Development of Mo Composite Material Coated High Corrsion Resistant Nitride under Severe Corrosion Enivronment

对在1073K ~ 1373K NH_3气体中氮化的纯Mo和Mo-0.5质量%合金，通过光学显微镜、透射电镜和x射线衍射分析对氮化钼层进行了显微组织观察。并对渗氮试样的腐蚀行为进行了研究。表面氮化层主要由两种Mo氮化物组成：外层是γ-Mo_2N，内层是β-Mo_2N。在β3-Mo_2N层中观察到大量的{011}<011>型微孪晶，而γ-Mo_2N层的微观结构几乎没有晶格缺陷。在沸点为4608 k的75%硫酸溶液中，与未渗氮的试样相比，渗氮后的试样仍具有较好的耐蚀性。随着渗氮时间的缩短，腐蚀速率降低，这是由于表面渗氮层厚度的减小抑制了裂纹的产生。在沸水75%硫酸中，1123K渗氮24h的腐蚀速率小于0.001 mm/y。在Mo-0.5Ti渗氮合金中，在表面渗氮层下形成了具有很高Hν-800线束的内渗氮层。高硬度被认为是由于极小的氮化钛颗粒在Mo基体中分散。随着与界面距离的增加，内渗层的硬度逐渐降低。

For pure Mo and Mo-0.5 mass% alloy nitrided at 1073K to 1373K in NH_3 gas, the microstructural observations of molybdenum nitride layer were carried out through an optical and a transmission electron microscope and X-ray diffraction analysis. Corrosion behavior of the nitrided specimens was also examined. A surface nitriding layer consisted mainly of two Mo nitrides : an outer one of γ-Mo_2N and an inner one of β-Mo_2N.A great number of {011}<011>-type micro-twins were observed in the β3-Mo_2N layer whereas the microstructure of the γ-Mo_2N layer is almost free from lattice defects. The nitrided specimens exhibited excellent corrosion resistance even in 75wt% sulfuric acid solution at the boiling temperature of 460.8K compared with unnitrided specimens. Its corrosion rate decreased with decreasing nitriding time because of the suppression of cracking by decreasing thickness of the surface nitriding layer. The corrosion rate of the specimen nitrided at 1123K for 24h was less than 0.001 mm/y in boiling 75% sulfuric acid. In a nitrided Mo-0.5Ti alloy an internal nitriding layer with remarkably high harness of Hν-800 was formed beneath the surface nitriding layer. The high hardness is considered to be ascribed from fine dispersion of extremely small titanium nitride particles in the Mo matrix. The hardness in the internal nitriding layer gradually decreased as the distance from the interface increased.