Maria José Marques

Surface Integrity of H13 ESR Mould Steel Milled by Carbide and CBN Tools

The quality of a mechanical component such as its geometrical accuracy stability and fatigue life are significantly affected by the surface integrity generated by machining process. Residual stresses are a major part of the mechanical state of a machined layer and they can be beneficial or detrimental depending of their nature and magnitude. This study concerns phase analysis and residual stress profile characterization by X-ray diffraction (XRD) technique and microhardness profile of AISI H13 ESR mould steel, milled using carbide and CBN tools. Analysis of the cross-section of the AISI H13 ESR samples, milled using both tools, reveal a martensitic microstructure, with a very thin layer heavily deformed due to the machining process. However, no phase transformation was detected by XRD. Concerning the residual stresses, the results show that they are predominantly compressive at the samples surface. However, depending of the cutting tools, the in-depth residual stresses profiles present different evolutions. This difference in the in-depth residual stresses profiles between the two kind of cutting tools is attributed to the different cutting tool parameters, including the tool geometry.

Quantifying the Drilling Effect during the Application of Incremental Hole-Drilling Technique in Laminate Composites

In this work, a methodology to quantify the effect of the drilling operation, during the application of the incremental hole-drilling technique (IHD) for measuring residual stresses in laminate composites, in particular, the polymer matrix composites (PMC), is presented. This technique will allow the optimization of the drilling procedures and its parameters, enabling the quantification of the drilling effect. This quantification is obtained by using an experimental calibration procedure followed by a numerical simulation of the whole process. The direct comparison of the experimental and numerical results will allow quantifying the effect of the drilling operation. As example, the methodology was applied to the case of carbon/epoxy cross-ply laminate [0°/90°]5s. The holes have been made by using two different drilling procedures, but the same tool geometry. High speed milling powered by air compression, a process usually employed in the case of the application of hole-drilling technique to metal alloys and a conventional computer numerically controlled (CNC) milling machine, were used. The results seem to show that incremental hole-drilling could be a reliable technique to determine residual stresses in fibre-reinforced polymers.

Influence of Surface Roughness on the Quality of Data Obtained by Pseudo-Grazing Incidence X-Ray Diffraction

The conventional Bragg diffraction geometry, normally used to characterize the residual surface stress state, it is not suitable to evaluate surface treated materials and thin films. The X-ray path lengths through a surface layer or thin film are too short to produce adequate diffraction intensities in relation to the bulk or the substrate. Another limitation of the conventional technique appears when a residual stress gradient is present in the irradiated surface. The technique only enables the evaluation of the mean value of this gradient. In these cases, a recently proposed Pseudo-Grazing Incident X-ray Diffraction method would be better applicable. In this study, the Pseudo-Grazing Incidence X-ray Diffraction is applied to characterize the residual stress depth profiles of several AISI 4140 samples, which were prepared, by mechanical polishing and grinding, in order to present different surface roughness parameters, Ra. The experimental results lead to the conclusion that the surface roughness limits the application of the Pseudo-Grazing Incidence methodology to a minimum X-ray incident angle. This angle is the one that enables a mean X-ray penetration depth with the same order of magnitude of the sample surface roughness parameter, Ra.

Texture Characterization of Stainless Steel Cladded Layers of Process Vessels

In this study local texture of process vessels made of carbon steel cladded by protective layers of stainless steel by submerged arc welding (SAW) were investigated by neutron diffraction using the diffractometer STRESSSPEC at FRM 2 (Garching, Germany). Different samples were prepared: as welded and as welded plus relevant industrial heat treatment. Local texture measurements with a gauge volume of 3 x 3 x 2 mm3 of the three cladding layers (at depths of 2 mm, 5 mm and 7.5 mm) for each sample were determined. Texture results indicated that there exists an annealed cube component in all the studied samples. Based on the measured pole figures at each depth and sample, the calculated orientation distribution functions data were used to calculate the Youngs modulus with respect to the main welding directions. The calculated local and bulk anisotropic Young’s modulus in depth is presented and discussed.

