Dr. Christopher W. Corti - COReGOLD Technology Consultancy, U.K.
Dr. Chris Corti holds a B.Sc. and Ph.D. in metallurgy from the University of Surrey (U.K.) and is the managing director of COReGOLD Technology Consultancy. He has more than 40 years of experience in the precious metals industry with Johnson Matthey PLC and World Gold Council. He is currently a consultant for the Worshipful Company of Goldsmiths in London and has edited the Goldsmiths’ Company Technical Journal. Chris is a recipient of the Santa Fe Symposium® Research, Technology (two times), Ambassador, Applied Engineering and Lifetime Achievement Awards. This is his 29th presentation at the Symposium.
Basic Metallurgy of the Precious Metals, Part III: Cracks and Other Defects—Their Causes and Prevention
In this third part of the Basic Metallurgy series, we examine some of the problems that can occur—defects in manufacture—that can lead to problems in both manufacture and later in service with the customer. Typically, the main problems are casting defects, such as pipes and porosity, and cracks that can occur during and after manufacture. Porosity can arise from solidification shrinkage or from gas evolution during solidification. There are many causes of cracking in alloys, with the cracks generally intergranular and all similar in appearance. It is not easy to pinpoint the cause.
The common causes of such defects, some of which can lead to difficulties in manufacturing quality and to cracking and fracture, and the steps that can be taken to minimize their occurrence are reviewed. These include poor quality start materials that lead to contamination and embrittlement; poor melting practice leading to casting defects, segregation, porosity and blisters; poor ingot or material working practice; incorrect annealing practice including quench cracking and fire cracking; and stress corrosion cracking.