Effect of WC particle size and Ag volume fraction on electrical contact resistance and thermal conductivity of Ag–WC contact materials

Abstract

In this work, theoretically dense (N 99%) composites of Ag and WC have been prepared by press-sintering-infiltration for making electrical contacts used as an arc-resistant material in a model switching device. Composites with varying silver content and WC particle size were investigated to get an insight on their electrical contact resistance (R c ) and their ability to withstand enormous thermal stresses during switching. A break-only model switching sequence was used, where the evolution of R c was measured over 50 cycles and the post-switching microstructures were investigated for thermal stress induced crack formation. A well-established 2D computational microstructure based model, object-oriented finite element analysis version 2 (OOF2), was used to determine the composite thermal conductivity (k) for various grades as a function of temperature. R c was observed to be consistently low for the coarser WC containing composite and higher silver content composites. This response was attributed to the ductility of the surface layers formed during switching. Crack formation after switching was found to be a direct consequence of large thermal gradients during 50 cycles, which was minimal for coarser WC grained and higher silver content composites which have a higher thermal shock resistance.

Electrical Contact Resistance of Contact Bodies With Cambered Surface

“…where the normalized mechanical load is defined as F * = F/(Er 2 ). And for cylinder-plane contact, according to (9), (21) and (22), when a/r ≤ 0.1, the relationship between the normalized contact resistance R * c and normalized mechanical load F * could be written by The continuous lines represent the theoretically calculated contact resistance by (24) and (25). And the discrete crosses are the simulated results for the given contact.…”

“…where the normalized contact length is defined as L * = L/r. Fig.18 shows the results of illustrative calculations of the dependence of normalized contact resistance R * c on the normalized mechanical load F * with curvature radius r = 1mm and varied normalized cylindrical length L * from 0.01 to 100 by using (24) and (25) when the normalized contact half-width a * ≤ 0.1. The normalized contact resistance R * c decreases with index m = 0.33 for sphere-plane contact with the normalized mechanical load F * increasing.…”

“…According to (24) and (25), the normalized mechanical load F * e , which make the contact resistance of sphere-plane contact equal to that of cylinder-plane contact, could be written into F * e = 9.97 × 10 −3 (L * ) 3.48 (26) Fig.19 illustrates the variations in normalized mechanical load F * e as a function of normalized contact length L * . It is noted that the calculated critical normalized contact load F * is equal to 2.87 × 10 −6 for the elastic sphere-plane contact, corresponding to the critical indentation depth in (4).…”

Arc erosion behavior of TiB2/Cu composites with single-scale and dual-scale TiB2 particles

“…Therefore, under the high temperature of arc erosion, cracks would inevitably appear in ceramic particle reinforced copper matrix composites. The maximum temperature gradient of material without forming cracks (∆T), namely thermal shock parameter of materials (R), is [25]…”

Optimization of Mechanical Alloying Parameters of Cu25W Electrical Contact Material

“…A lot of work has been done towards producing and evaluating the electrical performance of contact materials [14][15][16][17][18][19][20][21]. However, the effect of MA parameters on the production of Cu25W contact material has not yet been investigated in detail.…”