Age hardening by dendrite growth in a low-gold dental casting alloy.
Commercial low-gold dental casting alloy composed of Ag-Pd-In-Au-Zn was studied to clarify the age-hardening mechanism and related microstructural changes. The hardness of solution-treated specimen began to increase and reached the maximum value with ageing time, and then the maximum hardness value decreased by further ageing. The changes of X-ray diffraction (XRD) pattern during isothermal ageing revealed that the age hardening was not caused by phase transformation. By comparing the age-hardening curve with the changes in full-width at half-maximum of the XRD peaks at each ageing time, it was revealed that the coherency strains were formed in the Ag-rich matrix, which contributed to the hardness increase during ageing. From scanning electron microscopic observation and electron probe microanalysis, it was clarified that fine particle-like structures composed of InPd containing small amount of Zn gathered by diffusion in the Ag-rich matrix, and the coherency strains which formed during that time caused the hardness increase in the early stage of age-hardening process. The coherency strains were released by the progress of coarsening of Zn-containing InPd dendrite during further ageing, which caused the overaging in the later stage of age-hardening process.
Lee
Hee-Kyung
HK
Department of Dental Materials, College of Dentistry, Pusan National University, 1-10 Ami-dong, Seo-gu, Pusan 602-739, South Korea.
Moon
Hi-Man
HM
Seol
Hyo-Joung
HJ
Lee
Jung-Eun
JE
Kim
Hyung-Il
HI
D001672:Biocompatible Materials / Q000032:analysis / Q000737:chemistry*; D003460:Crystallization / Q000379:methods*; D003722:Dental Alloys / Q000032:analysis / Q000737:chemistry; D003734:Dental Casting Investment / Q000032:analysis / Q000737:chemistry*; D003735:Dental Casting Technique / Q000295:instrumentation; D006047:Gold Alloys / Q000032:analysis / Q000737:chemistry*; D006244:Hardness; D006245:Hardness Tests; D006358:Hot Temperature; D008422:Materials Testing / Q000379:methods*; D008968:Molecular Conformation; D013499:Surface Properties; D013997:Time Factors
D001672:Biocompatible Materials; D003722:Dental Alloys; D003734:Dental Casting Investment; D006047:Gold Alloys