Relationship between fracture toughness and relative density in iron and copper metal powder compacts

Abstract

Iron and copper powders are the two most commonly used metallic raw materials for components formation in the powder metallurgy (PM) industry. The quality of a PM component depends on the ability to achieve high green strength. Most PM components are susceptible to fracture failure due to unpredictable crack propagation and inhomogeneous density distribution. In this paper, we examined the influence of the relative density of green iron and copper powder compacts on the rate of crack propagation due to shear loading, or the mode II fracture toughness (KIIC). The integrated uniaxial compaction of a fixed amount of loose powder method was used to produce the modified diametrical compression test technique (MDCTT) samples used to evaluate the KIIC of the two metal powder compacts studied. The rate of the in-plane crack propagation in the powder compacts slows down as the powder compacts became denser. The inverse of the fracture toughness, 1/KIIC was found to be related to 1/1-1n(p_i)²by constants that are unique to each of the powders. The constants are 33.2 for the iron powder compacts and 55.5 for the copper powder compacts. Furthermore, the constants were found to be related to the coefficients of thermal expansivity for solid iron and solid copper. This study has provided a mathematical relation that can be used to estimate the KIIC for iron and copper based powder compacts from their relative densities. The mathematical relation is also capable of providing useful information about the thermal properties of the related metals.