Ti1−xAlxN films and/or their alloys are employed in many industrial applications due to their excellent mechanical and thermal properties. Synthesized by plasma-assisted vapor deposition, Ti1−xAlxN is reported to crystallize in the cubic NaCl (c) structure for AlN mole fractions below 0.4–0.91, whereas at larger Al contents the hexagonal ZnS-wurtzite (w) structure is observed. Here we use ab initio calculations to analyze the effect of composition and Al distribution on the metal sublattice on phase stability, structure, and elastic properties of c-Ti1−xAlxN and w-Ti1−xAlxN. We show that the phase stability of supersaturated c-Ti1−xAlxN not only depends on the chemical composition but also on the Al distribution of the metal sublattice. An increase of the metastable solubility limit of AlN in c-Ti1−xAlxN from 0.64 to 0.74 is obtained by decreasing the number of Ti–Al bonds. This can be understood by considering the Al distribution induced changes of the electronic structure, bond energy, and configuration...

Influence of the Al distribution on the structure, elastic properties, and phase stability of supersaturated Ti1- xAlxN

This work is focused on the combined study of the evolution of tool wear, quality of machined holes and surface integrity of work-piece, in the dry drilling of alloy Ti–6Al–4V. Tool wear was studied with optical microscope and SEM–EDS techniques. The quality of machined holes was estimated in terms of geometrical accuracy and burr formation. Surface integrity involves the study of surface roughness, metallurgical alterations and microhardness tests. The end of tool life was reached because of catastrophic failure of the drill, but no significant progressive wear in cutting zone was observed previously. High hole quality was observed even near tool catastrophic failure, evaluated from the point of view of dimensions, surface roughness and burr height. However, microhardness measurements and SEM–EDS analysis of work-piece showed important microstructural changes related with a loss of mechanical properties. Depending on the application of the machined component, the state of the work-piece could be more restrictive than the tool wear, and the end of tool life should be established from the point of view of controlled damage in a work-piece.

/pdf/dry-drilling-of-alloy-ti-6al-4v-12a72kf1n8.pdf

Dry drilling of alloy Ti–6Al–4V

Four nitride coatings (CrN, ZrN, CrAlN, and TiAlN) were deposited on YT15 cemented carbide by cathode arc-evaporation technique. Microstructural and fundamental properties of these nitride coatings were examined. Erosion wear tests were carried out, the erosion wear of these nitride coatings caused by abrasive particle impact was compared by determining the wear depth and the erosion rates of the coatings. The wear surface features were examined by scanning electron microscopy. Results showed that the coatings with Al (CrAlN and TiAlN) exhibited higher erosion wear resistance over those without Al (CrN and TiN). The H3/E2 of the coating seemed to play an important role with respect to its erosion wear in erosion tests. AlTiN and CrAlN coatings being with high H3/E2 exhibited lower erosion rates, while CrN coating with low H3/E2 showed higher erosion rates under the same test conditions. Analysis of eroded surface of the coatings demonstrated that the TiN and CrN coatings exhibited a typical brittle fracture induced removal process, while AlTiN and CrAlN coatings showed mainly micro cutting and cycle fatigue fracture of material removal mode.

Erosion wear of CrN, TiN, CrAlN, and TiAlN PVD nitride coatings

CrN/TiN and TiN/AlTiN multilayer coatings with different periods were deposited on cemented carbide cutting tools in an industrial-size cathodic arc evaporation device Nanolayer coatings were particularly studied and the influence of the superlattice period on mechanical behaviors have been investigated Mechanical properties were first correlated to the period of multilayer and nanolayer coatings Machining performance of coated cutting tools were then evaluated by turning Inconel 718 superalloy The decrease of layer periodicity leads to higher microhardness for both compositions Adhesion tests and surface topography analyses indicate better adhesion and lower roughness for CrN/TiN than for TiN/AlTiN coatings All these coatings, especially TiN/AlTiN nanolayers, favorably influence flank wear and cutting time for machining Inconel 718 in relatively severe cutting conditions The relationship between physical properties, coatings compositions and wear mechanisms during machining Inconel 718 is discussed

Deposition, characterization and machining performance of multilayer PVD coatings on cemented carbide cutting tools

This paper discusses the deposition parameters and the properties of cathodic arc deposited single layer and gradient (Ti,Al)N coatings using TiAl cathodes. We noted that the bias voltage had a significant influence on the formation of macro droplets and the number of macro droplets decreased with increasing bias voltage. The hardness decreased with increase of bias voltage from −75 to −300 V and a maximum hardness of 2783±25 HV was achieved at −75 V and at a N2 pressure of 0.66 Pa. The adhesion strengths of (Ti,Al)N coatings deposited on M2 steels were in the range of 44–92 N (Lc1). A high adhesion strength of 92 N (Lc1) was observed for a coating deposited at −75 V and at 1.33 Pa of N2. Gradient coatings deposited by continuously varying the bias voltage during the deposition of coatings exhibited higher values of critical loads of adhesion (Lc1 in the range of 87–97 N and Lc2>120 N) for both positive and negative gradient coatings. The higher critical loads of adhesion observed for gradient (Ti,Al)N coatings suggest that there is an excellent potential to further enhance the wear properties of (Ti,Al)N coatings.

