Gamma Grains Research Articles

Microstructure in gold-containing Ag3Sn-amalgam.

The present study was conducted in order to understand the microstructural characteristics in dental amalgam which consists of both spherical and irregular Ag3Sn alloy particles with gold substituted in varying amounts for silver (0, 9, and 15%). Spherical alloy particles were used as obtained from Western Gold and Platinum and irregular alloy particles were prepared in the laboratory and then employed in the present study. The amalgam was prepared from the alloy particles by the trituration and condensation method. The polished and etched samples were studied using the techniques of X-ray diffraction, optical metallography, scanning electron microscopy, and X-ray energy dispersive spectroscopy. The microstructure in both types amalgam studied after two weeks of preparation contains gamma (unreacted Ag3Sn particles), gamma1 (Ag2Hg3), and gamma2 (Sn7-8Hg) phases in pure Ag3Sn-amalgam and gamma, gamma1, and (Au-Sn) phases in gold-containing amalgam. The The (Au-Sn) phase existed in the form of rings surrounding the gamma grains and acted as a barrier for mercury diffusion in Ag3Sn particles.

Identification of Au-Sn phase in Ag3Sn alloys containing gold.

Substitution of gold in part for silver in Ag3Sn alloys is found to result in two separate phases: gamma (Ag3Sn particles) grains with a uniform distribution of gold within the grain and an Au-Sn phase in a form of ring surrounding the gamma grain. The thickness of this ring increases with increasing gold concentration. The phases were identified by using the techniques of x-ray diffraction, optical metallography, scanning electron microscopy, and x-ray energy dispersive spectroscopy.

Contribution of Boron to Radiation Effect for Pressure Vessel Steel Weldment

The fission-track etching technique was used to determine the B microdistribution in an ASTM A533B steel weldment. B segregates on gamma grain boundaries in the heat-affected zone; the B content is 12 ppM in the deposit and l ppM in the base metal. The effect of the B segregation on the radiation embrittlement was estimated. A possible reason for the wide scatter in the Charpy impact values of the heat-affected zone and bond interfaces is given. (DLC)

Network structures in uranium and its alloys

Network substructure were produced in uranium by the eutectoid decompositions' of the gamma and beta phases. One network, corresponding to the beta grain and subgrain boundaries, was composed of either 1. (a) incipient precipitates (zones of segregated impurity or alloying elements) when the cooling rate through the transformation was rapid, or of 2. (b) real particles when the cooling rate was slow or the alloy content high. A second network, corresponding to the gamma grain boundaries, was apparent because the beta phase nucleated at the gamma grain boundaries and, during rapid cooling, either incipient or real precipitates outlined each of the beta regions as they grew into the original gamma grains. The incipient precipitates could be revealed only by certain etchants, such as HNO 3, while the real precipitates could be delineated by either the HNO 3 etch or by electropolishing. The incipient precipitates were readily visible by transmission electron microscopy as tiny zones of high lattice strain. The presence of these network structures increased the work-hardening exponent and embrittled the uranium.