M. R. M. Toff

EFFECT OF COATING THICKNESS ON THE PROPERTIES OF TiN COATINGS DEPOSITED ON TOOL STEELS USING CATHODIC ARC PVD TECHNIQUE

Titanium nitride (TiN) widely used as hard coating material, was coated on tool steels, namely on high-speed steel (HSS) and D2 tool steel by physical vapor deposition method. The study concentrated on cathodic arc physical vapor deposition (CAPVD), a technique used for the deposition of hard coatings for tooling applications, and which has many advantages. The main drawback of this technique, however, is the formation of macrodroplets (MDs) during deposition, resulting in films with rougher morphology. Various standard characterization techniques and equipment, such as electron microscopy, atomic force microscopy, hardness testing machine, scratch tester, and pin-on-disc machine, were used to analyze and quantify the following properties and parameters: surface morphology, thickness, hardness, adhesion, and coefficient of friction (COF) of the deposited coatings. Surface morphology revealed that the MDs produced during the etching stage, protruded through the TiN film, resulting in film with deteriorated surface features. Both coating thickness and indentation loads influenced the hardness of the deposited coatings. The coatings deposited on HSS exhibit better adhesion compared to those on D2 tool steel. Standard deviation indicates that the coating deposited with thickness around 6.7 μm showed the most stable trend of COF versus sliding distance.

MACRODROPLET REDUCTION AND GROWTH MECHANISMS IN CATHODIC ARC PHYSICAL VAPOR DEPOSITION OF TiN FILMS

Cathodic arc physical vapor deposition (CAPVD) a technique used for the deposition of hard coatings for tooling applications has many advantages. The main drawback of this technique is the formation of macrodroplets (MDs) during deposition resulting in films with rougher morphology. The MDs contamination and growth mechanisms was investigated in TiN coatings over high-speed steel, as a function of metal ion etching, substrate bias, and nitrogen gas flow rate; it was observed that the latter is the most important factor in controlling the size and number of the macrodroplets.

EFFECT OF SUBSTRATE BIAS VOLTAGE ON THE MICROSTRUCTURAL AND MECHANICAL PROPERTIES OF TiN-COATED HSS SYNTHESIZED BY CAPVD TECHNIQUE

Titanium nitride (TiN) films were deposited on high-speed steel (HSS) using cathodic arc physical vapor deposition (CAPVD) technique. The effect of substrate bias on the crystallography, microstructure, deposition rate, coating thickness and composition, hardness, and adhesion strength of TiN films was investigated. The crystallography of the films was investigated using X-ray diffraction with glazing incidence angle technique. The coating microstructure and elemental composition analysis were carried out using field emission scanning electron microscopy (FE-SEM) together with energy-dispersive X-ray. Crystallography of the films revealed that the effect of substrate bias shows complex symmetry in crystal structure. The resputtering effect due to the high-energy ion bombardment on the film surface influenced the thickness as well as the color of deposited coatings. By increasing the substrate bias from 0 to - 150 V, the size and amount of macrodroplets decreased, whereas the micro-Vickers hardness decreased from 2530 HV0.05 to 1500 HV0.05. Scratch tester used to compare the critical loads for coatings and the adhesion achievable at substrate bias of - 50 V was demonstrated, with relevance to the various modes.

EFFECT OF SUBSTRATE BIAS ON FRICTION COEFFICIENT, ADHESION STRENGTH AND HARDNESS OF TiN-COATED TOOL STEEL

In the present study, TiN coatings have been deposited on D2 tool steel substrates by using cathodic arc physical vapor deposition technique. The objective of this research work is to determine the usefulness of TiN coatings in order to improve the micro-Vickers hardness and friction coefficient of TiN coating deposited on D2 tool steel, which is widely used in tooling applications. A Pin-on-Disc test was carried out to study the coefficient of friction versus sliding distance of TiN coating deposited at various substrate biases. The standard deviation parameter during tribo-test result showed that the coating deposited at substrate bias of -75 V was the most stable coating. A significant increase in micro-Vickers hardness was recorded, when substrate bias was reduced from -150 V to zero. Scratch tester was used to compare the critical loads for coatings deposited at different bias voltages and the adhesion achievable was demonstrated with relevance to the various modes, scratch macroscopic analysis, critical load, acoustic emission and penetration depth. A considerable improvement in TiN coatings was observed as a function of various substrate bias voltages.

DEPOSITION AND CHARACTERIZATION OF TiN-COATED STEELS AT VARIOUS N2 GAS FLOW RATES WITH CONSTANT ETCHING BY USING CAPVD TECHNIQUE

Cathodic Arc Physical Vapor Deposition (CAPVD), a technique used for the deposition of hard coatings, for tooling applications, has many advantages. The main drawback of this technique is the formation of macrodroplets (MDs) during deposition, resulting in films with rougher morphology. Constant etching, by increasing nitrogen gas flow rate up to 200 sccm, helped in reducing the MD size and number; at higher rates, of say 300 sccm, the behavior was reversed. Minimum value of surface roughness recorded at 200 sccm was measured via both surface roughness tester and atomic force microscopy (AFM). Micro-Vickers hardness of TiN-coated tool showed about 564% times increase in hardness than the uncoated one. Scratch tester was used to study the critical loads for the coating and the excellent adhesion achievable, of say 200 sccm, was demonstrated, with relevance to the various modes.

