热交换器用激光选区熔化成形FGH96镍基高温合金的腐蚀性能分析

Analysis on Corrosion Behavior of SLM Forming FGH96 Nickel Superalloy for Heat Exchanger

为了提高热交换器用激光选区熔化(SLM)成形FGH96镍基高温合金的耐腐蚀性能,测试研究了不同热处理方式合金在Na2SO4环境中的耐腐蚀性能,之后对合金腐蚀微观形貌进行了表征并分析了相关腐蚀机制。研究结果表明:未热处理试样获得了比热处理试样更大的腐蚀速率,48 h之后合金质量损失速率快速提高。达到120 h时,未热处理试样获得了13.2 mg/cm^(3)的质量损失速率,与时效热处理试样相比提高了3.5倍。在各热处理工艺下氧化膜形成了许多腐蚀坑,以均匀化热处理方式得到的试样表面腐蚀坑深度明显小于时效热处理的。时效处理后合金中Fe_(3)O_(4)氧化层中含有较多的微孔,较易发生腐蚀。均匀化处理后合金中包含片型NiO组织,形成了许多疏松微孔,提高了腐蚀速率。合金腐蚀组织都包含了3层结构:最外部由疏松氧化层构成,主要包含Cr_(2)O_(3)以及Fe_(3)O_(4);中间部分由网型硫化物构成,包含了Ni3S2等成分;底层属于合金基体组织。

In order to improve the corrosion resistance of laser selective melting(SLM)forming FGH96 superalloy used in heat exchanger,the corrosion resistance of the alloy with different heat treatment methods in Na_(2)SO_(4)environment was experimentally tested and studied.The corrosion microstructure of the alloy was characterized and the relevant corrosion mechanism was analyzed.Results showed that the corrosion rate of the untreated samples was higher than that of the heat-treated samples,and the mass loss rate of the alloy increased rapidly after 48 h.When it reached 120 h,the mass loss rate of the samples without heat treatment was 13.2 mg/cm^(3),which was 3.5 times higher than that of the aging heat-treated samples.Many corrosion pits were formed in the oxide film under various heat treatment processes.The depth of corrosion pits on the surface of the samples obtained by homogenization heat treatment was obviously less than that obtained by aging heat treatment.After aging treatment,the Fe_(3)O_(4)oxide layer in the alloy contained more micropores and was more prone to corrosion.After homogenization treatment,NiO microstructure was included in the alloy,which formed many loose micropores and increased the corrosion rate.The corrosion structure of the alloy consisted of three layers:the outermost loose oxide layer mainly containing Cr_(2)O_(3)and Fe3O4,the middle part composed of network sulfide Ni3S2 and other components,and the bottom layer belonging to the alloy matrix.