Precipitation of ferromagnetic phase induced by defect energies during creep deformation in Type 304 austenitic steel

Tsukada, Yuki*; Shiraki, Atsuhiro*; Murata, Yoshinori*; Takaya, Shigeru; Koyama, Toshiyuki*; Morinaga, Masahiko*

Journal of Nuclear Materials, 401(1-3), p.13 - 16, 2010/06

https://doi.org/10.1016/j.jnucmat.2010.03.013

The correlation of defect energies with precipitation of the ferromagnetic phase near MC carbide during creep tests at high temperature in Type 304 austenitic steel was examined by estimating the defect energies near the carbide, based on micromechanics. As one of the defect energies, the precipitation energy was calculated by assuming MC carbide to be a spherical inclusion. The other defect energy, creep dislocation energy, was calculated based on dislocation density data obtained from transmission electron microscopy observations of the creep samples. The dislocation energy density was much higher than the precipitation energy density in the initial stage of the creep process, when the ferromagnetic phase started to increase. Creep dislocation energy could be the main driving force for precipitation of the ferromagnetic phase.

An Electronic approach to the hydrogen overpotential for Zr alloys

Shibutani, Hideo*; Higashijima, Takahiro*; Ezaki, H.*; Morinaga, Masahiko*; Kikuchi, Keiichi

Electrochimica Acta, 43(21), p.3235 - 3239, 2002/00

None

Corrosion behavior of Nb-based and Mo-based super heat-resisting alloys in liquid Li

Saito, Junichi; Morinaga, Masahiko*; Kano, Shigeki

PNC TN9410 98-072, 97 Pages, 1998/07

PNC-TN9410-98-072.pdf:7.03MB

Research on structural materials which will be utilized even in the severe environment of high-temperature liquid alkali metals has been promoted in order to develop the frontiers of materials techniques. The super-heat resisting alloys which are based on refractory metals, Nb and Mo, are aimed as promising materials used in such an environment. The corrosion resistance in liquid Li and the mechanical properties such as creep and tensile strengths at high temperatures are important for these structural materials. On the basis of many expeliments and analyses of these properties at 1473K, the material design of Nb-based and Mo-based alloys has-been carried out successfully. In this report, all the previous experimental results of corrosion tests in liquid Li were summarized systematically for Nb-based and Mo-based alloys. The corrosion mechanism was proposed on the basis of a series of analyses, in particular, focussing on the deposition mechanism of corrosion products on the surface and also on the initiation and growth mechanism of cracks on the corroded surface of Nb-based alloys. The principal results are as follows. (1)For the deposition mechanism, a reaction took place first between dissolved metallic elements and nitrogen which existed as an impurity in liquid Li and then corrosion products (nitrides) precipitated on the metal surface. Subsequently, another reaction took place between dissolved metalic elements in liquid Li, and corrosion products (intermetallic compounds) precipitated on the metal surface. The composition of deposited corrosion products could be predicted on the basis of the deposition mechanism. (2)For the crack initiation mechanism, the chemical potential diagrams were utilized in order to understand the formation of Li-M-O ternary oxides which caused cracks to be formed on the corroded surface. Consequently, it was evident that not only the concentration of the dissolved oxygen in the alloy but also the concentration of Li which ...

Experimental evaluation of the characteristics of super-heat-resisting Nb-based and Mo-based alloys

Morinaga, Masahiko*; *; *

PNC TJ9603 98-002, 48 Pages, 1998/03

PNC-TJ9603-98-002.pdf:2.14MB

[PURPOSE]Both the Nb-based and Mo-based alloys have been designed and developed in order to establish the frontier technique for super-heat-resisting materials used in the liquid alkali metal environment at high temperatures. In this study, mechanical properties of the designed Nb-1Hf alloy were experimentally evaluated. In addition, the brittleness of Nb-based alloys observed at 1073K were discussed. Moreover, characteristics of both the designed Nb-based and the Mo-based alloys were summarized in a consistent way. [EXPERIMENTAL METHODS] (1)Tensile test : The tensile test was performed at room temperature and 1473K in an Ar gas atmosphere for the designed Nb-1Hf alloy and also for commercial Nb-1Zr alloy. (2)High temperature creep test:The creep test of the designed Nb-1Hf alloy was carried out at 1473K in an Ar gas atmosphere under several applied stress levels. (3)TEM observation : The TEM observation was performed with the creep specimens tested at both 1073K and 1273K in order to get information for the 1073K brittleness of the Nb-1Zr alloy. [RESULTS AND DISCUSSIONS] (1)Tensile test : The tensile stress and the proof stress of the designed Nb-1Hf alloy were slightly lower than those of commercial Nb-1Zr alloy at room tempetarure. But the alloy was superior in the elongation to the Nb-1Zr alloy. High temperature tensile properties were not able to be evaluated properly because of the large grain size of the specimens. (2)High temperature creep test : The Nb-1Hf alloy was superior in the ereep resistance to other solid solution hardened Nb-based alloys. (3)TEM observation : A modulated structure with about 1nm preiod was observed in the specimen which was brittle at 1073K. This was supposed to cause the 1073K brittleness of the Nb-1Zr alloy. [CONCLUSION] The tensile strength of the designed Nb-1Hf alloy was slightly lower at room temperature than that of the commercial Nb-1Zr alloy. But, the designed alloy was superior in high temperature creep properties to any

