Effects of Heat Treatment on Mechanical Properties of two Nickel-Chromium-Based Casting Alloys

Abstract

Mechanical and heat treatment characteristics of two nickel-chromium-based dental casting alloys were investigated. Both alloys showed rapid response to heat treatment. In their softened state the alloys lost 25 to 50% of their as-cast hardness. Elongation was 20 to 45%. Rehardening nearly restored as-cast strength, whereas elongation values remained at 10 to 17%.In recent years base metal alloys have almost replaced gold in the fabrication of large dental appliances and have made inroads with the smaller castings through the porcelain-fused-to-metal restoration. The main problems with the base metal alloys can be associated with their excessive hardness and inadequate elongation. Modification of the properties of cobalt-chromiumand of cobalt-nickel-chromium-based alloys through heat treatment, compositional alterations, and variations in investing and casting techniques have been described by other authors.1-8 Little information is available, however, regarding the properties of the newer nickel-chromium-based casting alloys.The purpose of this study was to investigate heat treatment effects on the mechanical properties of two commercial nickelchromium-based alloys,* to define critical treatment parameters such as heat treatment temperature and time, and to suggest practical application of the experimental results.

Microhardness of Ni-Cr alloys under different casting conditions

“…The results of this study demonstrated that the alloys in the as-received condition showed lower hardness values than that of the respective alloys after casting. It is likely that the as-received alloys are subjected to some heating treatment before commercialization, which increases the softness of the alloy and reduces the values of its mechanical properties 7,21 . Unfortunately, the manufacturers do not provide this information, which prevents us from confirming this hypothesis.…”

A Comparison of the Marginal Accuracy of Metal Copings Made with Three Different Brands of Nickel–Chromium Alloys and Various Sprue Designs

“…No research on the marginal accuracy of Ni–Cr complete coverage crowns produced with three brands of Ni–Cr alloy and with varied sprue designs have been published so far. [ 6 12 13 ] As a result, the goal of this study was to compare the marginal accuracy of Ni–Cr alloys from three distinct companies and three distinct sprue designs.…”

Effect of Aging Treatment on the Microstructures and Hardness of Fe-Ni-Cr Superalloy

“…As shown in Figure 9(a), there is no apparent difference in grain size after the aging process. This is because during aging, the energy supplied might not be sufficient to promote migration of the grain boundary to cause grain growth (Civjan et al, 1972). On the other hand, grain growth is also promoted by dissolution of pinning particles from the grain boundary, which is unlikely to occur during aging; instead, carbide precipitation will take place (Civjan et al, 1972).…”

“…This is because during aging, the energy supplied might not be sufficient to promote migration of the grain boundary to cause grain growth (Civjan et al, 1972). On the other hand, grain growth is also promoted by dissolution of pinning particles from the grain boundary, which is unlikely to occur during aging; instead, carbide precipitation will take place (Civjan et al, 1972). Thus, even if grain growth takes place during aging, which might be due to extremely long heating time, the amount will be so little that it will be hardly noticeable in the microstructure analysis.…”