1997 Fiscal Year Final Research Report Summary
Preparation and Properties of New Mo-based Alloys Strengthened by Dispersion of Nano-scale Nitride Superfine Particles
| Project/Area Number |
08455311
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Composite materials/Physical properties
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| Research Institution | OKAYAMA UNIVERSITY |
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Principal Investigator |
TAKADA Jun Okayama University, Faculty of Engineering, Professor, 工学部, 教授 (60093259)
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| Co-Investigator(Kenkyū-buntansha) |
NAKANISHI Makoto Okayama University, Faculty of Engineering, Research Associate, 工学部, 助手 (10284085)
FUJII Tatsuo Okayama University, Faculty of Engineering, Lecturer, 工学部, 講師 (10222259)
HIRAOKA Yutaka Okayama University of Science, Faculty of Science, Professor, 理学部, 教授 (70228774)
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| Project Period (FY) |
1996 – 1997
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| Keywords | Mo alloys / Nitriding / transmission electron microscopy / Mo_2N / microtwin / crystallographic relationship / superfine TiN particles / Dispersion-strengthening |
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| Research Abstract |
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
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[Publications] M.Nagae, M.Nakanishi, J.Takada, M.Kobayashi, Y.Hiraoka, H.Kuwahara, Y.Takemoto, M.Hida and M.K.Yoo: "Nitriding Behavior of Mo-Ti Alloys in NH_3 at 1373K" Proc.of the 14^<th> Int.Plansee Seminar, Eds.By G.Kneringer, P.Rodhammer and P.Wilhartitz, Reutte. vol.1. 819-829 (1997)
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