Interfacial indentation and shear tests to determine the adhesion of thermal spray coatings

A correlation between fracture toughness and cohesion strength of molybdenum thermal sprayed coatings

“…The fracture toughness is the ability of the coating to withstand at the highest level of stress intensity without fracturing and can be evaluated by using several methods such as scratch testing, double cantilever beams loaded in tension, Chevron notch bar and single-edge notched beams tested in three or four point bending [3][4]. One of the most used methods in recent years, providing good results for the evaluating of fracture toughness of thermal sprayed coatings, is the indentation method by Vickers indenter [3][4][5][6][7][8][9][10][11][12]. Beside the accessibility of this method, the major advantage is that the fracture toughness of coatings can be tested locally, on several levels such as, at the coating-substrate interface, also called interfacial fracture toughness, on the perpendicular and parallel direction to the coatingsubstrate interface, between layers or individual splats.…”

“…Beside the disadvantages of this method in terms of costs and time for preparation of specimens (machining, gluing, curing, etc. ), the penetration of the bonding agent into the coating due to the porosity of the coating, modifying its physical properties, and the impossibility to measure the adhesion strength of the coating when the rupture is cohesive and vice versa, represent the main limitations of this method [5][6]. Apart of this, more than eighty methods are reported to measure the coating adhesion, but many of them are also energy consuming in terms of time, cost and equipment [5].…”

“…), the penetration of the bonding agent into the coating due to the porosity of the coating, modifying its physical properties, and the impossibility to measure the adhesion strength of the coating when the rupture is cohesive and vice versa, represent the main limitations of this method [5][6]. Apart of this, more than eighty methods are reported to measure the coating adhesion, but many of them are also energy consuming in terms of time, cost and equipment [5]. Therefore, an additional method that is increasingly used for evaluating the adhesion strength due to its simplicity, accuracy and low costs is the Vickers indentation testing at the coating-substrate interface, with results that can be expressed either as a stress intensity factor, with units of MN·m 3/2 or as fracture surface energy, with unit of J·m -2 [5][6].…”

“…Apart of this, more than eighty methods are reported to measure the coating adhesion, but many of them are also energy consuming in terms of time, cost and equipment [5]. Therefore, an additional method that is increasingly used for evaluating the adhesion strength due to its simplicity, accuracy and low costs is the Vickers indentation testing at the coating-substrate interface, with results that can be expressed either as a stress intensity factor, with units of MN·m 3/2 or as fracture surface energy, with unit of J·m -2 [5][6]. In the same vein, in the case when the rupture of thermal sprayed coatings is produced only within the layers and splats, the Vickers indentation testing can be used as an additional method for evaluating the cohesion strength by locally testing the coating into splats and between layers.…”

Uniaxial Tensile and Cross-Sectional Indentation Tests to Investigate the Adhesion between the Brittle Cr Coating and the Ductile Steel Substrate

“…Also, the evaluation of the adhesion is considered to be an important task. Although great efforts have been made to develop effective techniques for determination of the adhesion between coating and substrate, industries still need quantitative adhesion tests that should be simple, reliable and representative as possible [2]. As stated in [3], more than 200 methods were developed to quantify the adhesion of the coating on its substrate.…”