Nan Wang

Competitive Nucleation and Rapid Growth of Co-Si Intermetallic Compounds during Eutectic Solidification under Containerless Processing Condition

The liquid-solid transitions of (Co 2 Si+CoSi) and (CoSi+CoSi 2 ) eutectic alloys were realized in drop tube and the rapid eutectic growth mechanism of intermetallic compounds was examined. The experimental and calculated results indicate that with increasing Co content, the intermetallic compound prefers nucleating primarily. The eutectic microstructures experience the transitions of lamellar-anomalous-divorced eutectic with undercooling. In undercooled state, the growth of CoSi intermetallic compound always lags behind others, and no matter how large the undercooling is, this intermetallic compound grows under the solutal diffusion control. The calculated coupled zone demonstrates that (Co 2 Si+CoSi) eutectic can form within certain undercooling regime, when the composition is in the range from 23.6% to 25.4% Si. And the calculated coupled zone of (CoSi+CoSi 2 ) covers a composition range from 40.8% to 43.8% Si.

Interactive Effect of Grain Orientation and Grain Size on Magnetic Properties of Fe–78 wt% Ni Ribbons

Fe–78 wt% Ni ribbons were prepared by the melt spinning technique and the interactive contribution of the grain size and grain orientation on the magnetic properties was examined. Heat treatment at 673 K for 1 h followed by furnace cooling was performed to show the annealing impact. At three wheel speeds of 10, 20, and 30 m/s, the saturation magnetization nearly does not change. High wheel speed and heat treatment are inclined to promote the growth of grains. Although the orientation is not the easy axis of magnetization, the improvement of the texture in this direction makes the coercivity decrease, which counteracts the inverse effect of the grain size at high wheel speed. It indicates that for preparing soft magnetic ribbons, the interactive contribution of grain orientation variation and the grain size should be considered.

Competition growth of α and β phases in Ti-50 at.%Al peritectic alloy during the rapid solidification by laser melting technique

Rapid solidification of Ti-50 at.%Al peritectic alloy is realized by laser melting technique at different conditions of laser power and scanning speed. The temperature field and the cooling rate under the corresponding conditions are derived from the finite element simulation. Comparing the measured pool size with the simulated result, the laser absorptivity of Ti-50 at.%Al peritectic alloy at different conditions can be deduced to establish the relationships between the laser absorptivity, the laser power and the scanning speed. The morphology evolution and the phase selection of Ti-50 at.%Al peritectic alloy are described by the temperature gradient and the cooling rate. With the increase of temperature gradient and cooling rate, β phase replaces α phase to become the leading growth phase. And the growth of α phase experiences the transition from facet to non-facet manner, while β phase is refined. To understand the underlying mechanism of the competition growth can bring benefit to the industrial application of Ti-Al alloy.

Rapid Solidification and Phase Composition of Gd-16wt%Co Alloy in Laser Melting Conditions

Solidification microstructure of Gd-16wt%Co master alloy is characterized by the primary (Gd), CoGd3, and Co7Gd12 dendrites plus (Co3Gd4+Co7Gd12) eutectic. In the laser melting conditions, the rapid solidification of melting pool shows three layers along the radial direction. The size of melting pool decreases with the increase of scanning speed. The dendrites are refined and the eutectic disappears in the pool. Near the top of the pool, the metastable phases and the peritectic reaction are restrained in the rapid solidification conditions.

Solute Distribution Ahead of Interface during Heteroepitaxial Growth

By establishing a diffusion model, the solute distribution is investigated during the growth of eutectic phase from the binary melt on the primary phase. Based on the eutectic reaction conditions, reasonable assumptions are carried out to build the partial differential equation. After the determination of the initial and boundary conditions, the analytical solutions have been derived from the method of variables separation. The solute distribution ahead of interface and the influence of this distribution on the growth rate of heteroepitaxial phase are discussed.

Rapid Growth and Magnetic Properties of Fe7CO3 Intermetallic Compound

By drop tube and melt spinning techniques, rapid growth of Fe7Co3 intermetallic compound has been realized. The microstructures and nucleation characteristics under different cooling rates are investigated. With the increase of cooling rate, Fe7Co3 intermetallic compound grains are refined in both rapid growth manners. Experimental observation and theoretical analysis indicate that the nucleation rate in single-roller quenching is much greater than that in free-fall method when the cooling rate is under a same level. The comparison of magnetic property between the alloy ribbons and other dimensional magnetic material were made. The superior soft magnetic properties of Fe-Co alloy ribbons changes sensitively with the cooling rate, which is mainly decided by the wheel velocity.