CrN Monolayer Research Articles

Tribological and corrosion testing of surface engineered surgical grade CoCrMo alloy

Abstract One of the main causes of hip prostheses failure is the premature wear of its components. Wear of metal-on-metal joints is a concern due to the toxicity and biological reaction of wear debris and metallic corrosion. The main aim of the present study was to investigate the tribological and corrosion behavior of surface engineering CoCrMo alloy. Different surface conditions were obtained on surgical grade wrought CoCrMo alloy: plasma nitrided (520 °C by 7 h at gas mixture of 10% N 2 + 90% H 2 ), PVD coated (monolayer CrN and multilayer (TiN/CrN) × 3) and modified using duplex surface engineering technology (a combination of the two previous approaches: plasma nitriding followed by plasma assisted PVD). Surfaces were characterized using scanning electron microscopy, nanoindentation, AFM and scratch test. The tribological response of the different surface conditions was studied by means of a ball-on-disc testing machine. Potentiodynamic polarization measurements were done to determine the corrosion rate. Ringer's solution was used as lubricant and electrolyte during the tribological and electrochemical tests, respectively. It was found that the duplex engineering technology enables a significant rise in the resistance of surfaces against concentrated loading modes (evaluated by scratch method); however it has no significant influence in the tribological performance of the samples during wear tests. PVD multilayer (TiN/CrN) × 3 coatings showed the higher wear and corrosion resistance whereas CoCrMo nitrided sample showed the lowest.

Cr 2N/CrN multilayer coatings for wood machining tools

The present paper describes results from a recent research project aimed at forming a wear resistant coating based on chromium on tools to wood machining. Cr 2N/CrN multilayer coatings deposited on HS6-5-2 steel substrates using cathodic arc evaporation were tested. These coatings were formed from 7 bilayers being ca. 340 nm thick and equally thick Cr 2N and CrN layers. For comparison, Cr 2N and CrN monolayer coatings were also prepared. Hardness measurements, indentation and scratch tests, friction and wear were performed to characterize the mechanical properties. The wear tracks and Rockwell indentations enable to assess wear mechanisms of the coatings. The results of the Cr 2N/CrN coatings investigated show high hardness: ca. about 22 GPa and a critical force being higher than 95 N and a low wear rate. The industrial tests of planer knives with Cr 2N/CrN multilayer coatings were carried out on a down-spindle milling machine to determine the durability of tools with wear resistant coatings for woodworking. These tools show increase of “life time” two times. Another positive feature of the use of such tools is the increase of the quality of wood surface machined when compared with uncoated tools.

Performance of nanolayer CrN/Ag coated cutting tools

A nanolayer CrN/Ag coating comprising a lamination of hard transition metal and soft metal was synthesised using an industrial scale four target dc closed field unbalanced magnetron sputtering ion plating system (CFUBMSIPS). For comparison, a monolayer CrN coating was also grown on the same deposition system. Characterisation was conducted using SEM, TEM, XRD and Vickers microhardness and scratch testers. Wear behaviour was studied on an SRV wear tester. Performance of coated cutting tools was evaluated via two kinds of machining tests: one was using the coated microdrills to continuously make through thickness holes on FR4 printed circuit boards and the other using the coated turning cutters to machine S45C steel bars. The structural analysis showed that the nanolayer CrN/Ag coating with bilayer thickness λ 30 nm was composed of alternative stacking layers of pure Ag and CrN phases. The nanolayer CrN/Ag coating, in spite of having lower hardness than the monolayer CrN coating, showed great improvements in the wear resistance and microdrilling and turning performance, which could be attributed to the combination of multilayer structure and lubricating function of Ag.

A comparative study of corrosion resistance in CrN and CrN/Cr coatings, electrodeposited chromium and epoxy paints

This work was aimed at comparing the corrosion resistance of CrN and CrN/Cr coatings deposited through unbalanced magnetron sputtering (UBM), Cr industrial coatings and epoxy paints. UBM coatings were optimised and produced at room temperature, using 400 mA discharge current. Ar and N2 flow rates were set at 9 standard cubic centimetres per minute (SCCM) and 3 SCCM, respectively. Deposition times were set to produce CrN monolayers and nanometric multilayers having 1μm total thickness and 100 nm period. Coating microstructure was determined through scanning electron microscopy as texture and crystalline phases were determined using x-ray diffraction and infrared spectroscopy. Corrosion resistance was studied with anodic polarisation tests using 0.5M H2SO4 and 0.05M KSCN solution. Nanometric multilayers improved stainless steel corrosion resistance and it was observed that coated CrN steel A36 could be an alternative for replacing stainless steel in acid environments. Corrosion mechanisms for the coatings so deposited are discussed.

