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International audience; 3D printed sand molds for the casting industry play a vital role in manufacturing intricate parts from a computer model. The possibility of producing fairly significant structural castings using a small job-box 3D sand mold printer is another advantage compared to the direct metal 3D printing processes. It is important to identify the relationship between the process parameters and the properties of the sand mold in order to produce a mold with the required strength, permeability and stiffness; to reduce gas emissions during casting and minimize the mass of combustible materials in the mold. Hence, it is possible to create an excellent casting by improving the design of such molds for liquid alloy filling and solidification. The relationship between the printing parameters and the properties of the mold can be a great tool for foundrymen, primarily to optimize the strength and permeability properties of these molds and therefore to provide exact boundary conditions for the solidification simulation prior to a casting trial. This paper reports on a study of a basic outline to quantify the role of the sand mold printing process parameters, particularly the recoater speed and print resolution, on the mold strength and permeability, and their impacts on the anisotropic behavior of the printed sand molds.

In the course of the selective laser melting (SLM) process, the part is built layer by layer involving partial remelting/heating of the previous layer, called as intrinsic heat treatment. Therefore, superficial properties of as-built parts are somewhat different from that of the inside of the part. In this work, the nano-tribological behavior of the commercial pure Ti (CP-Ti) sample built using SLM was investigated considering the near-surface regions with focus on the effect of intrinsic heat treatment. Microstructure and nano-testing allow identifying specific sliding behaviors in three attitude regions: (I) surface (0–50 µm), (II) subsurface (50–200 µm), and (III) inner-part (below 200 µm). The average hardness drops slightly when moving from Regions I and II (3.35 GPa) to Region III (3.09 GPa). The coefficient of friction (COF) values vary from 0.18 to 0.45 for all three regions, and the Region III presents highest worn trace width of 5.8 μm. Regions I and III promote a stick-and-slip behavior while sliding is smooth and continuous in Region II. This gradient microstructural characterization enables associating the behavior of Region II to large-sized lath martensite α′ morphology, which is different from the Regions I and III with finer microstructure. A finite element analysis (FEA) thermal model suggests that the existence of the three identified regions is the consequence of the intrinsic heat treatment induced by the SLM process, in which the remelting/heating and recrystallization have been considered as the main reasons for microstructure coarsening and refinement between Regions I and II, Regions II and III, respectively.

International audience; The friction of concrete on the interior skin of formworks takes place during the pouring of concrete into the molds. The present work investigates the friction of a granular material (i.e. fresh concrete) against metallic and polymeric surfaces. Interfacial behavior between different formulated concretes and formwork skins is characterized using a plane-plane tribometer dedicated to concrete tribometer. The formwork surface is measured before and after testing to quantify the wear issue. A Coulomb friction law is observed within the range of tested normal pressures. Tribological tests reveal that friction mechanisms depend on the interface properties. Two underlying mechanisms are hypothesized to explain the wearing of the formwork skin: a granulate-formwork solid-solid friction and a capillary-dominated friction.

International audience; The cosmetic aspect is one of the main functions of industrial surfaces in numerous applications. Even the smallest surface defects may have a critical effect on the cosmetic tolerability of such industrial surfaces. Thus, surfaces are generally coated at the last manufacturing process stage to cover existing defects and to certify their cosmetic quality. The surface quality is however constantly controlled after coating that induces an increase of lead-time increase and production costs. This is due to a various flaw patterns and a lack of uncoated surfaces specifications. Hence, the identification of relevant surface morphological parameters underlies an objective and automatic cosmetic control performance. In fact, this relevant parameter selection allows tracking surface flaws during the coating finishing operation. This paper presents a comprehensive overview of various feature selection tools for data analysis (Neighbourhood Component Analysis (NCA), ReliefF, Sequential wrapper method, Decision tree) to extract relevant information out of physical data. A design of experiment based on scratches test on amorphous polymers to generate typical controlled defects has been performed. Then, several cosmetic defects characteristics were extracted from experimental measurements. Feature selection approaches were applied and compared to determine the most relevant parameters. The advantages and limitations of each method for data analysis have been highlighted in the case of real engineering surface quality control.

