Secondary Dendrite Arm Spacing Research Articles

Effect of cooling rate and Nb addition on the strengthening in eutectic CoCr1.3FeMnNi0.7Nbx (0 ≤ x ≤ 0.45) high entropy alloys comprising of low stacking fault energy FCC phase

The CoCr1.3FeNi0.7MnNbx (0.3 ≤ x ≤ 0.45) eutectic high entropy alloy (EHEA) comprising of ultrafine lamellae of low stacking fault energy (SFE = 11 mJ/m2) face centered cubic (FCC) and Laves phase are synthesized at cooling rates of 2.5–10 K/s (arc melted ingots, AMIs) and 4.2 × 102 K/s (suction cast bars, SCBs). The microstructural investigation suggests that secondary dendritic arm spacing (SDAS) and interlamellar spacing are refined in SCBs due to a higher cooling rate than the AMIs. Whereas, deformation twins evolve in FCC phase due to its low SFE. The EHEAs exhibit a high yield strength of 1327 MPa for x = 0.367 SCB and a large fracture strain of 20% for x = 0.3 AMI under compression. Systematic investigation on the influence of Nb addition, microstructure refinement, and evolution of deformation twins during straining on the strengthening mechanisms reveals that the phase interface strengthening, solid solution strengthening, and twin boundary strengthening play critical roles in providing the high flow stress. The post-deformation analysis and the presence of multiple positive slopes in work hardening curves confirms that the concurrent effect of the evolution of dislocations, deformation twins, and their mutual interactions are solely responsible for the severe strain hardening at multiple stages during plastic deformation. The low values of strain rate sensitivity (0.0106–0.0111) and the activation volume (28b3-41b3) suggest that the deformation kinetics is governed by the dislocation interactions with the ultrafine lamellae interface and twin boundaries.

Effects of the synergistic addition of AlCrNiTi and Ce on the microstructure and mechanical properties of hypoeutectic Al-7Si alloy

A new strategy is proposed in this study to modify the microstructure of the Al-7Si alloy, which is widely employed in the aerospace and transportation sectors due to its lightweight, high specific strength, and specific modulus. The primary challenge of the Al-7Si alloy is its coarse microstructure, which undermines its mechanical properties. This research focuses on the effects of adding the AlCrNiTi master alloy and Ce to the Al-7Si alloy. The impact on both the microstructure evolution and the mechanical properties is examined, including analysis and discussion of the underlying mechanisms for refinement and strengthening. When the alloy was modified by 0.9 wt% of the AlCrNiTi master alloy and 0.1 wt% of Ce, there was a notable refinement of the α-Al phase, transforming it from a coarse dendritic structure to fine equiaxed grains. The addition of 0.9 wt% of the AlCrNiTi master alloy and 0.1 wt% of Ce can also reduce the secondary dendrite arm spacing (SDAS) to 5.9 μm. The eutectic Si phase underwent a significant transformation, changing from coarse flakes to fine granularity with rounded edges. Furthermore, CeSi2Ni2, Al3Ni intermetallic compounds, and nanoscale Al45Cr7 particles were observed in the modified Al-7Si alloy. Tensile tests showed that the addition of the inoculant in the Al-7Si alloy enhanced the ultimate tensile strength (UTS) from 173 MPa to 211 MPa and increased the elongation (El) from 7.9% to 14.1%.

Directed energy deposition of PH 13–8 Mo stainless steel: microstructure and mechanical property analysis

Laser metal deposition (LMD) is of the directed energy deposition (DED) process which is widely used for producing large-scale, dense, and functional parts in the field of additive manufacturing (AM). This research work investigates the microstructure and mechanical properties of PH 13–8 Mo martensitic stainless-steel parts produced via LMD. The workshop trials were conducted using an LMD system collaborated with a robotic arm to deposit single-track thin walls and horizontal blocks. The microstructural characteristics of the additively manufactured parts were analyzed using an optical microscope. The mechanical properties were evaluated through hardness measurements and uniaxial tensile tests. The influence of energy density and powder deposition density on the characteristic geometry of straight walls was also investigated. The microstructural analysis showed that the microstructure consisted of columnar dendrites that grew epitaxially from the substrate, with primary austenite cells containing intercellular ferrite and martensite laths that were roughly parallel with the retained austenite. When the energy density increased from 43 to 86 J/mm2 (a doubling of energy density), there was an increase in secondary dendritic arm spacing (SDAS) by approximately 250% in the first layer and approximately 90% in the top layer. The difference in SDAS change between the first and top layers can be attributed to the difference in cooling rates experienced by each layer during the additive manufacturing process. Increasing powder deposition density from 0.5 to 1 g/min results in a decrease in porosity from 3% to less than 1% and an increase in strength from 800 to over 1000 MPa. The hardness of the deposits was found to range from 300 to 400 HV. This variation in hardness can be attributed to differences in microstructure resulting from changes in cooling rates at different heights.

