Proceedings of the Symposium of Aeronautical and Aerospace Processes, Materials and Industrial Applications

This work presents the effects of the solid solution and double aging heat treatments of the superalloy Inconel 718 (I-718) and the characterization of their microstructure properties by optical microscope (OM), scanning electronic microscope (SEM), hardness Vickers (HV), and hardness (RA, RB, and RC). The relationship between microstructure and mechanical properties, according to the norm AMS5663 (Aerospace Material Standards, USA), was studied too. Solid solution heat treatments were performed at 1078 °C/1 h and water quenching. Double aging heat treatment was carried out at 720 °C/8 h and then cooling furnace 1 h to 620 °C/8 h and then cooling by air. Solid solution heat treatment dissolved precipitates, and boundary grains and δ phase (Ni₃/Nb) also reduced hardness which facilitates specimens machining with dimensions and morphology; these dimensions will be used for future ultrasonic fatigue testing and have been obtained according to a modal analysis by finite element method. Once specimen machining was completed, double aging heat treatment (precipitation hardening) was performed; this heat treatment leads to increased hardness according to the norm AMS5663 for subsequent tests in ultrasonic fatigue.

Welding as a manufacturing process on aeronautical industry is necessary for component integration. In the aircraft manufacturing, the use of aluminum alloys is widely extended. However, in these alloys if fusion welding is applied, some microstructural alterations, deleterious phases, and distortion are presented and decrease the mechanical properties of the joint. The aluminum matrix composites (AMCs) present many advantages of traditional aluminum alloys; superior properties are achieved when ceramic particles are added making them suitable for aeronautic industry. The disadvantages for AMCs with fusion welding processes are: agglomeration of the particles, lack of fusion, porosity, and many other welding defects. Recently, the solid-state welding processes are gaining acceptance due to high-quality joints, defect-free, and environmental cleaner processes, mainly the friction stir welding (FSW). Hence, FSW is commonly employed for joining these materials, and many studies have been published where the tool is the principal subject; they are mainly focused in tool wear rather than geometry influence on microstructure. Therefore, this investigation was performed in order to observe the effects of geometry differences; the aim was to examine the microstructural evolution of the welded joints. Optical and scanning microscopes (OM and SEM) were employed for the evaluation, resulting in a partial grain refinement in the thermomechanical affected zone, for the aluminum matrix and eutectic silicon, and for the fracture of the silicon carbides. In addition, orientation imaging microscopy (OIM) using electron backscatter diffraction (EBSD) technique was employed to analyze the dynamic recrystallization. Some welding defects were presented along the joint for one tool. Finally, hardness Vickers evaluation on the joints was completed resulting in differences between the two employed tools.

The decomposition of martensite and precipitation presented during this process in the FV535 high-chromium martensitic steel and the effect on mechanical properties were studied. FV535 steel is used in petrochemical plants, gas turbine engineering, aircraft, and aerospace industries. The decomposition of martensite has been divided in six different stages, occurring at different temperature ranges, which can vary depending on the steel composition and microstructure; these stages were analyzed by DSC, and in order to analyze the change in mechanical properties, the FV535 steel was characterized by microhardness tests. The precipitation phenomena that occurred in this type of steel were analyzed by DSC and transmission electron microscopy and were correlated with the change in mechanical properties at high temperatures.

An overview of the use of shock isolators based on dry friction is briefly presented, and the possibilities for the development of a more efficient shock isolation system are discussed. Cable isolators, also known as wire rope isolators, are studied and their characteristics are discussed. Such isolators present nonlinear stiffness behaviour in different directions, i.e. tension-compression, roll and shear, as well as dry friction damping. These isolators show hysteresis when subjected to cyclic loading and are known for being excellent shock isolators. However, little is known about the actual dynamic behaviour under shock loading. The Bouc-Wen model of hysteresis is widely used for representing the dynamic behaviour of nonlinear systems and structures under cyclic loading, as it can reproduce a variety of softening and hardening hysteresis loops by proper selection of its parameters. Recently, the interest towards the use of this model has increased, particularly for the modelling of dry friction isolators, such as wire rope springs. This chapter presents a theoretical analysis of the shock response of isolators based on the Bouc-Wen model, considering different scenarios for hardening and softening parameters. Different parameters such as absolute and relative response are studied, and the advantages and issues are discussed. It is concluded that the combination of nonlinear stiffness and damping could lead to improved vibration and shock isolation.