International audience; Solidification cracking is a weld defect common to certain susceptible alloys rendering many of them unweldable. It forms andgrows continuously behind a moving weld pool within the two-phase mushy zone and involves a complex interaction betweenthermal, metallurgical, and mechanical factors. Research has demonstrated the ability to minimize solidification cracking occurrenceby using appropriate welding parameters. Despite decade’s long efforts to investigate weld solidification cracking, thereremains a lack of understanding regarding the particular effect of travel speed. While the use of the fastest welding speed isusually recommended, this rule has not always been confirmed on site. Varying welding speed has many consequences both onstress cells surrounding the weld pool, grain structure, and mushy zone extent. Experimental data and models are compiled tohighlight the importance of welding speed on solidification cracking. This review is partitioned into three parts: part I focuses onthe effects of welding speed on weld metal characteristics, part II reviews the data of the literature to discuss the importance ofselecting properly the metrics, and part III details the different methods to model the effect of welding speed on solidificationcracking occurrence

The sticking of the concrete on metallic formworks during building construction generates many concrete wall defects. Several solutions have been proposed, among which surface lubrication and polymeric coatings are commonly applied. In this paper, the main functional signatures of a steel formwork skin and a polymeric coating were determined to understand their effect on the concrete sticking. The topographical, chemical and mechanical signatures of the surfaces were characterized at near-surface regions. The top of the steel formwork a 10 µm-thick layer is constituted of two oxides each one having specific tribological properties. Adding the polymeric coating on the formwork skin surface lowers its surface tension, which lowers the sticking by reducing the wettability. Moreover, the smaller roughness of the coating limits the susceptibility of mechanical anchoring. Nevertheless, scratch testing suggests a short durability of the polymeric coating due to its weak resistance to abrasion.

In this work, the nano-wear-induced behavior of selective laser melting (SLM) processed commercial pure titanium was investigated under several applied loads from 1 mN to 100 mN. The dense (over 99%) commercial pure titanium sample was manufactured using SLM process with optimized process parameters (900 J m-1). Nano-wear testing was performed on the polished surface of SLM processed commercial pure titanium. The friction coefficient increased from 0.04 to 0.9 as the load increased from 1 mN to 100 mN. Additionally, the sliding behavior changed along with the applied loads, from elastic to plastic and unstable friction behaviors. The elastic-plastic transition appeared at applied load of 50 mN, which was also confirmed by the calculation results. While the applied load ranged between 50 mN and 80 mN (plastic friction), the average friction coefficient was light smaller than that of the macroscopic ball-on-disc test. During the sliding, a friction vibration appeared and its mechanism was also investigated and discussed combine the wear surface morphologies.

International audience; Concrete, a commonly used material in the construction industry, interacts with metallic surfaces such as formwork during pouring and reinforced bar during lifespan. Formworks are designed to minimize hardened concrete adherence in order to avoid wall defects after formwork removal. In opposite, reinforced bar designs aim at maximizing their adherence to concrete for optimizing the transmission of mechanical solicitations. The present review investigates the surface properties that govern bonding of freshly poured concrete onto metallic surfaces. Identifying the underlying mechanisms of adhesion highlighted the importance of substrate characteristics (roughness, composition), concrete curing and compaction), and interfacial additives (release agents, wetting). This paper addresses the basic requirements in designing a functional surface interacting with concrete and emphasizes today challenges.

International audience; Solidification cracking is a weld defect common to certain susceptible alloys rendering many of them unweldable. It forms andgrows continuously behind a moving weld pool within the two-phase mushy zone and involves a complex interaction betweenthermal, metallurgical, and mechanical factors. Research has demonstrated the ability to minimize solidification cracking occurrenceby using appropriate welding parameters. Despite decade’s long efforts to investigate weld solidification cracking, thereremains a lack of understanding regarding the particular effect of travel speed. While the use of the fastest welding speed isusually recommended, this rule has not always been confirmed on site. Varying welding speed has many consequences both onstress cells surrounding the weld pool, grain structure, and mushy zone extent. Experimental data and models are compiled tohighlight the importance of welding speed on solidification cracking. This review is partitioned into three parts: part I focuses onthe effects of welding speed on weld metal characteristics, part II reviews the data of the literature to discuss the importance ofselecting properly the metrics, and part III details the different methods to model the effect of welding speed on solidificationcracking occurrence.

