Thermal characteristics and analysis of pyrolysis effects during the mechanical alloying process of Astaloy CrM powders

Abstract

Mechanical alloying processes are carried out usually with addition of some lubricants, referred to also as a process control agents (PCA). About 1-2 wt% of a PCA (usually stearic acid) is normally added to prevent excessive cold welding amongst the powder particles, especially when powders of ductile metals are milled. However, lubricants (maybe disintegrated after MA process) must be removed in the early stages of heating during the sintering process. The aim of the present study was to determine the effect of the MA process especially (i) milling time and (ii) influence of lubricant addition on thermal effects during heating of iron powder (Astaloy CrM) with the addition of 1 wt% stearic acid measured by differential scanning calorimeter (DSC) and thermogravimetry (TG) techniques. Removal of the lubricants during heating of the blended powders and exhaust gases from the furnace were monitored by quadruple mass spectrometry (QMS). Determination of the physical and technological properties of the powder mixture obtained from MA was performed with a laser particle sizer. Distribution of particle sizes, flow and apparent density were also measured. Furthermore, the shape and morphology of the powders were characterised by a light optical microscope (LOM) and scanning electron microscope (SEM).

Influence of the mechanical alloying process on the sintering behaviour of astaloy CrM powder mixture with silicon carbide addition

“…inert/controlled gas or vacuum), milling environment (e.g. dry milling or wet milling), powder to ball mass ratio, types and sizes of milling media, milling time and type of milled materials [6,7].…”

Application of a device used for observation of controlled thermal processes in a furnace

“…In most cases it is impossible to directly or simultaneously observe the visual changes taking place in the studied materials. Currently, in modern test equipment it is common to include the so-called coupled methods (allowing to perform several independent measurements at the same time, e.g., the measurement cycle in differential scanning calorimetry/thermogravimetry/quadrupole mass spectrometry; DSC/TG/QMS), which facilitate interpretation of the registered thermal effects, mass changes or released gas products [1][2][3][4][5][6][7][8][9]. From the results it can be concluded which phenomena are being dealt with, but observation of the sample can be conducted only before and/or after the experiment.…”

Dilatometric study of low-alloy steels with silicon carbide addition

“…MA works as an activator which intensifies the driving forces of the sintering process. This phenomenon is correlated with the fragmentation of particles, accumulated energy during MA and the presence of lubricant additions, which can also be disintegrated in the course of the MA process [9]. Moreover, in high temperatures, above 1000°C, the dominant mechanism for the reduction of oxides and the activation of the sintering process is the carbothermal reaction.…”

“…The common method of enhancing the properties of the material is by introducing additives that will improve the mechanical properties of the produced elements, e.g., their creep resistance, hardness, yield strength and elasticity. This may be achieved by the addition of silicon, e.g., through mechanical alloying-MA, to prealloyed low-alloy steels [8,9]. Silicon may also be introduced to the material in the form of silicon carbide (SiC) [10].…”