Microstructure and Mechanical Properties of Mg-Zn-Y-Yb Alloys Produced by Consolidation of Rapidly Solidified Ribbons

Sakamoto Yoshihito,Yamasaki Michiaki,Kawamura Yoshihito 한국분말야금학회 2006 한국분말야금학회 학술대회논문집 Vol.2006 No.1

Fabrication of bulk alloy has been performed through the consolidation of rapidly solidified ribbons. The bulk alloy exhibited excellent mechanical properties, high tensile yield strength of 530 MPa, and large elongation of 3 %. Microstructure of the alloy was characterized by equiaxed fine grains that consist of -Mg, long period ordered (LPO) structure phase, and -type cubic compound. The strengthening of the alloys may be due to fine grains with LPO structure phase and -type compound.

Changes in the Surface Characteristics of Gas-atomized Pure Aluminum Powder during Vacuum Degassing

Yamasaki Michiaki,Kawamura Yoshihito 한국분말야금학회 2006 한국분말야금학회 학술대회논문집 Vol.2006 No.1

Vacuum degassing is essential in the preparation of RS P/M aluminum alloys to remove adsorbates and for the decomposition of hydrated- on the powder surface. Changes in the surface characteristics during vacuum degassing were investigated by X-ray photoelectron spectroscopy and temperature-programmed desorption measurement. Hydrated- decomposition to crystalline- and hydrogen desorption on the surface of argon gas-atomized aluminum powder occurred at 623 K and 725 K, respectively. This temperature difference suggests that the reaction converting hydrated- to crystalline- during vacuum degassing should be divided into the two reactions .

Vacuum degassing behavior of Zr-, Ni- and Cu-based metallic glass powders

Yamasaki, Michiaki,Iwamoto, Kotaro,Tamagawa, Hirokazu,Kawamura, Yoshihito,Lee, Jin-Kyu,Kim, Hwi-Jun,Bae, Jung-Chan Elsevier 2007 Materials science & engineering. properties, micro Vol.449 No.-

<P><B>Abstract</B></P><P>The vacuum degassing behavior of Zr<SUB>55</SUB>Al<SUB>10</SUB>Ni<SUB>5</SUB>Cu<SUB>30</SUB>, Ni<SUB>59</SUB>Zr<SUB>15</SUB>Ti<SUB>13</SUB>Si<SUB>3</SUB>Sn<SUB>2</SUB>Nb<SUB>7</SUB>Al<SUB>1</SUB>, and Cu<SUB>54</SUB>Ni<SUB>6</SUB>Zr<SUB>22</SUB>Ti<SUB>18</SUB> (numbers indicate at.%) metallic glass powders has been investigated and compared with that of Al alloy powder. It was found that the alloy composition influenced the gas desorption behavior with heating <I>in vacuo</I>. Zr<SUB>55</SUB>Al<SUB>10</SUB>Ni<SUB>5</SUB>Cu<SUB>30</SUB> and Ni<SUB>59</SUB>Zr<SUB>15</SUB>Ti<SUB>13</SUB>Si<SUB>3</SUB>Sn<SUB>2</SUB>Nb<SUB>7</SUB>Al<SUB>1</SUB> metallic glass powders exhibited little H<SUB>2</SUB> gas desorption from powder surfaces during vacuum degassing. Because Zr in the Zr-based and Ni-based amorphous alloy powders produced a native zirconium oxide layer, the surface of the Zr<SUB>55</SUB>Al<SUB>10</SUB>Ni<SUB>5</SUB>Cu<SUB>30</SUB> and Ni<SUB>59</SUB>Zr<SUB>15</SUB>Ti<SUB>13</SUB>Si<SUB>3</SUB>Sn<SUB>2</SUB>Nb<SUB>7</SUB>Al<SUB>1</SUB> amorphous alloys had no influence on adsorbed H<SUB>2</SUB>O. Cu<SUB>54</SUB>Ni<SUB>6</SUB>Zr<SUB>22</SUB>Ti<SUB>18</SUB> metallic glass powder was the most affected by atmospheric H<SUB>2</SUB>O among the metallic glass powders examined in this study. The adsorbed H<SUB>2</SUB>O and Cu metal may react with each other with the formation of Cu<SUB>2</SUB>O and liberation of H<SUB>2</SUB> during vacuum degassing. In order to obtain sound P/M final products with Cu-based P/M alloys, oxygen-free copper powders should be used in well-controlled atmospheres with low H<SUB>2</SUB>O partial pressures.</P>

High‑Strength AZ91 Alloy Fabricated by Rapidly Solidified Flaky Powder Metallurgy and Hot Extrusion

이태경,Michiaki Yamasaki,Yoshihito Kawamura,Jongbin Go,Sung Hyuk Park 대한금속·재료학회 2019 METALS AND MATERIALS International Vol.25 No.2

A high-strength AZ91 alloy is produced via hot extrusion using flakes fabricated through the rapidly solidified flaky powdermetallurgy. The AZ91 alloy flakes have an extremely fine dendritic structure without any second-phase particles owing tothe fast cooling rate during solidification; these microstructural features considerably promote dynamic recrystallization andprecipitation behaviors during extrusion process. As a result, the AZ91 alloy extruded using the flakes exhibits an almostfully recrystallized microstructure with a very small average grain size of 1.2 μm owing to an increase in the number ofnucleation sites for recrystallization, and it shows a high microstructural homogeneity owing to the numerous Mg17Al12precipitates uniformly distributed throughout the material. This extruded AZ91 alloy has a tensile yield strength of 345 MPa,ultimate tensile strength of 417 MPa, and total elongation of 5.6%. These superior tensile strengths are mainly attributed tothe combined effects of precipitation hardening caused by abundant fine precipitates and grain boundary hardening causedby fine recrystallized grains.

