Machinability analysis of dry and liquid nitrogen–based cryogenic cutting of Inconel 718: experimental and FE analysis

Inconel 718 is famous for its applications in the aerospace industry due to its inherent properties of corrosion resistance, wear resistance, high creep strength, and high hot hardness. Despite the favorable properties, it has poor machinability due to low thermal conductivity and high hot hardness. To limit the influence of high cutting temperature in the cutting zone, application of cutting flood is recommended during the cutting operation. Cryogenic cooling is the recommended method when machining Inconel 718. However, there is very limited literature available when it comes to the numerical finite element modeling of the process. This current study is focused on the machinability analysis of Inconel 718 using numerical approach with experimental validations. Dry and cryogenic cooling methods were compared in terms of associated parameters such as chip compression ratio, shear angle, contact length, cutting forces, and energy consumption for the primary and secondary deformation zones. In addition, parameters related to chip morphology were also investigated under both lubrication methods. Chip formation in cryogenic machining was well captured by the finite element assisted model and found in good agreement with the experimental chip morphology. Both experimental and numerical observations revealed comparatively less chip compression ratio in the cryogenic cooling with larger value of shear plane angle. This results in the smaller tool–chip contact length and better comparative lubrication.

A Comparative Study on the Tribological Properties of a Cobalt-Free Superaustenitic Stainless Steel at Elevated Temperature

The properties of a cobalt-free cast superaustenitic stainless steel (SASS) is investigated comparatively to the commercial high-cobalt alloyed GX15CrNiCo21-20-20 (1.4957, N-155) steel regarding its global hardness and wear resistance at elevated temperature by means of in situ hot hardness tests and cyclic abrasive sliding wear tests against an Al2O3 (corundum) counter-body at 600 °C. In the aged condition, results show that the 1.4957 steel suffers a higher material loss due to brittle failure initiated by coarse eutectic Cr-rich carbides which are incorporated into a mechanically mixed layer during abrasive loading. In contrast, within the Co-free steel eutectic M6(C,N) carbonitrides are distributed more homogeneously showing less tendency to form network structures. Due to the combination of primary Nb-rich globular-blocky MX-type carbonitrides and eutectic M6(C,N) carbonitrides dispersed within an Laves phase strengthened austenitic matrix, this steel provides comparable hardness and significantly improved wear resistance at elevated temperature. Thus, it may be an adequate alternative material to commercial SASS and offers the possibility to save cobalt for future applications.

HOT HARDNESS MEASUREMENTS ON MATERIALS UP TO 600 °C DURING THE FIRST HOUR OF USING

In the aeronautical field, materials are used in severe environmental conditions (temperature, atmosphere, exposure time ...), particularly for engine applications. In order to characterize the use of these materials in the evaluation of their properties, it is necessary to carry out tests in conditions close to their operating environment. Hot hardness is a simple method which can be applied on many different materials such as oxidized layers, coatings, composite materials, brazing cords, additive manufacturing materials. ONERA is developing micromechanical characterization means to carry out Vickers microhardness tests from room temperature up to 600 °C. In principle, a pyramidal punch is applied on the surface of a material and the applied load is continuously measured during indenter’s moving in the material. The material is tested locally under conditions close to the actual conditions of employment. The goal of this research is to improve microindentation in order to achieve temperature test campaigns up to 600 °C under a controlled atmosphere of argon and to validate a method to produce a series of results during the first hour of using up to 600 °C. Stainless material is studied to compare the evolution of its hot hardness properties versus different parameters such as load, holding time at the maximum load, atmosphere, and thermal duration. A discussion about these measurements and the technical limits of hot hardness technology is presented.

Effect of C Content on High Temperature Erosive Wear Characteristics of Fe-Based V Containing Multi-Component Cast Steel with Ni

Hot hardness and oxidation property of target material influences greatly on the erosion behavior at elevated temperature. The correlation between hot hardness and oxidation property of multi component white cast irons and its erosion resistance were investigated, and try to estimate the high temperature erosion behavior in the study. Nine kinds of multi component white cast iron and cast steel were used in this study. Specimen were machined into a flat plate with dimension of 50×50×10 mm. High temperature erosion test machine was used to investigate the erosive wear property of experimental materials at 1173K. Alumina grits (average diameter: 1.16 mm, hardness: 1250 HV1) which were used as impact particles were heated to 1073K and shoot on the heated specimen by hot air at the velocity of 100 m/s. The total particle loading was 2 kg. In order to clarify the correlation of hot hardness, oxidation property and the erosion resistance of specimens, hot hardness test was carried out specimens, to estimate erosion damage caused by solid particle. Hot hardness of specimens showed a value comparable to 200～250HV1. Result of erosion and oxidation tests, erosion rate and amount of oxidation of the specimen were suppressed by Ni addition. It suggested that the more amount of Ni contents, the lower the erosion rate and the less the amount of oxidation.

