Thermal stability, mechanical properties, and tribological performance of TiAlXN coatings: Understanding the effects of alloying additions

In tribological applications, the degradation of metallic coatings due to oxidation and thermal softening at high temperatures is an issue of increasing concern. Recently, researchers have focused on the development of durable hard coatings that can perform well under elevated temperatures. The alloying of ternary TiAlN coatings with various elements has received considerable attention due to its ability to improve coating properties at high temperatures by solid solution hardening, grain refinement, formation of new phases, diffusion barriers, and self-lubricious tribo-oxides. This paper reviews the microstructure, thermal stability, oxidation behaviour, and mechanical and tribological properties of resultant quaternary TiAlXN coatings (X = Si, Cr, V, Ta and B). The effects of the deposition parameters, chemical composition, high-temperature annealing, and coating architecture on the coating properties are discussed in depth. The properties of quinary TiAlCrSiN coatings are also reviewed to provide a better understanding of the synergistic effects of Si and Cr additions to TiAlN. The maximum hardness and plastic deformation resistance (H/E and H3/E2) of TiAlXN coatings produced by various deposition techniques are compared. This paper provides useful insights into the challenges and future research perspectives of the reviewed coatings

Enhancement of thermal and mechanical stabilities of silicon doped titanium nitride coating by manipulation of sputtering conditions

This study investigates the influence of substrate (AISI M42 tool steel) bias voltage (from −30 to −80 V), on the mechanical properties of magnetron sputtered TiSiN coating derived from Ti and Si targets. Thermal stability, microstructure (crystallite size, microstrain, lattice constant), morphology and mechanical (hardness, Young's modulus, residual stresses) properties, of the deposited TiSiN coatings, were investigated with synchrotron powered X-ray diffraction (SR-XRD), X-ray photoelectron spectroscopy, field emission scanning electron microscopy, and nanoindentation techniques. Rietveld analysis, of the in-situ SR-XRD, in the temperature range of 25–800 °C, demonstrated cubic TiN form in (Ti,Si)N solid solutions, with TiO2 and Ti2O3 identified at lower bias voltages. Density functional theory supplemented the experimental results. Increase in the bias voltage resulted in: (i) a decrease in Si content, (ii) significant smoothening of surface morphology, (iii) change in the phase composition and microstructure, (iv) improved oxidation resistance and thermal oxidation threshold, and (v) hardness and Young's modulus of the coatings increased up to 50% to 33 GPa and 450 GPa, respectively

A short review on the phase structures, oxidation kinetics, and mechanical properties of complex Ti-Al alloys

This paper reviews the phase structures and oxidation kinetics of complex Ti-Al alloys at oxidation temperatures in the range of 600–1000 °C. The mass gain and parabolic rate constants of the alloys under isothermal exposure at 100 h (or equivalent to cyclic exposure for 300 cycles) is compared. Of the alloying elements investigated, Si appeared to be the most effective in improving the oxidation resistance of Ti-Al alloys at high temperatures. The effect of alloying elements on the mechanical properties of Ti-Al alloys is also discussed. Significant improvement of the mechanical properties of Ti-Al alloys by element additions has been observed through the formation of new phases, grain refinement, and solid solution strengthening

Wear behaviour of Al-SiC and Al-Al2O3 matrix composites sliding against automobile friction material

This paper presents a study on the wear behaviour of metal matrix composites (MMC), which is a criterion for potential material for the development of the automotive brake disc. The wear tests have been carried out on a wear and friction monitor machine, using commercial automobile brake pad as pin and Al-SiC MMC and Al-Al2O3 MMC as discs. Pins have been machined from commercial automobile brake pad of a passenger car. The Al-SiC MMC and Al-Al2O3 MMC discs have been fabricated by stir casting technique using BS 1470 aluminium alloy; 5 wt%, 10 wt% and 15 wt% of silicon carbide particles and alumina particles. The friction and wear behavior of MMCs and the automobile brake pad pins have been investigated at two applied loads; 5N and 10N. The worn surfaces formed on the MMCs discs have been analysed using scanning electron microscopy (SEM). The present investigation shows that the MMCs have considerable stable friction coefficient

Molecular interaction with defected h-BN

Density functional theory simulations studied molecular (Phenol, pyridine, oxygen, and carbon monoxide) interactions with defected h-BN (boron nitride) monolayer structures. The simulation comprised of a supercell modelling the monolayers which contained mono-vacancies (boron or nitrogen) and Stone-Wales defect. Predictions from this analysis indicate that h-BN with vacancies are more reactive to CO and phenol when compared with the Stone-Wales defected configurations. Reacted products entail semiconductor characteristics with a band gap residing in the range 2.6 to 3.96 eV. Outcomes herein reveal a relatively strong interaction of phenol and pyridine, in comparison with smaller diatomic O2 and CO, with defect BN surfaces. A wide array of properties was computed to elucidate an insight into the observed interactive behaviour, including Bader charge’s; local atomic spin polarisation magnetic moments in the vacancy region, and energy band gap of the reaction outcome. These results should be useful in applications that target deployment of BN-based materials in optoelectronic devices, physical–chemical sensors

Sliding wear of electro-carburized mild steel with different microstructures

The tribological behaviour of carburized steel with different microstructures, produced by varying the carburization time was investigated. Increasing the carburization time from 1 h to 3 h resulted in higher hardness and greater martensite content, which had a stronger tendency to form a better anti-wear oxide. In turn, these improved properties enhanced the adhesive wear resistance and delayed the occurrence of fracture. Longer carburization also resulted in the formation of expanded martensite and shallower grain boundaries with fewer precipitates, which further enhanced the fracture resistance of the steel. Larger scale fracture occurring on steel carburized for 1 h resulted in cracked WC grains, the formation of more undermined WC grains and cavities (due to the removal of WC grains) and severe grooving on the cemented carbide counterbody. In conclusion, this carburization process was effective in enhancing the wear resistance of mild steel which subsequently reduced the wear of the cemented carbide counterbody

High temperature (up to 1200 °C) thermal-mechanical stability of Si and Ni doped CrN framework coatings

High temperature thermal-mechanical stability of tribological thin coatings is extremely important to a large number of applications in modern industries. DC magnetron sputtering of single metallic element (Cr, Si) and alloy (Ni:Cr) targets formed transition metal nitrides film coatings, CrSiN and CrNiN onto M2 steel. High temperature in-situ synchrotron X-ray diffraction, in the range 25 °C–700 °C, obtained experimental data for a range of structural and mechanical properties. Furthermore, experimental room temperature Nanoindentation measurements, made before and after the in-situ heating cycle, provided corresponding hardness and shear modulus results. The structural results identified microstructure and phase transformation changes, while the mechanical results identified microstrain, hardness, elastic modulus and deformation resistance properties of the coatings. Density functional theory (DFT) and quasi-harmonic approximation (QHA) modelled the high temperature thermal and mechanical properties such as: Young's modulus, shear modulus and thermal expansion coefficients (populated up to 1200 °C). Estimates of hardness are made by correlating the bulk phase hardness and shear modulus, of the CrN and Ni phases, as a function of temperature. Results indicate that Si doping enhances the hardness of the CrN framework, increasing from 29 to 36 GPa and improves the coatings elastic modulus, and resistance to deformation. However the addition of Ni reduced these properties. Furthermore, formation of (Cr,Si)N and Ni(Cr) solid solutions is inferred from DFT, Rietveld and lattice constant analysis