Effect of nitrogen on the microstructure and mechanical properties of Co–33Cr–9W alloys prepared by dental casting

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4 Citations (Scopus)

Abstract

The effect of nitrogen concentration on the mechanical properties of Co–33Cr–9W alloy dental castings fabricated using the “high-Cr and high-N” concept was investigated. Microstructural analysis was performed on the alloys, and findings were discussed in relation to the mechanical properties. Owing to their high nitrogen concentrations (0.25–0.35 wt%), all alloys prepared exhibited face-centered cubic (fcc) γ-phase matrices with a-few-millimeter grains consisting of dendritic substructures. Strain-induced martensitic transformations to produce hexagonal close-packed (hcp) ε-phases were not identified under tensile deformation. The precipitation of the intermetallic σ-phase was identified at the interdendritic regions where solidification segregation of Cr and W occurred. The size and chemical composition of this σ-phase did not vary with the bulk nitrogen concentration. Adding nitrogen to the alloys did not alter their tensile yield stress or Vickers hardness values significantly, suggesting that the nitrogen strengthening effect is affected by the manufacturing route as well as local chemistry that is involved in the microstructural evolution during solidification. The tensile ductility, on the other hand, increased with an increase in nitrogen concentration; the alloy with 0.35 wt% nitrogen exhibited 21% elongation with a high 0.2% proof stress (589 MPa). This significant improvement in ductility was likely caused by the reduction in the amount of σ-phase precipitates at the interdendritic regions following the addition of nitrogen.

Original languageEnglish
Pages (from-to)693-700
Number of pages8
JournalJournal of the Mechanical Behavior of Biomedical Materials
Volume77
DOIs
Publication statusPublished - 2018 Jan

Keywords

  • Co–Cr–W alloys
  • Dental casting
  • Mechanical properties
  • Microstructure
  • Nitrogen addition
  • Precipitation
  • Segregation

ASJC Scopus subject areas

  • Biomaterials
  • Biomedical Engineering
  • Mechanics of Materials

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