Fjodor Sergejev

Performance of Cemented Carbides in Cyclic Loading Wear Conditions

The present study describes the wear and mechanical behaviour of some carbide composites (TiC-base cermets and WC-base hardmetals) in cyclic loading applications (blanking of sheet metal). Adhesive wear as well as fatigue endurance were tested, followed by XRD measurements. The results show that the blanking performance of a carbide composite is dependent on its level of resistance to adhesion wear and fatigue sensitivity. XRD measurement revealed that fatigue damage is preceded by plastic strain in both the ductile binder and the brittle carbide phase.

Influence of Laser Hardening to the Sliding Wear Resistance of the PVD (Al,Ti)N-G and nACo® Coatings

In the present article, the laser hardening of the carbon steel C45, previously coated by the physical vapour deposition (PVD) process, is studied. The (Al,Ti)N-G and nACo® (nc-AlxTi1-xN/α-Si3N4) coatings were applied. Nd:YAG laser with the laser beam power density of 1945 W/cm2 and scan speed of 300 mm/min was used for hardening process. Laser hardening lead to the formation of hardened layer under both coatings, consisting of austenite and ferrite. The approximate depth of the hardened layer and maximal microhardness was approximately 0.2 mm and 955 HV0.05 and 0.1 mm and 520 HV0.05 in the case of the (Al,Ti)N-G and the nACo® coating, respectively. After laser hardening the sliding wear of the (Al,Ti)N-G coating decreased by 1.25 times and of the nACo® coating by 1.05 times.

Comparison of Curvature and X-Ray Methods for Measuring of Residual Stresses in Hard PVD Coatings

Physical Vapour Deposition and PVD coatings are designed for several applications, from industrial to biomedical. Residual stresses, arising during coating deposition, have important effect on the coating’s service life as their influence to the mechanical and tribological properties. Our aim was to investigate the residual stresses in five different PVD coatings (TiN, TiCN, TiAlN, TiAlN, nc-(AlTi) N/α -Si3N4) (presence of the Ti as adhesion layer) by the layer growing curvature method and the X-ray diffraction techniques using a plate and a strip as the substrate. Residual stresses were compressive and very large (2.98 - 7.24) GPa in all coatings and comparable in TiN, TiAlN, TiAlN coatings in the case of both methods. The magnitude of residual stresses is influenced by intrinsic strain in the case of layer growth rather than by thermal stress.

Impact and Sliding Wear Properties of Single Layer, Multilayer and Nanocomposite Physical Vapour Deposited (PVD) Coatings on the Plasma Nitrided Low-Alloy 42CrMo4 Steel

Current paper handles the comparison of impact wear and sliding wear properties of the hard PVD single layer TiN and Ti(C,N), multilayer (Ti,Al)N and nanocomposite FiVIc® coatings on the plasma nitrided low-alloy 42CrMo4 steel. All the studied coatings demonstrated a relatively high impact wear resistance at the low (104) and medium (105) number of impacts, however, all the studied coatings vanished at the high number of impacts (106). Most extensive wear among the coatings during the sliding wear test was observed for the (Ti,Al)N coating, the FiVIc® showed the least extensive wear; the most extensive wear of the counterbody (hardened steel ball) was registered for the (Ti,Al)N coating, the lowest – for the FiVIc® and Ti(C,N) coatings. The principle wear mechanism of coatings was tribooxidation and mild abrasion, of the counterbody – plastic deformation

Fatigue mechanics of carbide composites

The present article is an overview of mechanical degradation during monotonic and cyclic loading of powder composite materials based on the tungsten- and titanium carbides, also known as hardmetals and cermets. Heterogeneous structure of powder metallurgy (PM) hardmetals and cermets make its difficult to predict their mechanical properties. The TiC-based cermets (with Fe/Ni binder) were tested and results are compared with that of conventional WC-Co hardmetal grades. The three-point bending cyclic and surface fatigue tests are performed in order to define fatigue properties of studied materials. Fatigue crack developments during testing are analysed by scanning electron microscopy (SEM). On the bases of received experimental results and fracture analysis, fatigue failure mechanisms are developed. New numerical model for prediction of fatigue properties is proposed. Tungsten-free composites (cermets) are prospective candidates to replace the hardmetals in metalforming operations (especially blanking of sheet metals). Comparative studies are shown the superiority of the cermets over ordinary hardmetals.

