Of Nb-w-zr-c System In Al-mg-sc - Zr Phase Diagram Determination

1. Two kinds of methods which are used to determining phase diagram -experiment and thermodynamic calculation have been briefly assessed. The experiment-measuring phase diagram is a indispensably part of the phase diagram study work among which diffusion-couple along with electron probe microalaysis(EPMA) technique is a high-efficiencyand precise method. To some diffcult determing system by experiment, the thermodynamic calculation has obvious advantage. Some important alloy phase thermodynamic model have been assessed. Based on experiment,combining with thermodynamic optimize and calculation are increasingly becoming the developing direction of thermodynamic calculation2. In the second part of this paper, Niobium-based alloys ' properties and application has been reviewed firstly. Then some relative equilibrium diagrams were assessed. The isothermal cross section of Niobium-Tungsten-Zirconium and Niobium-Tungsten-Zirconium-Carbon system at HOO'C were constructed by means of multiphase diffusion couples technique. No new ternary phases are formed in this system at this temperature. It is concluded that (W.Nb^Zr and W2ZrC all are intermetallic compoud based on intermediate phase W2Zr and they all are in equilibrium with the bcc a solid solution through X-ray diffraction analysis and EPMA. The maximum solid solubility of Niobium in W2Zr at 1100"C was determined as 10.7at.%, while graphite carbon in W2Zr was estimated to be 15.3at.%. A squre orthogonal projections of HOOT? isothermal tetrahedron of the Niobium-Tungsten- Zirconium-Carbon system were presented by means of diffusion quadruples, X-ray diffraction and EPMA.3. In the three part of this paper, the good influences of Zirconium and Scandium additions on Aluminium-based alloys have been firstly reviewed, followed with assessing the relative Al-Mg-Sc-Zr systems. The part of-in-isothermal cross section of Al-Mg-Sc-Zr at 430"C was presented by means of diffusion triple, X-ray diffraction and EPMA. There coexist three phases: MgnAli2, Mg2Al3 and AlsSc. No new ternary phase were formed in the system at this temperature. The maximum solid solubility of Sc in Mg2Ab and MgnAli2 at 430癈 was determined as 1.05at.% and 0.03at.% respectively.In order to determine the phase ralatives in the Aluminium-rich side of the system,eighteen alloys of different composition were melted and annealed at 43CTC for 360h. The samples were examined by optical microscopy, scanning electron microscopy and X-ray diffraction. The isothermal cross section of Al-4Mg-Sc-Zr system at 430癈 was constructed by means of equilibrium alloys. There coexisted three phases: a (Al), Al3Sc(Zr) and Al3Zr(Sc) in the system at 430癈. Al3Sc(Zr), Which has the same crystal structure as Al3Sc(Lh), is a intermetallic compound based on intermediate phase AljSc; The maxmium solid solubility of Zr in A^Sc at 430 癈 was determined as 12.5at.%, namely Zriconium atoms can subsititute 50% Scandium atoms; Whilist Al3Zr(Sc) ,which has DO23 tetragonal crystal structure like A^Zr, is a intermetallic compound based on intermediate phase AhZr, and the maxmium solid solubility in the A^Zr was 5.0at.%,viz it can subsititute 20% Zirconium atoms. From the experimental results of the X-ray spectral mocroanalysis on the Zirconium and Scandium content in the phase of the different alloys, their chemical formula might be written as follows: for phase AlsSc-* Al3Sci.o.sZro-o.5; for phase A^Zr?...