本研究運用氮氣氫氣混合氣體通入常壓電漿噴射束中對SKD11模具鋼做表面處理使表面硬化，在本實驗中通入不同氫氣比例之氮氣電漿，對SKD11模具鋼做表面處理，探討不同氫氣比例之氮氣電漿對於硬化效果之影響。使用維克氏硬度機分析試片表面與剖面之硬度變化、以光學顯微鏡分析試片之金相組織，利用X光繞射儀(XRD)、高解析度場發射掃描式電子顯微鏡(FE-SEM)、電子微探儀(EPMA)與X光光電子能譜儀(XPS)分析氮原子是否存在於試片表面，再以此分析氮原子是否有擴散到鋼材內部，並透過光學放射光譜儀(OES)探討使用混合氣體所產生之電漿對SKD11模具鋼之影響，最後再深入瞭解常壓電漿噴射束對SKD11模具鋼做硬化處理之反應機制。
本實驗已經成功的使用常壓電漿噴射束對SKD11模具鋼做表面硬化處理，根據實驗結果，發現硬化層之硬度會隨氫氣比例而改變，透過光學放射光譜儀分析電漿之物種，發現NH是控制硬化機制的主要關鍵，利用XRD探究出當氫氣比例達到一定值時，可以使氧化鐵還原成純鐵，但是當氫氣比例過高時，表面硬化之硬度會呈現出下降之趨勢。在研究中也發現了常壓電漿噴射束對SKD11做表面硬化處理之時間比傳統製程還來的短，即可達到高硬度之優異效果。

In this study, we used surface hardening on SKD11 die steel by atmospheric pressure plasma jet (APPJ) using the mixture (N2/H2) gas as working gas. The effect of hydrogen concentration in the working gas on the hardening effect of SKD11 die steel was investigated. The hardness profile and the microstructure were measured using a Vickers hardness tester and an optical microscope. The evolution of surface crystalline was observed using X-ray Diffractometer (XRD). The nitrogen distribution inside the bulk was measured using an Electron Probe Micro Analyzer (EPMA). The Energy Dispersive Spectroscopy (EDS) was carried out to determine the elemental composition of the nitrogen in the SKD11 die steel. The Optical Emission Spectroscopy (OES) was used to detect the optical emission of plasma species from atmospheric pressure plasma jet. Finally, we proposed the reaction mechanism of the surface hardening of SKD11 die steel by the atmospheric pressure plasma jet.
According to the materials characteristics, the surface hardness of SKD11 die steel was apparently raised by the atmospheric pressure plasma jet with varying the H2 gas content. Besides, hydrogen gas inside the plasma region generated by APPJ process was not only raised the surface hardness of SKD11 die steel, but also decreased Fe2O3 formation on the substrate surface. From OES observation, we proposed that the NH radicals were the key to control the hardening mechanism of SKD11 die steel. In the traditional process of gas nitriding under vacuum systems, however, NH3 is successively dissociated on the iron surface to form NH2, NH, and N and H radicals to harden the steel surface. Interestingly, the hardening mechanism by atmospheric pressure plasma jet, producing NH directly from N2 and H2 mixture gas, avoiding the complicated dissociation process from NH3 for gas nitriding and surface hardening. Meanwhile, due to the direct dissociation of NH3 and forced convention by APPJ process, the treatment time was accomplished for surface hardening within 1 hour, as compared to the traditional process of gas nitriding under vacuum systems.

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