Lattice Misfit between Inclusion and Acicular Ferrite in Weld Metal of Low Carbon Low Alloy Steel
To clarify the mechanism of acicular ferrite formation in low carbon submerged arc weld metals of a Ti-B system with different aluminum contents, the lattice misfit between inclusion and acicular ferrite was investigated. The inclusions were directly sliced into thin foils by a focused ion beam device and crystallographic analyses were performed using a transmission electron microscope. These inclusions were surrounded by a narrow Ti-enriched layer which was identified as TiO. Our results showed that the Baker-Nutting orientation relationship was satisfied between the narrow TiO on the inclusion surface and acicular ferrite.
Ferrite Nucleation at Ceramic/Austenite Interfaces
Pure polycrystal ceramics (TiC, TiN, TiO, VN, AIN and Al2O3) were heat-pressure-bonded to an Fe-0.1 mass%C-2 mass%Mn alloy and were isothermally reacted below the Ae3 temperature for the proeutectoid ferrite reaction to occur. The number of ferrite particles per unit area of bonded interfaces was measured using Schwartz-Saltykov method and was compared with the number of particles formed at grain boundaries. VN was most effective in stimulating ferrite nucleation whereas TiO was least effective. All other ceramics showed more or less similar potencies for ferrite formation. VN is capable of forming lower energy interfaces with ferrite than other ceramics, through the possibility of V diffusion into the alloy during and after bonding may not be ruled out in this experiment. On the other hand, the least effectiveness of TiO in stimulating ferrite nucleation is possibly due to the proximity of thermal expansion coefficient to iron.
Microstructure of the solder-casting zone in bridges of dental gold alloys.
The composition and structure were studied in the cast and in the solder of bridges which had failed clinically. Both materials were gold alloys but with different contents of Pt, Ag and Zn. The metallographic investigation revealed defects mostly in the solder, situated in the subsurface layer. SEM studied of the fracture surface revealed large porosites and a structure of dense parallel lines--striations--, indicating that the material had failed from fatigue. The materials in the fractured bridges were identified by micro-probe measurements. It was stated that cast material and solder material used together, were of different composition.