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The effectiveness of rotary degassing on the defect formation and mechanical properties of the final casting of aluminium alloy EN AC 46000 was investigated, along with its impact on the energy consumption in the casting furnace. In the melt preparation prior to casting, the molten metal is usually transported from the melting furnace to the casting furnace with rotary degassing as a cleaning procedure. Under the conditions of this specific study, negligible degradation was observed in the mechanical properties of the final cast component in an aluminium EN AC 46000 alloy after removing the rotary degassing step in the process. Furthermore, removing the rotary degassing step led to a reduced temperature drop in the melt, thus minimizing the need for reheating (energy consumption) by up to 75% in the casting furnace. The reduced energy consumption was up to 124,000 kWh in yearly production in a 1500 kg casting furnace. The environmental impact showed a ~1500 kg reduction in CO2 for one 1500 kg electrical casting furnace in a year.

Several studies had been performed on accumulative roll bonding (ARB) for AA1050; however, most of them were conducted at room temperature. Here, the ARB process was performed on AA1050 plates through nine cycles at elevated temperature. An innovation introduced a new parameter ( $$\frac{UTS\times El.}{\varepsilon }$$ ) to compare the strength-elongation balance between the present study and previous works. Also, as another parameter, the toughness was compared. Comparing these parameters with previous works showed that the considered samples in the present study performed 14 to 63% better than the other samples, so they were more industrially favorable in terms of mechanical behavior and performance. ARB process at elevated temperature may slightly lead to grain growth compared to room/cryogenic temperature, but creates a better elongation, which ultimately leads to a better balance of the strength-elongation parameter. The results showed that the effect of inter-cycle heating was found significant on microstructural evolution and mechanical behavior. Upon five cycles of the process, the grain size was decreased from 35 to 1.8 μm. The yield strength and ultimate strength increased up to 305% and 94%, respectively. Microhardness test showed that warm ARB reduces inhomogeneity factor in the thickness after 3 cycles. Fractography by SEM showed that the sample failed through shear ductile rupture and that the dimples became smaller, more elongated, and shallower onto the failure surface as the number of ARB cycles increased. In short, the warm process is preferred to the cold process to achieve better mechanical performance and toughness.

Using the Thermo-Calc implementation of the CALPHAD approach, high-throughput screening of the Co–Cr–Fe–Mn–Ni system was implemented to find ‘islands’ of single phase FCC structure within the compositional space in order to reduce the cost of this well-studied alloy system. The screening identified a region centred around Co10Cr12Fe43Mn18Ni17, reducing the material cost compared to the equiatomic alloy by ∼40%. The alloy was experimentally investigated at room and elevated temperatures, including in-situ tensile testing. The alloy was found to possess slightly lower strength compared to the equiatomic alloy at room temperature, however, exhibited excellent thermal strength up to 873K. Deformation twinning was observed after tensile testing at room temperature, primarily attributed to the reduced stacking fault energy (SFE), which was proven by a thermodynamic model for calculating the SFE. The softening behaviour at room temperature can be explained through solid solution hardening (SSH), whereby a modified approach to Labusch's model was used to calculate the SSH in reported alloys in this study within the Co–Cr–Fe–Mn–Ni system. The modified models for SFE and SSH are proposed to be implemented into high-throughput screening algorithms for accelerated alloy design towards specific mechanical properties.

Few systematic studies on the correlation between alloy microstructure and mechanical failure of the AlSi10Mg alloy produced by laser-based powder bed fusion (L-PBF) are available in the literature. This work investigates the fracture mechanisms of the L-PBF AlSi10Mg alloy in as-built (AB) condition and after three different heat treatments (T5 (4 h at 160 °C), standard T6 (T6B) (1 h at 540 °C followed by 4 h at 160 °C), and rapid T6 (T6R) (10 min at 510 °C followed by 6 h at 160 °C)). In-situ tensile tests were conducted with scanning electron microscopy combined with electron backscattering diffraction. In all samples the crack nucleation was at defects. In AB and T5, the interconnected Si network fostered damage at low strain due to the formation of voids and the fragmentation of the Si phase. T6 heat treatment (T6B and T6R) formed a discrete globular Si morphology with less stress concentration, which delayed the void nucleation and growth in the Al matrix. The analysis empirically confirmed the higher ductility of the T6 microstructure than that of the AB and T5, highlighting the positive effects on the mechanical performance of the more homogeneous distribution of finer Si particles in T6R.

