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

已知Mo合金是高熔化温度金属之一，用作高温材料，例如加热器、热处理托盘和X射线靶。为了使Mo-Ti合金得到更广泛的应用，对Mo-Ti合金提出了更高的强化要求，本研究的目的是通过氮化使Mo-Ti合金表面硬化，并通过优选氮化使弥散在Mo基体中的TiN颗粒析出来强化合金。特别是在此基础上，我们尝试在较低的氮化温度下制备出大量纳米TiN超细颗粒弥散分布的Mo基复合材料。结果表明，我们成功地研制出了一种比目前使用的任何材料都具有显著高强度的新型钼基复合材料。对于Mo-0.5wt%和1.0wt%的合金和纯Mo在1100 ℃（远低于130 ℃）的NH_3气氛中氮化，在1100 ℃下氮化的Mo基复合材料的强度比纯Mo的高10%。 关于我们 0-1500 ℃的温度范围内，对氮化行为、氮化试样横截面上的硬度分布以及细小氮化钛颗粒在钼基体中的显微组织和晶体学关系进行了讨论。主要结果总结如下。(1)阐明了氮化钼表面层的生长机理。发现最大硬度达到Hv = 1800。此外，表面层由两个不同的亚层组成：靠近试样表面的γ-Mo_2N亚层和γ-Mo_2N亚层之下的β-Mo_2N亚层。每个亚层都有一个不同的孪生兄弟。特别是在β-Mo_2N亚层中发现了一种新型的微孪晶。(2)氮化Mo-Ti合金在Mo_2表层下形成一层高强度的内氮化层。纯钼中未观察到内氮化层的形成。我们获得了Hv = 1000的显着高硬度，这是迄今为止在Mo合金中报道的Hv = 500的最大硬度的两倍。此外，我们在世界上首次发现，在1100 ℃的极低温度下渗氮，析出了厚度约为0.45nm（= 1单位长度的TiN）、直径为2 - 4nm的纳米级TiN超细颗粒。研究发现，所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