TEM STUDY OF PRECIPITATES IN LASER CLAD NI-AL BRONZE

Transmission electron microscopy (TEM) examination of sheet martensite in laser clad Ni-Al bronze reveals precipitates with diameter of about 20 nm. It is found that the hardness of the sheet martensite shows a pronounced decrease with increasing test temperature. Heat treatment at 673 K for 4 h doubled the size of the precipitates. Convergent beam electron diffraction (CBED) and microdiffraction (MD) in TEM are used to examine the crystal structure of the precipitates in heat treated material. CBED patterns suggest two point groups: 4/mmm and m3m. Three MD patterns of the precipitates show complete agreement with B2 Structure. The crystal structure of precipitates in as-clad material is studied by high resolution electron microscopy (HREM) and optical diffraction. The HREM images are a close match with simulated images based on a B2 crystal structure model.