Corrosion Behavior of Rapidly Solidified Mg-Zn-Y Alloys in NaCl Solution

Izumi Shogo,Yamasaki Michiaki,Sekigawa Takahiro,Kawamura Yoshihito 한국분말야금학회 2006 한국분말야금학회 학술대회논문집 Vol.2006 No.1

Compositional dependence of corrosion behavior of rapidly solidified Mg-rich Mg-Zn-Y alloys in NaCl aqueous solution has been investigated. Mg-Zn-Y ternary alloys containing small amounts of Zn exhibited low corrosion rate, although the (at. %) binary alloy showed severe corrosion with violet evolution of hydrogen. The alloy with highest corrosion-resistance was , its corrosion rate was about 1 mm year-1 in 0.17 M (1.0 wt. %) NaCl solution. alloy exhibited passive region in anodic polarization curves when immersed in NaCl solution. Rapidly solidification and small amount of Zn addition may bring about an increase in electrochemical homogeneity of Mg-Zn-Y alloys, resulting in enhancement of corrosion resistance.

Microstructure and Mechanical Properties of Rapidly Solidified Powder Metallurgy Al-Fe-V-Si-X Alloys

Genkawa Takuya,Yamasaki Michiaki,Kawamura Yoshihito 한국분말야금학회 2006 한국분말야금학회 학술대회논문집 Vol.2006 No.1

High heat-resistant Al-Fe-V-Si and Al-Fe-V-Si-X rapidly solidified powder metallurgy (RS P/M) alloys have been developed under well-controlled high purity argon gas atmosphere. The (at. %) RS P/M alloy exhibited high elevated-temperature strength exceeding 300 MPa and good ductility with elongation of 6 % at 573 K. Reduction of partical pressure in P/M processing atmosphere led to improvement in mechanical properties of the powder-consolidated alloys under elevated-temperature service conditions. Ti addition to the Al-Fe-V-Si conduced to enhancement of the strength at room temperature. The tensile yeild strength and ultimate strenght were 545 MPa and 722 MPa, respectively.

Development of High Strength Mg-Zn-Gd Alloys by Rapid Solidification Processing

Kim Min-Chul,Yamasaki Michiaki,Kawamura Yoshihito 한국분말야금학회 2006 한국분말야금학회 학술대회논문집 Vol.2006 No.1

Rapidly solidified ribbon-consolidation processing was applied for preparation of high strength bulk Mg-Zn-Gd alloys. Mg alloys have been used in automotive and aerospace industries. Rapid solidification (RS) process is suitable for the development of high strength Mg alloys, because the process realizes grain-refinement, increase in homogeneity, and so on. Recently, several nanocrystalline Mg-Zn-Y alloys with high specific tensile strength and large elongation have been developed by rapidly solidified powder metallurgy (RS P/M) process. Mg-Zn-Y RS P/M alloys are characterized by long period ordered (LPO) structure and sub-micron fine grains. The both additions of rare earth elements and zinc remarkably improved the mechanical properties of RS Mg alloys. Mg-Zn-Gd alloy also forms LPO structure in -Mg matrix coherently, therefore, it is expected that the RS Mg-Zn-Gd alloys have excellent mechanical properties. In this study, we have developed high strength RS Mg-Zn-Gd alloys with LPO structure and nanometer-scale precipitates by RS ribbon-consolidation processing. and and bulk alloys exhibited high tensile yield strength (470 MPa and 525 MPa and 566 MPa) and large elongation (5.5% and 2.8% and 2.4%).

Severe C8 or T1 Symptoms after Cervical Laminoplasty and Related Factors: Are There Any Differences between C3–C6 Laminoplasty and C3–C7 Laminoplasty?

Hitoshi Kudo,Kazunari Takeuchi,Toru Yokoyama,Yoshihito Yamasaki,Kanichiro Wada,Gentaro Kumagai,Toru Asari,Hironori Otsuka,Yasuyuki Ishibashi 대한척추외과학회 2019 Asian Spine Journal Vol.13 No.4

Study Design: Retrospective study. Purpose: We experienced the situation wherein some patients had new-onset pain or dysesthesia around the ring and little fingers (C8 symptom) or ulnar aspect of the forearm (T1 symptom) after cervical laminoplasty (LP). We investigated the incidence and the cause of new C8 or T1 symptoms and the clinical outcomes after C3–C6 LP or C3–C7 LP. Overview of Literature: There were some reports regarding complications after cervical LP. However, there was no report regarding C8 or T1 symptoms after cervical LP. Methods: Among the 33 patients enrolled in this study, 11 and 22 patients were treated with C3–C6 LP and C3–C7 LP, respectively. We prospectively evaluated C8 or T1 symptoms daily postoperatively for 1 week. The distance of the posterior spinal cord shifting and posterior subarachnoid space from C2 to T1 was measured by T2-weighted midsagittal magnetic resonance imaging (MRI). We evaluated pre- and postoperative axial neck pain, Japanese Orthopaedic Association (JOA) score, and JOA score improvement rate. Results: C8 or T1 symptoms occurred in five and three patients with C3–C6 LP (45.5%) and C3–C7 LP (13.6%), respectively. The distance of the posterior subarachnoid space in C3–C6 LP at C7 was significantly shorter than that in C3–C7 LP at T1 on MRI 24 hours postoperatively (p=0.0448). Postoperative axial neck pain, pre- and postoperative JOA scores, and JOA score improvement rate were not significantly different. Conclusions: The incidence of C8 or T1 symptoms in C3–C6 LP was higher than that in C3–C7 LP. C8 or T1 symptoms would be caused by the posterior fila radicularia and spinal cord impingement on the intact lower end of the lamina.