Nanolayer CrN x/WN y coatings used on micro drills for machining of printed circuit boards

A series of CrN x/WN y nanolayer coatings were synthesized using an industrial-scale four-target DC closed-field unbalanced magnetron sputtering ion plating system (CFUBMSIPS™), employing one W target and three Cr targets. For comparison, a monolayer CrN coating was also grown on the same deposition system. Characterization was conducted using EDX, SEM, TEM, AFM, XRD, nanohardness indentation tester, and scratch tester. Performance of cutting tools with the nanolayer coatings was carried out via machining tests using the coated micro drills to continuously make through-thickness holes on printed circuit boards. The results showed that nanolayer CrN x/WN y coatings with various modulation period ( λ) could be obtained on an industrial-size deposition machine by means of control in the current applied to the W target. Of the studied nanolayer CrN x/WN y coatings, the one with λ = 27 nm showed the highest nanohardness and best micro drilling performance. This nanolayer coating showed significant improvements in cutting performance as compared with the referred monolayer CrN coating.

Investigation of the microstructure and characterizations of TiN/CrN nanomultilayer deposited by unbalanced magnetron sputter process

In this study, TiN, and CrN, monolayer thin films and a TiN/CrN multilayer thin film were deposited onto WC substrates by unbalance DC magnetron sputtering. Single-layer TiN and CrN thin films were prepared at various nitrogen flow rates (20–30 sccm). TiN/CrN multilayers with a monolayer thickness of 4 nm were also deposited on the WC substrates. The morphology, and crystalline structures of the as-prepared films were characterized by SEM and XRD, and their mechanical properties and thermal stabilities were also evaluated. The experimental results show that the grain size of the columnar structure increased with the nitrogen flow rate. The increase in the size of the grains in the columnar structure, however, can be minimized with an applied bias voltage of 100 V. When the nitrogen flow rate was increased from 20 to 30 sccm, β-Cr 2N transformation to CrN was observed, while the TiN structure remained unchanged. The hardnesses of the TiN and CrN thin films were ~ 23.9 and 21.4 GPa, respectively. A significant increase in the hardness of the TiN/CrN multilayer thin film to 34.9 GPa (4 nm interval) could be observed. Scratch test results also show that the multilayer has more desirable properties than the monolayers. The critical load for the TiN/CrN multilayer thin film (45.0 N) was higher than that for the TiN (~ 24.8 N) or CrN (~ 37.3 N) monolayer thin films. After annealing at 800 °C, no significant phase transformation and decrease in mechanical properties of the TiN/CrN multilayer thin film could be observed.

Tribological behavior of CrN/WN multilayer coatings grown by ion-beam assisted deposition

CrN monolayer coating and CrN/WN multilayer coatings were deposited on the silicon (100) substrate by ion-beam assisted deposition process. The bilayer period of these coatings was controlled at 8 nm and 30 nm. The cross-sectional morphology of nanoscaled multilayer coatings was characterized by scanning electron microscopy and transmission electron microscopy. The wear resistance of CrN/WN multilayer coatings and CrN monolayer coating was investigated using a pin-on-disc tribometer. The surface roughness (Ra) of the coatings was evaluated by atomic force microscopy, and that of CrN and WN monolayer coating was 6.7 and 5.9 nm, respectively. The employment of multilayer configuration in CrN/WN coating with bilayer period of 8 nm and 30 nm effectively reduced the surface roughness down to 1.9 and 2.2 nm, respectively. The friction coefficient of CrN monolayer coating and CrN/WN multilayer film with a bilayer period of 30 nm was 0.63 and 0.31, respectively. Owing to the high hardness/elastic modulus ratio, as well as the dense structure and the smooth surface roughness, the CrN/WN multilayer coatings exhibited better wear resistance in the consideration of friction coefficient and the worn surface morphology.

