The fabrication of porous copper with ultrahigh porosity by adding 90% spacer content was an unsolved technical problem in the field. In this study, the green compacts placed on a layer wire mesh during the decomposition process of needlelike carbamide as space holder with volume content up to 90% was successfully conducted to fabricate nondestructive porous copper. Compared with the green compacts directly placed on an alumina plate, the use of this support was crucial for manufacturing highly-porous copper. Characterization of macro- and microscopic morphologies as well as quasi-static compressive test for the obtained porous copper samples was carried out. The results show that the porosity of porous copper samples with 87.3% was slightly smaller than the spacer content. The SEM observation indicates that the internal pores of porous copper formed an open-cell structure and its skeleton was very dense. The compressive tests show that the stress–strain curve of a porous copper sample exhibits the typical characteristics of elastic-plastic metal foam. The energy absorption properties of porous copper samples were also comparable. This study provides a possibility for the preparation of porous copper and other metals with ultrahigh porosity by the well-known space holder method.

Porous copper (Cu), with varying porosities, has been made using carbamide as a space holder through the powder metallurgy route. Two shapes of carbamide particles were used, (i) needlelike and (ii) spherical, in order to investigate the effect of the space holder shape on the pore structure and mechanical properties of porous Cu. The compressive deformation behavior of porous Cu was studied under a compression test. The pores’ structural characteristics and mechanical properties of the porous Cu varied significantly with the shape of the space holder. Although the effect of the space holder shape on the porosity was not regular, the effect on the mechanical properties was regular. The stress increased monotonically with the increase in the strain, and strain hardening occurred at the plastic yield stage. The elastic modulus and yield strength followed the power law, with the relative density irrespective of the space holder shape. The empirical constants associated with different empirically developed power law relations were different, according to the shape of space holder. A quantitative relationship between the elastic modulus and yield strength and the spacer content was obtained to control the mechanical properties of the present porous Cu or other porous metals and metal foams using the well-known space holder method.

The measurement and predictive functions of the model equation method in the preparation of porous copper were studied. Needlelike and spherical carbamide was used as a space holder with volume content between 10 and 80%. One step of heat treatment for green compacts was applied to fabricate porous copper. A criterion for determining the uniformity of external dimensions of porous copper was proposed. The results showed that the mass follows the law of conservation and the height of porous copper decreased as the increase of spacer content while there was no regularity for the diameter. The porosity of porous copper calculated by the model equation method was equal to those of by the mass volume method. The theoretical formula obtained to describe the relationship between porosity and spacer content of porous copper intersects with the empirical formula. The results indicated that the measurement function of the model equation method was easier to play than the prediction function.

Porosity is the single most important feature of porous materials. On the basis of the research work, a new method to measure the porosity of porous materials is proposed in this paper. This method is a system of equations composed of six formulas, so it is called model equation method. It is not only applicable to space holder technique but also applicable to metal prepared by pure powder metallurgy. Compared with mass volume method and immersion medium method, our new method is more simple and efficient. More importantly, it can be used as a standard measure. This study provides a fundamental basis for the measurement of porosity in porous materials.

In this paper, porous Cu with different porosity and pore size has been successfully prepared by the well-known lost carbamide sintering method. The effects of the space holder size on the pore structure and mechanical properties of porous Cu were studied with a wide porosity range. The results showed that the particle size of space holder has an effect on the porosity, pore size, elastic modulus, yield strength, densification stress & strain, energy density, plateau stress and fitting curve of porous Cu, but the law was complex when compared with the content. The correlation between the relative elastic modulus and the relative density of porous Cu was square exponential which can be well described by the standard Gibson-Ashby model. However, the correlation between the relative yield strength and the relative density of porous Cu was more suitable to describe by the power exponent instead of 3/2 which can be well described by the modified Gibson-Ashby model. The results indicated that the effect of space holder content on the pore structure and mechanical properties of porous Cu was more significant and regular than that of particle size, but the effect of space holder size cannot be ignored. The results of this study will provide reference for the design and preparation of porous Cu with different pore sizes in the future.