A new method for strengthening gold

Abstract

Metal-metal composites were first produced in a copper matrix in the 1970's, and they have since been produced in several other binary metal systems. This strengthening technique reinforces a ductile metal matrix with a ductile metal second phase. In some binary systems, this technique confers extraordinarily high strength and hardness while still maintaining low electrical resistivity. This article reports on the first gold matrix metal-metal composite, which was produced by deformation processing a 90%Au-l0%Ag powder compact. The Au-Ag specimen studied had an ultimate tensile strength of 550 MPa and an electrical resistivity only 8% higher than that of pure Au at a deformation processing true strain of 5.6. The 590 nm average Ag filament thickness in this composite was relatively coarse compared to other deformation processed composites, which suggests that substantially higher strengths would be possible in a gold matrix metal-metal composite using deformation processing to higher true strains to reduce the filament thickness. DEFORMATION PROCESSED METAL-METAL COMPOSITESDuring the past two decades, a new class of copperrefractory metal composites has been developed with extraordinary mechanical and electrical properties (1-3). These composites, composed of face-centered cubic Cu with 10 to 30% by volume element X (where X is a body-centered cubic metal immiscible in Cu, such as Nb, V, Ta, Cr, or Fe), are severely deformed by extrusion/swaging/wire drawing or by rolling to produce the nanometer-scale microstructure of X filaments in a Cu matrix shown in Figure 1. The Cu20%Nb system is the most thoroughly studied of these composites. These materials are best known for their extraordinary tensile strengths, which can be as high as 2400 MPa after deformation to a true strain (T) ) of 12 (4). However, they possess other unusual properties as well, including: strength-to-electrical-resistivity ratios much higher than those of any copper alloy the smallest filamentary microstructures (phase size) of any material available in bulk quantities phase structures with very low dislocation densities, approaching whisker quality in many cases The Cu-X deformation-processed metal metal £omposites (DMMC's) are characterized byremarkable ductility, which allows cast-or powder-processed 88 starting billets to be deformed as much as T) = 13.4 (5). Such deformations represent more than an 800-fold reduction in diameter and are accompanied by a concomitant reduction in the thickness and spacing of the X phase. Thus, an as-cast billet of Cu-20Nb, displaying Nb dendrites with an average thickness of

Al-Ca and Al-Fe metal-metal composite strength, conductivity, and microstructure relationships

“…Funkenbuch and Courtney [18] argue that strengthening is caused by the unusually high density of geometrically necessary dislocations generated at the many phase boundaries present during deformation. These dislocations act as barriers that separate each phase into many sub-cells.…”

“…Figure 3.27. [4,[15][16][17][18][19][20]. This topic is discussed in greater detail in Section 3.2.6.…”

“…Many studies [7,[10][11][12][13][14][15][16][17][18][19][20][21][22] where n is a factor that varies with Ag content [23]. By exponential regression ( Figure 3.28), it was found that the relationship between UTS and η that best fits the data for Al- (Fig.…”

“…Frommeyer et alia [18] and a Au-Ag DMMC studied by Russell et alia [19] have been reported. The typical microstructure for fcc/fcc DMMC's is cylindrical second phase filaments embedded in the matrix.…”

Kinetic transformation of nanofilamentary au Metal-Metal Composites

“…Au Deformation Processed Metal Metal Composites (Au DMMC's) are being developed for electronic applications requiring high conductivity and high strength (5,6). Au-Ag and Au-Pt DMMC's possess an extraordinary combination of properties due to their nanofilamentary microstructure of second phase metals in a Au matrix.…”