Mold Filling and Prevention of Gas Entrapment in High-pressure Die-casting

This paper presents some results of direct observation of mold filling in a specially designed die-casting by X-ray diffraction, including comparison with numerical simulation. Based on such work the authors discuss how to prevent gas entrapment and propose new methods.

Structure defect prediction of single crystal turbine blade by dendrite envelope tracking model

The structure defects such as stray grains during unidirectional solidification can severely reduce the performance of single crystal turbine blades. A dendrite envelope tracking model is developed for predicting the structure defects of unidirectional solidification turbine blade. The normal vector of dendrite envelope is estimated by the gradient of dendrite volume fraction, and the growth velocity of the dendrite envelope (dendrite tips) is calculated with considering the anisotropy of grain growth. The solute redistribution at dendrite envelope is calculated by introducing an effective solute partition coefficient. Simulation tests show that the solute-build-up due to the rejection at envelope greatly affects grain competition and consequently solidification structure. The model is applied to predict the structure defects (e.g. stray grain) of single crystal turbine blade during unidirectional solidification. The results show that the developed model is reliable and has the following abilities: reproduce the growth competition among the different-preferential-direction grains; predict the stray grain formation; simulate the structure evolution (single crystal or dendrite grains).

Direct Observation of Thermoelectric Magnetic Convection in Unidirectionally Solidified Al-Cu Alloys

This study performed the time-resolved and in-situ observation of unidirectional solidification of A1-Cu and Sn-Bi alloys under a static magnetic field up to 0.45 T.Irt the case of Sn-Bi alloy,the static magnetic field reduced the local convection around the primary dendrite arms.No thermoelectric convection was detected.On the other hand,the thermoelectric convection was clearly observed in Al-Cu alloy.The observed convection was consistently explained by the thermoelectric magnetic convection.According to a simplified model,the thermoelectric magnetic convection can be induced if the difference in the thermoelectric power between the solid and the liquid phases is in the order of 1 μV/K and temperature gradient is several K/mm.

Investigation on the Solidification and Phase Transformation in Pb-Free Solders Using In Situ Synchrotron Radiography and Diffraction:A Review

It is widely accepted that further development of Pb-free solder alloys for improved processing and in-service properties of next-generation electronics,can be accelerated through a fundamental understanding of phase transformation and microstructure control in Pb-free solder joints.Advanced characterization techniques including synchrotron radiation provide a comprehensive toolset to measure the composition,crystallography,morphology,and properties of the major components of solder alloys.The research using such techniques is reviewed in detail including the characterization of the eff ects of microalloy additions on the microstructure and properties of Pb-free solder joints,especially those on the intermetallic phases.The discoveries outlined are of scientific and industrial relevance and have implications for new solder alloy composition design and the reliability of lead-free solder joints.

Fabrication of Bulk β-FeSi_2 Crystal With ThreeDimensional Alignment by an Oscillating Magnetic Field

It has been reported that an anisotropic magnetic field could produce the three-dimensional alignment of fine single-crystal particles with the orthorhombic crystal structure.However,the three-dimensional alignment was achieved only in suspensions.Fabrication of bulk 'single' materials that have the three-dimensional alignment of grains has been desired.This study proposes a procedure for the fabrication,which consists of slip casting under an oscillating magnetic field and sintering.Optimization of casting and sintering conditions achieved the three-dimensionally aligned bulk β-FeSi_2.