Kunio Funami

Bio: Kunio Funami is an academic researcher from Chiba Institute of Technology. The author has contributed to research in topics: Magnesium alloy & Ultimate tensile strength. The author has an hindex of 7, co-authored 53 publications receiving 213 citations.

Low Temperature Superplasticity and Its Deformation Mechanism in Grain Refinement of Al-Mg Alloy by Multi-Axial Alternative Forging

Abstract: In practical application, an appearance of low temperature superplasticity (LSTP) is one of necessaries conditions. In this paper, to estimate an appearance and deformation mechanisms of this superplasticity, the role of grain boundary sliding (GBS), intragranular deformation and the change of microstructure during superplastic deformation have been investigated for ultrafine-grained Al-Mg alloy with a grain size of less than 1 μm using Multi-Axial Alternative Forging (MAF) technique. In these materials, it shows that the elongation and strain rate sensitivity (m-value) were 340% and 0.39, respectively, at 473 K under a strain rate of 2.8 x 10 -3 s -1 . These results show that superplastic appearance is possible at 473 K. The void formed at 473 K elongated in parallel to the tensile direction, with a length of 15 μm and a width of 5 μm. The intragranular deformation contribution was estimated from the aspect ratio of the grains after deformation and its contribution ratio was about 33.5 %. Therefore, for the appearance of lower temperature superplasticity with large elongation and m-value, the role of intragranular deformation was the most important factor together with GBS under these conditions. As described above, the MAF technique is one of the most effective methods to produce ultrafine-grained material and appearance of lower temperature superplasticity.

Feasibility of Friction Stir Welding for Joining and Microstructure Refinement in a ZK60 Magnesium Alloy

Abstract: Feasibility of FSW to produce defect-free welds and for microstructure refinement in a ZK60 magnesium alloy has been examined over wide ranges of rotational and welding speeds. The results showed that joined-state was affected very much by the thickness of plates to be joined: for ‘‘thin’’ 3-mm thick plates, FSW was successful in a relatively wide range of welding conditions, whereas all ‘‘thick’’ 6-mm welds were found to be defective irrespective of rotational and welding speeds used. We have demonstrated that FSW is a very effective tool for microstructure refinement in the ZK60 alloy plates: A coarse, mm-scale, original grain structure was efficiently refined down to fine-grained range. It appears that second-phase particles containing Zr play an important role in the grain refinement. [doi:10.2320/matertrans.MRA2007177]

Cross-Sectional Area Measurement and Monofilament Strength Test of Kenaf Bast Fibers

Abstract: The primary purpose of this study is to statistically characterize the tensile strength of kenaf (Hibiscus cannabi- nus L.) bast fibers, which are now using for fiber-reinforcing composite materials. This paper is the first part of the present study, and reports the experimental procedures and results for geometrical measurements and monofilament tensile strength test of the kenaf bast fibers sampled from the identical portion in an individual plant. Cross-sectional geometries of the fibers, which in the mesoscopic level consist of elementary fibrous cells and inter-cell materials, were found to vary severely along and among fibers. A method to estimate cross-sectional areas of this plant fiber from their mutually-perpendicular side views was also proposed. Large variations of monofilament strength of the fibers were observed. The strength with gauge length fixed was found to be well described by the two-parameter Weibull distribution in practice, but Weibull shape and scale parameters were different from each of different gauge lengths, which may be primary due to the along-and-among geometrical variation and "mesoscopic" internal struc- ture of the fibers.

Low Temperature Superplasticity and Its Deformation Mechanism in Grain Refinement of Al-Mg Alloy by Multi-Axial Alternative Forging

Abstract: In practical application, an appearance of low temperature superplasticity (LSTP) is one of necessaries conditions. In this paper, to estimate an appearance and deformation mechanisms of this superplasticity, the role of grain boundary sliding (GBS), intragranular deformation and the change of microstructure during superplastic deformation have been investigated for ultrafine-grained Al-Mg alloy with a grain size of less than 1 μm using Multi-Axial Alternative Forging (MAF) technique. In these materials, it shows that the elongation and strain rate sensitivity (m-value) were 340% and 0.39, respectively, at 473 K under a strain rate of 2.8 x 10 -3 s -1 . These results show that superplastic appearance is possible at 473 K. The void formed at 473 K elongated in parallel to the tensile direction, with a length of 15 μm and a width of 5 μm. The intragranular deformation contribution was estimated from the aspect ratio of the grains after deformation and its contribution ratio was about 33.5 %. Therefore, for the appearance of lower temperature superplasticity with large elongation and m-value, the role of intragranular deformation was the most important factor together with GBS under these conditions. As described above, the MAF technique is one of the most effective methods to produce ultrafine-grained material and appearance of lower temperature superplasticity.

Friction stir processing technology: A review

Abstract: Friction stir processing (FSP), developed based on the basic principles of friction stir welding (FSW), a solid-state joining process originally developed for aluminum alloys, is an emerging metalworking technique that can provide localized modification and control of microstructures in near-surface layers of processed metallic components. The FSP causes intense plastic deformation, material mixing, and thermal exposure, resulting in significant microstructural refinement, densification, and homogeneity of the processed zone. The FSP technique has been successfully used for producing the fine-grained structure and surface composite, modifying the microstructure of materials, and synthesizing the composite and intermetallic compound in situ. In this review article, the current state of the understanding and development of FSP is addressed.

Friction stir welded structural materials: beyond Al-alloys

Abstract: The friction stir welding (FSW) technique is widely accepted to be one of the most significant welding techniques to emerge in the last 20 years. Friction stir welding of Al-alloys is now commonplace and is covered in several recent reviews, including one in this journal. Consequently, the technique is currently being used for joining of these alloys in various industrial applications. Complementary to these developments has been a dramatic increase in research into joining of other alloys and systems by FSW. This field is very active, but less mature. Thus, the aim of this review article is to build on our understanding of the fundamentals, as applied to Al-alloys that laid out in the previous review in this journal, and to address the current state-of-the-art of FSW developing beyond Al-alloys, including Mg-alloys, Cu-alloys, steels, Ti-alloys and metal matrix composites, focusing particularly on microstructural aspects, including texture formation, and the resulting properties of these joints. ...

Processing and properties of titanium–titanium boride (TiBw) matrix composites—a review

Abstract: Although titanium (Ti) alloys possess desirable properties such as specific strength, corrosion resistance and low density, their low specific stiffness and wear resistance have restricted their widespread application. Recently, composite strategies have provided means for overcoming these limitations. Titanium boride (TiBw) in-situ whisker reinforcements are currently recognized as one of the most compatible and effective reinforcements for Ti. This paper provides an overview of recent activities in this evolving area of Ti–TiB composites, covering processing, properties and potential applications.