TiAlBN Coatings Research Articles

Influence of nitrogen gas flow on the hardness and the tribological properties of a TiAlBN coating deposited by using a magnetron sputtering process

With a view to improving the mechanical properties of coatings applied in the field of cutting tools and machine parts, the TiAlBN coatings were deposited by using direction-current (dc) magnetron sputtering with the various contents of nitrogen gas in an argon-nitrogen gas mixture. The structural characteristics of the coatings were determined by using X-ray diffraction, the friction coefficient, and the hardness and elastic modulus of the coatings were investigated by using a tribometer and nano-indentation. The surface morphologies and the roughnesses of the coatings were analyzed by using field emission scaning electron microscopy (FESEM) and atomic force microscopy (AFM). Additionally, the effects of nitrogen gas flow on the properties of the TiAlBN coatings were investigated. The structural characterization results revealed a typical face-centered cubic TiN structure with (111), (220), and (222) diffraction peaks. The strongest intensity in the (111) orientation was obtained for the coating prepared at a nitrogen gas flow of 4 sccm. For this kind of samples were obtained the highest values of the hardness and the stability, a low friction coefficient, and a smooth surface.

Nanocomposite TiAlBN Coatings as a Corrosion Protection Layer for AZ91 Mg Alloy Substrate in NaCl

Magnesium alloys create increasing interest in structural application where weight reduction is vast concern. However, one of magnesium drawback in various applications is low corrosion resistance. In general, a hard coating can be applied on metal to combat such a problem. AlN and TiN coatings are most widely utilized in manufacturing area i.e for structural application due to its high hardness, high chemical stability, and excellent adhesion to substrates. Most recent, TiAlBN coating catch many attentions due to its superior properties than other most studied hard coating. The incorporation of aluminium in the cubic face centered TiN structure on Ti sites leads to deformation and strengthening of the crystal structure of the coating together. Moreover, incorporation of BN in this coating should improve and enhanced the corrosion resistance of Mg alloy. Therefore, in this study, TiAlBN coating have been chosen to be deposited on Mg alloy using reactive magnetron sputtering together with AlN and TiN coatings for comparison study. During depositions, target power, working pressure and bias voltage are optimized for each coating. Analysis on the effect of AlN, TiN and TiAlBN coatings on Mg alloy substrate include thickness measurement and microstructure by scanning electron microscope (SEM). Coatings phase were analysed using glancing angle X-ray diffraction analysis (GAXRD) and corrosion properties were evaluated using potentiodynamic polarization in NaCl solution. TiAlBN shows better performance of corrosion protection with the least corrosion rate (penetration rate = 0.20 mm/yr; mass loss rate=0.97g/m2d) in sodium chloride (NaCl) solution although having the lowest coating thickness (412 nm).

Corrosion Performance of Nitrided Based Coating on AZ9I Mg Alloy in Hank’s Solution

The use of Magnesium alloys as bioresorsable metallic implant is interesting to study due to the properties of magnesium ions which can be found naturally in bone tissue as well as are essential to human metabolism. However, its fast degradation rate and excess of these ions in the body may cause undesirable health effects. Therefore, surface treatment such as coating can offer an alternative solution to slow down the fast degradation rate of magnesium alloy. Thus, in this study, attempt has been made to coat the AZ91 magnesium alloy substrate with TiN, AlN and TiAlBN coatings using single hot press target with r.f. magnetron sputtering technique. During deposition, target power, working pressure and bias voltage were optimized for each coating deposition. Coating microstructure and its crystal phases are analysed using SEM and glancing angle X-ray diffraction analysis (GAXRD). Corrosion properties were evaluated using potentiodynamic polarization using Hank’s Solution as a medium to simulate body fluid. Result showed that TiAlBN coating is acting most successfully as a protection layer by slowing down the penetration of corrosion towards AZ91 Mg alloy substrate. SEM micrographs show a minimum damage to the substrate’s surface seen after subjected to corrosion test. In conclusion, TiAlBN coating is able to protect AZ91 Mg alloy substrate surface from corrosion and able to slow down their degradation rate. The better performance of TiAlBN coating create interest to further works on exploring the potential of this hard coated on AZ91 Mg alloy for biomaterial application.