Experimental study of SS316L, Inconel 625, and SS316L-IN625 functionally graded material produced by direct laser metal deposition process

Three types of walls were produced by the direct laser metal deposition (DLMD) process; SS316L, Inconel 625 (IN625), and SS316L-Inconel 625 FGM. The thin walls were deposited on an AISI 4130 austenitic steel substrate in five layers with a length of 2 cm. The solidification behavior, secondary dendrite arm spacing (SADS) value, chemical composition, and hardness of samples were studied. Microstructures were evaluated using optical microscopy (OM) images, scanning electron microscopy (SEM), EDS Line, EDAX, and Map analyses. OM and SEM images showed an acceptable bonding between the layers in all samples. The main solidification was equiaxed dendritic and columnar dendritic in most parts. The growth of dendrites was perpendicular to the substrate. Some dendrites grew epitaxially at the interface of two sequential layers. The standard deviation of SDAS value for SS316L, IN625, and SS316L-IN625 FGM was 0.63, 0.71, and 0.73, respectively. The lowest value of SDAS was obtained in layer one, while the highest value was obtained in layer five of the thin walls. The average SDAS values for SS316L, IN625, and SS316L-IN625 FGM were 4.40, 4.53, and 4.76 µm, respectively. Therefore, the difference between the SDAS values was not significant. EDAX and Map analyses showed that the segregation of Nb and Mo to the dendritic boundary and the formation of eutectic, secondary phases, and brittle Laves phases have occurred. Additionally, the segregation of Nb and Mo to the dendritic boundary in the SS316L-IN625 FGM sample was higher than SS316L and IN625 samples. The microhardness values oscillated significantly and decreased by moving away from the substrate (in the build direction). The microhardness values of different points of the SS316L-IN625 FGM walls were in the range of 218–278 HV. EDS line scan, microstructure, and microhardness analyses indicated the successful fabrication of the SS316L-IN625 FGM by the DLMD process.

A novel method for evaluating solidification cracking susceptibility of austenitic stainless steel using trapezoidal hot cracking test during laser welding

A novel evaluation method was developed for evaluating solidification cracking susceptibility of austenitic stainless steel using trapezoidal hot cracking test laser welding. By changing different chemical compositions and welding speeds, the critical restraint width was named and regarded as a new index to evaluate cracking susceptibility. First of all, the average critical restraint width of SUS310S, 316 and 302 was measured as 22.97 mm, 18.17 mm and 17.38 mm during laser welding at a speed of 1.0 m/min, respectability. Single phase austenite under mode A appeared in 310S while the other could form austenite and a small amount of ferrite based on mode FA, therefore, the solidification cracking susceptibility was 310S > 316 > 302. Then, the critical restraint widths of SUS310S and 304 had a tendency of decrease with increasing welding speed from 0.5 m/min to 1.0 m/min during laser welding. The lower heat input could decrease primary and secondary dendrite arm spacings, causing a reduction in the segregation degree. In addition, the fine dendrite along grain boundary of weld center could contribute to form zigzag interface which would be beneficial to interrupt the continuous residual liquid film. Thus, the solidification cracking susceptibility tended to decrease with an increase in laser welding speed from 0.5 m/min to 1.0 m/min. Above all, the developed evaluation method could improve the applicability, feasibility and progressiveness of hot cracking test.

Effect of local loading on microstructure and enhanced mechanical property of large complex castings prepared by Al–Si–Fe–Mn–Mg–Cu alloy during squeeze casting

Flywheel shells with a complex structure and large wall-thickness difference, as key components in heavy trucks, serve to connect the engine and transmission. Formability and mechanical performance control of such components should be taken into consideration. In this work, an Al–Si–Fe–Mn–Mg–Cu alloy was used to manufacture the flywheel shell via squeeze casting. The role of local loading on microstructure and mechanical property at thick-walled positions was investigated. Furthermore, the effect of the squeeze casting specific pressure and heat treatment on the microstructure and mechanical property of the Al–Si–Fe–Mn–Mg–Cu alloy flywheel shells was also analyzed. The results showed that at the thick-walled positions, local loading not only helps eliminate the solidification defects, but also refines the microstructure including α-Al grains and secondary dendrite arm spacing. With increasing the squeeze casting specific pressure from 24 MPa to 32 MPa, microstructure refinement and mechanical property enhancement of squeeze casting flywheel shells were obtained. After T6 heat treatment, the yield strength and ultimate tensile strength of flywheel shells were further increased to 261.8 and 318.4 MPa, respectively, owing to the formation of spherical eutectic Si phases and nano-sized β'', Q and S precipitates.

