We review results on the growth of metastable Ti1−xAlxN alloy films by hybrid high-power pulsed and dc magnetron co-sputtering (HIPIMS/DCMS) using the time domain to apply substrate bias either in ...synchronous with the entire HIPIMS pulse or just the metal-rich portion of the pulse in mixed Ar/N2 discharges. Depending upon which elemental target, Ti or Al, is powered by HIPIMS, distinctly different film-growth kinetic pathways are observed due to charge and mass differences in the metal-ion fluxes incident at the growth surface. Al+ ion irradiation during Al–HIPIMS/Ti–DCMS at 500°C, with a negative substrate bias Vs=60V synchronized to the HIPIMS pulse (thus suppressing Ar+ ion irradiation due to DCMS), leads to single-phase NaCl-structure Ti1−xAlxN films (x≤0.60) with high hardness (>30GPa with x>0.55) and low stress (0.2–0.8GPa compressive). Ar+ ion bombardment can be further suppressed in favor of predominantly Al+ ion irradiation by synchronizing the substrate bias to only the metal-ion-rich portion of the Al–HIPIMS pulse. In distinct contrast, Ti–HIPIMS/Al–DCMS Ti1−xAlxN layers grown with Ti+/Ti2+ metal ion irradiation and the same HIPIMS-synchronized Vs value, are two-phase mixtures, NaCl-structure Ti1−xAlxN plus wurtzite AlN, exhibiting low hardness (≃18GPa) with high compressive stresses, up to −3.5GPa. In both cases, film properties are controlled by the average metal-ion momentum per deposited atom transferred to the film surface. During Ti–HIPIMS, the growing film is subjected to an intense flux of doubly-ionized Ti2+, while Al2+ irradiation is insignificant during Al–HIPIMS. This asymmetry is decisive since the critical limit for precipitation of w-AlN, 135 eV-amu1/2, is easily exceeded during Ti–HIPIMS, even with no intentional bias. The high Ti2+ ion flux is primarily due to the second ionization potential (IP2) of Ti being lower than the first IP (IP1) of Ar. New results involving the HIPIMS growth of metastable Ti1−xAlxN alloy films from segmented TiAl targets are consistent with the above conclusions.
•Ti1−xAlxN alloys with high hardness and low residual stress are demonstrated.•Hybrid HIPIMS/DCMS approach with opposing metal targets is used.•Film growth pathways depend upon which metal target is powered by HIPIMS.•Al–HIPIMS/Ti–DCMS alloys have a much higher solid-solubility limit, xmax=0.64.•Low mass and single charge of the Al+ ion permit tuning properties of metastable cubic Ti0.38Al0.62N by adjusting Vs.
A hybrid deposition process consisting of reactive high-power pulsed and dc magnetron cosputtering (HIPIMS and DCMS) from Ti and Al targets is used to grow Ti1−xAlxN alloys, with x~0.6, on Si(001) at ...500°C. Two series of films are deposited in which the energy and momentum of metal ions incident at the growing film are individually varied. In both sets of experiments, a negative bias Vs ranging from 20 to 280V is applied to the substrate in synchronous, as determined by in-situ mass spectrometry, with the metal-ion-rich part of the HIPIMS pulse. Ion momentum is varied by switching the HIPIMS and dc power supplies to change the mass m and average charge of the primary metal ion. Al-HIPIMS/Ti-DCMS layers grown under Al+ (mAl=26.98amu) bombardment with 20≤Vs≤160V are single-phase NaCl-structure alloys, while films deposited with Vs>160V are two-phase, cubic plus wurtzite. The corresponding critical average metal-ion momentum transfer per deposited atom for phase separation is 〈pd⁎〉≥135 eV-amu1/2. In distinct contrast, layers deposited in the Ti-HIPIMS/Al-DCMS configuration with Ti+/Ti2+ (mTi=47.88amu) ion irradiation are two-phase even with the lowest bias, Vs=20V, for which 〈pd⁎〉>135 eV-amu1/2. Precipitation of wurtzite-structure AlN is primarily determined by the average metal-ion momentum transfer to the growing film, rather than by the deposited metal-ion energy. Ti-HIPIMS/Al-DCMS layers grown with Vs=20V are two-phase with compressive stress σ=−2GPa which increases to −6.2GPa at Vs=120V; hardness H values range from 17.5 to 27GPa and are directly correlated with σ. However, for Al-HIPIMS/Ti-DCMS, the relatively low mass and single charge of the Al+ ion permits tuning properties of metastable cubic Ti0.38Al0.62N by adjusting Vs to vary, for example, the hardness from 12 to 31GPa while maintaining σ~0.
