Study of solid solution strengtheing of alloying element with phase structure factors

2003 ◽  
Vol 13 (1) ◽  
pp. 69
Author(s):  
Yan LIU
Keyword(s):  
Solid Solution ◽  
Phase Structure ◽  
Alloying Element ◽  
Structure Factors

Three-phase structure invariants and structure factors determined with the quantitative convergent-beam electron diffraction method

1999 ◽  
Vol 55 (2) ◽  
pp. 188-196 ◽  
Author(s):  
R. Høier ◽  
C. R. Birkeland ◽  
R. Holmestad ◽  
K Marthinsen
Keyword(s):  
Electron Diffraction ◽  
Phase Structure ◽  
Diffraction Method ◽  
Convergent Beam Electron Diffraction ◽  
Beam Electron ◽  
Structure Factors ◽  
Refinement Method ◽  
Three Phase ◽  
Phase Sensitive ◽  
Convergent Beam

Quantitative convergent-beam electron diffraction is used to determine structure factors and three-phase structure invariants. The refinements are based on centre-disc intensities only. An algorithm for parameter-sensitive pixel sampling of experimental intensities is implemented in the refinement procedure to increase sensitivity and computer speed. Typical three-beam effects are illustrated for the centrosymmetric case. The modified refinement method is applied to determine amplitudes and three-phase structure invariants in noncentrosymmetric InP. The accuracy of the results is shown to depend on the choice of the initial parameters in the refinement. Even unrealistic starting assumptions and incorrect temperature factor lead to stable results for the structure invariant. The examples show that the accuracy varies from 1 to 10° in the electron three-phase invariants determined and from 0.5 to 5% for the amplitudes. Individual phases could not be determined in the present case owing to spatial intensity correlations between phase-sensitive pixels. However, for the three-phase structure invariant, stable solutions were found.

Self-propagating high-temperature synthesis microalloying of MoSi2 with Nb and V

2003 ◽  
Vol 18 (8) ◽  
pp. 1842-1848 ◽  
Author(s):  
F. Maglia ◽  
C. Milanese ◽  
U. Anselmi-Tamburini ◽  
Z. A. Munir
Keyword(s):  
Solid Solution ◽  
High Temperature ◽  
Tetragonal Phase ◽  
Synthesis Method ◽  
The Self ◽  
Alloying Elements ◽  
Alloying Element ◽  
Temperature Synthesis ◽  
Starting Mixture ◽  
High Temperature Synthesis

Microalloying of MoSi2 to form Mo(1−x)MexSi2 (Me = Nb or V) was investigated by the self-propagating high-temperature synthesis method. With alloying element contents up to 5 at.%, a homogeneous C11b solid solution was obtained. For higher contents of alloying elements, the product contained both the C11b and the hexagonal C40 phases. The relative amount of the C40 phase increases with an increase in the content of alloying metals in the starting mixture. The alloying element content in the hexagonal C40 Mo(1−x)MexSi2 phase was nearly constant at a level of about 12 at.% for all starting compositions. In contrast, the content of the alloying elements in the tetragonal phase is considerably lower (around 4 at.%) and increases slightly as the Me content in the starting mixture is increased.

Mixing entropy and the nucleation of silicides: Ni–Pd–Si and Co–Mn–Si ternary systems

2003 ◽  
Vol 18 (7) ◽  
pp. 1668-1678 ◽  
Author(s):  
C. Detavernier ◽  
X. P. Qu ◽  
R. L. Van Meirhaeghe ◽  
B. Z. Li ◽  
K. Maex
Keyword(s):  
Solid Solution ◽  
Free Energy ◽  
Gibbs Free Energy ◽  
Ternary Systems ◽  
Nucleation Temperature ◽  
Alloying Element ◽  
Entropy Of Mixing ◽  
Mixing Entropy ◽  
Nucleation Barrier ◽  
The Difference

Nucleation can play an important role during the formation of silicides, especially when the difference in Gibbs free energy ΔG between the existing and newly formed phase is small. In this work, it is shown that the addition of elements that form a solid solution with either the existing or nucleating phase influences the entropy of mixing and thus changes ΔG. In this way, the height of the nucleation barrier may be controlled, thus controlling the nucleation temperature. The influence of mixing entropy on silicide nucleation is illustrated by experiments for two ternary systems: Co–Mn–Si and Ni–Pd–Si. It is shown that the nucleation temperature of CoSi2 is increased by the addition of Mn, the nucleation temperature of MnSi1.7 is increased by the presence of Co, the nucleation temperature of NiSi2 is increased by the addition of Pd, and the nucleation temperature of PdSi is decreased by the addition of Ni. In all four cases, the effect of the alloying element on the nucleation temperature can be explained by a model on the basis of the concept of mixing entropy.

Microstructures and Properties of Refractory Niobium-Silicide-Based Composites

2005 ◽  
Vol 475-479 ◽  
pp. 737-740 ◽  
Author(s):  
Shi Yu Qu ◽  
Ya Fang Han ◽  
Liguo Song
Keyword(s):  
Solid Solution ◽  
High Temperature ◽  
Phase Structure ◽  
High Temperature Oxidation ◽  
Multicomponent System ◽  
Compression Tests ◽  
Two Phase ◽  
Temperature Oxidation ◽  
Al Content ◽  
Oxidation Rates

The microstructures, mechanical properties and oxidation resistance of the refractory Nb-silicide-based composites have been investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), compression tests and high-temperature oxidation experiments. The results showed that 1773K/100h heat-treatment was an optimum processing for acquiring equilibrium Nb solid solution and silicides microstructure. In the binary Nb-Si system, the microstructure consisted of continuous Nb5Si3 equilibrium matrix and dispersed Nb particles, while in the the Nb-Ti-Cr-Al-Si-(Hf) multicomponent system, there are two typical microstructures, i.e., a two-phase structure of β (Nb solid solution)+D81 Nb5Si3-type silicide in the alloys with the Si+Al content (15at.% and 6at.%, respectively), and a three-phase structure of β+D81 Nb5Si3-type + D88 Ti5Si3-type silicides in the alloys with lower Si+Al content (10at.% and 8at.%, respectively). The results of compression tests showed that all alloys display high strength at both room and high temperatures, only a slight decrease in compression properties occured for Nb-Ti-Cr-Al-Si alloys, comparing to the binary Nb-Si in-situ composites. This type of alloys possesses good high temperature strengths up to at least 1473K. The results of high-temperature oxidation experiments showed that the oxidation rates of the alloys with Ti, Cr, Al and Hf addition were at least one order of magnitude lower than those of the Nb-Si binary alloys.

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