Nodular corrosion of zirconium alloys and XPS analysis of surface oxide layer

Shibutani, Hideo*; Morinaga, Masahiko*; Kikuchi, Keiichi

Nihon Kinzoku Gakkai-Shi, 62(6), p.534 - 541, 1998/00

None

Design and evaluation of super-heat-resisting Nb-based and Mo-based alloys

Morinaga, Masahiko*; *; *; *; Inoue, Satoshi*

PNC TJ9603 96-001, 79 Pages, 1996/03

PNC-TJ9603-96-001.pdf:3.48MB

[PURPOSE] In order to develop the frontier domain of technique for the high temperature liquid alkali metal, candidate Nb-based and Mo-based alloys are needed. They are needed to have excellent compatibility with liquid Li (max. 1200C) and super-heat-resistance. In this study, alloy design using a d-electrons alloy theory and estimation of designed alloy were performed. [EXPERIMENTAL METHODS] (1)Workability : A bend test was carried out with the provisionally designed Mo-based alloys, but by modifying the compositions by adding intergranular strengthening elements, Ti, B, C, Hf, into them to improve the ductility. (2)Corrosion resistance to liquid Li : The provisionally desingned Nb-based alloys were immersed in liquid Li at 1200C for three hundred hours, and the weight change due to the corrosion was measured. The corrosion surface was also analyzed using SEM and EPMA. In addition, a similar corrosion test was carried out with binary Nb-based and Mo-based alloys. (3)Embrittlement at 800C : A series of experiments such as the hardness test, X-ray analysis and microstructure observation was perfomed with the Nb-1Zr alloy which was creep-tested at 800C or 1200C. Also, a Nb-1Zr alloy specimen which was not creep-tested, was used as a reference specimen. [RESULTS AND DISCUSSIONS] (1)Workability : The Ti addition into the Mo-based alloys was effective in improving workability. The brittleness of Mo may be caused by the existence of oxygen in the grain boundaries, so that the formation of Ti oxides probably weakened the oxygen effect, resulting in the better workability of the alloy. However, B, C and Hf additions into Mo-based alloys never improved the workability. (2)Corrosion resistance to liquid Li : Many cracks were observed on the corroded surface of the provisionally designed Nb-based alloys despite the addition of a corrosion resistant element, Hf, into them. In paticular, such cracks were developed ...

None

Morinaga, Masahiko*; Saito, Junichi*; Murata, Yoshinori*; Kano, Shigeki; *; Tachi, Yoshiaki; Inoue, Satoshi*

PNC TY9623 95-001, 165 Pages, 1995/03

PNC-TY9623-95-001.pdf:5.61MB

None

Alloying Effect on the Electronic Structures of Nb and Mo

Kano, Shigeki; Saito, Junichi*; Morinaga, Masahiko*

Journal of Physics; Condensed Matter, 6(27), p.5081 - 5096, 1994/00

https://doi.org/10.1088/0953-8984/6/27/017

None

Design of Super Heat-Resisting Mo-Based Alloys for Nuclear Applications

Kato, Masahito*; Kano, Shigeki; Inoue, Satoshi*; Isshiki, Yasushi*; Saito, Junichi*; Yoshida, Eiichi; Morinaga, Masahiko*

Nihon Kinzoku Gakkai-Shi, 57(2), p.233 - 240, 1993/00

None

Design of super-heat-resisting structural materials using a d-electron alloy theory (II)

*; Morinaga, Masahiko*; Saito, Junichi*; *; *

PNC TJ9623 92-001, 81 Pages, 1991/07

PNC-TJ9623-92-001.pdf:6.46MB

[PURPOSE] For structural materials serviced in the Li environments, both Nb-based and Mo-based alloys are selected as the candidate materials. In this study, a simple method was proposed for evaluating the high temperature strength of these alloys. Also, the corrosion resistance in liquid metals was investigated in order to get fundamental information for the design and development of high performance alloys. [EXPERIMENTAL AND CALCULATING METHODS] With a variety of ternary alloys high temperature micro-hardness was measured systematically. The results were analyzed by referring to the relationship between the hardness and the tensile strength reported in previous publications. Also, some alloys designed last year were exposed to the liquid Na at 650 C, and the attendant changes were examined with respect to the weight, microstructure and local composition of alloys. Some of the results were understood in terms of the free energy for the oxide formation of Na and other elements in alloys. Another effort to understand the corrosion properties was made by the molecular orbital calculation of the electronic states of various elements in liquid Li, K and Na. [RESULTS] The high temperature tensile strength of both the alloys was found to be predictable by using a linear relationship between the hardness and the tensile strength of room temperature to 1200 C. The corrosion resistance was much poorer in the Nb-based alloys than in the Mo-based alloys. This is partially due to the enhancement of corrosion by the preferred oxidation of Nb and Ta in the Nb-based alloys, whereas no such oxidation took place in the Mo-based alloys. In addition, it was found from the molecular orbital calculation that Li is the liquid metal of more strongly-bonded with every alloying element, compared to K and Na liquid metals. Futhermore, it was shown that the hardness of each alloy correlated well with the atomic-size difference and also the young's modulus difference ...