Some considerations in using the small punch testing for thermally sprayed CoNiCrAlY coatings

Abstract

Small punch testing exhibits great potential in mechanical characterisation of thin coatings.This testing method can be used to determine the mechanical performance of thermally sprayed coatings, especially to qualitatively characterise the effects of coating defects on the mechanical behaviour. In this work, some considerations in using the small punch testing for coatings are presented through a microstructure evolution analysis of a vacuum plasma sprayed CoNiCrAlY coating under small punch test. The CoNiCrAlY coating was characterised with a large number of un-melted particles as the coating defects. It is shown that the clamping in the small punch test rig can result in micro-cracking around the unmelted particles in the coating prior to testing. It is also found that the un-melted particles in the coating act as predominant cracking sites and fast failure occurred around the un-melted particles. Careful considerations need to be taken into account when using the small punch test for coatings to avoid any changes in the coating microstructure and plasticity during the clamping stage.

Influence of Atmospheric Plasma Spray Parameters (APS) on the Mechanical Properties of Ni-Al Coatings on Aluminum Alloy Substrate

“…As an application example, SPT methodology has been used to mimic the expansion of stents inserted into arteries and, to this purpose, to study the failure of polymer-coated stents [56]. Chen et al [57] studied the behavior of thermally sprayed CoNiCrAlY coatings using the vacuum plasma method. Tests were carried on at high temperature and constant load, i.e., small punch creep test.…”

Characterisation of deformation process and fracture mechanisms of P91 steel at 600 °C in small punch tensile testing

“…Moreover, the SPTT specimen can be taken directly from in-service components without significantly affecting their structural integrity [9], allowing the mechanical behaviour to be examined [10][11][12]. A wide range of small punch creep tests have been conducted to evaluate fracture and creep properties [13][14][15][16][17][18][19][20][21], in which the creep strength and minimum strain rate estimation from small punch creep tests can be correlated to the uniaxial data through finite element analysis or analytical approaches [21,22]. In recent years even pre-cracked [23] or pre-notched specimens have been tested [24,25].…”

Effects of temperature on the β-phase depletion in MCrAlYs: A modelling and experimental study towards designing new bond coat alloys

“…Surface protection is thus widely used to protect high temperature components against oxidation and corrosion [5][6][7]. Among the available high temperature coatings, MCrAlYs appear to be of particular interests due to their capability in forming a stable and protective alumina scale at the coating surface and their customised composition design to meet specific requirements [8][9][10][11]. MCrAlYs (where M = Co and/or Ni) are multi-component alloys and usually consist of fcc γ-Ni and, more importantly, the bcc β-NiAl phase [12].…”