On carbide dissolution in an as-cast ASTM F-75 alloy.

Area of Science:

• Materials Science
• Metallurgy
• Physical Chemistry

Background:

• ASTM F-75 alloy is a critical biomaterial, but its high-temperature behavior, particularly carbide evolution during solution treatment, requires detailed understanding.
• Carbide precipitation and dissolution significantly influence the mechanical properties and corrosion resistance of cobalt-based alloys.

Purpose of the Study:

• To investigate the microstructural evolution of as-cast ASTM F-75 alloy during solution treatment.
• To determine the effect of heating rates on carbide transformation and dissolution kinetics.
• To clarify the dissolution mechanism of carbides in the alloy matrix.

Main Methods:

• Microstructural characterization using image analysis and scanning electron microscopy.
• Electrolytic extraction of precipitates followed by X-ray diffraction for phase identification.
• Analysis of phase diagrams for the Co-Cr-Mo-C system.

Main Results:

• As-cast alloy contained M(23)C(6) carbide and a sigma phase; only M(23)C(6) was present after solution treatment.
• M(23)C(6) carbide dissolved directly into the matrix, without prior transformation to M(6)C carbide.
• Dissolution kinetics of M(23)C(6) decreased over time and were sensitive to heating rate, slowing with lower rates.

Conclusions:

• The heating rate influences M(23)C(6) carbide dissolution kinetics primarily through morphological changes, not phase transformations.
• Direct dissolution of M(23)C(6) into the matrix is confirmed, differing from some literature findings.
• Understanding these dissolution mechanisms is crucial for optimizing heat treatments of ASTM F-75 alloy for enhanced performance.