International audience; Solidification cracking is a weld defect common to certain susceptible alloys rendering many of them unweldable. It forms andgrows continuously behind a moving weld pool within the two-phase mushy zone and involves a complex interaction betweenthermal, metallurgical, and mechanical factors. Research has demonstrated the ability to minimize solidification cracking occurrenceby using appropriate welding parameters. Despite decade’s long efforts to investigate weld solidification cracking, thereremains a lack of understanding regarding the particular effect of travel speed. While the use of the fastest welding speed isusually recommended, this rule has not always been confirmed on site. Varying welding speed has many consequences both onstress cells surrounding the weld pool, grain structure, and mushy zone extent. Experimental data and models are compiled tohighlight the importance of welding speed on solidification cracking. This review is partitioned into three parts: part I focuses onthe effects of welding speed on weld metal characteristics, part II reviews the data of the literature to discuss the importance ofselecting properly the metrics, and part III details the different methods to model the effect of welding speed on solidificationcracking occurrence.

The Welding Institute of Canada (WIC) test is a simple and standardised weldability test for hydrogen assisted cold cracking that was developed in the 80s. It has been extensively utilised by the industry to qualify safe welding envelopes but the difficult access to the weldment by instrumentation hinders its use for scientific research. Moreover the lack of repeatability arising from the traditional manual deposit and the short weld length causes industrial trials to have a low success rate. The present work proposes a modified geometry, referred to as the modified WIC (MWIC) test that shows: (1) an improved success rate of weld deposition, (2) an enhancement to instrument the weldment and (3) welding conditions in better accordance with the field pipeline girth welding conditions. The design is validated under a mechanised, shielded metal arc welding process with the cellulosic electrodes used for in-field pipeline construction The research work was funded by the Energy Pipeline CRC supported through the Australian Government’s Cooperative Research Centres Program. The cash and in-kind support from the APIA-RSC is gratefully acknowledged.

Surface texturation at micro- and meso-scales plays an important role in applications where cosmetic, aesthetic and self-cleaning functionalities are specified. This research paper deals with a multiscale surface, in which texturing and texture have a larger influence because they are scaled differently. The experimental approach highlights the important effect of texture and texturing on the anti-fingerprinting performance rated in term of surface wettability. We examine first, in detail, the wetting response of surfaces textured on aluminum alloy 6063 plates using nano-peening with various processing parameters. Roughness was measured by atomic force microscopy (AFM) and interferometry. Surface wettability was quantified using the sessile drop method. The calculation takes into account the wetting behavior of the textured surfaces at different scales. Correlations were made between the surface roughness and its functionality.

International audience; Nowadays buildings construction is performed by pouring concrete into molds called formworks that are usually prefabricated metallic modules. Defects such as stripping may possibly form during the removal of the formwork if the interfacial bonding between the concrete and the formwork is high. Making use of a new pull-off tensile test designed in our laboratory, a correlation has been established between the formwork surface functional signatures and its adherence propensity to concrete. The originality of this near-to-surface test was to characterizethe concrete-to-formwork adherence by measuring the required force to pull the concrete from the formwork surface. The design of the test coupon was validated by finite element analysis that proves the small deformation of the tested formwork specimen under the tensile loading and the homogeneity of the applied tensile stress at the interface. The interfacial bonding to concrete has been compared between bare and coated formwork. Both metallic and polymer coatings have been studied. The analyses of the pull-off test results enabled us to understand the bonding mechanisms at the concrete-coating interfaces. The pull-off tensile test was proven capable of ranking formwork coatings according to their adherence to concrete.

International audience; The development of sand mold three-dimensionalprinting technologies enables the manufacturing of moldswithout the use of a physical model. However, the effects ofthe three-dimensional printing process parameters on the moldpermeability and strength are not well known, leading theindustries to keep old settings until castings have recurringdefects. In the present work, the influence of these parameterswas experimentally investigated to understand their effect onthe mold strength and permeability. Cylindrical and barshapedtest specimens were printed to perform, respectively,permeability and bending strength measurements.Experiments were designed to statistically quantify the individualand combined effect of these process parameters.While the binder quantity only affects the mold strength, increasingthe recoater speed leads to both greater permeabilityand reduced strength due to the reduced sand compaction.Recommendations for optimizing some 3D printer settingsare proposed to attain predefined mold properties and minimizethe anisotropic behavior of the sand mold in regard toboth the orientation and the position in the job box.

