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通过高能喷丸方法在SUS430不锈钢表面制备纳米表层,利用X射线衍射(XRD)、热分析(TGA)、扫描电镜(SEM)及能谱(EDS)进行测试,研究了纳米表层在不同气氛中的高温氧化行为,并分析了表面自身纳米化对SUS430不锈钢耐氧化性能的影响。结果表明:纳米表层在氧化初期氧化强烈,呈线性规律迅速增重,但达到钝化的时间短,氧化膜薄且致密,厚度仅为原始表面氧化膜的1/4,使钝化以后的氧化速率比原始表面低,总的氧化增重仅为原始表面的1/3,耐氧化性大大提高。其原因是表面自身纳米化处理增加了表层的晶界面积,提高了氧化物的形核几率,也为元素的扩散提供了更多通道,因而促进了Cr元素的选择性氧化。在最表层形成的是疏松的富Fe氧化物,该层氧化物对耐氧化性的提高贡献不大,在靠近基体的底层形成致密的富Cr氧化物,能很好地抵抗基体的进一步氧化;纳米表层比原始表面更容易形成连续的氧化膜,该氧化膜的内应力小,韧性好,与基体的结合力强。
The surface of SUS430 stainless steel was prepared by high-energy shot peening. The surface of the nano-scale was tested by X-ray diffraction (XRD), thermal analysis (TGA), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) The oxidation behavior of SUS430 stainless steel was analyzed at different temperatures. The effect of nanocrystallization on the oxidation resistance of SUS430 stainless steel was also analyzed. The results showed that the nano-scale surface oxidized strongly during the initial oxidation stage and increased linearly rapidly. However, the passivation time was short, the oxide film was thin and dense, and the thickness was only 1/4 of that of the original surface oxide film. The rate is lower than the original surface, the total oxidation weight gain is only 1/3 of the original surface, oxidation resistance greatly increased. The reason is that the self-nanocrystallization of the surface increases the grain boundary area of the surface layer, increases the probability of nucleation of the oxide, and provides more channels for diffusion of the element, thereby promoting the selective oxidation of the Cr element. In the outermost layer, loose Fe-rich oxide is formed, which contributes little to the improvement of oxidation resistance. A dense Cr-rich oxide is formed near the bottom of the substrate, which can resist the further oxidation of the substrate. The nano-scale surface is easier to form a continuous oxide film than the original surface, the internal stress of the oxide film is small, the toughness is good, and the binding force with the matrix is strong.