Crystallographic Structure Study of a Japanese Sword Masamitsu made in the 1969 using Pulsed Neutron Imaging

Energy-resolved neutron transmission imaging technique using an accelerator-driven pulsed neutron source and a time-resolved two-dimensional detector can obtain the Bragg-edge transmission spectrum at each pixel. In this technique, crystallographic information can be visualized over a wide area of a sample. We used this method to investigate the crystallographic information of a modern Japanese sword produced by Masamitsu in 1969. As a result, shifting and broadening of the (110) Bragg-edge was confirmed at the cutting-edge side. It is evidence that the martensite phase exists at the cutting-edge side as a result of the quenching process. By comparing with results of the old Japanese swords, it is found that the martensite region in the modern Japanese sword is wider or deeper than one in the old swords. In addition, we can see strongly preferred orientation of the crystal grains at the boundary between the martensite phase on the cutting-edge side and the ferrite phase on the back-edge side. Introduction The metallographic characteristics are essential information to clarify making processes of the Japanese swords, because these processes were not documented well in the past. The Japanese swords have been produced in various eras and areas since ancient times. In order to discuss characteristics of the Japanese swords depending on areas and eras, we need to analyze many Japanese swords. It is necessary to analyze them non-destructively because the old Japanese swords have historical value. Neutron imaging is a powerful tool to study metallic cultural heritages because of non-destructive, high penetrating power and capability to get crystallographic information [1-2]. By analyzing the position dependent Bragg-edge spectra, Neutron Radiography WCNR-11 Materials Research Forum LLC Materials Research Proceedings 15 (2020) 227-232 https://doi.org/10.21741/9781644900574-35 228 quantitative visualization of the crystallographic information of the Japanese swords can be achieved [3]. We plan to investigate historical Japanese swords. The comparison of modern and historical swards will lead to a better understanding of the various crystallographic characteristics. In this work, we investigated crystallographic information of the modern Japanese sword made by Masamitsu in 1969. Experimental procedure In this work, we measured a modern Japanese sword in order to compare with the old Japanese swords. The Japanese swords are generally made of a carbon steel and was quenched and tempered. Overview of the modern Japanese sword made by Masamitsu in 1969 is shown in Fig. 1. This experiment was performed at BL22 RADEN in JPARC MLF [4]. The proton beam power in the present work was 150 kW. The neutron moderator was a decoupled-type supercritical para-H2 moderator. As a time-resolved two-dimensional detector, we adopted a neutron sensitive gas electron multiplier (n-GEM) detector [5] with a 0.8 × 0.8 mm pixel resolution and a 10.24 × 10.24 cm detection area (128ch × 128ch). The sword and a detector were placed at 24 m from the neutron source. The collimator ratio L/D was 1000 since a pinhole placed at 8 m from the neutron source was set in the diameter of 15 mm. The wavelength resolution Δλ/λ at λ = 0.4 nm was 0.2%. The experimental setup used is shown in Fig. 2. As shown in Fig. 3, the Japanese sword was measured in three different areas, Tang, Middle and Tip areas. Measurement time was 7.2 hours in the Tang area, 8.6 hours in the Middle area, 7.2 hours in the Tip area and 6 hours for the direct beam. Fig. 1 A photograph of the Masamitsu sword (1969). Fig.2 The experimental setup of the present work at RADEN. Japanese sword Masamitsu