A mass balance model has been evaluated that estimates the critical conditions for sustaining continuous crack growth in the mushy weld zone. With the aid of a strain partition model, the critical local strain rate (across the weld) has been related to the critical grain boundary deformation rate needed for crack growth. In the present work, these two models are applied to aluminum welds to investigate the theoretical effects of several metallurgical factors on solidification cracking susceptibility. Calculations quantify the improved cracking resistance associated with a smaller coherent temperature range, grain refinement, high solid fraction at coherency, and rapid development of tensile strength through solid-solid bonding.

Al-Mg-Si alloys are known to be highly susceptible to solidification cracking. Weldability results of laminated AA6061-T6 plates are presented in this paper when welded in full penetration keyhole mode using a 1030 nm, 10 kW Yb:YAG disk laser welding source with different welding conditions. Making use of the controlled restraint weldability (CRW) cracking test, a boundary has been established between crack and no crack conditions for different preloads. The originality of the CRW test is the cross-shaped test coupon that partitions the pre-stress unequally along the welding path. The CRW is proven capable of ranking the solidification cracking behaviour of weld metals deposited under different welding conditions. © 2013 Crown in Right of Canada Published by Maney on behalf of the Institute.

In some regions of Australia, epoxy-based coatings are commonly used to isolate the outer steel surface of a buried gas pipeline from the aggressive soil environment, but the rate at which the ability of the coating to exclude the environment deteriorates is unknown. The aim of this project was to investigate the accelerated ageing of a pipeline organic coating using a hydrothermal test as a proxy of pipeline's long-term exposure in the field. API-5L-X65 pipeline steel specimens were coated with a commercial 100% solids epoxy coating and immersed into an 80 °C distilled water bath with traces of carbonate–bicarbonate salts whilst electrically connected to an aluminium sacrificial anode. A limited number of specimens were taken out at different predefined ageing times, providing data to evaluate the degradation rate of the coating. Samples aged for 28 weeks were found to have a lower Barcol hardness, greater electrical permeability, and lower dry adhesion strength than non-aged samples.

In the present work, water sorption kinetics and equilibrium in 100% solids epoxy coatings are investigated by immersion into distilled water baths from 20 to 85 °C (absorption tests) and drying in a furnace between 60 and 85 °C (desorption tests). The gravimetric liquid sorption measurements reveal a non-Fickian two-stage diffusion behaviour during both absorption and desorption. The effect of hydrothermal history was also investigated. Cycling the immersion bath temperature increases the saturation values. Alternating sorption–desorption cycles increases the speed of water movement. The hydrothermal-induced coating degradation and the sorption modes are discussed.

Solidification cracking is a weld defect common to certain susceptible alloys rendering many of them unweldable. It forms and grows continuously behind a moving weld pool within the two phase mushy zone and involves a complex interaction between thermal, metallurgical and mechanical factors. Despite decades long efforts to investigate weld solidification cracking, there remains a significant lack of understanding regarding its underlying mechanisms. Criteria developed to evaluate alloy weldability will be examined in terms of proposed solidification cracking models. Crack initiation is discussed in terms of different criteria: critical stress to fracture the interdendritic liquid, critical strain to exceed the mushy zone ductility and critical hydrogen content to nucleate and grow a pore. Crack growth has been characterised in terms of a critical stress to fracture the liquid film surrounding a grain and critical strain rate interdependent with liquid feeding of the mushy zone opening. Experimenta...

The sand mold 3D printing technologies enable the manufacturing of molds with great dimensional accuracy. However, the roughness of as-cast components is higher when cast in a 3D printed mold rather than in a traditional sand mold. Coating the inner cavity is an efficient solution but can be costly and, in the narrowest cavities, not achievable. Finding a procedure to reduce the as-cast roughness without coating would ease the casting procedures. In the present work, surface analysis of ZE41 magnesium alloy is presented after being cast in 3D printed furan sand molds without coating using the low-pressure casting process. The molten metal temperature was measured during casting at different positions along the cast cavity. The as-cast surface roughness was correlated to the molten metal temperature and solid fraction at the time of contact against the sand mold surface.