This work investigates the role of primary austenite morphology on the eutectic and eutectoid microstructures and the ultimate tensile strength (UTS) in a hypoeutectic compacted graphite iron (CGI) alloy. The morphology of primary austenite is modified by isothermal coarsening experiments in which holding times up to 60 min are applied to the solid–liquid region after coherency. The cooling conditions for the subsequent eutectic and eutectoid reactions are similar. Miniaturized tensile tests are performed to evaluate the UTS. The morphological characteristics related to the surface area of primary austenite, the modulus of primary austenite,$$ {M}_{\upgamma} $$Mγ, and the hydraulic diameter of the interdendritic region,$$ {D}_{\text{ID}}^{\text{Hyd}} $$DIDHyd, increase with the cube root of coarsening time. The eutectic and eutectoid microstructures are not significantly affected by the morphology of primary austenite, thus indicating that the morphology of the interdendritic regions does not control the nucleation frequency and growth of eutectic cells or graphite. UTS decreases linearly with the increasing coarseness of primary austenite for similar eutectic and eutectoid microstructures, demonstrating the strong influence of primary austenite morphology on the UTS in hypoeutectic CGI alloys.

The void formation and plastic deformation micromechanisms of a cold-rolled DP600 steel during tensile loading were studied by scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). The SEM observations revealed that the main void nucleation mechanism in the DP600 steel is decohesion at the ferrite–martensite interfaces. The voids were mostly observed between the closely spaced martensite islands situated at the boundaries of relatively finer ferrite grains. The EBSD results indicated a strain gradient developed from the ferrite–martensite and ferrite–ferrite interfaces into the interior of ferrite grains during the tensile deformation, which led to a stress concentration at these interfaces. Moreover, it was demonstrated that local misorientation inside the finer ferrite grains surrounded by martensite islands was higher than that for the coarser ferrite grains, which made the former more prone to void initiation.

To evaluate the role of Fe-rich intermetallics on crack initiation, two fully modified Al-Si alloys, one containing plate-like β-Fe and the second containing primary α-Fe intermetallics, were inves ...

The growth mechanism of graphite nodules in ductile iron was experimentally investigated using high-resolution 3D tomography of an individual graphite nodule in a near-eutectic ductile iron. The dual beam scanning electron microscopy (FIB-SEM) technique was used for this purpose. Iron particles elongated in the radial direction were observed inside a graphite nodule. Some micro-voids were detected inside the nodule, mostly located at the end of the iron particles. These observations were compared with established theories about the growth of graphite nodules and iron entrapment/engulfment in between the graphite sectors during solidification of ductile iron.

The hot deformation characteristics of a FeCrMnN austenitic stainless steel containing 0.28 wt.% nitrogen (N) was investigated by hot compression tests using a Gleeble simulator in the temperature range of 800−1200 °C and at constant true strain rates of 0.01–10 s−1 with all specimens deformed to ∼0.9 true strain. The influence of deformation conditions on microstructural mechanisms and phase transformations was characterized. A processing map based on dynamic materials modelling (DMM) was designed and interpreted for predicting the domain of stable flow for safe, defect-free hot deformation. The results revealed the occurrence of dynamic recrystallization (DRX) in a domain extending over the temperature and strain rate ranges of 1100−1200 °C and 0.1–1 s−1, respectively, with the efficiency of power dissipation (η) of 45–55 %. Decreasing temperature and increasing strain rate led to a reduction in DRX grain size following microstructural reconstitution. Another small deterministic domain of 820−1000 °C and 0.01−0.05 s−1 was identified showing occurrence of partial DRX in shear bands leading to formation of a mixed microstructure. The instability criteria delineated the regime of unstable flow covering a large part of the processing map extending over low temperatures (800−950 °C) and high strain rates (0.1–10 s−1) that must be avoided during processing.

