Kazuya Miyahara

Bio: Kazuya Miyahara is an academic researcher from Nagoya University. The author has contributed to research in topics: Microstructure & Creep. The author has an hindex of 11, co-authored 48 publications receiving 735 citations. Previous affiliations of Kazuya Miyahara include University of Tokyo.

Effects of Cu, Ag and Sb on the creep-rupture strength of lead-free solder alloys

Abstract: The materials used in the present research are pure Sn metal and Sn-0.5% Cu, Sn-3.5%Ag, Sn-0.3%Sb, and Sn-3.5%Ag-0.5%Cu alloys. Effects of Cu, Ag and Sb on the creep-rupture strength of lead-free solder alloys have been investigated. Creep tests are performed at the stress and temperature range of 3 to 12 MPa and 378 to 403 K, respectively. A 3.5% addition of Ag had the largest contribution to the creep-rupture strength of Sn metal among the single addition of 0.5%Cu, 3.5%Ag, and 0.3%Sb. The combined addition of 3.5%Ag and 0.5%Cu makes the largest creep-rupture strength. The effects of these elements on the microstructure of the lead-free alloys are also investigated with optical microscope (OM) and transmission electron microscope (TEM) observations.

Effect of Ti and W on the Mechanical Properties and Microstructure of 12% Cr Base Mechanical-alloyed Nano-sized ODS Ferritic Alloys

Abstract: In recent years, research and development of high-temperature structural materials for ultra-super critical pressure plant with increased energy efficiency have actively been in progress so as to solve global environmental pollution and resource exhaustion issues. Oxide-dispersed-strengthened (ODS) ferritic alloys produced by mechanical alloying (MA) have been developed as alternative materials with very high-temperature strength at the ultra-super critical pressure. In this study, Fe-12%Cr ODS based alloys containing Ti and W have been made and the effects of Ti and W on the high-temperature strength of the alloys were investigated. The results show that high-temperature tensile strength and creep rupture strength of the 12YWT steel containing 0.4% Ti and 3 % W were the highest. This is mainly due to the formation of fine complex oxides of Ti-Y-O by the addition of T and their homogeneous distribution. It is also suggested that solid solution hardening by W occurs as a result of uniform distribution of W in solution.

Microstructural effect on the creep strength of a Sn-3.5%Ag solder alloy

Abstract: The effect of microstructure obtained by rapid or slow solidification and cooling of a Sn-3.5%Ag lead-free solder alloy on the creep strength has been investigated. The rapidly cooled alloy showed that the microstructure consisted of the primarily crystallized Sn phase and the quasi-eutectic phase, where fine Ag3Sn particles dispersed in the Sn matrix. In the slowly cooled alloy, large platelets of Ag3Sn were formed sparsely in the Sn matrix. A difference of about 2.5 orders of magnitude in the cooling rate translates to about 1.5 orders of magnitude in the creep-rupture time. Accordingly, fine particle dispersion of Ag3Sn is considered to be very beneficial for the restraining of creep deformation, that is, for the decreasing of creep rate of the Sn-3.5%Ag alloy, compared with the effect of large platelets of Ag3Sn sparsely formed in the Sn matrix.

Recent developments in stainless steels

Abstract: This article presents an overview of the developments in stainless steels made since the 1990s. Some of the new applications that involve the use of stainless steel are also introduced. A brief introduction to the various classes of stainless steels, their precipitate phases and the status quo of their production around the globe is given first. The advances in a variety of subject areas that have been made recently will then be presented. These recent advances include (1) new findings on the various precipitate phases (the new J phase, new orientation relationships, new phase diagram for the Fe–Cr system, etc.); (2) new suggestions for the prevention/mitigation of the different problems and new methods for their detection/measurement and (3) new techniques for surface/bulk property enhancement (such as laser shot peening, grain boundary engineering and grain refinement). Recent developments in topics like phase prediction, stacking fault energy, superplasticity, metadynamic recrystallisation and the calculation of mechanical properties are introduced, too. In the end of this article, several new applications that involve the use of stainless steels are presented. Some of these are the use of austenitic stainless steels for signature authentication (magnetic recording), the utilisation of the cryogenic magnetic transition of the sigma phase for hot spot detection (the Sigmaplugs), the new Pt-enhanced radiopaque stainless steel (PERSS) coronary stents and stainless steel stents that may be used for magnetic drug targeting. Besides recent developments in conventional stainless steels, those in the high-nitrogen, low-Ni (or Ni-free) varieties are also introduced. These recent developments include new methods for attaining very high nitrogen contents, new guidelines for alloy design, the merits/demerits associated with high nitrogen contents, etc.

Recent Developments in Irradiation-Resistant Steels

Abstract: Advanced fission and future fusion energy will require new high-performance structural alloys with outstanding properties that are sustained under long-term service in ultrasevere environments, including neutron damage producing up to 200 atomic displacements per atom and, for fusion, 2000 appm of He. Following a brief description of irradiation damage and damage resistance, we focus on an emerging class of nanostructured ferritic alloys (NFAs) that show promise for meeting these challenges. NFAs contain an ultrahigh density of Y-Ti-O-enriched dispersion-strengthening nanofeatures (NFs) that, along with fine grains and high dislocation densities, provide remarkably high tensile, creep, and fatigue strength. The NFs are stable under irradiation up to 800°C and trap He in fine-scale bubbles, suppressing void swelling and fast fracture embrittlement at lower temperatures and creep rupture embrittlement at high temperatures. The current state of the development and understanding of NFAs is described, along wi...

Designing Radiation Resistance in Materials for Fusion Energy

Abstract: Proposed fusion and advanced (Generation IV) fission energy systems require high-performance materials capable of satisfactory operation up to neutron damage levels approaching 200 atomic displacements per atom with large amounts of transmutant hydrogen and helium isotopes. After a brief overview of fusion reactor concepts and radiation effects phenomena in structural and functional (nonstructural) materials, three fundamental options for designing radiation resistance are outlined: Utilize matrix phases with inherent radiation tolerance, select materials in which vacancies are immobile at the design operating temperatures, or engineer materials with high sink densities for point defect recombination. Environmental and safety considerations impose several additional restrictions on potential materials systems, but reduced-activation ferritic/martensitic steels (including thermomechanically treated and oxide dispersion–strengthened options) and silicon carbide ceramic composites emerge as robust structural...