•High AlN-content TiAlN films are grown using a hybrid HIPIMS/DCMS.•The average metal-ion momentum transfer per deposited atom determines phase content.•Layers grown with Ti+/Ti2+ ion irradiation are two-phase for each substrate bias Vs.•Layers grown under Al+ bombardment with Vs≤160V are single-phase cubic alloys.
The effect of brittleness and fatigue of mono- and multi-layer PVD films on coated tools cutting performance is introduced. Cemented carbide inserts were coated to the same overall film thickness ...with various numbers of layers. Nanoindentations were conducted to evaluate the hardness of the diverse coating structures. The film brittleness and fatigue were characterized by nano- and macro-impact tests respectively. The coated inserts’ wear behaviour was investigated in milling hardened steel. The attained results revealed the coatings’ brittleness and fatigue endurance enhancement by increasing the number of film's layers. This increase leads simultaneously to the coated tool life improvement.
The inclined impact test is an efficient method for characterizing the fatigue strength of interfaces of nanocrystalline diamond coatings (NCD). During this test, an oscillating oblique load induces ...repetitive shear stresses into the region between film and its substrate. Inclined impact tests were conducted on NCD coated specimens with a thickness of ca. 5μm at forces up to 850N and 1.5million loading cycles. The related imprints were evaluated by confocal microscopy measurements and EDX micro-analyses. Dependent on the applied load, after a certain number of impacts, damages in the film interface region develop resulting in coating detachment. In this way, residual stresses of the film are released leading to its lifting (bulge formation). The bulges are destroyed by further repetitive impacts and the coating is totally removed. The geometry of the developed NCD coating's bulges can be effectively described by appropriate Finite Element Method (FEM) supported calculations. Based on the attained impact test results, Woehler-like diagrams were developed for monitoring the fatigue failure or endurance of NCD coatings at various impact conditions. Employing such diagrams, the fatigue strength of NCD coatings can be assessed. According to the attained Woehler-like diagrams, a threshold load of 730N exists for the film delamination by fatigue in the investigated case.
•The inclined impact test was used for assessing NCD film interface fatigue strength.•Woehler-like graphs show the lower threshold load for film delamination by fatigue.•Above this load, the interface and the film fail as a function of impact conditions.•After the coating detachment, residual stresses are released and film bulges develop.•The film bulge formation is accurately described by FEM-supported calculations.
The effect of two different treatments of cemented carbide substrates, prior to the deposition of a nanocrystalline diamond (NCD) coating, on the film interface fatigue strength was investigated at ...ambient and elevated temperatures. The first substrate treatment of the cemented carbide substrate was a selective chemical Co-etching and the second one the deposition of a Cr-adhesive layer. Inclined impact tests at 25°C and 300°C were performed on the NCD coated specimens. The related imprints were evaluated by confocal microscopy measurements and EDX micro-analyses. The thermal residual stresses developed in the film structure at various temperatures were estimated by Finite Element Method (FEM) calculations. A fatigue damage in the NCD coating interface region was induced by the repetitive impacts. After this damage, the compressive residual stresses in the NCD film are released leading to its lifting from the substrate (bulge formation) and subsequent coating failure. The NCD film-substrate interface fatigue behavior is significantly affected by the test temperature. Based on the attained results at diverse substrate treatments, Woehler-like diagrams were developed for monitoring the fatigue failure of NCD coating interface area at 25°C and 300°C. The interfacial fatigue strength worsens as the impact test temperature grows in both examined substrate treatment cases. Moreover, Co-etched substrates compared to coated ones by an adhesive Cr-interlayer possess higher interfacial strength at ambient and elevated temperatures. These phenomena were investigated and related explanations are described in the paper.
•NCD films' interface fatigue was assessed by inclined impact test at 25°C and 300°C.•During this test, an interfacial damage leads to film detachment and bulge formation.•The fatigue strength of NCD coatings interface worsens as the temperature grows.•This deterioration is more intense in the case of Co-etched hardmetal substrates.•Co-etching leads to higher interface fatigue strength compared to Cr-interlayers.
