Effect of Microstructure on the Physical Properties of Cobalt-Base Alloys

Abstract

Relatively little is known about the microstructure of cobalt-base alloys in dentistry. Manufacturers of dental cobalt-base alloys have published very little on this subject. No research has been conducted on the microstructure of the cobalt-base alloys used in dentistry. The need for research in this field is recognized, however, by both the manufacturers of the alloys and researchers in the dental field.It appears that it would be profitable to dentistry if a study were made in which the effect of different casting conditions on the grain size and the microstructures of the cast product was established. It would also be useful to determine the physical properties of cast pieces having different microstructures. Today the mechanical properties listed for dental alloys vary a great deal from one type of alloy to another and also within the alloy. For example, elongation values from very small values to as high as 12 per cent are given for these alloys, and the modulus of elasticity determined for these alloys varies from approximately 20 to 40 million pounds per square inch.1 2 No satisfactory explanation is given for such a wide range of different physical properties. A study seems to be in order, therefore, to check these values and to determine whether such a variation is inherent in these alloys or is due to different testing conditions, such as sample size, casting condition, or equipment used. With these problems in mind, this study was undertaken in an effort to answer, with a certain amount of confidence, some of the above questions, the importance of which is becoming increasingly more obvious to the dental profession. MATERIALS AND METHODSIn this study more than 120 specimens were cast under different conditions, and their physical properties as well as their microstructures were studied. All specimens were cast of a cobalt-base alloy* which is of a composition similar to a typical dental alloy.t The investment used was a phosphate-bonded type.: Specimen size and manner of spruing were patterned after the recommendation of the A.D.A. specification for chromiumcobalt alloys.3 The conditions studied were related to changing the metal casting tem-

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Electrochemical and corrosion behavior of two chromium dental alloys in artificial bioenvironments

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