Application and evaluation of nitriding treatment using active screen plasma
Application and evaluation of nitriding treatment using active screen plasma
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DOI：
10.1016/j.surfcoat.2019.05.075
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发表时间：
2019-09
影响因子：
5.4
通讯作者：
S. Ichimura;S. Takashima;Ippei Tsuru;Daichi Ohkubo;H. Matsuo;Mineo Goto
中科院分区：
文献类型：
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作者：
S. Ichimura;S. Takashima;Ippei Tsuru;Daichi Ohkubo;H. Matsuo;Mineo Goto
对JIS SKD61模具钢试样进行了等离子渗氮处理，并对其近表面组织进行了分析。采用有源屏等离子体（ASP）进行等离子体渗氮。在ASP渗氮过程中，发现与施加到样品上的偏置电流有关。发射光谱显示存在原子态氮离子（N+）、分子态氮离子（N2+）、氢自由基（Hradical dot）、氮自由基（Nradical dot）和氮氢自由基（NiHi）。真空紫外吸收光谱观察到氮自由基和氢自由基的密度分别为1.5 × 1011和1.0 × 1011cm−3。一旦设备电流达到0.25 A或更高，表面就会变得浑浊。通过x射线衍射和横截面亮场扫描透射电子显微镜研究了这种混浊的原因，发现这是一层厚度约为50 nm的混合晶体，其中含有ε相fe2单键3n和γ′相Fe4N，表面形成了一个周期约为300 nm的结构。虽然没有浑浊的样品表面也有fe2单键3n和Fe4N的沉积，但沉积层厚度仅在10 nm左右，没有形成周期结构。通过扫描透射电镜和电子能谱分析，在fe2单键3n和Fe4N沉积层的正下方发现了一层富氧化铬层。这种富含氧化铬的层可能是由于氧化铁和氧化铬的选择性蚀刻而产生的。在ASP渗氮法中，实验证明N2+和N+带电粒子的溅射作用对渗氮和表面形貌起重要作用。此外，还发现在渗氮过程中没有形成几微米厚的复合层。
Plasma nitriding was performed on samples of JIS SKD61 die steel, and the microstructure near the surface was analyzed. The plasma nitriding was performed using active screen plasma (ASP). In the ASP nitriding process, a dependency on the bias current applied to the sample was found.Emission spectra showed the presence of atomic nitrogen ions (N+), molecular nitrogen ions (N2+), hydrogen radicals (Hradical dot), nitrogen radicals (Nradical dot), and radicals consisting of nitrogen and hydrogen (NiHi). The densities of nitrogen and hydrogen radicals observed by vacuum ultraviolet absorption spectroscopy were 1.5 × 1011and 1.0 × 1011cm−3, respectively. Once the device current reached 0.25 A or more, the surface became cloudy. The cause of this cloudiness was investigated by X-ray diffraction and cross-sectional bright-field scanning transmission electron microscopy and was found to be a deposition layer around 50 nm thick of a mixed crystal containing the ε phase Fe2single bond3N and γ' phase Fe4N and the formation of a structure with a period of around 300 nm at the surface. Although deposition of Fe2single bond3N and Fe4N also occurred at the surface in samples without cloudiness, the deposition layer was only around 10 nm thick, and no periodic structure was formed. A chromium oxide-rich layer was found directly under the Fe2single bond3N and Fe4N deposition layer by scanning transmission electron microscopy with electron energy-loss spectroscopy. This chromium oxide-rich layer likely occurred due to selective etching of iron oxide and chromium oxide. In ASP nitriding method, the sputtering action of charged particles of N2+and N+was experimentally shown to play an important role in nitriding and surface morphology. Furthermore, it was discovered that there was no compound layer several micrometers thick as would form in the conventional nitriding process.