Effect of Al-Sr-Y intermediate alloy on microstructure and mechanical properties of A356 alloy

In this experiment, an intermediate alloy (Al-3Sr-8Y) that can refine and modify A356 alloy simultaneously was developed, and the synergistic effect of Sr and Y on the microstructure and mechanical properties of A356 alloy was investigated. The results show that when the content of Al-3Sr-8Y intermediate alloy reaches 0.3 wt%, the morphology of α-Al dendrites is significantly refined and the secondary dendrite arm spacing (SDAS) was significantly reduced. Moreover, the morphology of eutectic Si transforms from acicular to small fibrous, and the average area and aspect ratio of eutectic Si decrease to 0.81 μm2, and 2.01. This change is caused by the twin plane re-entrant edge (TPRE) poisoning mechanism, where the addition of Al-3Sr-8Y can poison the intrinsic growth position of the Si phase, reduce the growth rate of the Si phase, promote isotropic growth, and achieve a highly branched morphology of the Si phase to form a fibrous structure. Due to the excellent synergistic effect of Sr and Y, the tensile strength and elongation of the alloy reached the maximum values of 303.5 MPa and 9.5% when 0.3 wt% Al-3Sr-8Y was added after heat treatment, which is an increase of 18.2% and 86.3% compared with the untreated A356 alloy, respectively.

Effect of Al–5Ti–1B–La intermediate alloy on microstructure and mechanical properties of A356.2 aluminum alloy

This study delves into the effects of Al–5Ti–1B–1La intermediate alloy, a newly developed refinement agent, on the microstructure and mechanical properties of A356.2 aluminum-silicon alloy modified by Al–10Sr. The decomposition of Ti2Al20La, where La element was concentrated in the Al–5Ti–1B–1La intermediate alloy, hardly affected the conventional nucleation mechanism of TiAl3–TiB2; nonetheless, the La element significantly refined the dendritic arms of α-Al. Notably, the secondary dendrite arm spacing was reduced from 49 μm to 27 μm, when 0.025 wt% ∼0.2 wt% Al–5Ti–1B–1La intermediate alloy and 0.014 wt% Al–10Sr modifier was incorporated to the A356.2 aluminum alloy. Although the room-temperature ultimate tensile strength was increased only by 30 MPa, the elongation was remarkably improved from 10% to 26%. The hardness of the alloy was also enhanced from 75 HBW to 84 HBW. The experimental outcomes underscore the efficacy of minimal La element incorporation in enhancing the performance of Al–5Ti–1B intermediate alloy, and the findings are significant for improving the serviceability of automobile wheels made from A356.2 aluminum alloy. The method used in this study can also be employed to regulate the microstructure and enhance mechanical properties of other sub-eutectic aluminum-silicon alloys.

Crystalline Microstructure, Microsegregations, and Mechanical Properties of Inconel 718 Alloy Samples Processed in Electromagnetic Levitation Facility

The solidification of Inconel 718 alloy (IN718) from undercooled liquid is studied. The solidification kinetics is evaluated in melted and undercooled droplets processed using the electromagnetic levitation (EML) technique by the temperature–time profiles and solid/liquid (S/L) interface movement during recalescence. The kinetics is monitored in real time by special pyrometrical measurements and high-speed digital camera. It is shown that the growth velocity of γ-phase (the primary phase in IN718), the final crystalline microstructure (dendritic and grained), and the mechanical properties (microhardness) are strongly dependent on the initial undercooling ΔT at which the samples started to solidify with the originating γ-phase. Particularly, with the increase in undercooling, the secondary dendrite arm spacing decreases from 28 μm to 5 μm. At small and intermediate ranges of undercooling, the solidified droplets have a dendritic crystalline microstructure. At higher undercooling values reached in the experiment, ΔT>160 K (namely, for samples solidified with ΔT=170 K and ΔT=263 K), fine crystalline grains are observed instead of the dendritic structure of solidified drops. Such change in the crystalline morphology is qualitatively consistent with the behavior of crystal growth kinetics which exhibits the change from the power law to linear law at ΔT≈160 K in the velocity–undercooling relationship (measured by the advancement of the recalescence front in solidifying droplets). Study of the local mechanical properties shows that the microhardness increases with the increase in the γ″-phase within interdendritic spacing. The obtained data are the basis for testing the theoretical and computational of multicomponent alloy samples.