Effect of Nitrogen-to-Total Gas Flow Ratio on the Nanocomposite TiAlBN Coating

A nanocomposite TiAlBN (n-TiAlBN) coating has been successfully deposited via RF magnetron sputtering by varying the nitrogen-to-total gas flow ratio (RN) at a substrate temperature of 300 °C. The coating was deposited on AISI 316 substrates using a single Ti-Al-BN hot-pressed target. The crystal phases, grain size and chemical composition of the coatings were measured using the glancing angle X-ray diffraction analysis (GAXRD) and X-ray photoelectron spectroscopy (XPS). The grains size of the n-TiAlBN coating was found to be within the range of 3.5 to 5.7 nm calculated using Scherrer’s formula. The n-TiAlBN coating reached a nitride saturated state at a higher RN (e.g >15%) with the amount of boron concentration to be around 9 at. %. Further, reducing the RN (e.g. 5%) has increased the boron concentration to 16.17 at. %. This paper shows that by carefully control the nitrogen-to-total gas flow ratio (RN) in the n-TiAlBN coating, it indeed gives a significant effect on its crystallographic structure, grain size, and chemical compositions.

Characterization of TiAlBN Nanocomposite Coating Deposited via Radio Frequency Magnetron Sputtering Using Single Hot-Pressed Target

TiAlBN coatings have been deposited at varying bias voltage of 0, -60, and-150 V by radio frequency (RF) magnetron sputtering technique. A single hot-pressed Ti-Al-BN target was used for the deposition process. With glancing angle X-ray diffraction analysis (GAXRD), the nanocrystalline (nc-) (Ti,Al)N phase was identified. In addition, the existence of BN and TiB2amorphous (a-) phase were detected by X-ray photoelectron spectroscopy (XPS) analysis. Thus, the deposited TiAlBN coatings were confirmed as nc-(Ti,Al)N/a-BN/a-TiB2nanocomposite. On the other hand, it was found that optimum bias voltage used in present study is-60 V where the deposited TiAlBN coating exhibits an excellent adhesion quality. The adhesion quality of the coatings deposited at-60V bias voltage is classified as HF 1 evaluated using the Rockwell-C adhesion test method (developed by the Union of German Engineers).

A study of the nanostructure and hardness of electron beam evaporated TiAlBN Coatings

TiAlBN coatings have been deposited by electron beam (EB) evaporation from a single TiAlBN material source onto AISI 316 stainless steel substrates at a temperature of 450 °C and substrate bias of − 100 V. The stoichiometry and nanostructure have been studied by X-ray photoelectron spectroscopy, X-ray diffraction and transmission electron microscopy. The hardness and elastic modulus were determined by nanoindentation. Five coatings have been deposited, three from hot-pressed TiAlBN material and two from hot isostatically pressed (HIPped) material. The coatings deposited from the hot-pressed material exhibited a nanocomposite nc-(Ti,Al)N/a-BN/a-(Ti,Al)B 2 structure, the relative phase fraction being consistent with that predicted by the equilibrium Ti–B–N phase diagram. Nanoindentation hardness values were in the range of 22 to 32 GPa. Using the HIPped material, coating (Ti,Al)B 0.29N 0.46 was found to have a phase composition of 72–79 mol.% nc-(Ti,Al)(N,B) 1 − x + 21–28 mol.% amorphous titanium boride and a hardness of 32 GPa. The second coating, (Ti,Al)B 0.66N 0.25, was X-ray amorphous with a nitride+boride multiphase composition and a hardness of 26 GPa. The nanostructure and structure–property relationships of all coatings are discussed in detail. Comparisons are made between the single-EB coatings deposited in this work and previously deposited twin-EB coatings. Twin-EB deposition gives rise to lower adatom mobilities, leading to (111) (Ti,Al)N preferential orientation, smaller grain sizes, less dense coatings and lower hardnesses.