The paper aims at clarifying whether thick HPPMS (High Power Pulsed Magnetron Sputtering) PVD coatings can be used more effectively in cutting processes compared to thin ones. In this context, ...nano-structured multilayer HPPMS PVD coatings with diverse thickness were deposited on cemented carbide inserts of the same specifications. The deposition of multilayer PVD coatings instead of mono-layer ones on cemented carbide tools contributes to a significant improvement of the coated tool life due to their capability to prevent the crack propagation. The coating's mechanical properties and their gradation versus the film thickness were determined by analytical results' evaluation of nanoindentations on annealed coated specimens. The films' brittleness was assessed by nano-impact tests. The strain rate-dependent fatigue endurance of the applied coatings was determined by means of impact tests with modulated force signals, resembling the developed ones during milling. The coated inserts were used in milling hardened steel. A Finite Elements Method (FEM) simulation of the contact between the coated tool and the workpiece provided information for elucidating the effect of the film thickness on the tool wear evolution. These investigations revealed that via increasing the film thickness the tool life is prolonged almost proportionally with the coating thickness augmentation, thus compensating for their higher cost compared to thin coatings.
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•Cutting tools were coated with nano-structured multilayer films of diverse thickness.•The coating's mechanical properties were determined via innovative test methods.•The film mechanical properties deteriorate when increasing the coating thickness.•The raise in coating thickness enlarges almost proportionally the coated tool life.•The prolonged tool life compensates for the higher cost of a thick coating.
This article deals with the wear mechanisms of variously adherent nano-composite or multi-layer diamond coated tools in milling. The adhesion and residual stresses of these films on cemented-carbide ...inserts were characterized via inclined impact tests at diverse temperatures. The obtained results were evaluated through FEM-supported mathematical methods for estimating the maximum film residual stress and the shear failure stress (SFLS) of the coating-substrate interface. The coated inserts were used in milling AA7075 T6. The developed wear mechanisms were elucidated considering the film structure, the defined temperature-dependent SFLS and the FEM-determined stress and temperature distribution in the tool wedge region during cutting.
The interface fatigue strength of coated tools with nano-crystalline diamond (NCD) coatings affects their milling performance. Depending on the developed cutting loads and temperatures, the ...repetitive impacts on the tool deteriorate progressively the coating-substrate interface strength, thus influencing the effective NCD film adhesion. Aiming at a comprehensive investigation of this effect, NCD coated cemented carbide inserts with improved or insufficient adhesion were manufactured. Hereupon, a parameter characterizing the coatings' interface adhesion strength, the shear failure stress (SFLS) was estimated by inclined impact tests and FEM calculations at ambient and elevated temperatures. This metric is significantly affected, among others, by the compressive residual stresses developed in the NCD film during cooling after its deposition and the coating operational temperature. A correlation between the determined SFLS at the investigated adhesion levels and the FEM calculated maximum shear stress in the coating interface during milling AA 7075T6 contributed to the explanation of the wear evolution on the employed NCD coated tools.
The submitted paper aims at investigating the effect of the interface fatigue strength of NCD coated hardmetal inserts on their cutting performance in milling. The fatigue strength of the NCD coating-substrate interface is a dominant mechanical property for the NCD coated tool life. In the submitted work, NCD coated cemented carbide inserts with different adhesion qualities were manufactured. The interface fatigue strength at temperatures up to 400°C was quantified using a critical shear failure stress (SFLS). This was attained by conducting appropriate FEM supported evaluation of the inclined impact test results at ambient and elevated temperatures. A correlation between the determined SFLS at various adhesion levels and the FEM calculated maximum shear stress in the film interface during milling AA 7075T6 contributed to the explanation of the wear evolution on the employed NCD coated tools. This is a new and original contribution to the field of testing NCD coatings and their effective application in cutting. The submitted paper is not being considered for publication elsewhere.
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•The shear failure stress (SFLS) characterizes the NCD film-substrate adhesion.•The NCD film interface strength was assessed by inclined impact tests up to 400°C.•The obtained results were FEM-evaluated for defining the temperature-dependent SFLS.•The maximum shear stress (τmax) in the film interface during milling was determined.•The wear evolution on the NCD-coated tools was explained by comparing τmax with SFLS.
Micro-crystalline diamond (MCD) coatings were deposited on cemented carbide inserts at different temperatures using hot filament chemical vapor deposition technique. For investigating the effect of ...the developed diamond crystallinity on the fatigue strength and wear behaviour of the prepared MCD coated inserts, inclined impact tests and milling investigations were conducted correspondingly. Raman spectra were recorded for capturing the crystalline phases after the film deposition and their potential changes after the impact and milling experiments induced by the mechanical and thermal loads. Thus, the explanation of the cutting performance of the employed diamond coated inserts with various crystalline phases was enabled.
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