Pipeline construction has been moving towards the use of higher strength low carbon steels as these become available. In order to achieve the required high strength and toughness to match those of the parent pipe, girth weld metals have to rely mostly on their composition. The aim of the present study was to characterise the influence of the consumable chemistry and moisture content, and the welding parameters on the composition of weld metals produced by E8010 and E9010 shielded metal arc (SMA) cellulosic consumables. The alloying compounds in the consumable coating were isolated using a caustic soda solution, analysed with electron backscattered diffraction and identified as a variety of oxides. Making use of a mechanised SMA welding machine, the effect on weld metal alloying element contents of the welding conditions was evaluated. Smaller welding arc voltages and lower consumable coating moisture content produced weld metals with richer chemistry. The element transfer mechanisms from the cons...

In the present work, mechanisms are proposed for solidification crack initiation and growth in aluminum alloy 6060 arc welds. Calculations for an interdendritic liquid pressure drop, made using the Rappaz–Drezet–Gremaud (RDG) model, demonstrate that cavitation as a liquid fracture mechanism is not likely to occur except at elevated levels of hydrogen content. Instead, a porosity-based crack initiation model has been developed based upon pore stability criteria, assuming that gas pores expand from pre-existing nuclei. Crack initiation is taken to occur when stable pores form within the coherent dendrite region, depending upon hydrogen content. Following initiation, crack growth is modeled using a mass balance approach, controlled by local strain rate conditions. The critical grain boundary liquid deformation rate needed for solidification crack growth has been determined for a weld made with a 16 pct 4043 filler addition, based upon the local strain rate measurement and a simplified strain rate partitioning model. Combined models show that hydrogen and strain rate control crack initiation and growth, respectively. A hypothetical hydrogen strain rate map is presented, defining conceptually the combined conditions needed for cracking and porosity.

Weld metal microstructure for alloy 6060 aluminum welds, made using the gas-tungsten arc process and alloy 4043 filler metal, has been characterized using optical metallography, EPMA microprobe analysis, SEM/EBSD and STEM/EDX electron microscopy, and single-sensor differential thermal analysis (SS-DTA). In addition, alloy 6060 castings were solidified at variable cooling rates approaching that of welding, to provide a reference for comparison with weld microstructure. It was found that a major change in cast microstructure occurs at cooling rates higher than 27 K/s resulting in a structure similar to that observed in weld metal. Rapid cooling is believed to favor low temperature solidification reactions that normally would be achieved only at higher silicon content. Accordingly, additions of 4043 filler metal that increase the weld metal silicon content have only limited affect on weld solidification range and microstructure. This has direct implications regarding how 4043 filler additions improve weldability and weld quality.

The search for an efficient on-line monitoring system focused on the real-time analysis of arc welding quality is an active area of research. The topography and the superficial temperature field of the weld pool can provide important information which can be used to regulate the welding parameters for depositing consistent welds. One difficulty relies on accessing this information despite the bright dazzling welding arc. In the present work, Stokes polarimetry and associated shape-from-polarization methods are applied for the analysis of the weld pool through its 810 nm-wavelength infrared emissions. The obtained information can provide a better understanding of the process, such as the usage of the topography to seek Marangoni flows direction, or to have a denser 3D map to improve numerical simulation models.

Aluminium alloy 6060 is typical of a family of Al-Mg-Si extrusion alloys, which are considered weldable only when using an appropriate filler alloy such as 4043 (Al-5 Si) or 5356 (Al-5 Mg). This study concerns the thermal analysis and solidification path determination of aluminium alloy 6060 diluted with variable amounts of 4043. Casting of controlled mixtures of alloys 6060 and 4043 was used to simulate different weld dilutions in order to facilitate thermal analysis. Thermal analysis and metallography were applied in order to reveal solidification reactions and phases, and allow calculation of solid fraction versus temperature curves. Although the liquidus temperature was little affected, different phases formed with increased 4043 dilution, with a trend toward lower temperature reactions and a larger fraction interdendritic constituent.

