PubMed · 2135763
The source did not provide an abstract. Follow the original record for more information.
Explore connections, maps & timelines
M E Cuartas. [Casting alloys].. https://pubmed.ncbi.nlm.nih.gov/2135763/
Cite the original work for its findings. Save a collection to share your selection of sources.
KEEP EXPLORING
The fatigue limits and fracture characteristics for three Pd-Ag dental casting alloys (Super Star, Heraeus Kulzer; Rx 91, Pentron; W-1, Ivoclar Vivadent) were studied. Specimens meeting the dimensions for ADA Specifications No. 5 and 38, and having the as-cast surface condition, were subjected to heat treatment simulating dental porcelain firing cycles and fatigued in air at room temperature under uniaxial tension-compression at 10 Hz. A ratio of compressive stress amplitude to tensile stress amplitude (R-ratio) of -1 was used. Alloy microstructures and fracture surfaces were examined with a scanning electron microscope and a transmission electron microscope. Fatigue limits for the three alloys had low values of approximately 15% of the yield strength for 0.2% permanent tensile strain. Complex fracture surfaces with characteristic striations were observed for all three fatigued alloys. Planar slip of dislocations occurred in the Pd solid solution matrix, along with dislocation-precipitate interactions and dislocation networks in the interfaces between the precipitates and surrounding matrix. Twinning occurred in the Pd solid solution matrix of Rx 91, and within discontinuous precipitates in Super Star and Rx 91. The low fatigue limits for these alloys are attributed to their complex microstructures and perhaps to casting defects.
OBJECTIVES: The purpose of the present investigation was to report a Pd-free high gold alloy for porcelain bonding based on the ternary system of Au-Pt-Zn with a nominal composition of 86Au-11Pt-1.5Zn-0.5In-0.7Rh-0.2Fe-0.1Ir (wt.%). Emphasis was put on the effect of a pre-firing heat treatment on the mechanical properties of the alloy. METHODS: The strengthening effect of the pre-firing heat treatment was investigated by means of hardness measurement, tensile testing, X-ray diffraction, optical microscopy and scanning electron microscopy. RESULTS: Experimental results showed that both the hardness and tensile strength of the alloy can be significantly improved after heat treatment at the temperature of 980 degrees C for 15 min. The strengthening could be attributed to homogenization of microstructure and alloying elements and precipitation of new fine particles. SIGNIFICANCE: The cast framework of the present new Pd-free alloy could be heat treated before actual firing, and this would improve the processing properties of the alloy during firing.
A contributing mechanism for clinical failure of NiTi rotary instruments might be excessive work hardening. Vickers hardness was measured with 300 gm load near the flutes in three regions (D2-D4, D6-D10, and D14 towards the shank) for nine representative clinically used ProFile GT instruments that had been axially sectioned (10 measurements in each region). Consistent values could not be obtained at D1. Minimum hardness occurred at D2 to D4, with means from 313 to 324 (SD from 7 to 16). Maximum hardness with means ranging widely from 330 to 481 was found beyond D14. Mean hardness at D2 to D4 was 320 for an as-received ProFile instrument. Because a mean Vickers hardness of 326 has been reported for a shape-memory NiTi orthodontic wire product, it can be concluded that the NiTi instruments did not experience substantial work hardening at D2 to D4 during clinical use, in agreement with previous differential scanning calorimetric analyses.