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Orthotropic yield criterion for Ti-6Al-4V titanium alloy after friction stir processing (FSP)

Farias A., Delijaicov S., Bordinassi E. C., Batalha M. H. F., Batalha G. F.

Archives of Materials Science and Engineering

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2015

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Vol. 72, nr 1

33--45

EN

Purpose: This works aims at applying friction stir processing (FSP) to Ti-6Al-4V titanium alloy. Derived from friction stir welding (FSW), it is a recent process developed in the 1990s for aluminum joining. Its application to other types of materials such as steel and high performance alloys, in particular titanium, has interested industry. Design/methodology/approach: The methodology applied to evaluate FSP in this work consisted in tensile testing Ti-6Al-4V sheets in mixed conditions. The workpieces were processed in a conventional CNC milling machine with special fixture devices. Findings: A contribution to the modeling of anisotropic materials yield stress is proposed based on an orthotropic yield criterion. Additional equations based on the mixed tests for tensile and shear loadings are proposed to modify the former Cazacu orthotropic model. Research limitations/implications: Although the application limit for the model appears to be small, sheet forming process similar to those used in this work, are predominantly in the region of this analysis. Practical implications: The purpose of the model is to indicate the conditions under which the material has reached its yield regime, and may be a basis for practical simulations in similar conditions. Originality/value: The purpose of this model is to indicate the conditions under which the material has reached its yield regime, and may be a basis for practical simulations in similar conditions.

2

Evaluation of an AICrN coated FSW tool

Batalha G. F., Farias A., Magnabosco R, Delijaicov S., Adamiak M., Dobrzański L.A.

Journal of Achievements in Materials and Manufacturing Engineering

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2012

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Vol. 55, nr 2

607--615

EN

Purpose: This paper aims to evaluate the wear performance of a physical vapor deposition (PVD) coating on cemented carbide (WC) tool used in friction stir welding FSW processing of Ti alloy sheets. Design/methodology/approach: A coating of AlCrN material was applied to a WC tool in order to increase its wear resistance, thermal shock stability and hot hardness. In comparison to the conventional coatings, the AlCrN coating system had a higher resistance to abrasive wear as well as higher hot hardness and oxidation resistance. FSW processing of Ti with a coated WC tool was expected to have better performance than an uncoated tool. Back Scattering Electron (BSE) imaging mode at scanning electron microscope was used to determine the main mechanism of tool wear, which was found to be hot adhesion and inter-diffusion of tool constituents with the workpiece materials. Findings: The tool degradation was evaluated by scanning electron microscopy in order to observe the main tool wear mechanism. The real contribution of the (Al,Cr)N coating layer could not be correctly evaluated, since there is no residual trace of its components at the worn tool. What was probably found left from the coating layer was the N component which formed the nitride TiN observed by EDS mapping. The parameter conditions were probably too severe, overcoming the layer limit strength. Research limitations/implications: The research were carried out as a preliminary evaluation and this initial results in the need of a further analysis that should be performed looking for a suitable tool material and coating optimization for the FSW processing of titanium alloys. Practical implications: Despite being successfully used in other manufacturing applications like machining operations in which friction and temperature are also high, the WC tool material and the coating had an unsatisfactory wear resistance, and the AlCrN coating was totally worn during the FSW processing. This suggests that new materials and coatings are still needed for FSW tools. Originality/value: FSW process is gaining importance as an industrial joining method, but the tool wear is still an important challenge to achieve efficient and economic operation. Because of the low thermal conductivity and high chemical reactivity of Ti, tools wear rapidly due to high temperature and strong adhesion. In order to achieve higher processing speeds, reducing heat at the interface tool/work material is required, as is the use of tool materials that have little or no chemical affinity.

3

Surface integrity functional analysis in hard turning AISI 8620 case hardened steel through 3D topographical measurement

Farias A., Delijaicov S., Batalha G.

Archives of Materials Science and Engineering

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2010

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Vol. 46, nr 1

47-52

EN

Purpose: This work aims investigate the resulting machined surface condition from hard turning process of mechanical components manufactured from case hardened steel. Design/methodology/approach: The surface was examined by parameters obtained from the three-dimensional surface topography obtained with an interferometric laser instrument. Findings: The selected roughness parameters analysis intends to have a functional characterization such as bearing capacity, fluid and lubricants retention ability and contact wear resistance. Research limitations/implications: The obtained results were validated against similar ones, showing that the employed measuring techniques and analyses were correctly conducted. Practical implications: The functional bearing area curve analysis parameters indicates that the resulting surface has a good area contact, good bearing capacity and reasonable ability to fluid retention as the reduced valley depth parameter Svk not produced higher values for all conditions tested. Originality/value: The obtained results in the surface roughness measurement shows consistency with other authors results, and it shows that the technique of hardened material turning is capable of producing surfaces with functionality and quality.