreated Q235A specimen and the thickness was 2 mm±0.5 mm,reserving 2-3 mm arc end.Secondly, the sample was placed in the vacuum drying oven and were dried under 80 ℃ during12 hours, then cooled the sample to room temperature.Using the plasma arc column of DML-300 plasma welding machineas an external heat source, condition of the arc could be ignited successfully, increased appropriately the working distance(about 8 to 10 mm) and reduce the cladding current(120 A).The plasma arc single channel was used to scan the clad andreached thermite ignition temperature, then the thermite in the pre coated raw material occurred chemical reaction togenerate Al2O3 and Fe.After the first cladding operation was finished, it immediately reduced the operating distance andappropriately increased the cladding current, using the optimized process parameters: cladding current of 200 A, claddingspeed of 2.5 mm/s, preset coating thickness of 2.0 mm, ion gas flow of 0.6 L/min, working distance of 4 mm.Then the in situ synthesized Al2O3-Ti(C,N) composite coating was remelted and placed in Argon protection atmosphere cooling.Thecomposition, microstructure, phase and performance of Al2O3-Ti(C,N) composite coating were analyzed by scanningelectron microscope (SEM), energy disperse spectrometer(EDS), X ray diffractometer(XRD), micro hardness tester andfriction testing machine.The results indicated that the new phase Al2O3 and Ti(C,N) were synthesized in situ on Q235Asteel during the plasma cladding process and the composite coatings were made, which had a good metallurgicalcombination with Q235A steel substrate.The coating was mainly composed of reticular structure, nested structure andspherical structure.The hard phase Al2O3 and Ti(C,N) and Fe Ni binding phase were mutual inclusion between themselvesbody, nested within each other, constituting the spatial reticulate structure.The highest hardness value of the coatings wasup to HV0.52160, and the average hardness was HV0.51870, and about 7.7 times of Q235A steel substrate.The frictioncoefficient of AT composite coating was about 0.372 and the wear loss of the AT composite coating was about 1/7 of 65Mnsteel, and 1/17 of Q235A substrate surface.Compared with the substrate materials, the AT composite coating had higherhardness and more excellent friction and wear properties, which provided an experimental and theoretical reference for thesurface strengthening of agricultural machinery materials.

TG174.44

河北省教育厅青年基金(QN20131022)；国家公益性行业科研 (农业 )专项经费项目(201203016)；河北省科技创新平台建设运行经费(13967662D)；河北省科技支撑计划项目(12211025)