Abstract
The paper describes an attempt to obtain harmonic structure (HS) in AISI308L steel. Harmonic structure is the term related to the microstructure fabricated by mechanical milling of metallic powders under soft milling conditions, resulting in the formation of plastically deformed, grain-refined shell and unchanged core. This microstructure can be preserved after successful powder compaction. The powders of AISI308L steel were milled under soft condition up to 50 h and then compacted by pulse plasma sintering at 900–1100 °C. For powders and compacts XRD, SEM and hardness measurements were applied as characterization techniques. The milling process resulted in austenite transformation into nanocrystalline ferrite and formation of grain refined outer layer. The applied pulse plasma sintering parameters allowed preservation of this microstructure and manufacturing of compacts with homogeneous distribution of elements, relative density above 95% and hardness in the range 167–185 HV, depending on sintering temperature. Simultaneously, the starting phase composition was restored, i.e., austenite with 12% contribution of ferrite. The crystallite size of austenite was about 20 nm and was significantly smaller then in starting powders.
Highlights
The expected properties of the materials can be achieved at different stages of their processing
In many cases the desired final microstructure can be obtained by mechanical alloying/milling of powders followed by their compaction
If mechanical milling process is performed in soft energy conditions, two areas are distinguishable on the cross section of powder particle
Summary
The expected properties of the materials can be achieved at different stages of their processing. It is possible to modify the properties by changing chemical or phase composition, resulting in specific microstructure. One of the manufacturing techniques commonly used is powder metallurgy. This technique includes many various specific processes. In many cases the desired final microstructure can be obtained by mechanical alloying/milling of powders followed by their compaction. Mechanical alloying is widely applied to produce many types of phases or structures, like amorphous, nanocrystalline, intermetallics, extended solid solutions, composite materials, etc. If mechanical milling process is performed in soft energy conditions, two areas are distinguishable on the cross section of powder particle.
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