研究了预氧化对42CrMo钢离子渗氮的催渗作用及机理.采用光学显微镜、显微硬度计、XRD、SEM和接触角测量仪研究了渗氮层厚度、渗氮层物相、预氧化后表面形貌和表面自由能.结果表明,预氧化对离子渗氮具有明显的催渗作用,在300℃预氧化30 min后进行离子渗氮(500℃、4h),化合物层厚度达到15 μm,是不经预氧化处理的传统离子渗氮化合物层厚度的2倍以上;有效扩散层厚度达到最大值570 μm,明显高于传统离子渗氮的有效扩散层厚度.研究还表明,300℃预氧化30 min后表面产生了大量纳米级氧化物颗粒和微裂纹、孔洞,同时接触角最小、表面自由能最大,离子渗氮阶段氧化物可以有效地转化为氮化物.由此推测预氧化催渗机理可能是表面纳米级氧化物颗粒和微裂纹、孔洞的形成,一方面有利于活性氮原子的吸附,从而促进化合层的形成,另一方面为氮原子提供的扩散通道,有利于扩散层的增加.
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