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利用高能喷丸法(HESP)在工业纯铁表面制备了一定厚度无污染、空位、杂质等缺陷的纳米晶层,其平均晶粒尺寸为50 nm,厚度为100μm。在Gleeble 1500热模拟机上,采用脉冲加压扩散(PPD)和恒定加压扩散(CPD)对纳米晶铁在850℃下进行渗镍处理。结果表明,镍原子在纳米晶铁中的扩散系数比常规粗晶中高1个数量级;而采用脉冲加压扩散时,镍原子的扩散系数要比采用恒压扩散高1个数量级。镍原子扩散系数的提高主要包括三方面的原因,一是脉冲加压能击碎扩撒界面上形成的阻碍镍原子扩散的金属件化合物;二是纳米晶铁中形成的大量三叉晶界;三是纳米晶铁中形成大量的非平衡晶界。
Nanocrystalline layers with certain thickness of non-polluting, vacancies, impurities and other defects were prepared by high energy shot peening (HESP) on the surface of industrial pure iron. The average grain size was 50 nm and the thickness was 100 μm. On the Gleeble 1500 thermal simulator, nanocrystalline iron was infiltrated at 850 ℃ by pulsed pressure diffusion (PPD) and constant pressure diffusion (CPD). The results show that the diffusion coefficient of nickel atom in nanocrystalline iron is 1 order of magnitude higher than that of conventional coarse grains. The diffusion coefficient of nickel atoms is 1 order of magnitude higher than that of diffusion by pulsed pressurized diffusion. There are three reasons for the increase of diffusion coefficient of nickel atom. One is that pulsed pressure can break the metal compound which hinders the diffusion of nickel atom in the diffusion interface; the other is the large number of trigeminal grain formed in nanocrystalline iron; Nanocrystalline iron is the formation of a large number of non-equilibrium grain boundaries.