Edson Costa Santos

Optimization of Laser Deposited Ni-Based Single Crystal Superalloys Microstructure

In this paper, results concerning the microstructure of Rene N4 alloy layers produced by laser cladding on oriented CMSX-4 single crystal substrates are presented. The microstructure of the deposits was analyzed in the solidification condition after different temperature/time ageing cycles in order to assess the possibility of improving high temperature strength of laser deposited superalloys. The present work demonstrates that single crystalline deposits of René N4 nickel superalloy can be obtained provided that the deposition direction and the processing parameters are properly selected. The clad layer is perfectly bonded to the substrate and presents no pores or cracks. The deposits grow epitaxially on the substrate, so they inherit its orientation. For laser beam powers and scanning speeds varying between 500 to 800 W and 4 to 12 mm/s, respectively and (001) substrates, the deposited material presents a columnar dendritic structure consisting of arrays of similarly oriented dendrites, separated by subgrain boundaries, forming a single crystal. Heat treatments effective for the dissolution of detrimental phases and for inducing the precipitation of cuboid ’-Ni3Al strengthening phase precipitates in the laser clads were established.

Fatigue Strength Improvement of AISI E52100 Bearing Steel by Induction Heating and Repeated Quenching

Martensitic high-carbon high-strength AISI E52100 steel (JIS SUJ2) is one of the main alloys used in rolling contact applications when high wear and fatigue resistance are required. In this work, repeated induction heating and quenching of AISI E52100 is proposed, and the refinement of the martensite structure and consequent improvement of the fatigue properties measured by rotating bending fatigue tests of steel parts is reported.

Homology analysis of structures of high carbon bearing steel: effect of repeated quenching on prior austenite grain size

Abstract To estimate the effect of quenching on metal structures, the analysis process is very important. It was found that use of quenching reduced the prior austenite grain size greatly and the change in compressive stress at the surface of the material had a great effect on its strength. If we can estimate the change of the grains in the structure quantitatively, we can easily evaluate the effect of the quenching process. However, the structures are too complex to apply ordinary image analysis methods. In this paper, we propose a new method for analysing changes in steel structures. By use of this method, we confirm the effect of repeated quenching on the distribution of grains.

Wear Resistance Improvement of Titanium Bearings by Laser Gas Nitriding

The influence of gas nitriding on commercial pure titanium and Ti-6Al-4V (Ti64) alloy bearings by using a Q-sw laser on the wear loss during rolling contact fatigue is investigated. By optimizing the laser processing parameters, such as laser scanning speed, power and beam diameter thin TiN coats of 0.5 to 3 µm were produced. Non-coated and coated bearings made of pure Titanium and Ti-6Al-4V alloy were tested in equal conditions and it was found that the titanium nitride layers significantly improve the rolling contact fatigue performance of titanium components. For tests up to 106 cycles the wear loss of the coated samples was at least ten fold lower than that of the uncoated ones and for 7.76 x 106 cycles, the wear resistance improved almost 100-fold.

Effect of PTFE Retainer on Friction Coefficient in Polymer Thrust Bearings under Dry Contact

Polyetheretherketone (PEEK) is a tough semi-crystalline thermoplastic polymer with excellent mechanical properties. While abilities of polyphenylenesulfide (PPS) are similar to PEEK, former material cost was lower than later. Polytetrafluoroethylene (PTFE) is well known because of its low friction coefficient and self lubrication ability. The objective of this study is to observe the friction coefficient of hybrid bearings, PTFE retainer sandwiched with PPS-races or PEEK-races. Rolling contact fatigue tests were performed and in situ friction forces wear measured. It is concluded that the PTFE retainer reduced friction coefficient.

Observation of non-metallic inclusions on repeatedly quenched SAE 52100 bearing steel fracture surfaces

Martensitic high carbon high strength SAE 52100 bearing steel is one of the main alloys used for rolling contact applications where high wear resistance are required. Due to its high fatigue strength, SAE 52100 is recently being used not only for the production of bearings but also shafts. Refining of prior austenite grain through repeated quenching is a procedure that can be used to enhance the material’s strength. In this work, the microstructure of repeatedly quenched SAE 52100 steel and its fatigue strength under rotating bending were investigated. It was found that repeated furnace heating and quenching effectively refined the martensitic structure and increased the retained austenite content. Repeated quenching was found to improve the fatigue strength of SAE 52100.

Investigation of wear in induction-heated AISI E 52100 steel bars under reciprocating motion

AISI E52100 steel (JIS SUJ2) is used in the manufacture of bearings and linear guides because of its high hardness and wear resistance under rolling contact. The life estimation methods for components working under rolling contact developed up to now were designed for bearings. In this study, fatigue testing under reciprocating motion was performed and based on the microstructure, wear track observation, electron backscattered diffraction (EBSD), hardness and retained austenite measurements, an evaluation method for linear guides is proposed. The results obtained from three different areas of the sample including wear tracks and non-damaged area are as follows: 1 there was little microstructure difference between the centre and the edge of the wear track 2 a clear difference of the retained austenite content at the wear track and at the non-damaged area could be observed, however the percentage within different areas inside the track was similar.

Structure of NiCrAlY Coatings Deposited on Oriented Single Crystal Superalloy Substrates by Laser Cladding

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.

Changes in the microstructure of 13Cr-2Ni-2Mo stainless steels through the quenching process by induction heating

A 5 mm diameter shaft of 13Cr-2Ni-2Mo stainless steel was induction heated using a 15 mm diameter coil and subsequently quenched. The material’s microstructure before and after heat treatment were investigated by laser confocal scanning microscopy (LCM), X-ray diffraction (XRD) system, field emission scanning electron microscope (FE-SEM). The Vickers hardness distribution at the cross-section was measured. It was found that through the heat treatment process, the XRD pattern changed; the α-Fe peaks shifted and broadened. Grain boundaries as well as fine structures formed within grains were visible in the IH-hardened sample micrographs. This indicates the occurrence of martensitic transformation, resulting in an approximately two-fold hardness increase.

Effect of Thrust Load and Rotation Speed on Wear Loss in PPS Race - PTFE Retainer Hybrid Polymer Thrust Bearings under Dry Contact

In order to establish an optimal material combination for the production of polymer thrust bearings, two types of components: retainer and PPS races - PPS retainer were tested by rolling contact fatigue (RCF). The wear properties of both bearing types were investigated and a relationship between thrust load, rotation speed and wear loss was established. It is concluded that by using a PTFE retainer, it is possible to improve the