Publications

This report is the latest in a continuing series that highlights the recent technical accomplishments associated with the work being performed within the Materials and Process Sciences Center. Our research and development activities primarily address the materials-engineering needs of Sandia's Nuclear-Weapons (NW) program. In addition, we have significant efforts that support programs managed by the other laboratory business units. Our wide range of activities occurs within six thematic areas: Materials Aging and Reliability, Scientifically Engineered Materials, Materials Processing, Materials Characterization, Materials for Microsystems, and Materials Modeling and Simulation. We believe these highlights collectively demonstrate the importance that a strong materials-science base has on the ultimate success of the NW program and the overall DOE technology portfolio.

Abstract not provided.

This report is the latest in a continuing series that highlights the recent technical accomplishments associated with the work being performed within the Materials and Process Sciences Center. Our research and development activities primarily address the materials-engineering needs of Sandia's Nuclear-Weapons (NW) program. In addition, we have significant efforts that support programs managed by the other laboratory business units. Our wide range of activities occurs within six thematic areas: Materials Aging and Reliability, Scientifically Engineered Materials, Materials Processing, Materials Characterization, Materials for Microsystems, and Materials Modeling and Simulation. We believe these highlights collectively demonstrate the importance that a strong materials-science base has on the ultimate success of the NW program and the overall DOE technology portfolio.

This report is the latest in a continuing series that highlights the recent technical accomplishments associated with the work being performed within the Materials and Process Sciences Center. Our research and development activities primarily address the materials-engineering needs of Sandia's Nuclear-Weapons (NW) program. In addition, we have significant efforts that support programs managed by the other laboratory business units. Our wide range of activities occurs within six thematic areas: Materials Aging and Reliability, Scientifically Engineered Materials, Materials Processing, Materials Characterization, Materials for Microsystems and Materials Modeling and Computational Simulation. We believe these highlights collectively demonstrate the importance that a strong materials-science base has on the ultimate success of the NW program and the overall DOE technology portfolio.

The last decade has offered many challenges to the welding metallurgist: new types of materials requiring welded construction, describing the microstructural evolution of traditional materials, and explaining non-equilibrium microstructures arising from rapid thermal cycle weld processing. In this paper, the author will briefly review several advancements made in these areas, often citing specific examples of where new insights were required to describe new observations, and to show how traditional physical metallurgy methods can be used to describe transformation phenomena in advanced, non-traditional materials. The paper will close with comments and suggestions as to the needs required for continued advancement in the field.

Hot cracking, or solidification cracking, is one of the most extensively studied phenomenon in welding metallurgy. The efforts made to identify the causes of this type of cracking have been driven by the negative commercial and engineering consequences resulting from the formation of these defects. Through judicious weld joint design, the mechanical restraint can be minimized, but it can never be entirely eliminated simply because metals expand and contract when heated and cooled, respectively. The localized nature of heat input in fusion welding insures a non-homogeneous thermal field being applied to the parts being welded, resulting in the development of strains in the as-solidifying weld metal. With the inherent limitations on the mechanical restraint factor, much research has gone into identifying those alloy compositions which minimize the microstructural factor required for hot cracking to occur. Examples from the author`s own research are presented as a tutorial to show how differential thermal analysis techniques have been used to study the chemical/microstructural factors associated with solidification and fusion zone hot cracking in nickel based engineering alloys. References to other uses of these techniques in related welding metallurgy studies are also given.

The solidification behavior of Custom Age 625 PLUS{reg sign} is examined using an integrated analytical approach. Like its predecessors, Alloys 625 and 718, the solidification behavior of this new alloy is dominated by the presence and segregation of Nb, which gives rise to a {gamma}/Laves terminal solidification constituent. 8 refs., 5 figs., 2 tabs.

The influence of postweld heat treatment (PWHT) on the structure, mechanical properties and fracture characteristics of pulsed, Nd: YAG laser welds in a Ti-14.8 wt % Al-21.3 wt % Nb titanium aluminide has been investigated. Significant microstructure variations within the fusion zone (FZ) of all heat-treated welds were attributed primarily to the influence of local compositional fluctuations on decomposition of the metastable-{beta} microstructure present in the as-welded FZ. An increase in PWHT temperature promoted a decrease in the maximum FZ hardness and an increase in the longitudinal-weld bend ductility. Correspondingly, the proportion of ductile tearing to cleavage fracture within the FZ increased with an increase in PWHT temperature. 8 refs., 6 figs.

The solidification behavior of Alloy 718 and other Nb-bearing austenitic superalloys has been examined using an integrated analytical approach. All alloys of this type begin solidification with the formation of Nb-lean austenitic dendrites. Interdendritic eutectic-type solidification constituents involving MC-type carbides and a Nb-rich Laves phase occur in these alloys. The ..gamma../Laves eutectic constituent terminates solidification in these alloys. Nb is the dominant element in the evolution of solidification microstructure with C and Si affecting the amounts of ..gamma../MC and ..gamma../Laves constituent observed. Simple solidification models predict reasonably well the amount of eutectic constituent observed. 11 refs., 9 figs., 2 tabs.