Properties of cobalt-chromium heat treatment



Participants of CSP No. 147/242*, and Harold F. Morris, Veterans Administration Medical Center, Ann Arbor, Mich.





A comparison of mechanical properties of seven metal ceramic alloys in as-cast and heat-treated conditions resulted in significant differences. The alloys that were tested included seven cobalt-chromium metal ceramic alloys. Mechanical properties include strength, elongation, modulus of elasticity, and microhardness. Twenty-four tensile bars were cast for each alloy. Twelve of the 24 bars for each alloy were randomly selected for heat treatment with the Ceramco technique. Results indicated that the tested alloys had similar mechanical property values as a group in both the as-cast and the heat-treated conditions. The heat treatment had little effect on the cobalt-chromium alloys, although several did become significantly harder. In either condition, the cobalt-chromium alloys showed a high value of strength, a low percent of elongation, a high modulus of elasticity, and a high value of hardness. The high value of hardness and the low percent of elongation would make these alloys difficult to handle clinically. (J PROSTBET DENT 1989;62:426-33.)



of results

has been reported



selection, handling, and use of cobalt-chromium (Co-Cr) alloys for crowns and fixed partial dentures.lm3Reported problem areas include working characteristics, accuracy, porcelain bonding, and biocompatibility. Little information exists, however, concerning the effects of simulated porcelain firing cycles (heat treated) on the mechanical properties of Co-Cr metal ceramic alloys.4-6 Veterans Administration Cooperative Studies Project Nos. 147and 242were designedto comprehensivelystudy the clinical serviceability of several alternative metal ceramic alloy systems.7One goal of these projects was to evaluate certain mechanicalproperties of various alternative alloys before and after they were subjectedto a simulated porcelain firing cycle. Part VII of CSP 147/242 reported on the mechanical properties of the following types of alloys after heat treatment: three nickel-based, three palladium-based,and one gold-based.8This report provides mechanicalproperties information on seven CoCr metal ceramic alloys.




Table I lists the Co-Cr alloys chosenfor this investigation, and Table II provides their approximate chemical

Supported by the Veterans Administration (VA) Medical Research Service/Cooperative Studies Program and the National Institute of Dental Research, Interagency Contract No. lYOlDE-50004-00, and conducted by the Veterans Administration CSP No. 147/242 Dental Research Group. *Complete authorship appears on last page of article. **Study Chairman and Director, Clinical Research Center for Restorative Materials, Veterans Administration Medical Center; Clinical Associate Professor, University of Michigan, School of Dentistry, Ann Arbor, Mich. 10/1/16022



I. Alloys studied Alloy



Austenal Dental, Inc., a Nobelpharma Chicago, Ill. Dentsply International York, Pa. J.F. Jelenko and Co. Armonk, N.Y. Williams Dental Co., Inc. Buffalo, N.Y. Jeneric Industries, Inc. Wallingford, Conn. Jeneric Industries, Inc. Austenal Dental, Inc., a Nobelpharma

Cobond Genesis II Master Tee Novarex Novarex II Vi-Comp



compositions.For each of the seven alloys, 24 plastic tensile bar patterns with dimensionsof thoserecommendedin American National Standards Institute/American Dental Association (ANSI/ADA) specification No. 5gfor cast-gold alloys and a designmodified from Moffa et al.1°weresprued in the manner recommendedby Asgar et al.ll and invested in a phosphate-bondedinvestment (Hi-Temp, Whip Mix Corp., Louisville, KY.). The patterns were burned out at 1500“ F, and the alloy ingots were melted and cast in an induction castingmachine(Williams Inductocast, Williams Dental Co., Inc., Buffalo, N.Y.). Completed castingswere bench-cooled1 hour before removal from the investment. With aluminum oxide air abrasion, residual investment wasremoved from the casting. With a separatingdisk, the tensile bars were cut from the sprue assembly. Twelve of the 24 tensile bars cast for each of the seven alloys were randomly selected for heat treatment. This procedure was designedto closely simulate the porcelain bake cyclesan alloy would undergoto makea metal ceramic APRIL








Table II. Approximate




chemical compositions of study alloys (weight %) Co-Cr

Elements co Cr

MO Ga Ru W 0 Si AI C



63.1 29.0 3.5 0 0 0 0 1.4 0 0.2

68.0 27.0 6.0 0 0 0 0

Properties of cobalt-chromium metal ceramic alloys after heat treatment.

A comparison of mechanical properties of seven metal ceramic alloys in as-cast and heat-treated conditions resulted in significant differences. The al...
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