Grain size and microstructural features of cast superalloy K4169 were investigated under various melting and casting conditions with and without the addition of grain refiners. It is found that lowering pouring temperature and adding refiners to the melt can lead to grain refinement of γmatrix and improve the proportion of equiaxed grains. At a conventional pouring temperature of 1400 ℃, the average size of equiaxed grains could be refined to the order of ASTM 3.2, the proportion of equiaxed grains at transverse cross-section could be improved from 56% to 99%. The results also indicate that the average length of primary dendrite axis is shortened with the addition of refiners, but the secondary dendrite arm spacing keeps almost unchanged because local solidification time remained constant. In addition, the microsegregation of main elements such as Fe, Cr, Nb, Mo and Ti is alleviated with the decrease in grain size, and the grain morphology have transformed from dendrite in coarse- to granulate in fine-grained castings. At higher melt pouring temperature, the amount of microporosity in samples with the addition of refiners can be greatly reduced. The mechanisms of grain refinement and increase in equiaxed grain proportion were proposed.

The interface morphologies of single crystal superalloy CMSX-2 have been studied over a range of cooling rate with large variations in withdrawal speeds in directional solidification. A superfine cellular structure was obtained under both high thermal gradient up to 1000K/cm and fast withdrawal rate up to 1mm/sec. The high rate directional solidification results in reduction in primary and secondary dendrite arm spacing, refinement of λ’ phase, reduced microsegregation of alloying elements and smaller size of γ-γ’ eutectics. Rupture life and plasticity of fine structure samples at 1323K increase significantly than that in conventional directional solidification process.

Suitable inoculants for superalloy IN718C have been selected and prepared. They are composed of two ternary intermetallic compounds: Co3FeNb2 and CrFeNb. Their effects on the structures of superalloy IN718C were omvestogated. It is found that adding mixed inoculants consisting of Co3FeNb2 and CrFcNb to the melt could significantly refine grains of the γ matrix of superalloy IN178C and increase the proportion of equiaxed grains in cross seetion, which was theorctically analyzed. In addition, experimental results indicate that trace addition of inoculants to the melt neither introduces inclusions nor changes the phase constituent of the alloy. At the same pouring temperature, the amount of shrinkage porosity in specimens can be greatly deereased if inoculants are added into the melt.

This paper aims to introduce two novel techniques of electromagnetic confinement to process Ni-base alloys for castings and ingots with shaped cross-section. Based on systematically investigation on the distribution of magnetic and temperature fields and their coupling effect, a containerless electromagnetic shaping of aluminum alloy and superalloys samples was successfully realized by means of a specially designed apparatus with dual induction coils and dual-frequencies and by using a tailor-made crystallizer under vacuum condition.Anear-net shaped turbine blade of superalloys with directionally solidified microstructure by electromagnetic soft-contact confinement technology was also obtained. The dynamic stability and profile behavior of melt and temperature gradient during electromagnetic confinement are presented.

Most of materials have long been considered to be mechanical and/or physical anisotropy. Permitting materials to grow along specific orientation by means of directional solidification technique can optimize their structural or functional properties. The present paper attempts to introduce the research work in the field of processing of some advanced materials by innovative directional solidification techniques performed at State Key Laboratory of Solidification Processing and with author's intended research work. The paper deals with the specific topics on directional solidification of following advanced materials: column and single crystal superalloys under high thermal gradient, Ni-Cu alloys under deep supercooling of the melt, intermetallic compounds with selected preferential crystal orientation, superalloys with container less electromagnetic confinement, high Tc superconducting oxides, high temperature structural ceramics, continuous cast single crystal copper and copper-based composites. The relevant solidification phenomena, such as morphological evolution, phase selection, peritectic reaction and aligned orientation relationship of crystal growth for multi-phases in the processing of directional solidification, are discussed briefly. The trends of developments of directional solidification technique are also prospected.