Prediction of the Secondary Arms Spacing Based on Dendrite Tip Kinetics and Cooling Rate.

Secondary dendrite arm spacing (SDAS) is one of the most important factors affecting macrosegregation and mechanical properties in solidification processes. Predicting SDAS is one of the major parameters in foundry technology. In order to predict the evolution of microstructures during the solidification process, we proposed a simple model which predicted the secondary dendrite arm spacing based solely on the tip velocity (related to the tip supersaturation) and cooling rate. The model consisted of a growing cylinder inside a liquid cylindrical envelope. Two important hypotheses were made: (1) Initially the cylinder radius was assumed to equal the dendrite tip radius and (2) the cylindrical envelope had a fixed radius in the order of the dendrite tip diffusion length. The numerical model was tested against experiments using various Pb-Sn alloys for a fixed temperature gradient. The results were found to be in excellent agreement with experimental measurements in terms of SDAS and dendrite tip velocity prediction. This simple model is naturally destined to be implemented as a sub-grid model in volume-averaging models to predict the local microstructure, which in turn directly controls the mushy zone permeability and macrosegregation phenomena.

Effects of scanning speed on the microstructure, hardness and corrosion properties of high-speed laser cladding Fe-based stainless coatings

Fe-based coatings have been prepared by utilizing laser cladding with the scanning speed ranging from 1.57 to 20.4 m/min. The microstructure and corrosion properties have been further investigated to evaluate the effects of scanning speed. The results show that, both coating's thickness and dilution rate gradually decrease with the increase of scanning speed. However, the deposition efficiency on the surface can be greatly improved by around 4 times. Under high scanning speed, the Fe-based coatings show the similar microstructure feature, comprising with dendrites and inter-dendritic structures. But the coating's microstructure can be significantly refined with the secondary dendritic arm spacing less than 1 μm. Furthermore, the gap of Cr concentration between the two structures can be effectively reduced, which shrinks the difference in corrosion resistance. On the other hand, the Fe-based coating's hardness gradually decreases resulting from the retained austenite and ferrite under high scanning speed. Compared to Q235 steel, the cladded Fe-based coatings show superior corrosion resistance with much higher corrosion potential and lower corrosion current density. Pitting dominates the corrosion forms of high-speed laser Fe-based coatings, which initially takes place on the boundaries of different structures. With the increase of scanning speed, the coating's corrosion resistance increases firstly and then decreases, and the coating cladded with the speed of 15.7 m/min shows the best corrosion resistance. Higher average Cr content and more uniform Cr distribution account for the better corrosion resistance. However, excessive microstructure refinement plays a negative role in the coating's corrosion resistance owing to more grain boundaries.

Effect of Microstructure on the Precipitation of β-Mg2Si during Cooling after Homogenisation of Al-Mg-Si Alloys

For Al-Mg-Si alloys, cooling after homogenisation is a crucial step because the precipitation of the equilibrium β-Mg2Si phase determines the processing capabilities in subsequent steps, as well as the subsequent precipitation age hardening potential, and thus, the final properties. It is therefore important to understand how microstructural variations affect the transformation of β-Mg2Si during cooling after homogenisation. In the present work, alloys with similar effective solute contents of Mg and Si, but with different microstructures and a different amount of primary Al-Fe-Si phases, were produced. Characterisation of the precipitation reaction was performed using interrupted quench experiments with cooling rates of 1–6 K/min, monitored by light optical microscopy (LOM), scanning electron microscopy (SEM) and conductivity measurements. Precipitation kinetics for β-Mg2Si was found to increase in microstructures with shorter secondary dendrite arm spacing (DAS). However, despite measuring both a higher density and volume fraction of the primary phases, no effect on the phase transformation from an increased iron content was found in terms of precipitation kinetics or particle count statistics. Furthermore, comparisons with iron-free high-purity-based alloys revealed that the precipitation reaction for β-Mg2Si was identical in the two different microstructures both in terms of onset temperature and overall kinetics. The present results show that nucleation of β-Mg2Si is not dependent on the larger constituent phases and indicates that overall transformation kinetics is governed by bulk diffusion rates.