Comparative Study of Adhesive Wear for CoCr, TiC-NiMo, WC-Co as Potential FSW Tool Materials

Friction stir welding is a novel and promising joining process and most common welding tool failure is transformation of geometry caused by wear. In our point of view, this is adhesion wear. The lathe testing of adhesion wear was conducted to compare wear resistance of following materials: Co-25wt%Cr, TiC-25wt%Ni/Mo and WC-6wt%Co. According to characteristics of investigated materials, they are capable to become alternatives for conventional frictional stir welding (FSW) tool materials. Adhesive wear tests were performed by turning aluminium alloy AW6082-T6 at low speed – travel length, turning speed and feed rate were selected to simulate FSW conditions. The adhesive wear was determined as the change of the geometry of the cutting edges of the tool measured using SEM images. Most promising tool material in terms of adhesion wear resistance is WC-Co hardmetal. The two main stages of wear were distinguished: at first, the appearance of intensive adhesion wear followed by steady state wear. Surface fatigue wear complements development of the adhesive wear.

Cyclic Loading of TiCN Coating by Vickers Indentation

Physical Vapour Deposited (PVD) coatings are used in wide range of industrial applications where requirements differ. For example, in cutting applications adhesive-abrasive wear along with high contact stresses prevail and PVD coating with thickness of ~2 μm are used. In forming applications adhesive wear usually dominates and relatively thick PVD coatings (~5 μm) are preferred. For both the applications coatings are subjected to cyclic stress and therefore it is a point of interest to learn the behaviour of PVD coatings with different thickness under cyclic loading. Cracking resistance and fatigue properties of gradient TiCN on hard metal substrate was evaluated by means of the cyclic Vickers indentation method. Hard metal was chosen as a substrate material to avoid pile-up effect and support the hard coating during indentation. The results of the single indentation Vickers test show that secondary radial and circumferential cracks appear in tested coatings already after the first indent. With increasing cycles the cracks grow up to a critical crack length after which the crack length doesn’t increase further. The tested coating thickness has no significant effect on cracking behaviour.

Effect of Sintering Method on Surface Fatigue of Carbide Composites

In this work the influence of sintering method on the surface fatigue of carbide composite was studied. The research focuses on WC-15wt%Co hardmetals prepared using different powders and different sintering techniques and as a result different microstructure: conventional WC+Co powder and novel reactive powder type W+C+Co are sintered using vacuum furnace, compression sintering (sinterhipping) and spark plasma sintering (SPS method). As tungsten carbide is a common material for cold forming punches and surface degradation causes punch failure [1], the tool life can be significantly extended by material surface fatigue life improvement. It is expected that SPS production route of WC-15wt%Co hardmetal will conclude in better microstructure, more even average grain size distribution and smaller residual porosity, and respectively better mechanical and surface fatigue properties compared to conventional production routes. There are some expectations related to the reactive sintering production routes, as this technique promotes the fine microstructure and better mechanical properties.

Comparative Analysis of Residual Stresses Determined by Various Methods in Brush-Plated Hard Gold and Silver Coatings

The investigated brush-plated silver and gold coatings are used for refining the surface properties of electric apparatuses. Tensile residual stresses generated in the plated coatings were determined with a thin-walled ring substrate using the curvature and instrumented indentation techniques. These stresses relax over time; the dependence of relaxation time was approximated by a linear-fractional function. The modulus of elasticity and the nanohardness of the coatings were determined by nanoindentation. The surface morphology and structure in cross-section of the coated substrates are presented.

Investigation of Residual Stresses and some Elastic Properties of Brush-Plated Gold and Silver Galvanic Coatings

Nickel-hardened gold and silver coatings were brush-plated from a commercial SIFCO Dalic Solution (Gold Hard Alloy), Code SPS 5370, and Silver Hard Heavy Build, Code SPS 3080, on unclosed thin-walled copper ring substrates. To determine residual stresses, the conventional curvature method (common among the electrodeposition methods) was applied, where the substrate was coated with certain thickness and then the slit increment (bending deflection) of the substrate was measured as an experimental parameter. Residual stresses on gold coatings were also determined by X-ray diffraction (XRD) based on the sin2 method. The values of residual stresses determined by the curvature method and by the XRD technique were comparable. Relaxation of residual stresses was observed. An equation for approximation of the change of residual stresses was applied assuming that the dependence of residual stresses on relaxation time is linear-fractional. The surface morphology and microstructure of the coatings was studied by means of scanning electron microscopy (SEM). The magnitudes of the modulus of elasticity and of the nanohardness of the coatings were obtained by instrumented indentation.