INFLUENCE OF NITROGEN FLOW RATE ON FRICTION COEFFICIENT AND SURFACE ROUGHNESS OF TiN COATINGS DEPOSITED ON TOOL STEEL USING ARC METHOD

In the present study, the effect of various N2 gas flow rates on friction coefficient and surface roughness of TiN-coated D2 tool steel was examined by a commercially available cathodic arc physical vapor deposition (CAPVD) technique. A Pin-on-Disc test was carried out to study the Coefficient of friction (COF) versus sliding distance. A surface roughness tester measured the surface roughness parameters. The minimum values for the COF and surface roughness were recorded at a N2 gas flow rate of 200 sccm. The increase in the COF and surface roughness at a N2 gas flow rate of 100 sccm was mainly attributed to an increase in both size and number of titanium particles, whereas the increase at 300 sccm was attributed to a larger number of growth defects generated during the coating process. These ideas make it possible to optimize the coating properties as a function of N2 gas flow rate for specific applications, e.g. cutting tools for automobiles, aircraft, and various mechanical parts.

An Investigation of Phase Crystallinity in Laser Modified Yttria Stabilized Zirconia (YSZ) Thermal Barrier Coating

This paper presents laser surface modification process of plasma sprayed yttria stabilized zirconia (YSZ) thermal barrier coating (TBC) for enhanced hardness properties and low surface roughness. A 300W JK300HPS Nd: YAG laser was used to process YSZ TBC sample surface. The parameters selected for examination were laser power, pulse repetition frequency (PRF) and residence time. Micrographs of the TBC system were captured using EVO 15 Scanning Electron Microscope (SEM). Surface roughness was measured using 2-dimensional stylus profilometer. X-ray diffraction analysis (XRD) was conducted to measure phase crystallinity of the laser-modified coating surface. X-ray diffraction patterns were recorded in the 2θ range of 10 to 80° using Bruker D8 Advance system with 0.7Å wavelength from a copper source (~1.5Å). The laser modified surface exhibited higher crystallinity compared to the as-sprayed samples. The presence of tetragonal phase was detected in the as-sprayed and laser processed samples. The hardness properties of laser modified TBC increased 15% of the as-sprayed sample. These finding are significant to development of thermal barrier coating design optimization for enhanced surface properties of semi-solid forming die.

Thermal barrier coatings on laser surface modified AISI H13 tool steel using atmospheric plasma spray technique

This paper presents yttria-stabilized zirconia (YSZ) coating deposition on laser surface modified H13 tool steel using atmospheric plasma spray (APS) technique. A Praxair Plasma Spray System with SG-100 gun was used to deposit coating materials on laser-modified H13 tool steel substrate surface. A bond coat layer material was NiCrAlY alloy while the top coat was yttria stabilized zirconia (YSZ) with powder size distribution range of-106 μm to +45 μm. A 23 design of experiment (DOE) was used to deposit bond coat and top coat powders with three controlled factors of input current, powder feed rate and stand-off-distance. The design was optimised for minimum porosity and maximum hardness. The coating thickness and percentage of porosity were measured using IM7000 inverted optical microscope. Hardness properties of top coating layer were measured by using MMT-X7 Matsuzawa Hardness Tester Machine with Vickers hardness scale. The microscopy findings indicated variations of coating thickness at different parameters settings. Samples at the highest current and powder feed rate and lowest stand-off distance settings produced a lower porosity percentage and higher hardness. A higher powder feed rate with the smallest stand-off-distance allowed melted powders to travel uniformly onto the substrate surface. These findings were significant to development of thermal barrier coatings on semi-solid forming die surface.

Growth Defects and Surface Roughness in TiN-Coated Tool Steel at Various N2 Gas Flow Rates Using Cathodic Arc PVD Technique

In the present study, titanium nitride coatings on tool steel were deposited using cathodic arc physical vapour deposition technique. We studied and discussed the effect of various nitrogen gas flow rate on the surface properties of TiN-coated steel. The coating properties investigated in this work include the surface morphology, surface roughness, line profile and fractal dimension analyses using atomic force microscope. Minimum values for surface roughness, line profile and fractal dimension analyses were recorded at nitrogen gas flow rate of 200 sccm. This is mainly because of the reduction in macro-droplets and minimization of the growth defects, usually produced during etching and deposition stages. Critical limit of nitrogen gas flow rate in TiN coatings were identified and considered an important aspect to understand the performance of TiN PVD-coated steel.

Effect of substrate temperature on the properties of TiN coatings deposited on tool steels using ARC

TiN coatings on tool steels were produced via cathodic arc PVD technique. We studied and discussed the effect of substrate temperature on microstructural and mechanical properties of TiN-coated tool steels. The coating properties investigated include crystallography, surface morphology, thickness, adhesion and microhardness. XRD studies revealed that the peaks intensities increased with substrate temperature. SEM analysis of coating showed uniform and dense structure. Coating deposited at 450°C shows about 11% increase in hardness compared to coating deposited at 150°C. The coatings deposited on HSS exhibited better adhesion compared to those on D2 tool steel.