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Metallurgical Structure and Microhardness of Four New Palladium‐Based Alloys
Author(s) -
Vermilyea Stanley G.,
Cai Zhuo,
Brantley William A.,
Mitchell John C.
Publication year - 1996
Publication title -
journal of prosthodontics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.902
H-Index - 60
eISSN - 1532-849X
pISSN - 1059-941X
DOI - 10.1111/j.1532-849x.1996.tb00513.x
Subject(s) - materials science , indentation hardness , metallurgy , alloy , microstructure , palladium , vickers hardness test , scanning electron microscope , optical microscope , copper , composite material , biochemistry , chemistry , catalysis
Purpose This investigation compared the Vickers hardness and microstructures of four recently marketed, palladium‐based alloys for metal‐ceramic restorations. Materials and Methods Wax patterns simulating copings for maxillary central incisors were invested in a fine‐grained, carbon‐free, phosphate‐bonded investment. Following burnout, the palladium alloys were fused with a gas‐oxygen torch, centrifugally cast, and bench‐cooled. Representative castings were embedded in transparent metallographic resin and sectioned to yield two mirror‐image specimens. The specimens were evaluated in either the as‐cast condition or following heat treatment simulating the firing cycles for Vita VMK porcelain. Vickers hardness measurements (n = 50) were made using a 1‐kg load, and photomicrographs of polished and etched specimens were obtained with a scanning electron microscope. Results The measured values of microhardness for the as‐cast alloys were in excellent agreement with values reported by the manufacturer. The hardness in the as‐cast condition was significantly greater for the Pd‐Cu‐Ga‐In alloy, compared with the other three alloys, which did not contain copper. For the three high‐palladium (≥ 75 wt%) alloys, there were small (4%‐8%) decreases in hardness following heat treatment, whereas a larger decrease (13%) in hardness occurred for the Pd‐Ag‐In‐Sn alloy after heat treatment. The porcelain firing cycles caused microstructural homogenization for all four alloys, and the relatively thick near‐surface oxidation region in the Pd‐Cu‐Ga‐In and Pd‐Ag‐In‐Sn alloys was not observed in the two heat‐treated Pd‐Ga‐Ag‐In‐Au alloys. Conclusions The multiphasic microstructures of these alloys may have some significance for the in vitro and clinical corrosion behavior and the metal‐ceramic bond strength. The hardness for the three high‐palladium alloys may be controlled by submicroscopic precipitates that remain unaltered by heat treatment. The significantly greater hardness for the Pd‐Cu‐Ga‐In alloy may cause greater difficulty for finishing castings in the dental laboratory compared with the other three alloys studied. The strengthening mechanism for the Pd‐Ag‐In‐Sn alloy has significant temperature dependence, which might be exploited to achieve optimum mechanical properties.