The ferrite-pearlite microstructure was cold-rolled to form dual phase (DP) steels, the percentage reduction of which varied. To do so, the steels were annealed in two steps and then the workpiece underwent water quenching. Accordingly, a decrease was observed in the average size of the ferrite grains, from above 15 &micro, m to below 2 &micro, m, subsequent to the thermomechanical processing. By an increase in the reduction percentage, the volume fraction of martensite grew. The balance between strength and elongation also improved nearly 3 times, equivalent to approximately 37,297 MPa% in DP in comparison to 11,501 MPa% in the ferrite-pearlite microstructure, even after 50% cold-rolling. Based on Hollomon and differential Crussard-Jaoul (DC&ndash, J) analyses, the DP steels under investigation deformed in two and three stages, respectively. The modified C&ndash, J (MC&ndash, J) analysis, however, revealed that the deformation process took place in four stages. The rate of strain hardening at the onset of the deformation process was rather high in all DP steels. The given rate increased once the size of the ferrite grains reduced, an increase in the volume fraction of martensite due to larger percentage of reduction also contributed to the higher rate of strain hardening. The observation of the fractured surfaces of the tensile specimens indicated ductile fracture of the studied DP steels.

The martensite reversion treatment was conducted on two grades of Ni-free austenitic stainless steels interstitially alloyed with C and N. The hot rolled sheets of steels were cold rolled up to 80% thickness reduction to acquire strain-induced α′-martensite and subsequently reversion annealed at temperatures from 700 to 850 °C for 1 to 1000 s to revert the α′-martensite to austenite. Microstructural evolution was investigated using optical microscopy, X-ray diffraction, electron backscatter diffraction, and magnetic measurement techniques. Mechanical properties were measured using tensile tests at room temperature. The resultant microstructures contained both reverted and recrystallized austenite when reverted at 700 and 750 °C with the annealing time less than 100 s. A nonuniform grain structure was characterized under these conditions consisting of nano/ultrafine grains formed via α′-martensite reversion and coarser grains by recrystallization of the retained austenite. However, a more uniform austenite grain size with average size of 1 μm was obtained at 850 °C for 1000 s. The specimens having nonuniform grain structure exhibited excellent combinations of strength and ductility. A variety of mechanical properties was achieved depending on the annealing condition. The work hardening behavior affected UTS and ductility of the studied steels. The shift of the work hardening peaks to the higher strains was found suitable for ductility. Addition of C to N-containing Ni-free steels deteriorated mechanical properties. Best combination of strength and elongation was obtained in the test material with lower C/N ratio.

The effect of a possible phase transformation or precipitation of the face-centred cubic (FCC) phase on intermediate-temperature deformation of a dual-phase AlCoCrFeNi high-entropy alloy has been s...

Oxynitride phosphate glasses and glass-ceramics were prepared using new synthesis routes for phosphate glasses. Materials were melted from pre-prepared glass samples in the system Na-Ca-P-O with addition of Mg and/or Si3N4 powders under different preparation conditions. The melting process was conducted at 1000–1500 °C either under air or nitrogen atmosphere to obtain materials with different nitrogen content. Their topography and structure were characterized by Confocal Microscopy, Scanning Electron Microscopy, X-ray powder diffraction and Raman and infrared spectroscopy techniques, while their chemical compositions were examined by Energy Dispersive X-ray spectroscopy (EDS). All materials prepared under nitrogen atmosphere were found to contain a relative low quantity of nitrogen and high amount of Nb leached from the crucible. The reaction with the Nb crucible was not previously observed for silicon-based oxynitride glasses. The synthesized materials form two groups: glasses and glass-ceramics. The first ones, were prepared under air and nitrogen atmospheres at temperatures up to 1400 °C, and were found to be amorphous and homogeneous. Raman and infrared spectroscopy measurements confirm the presence of amorphous phosphates in the synthesized materials. The samples of the second group were prepared at temperatures above 1400 °C and were found to be translucent and partially crystallized. They contain nanocrystallites of calcium and sodium phosphates including hydroxyapatite (HAp). The thermal properties of samples were studied by Differential Scanning Calorimetry (DSC). The obtained glass transition temperatures range from about 360 °C to 640 °C and exhibit high values for glass-ceramic materials. Stability is improved in the studied glass-ceramics because of the increased degree of network polymerization of the remaining glassy matrix. The approximate fragility index decreases two times for oxynitride materials compared to the primary glass. The synthesized new materials may be competitive to well-known bioactive phosphate glasses thanks to their improved stability by Mg, Si, N and Nb doping.