Properties of single layer and gradient (Ti,Al)N coatings

Influence of chromium content on the dry machining performance of cathodic arc evaporated TiAlN coatings

During high-pressure die-casting (HPDC) of aluminium alloys, there is a tendency for the molten alloy to react with the tool steel die, core pins and inserts. This occurrence within the high pressure die casting (HPDC) industry is referred to as ‘soldering’. It is of concern to high-pressure die casters because of down-time due to the regular removal of the soldered layer and its detrimental affect on die life and casting quality. In this investigation, several physical vapour deposited (PVD) coatings, namely, TiN, CrN and TiCN, were evaluated for their ability to eliminate soldering during HPDC of aluminium alloys. Accelerated semi-industrial trials were carried out in a 250-t Toshiba HPDC machine using a specially designed die made of P20 tool steel with removable core pins. The results from these trials showed that PVD coatings can act as a physical barrier coating preventing any reaction between the molten aluminium alloy and the tool steel. Thus the problem of soldering on such tools as core pins can be eliminated in high HPDC of aluminium alloys. In the accelerated trials, it was found that soldering was replaced by a built-up layer of cast aluminium alloy, which was less detrimental to tool life and reduced machine down-time due to the reduced need for tool polishing. The experimental results were confirmed by conducting in-plant HPDC trials.

Performance evaluation of PVD coatings for high pressure die casting

PVD titanium aluminium nitride coatings are known to improve the performance of cutting tools in aggressive machining applications, such as high-speed dry machining. This is generally acknowledged to be due to the fact that these coatings are able to maintain high hardness and resistance to oxidation at the elevated temperatures typically experienced in such metal cutting applications. In this investigation, the performance of single layer coatings of TiN and CrN, and double layer coatings of TiN/TiAlN and CrN/TiAlN were assessed on Co-HSS drills used to machine grey cast iron. It was found that the CrN coatings performed as well as the TiN coatings when drilling grey cast iron. In addition, the double layer coatings outperformed the single layer coatings with the CrN/TiAlN coatings having a 20% improvement in tool life compared with the TiN/TiAlN-coated drills. This result is particularly interesting since the Daimler–Benz indentation test suggested that the TiN/TiAlN had much lower adhesion than the CrN/TiAlN. These results are discussed in terms of an analysis of the physical and mechanical properties of the coatings but it highlights the need for meaningful measurement of critical coating properties which might relate to their performance in metal cutting.

Dry cutting performance of partially filtered arc deposited titanium aluminium nitride coatings with various metal nitride base coatings

Critical to the economic viability of dry machining is justifying increased tool costs in terms of productivity and ecological savings achievable through the elimination of metal cutting fluids. The automotive industry is a large-scale commercial manufacturing sector in which emphasis is placed on reducing impact on the environment as well as seeking to reduce costs in manufacturing. This paper presents results for dry drilling fully pearlitic grey cast iron with uncoated and partially filtered arc deposited TiN and TiAlN coated Co-HSS split point twist drills using two methods to distinguish drill failure, namely audible screech and measurement of outer corner wear lands. The latter method proved to be of most relevance in manufacturing because it is more closely related to the industrial practice of on-condition assessment prior to drill resharpening. Using the outer corner wear method, TiN coatings (3.0 μm thickness) achieved a modest increase in drill life of 1.4 times, compared with significant improvements of 2.6 times, achieved from a TiAlN top coating (0.8 μm thickness) on a base coating of TiN (1.2 μm thickness). This is a novel result in that a thin top coating of the expensive TiAlN coating over the much cheaper TiN coating can provide a very cost-effective tool coating combination.

E.D. Doyle

Papers

Influence of chromium content on the dry machining performance of cathodic arc evaporated TiAlN coatings

Performance evaluation of PVD coatings for high pressure die casting

Dry cutting performance of partially filtered arc deposited titanium aluminium nitride coatings with various metal nitride base coatings

Dry machining — commercial viability through filtered arc vapour deposited coatings

Implications of high strain deformation in grinding