Turbula mixing characteristics of carbide powders and its influence on laser processing of stainless steel composite coatings

• Published in: Powder technology Vol. 230; pp. 169 - 182
• Main Authors: Obadele, B.A., Masuku, Z.H., Olubambi, P.A.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01-11-2012; Elsevier
• Subjects: Agglomeration; Applied sciences; Carbide powders; Carbides; Chemical engineering; coatings; Diffusion; energy; Exact sciences and technology; Feedstock; feedstocks; Homogeneity; Laser processing; Lasers; melting; Miscellaneous; Mixers; Mixing; particle size; powders; scanning electron microscopes; Scanning electron microscopy; Sintering, pelletization, granulation; Solid-solid systems; Stainless steel; Titanium carbide; X-radiation; X-ray diffraction; Homogeneity; Laser processing; Mixing; Carbide powders; Stainless steel; Scanning electron microscopy; Particle size; Shear; Segregation; Mixing time; Mixer; Agglomeration; Composite material; Powder; Laser; Diffusion
• ISSN: 0032-5910; 1873-328X
• DOI: 10.1016/j.powtec.2012.07.025

In this study, the mixing characteristics of feedstock carbides powders for laser synthesis of stainless steel composite coatings were investigated in a Turbula Shaker Mixer T2F. This research was aimed at determining the mixing parameters that give optimal powder homogeneity and determining any metallurgical interactions and/or bonding amongst powder during mixing. Blending/mixing of WC-9Co-4Cr, WC-10Ni and TiC powders mixture was performed in the mixer to prepare WC/TiC feedstock for laser melt injection. The constituent phases and microstructural characteristics of the as-received and feedstock powders were studied by Malvern particle size analyser, an X-ray diffractometer (XRD), a scanning electron microscope (SEM) equipped with an energy dispersive X-ray spectrometer (EDS). From the results obtained, it showed that the feedstock powder particles underwent diffusion and agglomeration. For a longer mixing time of 8h, homogeneous distribution of the powder was obtained. However, it could be seen that diffusion, shear, segregation, random mixing and partial agglomeration of the powders were prominent. No new phases were formed. Also, the homogenized feedstock substantially improved the uniform distribution of the different carbides in the coatings as less dense powder particles were injected close to the bottom of the coated zone.
The mixing characteristics of feedstock carbide powders for laser synthesis of stainless steel composite coatings were investigated using a Turbula Shaker Mixer T2F. The shear force of the Turbula mixer and the drop impact of the powders decreased particle sizes to submicron and nanoscale with no new phase formation. [Display omitted]
► WC-9Co-4Cr, WC-10Ni and TiC powders were blended in a Turbula mixer. ► Powder homogenizations were achieved after 8h of mixing. ► Blended powder were injected unto 2205 duplex stainless steel using an Nd:YAG laser. ► Agglomeration in powder blend improved uniform distribution of carbides in meltpool. ► This resulted unto elimination of pores and crack formation in the meltpool.