We have investigated the heat resistance properties of Fe-W alloy films electroplated using an ion exchange membranes - multiple anodes systems. The room temperature hardness of Fe-W alloy film increased with increasing heat treatment temperature and reached HV1200 after the heat treatment at 700°C. While the film was amorphous in the as-plated state, it was partially crystallized by heat treatment at over 600°C, indicating that the increase in the hardness was caused by mechanism of precipitation hardening. The high hardness of the Fe-W film was maintained even when the hardness was measured at high temperatures. Wear resistance of Fe-W alloy film was lower than those of electroplated Ni-W alloy and Cr films in the as-plated states. However, the wear resistance of Fe-W alloy increased and surpassed the values of the Ni-W alloy and Cr films after heat treatment. Fe-W alloy film with a higher W content showed higher resistance to the erosion by molten zinc. No erosion by molten zinc was observed for the Fe-W alloy films containing W more than 35 wt%. The Fe-W alloy film was found to form layered oxide phases on its surface. The oxide layer formed on the surfaces of the Fe-W film, including the inner surface of the cracks in the film, seemed to work effectively as a barrier to the molten zinc erosion.
The effect of substrate crystal orientation on the initial distribution of electrodeposit in Zn and Ni plating with a deposit of 10 mg/m2 or less was investigated by using chemically polished polycrystalline low carbon Al-killed steel sheets. Both Zn and Ni distributed according to the substrate crystalline grain size were identified. However, the trend of the initial distribution was different between Zn and Ni. Zinc mainly deposited on crystal grains that indicated the orientation of α-Fe(110), α-Fe(111) and α-Fe(112). In addition, the deposited Zn had the orientation of Zn (002) in respect of the substrate crystal orientation. These orientations of α-Fe were consistent with those of Zn(002), better than any other orientations. This indicates that the distribution of Zn deposits was affected by the consistency between the Zn(002) and α-Fe orientation. On the other hand, Nickel mainly deposited on crystal grains that indicated the orientation of α-Fe(111), α-Fe(112) and α-Fe(221). The face density of these α-Fe orientations was lower than that of any of the others. Therefore, the Ni deposits had a distribution depending on the face density of α-Fe. This trend is the same as that in displaced Ni plating.
The effect of boron (B) on the recrystallization behavior, in particular the growth of the recrystallized grain into unrecrystallized grain, of titanium (Ti) added interstitial atom free (IF) steel sheets was studied from the viewpoint of the solute drag effect considering the interaction between B and Ti atoms. The growth rate of the recrystallized grain at 5% fraction recrystallized decreased with increasing B content. Furthermore, the decrease became more pronounced in the B added steels with the higher Ti content. The interaction energy between B and Ti atoms at the grain boundary was evaluated by the first-principles calculation in the bcc-Fe(111)Σ3 symmetrical tilt grain boundary. Attractive interaction between B and Ti atoms was obtained in most of the grain boundary atom sites examined. B segregation at the interface between recrystallized and unrecrystallized grains was concluded to induce Ti segregation through the attractive interaction between B and Ti atoms during interface migration. The mechanism for the suppression in the growth of the recrystallized grains was proposed to be caused by the decrease in the interface mobility caused by the enhanced Ti segregation.
The dislocation strengthening was estimated by applying the dislocation theory for a Fe-18%Ni alloy which has a lath martensitic structure. The yield stress of highly dislocated metals is dependent on both the friction stress and the dislocation strengthening. Regarding the coefficient of dislocation strengthening, it is governed by the shear modulus of metals. Ni addition plays a role in increasing the friction stress but decreases the shear modulus. This means that the coefficient of dislocation strengthening is smaller in the Fe-18%Ni alloy than pure iron. It was confirmed that the yield stress, which was experimentally obtained in Fe-18%Ni alloy, is reasonably explained by the mechanism of dislocation strengthening, taking the effects of Ni into consideration. On the other hand, in the case of lath martensite with a dislocation density of 2×1015 /m2, it was also found that the effect of Ni addition does not appear on the yield stress because the increment of solid solution strengthening is cancelled out by the decrement of dislocation strengthening.