Cr-Si合金钢表面纳米层对低温离子渗硫的影响

Effect of surface nanocrystallization on low temperature ion sulphurizing behavior of Cr-Si alloy steel

利用超音速微粒轰击技术在调质处理的Cr-Si合金钢表面制备了厚度约25μm的纳米晶层。透射电镜（TEM）对表面结构的观察表明,最表面层形成了具有随机取向等轴的纳米晶粒,晶粒的平均尺寸约为16nm。对表面纳米化试样进行低温离子渗硫处理,在纳米结构表层形成了厚度约10μm的硫化物固体润滑薄膜。对硫化物层的结构分析结果表明,试样经表面纳米化处理后表面的扩渗性能和化学反应能力明显提高,在硫化物层和基体的界面处出现了厚度约为1-2μm的硫元素的扩渗层。表面纳米化试样表面硫化物的含量明显高于原始试样的硫化物的含量,且硫化物层主要由FeS相所构成,而在原始试样的硫化物层中FeS2的含量相对较高。表面层的晶界体积分数以及原子活性提高是表面纳米化试样表面化学反应能力和扩渗能力提高的主要原因。

A nanocrystallized surface layer of about 25μm thickness was fabricated on a quenched and tempered chrome-silicon alloy steel using supersonic fine particles bombardment（SFPB）.The microstructure of the top surface layer was characterized by using transmission electron microscopy（TEM）. The results show that the average size of equiaxed nanocrystalline grain with random crystallographic orientation on the top surface layer is approximately 16nm.The solid lubrication film containing sulfide of about 10μm thickness was fabricated by low temperature ion sulfurization.The ion sulphurizing behavior for surface nanocrystallzed samples were analyzed by means of scanning electron microscopy（SEM）,X-ray diffraction（XRD） and X-ray photoelectron spectroscope（XPS）.The results indicate that S-penetration depth and compounds（Fe-S phases） formation ability increase markedly in the surface nanostructured layer.The S-penetration layer of about 1～2μm is observed at the interface of the sulfide layer and the matrix.The content of sulfide in surface nanocrystallized sample is evidently higher than that in original samples.The sulfide layer in the surface nanocrystallized sample is mainly composed of FeS phase and a little of FeS2,whereas the content of FeS2 is higher in the sulfide layer of the original sample.The enhanced sulphurizing behaviors may originate from a large volume fraction of grain boundarie and surface activity.