Alumina grit blasting parameters for surface preparation in the plasma spraying operation

Abstract

This paper examines how the grit blasting process influences the surface roughness of different substrates, the grit residue, and the grit erosion. The influence of grit blasting conditions on induced substrate residual stresses is also discussed. Aluminum alloy, cast iron, and hard steel were blasted with white alumina grits of 0.5, 1, and 1.4 mm mean diameters. Grit blasting was performed using either a suctiontype or a pressure-type machine equipped with straight nozzles made of B4C. The influence of the following parameters was studied: grit blasting distance (56 to 200 mm), blasting time (3 to 30 s), angle between nozzle and blasted surface (30 ~ 60 ~ 90~ and blasting pressure (0.2 to 0.7 MPa). The roughness of the substrate was characterized either by using a perthometer or by image analysis. The grit residue remaining at the blasted surface was evaluated after cleaning by image analysis. The residual stresses induced by grit blasting were determined by using the incremental hole drilling method and by measuring the deflection of grit-blasted beams. Grit size was determined to be the most important influence on roughness. The average values of Ra andRt and the percentage of grit residue increased with grit size as well as the depth of the plastic zone under the substrate. An increase of the pressure slightly increased the values of Ra and Rt but also promoted grit breakdown and grit residue.A blasting time of 3 to 6 s was sufficient to obtain the highest roughness and limit the grit breakdown. The residual stresses generated under the blasted surface were compressive, and the depth of the affected zone depended on the grit diameter, the blasting pressure, and the Young's modulus of the substrate. Moreover, the maximum residual stress was reached at the limit of the plastic zone (i.e., several tenths of a millimeter below the substrate surface).

Adhesion Strength of HVOF Sprayed IN718 Coatings

“…The role of substrate preparation is another key characteristic that might strongly influence the adhesion strength and that has been explored for flame and plasma spraying ( Ref 12,13). Prior to spraying, substrate grit blasting and preheating are usually used to optimize substrate surface conditions in terms of minimal oxidation, cleanliness, and optimal roughness (Ref 13).…”

Resistencia al desgaste de recubrimientos Fe-Nb-Cr-W, Nb, AISI 1020 y AISI 420 producidos por proyección térmica por arco eléctrico

“…Todos los recubrimientos fueron depositados sobre el acero AISI 4340 como sustrato [5] con dureza ~5 GPa, pulido con disco abrasivo hasta una rugosidad (Ra) de 0,5 y limpiado con isopropanol y acetona en inmersión ultrasónica. Posteriormente los sustratos fueron granallados con óxido de aluminio de pureza 96,04%, malla 30 y presión de 413 MPa de acuerdo con las recomendaciones de los fabricantes [24][25][26] , consumiendo en promedio 3,108 cm 3 de abrasivo por cada cm 2 tratado hasta obtener metal blanco con rugosidad (Ra) de 2,2.…”

Untersuchung der Einflüsse von Substratrauheit und Spritzpartikelgröße auf die Haftung thermisch gespritzter Schichten

“…Um reproduzierbare Substratrauheiten gewährleisten zu können, wurden zunächst Versuche zur Optimierung der Strahlparameter durchgeführt. Dabei wurden die nach [1] am stärksten wirkenden Strahlparameter Körnung des Strahlmittels (EKF 20, EKF 54, EKF 100), Strahldruck (0,4 MPa,0,6 MPa) Beim Spritzwerkstoff Ni20Cr wurden mit zunehmender Substratrauheit höhere Haftzugfestigkeitswerte erreicht, unabhängig davon, mit welcher Spritzwerkstofffraktion gespritzt wurde, Bild 2 c. Dabei wurden die höchsten Werte bei Verwendung der groben Spritzwerkstofffraktion (-90+45 lm) beobachtet. Bei Verwendung der feineren Spritzwerkstofffraktionen bewegten sich die Werte jeweils auf niedrigeren Niveaus.…”