結晶成長・凝固・鋳造の原理解明とそれを利用したものづくり

融液成長は液相から固相への相変態ですが，その過程においては複雑な形状をとるものや，合金元素の濃度が場所によって変化するなど，制御しなくてはいけない因子が無数に存在します．宮原研では金属，半導体，セラミックスなどの種々の構造材料及び機能材料について，目的を達成しうる「組織」へと制御するプロセスについて研究しています．例えば太陽電池に用いられるシリコン結晶は，シリコンを融液内で一方向に成長させて作製します．結晶品位はエネルギー変換効率に大きく影響しますので，高い性能を持つ多結晶シリコンを目指して組織制御を行います．また，自動車などの輸送機器の一部の部品では軽量なアルミニウム合金やマグネシウム合金を溶解・凝固して製造します．溶融合金の湯流れでは不純物や気泡を巻き込む恐れがあるため，分散する不純物の除去を目的とした，湯流れと凝固組織の制御について研究しています．さらに，製鉄所で製造される鋼板や鋳型内で凝固する鋳鉄等の大きなものから，金属３Dプリンターで繰り返される小さなものまで，組織の形状及び分布が製品の性質を大きく左右します．高性能の材料の実現を目指して，結晶成長・凝固・鋳造の原理解明とその制御方法について研究しています．

Crystal growth from melt is a phase transformation from the liquid phase to the solid phase, and there are a myriad of factors that must be controlled during this process, such as complex shapes and variations in the concentration of alloying elements within the melt. In Miyahara Laboratory, we are studying the control process so as to allow various structural and functional materials such as metals, semiconductors, and ceramics to develop into microstructures that achieve the desired properties. For example, silicon crystals for solar cells are manufactured by unidirectional crystal growth in silicon melt. Since the crystal quality greatly affects the energy conversion efficiency, microstructure control is performed to achieve polycrystalline silicon with a high performance. In addition, some components of transportation machines such as automobiles are manufactured by melting and solidifying lightweight aluminum and magnesium alloys. Since impurities and bubbles may be entrained in the molten alloy flow, we are studying the control of flow and solidification structure to remove dispersed impurities. In addition, the properties of products are affected greatly by the shape and distribution of microstructures, which are determined in a large range for some products such as steel plates manufactured in steel plants and cast iron solidified in molds, or in a small range for other products such as objects fabricated with metal 3D printers by repeated melting and solidification. We are investigating the principles of crystal growth, solidification and casting, and their control methods to realize high-performance materials.