Variables affecting the fatigue resistance of PVD-coated components

The effect of intrinsic properties of CrN coatings on fatigue behaviour was studied in this paper. The coating layer microhardness and the residual stresses characterising the surface film were measured and the obtained results were introduced in a numerical modelling predicting fatigue life procedure of coated components. The effect of a CrN monolayer film deposited on bulk samples, produced in 2205 duplex stainless steel, H11 tool steel or 6082 aluminium alloy was investigated. The fatigue limit of coated and uncoated samples was experimentally determined while the development of FEM models, confirmed by means of experimental tests, represents a powerful tool to predict fatigue life of coated components. The effects on the fatigue strength of coating and bulk material defects like droplets and non-metallic inclusions were considered along with the residual stress gradient characterising the coating and evaluated by means of X-ray measurements. The influence of the substrate material plastic deformation on the integrity of the coating was evaluated too.

Structure and properties of wear resistance PVD coatings deposited onto X37CrMoV5-1 type hot work steel

The paper presents results of the investigation of the structure, mechanical properties and tribological tests of CrN, TiN, TiN/(Ti,Al)N PVD coatings deposited onto X37CrMoV5-1 type hot work steel. Thin hard coatings are today employed in vast number of applications for reducing friction and wear of tools and mechanical components, however there are still big interest to improve tools used in hot-working process e.g. metal die casting, hot extrusion and hot forging as well as glass and plastics processing. The goal of this investigation is to determine usefulness of that coatings type deposition in order to improve wear resistance of tools made from hot work steels. Based on the results of metallographic examinations of microstructure it was shown that TiN, TiN/(Ti,Al)N coatings have compacted, columnar structure while CrN coating has compacted submicrocrystalline structure. According to the observations made after scratch test we found the highest adhesion for CrN monolayer coating and the lowest one for multilayers TiN/(Ti,Al)N coating. Moreover it was found that failure mechanism during scratch test in all investigated coatings begins with multiple spallings located on the scratch edges followed by cracking and total delamination of coating. The wear resistance was investigated by pin-on-disc method performed in room and elevated to 500 °C temperatures. We found that the lowest wear at certain conditions in both room and elevated temperatures shows TiN monolayer coating what can be connected with their good adherence to the substrate materials as well as the highest hardness.

Improvement of wear resistance of hot work steels by PVD coatings deposition

The paper presents results of structure, phase composition, tribological and adhesion investigations of wear resistance PVD coatings TiN, TiN/(Ti, Al)N and CrN types deposited in ion plating PVD process onto X37CrMoV5-l type hot work tool steel.The X-ray quantitative phase analysis makes it possible to find out the preferential crystallographic orientation (111) for the monolayer TiN coating and for the multilayer TiN/(Ti, Al)N one. The diffraction line broadening in case of the CrN coating attests to occurrence of strong internal stresses or to small sizes of its constituent crystallites.It was found that failure mechanism during the scratch test in all investigated coatings begins with multiple spallings located on the scratch edges followed by cracking and total delamination of coating. Regarding to the coating types different location of such damages and loads typical for them can be seen. According to those observations we found that highest adhesion among investigated coating present, CrN monolayer coating and the lowest one for multilayers TiN/(Ti, Al)N coating.The wear resistance was investigated by the pin-on-disk method performed at the room temperature and the one elevated to 500°C. We found that the lowest wear in to fixed investigation conditions in both room and elevated temperatures show TiN monolayer coating. Additionally, one can see that TiN coatings application improves wear resistance for about five times.

Fine structure of tempered Fe-Cr-N martensite

Abstract The structure of Fe-5.9%Cr-0.5%N, quenched and tempered in the range 25–550°C, has been investigated by electron microscopy, electron and X-ray diffraction, and measurement of microhardness. The observations are interpreted in terms of a continuous precipitation series of structural intermediates between the solid solution and equilibrium fcc CrN. At low temperatures the atomic arrangement of the finely dispersed precipitates or zones is similar to that in α″-Fe16N2, whereas at higher temperatures the zones consist of Cr-N monolayer plates on the cube planes of the matrix. At all stages of tempering the precipitation gives rise to ‘tweed’ contrast in electron micrographs and associated electron diffraction streaking, which is shown to arise from an array of tetragonal strain centres arranged such that the total strain energy is minimized.