Structure, hardness and thermal stability of TiAlBN coatings grown by alternating deposition of TiAlN and BN

Hardness and thermal stability of TiAlBN coatings prepared by alternating deposition of TiAlN and BN with high rotation speed of substrate holder (∼7 rpm) have been investigated. The TiAlN and BN were deposited by reactive sputtering of Ti 0.5Al 0.5 and BN targets with N 2 and Ar reactive gases, respectively. Despite alternating deposition, the TiAlBN coating did not show layered structure due to high rotation speed of substrate holder. By TEM analysis, the TiAlBN coating was observed to be nanocomposite with grain less than 10 nm in size. Compared to TiAlN coating, the TiAlBN nanocomposite coating showed superior hardness. Furthermore, the hardness of the coating increased after the heat-treatment in N 2 atmosphere up to 800 °C. By comparison with TiAlN/BN nanoscale multilayered coating prepared by the same deposition method except the lower rotation speed of substrate holder (∼1 rpm), the hardness enhancement after annealing, ‘self-hardening’, of the TiAlBN nanocomposite coating is believed to be due to the sharpness in chemical composition at the interface between TiAlN and BN phase.

Internal stress in TiAlBN at high temperatures

Hard TiAl(B)N coatings were deposited by radio-frequency magnetron sputtering in reactive mode in an argon and nitrogen environment using a TiAlB target with 12 at.% of boron. The deposition was carried out under ion bombardment at various negative bias voltages in the range of 0 to 170 V, and at substrate temperatures between 453 and 523 K. The internal stress in the coatings was studied at room temperature as a function of annealing temperatures in ambient air up to 1123 K. The heating duration was 2 h followed by annealing for 1 h. The microstructure, phase composition and hardness were also studied prior to and after annealing. We found that the TiAlBN coatings consist of TiAl 3 and TiN phases. With increasing ion bombardment, the structure of the coatings changes from columnar to nano-scale features. Prior to annealing we also observed a correlation between the residual stress and hardness. After annealing, the compressive stresses of the TiAl(B)N coatings decreased from 1.0 GPa to less than 0.2 GPa, while the hardness remained constant or increased from ∼ 10 GPa to ∼ 25 GPa. The hardness increase of the coatings after annealing is related to a self-hardening effect.

Hard and superhard TiAlBN coatings deposited by twin electron-beam evaporation

Superhard nanostructured coatings, prepared by plasma-assisted chemical vapour deposition (PACVD) and physical vapour deposition (PAPVD) techniques, such as vacuum arc evaporation and magnetron sputtering, are receiving increasing attention due to their potential applications for wear protection. In this study nanocomposite (TiAl)B x N y (0.09 ≤ x ≤ 1.35; 1.07 ≤ y ≤ 2.30) coatings, consisting of nanocrystalline (Ti,Al)N and amorphous BN, were deposited onto Si (100), AISI 316 stainless steel and AISI M2 tool steel substrates by co-evaporation of Ti and hot isostatically pressed (HIPped) Ti–Al–B–N material from a thermionically enhanced twin crucible electron-beam (EB) evaporation source in an Ar plasma at 450 °C. The coating stoichiometry, relative phase composition, nanostructure and mechanical properties were determined using X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD), in combination with nanoindentation measurements. Aluminium (∼ 10 at.% in coatings) was found to substitute for titanium in the cubic TiN based structure. (Ti,Al)B 0.14N 1.12 and (Ti,Al)B 0.45N 1.37 coatings with average (Ti,Al)N grain sizes of 5–6 nm and either ∼ 70, or ∼ 90, mol% (Ti,Al)N showed hardness and elastic modulus values of ∼ 40 and ∼ 340 GPa, respectively. (Ti,Al)B 0.14N 1.12 coatings retained their ‘as-deposited’ mechanical properties for more than 90 months at room temperature in air, comparing results gathered from eight different nanoindentation systems. During vacuum annealing, all coatings examined exhibited structural stability to temperatures in excess of 900 °C, and revealed a moderate, but significant, increase in hardness. For (Ti,Al)B 0.14N 1.12 coatings the hardness increased from ∼ 40 to ∼ 45 GPa.

