Influence of substrate microstructure and surface finish on cracking and delamination response of TiN-coated cemented carbides

Abstract

The cracking and delamination of TiN-coated hardmetals (WC-Co cemented carbides) when subjected to Brale indentation were studied. Experimental variables were substrate microstructure related to low (6 wt% Co) and medium (13 wt% Co) binder content, and surface finishes associated with grinding and polishing stages before film deposition. Brale indentation tests were conducted on both coated and uncoated hardmetals. Emphasis has been placed on assessing substrate microstructure and subsurface finish effects on load levels at which cracking and delamination phenomena emerge, the type of cracking pattern developed, and how fracture mechanisms evolve with increasing load. It is found that polished and coated hardmetals are more brittle (radial cracking) and the adhesion strength (coating delamination) diminishes with decreasing binder content. Such a response is discussed on the basis of the influence of intrinsic hardness/brittleness of the hardmetal substrate on both cracking at the subsurface level and effective stress state, particularly regarding changes in shear stress component. Grinding promotes delamination compared to the polished condition, but strongly inhibits radial cracking. This is a result of the interaction between elastic-plastic deformation imposed during indentation and several grinding-induced effects: remnant compressive stress field, pronounced surface texture and micro cracking within a thin altered subsurface layer. As a consequence, coating spallation prevails over radial cracking as the main mechanism for energy dissipation in ground and coated hardmetals. (C) 2016 Elsevier B.V. All rights reserved.<p>Funding Agencies|Spanish MINECO [MAT 2012-34602]; Erasmus Mundus joint European Doctoral Programme DocMASE</p

Comparative Study of Mechanical Performance of AlCrSiN Coating Deposited on WC-Co and cBN Hard Substrates

“…In the case of the cBN substrate, d is clearly present even for the smaller loads. As the load increases, more spa coating is observed, similar to previous research on similar materials[34,45,46…”

Mechanical strength of ground WC-Co cemented carbides after coating deposition

“…Accordingly, strength is effectively defined by the combined influence of the depth and magnitude of the residual stresses induced within the subsurface, geometry of the induced cracks, and the synergic interaction of these features with microstructure and processing defects [22][23][24][25][26][27]. Studies reporting the combined influence of grinding and coating on induced changes in residual stress state, adhesion strength, and contact damage resistance exist [20,[28][29][30][31]. However, information of how grinding and coating collectively affect the fracture resistance is limited for these materials [32,33].…”

Grinding-induced metallurgical alterations in the binder phase of WC-Co cemented carbides

“…In recent publications, authors have shown that grinding induced microcracks exist down to a depth of about 2 μm, and microcracking followed two different microstructural paths: either WC/Co interfaces or transgranular within the carbide phase, whereas the former being more predominant than the latter for the same material and grinding conditions used in the current study [15,18,19].…”

“…However, similar to other hard and brittle materials [8][9][10], as a result of the abrasive operation, surface integrity of hardmetals is altered at both surface and subsurface levels, particularly in terms of microcracks, residual stresses, and metallurgical alterations within the metallic binder. Thus, mechanical and tribological performance of corresponding tools and components are also affected [6,[11][12][13][14][15][16][17][18][19].…”