Eeffect of Boron addition on the microstructure and mechanical properties of ductile iron, GJS-500-7 grade was studied. Three cast batches with the Boron content of 10, 49 and 131ppm were cast in a casting geometry containing plates with thicknesses of 7, 15, 30, 50 and 75mm. Microstructure analysis, tensile test, and hardness test were performed on the samples which were machined from the casting plates. Addition of 49 ppm Boron decreased pearlite fraction by an average of 34±6% in all the cast plates. However, minor changes were observed in the pearlite fraction by increasing Boron from 49 to 131 ppm. Variation in the plate thickness did not affect the pearlite fraction. The 0.2% offset yield and ultimate tensile strength was decreased by an average of 11±1% and 18±2%, respectively. Addition of 49 ppm Boron decreased Brinell hardness by 16±1%, while 11±2% reduction was obtained by addition of 131ppm Boron.

A new transformation induced plasticity (TRIP) steel containing high volume fraction of martensite was produced by austempering heat treatment cycle. Microstructure and tensile properties of this TRIP steel were investigated and compared to those of a dual phase (DP) steel with high martensite volume fraction. Microstructural analysis showed a mixture of ferrite, bainite, retained austenite and about 25–30 vol% of martensite in the TRIP steel. As a result of the strain induced transformation of retained austenite to martensite, the TRIP steel showed a strength elongation balance of 86% higher than that for the DP steel. In comparison to the commercial TRIP780 steel, the current TRIP steel showed a 15% higher ultimate tensile strength value while maintaining the same level of ductility. TRIP steel also had a larger work hardening exponent than DP steel at all strains.

A dislocation density-based constitutive model, including effects of microstructure scale and temperature, was calibrated to predict flow stress of an as-cast AZ91D (Mg-9%Al-1%Zn) alloy. Tensile st ...

The study aimed to investigate crack initiation and propagation at the micro-scale in heat-treated Al–7Si–Mg cast alloys with different copper (Cu) contents. In-situ cyclic testing in a scanning electron microscope coupled with electron back-scattered diffraction and digital image correlation was used to evaluate the complex interaction between the crack path and the microstructural features. The three-nearest-neighbour distance of secondary particles was a new tool to describe the crack propagation in the alloys. The amount of Cu retained in the α-Al matrix after heat treatment increased with the Cu content in the alloy and enhanced the strength with a slight decrease in elongation. During cyclic testing, the two-dimensional (2D) crack path appeared with a mixed propagation, both trans- and inter-granular, regardless of the Cu content of the alloy. On fracture surfaces, multiple crack initiation points were detected along the thickness of the samples. The debonding of silicon (Si) particles took place during crack propagation in the Cu-free alloy, while cracking of Si particles and intermetallic phases occurred in the alloy with 3.2 wt% Cu. Three-dimensional tomography using focused ion beam revealed that the improved strength of the α-Al matrix changes the number of cracked particles ahead of the propagating crack with Cu concentration above 1.5 wt%.

This paper investigates the effect of the solidification conditions and silicon content on the mechanical properties of ductile iron and presents empirical models for predicting the tensile behavior based on the microstructural characterizations. Two ductile iron grades of GJS-500-7 and GJS-500-14 were cast with silicon content of 2.36% and 3.71%, respectively. The cast geometry consisted of six plates with different thicknesses that provided different cooling rates during the solidification. Microstructure analysis, tensile and hardness tests were performed on the as-cast material. Tensile behavior was characterized by the Ludwigson equation. The tensile fracture surfaces were analyzed to quantify the fraction of porosity. The results showed that graphite content, graphite nodule count, ferrite fraction and yield strength were increased by increasing the silicon content. A higher silicon content resulted in lower work hardening exponent and strength coefficient on the Ludwigson equation. The results for 0.2% offset yield and the Ludwigson equation parameters were modeled based on microstructural characteristics, with influence of silicon content as the main contributing factor. The models were implemented into a casting process simulation to enable prediction of microstructure-based tensile behavior. A good agreement was obtained between measured and simulated tensile behavior, validating the predictions of simulation in cast components with similar microstructural characteristics.

If high-performance aluminium castings are to be produced, the melt quality needs to be properly assured. Multiple tests for melt quality assessment exist and have previously been analysed. In most ...

