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Title: The influence of silicon on the strength and fracture toughness of molybdenum

Authors:
 [1];  [1];  [2];  [3];  [4];  [1]
  1. University of Magdeburg, Germany
  2. ORNL
  3. Plansee SE, Technologiezentrum, Austria
  4. Otto-von-Guericke Universitat, Magdeburg, Germany
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
936532
DOE Contract Number:
DE-AC05-00OR22725
Resource Type:
Journal Article
Resource Relation:
Journal Name: Materials Science and Engineering A; Journal Volume: 463; Journal Issue: 1-2
Country of Publication:
United States
Language:
English

Citation Formats

Sturm, D., Heilmaier, M., Schneibel, Joachim H, Jehanno, P., Skrotzki, B., and Saage, H. The influence of silicon on the strength and fracture toughness of molybdenum. United States: N. p., 2007. Web. doi:10.1016/j.msea.2006.07.153.
Sturm, D., Heilmaier, M., Schneibel, Joachim H, Jehanno, P., Skrotzki, B., & Saage, H. The influence of silicon on the strength and fracture toughness of molybdenum. United States. doi:10.1016/j.msea.2006.07.153.
Sturm, D., Heilmaier, M., Schneibel, Joachim H, Jehanno, P., Skrotzki, B., and Saage, H. Mon . "The influence of silicon on the strength and fracture toughness of molybdenum". United States. doi:10.1016/j.msea.2006.07.153.
@article{osti_936532,
title = {The influence of silicon on the strength and fracture toughness of molybdenum},
author = {Sturm, D. and Heilmaier, M. and Schneibel, Joachim H and Jehanno, P. and Skrotzki, B. and Saage, H.},
abstractNote = {},
doi = {10.1016/j.msea.2006.07.153},
journal = {Materials Science and Engineering A},
number = 1-2,
volume = 463,
place = {United States},
year = {Mon Jan 01 00:00:00 EST 2007},
month = {Mon Jan 01 00:00:00 EST 2007}
}
  • [beta]-Si[sub 3]N[sub 4] powder containing 1 mol% of equimolar Y[sub 2]O[sub 3]-Nd[sub 2]O[sub 3] was gas-pressure sintered at 2,000C for 2 h (SN2), 4 h (SN4), and 8 h (SN8) in 30-MPa nitrogen gas. These materials had a microstructure of in-situ composites'' as a result of exaggerated grain growth of some [beta]-Si[sub 3]N[sub 4] grains during firing. Growth of elongated grains was controlled by the sintering time, so that the desired microstructures were obtained. SN2 had a Weibull modulus as high as 53 because of the uniform size and spatial distribution of its large grains. SN4 had a fracture toughnessmore » of 10.3 MPa[center dot]m[sup 1/2] because of toughening provided by the bridging of elongated grains, whereas SN8 showed a lower fracture toughness, possibly caused by extensive microcracking resulting from excessively large grains. Gas-pressure sintering of [beta]-Si[sub 3]N[sub 4] powder was shown to be effective in fostering selective grain growth for obtaining the desired composite microstructure.« less
  • The influence of small additions of three selected oxides on the microstructure and the mechanical behavior of high-purity silicon nitride was systematically investigated. Dense silicon nitride bodies doped respectively with SiO[sub 2], Y[sub 2]O[sub 3], and Yb[sub 2]O[sub 3] were fabricated by hot isostatic pressing (HIP). Two different compositions of the intergranular phase were examined for Y[sub 2]O[sub 3] and Yb[sub 2]O[sub 3] in comparison with the same volume of pure SiO[sub 2]. Only in the material with the higher Y[sub 2]O[sub 3] and Yb[sub 2]O[sub 3] content was an improved level of fracture toughness obtained. The mechanical properties atmore » 1,400 C were evaluated with emphasis placed on time-dependent strength and deformation behavior. The materials containing only SiO[sub 2] or doped with the small amount of Y[sub 2]O[sub 3] showed linear elastic K[sub I]-controlled fracture behavior of 1,400 C and the critical phenomenon for failure was subcritical crack growth (SCG) from preexisting defects. In the materials with additions of Yb[sub 2]O[sub 3] or the larger amount of Y[sub 2]O[sub 3], crack extension was governed by creep crack growth as a result of the exhibited strong creep effects. In the silicon nitride doped with 1.7 vol% Yb[sub 2]O[sub 3], however, a considerably improved creep behavior as a consequence of crystallization processes in the intergranular phase (Yb[sub 2]Si[sub 2]O[sub 7]) caused by both thermal treatment and stress-initiated effects during the mechanical testing at 1,400 C was found.« less
  • Abstract not provided.
  • It is generally found that grinding transverse to the tensile stress direction in flexure bars subjected to four-point bending results in a lower strength compared to grinding in the longitudinal direction. In the present study, standard flexure specimens made from a reaction-bonded and a sintered reaction-bonded silicon nitride (RBSN and SRBSN) were surface ground under three different conditions in both longitudinal and transverse directions to assess the effect of grinding direction on strength. Four-point flexure tests were performed on the specimens and Weibull parameters were calculated. The results showed that while the strength was not affected by the grinding conditionmore » when grinding was performed in the longitudinal direction, the strength of the samples ground in the transverse direction was reduced as the material removal rate was increased by a factor of 30. This result was confirmed by fractography, which showed that almost all the fracture initiation sites in the longitudinally ground samples were associated with near-surface microstructural features, whereas in the transverse ground samples fracture initiated from damage introduced by grinding. The strength reduction by grinding in the transverse direction was found to be material dependent, and was larger for SRBSN than for RBSN.« less
  • Commercially available unalloyed molybdenum (Low Carbon Arc Cast (LCAC)), Oxide Dispersion Strengthened (ODS) molybdenum, and TZM molybdenum were neutron irradiated at temperatures of nominally 244 C, 407 C, and 509 C to neutron fluences between 1.0 to 4.6x1025 n/m2 (E>0.1 MeV). Post-irradiation fracture toughness testing was performed. All alloys exhibited a Ductile to Brittle Transition Temperature that was defined to occur at 30 4 MPa-m1/2. The highest post-irradiated fracture toughness values (26-107 MPa-m1/2) and lowest DBTT (100-150 C) was observed for ODS molybdenum in the L-T orientation. The finer grain size for ODS molybdenum results in fine laminates that improvemore » the ductile laminate toughening. The results for ODS molybdenum are anisotropic with lower post-irradiated toughness values (20-30 MPa-m1/2) and higher DBTT (450-600 C) in the T-L orientation. The results for T-L ODS molybdenum are consistent or slightly better than those for LCAC molybdenum (21-71 MPa-m1/2 and 450-800 C DBTT). The fracture toughness values measured for LCAC and T-L ODS molybdenum at temperatures below the DBTT were determined to be 8-18 MPa-m1/2. Lower non-irradiated fracture toughness values were measured for TZM molybdenum that are attributed to the large carbide precipitates serving as preferential fracture initiation sites. The role of microstructure and grain size on post-irradiated fracture toughness was evaluated by comparing the results for LCAC molybdenum and ODS molybdenum.« less