Effect of alloyed target vis-à-vis pure target on machining performance of TiAlN coating

Typically closed-field unbalanced magnetron sputtering (CFUBMS) and controlled cathodic arc deposition techniques having four or six pure or alloyed targets are employed for commercial titanium aluminium nitride (TiAlN) coating of cutting tools. The role of the use of alloyed target vis-à-vis pure target on the coating characteristics and the machining performance of TiAlN-coated tools has not been studied in detail. In the present work, TiAlN coating has been deposited on cutting tools using a pulsed DC, dual-cathode CFUBMS system to capture the role of the type of target on machining performance. The deposition rate in the case of the alloyed target has been found to be much higher as compared to the pure target. Such coatings deposited from alloyed targets also provided significantly better machining performance in dry turning of low-carbon and high-carbon steel. Dry turning of SAE 1070 high-carbon steel at 160 m/min did not yield more than 100 μm of average flank wear on the same insert coated using alloyed targets for a machining time of more than 3 min

Lubricated sliding wear mechanism of chromium-doped graphite-like carbon coating

The current research aims to discuss the tribological behaviour of Chromium-doped graphite-like carbon coatings and suggest a wear mechanism under both dry (in air) and boundary lubricated sliding condition based on phase composition of the wear product generated in wear track during pin-on-disc experiments. As expected, the friction coefficient reduces from 0.22 to 0.12 due to addition of lubricant. Raman analysis indicates that wear mechanism is oxidative in dry sliding condition whereas it is chemically reactive in the presence of lubricant. It is speculated that the key-factor of reduced friction and wear coefficient in lubricated condition is the formation of CrCl3 due to tribochemical reaction between coating and oil. CrCl3 has graphite-like layered structure; therefore it acts like solid lubricant

Isothermal and dynamic oxidation behaviour of Mo−W doped carbon-based coating

The oxidation behaviour of Mo−W doped carbon-based coating (Mo−W−C) is investigated in elevated temperature (400°C−1000°C). Strong metallurgical bond between Mo−W−C coating and substrate prevents any sort of delamination during heat-treatment. Isothermal oxidation tests show initial growth of metal oxides at 500°C, however graphitic nature of the as-deposited coating is preserved. The oxidation progresses with further rise in temperature and the substrate is eventually exposed at 700°C. The performance of Mo−W−C coating is compared with a state-of-the-art coating, which shows preliminary oxidation at 400°C and local delamination of the coating at 500°C leading to substrate exposure. The graphitisation starts at 400°C and the diamond-like structure is completely converted into the graphite-like structure at 500°C. Dynamic oxidation behaviour of both the coatings is investigated using Thermo-gravimetric analysis carried out with a slow heating rate of 1°C/min from ambient temperature to 1000°C. Mo−W−C coating resists oxidation up to ~800°C whereas delamination of coating is observed beyond ~380°C. In summary, Mo−W−C coating provides improved oxidation resistance at elevated temperature compared to coating

Tribological study of novel metal-doped carbon-based coatings with enhanced thermal stability.

Low friction and high temperature wear resistant PVD coatings are in high demand for use on engine components, which operate in extreme environment. Diamond-like-carbon (DLC) coatings are extensively used for this purpose due to their excellent tribological properties. However, DLC degrades at high temperature and pressure conditions leading to significant increase in friction and wear rate even in the presence of lubricant. To withstand high working temperature and simultaneously maintain improved tribological properties in lubricated condition at ambient and at high temperature, both the transitional metals Mo and W are simultaneously introduced in a carbon-based coating (Mo-W-C) for the first time utilising the benefits of smart material combination and High Power Impulse Magnetron Sputtering (HIPIMS).This research includes development of Mo-W-C coating and investigation of thermal stability and tribological properties at ambient and high temperatures. The as-deposited Mo-W-C coating contains nanocrystalline almost X-ray amorphous structure and show dense microstructure, good adhesion with substrate (Lc -80 N) and high hardness (-17 GPa). During boundary lubricated sliding (commercially available engine oil without friction modifier used as lubricant) at ambient temperature, Mo-W-C coating outperforms commercially available state-of-the-art DLC coatings by providing significantly low friction (u- 0.03 - 0.05) and excellent wear resistance (no measurable wear). When lubricated sliding tests are carried out at 200°C, Mo-W-C coating provides low friction similar to ambient temperature, whereas degradation of DLC coating properties fails to maintain low friction coefficient.A range of surface analyses techniques reveal "in-situ" formation of solid lubricants (WS2 and M0S2) at the tribo-contacts due to tribochemically reactive wear mechanism at ambient and high temperature. Mo-W-C coating reacts with EP additives present in the engine oil during sliding to form WS2 and M0S2. This mechanism is believed to be the key-factor for low friction properties of Mo-W-C coating and presence of graphitic carbon particles further benefits the friction behaviour. It is observed that low friction is achieved mostly due to formation of WS2 at ambient temperature, whereas formation of both WS2 and M0S2 significantly decreases the friction of Mo-W-C coating at high temperature. This further indicates importance of combined Mo and W doping over single-metal doping into carbon-based coatings.Isothermal oxidation tests indicate that Mo-W-C coating preserves it's as-deposited graphitic nature up to 500°C, whereas local delamination of DLC coating leads to substrate exposure and loss of its diamond-like structure at the same temperature. Further, thermo-gravimetric tests confirm excellent thermal stability of Mo-W-C coating compared to DLC. Mo-W-C coating resists oxidation up to ~800°C and no coating delamination is observed due to retained coating integrity and its strong adhesion with substrate. On the other hand, state-of-the-art DLC coating starts to delaminate beyond ~380°C.The test results confirm that Mo-W-C coating sustains high working temperature and simultaneously maintains improved tribological properties during boundary lubricated condition at ambient and high temperature. Thus Mo-W-C coating is a suitable candidate for low friction and high temperature wear resistant applications compared to commercially available state-of-the-art DLC coatings

