Papers by Author: Edson Costa Santos

Abstract: In this work, wear of reinforced poly-ether-ether-ketone (PEEK containing PTFE, graphite and carbon fibres) polymer bushes in friction against 7075 aluminium alloy cam plates is investigated in order to establish the application possibilities in transmission parts in humanoid robot joints. The PEEK bush surface conditions as well as the input axis-output axis transmission error (backlash) require close examination. Sliding wear tests were performed on bushes under 900 kgfcm loaded torque, while the cam plate oscillated. Based on the wear observation, it was found that PEEK wear fragments in the interface between PEEK bush and aluminium alloy cam plate formed a PEEK film.

Abstract: Failure of dies and molds is caused by wear and deformation during the metal sheet forming process. Die wear takes various forms, and the contact conditions in die-parts affect the strength of the components. Non-destructive methods that can be related to contact conditions are necessary to study and understand the phenomena caused by the contact stresses. In the present work, a newly developed scanning Hall probe microscope (SHPM) equipped with a GaAs film sensor was used to observe the three-dimensional magnetic fields in tool steel plates before and after contact tests at room temperature in air. It was found that the intensity of three-dimensional magnetic fields is only slightly affected by the spherical Hertzian contact. However, all of the three-dimensional components of the magnetic fields change significantly. The extent of the changes depends not on the distribution of stress under spherical Hertzian contact but on the initial distribution of the magnetic fields.

Abstract: The influence of surface oxidizing using a Q-sw laser on the wear loss of titanium-4Al-6V (Ti64) alloy during rolling contact fatigue is investigated. Titanium components are widely appreciated for their superb biocompatibility, high strength to weight ratio and corrosion resistance. Due to the above mentioned advantages titanium bearings are a popular choice in applications requiring high strength, light weight, and minimum maintenance (for example, aerospace and defence industries). In these rolling contact applications however issues such as fretting and wear related problems are a common occurrence as the tribological properties of titanium alloys are inferior to those of other metal alloys, such as steel. In an attempt to tackle this problem, a Q-sw laser was used in this work to coat Ti64 bearings with complex titanium oxide layers in a closed chamber without any protective gas. Non-coated and coated samples were tested under water by using a thrust-type rolling contact fatigue machine. The morphology and crystallographic texture of the layers were observed by laser confocal microscope, scanning electron microscope and X-ray diffraction. The wear loss of the coated samples was at least fifty-fold lower than that of the non-coated bearings and a 3-fold increase in the maximum load capacity compared with TiN layers was achieved.

Abstract: Retracted article: In this paper, epitaxial growth on Ni-based single crystals was achieved by using spark deposition and laser powder deposition. Different Ni-based substrates, such as CMSX-4, TMS 138A as well as deposition materials: NiCrAl, Rene N4 and modified 4.5^th generation single crystal alloys were used. The deposited layers were analysed by laser confocal microscopy, FEG-SEM, X-ray and electron backscatter diffraction (EBSD), had very little dilution and epitaxial growth was confirmed for the deposits made using Rene N4 electrodes. The deposition time at 100 V voltage, 850 W power and 110 Hz frequency was 3min and the layer thickness varied from 0.3 to 0.5 mm. Cracks were observed in certain areas with the formation of stray grains. In order to investigate the influence of the laser processing during multiple build up, specimens with one and ten layers were manufactured. The total layer thickness on substrates was 0.3 mm and 2 mm, respectively. The processing parameters were: laser power of 500 W, laser beam diameter of 0.6 mm and the z displacement was equal to 80% of the layer height. The laser deposition also resulted in successful epitaxial growth and minimal defects (pores or cracks), however the clads presented high dilution.

Abstract: Fatigue failure of steel occurs when cracks form in a component and continue to grow to a size large enough to cause rupture. In order to understand the crack initiation and propagation phenomena, non-destructive evaluation methods that can be correlated to in-situ measurements around the crack tips are necessary. In the present work, we developed a scanning Hall probe microscope (SHPM) equipped in a GaAs film sensor to observe fatigue cracks at room temperature in air while they were growing. Medium carbon low alloy steels specimens (JIS S45C) were used in the experiments. Only the area around the crack tip was magnetized and the changes at the crack tips were observed.

