B.J. Fernández

Characterization of the SCC behaviour of 8090 Al-Li alloy by means of the slow-strain-rate technique

Abstract Aluminium-lithium alloys possess a high resistance to stress corrosion cracking (SCC) compared with more conventional alloys. With traditional testing techniques and in conventional media some Al-Li alloys, such as 8090, show no susceptibility to SCC owing to the fact that such techniques and solutions are not appropriate for determining their behaviour. The slow-strain-rate technique makes it possible to detect the susceptibility to SCC in systems for which it cannot be detected with other testing techniques or takes much longer to detect. In the literature there are no unanimous criteria for establishing whether this technique permits characterization of the SCC behaviour of 8090-T8171 sheet in the L and LT directions, when used in standard solutions and at strain rates of between 10 −7 and 10 −4 . In this work, a strain rate value has been found for which the fracture of alloy 8090-T8171, in 1 M NaCl + 0.3% H 2 O 2 , occurs as a consequence of an SCC process. Higher and lower strain rates lead to failure as a result of other mechanisms.

Cladding of Ni superalloy powders on AISI 4140 steel with concentrated solar energy

Abstract The Present work deals with Ni alloy cladding on AISI 4140 steel samples made with high power density concentrated solar beams. The quality of the cladding is high concerning the adherence, low dilution and high hardness of the coating. Some considerations are presented concerning the future of high power density beams related to SUrface Modification of Metallic mAterials with SOLar Energy (SUMMA cum SOLE)

Effect of surface laser treatment on the microstructure and wear behaviour of grey iron

Abstract The effect of the laser surface treatment on the microstructure and wear behaviour of grey iron was studied. Experiments were performed using a continuous CO 2 laser with a square 10 × 10 mm beam and uniform power density for 2.5 and 5 kW power output and different scan rates. The achieved microstructure and hardness of the different zones of the treated material and its wear behaviour were analyzed. By choosing the adequate working conditions, a wide range of microstructures can be obtained on the material surface layer. The wear test results showed that surface laser hardening treatment causes an improvement of the material wear behaviour.

Laser-clad 316 stainless steel with NiCr powder mixtures

Abstract Laser surface cladding of a NiCr powder mixture onto a 316 stainless steel was carried out. The coating microstructure, depth and composition were studied. The main variables of the process (scan speed and powder feed) were linked to the roughness, hardness and pitting corrosion properties in a saline solution of the layers obtained. A comparison with samples of a similar composition and the base stainless steel is given. Finally, resistance to oxidation at 900°C is tested. By optimizing the laser cladding parameters, layers with a high-quality surface can be produced. The new coating enhances mechanical and corrosion properties of the base materials.

Modelling of steel surface heating with concentrated solar energy

Abstract A finite element computer program was developed based on a model of unidirectional heat transmission to predict the effects of concentrated solar energy treatment on steel specimens. The recorded experimental heating curves enabled us to estimate with the program the net power density values under different solar equipment heating conditions. The extent of the microstructural changes observed in the treated steel specimens showed a good agreement with the programs estimates. The results were validated by surface heat treatment tests at two solar energy facilities.

Effect of high-temperature surface hardening of metallic materials on their dimensional stability

Abstract Surface hardening thermo-chemical treatments provide metallic alloys with very hard corrosion and wear resistant coatings. As the layers obtained are so thin that dissuade from any machining operation after the treatment, it is useful to evaluate possible dimensional changes. This work studies the dimensional stability of alloy Ti6A14V after gas nitriding at 1100 °C and of superalloy MA956 after surface oxidation at the same temperature. For reference purposes, an analysis is also made of the deformations that appear on steel after conventional pack carburising treatment. In this study flat test specimens of 3 mm thickness were used, each of which had central drilled holes surrounded by six smaller outlying drilled holes. A calculation program allows the determination of changes in the drilled hole diameters and in the position of their centres as a consequence of the treatment.

Electrochemical noise measurements during exfoliation of aluminum alloys

Aluminum alloys are one of the most widely used materials in the aerospace industry because of their intrinsic low density, high mechanical strength, and corrosion resistance. The performance of aircraft is improved by the use of lighter materials. Electrochemical noise measurements (ENMs) have been carried out during exfoliation corrosion of an aluminum-lithium alloy (8090) in the EXCO (ASTM Test Method for Exfoliation Corrosion Susceptibility in 2XXX and 7XXX Series Aluminum Alloys [EXCO Test] [G 34]) test solution. By means of the maximum entropy method (MEM), the potential and current fluctuations were converted into power spectral density (PSD) plots to study the specific variables related to electrochemical noise (low frequency amplitude, slopes). Noise resistance obtained from the standard deviation of potential and current was compared with the charge transference resistance (R{sub ct}) from electrochemical impedance spectroscopy (EIS) measurements. The results show that ENM can be used to detect early stages in localized corrosion. However, when the solution is very aggressive, indications of localized corrosion can be masked by uniform corrosion.