Superplastic behaviour of Ti54M and Ti64

Even though TIMETAL-54M (Ti-5Al-4V-0.6Mo-0.4Fe or Ti54M) has been commercially available for over 10 years, further study of its superplastic properties is still required in order to assess its applicability within the aerospace industry as a potential replacement for other commercial titanium alloys such as Ti-6Al-4V (Ti64). Ti54M is expected to obtain superplastic characteristics at a lower temperature than Ti64 due to its lower beta-transus temperature. The superplastic forming (SPF) capability of alloys that can be formed at lower temperatures has always attracted the interest of industry as it reduces the grain growth and alpha-case formation, leading to longer life for costly high temperature resistant forming tools. In this work, the SPF characteristics of both Ti54M and Ti64 have been examined by conducting tensile tests according to the ASTM E2448 standard within a range of temperatures and strain values at a fixed strain rate of 1x104/s. A high strain rate sensitivity and uniform deformation at high strains are key indicators in selecting the optimum superplastic temperature. This was observed at 815˚C and 925˚C for Ti54M and Ti64 respectively. The tensile samples were water quenched to freeze their respective microstructure evolution following superplastic deformation and SEM images were captured for grain size and volume fraction of alpha-phase analyses. A slightly higher alpha-grain growth rate was observed during superplastic deformation of Ti64. The initial fine-grain microstructure of Ti54M (~1.6 micron) resulted in a final microstructure with an average grain size of ~3.4 micron and optimum the alpha/beta ratio. Both the fine-grained microstructure and increased amount of beta-volume fraction promotes the superplastic behaviour of Ti54M by grain boundary sliding (GBS). Thus superplastic properties were observed for Ti54M at a lower temperature (~100˚C) than for Ti64

Microstructural evolution of SA508 grade 3 steel during hot deformation

SA508 grade 3 steel is widely used in the manufacture of large-scale forged components for nuclear reactor applications. Numerical models have already been established to simulate industrial forging process of grade 3 steel; however, limited information is available on the microstructural evolution of this steel during hot forging operation. This work focuses on the flow behavior and related microstructural evolution in grade 3 steel with detailed analysis on the interfacial friction, texture and hardness evolution. Uniaxial hot compression tests were conducted over a range of test temperatures (880-1130 °C) and true strain rates (0.001-1/s), representative of the industrial hot forging conditions. Two different deformation mechanisms, MDRX at the lowest forging temperature and DRV along with DRX at the highest forging temperature, were observed showing marked impact on the final microstructure and hardness. A random fiber-type weak deformation texture was observed irrespective of the test temperatures and strain rates used. The microstructural changes from the as-received to the various deformed conditions were quantified. The quantitative data are the key to obtain accurate parameters for DRV and DRX processes that affect the accuracy of the mathematical models

A study on microstructural evolution in cold rotary forged nickel-superalloys : C263 and Inconel 718