This study aims to clarify the effect of grain size and Si modification on the microstructure and tensile properties of the Al-10Si cast alloy, solidified under various cooling rates. To replicate the effect of cooling rate, directionally solidified samples were produced by remelting of the as-cast cylindrical bars. Tensile properties, grain sizes, Si modification level and chemical composition profiles were evaluated. Results showed that fast cooling rates alone, without the addition of grain refiners (Al-5Ti-1B master alloy), did not lead to equiaxed grain morphologies. On the other hand, for the slowest cooling rate tested, combined additions of the Al-5Ti-1B and the Al-10Sr master alloys resulted in equiaxed grain structures while addition of only grain refiner resulted in columnar grains. The combined additions effectively produced an equiaxed grain structure at all cooling rates tested, and further improved the tensile properties.

The effect of copper (Cu) addition up to 3.2 wt.% on crack initiation and propagation in an Al-Si-Mg cast alloy was investigated using in-situ cyclic testing in the as-cast condition. A novel combination of digital image correlation, electron backscatter diffraction, and scanning electron microscopy was used to investigate crack initiation and propagation behaviour during in-situ cyclic testing. The results showed that Cu-rich intermetallic compounds with the addition of Cu up to 1.5 wt.% do not affect the fatigue behaviour of these alloys, and that crack propagation in these cases is trans-granular and trans-dendritic. However, increasing the concentration of the Cu retained in the primary α-Al matrix in solid solution and Cu-containing precipitates delayed crack propagation during cyclic testing. The results showed that strain accumulation was highest at the grain boundaries; however, the crack preferred to propagate along or across primary α-Al dendrites due to the relatively lower mechanical strength of the matrix compared to the eutectic and intermetallic phases. Moreover, the addition of Cu of more than 3.0 wt.% to Al-Si-Mg alloys changes the fatigue behaviour such that an almost static failure occurs, with limited crack propagation.

Cerium-based conversion coating formation is triggered by a local rise in pH at cathodic sites produced by the oxygen reduction reaction. Therefore, size, morphology distribution and electrochemical potential of those sites play a crucial role. While the deposition reaction is sensitive to both immersion bath concentrations and underlying substrate microstructure, only the former has been widely investigated. This research attempts to fill the gap by studying the effect of controlled microstructure variables like the cathodic intermetallics' geometry and spatial distribution on the conversion compound deposit initiation. A controlled cast Al alloy was synthesised for this study and consisted of distinct cathodic phases: Cu-rich intermetallics, Fe-rich intermetallics and Si particles. The localised deposition preferentially formed only on strong cathodic Cu-rich intermetallics. Size (surface area) of the Cu-rich intermetallic correlated linearly with the deposited area over it in terms of lateral and z-direction spread. The pH gradient occurring from the oxygen reduction near an IM is very local and does not affect pH gradients of a neighbouring IM. When immersion time is increased from 0.5 h to 1 h, the percentage of Cu-rich IM covered with conversion coating increases. Big Cu-rich IM activate faster for deposition reaction than small Cu-rich IM.

s Despite numerous studies making an effort to attain a thorough understanding of the liquid-metal-embrittlement (LME) phenomenon, the metallurgical facet of this catastrophic event remains unclear in iron/zinc (Fe/Zn) systems. While it has been frequently reported that the presence of austenite is an essential prerequisite for LME formation, the present study showed that fully ferritic structure is prone to LME phenomenon and has a high susceptibility to LME-cracking which makes it a novel observation adding to a pool of knowledge regarding LME occurrence. The elemental distribution analysis near the LME crack-tip indicated that liquid Zn was not present which confirmed solid-state grain boundary diffusion was a plausible description of LME-cracking. The occurrence of grain dropout as well as a Zn-containing crack in grain boundary without any branches with other cracks showed that grain boundary sensitization has assisted LME-cracking.

Dual phase (DP) steels with different amounts of Nb were produced by utilizing cold rolling and intercritical annealing of a ferrite-martensite duplex starting structure. The effects of Nb contents ...

Ultrafine-grained dual phase (DP) steels with different Nb contents (0.00, 0.06 and 0.12 wt%) were produced by cold-rolling followed by intercritical annealing of ferrite/martensite starting micros ...

