Annealing study of palladium–silver dental alloys: Vickers hardness measurements and SEM microstructural observations

Abstract

Three Pd-Ag dental alloys for metal-ceramic restorations, W-1 (Ivoclar Vivadent), Rx 91 (Pentron) and Super Star (Heraeus Kulzer), were subjected to isothermal annealing for 0.5 hr periods in a nitrogen atmosphere at temperatures from approximately 400 degrees to 950 degrees C. The annealing behavior was investigated by Vickers hardness measurements (1 kg load) and SEM microstructural observations. The highest Vickers hardness occurred at approximately 700 degrees C for W-1 and 650 degrees C for Rx 91. For Super Star, there were two peaks in hardness at approximately 500 degrees and 650 degrees C. Additional use of light indenting loads (25 g for W-1; 10 g for Rx 91 and Super Star) revealed that hardness variations during annealing for W-1 and Rx 91 were related to the palladium solid solution matrix phase. For Super Star, the lower-temperature peak was controlled by multi-phase regions and the higher-temperature peak by the matrix phase. While microstructural changes due to annealing were evident with the SEM for Rx 91 and Super Star, no correlation was possible for W-1 because of its finer-scale microstructure. Although commercial Pd-Ag alloys have a relatively narrow composition range, their microstructures and annealing behavior can vary because of differences in proportions of secondary elements utilized for porcelain adherence and grain refinement elements, as well as other proprietary strategies employed by the manufacturers.

Change in hardness of an as-cast and softening heat-treated low-gold-content alloy for bonding porcelain by simulated porcelain firing and its mechanism

“…Such softening from microstructural coarsening has been reported in many dental casting alloys that are overaged for long periods of time at temperatures where age-hardening occurs [10][11][12]. Compared to dental casting alloys, dental alloys for bonding porcelain undergo heat treatment at much higher temperatures for porcelain firing, which resulted in apparent microstructural coarsening during a much shorter firing time [13]. In the solution-treated specimen after casting in Fig.…”

Heat Treatment of Dental Alloys: A Review

“…Peaks in Vickers hardness for heat treatments at temperatures that span the porcelain-firing temperature range indicate that influential precipitation processes can occur in some noble alloys for fixed prosthodontics [13,16]. For the gold-palladium-silver alloy in Table 1, heating an as-cast specimen to 980°C caused a pronounced decrease in Vickers hardness, and subsequent heat treatments at temperatures from 200° to 980°C revealed a pronounced peak in Vickers hardness at approximately 760°C.…”

“…The absence of substantial changes in Vickers hardness for similar heat treatments of the gold-palladium alloy in Table 2 arises from differences in the precipitates that form in the two complex alloy compositions. Figure 2 presents the age hardening behavior of a palladium-silver alloy, where specimens were subjected to isothermal annealing for 30 minute time periods at temperatures from 400°C to 900°C that span the range for the porcelain firing cycles [16]. Bulk values of Vickers hardness were obtained with 1 kg loads, and 25 g loads were used to obtain hardness values for specific microstructural regions.…”

Hardness and Composition of Solution-Treated Ag-Pd-Cu-Au Alloy Microstructures

“…[3][4][5][6] Seol et al 6) examined isothermal age-hardening behavior, phase transformation, and related microstructural changes. Guo et al 7) investigated hardness and microstructure of heat-treated Pd-Ag dental alloys containing Sn and In, examining the relationship between precipitation and change in hardness. Increasing tensile strength and hardness of Ag-Pd-Cu-Au alloys by hightemperature solution treatment has been reported.…”