Industry and research have long desired the establishment of standards for weldability testing in regards to hydrogen assisted cold cracking formation. This would have the obvious advantage of allowing data to be reliably compared between different research labs. But making decisions regarding standards requires some careful thought and agreement on i) how test parameters affect test results, ii) what exactly needs to be measured, and iii) how test results should be interpreted and reported. Our depth of understanding on these points has matured significantly over time and, while there is not always universal agreement, it is at least possible to start highlighting factors important to standards. This paper examines these factors, including the welding parameters, restraint, hydrogen, and cracking index. When comparing different alloys having different thermal characteristics, the use of constant welding parameters (common practice) will result in variable weld penetration and weld pool shape, which can influence grain shape and microstructural features, which can result in inequitable weldability comparisons. Welding on test coupons having different dimensions can affect restraint, which will influence the residual stresses around the weldment. High restraint usually results in higher crack susceptibility. Also, hydrogen content present in a weldment depends on the thermal history, welding parameters, and surrounding atmosphere humidity; with high hydrogen contents associated to great cracking susceptibility. Finally, the selection of an appropriate cracking index is required for data analysis. Quantifications of crack length and minimum preheat temperature are common indexes used for comparison. Critical stress and hydrogen content are other indexes. But how well these indexes actually represent weldability are contentious issues. This paper will examine and quantify these issues in detail, thus providing the reader with an appreciation of all things that must be considered when preparing a standardized procedure for weldability testing. The research work was funded by the Energy Pipeline CRC supported through the Australian Government’s Cooperative Research Centres Program. The cash and in-kind support from the APIA-RSC is gratefully acknowledged.

This paper presents a passive polarimetry method using a division of aperture optical device in order to measure the temperature distribution at the weld pool surface. Thermal emission from a hot liquid metal was investigated at a near-infrared wavelength corresponding to a blind spectral window of a helium plasma generated during gas tungsten arc welding process. The refractive index of liquid metal and the surface radiance are deduced from the polarisation state of thermal emissions. Based upon the knowledge of both characteristics, the temperature distribution can be calculated. Conseil Régional de Bourgogne

The polarimetric state of the thermal radiations emitted by the weld metal contains geometric information about the emitting surface. Even though the analysed thermal radiation has a wavelength corresponding to a blind spectral window of the arc plasma, the physical presence of the arc plasma itself interferes with the rays radiated by the weld pool surface before attaining the polarimeter, thus modifying the geometric information transported by the ray. In the present work, the effect of the arc plasma-surrounding zone on the polarimetric state and propagation direction of the radiated ray is analyzed. The interaction with the arc plasma zone induces a drop in ray intensity and a refraction of ray optical path.

A new laser weldability test has been developed based upon the experimental determination of a critical applied displacement rate needed to generate solidification cracking, thus allowing the cracking susceptibility of different stainless steel grades to be compared. In particular, the Controlled Tensile Weldability (CTW) test has been used in conjunction with CO2 laser keyhole welds made on select grades of austenitic and duplex stainless steels. Weldability rankings generated from this test are presented and discussed in relation to documented behavior for arc welds and examined in terms of chromium/nickel equivalent ratios. Both limitations and advantages of the CTW test are identified and compared with other laser weldability tests.

A perspective will be given that outlines important considerations in evaluating and predicting weldability. An examination will be made of the local conditions necessary for solidification crack initiation and growth in a weld. This will be done in light of two prominent thermo-mechanical approaches involving critical strain and critical strain rate. Critical conditions will be identified based upon values available in the literature. Methods used to measure strain and strain rate will be compared. The interpretation of crack length measurements commonly used to quantify weldability will be questioned, based upon our current understanding of the problem. Complications and problem areas needing better definition will be identified and discussed, including strain distribution in the mushy zone, segregation at grain boundaries, effect of impurities, and effect of cooling rate on solidification path. Finally, a suggestion will be made for a new approach to weld development using in-situ strain rate measurement and new composition-strain rate maps that define the boundary between crack and no-crack conditions.

International audience; In this Letter, a vision-based remote sensing methodology is proposed to measure the topography of weld pool surfaces from one single view. Thermal radiations emitted by the hot liquid metal at a wavelength within the arc plasma blind spectral window are acquired by a wavefront division polarimetric system. The refractive index of the liquid metal and the topography of the weld pool surface are inferred from the polarimetric state of the thermal radiations.