Electron spectroscopic studies of nanocomposite PVD TiAlBN coatings

A range of TiAlBN coatings have been deposited by electron beam evaporation and the optimised composition exhibits a 150% improvement over single phase TiAlN coatings in drilling tests. The coatings have been analysed by core level XPS to investigate the phase composition and bonding. Grain sizes have been determined by TEM. Al substitutes into the TiN phase and the coatings show a phase composition in agreement with that predicted by the (Ti,Al)BN equilibrium phase diagram. The optimum microstructure for wet drilling applications consists of 26 nm (Ti,Al)N grains separated by 3 nm regions of amorphous BN. As the grain size increases, a new B 1s component develops, attributable to B either incorporated into the (Ti,Al)N phase or located at grain boundaries.

Evaluating the microstructure and performance of nanocomposite PVD TiAlBN coatings

Physical vapour deposition (PVD) TiAlBN coatings can exhibit excellent wear resistance, with optimised coating compositions demonstrating a 150% increase in lifetime compared to standard TiAlN coatings in wet-cutting drill tests. For various TiAlBN compositions deposited by electron-beam evaporation, the stoichiometry and relative phase composition were determined using X-ray photoelectron spectroscopy (XPS) and the microstructure was examined by transmission electron microscopy (TEM). Al was found to substitute for Ti into the cubic TiN structure. In accordance with their position in the Ti(Al)BN phase diagram, all coatings exhibited a three-phase composition of (Ti,Al)N+BN+TiB 2. The TiB 2 content was very small and the microstructure was effectively that of a (Ti,Al)N and BN dual-phase coating. Optimum drilling performance was obtained for a coating with a phase fraction of approximately 90% (Ti,Al)N and 10% BN. The microstructure can be described as nanocrystalline (Ti,Al)N grains separated by an intergranular amorphous BN phase, in which the average (Ti,Al)N grain size and grain separation was determined to be 26 and 3 nm, respectively. The presence of a compliant intergranular phase permits some degree of grain displacement under load, reducing the elastic modulus, leading to greater toughness and wear resistance.

Deposition and characterisation of TiAlBN coatings produced by direct electron-beam evaporation of Ti and Ti-Al-B-N material from a twin crucible source

TiAlBN coatings were synthesised by evaporating Ti and hot isostatically pressed TiAl 0.68B 3.67N 2.44 material from a twin crucible source in an Ar plasma at 450 °C. A combination of optical emission spectroscopy and partial pressure control was utilised to control the Ti and TiAl 0.68B 3.67N 2.44 evaporation rates and hence the Ti-Al-B-N composition in the coating. The goal of this investigation was to study the influence of composition on the structural and mechanical properties of these coatings. The influence of the Ti/B ratio (in the range of 0.34–2.31) in TiAlBN coatings containing approximately 12 at. % Al and 40 at. % N (calculated from glow discharge optical emission spectroscopy data) is described. All coatings, consisting of two hard phases TiB 2 and TiN, and a soft hexagonal BN phase, showed dense structures and a decrease in roughness values with increasing Ti/B ratios. The hardness and elastic modulus increased with increasing Ti/B ratios from 0.34 to 2.31 up to 37 GPa and 320 GPa, respectively. Coatings with Ti/B = 1.73–2.31 showed a twofold increase in wet cutting performance compared to commercially available TiN and TiAlN. However, due to the rather low amount of Al in the TiAlBN coatings no significant improvement in dry cutting compared to TiN was observed.