A comprehensive three-year research project is proposed to investigate the metallurgical structures of eight representative high-Pd alloys and establish a scientific basis for their creep behavior and conventional mechanical properties.The first area of research will employ transmission electron microscopy (TEM) to determine the structures of metallurgical phases in these alloys for the as-cast condition and after the porcelain firing cycle heat treatment. The TEM experiments will be complemented by scanning electron microscopy (SEM) and x-ray energy- dispersive spectroscopy to obtain the elemental compositions of the alloy phases. Special model high-Pd alloys will also be studied. The second area of research will focus on the high-temperature creep and room temperature mechanical properties of the commercial high-Pd alloys.Creep of these alloys during the porcelain firing cycles can result in an unacceptable clinical fit of the castings, and creep behavior will be determined for flexural and tensile loading, and for temperature and stress ranges appropriate to the fabrication of fixed dental prostheses. Use of tensile loading permits comparison of observed creep rates to predictions from materials science for possible creep mechanisms. TEM studies will establish the relationships between metallurgical structures and creep rates for these alloys. Tensile test specimens which meet the ANSI/ADA specification no. 5 for dental alloys will be cast, and the elastic modulus, yield strength, tensile strength, percentage elongation, and Vickers hardness will be determined for each alloy in the as-cast and heat-treated conditions. Fracture surfaces of these specimens will be examined by SEM, Auger electron spectroscopy, and x-ray photoelectron spectroscopy to obtain complementary information about the failure processes. TEM will be employed to characterize the dislocation interaction processes which control the strengthening mechanisms for these alloys.
Specific Aim #1 is to determine and characterize the metallurgical phases present in representative commercial high-palladium alloys and model alloy systems.
Specific Aim #2 is to determine the elevated-temperature creep behavior of these high-Pd alloys and the relationships of creep rates and mechanisms to the alloy compositions and metallurgical structures.
Specific Aim #3 is to establish the relationships among compositions, metallurgical phases and microstructures for the conventional mechanical properties of the high-Pd alloys.
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