It is well known that sprayed Ni-based alloy coatings show good corrosion resistance. They have good wear resistance after adding W and Mo elements to the alloy. High-velocity oxygen-fuel (HVOF) spraying is a thermal spray technique well matched to obtain corrosion- and wear-resistant coatings. Post-spray treatments such as laser remelting, shot peening, HIP, sealing, and furnace heat treatments are also used to improve the density and homogeneity of sprayed coatings. The corrosion properties of Ni-based alloy coatings processed by HVOF thermal spraying were studied as a function of annealing heat treatment at 850 and 950 °C in atmosphere of vacuum and air. Immersion tests in HCl, NaOH, and water media with various electrochemical techniques such as linear polarization resistance (LPR) and potentiodynamic anodic polarization curves (PAPC) were employed to perform such evaluation. The microstructural characterization of the as-sprayed coatings was analyzed by scanning electron microscopy (SEM). The results show that when the heat treatment temperature increases, the corrosion current density gradually decreases. This implies that thermally treated coatings increase its corrosion resistance relative to the coating of the substrate and heat treatment. Finally, it was found that a heat treatment at 950 °C in vacuum atmosphere improves the corrosion resistance of Ni-based coating applied by HVOF thermal spray.

In the aeronautical industry, precipitation hardenable (PH) stainless steels are accessories used in aircraft, turbine blades, and other parts. These alloys are alloys of iron, chromium, and nickel, characterized by mechanical strength obtained through age hardening by heat treatment. The addition of elements such as Al, Ti, Mo, and Cu lead to the appearance of intermetallic compounds. In this work, we performed electrochemical corrosion testing of 17-4 PH and 17-7 PH stainless steels with cyclic polarization and linear polarization resistance tests, showing the susceptibly of these stainless steels to pitting and intergranular corrosion. These tests were carried out in an electrochemical cell with a saturated calomel reference electrode at room temperature. The solutions were hydrochloric acid (HCl), sodium chloride (NaCl), and neutral (H₂O) environments. The results in the neutral environment showed that 17-4 PH had more pitting than 17-7 PH; they had similar behavior in a salty environment. 17-4 PH and 17-7 PH generally presented corrosion in an acid environment. The susceptibility to corrosion of stainless steel types 17-4 PH and 17-7 PH was demonstrated; however, the environment is a vital factor in the behavior of this steel.

The austempered ductile iron (ADI) is a material which has great potential when talking about applications relating wear resistance, high strength, toughness, and ductility. This material has a unique microstructure, consisting of a matrix of high carbon austenite and a mixture of ferrite and carbides. This microstructure provides mechanical properties much higher than other iron castings. Usually ADI is used on automotive industry, such as suspension parts, arrows, and crankshafts. It is also used on the aeronautical industry, in the building process of aircraft landing gear. In certain applications where ADI is used, its corrosion resistance must be a transcendental property; nonetheless owing to its structure, the ADI doesn’t possess pretty noticeable resistance to corrosion. Despite this, it’s of huge interest to know how different parameters on heat treatment (applied to ADI) may affect the ADI microstructure, and it can disturb its behavior due to those variables, and in consequence its application areas could be reduced. In this paper we analyze the corrosion resistance presented by ADI irons, after having been subjected to different austempered treatments (different temperatures within the austenitizing muffle furnace and salt bath). The austenitizing temperatures evaluated were 815, 870, and 930 °C, where the waiting time used was 90 min. On the other hand, the salt bath was used at a temperature of 250 and 400 °C, having the waiting time of 60 min. The corrosion resistance was evaluated on two different solutions (NaCl and H₂SO₄), supporting this with two different electrochemical techniques, the linear polarization resistance (LPR) and potentiodynamic polarization curves (CPC). The outcomes show that the temperatures of the salt bath play a crucial role in evaluating the corrosion resistance of these irons.

