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Volume 80, Issue 11
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Overview
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Yoshinori Murata2016 Volume 80 Issue 11 Pages 669-683
Published: 2016
Released on J-STAGE: October 25, 2016
JOURNAL FREE ACCESSLath Martensite is formed in low carbon steels and plays an important role in the mechanical properties of heat resistant steels containing about 0.1 mass%C. The lath martensite shows the hierarchic microstructure being composed of packet, block and lath. Martensitic transformation is the phase transformation accompanying orderly shear deformation without atomic diffusion. Relaxation of the strain energy caused by the deformation is the origin of the hierarchic microstructure but the formation mechanism of this microstructure has heretofore not been understood. In this paper, we survey first both the experimental results and phenomenological formation mechanism of the lath martensite reported so far and introduce a new mechanism (Two Types of Slip Deformation model: TTSD model), which is constructed by considering, independently, two kinds of slip deformations using the slip deformation model proposed by Khachaturyan. It is also introduced that TTSD model enables us to simulate the martensite phase formation by the phase-field method. Furthermore, it is found that TTSD model allow us to predict the features of lath martensite, such as the existence of sub-blocks and high dislocation density in lath. In particular, for the first time, the reason why laths in a block structure exist, can be clearly explained by TTSD model.
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Regular Article
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Akinori Nakamura, Satoshi Oue, Hiroki Koga, Hiroaki Nakano2016 Volume 80 Issue 11 Pages 684-690
Published: 2016
Released on J-STAGE: October 25, 2016
Advance online publication: September 16, 2016JOURNAL FREE ACCESSThe phosphate coating for Mg alloy was performed in the unagitated solutions containing 1 g•dm−3 of Mg, Ca, Sr and Ba as alkali-earth metal and 50 g•dm−3 of H3PO4 of pH 3 and 40℃ for 3 min, and the structure and formation behavior of the phosphate films were investigated. The X-ray diffraction patterns of phosphate films broadened regardless of the kinds of alkali-earth metal, which was a characteristic of an amorphous structure. XPS analysis revealed that the valence of P in the phosphate films was pentavalent. The pH in the vicinity of the Mg alloy during the phosphate coating, as measured using an Sb microelectrode, was approximately 10.4, 11.4, 10.7, 12.0 in the solutions containing Mg, Ca, Sr and Ba, respectively, which shows that the phosphoric acid dissociates to the third stage during the phosphate coating and the phosphate films composed of M3(PO4)2 containing alkali-earth metal (M) are formed. The phosphate coating were successively performed in the two kinds of solutions containing different alkali-earth metals and the cross section was analyzed, as a result, it was suggested that the new phosphate films were formed at the interface between Mg alloy substrate and phosphate films and the previously formed phosphate films were boosted up in films.
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Masataka Ijiri, Akira Okumura, Takafumi Ishikawa, Kenji Kadowaki, Yosh ...2016 Volume 80 Issue 11 Pages 691-696
Published: 2016
Released on J-STAGE: October 25, 2016
JOURNAL FREE ACCESSThe Ti-4Fe-7Al alloy exhibits some interesting phenomena upon tempering. The noteworthy features are rapid hardening and shape change in a U-shaped specimen with heating, which are caused by the β(bcc)→α″ (orthorhombic) transformation at elevated temperature. The transformation behavior on the TTT (time-temperature-transformation) diagram estimated from the age hardening at various temperatures indicated a C-curve with a nose at 450℃, which means that the transformation occurs through a thermal activation process. However, STEM-EDS analysis of α″ revealed that the transformation had occurred without atom diffusion. In this study, every solution treatment was carried out at 1050℃ for 30 min under a vacuum, then the specimen was quenched into a salt bath of 200–550℃ and held for a certain period prior to water quenching. These treated specimens were compared with the quenched and tempered specimens with respect to the microstructure and the hardening behavior. The hardness of the specimens held at 200–500℃ (30 s) increased with increasing holding temperature. The maximum hardness, 610Hv, which was almost the same as that of a tempered specimen, was obtained at around 450℃. The microstructure of the specimen held at 450℃ (30 s) showed a common morphology composed of acicular martensite variants, except for the size. Because the several variants would cancel the transformation strain of each other, no severe unevenness of the surface was generated, unlike the tempered specimen. On the other hand, the hardness of the specimen held at 550℃ (30 s) decreased drastically owing to the phase separation to α+β, and the TiFe precipitates were generated from β upon the extension of the holding time.
