Differences of the microstructural evolution of Cu powder during continuous and interrupted mechanical milling

ABSTRACT

Water atomised copper powders (AT-Cu) have been processed by continuous and interrupted mechanical milling (MM) for different milling times. For continuous cycle the powders are subjected first to a severe flattening process and then to an intense welding phenomenon. In the case of interrupted cycle MM behaviour proceeds with an intense fracturing process. By quantitative X-ray-diffraction analysis the interrupted cycle shows constantly a delay of the microstructure evolution with all the phenomena shifted at longer milling time. For both types of cycle crystalline size decreases down to 20 nm. After 6000 min of interrupted MM the formation of Cu₂O has been revealed and a strong dependency between oxygen content and microstructural parameter has been attested analysing the variations of lattice parameter and lattice strain. When the interstitial oxygen atoms lose their Cottrell locking action dislocation annihilation occurs leading to a reduction of dislocation density and lattice strain.

KEYWORDS:

• Copper powder
• mechanical milling
• milling time
• XRD
• microstructural parameters
• copper oxide

Disclosure statement

No potential conflict of interest was reported by the authors.

ORCID

Massimo Pellizzari http://orcid.org/0000-0002-6832-578X

Notes on contributors

Giulia Cipolloni was born in 1986, in Pisa, Italy and got her master's degree in Material Science and Engineering in 2012 at the University of Trento. In 2016, she got a PhD in Material Science and Engineering at the University of Trento. At the moment, she is Research Assistant at the Department of Industrial Engineering of the University of Trento, in the area of Metallurgy. Her research activity is mostly focused on the development of powder metallurgical tool steel and nanostructured composites by ball milling and Spark Plasma Sintering.

Cinzia Menapace is Research Assistant at the Department of Industrial Engineering of the University of Trento, in the area of Metallurgy. She has been working in Powder Metallurgy for 16 years, discussing a PhD thesis about the sintering of bronze. In the Powder Metallurgy field, she worked on conventional press and sinter (solid phase and liquid phase sintering, dimensional control during sintering); SPS (Spark Plasma Sintering); milling of powders in order to get nano-structured powders; MIM (Metal Injection Moulding); Tape Casting. Currently, she is lecturer of Metallurgical Technologies at the bachelor’s degree course of Industrial Engineering by the University of Trento.

Massimo Pellizzari was born in 1970, in Bolzano, Italy and got his Master Degree in Materials Engineering in 1996 at the University of Trento. In 2000 he got a PhD in Metallurgical Engineering at the University of Padova. Since 2006, Pellizzari has been associate professor at the University of Trento. His research activity is mostly focused on heat treatment and surface engineering of steels, deep cryogenic treatment, the properties of tool steels, special cast irons and the development of powder metallurgical tool steel and nanostructured copper composites by ball milling and Spark Plasma Sintering. He is the author of more than 60 papers in peer-reviewed international journals and, since 2015, he has been a member of the executive committee of the International Federation for Heat Treatment and Surface Engineering (IFHTSE).

Dr Gloria Ischia is the technical manager of Transmission Electron Microscopy unit at the University of Trento (Italy). She obtained her PhD in materials engineering from the University of Trento in 2005 discussing a thesis about synthetic material for high pressure sintering. She is interested in electron microscopy (TEM, SEM, EDXS) in material science and XRD analysis.