Corrosion is one of the greatest threats to civil and military aircraft. In general, the materials that make up aircraft structures are subjected to stresses, causing embrittlement and consequent cracks and fractures. Corrosion and erosion of the aircraft coating, induced by the dynamic chemical environment of the atmosphere, manifests as pitting on the surface material. Because they concentrate the stress, these pits are vulnerable to stress corrosion cracking. In current stress corrosion cracking tests on aeronautics materials, parts constructed from corrosive media are held in universal machines. However, the obtained results do not reflect the flight conditions of the aircraft. Therefore, we propose wind tunnel tests that can assess stress corrosion cracking under simulated flight conditions.

In the aeronautical industry, the effects of corrosion are reflected in high costs of maintenance and equipment inactivity, as well as in safety risks for personnel. Modern aircraft are manufactured using different types of metal alloys, for example, civil aircraft are constructed with heat-treated aluminum alloys and military aircraft with titanium alloys and stainless steels. The objective of this study is to use electrochemical techniques to determinate the layer passivate of stainless steel (SS) 304, 17-4PH, and 15-5PH. Passivation of the SS was performed in 15% citric acid at temperatures of 25 and 49 °C. The corrosion kinetics was obtained using the electrochemical technique as potentiodynamic polarization curves (PPC) in a three-electrode system: the electrolytes used were sodium chloride (NaCl) and sulfuric acid (H₂SO₄). Passivation in citric acid allows obtain passive layers at temperatures of 49 °C with immersion times of 30 min. Precipitation hardening steels allow to obtain passive layers up to 360 mV in sodium chloride (NaCl), and in sulfuric acid there is a mechanism of passivation-transpassivation-secondary passivation, this due to the high electropositive values ​​of potential above 1000 mV.

The components of aircraft engines require high strength materials at high temperatures and corrosion. The nickel-based superalloys possess mechanical properties that are directly dependent on grain size; the aeronautical components with coarse grain size are usually employed to minimize creep deformation, while those with finer grain size have the mission to increase the fatigue resistance. One of the advantages of the ring rolling process is the favorable grain flow and good surface quality of the rolled rings. This paper shows the numerical simulation of the hot ring rolling process, where two initial grain sizes are used, one of 20 μm, this being the fine grain size, and 80 μm for analysis of coarse grain size. Both simulations are conducted at an initial temperature of 1100 ° C. At the conclusion of the process, both simulations presented a refinement in grain size, proving the efficiency of rolling.

Titanium alloys, especially Ti-6Al-4V, have been widely used in the aerospace industry due to their high specific strength, high heat-resistant, and high corrosion-resistant properties. This alloy is used in current airframe applications for medium-sized forgings in high load transfer components such as the engine pylon and undercarriage support fittings on the wing, adopting the friction stir spot welding to reduce the use of bolts on structural components. Based on finite element analysis, the three-dimensional model, described in this work, combines the mechanical action of the shoulder and the thermomechanical effect of the welded. Johnson–Cook  model is used as a basis of constitutive law in which the yield strength is affected by the temperature and strain rate for the Ti-6Al-4V alloy. The sheet of 2.3 mm thickness were friction stir spot welded using a tool with a convex scrolled shoulder made of a polycrystalline cubic boron nitride (PCBN). The parameter processes employed in this study are rotational speed, plunge speed, and dwell time and plunge depths. The material flow was also numerically simulated using the DEFORM-3D FE software. Results indicated with the incremental penetration of the pin; material from below the pin was displaced upward along the sides of the pin. FE results were verified by experimental results.

Composite materials technology in aircrafts needs improved damage growth predictions and effective repair techniques for damaged structures. Improper joint design may lead to overweight or defective structures. The joining of composite materials has traditionally been achieved by mechanical fastening or adhesive bonding. Hybrid joints are a combination of adhesive bonding and mechanical fastening; these joint systems have attracted the attention in aerospace and general mechanical industries due to its higher strength and stiffness and higher energy absorption prior to failure. In this work a parametric study was performed using a finite element software to determine the mechanical resistance of hybrid and simple lap joints. The parametric study consists in the numerical modeling of different conditions that permit estimates the main characteristics of lap joining. The study performed in this investigation seeks for a better understanding of joining of composite materials.