Springer Online Journal Archives 1860-2000
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
Abstract The structure of a typical dental Ni-Cr-Be alloy with 1.8 wt% Be has been investigated by SEM and TEM as well as by quantitative X-ray microanalyses in both instruments. Due to its low atomic weight the atomic fraction of Be is as high as 0.10. During solidification beryllium segregates substantially, and a large volume fraction of the casting is made up of a eutectic with coarse (≈ 1 µm diameter) alternating rods of fcc Ni-Cr and NiBe with a CsCl-type structure (ordered bcc). Smaller (≈ 0.1 µm diameter) rods of NiBe are precipitated in matrix in the solid state. Microanalyses of the NiBe rods show that they have a low chromium content (≈ 1.5 wt%). The cube boundary planes of the ordered b cc and fcc structures have a slight difference in orientation of about 7° which is most probably due to a small coherency misfit of the two types of lattices. The 〈100〉 directions in cube boundary plane of the fcc structure are nearly parallel to the 〈110〉 directions of the ordered bcc cube boundary plane. Sometimes another and more complex relationship between the two lattices occurs. The alloy contains 3.9 wt% Al which gives rise to numerous small (≈ 10 nm), spherical, ordered particles of Ni3Al both in matrix as well as in the fcc eutectic rods.
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