Growth of Oriented Nickel-Manganese-Gallium Single Crystals via the Bridgman Method

摘要

A Bridgman furnace was designed and built to grow oriented single crystals of nickel-manganese-gallium. The starting alloys were produced from high purity elements. The compositions of the alloys and single crystals were determined with energy dispersive x-ray spectroscopy. Oxygen concentration of the starting elements, the alloys, and single crystal were determined with the LECO combustion method. Starting seeds were produced from single crystal ingots produced at ETH Zurich, Switzerland, and from a single crystal grown from these seeds. Crystallographic orientation of the starting seeds and the single crystals were determined with x-ray diffraction. Mechanical testing was performed on a single crystal to determine the stress-strain curve.Pulling speeds of 6.0 mm/hr or lower produced oriented single crystals. Crystal composition was kept constant to approximately 60% of the total crystal length. Oxygen concentration was reduced when an argon-6% hydrogen atmosphere flowed through the crystal growth assembly. Twinning stress was approximately 27 MPa with a twinning strain of approximately 4.3%.