Welding Parameters and their Influence on the Abrasion Resistance of Structural Steels at Elevated Temperatures

In several industrial applications wear resistance of structural steels is required. Also enhanced temperature can occur when handling hot materials, e.g. in steel industry. Within this study a low alloyed structural steel (carbon steel S355) and a high temperature (HT) 9 % Cr steel ASTM A332 P92 were chosen for investigation. Repair welds with flux cored wires which are often required in applications were investigated, aiming on the role of interpass temperatures, the resulting effect of cooling conditions on the microstructure and their HT abrasion resistance. The influence of different microstructural parameters such as phase content, processing and the resulting temperature-hardness coherence on the wear resistance are evaluated within a high temperature abrasion test and a hot hardness test rig. Results indicate a strong influence of interpass temperature and heat input on the hot hardness and wear behaviour of welded structural steels.

Towards High Productive Roughing of Profiled Grooves in Nickel Based Alloys

Facing a high demand for aircraft engines over the next decades in combination with new challenging materials, aircraft engine manufacturers are striving for new manufacturing processes. The manufacturing of profiled grooves for the mounting of the turbine blades on the disc is a bottle neck process today due to the exclusive use of High Speed Steel (HSS) tools in broaching. Because of the limited hot hardness of HSS, the applied cutting speeds are low compared to other conventional machining processes, i.e. 2–5 m/min. Furthermore, the broaching process has some more drawbacks regarding flexibility, capital commitment for machinery and tools as well as costs. Nevertheless, broaching offers outstanding properties regarding surface finish, manufacturing accuracy and is still a productive process due to the many cutting edges applied. There are some alternative process chains which are not yet in industrial use, which are able to substitute and/or complement the HSS-broaching process. In this paper, results are presented on two different roughing strategies for the manufacturing of profiled grooves in Nickel Based Alloys Allvac718plus and Inconel718. On the one hand, rough broaching with cemented carbide tools using indexable inserts was investigated at different cutting speeds, which are up to five times higher than the applied cutting speeds in industrial applications with HSS-tools. Two different carbide grades were investigated varying the cobalt content and the grain size. Cemented carbide is not state of the art in broaching Nickel Based Alloys due to its low fracture toughness. Different cutting edge inclination angles were applied and their effect on cutting forces, wear and tool chipping tendency were analyzed. On the other hand, rough side milling with ceramic cutting tools was investigated. Ceramic cutting tools excel in high hot hardness and thus can be used at very high cutting speeds i.e. up to 1000 m/min in Nickel Based Alloys. However, being very brittle and sensitive to alternating loads and thermal shock, machining processes with ceramic tools require extensive process design. In side milling experiments, Whisker reinforced as well as SiAlON and Oxide ceramic were investigated. In a first step, a window for machining parameters was identified. Then, tool life tests were conducted varying the feed at a fixed cutting speed of 1000 m/min. Subsequent to the experiments, the rim zone of the roughed grooves was investigated depending on the wear state of the used tools. The condition of the rim zone is a major criterion for the assessment of the adequacy of the roughing processes, because it can affect the subsequent finishing process. In further work, the interdependencies between the investigated roughing processes and finishing will be addressed.

Analysis of Properties of Hard Coatings and Wear Resistance of Chemical Vapour Deposition (PVD) Coated Technology

Modern coating methods are having become an important part of industry. Wear resistance, durability, toughness (breakage resistance) and hot hardness (high hardness and chemical stability at high temperature) are the four main technological properties necessary for durability and long life time. These proprieties are for productivity, economy and ecology very important point. This resource deals with the analysis of properties of hard coatings and wear resistance of chemical vapour deposition (PVD) coated technology. It focuses on the preparation, execution and evaluation of test coatings on the front ball-milling cutters. Examination of these characteristic properties may give into an insight to the reason why some systems show excellent wear characteristic.

Effect of Heat Treatment Process of Sintered M3/2 High Speed Steel Parts

Dry machining is one of the ways to achieve a reduction of cooling lubricants, as well as reduced environmental pollution and lower health risk to workers. This leads to higher mechanical and thermal loading on cutting edges. The adaptation of cutting tools to the requirements of dry machining includes the optimisation of manufacturing technologies, the development of cutting materials of sufficient toughness and high hot hardness, the design of tool geometries as well as the coating of tools [.