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The thermal properties of metal powders strongly influence the sintering, final density, and quality of PM parts. Properties such as thermal conductivity and specific heat capacity can be used for quality evaluation of PM components, simulations/ modelling, process parameter optimisation and more. Here, Dr Artem A Trofimov, Orton Ceramic Foundation, evaluates the relatively new Hot Disk Transient Plane Source (TPS) technique for measuring the thermal properties of loose powders and compressed tablets, and discusses its potential for quality control via quick differentiation between powders of different metals and/or particle sizes using thermal property calibration curves. Powder is, naturally, a fundamental building block of the Powder Metallurgy industry, for which it must be precisely formulated and optimised for specific applications. Metal powder is notoriously different from its end-part equivalent, and, regardless of the nature of a material, from metal to ceramic, the parameters of powder particles directly impact each manufacturing stage. Particle size, shape, distribution, compaction, morphology; all can have a profound effect on the resulting product. Among the material characteristics that are rather sensitive to these parameters are thermal properties – namely, thermal conductivity and heat capacity. Both properties play a defining role in heat conduction, which is crucial not just for the burnout of lubricant/binder, but for the critical sintering stage (the latter directly affects the mechanical properties of the final part). The thermal conductivity of a powder can be used to differentiate between powders of the same material with different particle characteristics, since conductivity is
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affected by the packing, particle size, efficiency of contacts, and type of gas in the voids. On the other hand, heat capacity is primarily affected by the nature of the material, and can be used to distinguish materials of different types even when the particle parameters are similar.
In this article, we present a case study using the Hot Disk Transient Plane Source (TPS), a relatively new and rapid thermal analysis technique for measuring the thermal properties of both loose and compressed powders in green compacts.
Fig. 1 The Hot Disk Thermal Constants Analyzer, used to characterise thermal conductivity, thermal diffusivity, and heat capacity
Winter 2022
Powder Metallurgy Review
95
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Understanding the thermal properties of metal powders: Characterisation of powders using the Hot Disk technique
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Thermal properties of metal powders
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