摘要
排气门是发动机的重要部件,由于它长期工作在高温、承受冲击载荷、环境气氛腐蚀等恶劣的工况条件下,因此要求它具有优良的高温性能、耐磨损性能和耐腐蚀性能。为了提高发动机排气门密封面的性能,目前国内外在高品质的排气门密封锥面上大多进行堆焊钴基合金的强化处理,以满足排气门苛刻的工作条件要求。钴基合金在热稳定性、耐磨性、耐蚀性等方面均有突出的优势,但价格昂贵,成本太高。本课题旨在研制一种适用于排气门密封面强化的铁基合金粉末材料,以降低排气门的生产成本。
本课题设计了适合于排气门密封面强化的铁基合金粉末(Fe38)的成分,采用雾化法制备该合金粉末;并研究了其物理特性和结构;探讨了等离子弧堆焊工艺参数对Fe38堆焊层质量的影响,确定了最佳堆焊工艺参数;分析和测试了Fe38合金等离子堆焊层的微观组织和结构,耐高温性能,摩擦磨损性能和耐腐蚀性能,并与钴基合金涂层进行了对比。最终通过台架试验模拟了实际工况下涂层的耐磨性。
实验结果表明,设计制备的Fe38合金粉末由γ固溶体和(Cr,Fe)7C3碳化物组成,粉末的尺寸均匀,结构致密,成球性良好;该铁基合金等离子堆焊层具有优良的抗高温氧化性、耐磨性和耐蚀性。当工作温度低于800℃时,该堆焊层可满足工件的硬度要求。当工作温度高于800℃时,由于基体中第二相颗粒的析出和粗化使材料的硬度明显降低。
与钴基合金Co02相比,等离子弧堆焊铁基合金Fe38在800℃以下使用时,其使用性能基本达到了Co02的水平,同时具有突出的经济性能。因此,该项研究为等离子堆焊强化气门密封锥面提供了一种新的合金粉末材料,同时该材料也可用于要求相近的其他机械零件的表面强化,具有较大的应用价值。
Air outlet valve is an important part in the engine. Since the valve always works under the inclement conditions, such as high temperature, impact load, corrosion media, etc., it is necessary to have the excellent high temperature behavior, wear resistance and corrosion resistance. In order to increase the properties of the air outlet valve sealing face, at present, a cobalt-based alloy coating is employed because of its outstanding properties. But the expensive price of the cobalt coating will enhance the valve’s cost. This research aims to obtain a kind of iron-based alloy powder for strengthening the air outlet valve with a lower price.
The composition of the iron-based alloy powder (Fe38) for strengthening coating has been designed and prepared using the atomization technique; the effects of the plasma arc build-up welding parameters on the Fe38 coating quality have been investigated, and the optimal technology parameters are suggested; the microstructure,the thermal and wear resistence as well as the corrosion resistence of the Fe38 coating have been tested and analysed; the comparison tests with the cobalt coating have been accepted. At last, the bench test of the valve has been made to simulate the working condition.
The experimental result shows that the microstructure of iron-based alloy powder consists of theγsolid solution and the (Cr,Fe)7C3 carbide. The prepared powders have round shape, even particle size and compact structure; the plasma arc welding coating exhibits the good oxidation resistance properties at elevated temperature, wear resistance and anti-corrosive capacity. The coating can keep required hardness up to 800℃working temperature. When the temperature is higher than 800℃, the precipitation will separate from the solid solution and coarsen resulting in the hardness decreasing obviously.
The iron-based alloy (Fe38) coating by plasma arc welding has similar properties below 800℃compared with cobalt-based alloy, which exhibits the economical advantage. Therefore, this issue has provided a new alloy powders for strengthening the air outlet valve. And also, the powders can be used for surface-strengthening of other machine elements requiring similar properties.
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