C263 and Inconel 718 are precipitation hardenable nickel-superalloys widely used in different sections of a gas turbine engine dependent on their strength and temperature capability. Cold rotary forging is an effective route for manufacturing axisymmetric components with significantly higher material utilisation as compared to machining from conventional hot forgings. This paper presents a study on how C263, an alloy system strengthened by γ', and Inconel 718, an alloy system strengthened by γ'' and δ, deform during the cold rotary forging process and how their microstructures evolve. The two alloys exhibit maximum formability in solution-annealed condition. In this study, both C263 and Inconel 718 were annealed before the cold rotary forging operation. Parts with a 90° bend flange were successfully cold rotary forged from tubular preforms with a wall thickness of 6 mm. For both the alloys, the cold rotary forged parts exhibit significant differences in material properties from the undeformed sections to the most deformed section (i.e. the flanges). Post-forging heat-treatments are required to impart the desired material properties throughout the part. Therefore, appropriate annealing and aging treatments were identified for each of the two alloys. These heat-treatments led to uniform material properties for both deformed and undeformed sections of the cold rotary forged flanges in case of both the alloys

Cold rotary forging of Inconel 718

The present work includes an in-depth study of microstructure and mechanical property development in a cold rotary forged component manufactured from Inconel 718 alloy. This work is pioneering in that there is no detailed study available in the literature focussing on cold rotary forging of Inconel 718. A tubular preform of 6 mm wall thickness was cold rotary forged into a 90 degree flange part followed by annealing with double aging. The present study provides a thorough analysis of microstructure, hardness and surface roughness evolution from as-received to final cold rotary forged and heat-treated condition including crystallographic texture changes occurring at different stages. The solution-annealed condition of the preform was found to be most suitable for cold rotary forging of Inconel 718. An annealing treatment followed by double-aging imparted desired properties such as homogeneous microstructure, uniform hardness distribution and improved surface roughness into the cold rotary forged Inconel 718 flange. The cold rotary forging can be a cost-effective route for manufacture of axisymmetric components with high material yield and low buy-to-fly ratio for expensive materials such as Inconel 718

Impact of a multi-step heat treatment on different manufacturing routes of 18CrNiMo7-6 steel

Effect of an optimized multi-step heat treatment routine on conventional (machining from wrought bar stock) and alternate manufacturing routes (hot forging and cold rotary forging) for producing flat cylindrical-shaped machine drive components from 18CrNiMo7-6 steel was investigated. The microstructure and mechanical properties of the final component manufactured using these three different routes were analyzed using optical microscopy, electron backscatter diffraction (EBSD), hardness testing, electro-thermal mechanical testing (ETMT), and rotary bending fatigue testing (RBFT) before and after implementing the multi-step heat treatment. It was found that the multi-step heat treatment transformed the as-received microstructure into the tempered martensitic microstructure, improving hardness, tensile, and fatigue properties. The heat treatment produced desired properties for the components manufactured by all three different routes. However the cold rotary forging, which is the most material utilizing route over the others, benefited the most from the optimized heat treatment

Mechanical and microstructural analysis of Ti-6Al-4V material in a wide range of superplastic forming conditions

In order to accurately define the superplastic forming (SPF) conditions of Ti-6Al-4V material, an understanding of the stress-strain behaviour, the initial microstructure, and their evolution during superplastic deformation are required. Ti-6Al-4V material with microstructure beneficial for SPF was superplastically tested according to the ASTM E2448 standard considering a wide range of forming conditions in terms of temperatures (750°C – 830°C) and strain-rates (seven strain-rates ranging from 5∙10^(-5) s^(-1) to 〖5∙10〗^(-2) s^(-1)) – some of the tests of the 3×7 matrix are considered “extreme” conditions from an SPF point of view. The material showed improved superplastic behaviour, which was evident from the stress levels and strain-rate sensitivity values as estimated from the flow curves obtained for the different conditions. In comparison with other commercial alloys or results from similar analyses published in the last decades, low stress values and high strain-rate sensitivity (m) values were obtained despite the low temperatures and high strain-rates used in this analysis. The tests were interrupted when 0.5 true strain (65% engineering strain) was achieved followed by quenching, as this was the maximum local strain achieved when forming the component of interest. Samples did not show any sign of premature necking or failure, with the exception of the two most “extreme” cases. Particularly for the lower strain-rates (below 10^(-4) s^(-1)), some level of material hardening associated with a minimum grain growth was observed in the flow curves. In contrast, a noticeable material softening was observed for the higher strain-rate conditions (above 5∙10^(-3) s^(-1)), associated with the microstructural changes occurring due to dynamic recrystallization. These higher strain-rates led to formation of submicron-sized grains, which could have helped in the superplastic response of the material under these strain-rate conditions. Intermediate strain-rates (5∙10^(-4) s^(-1) and 10^(-3) s^(-1)) showed a different type of response in terms of microstructural behaviour (and flow curve outline) depending on the testing temperature. A negligible amount of cavitation was observed in the samples tested under extreme conditions