Combined refinement of diffusion coefficients applied on the Nb-C and Nb-N systems

Journal Article · Sun Feb 01 04:00:00 EST 1998 · Metallurgical and Materials Transactions. A, Physical Metallurgy and Materials Science

DOI:https://doi.org/10.1007/s11661-998-0124-z· OSTI ID:611577

Rafaja, D; Lengauer, W; Wiesenberger, H ^[1]; Joguet, M ^[2]

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1. Vienna Univ. of Technology (Austria). Inst. for Chemical Technology of Inorganic Materials
2. Lab. of Metallurgy and Physical Chemistry of Materials, Rennes (France)

A novel technique was used for the calculation of diffusion coefficients in the niobium carbides and nitrides prepared by reaction diffusion. The temperature ranges investigated were 1,500 C to 2,100 C for the Nb-C system and 1,400 C to 1,800 C for the Nb-N system. Three independent theoretical approaches were applied and their results are compared. In the metalloid-rich phases, the concentration-dependent diffusion coefficients were calculated from the concentration profiles; two models of layer growth were used to obtain the concentration-independent diffusion coefficients in all phases. It was found that the diffusion coefficient of carbon in {delta}-NbC{sub 1{minus}x} shows a decrease with increasing metalloid concentration, whereas the diffusivity of nitrogen in {delta}-NbN{sub 1{minus}x} is nearly independent of the nonmetal concentration. The concentration dependence of the carbon diffusion coefficients in {delta}-NbC{sub 1{minus}x} is a result of a lower activation energy of carbon diffusion in the substoichiometric {delta}-NbC{sub 1{minus}x} than in the {delta}-NbC. On the contrary, the activation energy of nitrogen in {delta}-NbN{sub 1{minus}x} does not change with the nitrogen concentration. This behavior could be explained by the different occupancies of metal sublattices, which remain constant in {delta}-NbC{sub 1{minus}x} but decrease with increasing nonmetal concentration in {delta}-NbN{sub 1{minus}x}.

• Sponsoring Organization: USDOE
• OSTI ID: 611577
• Journal Information: Metallurgical and Materials Transactions. A, Physical Metallurgy and Materials Science, Journal Name: Metallurgical and Materials Transactions. A, Physical Metallurgy and Materials Science Journal Issue: 2 Vol. 29; ISSN 1073-5623; ISSN MMTAEB
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
ATOM TRANSPORT
CALCULATION METHODS
DIFFUSION
FABRICATION
HEAT RESISTANT MATERIALS
NIOBIUM CARBIDES
NIOBIUM NITRIDES
PHASE STUDIES
TEMPERATURE RANGE 1000-4000 K