Microalloying of an eutectoid steel with V may facilitate formation of dispersed nano-scaled VC particles in the microstructure during thermomechanical processing or subsequent heat treatment. In this research, the constitutive flow behavior of vanadium microalloyed eutectoid steel has been investigated in the temperature range 620–770 °C at strain rates in the range 0.01–10 s−1. Microstructural characterization of the deformed specimens was conducted using SEM and EBSD techniques. In this context, various deformation mechanisms occurring during warm deformation have been characterized and delineated through construction of a processing map by establishing a power dissipation map and an instability map for the steel and superimposing them. The results show that the pearlitic microstructure exhibits several deformation mechanisms within these warm working conditions. Dynamic spheroidization of cementite lamella takes place in the range 660–720 °C and 0.01–0.1 s−1 with a power dissipation efficiency of 27–33%, characterizing a safe window of processing this steel. The presence of vanadium carbides at grain boundaries strengthened the pearlitic microstructure and retarded the occurrence of some deformation defects during low temperature, high speed deformation in the range 620–720 °C and 1–10 s−1.

The effect of copper (Cu) addition up to 3.2 wt% on crack initiation and propagation in an Al–Si–Mg cast alloy was investigated using in-situ cyclic testing in the as-cast condition. A combination ...

Prototyping prior high pressure die casting (HPDC) is used for product/mold design optimization. Plaster mold casting is a cost-efficient prototyping technique providing good surface quality and dimension accuracy, similar to HPDC components. However, the corresponding mechanical properties of a component produced with these two methods are diverging significantly, mainly due to differences in the cooling rate. This work presents a procedure to optimize the plaster mold casting for prototyping to replicate mechanical properties of a commonly used Al-Si alloy (A380). Two commercial alloys with compositions close to the A380 alloy (A356.0 and A360.2) were used. Yield strength was considered as the main design criteria, thus the target mechanical property. Tensile testing results showed that with an optimized T6 heat treatment, not only the yield strength, but also ultimate tensile strength and elongation correspond well to the properties in the HPDC component.

The effect of primary austenite morphology on the ultimate tensile strength (UTS) of hypoeutectic compacted graphite Fe-C-Si alloys (CGI) is studied by isothermal coarsening experiments. Secondary dendrite arm spacing (SDAS) and the morphological characteristics related to the surface area of primary austenite, Mγ and DIDHyd, increase with the cube root of coarsening time. UTS decreases linearly with increasing coarseness of primary austenite. The eutectic and eutectoid microstructures are unaffected by the primary austenite morphology. These observations demonstrate the strong influence of primary austenite morphology on the mechanical properties of hypoeutectic CGI alloys.

A combination of direct austempering after solidification (DAAS) treatment and electron backscatter diffraction (EBSD) method was used to study the formation of micro-shrinkage porosities in ductile iron. Analyzing the aus-ferritic microstructure revealed that most of micro-shrinkage porosities are formed at the retained austenite grain boundaries. There was no obvious correlation between the ferrite grains or graphite nodules and micro-shrinkage porosities. Due to the absolute pressure change at the (purely) shrinkage porosities, the dendrite fragmentation rate during the DAAS process would be altered locally, which caused a relatively finer parent-austenite grain structure near such porosities.

This paper presents a study on micro-scale deformation and the effect of microstructure on localised deformation of ductile iron, utilizing in-situ tension testing, digital image correlation (DIC) ...

This paper focuses on local strain distribution in the microstructure of high silicon ductile iron during cyclic loading. In-situ cyclic test was performed on compact-tension (CT) samples inside the scanning electron microscope (SEM) to record the whole deformation and obtain micrographs for microstructural strain measurement by means of digital image correlation (DIC) technique. Focused ion beam (FIB) milling was used to generate speckle patterns necessary for DIC measurement. The equivalent Von Mises strain distribution was measured in the microstructure at the maximum applied load. The results revealed a heterogeneous strain distribution at the microstructural level with higher strain gradients close to the notch of the CT sample and accumulated strain bands between graphite particles. Local strain ahead of the early initiated micro-cracks was quantitatively measured, showing high strain localization, which decreased by moving away from the micro-crack tip. It could be observed that the peak of strain in the field of view was not necessarily located ahead of the micro-cracks tip which could be because of the (i) strain relaxation due to the presence of other micro-cracks and/or (ii) presence of subsurface microstructural features such as graphite particles that influenced the strain concentration on the surface. The RightsLink Digital Licensing and Rights Management Service (including RightsLink for Open Access) is available (A) to users of copyrighted works found at the websites of participating publishers who are seeking permissions or licenses to use those works, and (B) to authors of articles and other manuscripts who are seeking to pay author publication charges in connection with the submission of their works to publishers.

