The effect of PVD coatings on the tensile strength and low-cycle fatigue resistance of stainless steel and titanium alloys

Abstract

A B S T R A C T PVD coatings applied to components form hard, stronger layers and generate high residual compressive stresses that limit the plastic deformation in surface layers of the base metal thus increasing its tensile strength and resistance to fatigue loading. The purpose of this paper is to experimentally determine the influence of the deposition of 2 to 16.5-μm-thick PVD coatings of TiN , Cr, (Cr+TiN), (TiC)N, (TiAl)N onto specimens of stainless steel 321 and titanium alloys of types MILT-81556A and (10-2-3; 4966) on their tensile strength and low-cycle fatigue resistance when the development of large elastic-plastic strains takes place. The tensile and low-cycle fatigue tests were conducted under conditions of axial zero-to-tension cycle of the stress-controlled loading on flat 1-to 1.5-mm-thick specimens in the initial state (uncoated specimens) and after application of a PVD coating, including those after pretensioning or after cyclic prestraining in the low-cycle fatigue range. The deposition of PVD coatings is found to enhance the characteristics of tensile strength and low-cycle fatigue resistance in the quasi-static fracture range. The deposition of PVD coatings on specimens cyclically prestrained to the values of 53-86% of the number of cycles to fracture, changes the cyclic properties of the material and predetermines the fatigue fracture mode only.

Low‐cycle fatigue behaviour of polyamides

“…Figure 11 depicts the variation with strain of the stress and the instantaneous elastic modulus for the first and for the 5000th cycle of tests performed at 5 Hz, 0.025 mm mm À1 reference strain and 5000 cycles. It can be observed that a higher stress response (17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28)(29)(30) MPa, characteristic to the first cycle) corresponds to a lower stiffness (950-800 MPa) and vice versa, lower stress responses (0-15 MPa, characteristic to the 5000th cycle) exhibit higher stiffness (1030-930 MPa). Figure 12 presents the stress-strain and modulusstrain curves from a tensile test performed at 0.1 s À1 strain rate; value that is close to the strain rate resulted from tests performed at 5 Hz (0.075 s À1 ).…”

“…19 Low-cycle fatigue (LCF) tests were developed for investigating the fatigue behaviour of metals at relative high strain/stress levels as a way to replicate the in-service loading patterns of some components. 20 The cycle strain/stress ratio R of LCF tests on metals can vary from negative values 21 to positive values, 22 and the tests are usually performed at low frequencies (<1 Hz). 22,23 The behaviour of fibre-reinforced composites is also investigated under LCF [24][25][26][27] and similarly, tests on polymers mostly demonstrate the Mullin's effect, and procedures rarely exceed 10 2 cycles.…”

“…20 The cycle strain/stress ratio R of LCF tests on metals can vary from negative values 21 to positive values, 22 and the tests are usually performed at low frequencies (<1 Hz). 22,23 The behaviour of fibre-reinforced composites is also investigated under LCF [24][25][26][27] and similarly, tests on polymers mostly demonstrate the Mullin's effect, and procedures rarely exceed 10 2 cycles. [28][29][30][31] Future work in this field can be oriented in the direction of developing or adapting already existing fatigue criteria for thermoplastic polymers that can be successfully implemented in the design stage of products and components manufactured from this type of material.…”

Control of fatigue failure mechanisms in multilayer coatings by varying the architectural parameters of an intermetallic interlayer

“…The residual stress is well known to be dependent on the coating layers organization and thickness, for example, the TiN hard coating 12 and Cu/W nanomultilayers 13 . The microstructure and mechanical properties of some layers in these multilayer coatings may change substantially with changing layer thickness across a thickness range, such as the electroplated Ni/Sn multilayered composites, 14 (Na 0.85 K 0.15 ) 0.5 Bi 0.5 TiO 3 multilayer thin films produced by spin coating 15 and multiple type of PVD coatings 16 . Multiple crack initiation mechanisms, including surface crack initiation and a series of different subsurface crack initiation mechanisms, may occur in the failure of multilayer coatings.…”

The Numerical Modeling of Thermal Stress Distribution in Thermal Barrier Coatings

“…As a result of thermal stresses which accompany the processes of production and operation of elements consisting of parts characterised by different mechanical and thermal properties, one must account for the possibility of internal stresses occurring in the element after its temperature has settled. This problem matters for numerous reasons, including those related to interfaces between ceramic and metallic materials [2][3][4][5][6]. Internal stresses combined with stresses triggered by thermal or mechanical loads may lead to destruction of an element.…”