Abstract: Fatigue failure of steel occurs when cracks form in a component and continue to grow to a size large enough to cause fracture. In order to understand the strength of a steel component, it is important to locate these cracks. We developed a scanning Hall probe microscope (SHPM), equipped with GaAs film sensors to observe fatigue cracks at room temperature in air while they were growing. In our previous works [1,2], the correlation between crack growth and magnetic field in high carbon tool steels (JIS SKS93 and JIS SUJ2) were determined. We also reported the sensitivity of the SHPM equipped with a three-dimensional line-probe that was developed to decrease the sensor gaps. By using the line-probe sensor we succeeded to measure the magnetic flux density distributions in very close proximity to the specimen’s surface. However, in order to further understand the relation between magnetic flux density and crack growth, other materials, microstructures and fatigue test conditions should be evaluated. In the present work, we focus on the effect of stress ratios on the changes of the magnetic flux density in annealed carbon tool steel.

Abstract: The influence of gas nitriding of commercial pure titanium and Ti-6Al-4V (Ti64) alloy by using a Q-sw laser on the wear loss during rolling contact fatigue is investigated. Despite very good biocompatibility, high strength to weight ratio and corrosion resistance, the tribological properties of titanium alloys are inferior to those of other metal alloys, such as steel. Fretting and wear related aspects become important issues when titanium alloys are used in rolling contact applications. Titanium bearings are employed in applications requiring high strength, light weight, and minimum maintenance (for example, aerospace and defense industries). In this work, a Q-sw laser was used to coat pure commercial titanium and Ti-6Al-4V bearings with TiN in a closed chamber in nitrogen atmosphere. The samples were tested under water by using a thrust-type rolling contact fatigue machine. The microstructure, morphology and crystallographic texture of the layers were observed by laser confocal microscope, scanning electron microscope and electron backscatter diffraction (EBSD). By optimizing the laser processing parameters, such as laser scanning speed, power and beam diameter, thin TiN coats of 1 to 3 mm were produced. The wear loss of the coated samples was at least ten times lower than that of the uncoated bearings.

Abstract: In the present work single and multiple layer NiCrAlY coatings were produced by laser cladding on (100) single-crystalline substrates of SRR99 Ni-based superalloy. Detailed structural characterisation and texture analysis by optical microscopy, scanning electron microscopy, X-ray diffraction and Rutherford backscattering showed that the NiCrAlY coatings consisted essentially of gamma phase with yttrium oxide (Y2O3) and a small proportion of yttrium–aluminium garnet (Al5Y3O12) precipitated in the interdendritic regions. The coatings presented a columnar dendritic structure grown by epitaxial solidification on the substrate and inherited the single-crystalline nature and the orientation of the substrate. The coating material also showed a mosaicity and a defect density similar to those of the substrate. It can be expected that the protective effect of these coatings against oxidation is greatly enhanced compared with polycrystalline coatings because high diffusivity paths, such as grain boundaries, are eliminated in single-crystalline coatings, thus reducing mass transport through the coating.

Abstract: Radial ball bearings made of metal, ceramics and plastics are commonly used as important components in industrial machinery. Usage of high performance engineering plastic polymers is increasing progressively as a replacement for metal components due to the latest markets demands. Poly-ether-ether-ketone (PEEK) is a promising material for precision-machined custom bearings, products that are expected to suit special market needs. In the present study, PEEK radial ball bearings were manufactured by lathe machining under different parameters and their rolling contact fatigue (RCF) resistance under water lubricated conditions was investigated. We observed the surface of the bearings prior and after testing by laser confocal microscope. The wear loss was measured by weighing the bearings before and after test. Cracks and/or flaking failures were identified on the bearing surface after testing. From the RCF tests results, we found that, at water lubricated conditions, crack initiation occurred later in the material that was machined at slower feed rate while at dry condition, the feed rate had little influence on the wear loss and cracking. Wear loss in the case of bearings tested under water was much less severe than that of bearings tested at dry conditions.

Abstract: Martensitic high carbon high strength SAE 52100 bearing steel is one of the main alloys used for rolling contact applications when high wear and fatigue resistance are required. Refining the microstructure of steel improves its mechanical properties (e.g. toughness). In this work SAE 52100 specimens were exposed to repeated induction heating process and rotation bending tests were performed using single- and repeatedly heat-treated material in order to investigate the influence of this cyclic heat treatment on the mechanical properties of SAE 52100. In an attempt to determine the effect of the repeated induction heating and quenching on the material, we focused our observations on the internal fatigue “fisheye" cracks. It was noted that crack propagation was successfully halted by the refined microstructure in heat affected zone, therefore it can be concluded that repeated induction heating and quenching processes help to slow down the propagation of fisheye cracks in SAE52100 steel bars.