In the present study, the microstructural and mechanical properties of laser beam-welded thin sheet twinning-induced plasticity (TWIP) steel were investigated. The pulsed neodymium: yttrium-aluminum-garnet (Nd: YAG) laser beam welding process parameters were modeled and optimized based on experimental data and statistical analysis using response surface methodology (RSM) technique. Process parameters range, i.e. the power input (2000–3000 W), welding speed (0.2–1 mm/min), and spot size (0.3–0.7 mm) were selected properly in order to obtain the desired mechanical properties. Main effects of each factor along with interaction effect with other factors were determined quantitatively. The predicted and actual values of the mechanical properties compared using analysis of variance (ANOVA) in order to verify the adequacy of the developed model. Optimal laser beam welding parameters were identified as the power input, welding speed and spot size of 2586 W, 0.53 mm/min, and 0.48 mm, respectively. Using parameters in the optimal conditions, a welding joint with tensile load of 2001 N (% 94 strength of the base metal) was obtained. In addition, the welding zone with an average grain size coarser than the one for the base metal and a random texture was identified.

In microforming processes it is preferred to not to use lubricants, due to their complex behavior in micro-scale. Nevertheless, using lubricants could increase the life time and decrease the required forming load. Thus, it is necessary to study and develop an analytical solution for different lubrication conditions in microforming processes. A previously studied upper bound model was modified in this study for various lubrication conditions in an open-die micro-forging/extrusion process. Two approaches were chosen for identifying the friction factor in the model: (i) global friction factor, (ii) localized friction factor. Comparison of the modeling results with the experimental showed the reliability of the second approach, providing a better fit. Published version

There is a trend towards component miniaturization and strong drive towards cost effective and sustainable metal forming techniques of miniaturized components. This paper presents an upper bound solution for the optimization of open-die forging/extrusion processes in the forming of micro-pins from a sheet metal. Using such an analytical modeling approach, the critical blank thickness, the resulting final part geometry, together with the required forming load were predicted based on the location of the neutral plane under the punch during the process. Based on the phenomenological findings of the process, the geometry size factor, x, was introduced explaining its relative importance to the model. Experimental results obtained from C11000 copper samples using a progressive microforming process was found to agree well with the results predicted by the model. The results were also validated with other results reported before from a similar process.

The Al-Si cast alloy family is widely used in the production of complex castings for various applications and known for its very good castability and high strength-to-weight ratio. However, early cracking under tensile loading is sometimes a limiting factor. Among other parameters, it is yet controversial whether grain boundaries are dominant strengthening factor in cast alloys, instead of dendrite/eutectic boundaries. This study presents the effect of secondary dendrite arm spacing (SDAS) and grain size on crack initiation and propagation of Al-Si cast alloys under tensile loading. The Al-10Si (wt.%) alloy with modified Si morphology was cast using inoculants (Al-5Ti-B master alloy) under different cooling rates to obtain a range of grain sizes (from below 138 μm to above 300 μm) and SDAS (6, 15 and 35 μm). Conventional tensile test as well as in-situ tensile test in a scanning electron microscope, equipped with an electron backscatter diffraction (EBSD) was carried out to understand the deformation mechanisms of the alloy. Observation of slip bands within the dendrites showed that in modified Si structure, the interdendritic (eutectic) area takes more portion of the strain during plastic deformation. Besides, only a few cracks were initiated at the grain boundaries; they were mostly initiated from dendrite/eutectic interface. All cracks propagated trans-granularly. Hall-Petch calculations also showed a strong relationship between SDAS and flow stress of the cast alloy. Although statistically correct, there was no physically meaningful relationship between the grain size and the flow stress. Nevertheless, formation of identical slip bands in each grain could be an evidence for the marginal effect of the grain size on the overall strength development of the alloy. Consequently, among other effects, the combinational dominant effect of SDAS and modest effect of grain size shall be considered for modification of the Hall-Petch equation for precise prediction of mechanical properties of cast alloys.