By the TEM observation of the electropolished thin foil of the specimen held at 450℃ (30 s), unreasonable microstructure that was different from the XRD result was obtained. Just after the electropolishing, the SAD patterns showed that the α″-structure has a commensurate relation with the β-lattice. However, α″ turned spontaneously into an incommensurate relation after one year. On the other hand, TEM observations of the foil prepared by FIB (focused ion beam) were consistent with the XRD result. It was suggested that the hydrogen absorption during electropolishing caused a structural transition of α″ martensite.
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Yuki Muto, Takayuki Shiraiwa, Manabu Enoki2016 Volume 80 Issue 11 Pages 697-701
Published: 2016
Released on J-STAGE: October 25, 2016
Advance online publication: September 02, 2016JOURNAL FREE ACCESSLong-period Stacking ordered (LPSO) Mg alloys were focused on owing to its high properties. In this study, compression tests of unidirectional solidification (DS) Mg85Y6Zn9 were carried out with AE measurement. The three type specimens of load direction to solidification direction were manufactured for estimation of anisotropy. The continuous AE clustering analysis divided the AE waves measured in one type specimen into three clusters. By compared with the observation results and clustering results, a cluster was considered as the AE waves of noise and one of the other two clusters was considered as the AE waves of kink deformation. The results showed the possibility of evaluating the effect of anisotropy and the deformation mechanism of LPSO-Mg alloys.
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Masahiro Nagae, Naoko Ise, Jun Takada, Yutaka Hiraoka2016 Volume 80 Issue 11 Pages 702-706
Published: 2016
Released on J-STAGE: October 25, 2016
Advance online publication: September 30, 2016JOURNAL FREE ACCESSIn order to overcome the problem of recrystallization embrittlement of molybdenum, internally nitrided dilute Mo-Zr alloys with a heavily deformed microstructure near their surface were prepared by a novel method involving three-step nitriding at 1000 to 1600℃ in N2 gas. The grain structure was investigated after each nitriding step, and the mechanical properties of the final specimens were then evaluated. The first nitriding step was carried out below the recrystallization temperature for the alloys, and resulted in a uniform dispersion of ultrafine Zr-nitride precipitates within the unrecrystallized molybdenum matrix. After the second and third nitriding steps, these precipitates grew into disk-shaped particles with a diameter of 20 to 50 nm, and acted as pinning sites for grain boundary migration in the matrix, thus maintaining its deformed microstructure. The recrystallization temperature for specimens subjected to three-step nitriding was increased to above 1700℃. This is 100℃ higher than that for a Mo-Ti alloy subjected to almost the same multi-step internal nitriding procedure. A nitrided Mo-1.0 wt%Zr alloy exhibited high ductility even at about −40℃, and its yield strength at 1500℃ was about 2 times higher than that of a nitrided Mo-0.5 wt%Ti alloy.
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Yoshihiko Hangai, Yukiko Nakano, Takao Utsunomiya, Osamu Kuwazuru, Soi ...2016 Volume 80 Issue 11 Pages 707-712
Published: 2016
Released on J-STAGE: October 25, 2016
Advance online publication: September 09, 2016JOURNAL FREE ACCESSIn this study, compression deformation behavior of aluminum (Al) foam-filled thin-walled steel tubes was controlled by introducing slits on the tube and varying length and number of the slits. The deformation of the foam-filled tubes without slits started from various layers depending on the specimens. In contrast, the deformation of foam-filled tubes with slits started from the layer with a longest slit and largest number of slits, and spread to the layer with shorter slits and smaller number of slits. In addition, it was revealed that introducing of the slits on the tube had no effect on compression properties.
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Hiroshi Kobayashi, Hirofumi Shoji, Satoshi Asano, Masaki Imamura2016 Volume 80 Issue 11 Pages 713-718
Published: 2016
Released on J-STAGE: October 25, 2016
Advance online publication: September 30, 2016JOURNAL FREE ACCESSMCLE (Matte Chlorine Leach and Electro-winning) process developed by Sumitomo Metal Mining Co., LTD. is well known as a unique commercial nickel refining process with high nickel recovery ratio. Two types of nickel sulfide, nickel matte and mixed sulfide (MS: mixture sulfide of nickel and cobalt), are treated in the MCLE process, and the leaching rate difference for each materials become obvious in this process. Bench scale tests had been carried out and leaching rates and activation energies of chlorine leaching reactions were identified. The nickel leaching rate of MS in chlorine leaching reaction is 60% smaller than that of nickel matte.
The nickel leaching rate difference between nickel matte and MS in chlorine leaching reaction is derived from their reaction free energy difference. The determinants of the chlorine leaching reaction rate of nickel matte and MS are respectively a chemical reaction rate and elements diffusion ratio on their surface.
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