Flammulina velutipes belonging to white rot fungi is one of the commercially important edible mushrooms and is produced in large quantities due to the introduction of a automated and mechanized cultivation system in Korea. Despite the chief item of export among edible mushrooms, Flammulina velutipes has the lowest distribution rate of domestic cultivar, estimated that about 20 percent. As the result that most white cultivars of Flammulina velutipes produced and exported in Korea were introduced from Japan, farmers pay a large amount of royalties. Therefore, we try to develop a new pure domestic cultivars as a substitute for Japanese cultivars. To breed both white and gold superior strains, we selected the crossing mother groups including 10 white strains of ASI 4198 etc. and 7 brown strains of ASI 4049 etc. and mated each of the 17 strains by mon-mon hybridization. 19 white and 14 brown strains were chosen through two selection experiment over 2014 2016. In the third selection experiment this year, we finally selected one white(Fv 16 c 37) and the other gold(Fv 15 a 31) strain. Two selected strains were cultivated in the same environmental conditions. Spawn running period on the sawdust substrate required 30days at 20°C. The cultivation period and optimum temperature were 12±1 days at 14°C for primordia formation, 5 days at 4°C for inhibition phase, and 14±1 days at 7°C for fruiting body development. The length of pilei and stipes in two selected strains and Megumi as a control Japanese cultivar harvested in optimal stage was as follows: 10.5±0.81mm and 139.7±4.23mm in Fv 16 c 37, 10.8±0.43mm and 128..2±7.31mm in Fv 15 a 31, and 10.9±0.41mm and 141.8±4.64mm in Megumi respectively. The Yield of Fv 16 c 37, Fv 15 a 31 and Megumi was 271.2±11.84g, 237.7±9.05g and 270.7±16.87g per 1100ml in bottle cultivation.

Using a customized diffusion bonder, we executed diffusion bonding for ring shaped white gold and red gold samples (inner, outer diameter, and thickness were 15.7, 18.7, and 3.0 mm, respectively) at a temperature of 780 °C and applied pressure of 2300 N in a vacuum of 5 × 10−2 torr for 180 seconds. Optical microscopy, field emission scanning electron microscopy (FE-SEM), and energy-dispersive X-ray spectroscopy (EDS) were used to investigate the microstructure and compositional changes. The mechanical properties were confirmed by Vickers hardness and shear strength tests. Optical microscopy and FE-SEM confirmed the uniform bonding interface, which was without defects such as micro pores. EDS mapping analysis confirmed that each gold alloy was 14K with the intended composition; Ni and Cu was included as coloring metals in the white and red gold alloys, respectively. The effective diffusion coefficient was estimated based on EDS line scanning. Individual values of Ni and Cu were 5.0 × 10−8 cm2/s and 8.9 × 10−8 cm2/s, respectively. These values were as large as those of the melting points due to the accelerated diffusion in this customized diffusion bonder. Vickers hardness results showed that the hardness values of white gold and red gold were 127.83 and 103.04, respectively, due to solid solution strengthening. In addition, the value at the interface indicated no formation of intermetallic compound around the bonding interface. From the shear strength test, the sample was found not to be destroyed at up to 100,000 gf due to the high bonding strength. Therefore, these results confirm the successful diffusion bonding of 14K white-red golds with a diffusion bonder at a low temperature of 780 °C and a short processing time of 180 seconds.

We prepared 8 samples of non-silver and silver-added master alloys containing silicon to confirm the existence of nickel-silicides. We then prepared products made of 14K and 18K white gold by using the prepared master alloys containing 0.25, 0.35, and 0.50 wt% silicon to check for nickel release. We then employed the EN 1811 testing standard to investigate the nickel release of the white gold products, and we also confirmed the color of the white gold products with an UV-VISNIR- color meter. We observed NiSix residue in all master alloys containing more than 0.50 wt% Si with EDS-nitric acid etching. For the white gold products, we could not confirm the existence of NiSix through XRD after aqua regia etching. In the EN 1811 test, only the white gold products with 0.25 wt% silicon master alloys successfully passed the nickel release regulations. Moreover, we confirmed that our white gold products showed excellent Lab indices as compared to those of commercial white gold ones, and the silver-added master alloys offered a larger L index. Our results indicate that employing 0.25 wt% silicon master alloys might be suitable for white gold products without nickel-silicide defects and nickel release problems.