Graphite nodules in spheroidal graphite cast iron (SGI) play a vital role in fatigue crack initiation and propagation. Graphite nodules growth morphology can go through transitions to form degenerated graphite elements other than spheroidal graphite nodules in SGI microstructure. These graphite particles significantly influence damage micromechanisms in SGI and could act differently than spheroidal graphite nodules. Most of the damage mechanism studies on SGI focused on the role of spheroidal graphite nodules on the stable crack propagation region. The role of degenerated graphite elements on SGI damage mechanisms has not been frequently studied. In this work, fatigue crack initiation and propagation tests were conducted on EN-GJS-500-14 and observed under scanning electron microscope to understand the damage mechanisms for different graphite shapes. Crack initiation tests showed a dominant influence of degenerated graphite elements where early cracks initiated in the microstructure. Most of the spheroidal graphite nodules were unaffected at the early crack initiation stage, but few of them showed decohesion from the ferrite matrix and internal cracking. In the crack propagation region, graphite/ferrite matrix decohesion was the frequent damage mechanism observed with noticeable crack branching around graphite nodules and the crack passing through degenerated graphite elements. Finally, graphite nodules after decohesion acted like voids which grew and coalesced to form microcracks eventually causing rapid fracture of the remaining section.

The morphological evolution of primary austenite in an industrial hypoeutectic lamellar cast iron was studied under isothermal conditions for coarsening times varying from 0 min to 96 h. The dendritic austenite structure formed during the primary solidification suffered major morphological changes during the isothermal coarsening process. After a sufficient coarsening time, dendrite fragmentation, globularization, and coalescence of austenite were studied using electron backscatter diffraction (EBSD) technique. This study confirmed that the secondary dendrite arm spacing (SDAS) is an inappropriate length scale to describe the primary austenite coarsening process for longer times. The application of shape independent quantitative parameters confirmed the reduction of the total interfacial area during microstructural coarsening. The modulus of the primary austenite, Mγ, which represents the volume-surface ratio for the austenite phase, and the spatial distribution of the austenite particles, measured as the nearest distance between the center of gravity of neighboring particles, Dγ, followed a linear relation with the cube root of coarsening time during the whole coarsening process. The mean curvature of the austenite interface, characterized through stereological relations, showed a linear relation to Mγ and Dγ, allowing the quantitative characterization and modeling of the complete coarsening process of primary austenite. Included in licentiate thesis in submitted form.

© 2017 Elsevier B.V. The strain localization and crack formation in ferritic-pearlitic ductile iron under tension was investigated by in-situ tensile tests. In-situ tensile tests under optical microscope were performed and the onset of the early ferrite-graphite decohesions and micro-cracks inside the matrix were studied. The results revealed that early ferrite-graphite decohesion and micro-cracks inside the ferrite were formed at the stress range of 280–330 MPa, where a kink occurred in the stress-strain response, suggesting the dissipation of energy in both plastic deformation and crack initiation. Some micro-cracks initiated and propagated inside the ferrite but were arrested within the ferrite zone before propagating in the pearlite. Digital Image Correlation (DIC) was used to measure local strains in the deformed micrographs obtained from the in-situ tensile test. Higher strain localization in the microstructure was measured for the areas in which the early ferrite-graphite decohesions occurred or the micro-cracks initiated. ispartof: Materials Science and Engineering A, Structural Materials: Properties, Microstructure and Processing vol:702 pages:265-271 status: published

Although there is considerable published literature on micro-metal forming processes, there is still a lack of research towards implementing these processes commercially. Some of the challenges are handling of micro-parts and process intermittency. This work demonstrates the feasibility of producing symmetric micro-parts using a progressive forming set-up. Such a progressive forming process alleviates the challenges in handling and removal of micro-parts. Micro-pins with diameters of 0.3, 0.5, and 0.8 mm were successfully manufactured without defects. Experimental observations together with process simulation results showed that this process has three main stages: (1) indentation at the very beginning, (2) upsetting, and (3) extrusion predominantly occurring at the very end stage of the stroke. The bulk of the pin forming occurs at the end stroke of the process (extrusion stage). The effects of punch/pin diameter ratio on the pin aspect ratio and the maximum forming load were also investigated. In addition, the finite element results also revealed that a hybrid friction model was required to be implemented for better fit with experimental results as compared to the shear and Coulomb friction models.