A utilização da difração de neutrões na determinação do perfil de tensões residuais em revestimentos por soldadura

A tecnica de difracao de neutroes e usada neste artigo para estudar amostras ferriticas, revestidas comacos inoxidaveisausteniticos atraves de soldadura por arco submerso. Este procedimento e frequentemente usado no fabrico de equipamentos de processo para as industrias quimica e nuclear, por facilidade de execucao e razoes economicas. A principal desvantagem deste processo de revestimento e a fissuracao que frequentemente ocorre na interface material base/soldadura, potenciada pela presenca de tensoes residuais resultantes da operacao de soldadura, a qual pode ser minimizada com a realizacao de tratamentos termicos de relaxacao de tensoes. As amostras foram produzidas a partir de placas em aco ao carbono, tendo uma das superficies sido revestida com dois tipos de aco inoxidavel. Para a primeira camada foi usado um eletrodo EN 12072 - S 23 12 2 L e para a segunda e a terceira camadas foi usado um eletrodo EN 12072 - S 19 12 3 L. Apos a soldadura, as amostras foram submetidas a um tratamento termico de relaxacao de tensoes, durante 1 hora, a temperatura de 620oC. Os perfis de tensoes residuais obtidos por difracao de neutroes evidenciam a relaxacao de tensoes residuais apos o tratamento termico realizado. A tecnica de difracao de neutroes revelou-se muito adequada na avaliacao de tensoes residuais neste tipo de ligacoes.

Residual Stresses Profiles of Cladded Austenitic Stainless Steel Evaluated by X-Ray Diffraction and by Incremental Hole-Drilling Method

The samples studied in this paper were performed from carbon steel plates, cladded in one of the faces with stainless steel filler metals by submerged arc welding (SAW). After cladding work, the samples were submitted to post-weld heat treatments at different conditions and afterwards stainless steel coating surfaces were milled and mechanically polished, as in the industrial application. The residual stress analysis was performed by X-ray diffraction (XRD) and incremental hole-drilling methods (IHDM). The residual stresses profiles presented different in depth values in each sample, depending on the heat treatment conditions. The hole-drilling method was applied in several points of each stainless steel sample surface and the results presented similar evolution profiles. However compressive stresses increase with the increase of heat treatment temperature.

Evaluation of residual stresses induced by ultra-high-speed drilling in aluminium alloys

A hybrid experimental-numerical methodology is applied to evaluate the unwanted stresses induced by hole-drilling in two 5000 and 7000 series aluminium alloys. The influence of the cutting speed of ultra-high speed drills powered by turbine systems by compressed air, which are commonly used in the hole-drilling equipments for residual stress measurements, is analyzed. The comparison of the effect of different drilling conditions on the drilled material using a quantitative approach is now possible. The applied methodology can play an important role on the improvement and optimization of the hole-drilling technique for residual stress measurements in particular and the drilling process in general.

Evaluation of stress-strain behavior of surface treated steels by X-ray diffraction

X-ray diffraction assisted four-point bending method (XRDABM) enables to analyze the evolution of surface stress with the strain during bending of specimens. This experimental methodology was used to characterize the stress-strain behavior of two plasma nitriding steels, DIN 40 Cr Mn Mo 7 and DIN 32 Cr Mo V 13, with gradients of mechanical properties across the surface layers, allowing the characterization of the in-depth evolution of the local yield strength in the nitrided layer. The results show a significantly increase of the yield strength of the nitride layers and a good agreement between the in-depth evolution of the yield strength and the XRD peak breadth for the two nitrided steels.

Residual Stress Fields after Heat Treatment in Cladded Steel of Process Vessels

The influence of the heat treatment on the residual stress fields of weld cladded samples is discussed in this paper. The samples were elaborated from carbon steel plates, cladded in one of the faces with stainless steel filler metals by submerged arc welding. After the cladding process some of the samples were submitted to heat treatments with different parameters: one at 620° C for a holding time of 1 hour and the other at 540° C for a period of ten hours. The in‑depth residual stress profiles were determined by neutron diffraction. The results shown that the sample treated to 620 °C, presented the highest residual stress relaxation. The corresponding heat treatment has the industrial benefit to be shorter than the other heat treatment.

Stress and texture analysis in thin films and coatings by X-ray diffraction

The thin and textured coatings present a double difficulty for characterization by conventional X-ray diffraction. Their shallow depth reduces the diffracted intensity and allows the interference of the underlying material. Frequently they present a crystallographic texture which limits the number of orientations that provide good intensity and induces anisotropy effects on their mechanical behavior. Reliable results can be determined using diffraction geometry of lowincidence angle. This paper describes the application of the technique to several films, characterized by thicknesses of the order of 1 μm and crystallographic textures. Examples are proposed of chromium films applied by PVD on molybdenum substrates, decorative electroplated coatings, and aluminum coatings used for interconnections in microelectronic circuits. The Cr films are 1.5 μm thick and exhibit a strong <100> fiber texture. The decorative coatings were studied both on the nickel undercoat and in the Cr top layer. Results are presented for chromium where tensile stresses and a <110> fiber texture were observed. The Al films are 1.0 μm thick. Some samples were heattreated at different annealing temperatures. Tensile stresses were always observed, which increase in the annealed samples.