  Cu-Cr-based alloys with Cr content from 5 to 50 wt.% are widely used as
electrical contacts for vacuum interrupters for medium voltage applications
because of their excellent combination of mechanical, thermal, and electrical
conductivity. Cu-Cr electrical contacts are usually processed by sintering or
casting processes. For solid-state sintered Cu-Cr materials, the physical
properties vary as a function of the Cr content, phase morphology and porosity
volume fraction. Some studies have investigated the effect of the
microstructural characteristics of Cu-Cr alloys with different Cr content and
morphology on their properties. However, the porosity characterization and Cr
spatial distribution and how they affect these alloys' physical properties are
not as well documented. In this study, we report an in-depth 3D
characterization of the porosity and Cr-phase of solid-state sintered Cu-25Cr
alloys with three final relative densities using X-ray Computed Tomography
(XCT). An image analysis algorithm assisted by a machine learning-based
segmentation method has been specifically developed. Results show that for
Cu-25Cr solid sintered alloys there are mainly two types of pores, pores
located at the Cu/Cr interfaces, and pores within the Cu matrix. The
interfacial porosity represents the larger volume fraction, over 75% of the
total porosity for all cases, forming a large network of interconnected pores.
With the increase of final density, the Cu-matrix becomes nearly fully dense
while interfacial pores still represent the largest fraction decreases in size
and volume. These interfacial pores networks are believed to be formed due to
poor filling and packing of Cu around the percolated Cr-phase. These
observations might be helpful to optimize the functional properties of Cu-Cr
sintered alloys.

Applied Physics;Materials Science