Preparation and Properties of New Mo-based Alloys Strengthened by Dispersion of Nano-scale Nitride Superfine Particles

Mo合金是已知的高温金属之一，被用作加热器、热处理托盘和x射线靶等高温材料。进一步的广泛应用需要合金的高强度。本研究旨在强化氮化形成的Mo-氮化物表面层，并通过稀Mo- ti合金的优先氮化沉淀分散在Mo基体中的极细TiN颗粒来强化合金。特别是在基础和系统研究的基础上，我们试图开发一种新的mo基复合材料，其中大量的纳米级TiN超细颗粒通过氮化在比目前低得多的温度下分散。因此，我们非常幸运地成功开发了一种新的钼基复合材料，与目前使用的任何材料相比，它的强度都要高得多。本文讨论了Mo-0.5和1.0wt%合金和纯Mo在1100℃（远低于130℃）的NH_3气体中氮化的渗氮行为、渗氮试样截面上的硬度分布以及Mo基体中细小ti -氮化颗粒的显微组织和结晶学关系。主要结果总结如下。(1)明确了mo -氮化物表面层的生长机理。发现其最大硬度达到Hv=1800。此外，发现表层由两个不同的亚层组成：靠近样品表面的γ - mo_2n亚层和γ - mo_2n层下方的β - mo_2n亚层。每个子层都有一个不同的双胞胎。特别是在β - mo_2n亚层中发现了一种新型微孪晶的形成。(2)氮化Mo-Ti合金在Mo_2表面层下形成了高强度的内氮化层。在纯Mo中没有观察到内部氮化层的形成。我们获得了显著的高硬度Hv=1000，这是迄今为止报道的Mo合金最大硬度Hv=500的两倍。此外，我们在国际上首次发现，在1100℃的极低温度下氮化可以析出厚度约为0.45nm （= TiN的1单位长度）、直径为2-4nm的纳米级TiN超细颗粒。发现形成的超细颗粒具有特殊的晶体学关系，并使强度大大提高。少

Mo alloys, which are known to be one of high melgin-temperature metals, are used as high-temperature materials such as heaters, trays for heat-treatments and a X-ray target. Further wide use requires high strengthening of the alloys.The present research aims to harden a Mo-nitride surface layr formed by nitriding and also to strengthen the alloy by precipitation of very fine TiN particles dispersed in Mo matrix through preferred nitriding of dilute Mo-Ti alloys. Especially on the basis of basic and systematic investigations we tried to develop a new Mo-based composities in which a great number of nano-scale TiN superfine particles disperse through nitriding at much lower temperatures thatn those so far. As a result, it is quite lucky for us to succeed the development of a new Mo-based composite material having remarkably higher strength in comparison with any materials used at present.For Mo-0.5 and 1.0wt% alloys and pure Mo nitrided in a NH_3 gas at 1100ﾟC which is much lower than 130 … More 0-1500ﾟC in previous works, nitriding behavior, hardness profiles on cross sections of nitrided specimens, and microstructure and crystallographic relationship of fine Ti-nitride particles in the Mo matrix were discussed. Main results are summarized below.(1) The growth mechanism of the Mo-nitride surface layr was made clear. A maximum hardness was found to reach Hv=1800. Furthermore, the surface layr was found to consist of two different sublayrs : a gamma-Mo_2N sublayr near the specimen surface and a beta-Mo_2N sublayr beneath the gamma-Mo_2N layr. Each sublayr has a different twin. In particular, the formation of a new type of microtwin was found in the beta-Mo_2N sublayr.(2) In nitrided Mo-Ti alloys an internal nitriding layr having high strength was formed beneath the Mo_2 surface layr. The formation of the internal nitriding layr was not observed in pure Mo. We attained markedly high hardness of Hv=1000, which is twice a maximum hardness of Hv=500 reported in Mo alloys so far. Moreover, we found first in the world that the nitriding at the very low temperature of 1100ﾟC brought the precipitation of nano-scale TiN superfine particles with a thickness of about 0.45nm (=1 unit length of TiN) and a diameter of 2-4nm. The superfine particles formed were found to have a special crystallographic-relationship and to give the great increase in strength. Less