Effects of impurities and pores on fire-cracking of lead-containing α-nickel silvers

Abstract

Abstract Work on α-Cu-18Ni-19Zn- Pb alloys showed that fire-cracking sensitivity is caused primarily by impurities and by micropores around Pb particles along grain boundaries. In a certain impurity range, fire cracking depends also on the type of heat treatment preceding cold work. In the case of cyclic heat treatments, only the last cycle is responsible for the fire-cracking behaviour of such alloys. Specimens can thus be sensitized at will for fire cracking. Heat treatment also influences fire cracking through the formation of micro pores which subsequently act as crack initiators. Reversible pore formation must be caused by the variability of the wetting capacity of liquid lead and the matrix. Good wetting, as a result of liquid metal embrittlement, produces many pores around lead particles and conditions an alloy for fire cracking. Furthermore, wettability is influenced by the impurity content. In order to avoid fire cracking, appropriate additions must be made to reduce wettability below a critical ...