Improvement of mechanical properties of Al-Si-Mg composites by in-situ formation of small-sized (Al, Si)3(Ti, Zr) particles

In this study, Al-Si-Mg composites were prepared by adding different combinations of titanium (Ti), zirconium (Zr), boron (B), and antimony (Sb)，and its micro-structure and mechanical properties were investigated. The results revealed that the average diameter of α-Al grains in the novel alloy, prepared through the combined addition of Ti, Zr, B, and Sb, was 110 µm, with a secondary dendritic arm spacing (SDAS) of 22.4 µm. This grain refinement is attributed to the in-situ formation of heterogeneous nucleation sites L12-(Al, Si)3(Ti, Zr). The alloy heat-treated at T6 exhibited notable mechanical characteristics, including a tensile strength of 354.5 MPa, a yield strength of 317.9 MPa, and an elongation at break of 5.6%. Significantly, the enhancement in mechanical properties is found to be independent of the modifications of eutectic silicon. This improved strength and elongation are attributed to both grain refinement and the in-situ formation of I4-(Al, Si)3(Ti, Zr). Overall, these findings provide an effective and direct method for obtaining high-performance Al-Si-Mg composites.

Effect of heat treatment on microstructural characteristics and mechanical properties of hypereutectic B390 aluminium alloys modified by phosphorus and bismuth

This study investigated the effects of solution treatment and aging processes on microstructural characteristics and mechanical properties of hypereutectic B390 Al-Si Alloy modified by phosphorus (P) and bismuth (Bi). The morphology evolution of primary Si, eutectic Si, intermetallic compounds, and secondary dendrite arm spacing (SDAS) of both initial and modified alloys were investigated in as-cast and heat-treated conditions. It was found that the combination of 0.1 wt%P and 0.5 wt%Bi in B390 alloy resulted in a remarkable modification and refinement of primary Si, eutectic Si, and SDAS compared to initial specimens in the as-cast condition. After heat treating, the fine lamellar eutectic Si and intermetallic compounds underwent a higher degree of fragmentation and coarsening, appearing as small round particles, leading to a more pronounced formation of a supersaturated solid solution. Additionally, the peak aging time of the B390-P-Bi alloy was only 7 h, 2 h less than the initial specimen. After T6 treatment and addition of both 0.1 wt%P and 0.5 wt%Bi, the B390-P-Bi alloy exhibited a smaller rounded Mg3Bi2 phase at peak aging with a 62.07% size reduction compared to the B390-Bi alloy. The results show that adding P with Bi enhanced hardness, ultimate tensile strength (UTS) and elongation because of refinement of the SDAS, primary Si and eutectic Si. These refinements played a crucial role in increasing tensile strength by more effective strengthening through precipitation and grain size reduction. The B390-P-Bi alloy is a promising choice for applications requiring a balance between strength and ductility.

On the properties of cast and powder metallurgical Cu–6Ni-1.5Si-0.15Al (wt.%) alloy

In this study, Cu–6Ni-1.5Si-xAl (x = 0 and 0.15 wt%) alloys are manufactured as billet materials by casting and their metallurgical and physical properties are characterized. Aluminum modified alloy is obtained also by a powder metallurgical (PM) route and its structural properties are determined to be compared with the cast materials. The findings indicate that (i) solidified alloys have distributed nickel silicides (27.01 %) embedded in α-Cu(Ni,Si) solid solution, (ii) the addition of aluminum increases the amount of silicides (29.09 %) in the solidified matrix and reduces both the grain size and the secondary dendrite arm spacing, (iii) although PM alloy has similar microstructural features as cast alloys, it exhibits the highest hardness (159 HV1) due to both finer grain structure and better distribution of silicides, (iv) both impurity and porosity have a determining effect on the electrical conductivity (27–32 % IACS, International Annealed Copper Standard) values of the alloys.

Microstructural Heterogeneity and Property Variations in Cast and Vacuum Hot-Pressed CoCrPtB Alloy.

Limited research has been undertaken regarding the homogeneity of CoCrPtB alloy billets. A CoCrPtB alloy was processed through casting and vacuum hot pressing. This investigation delved into the interconnection between the secondary dendrite arm spacing (SDAS) in the as-hot-pressed samples and their corresponding attributes, specifically Vickers hardness and magnetic properties. Systematic sampling was conducted on the cross-sectional layer and longitudinal surface. Upon examination of the cross-sectional layer proximate to the uppermost region of the hot casting, a discernible parabolic trend was observed for the SDAS that exhibited a gradual increment from the peripheral regions toward the central area along the width. Simultaneously, the fraction of the dendrite phase displayed a consistent linear decline, attaining its peak value at the central portion of the billet. Conversely, on the longitudinal surface, SDAS and the fraction of the dendrite phase remained fairly uniform within the same column sampling regions. However, a notable divergence was identified in the central section, characterized by an augmented SDAS and diminished dendrite phase content. This inherent microstructural inhomogeneity within the CoCrPtB alloy engendered discernible disparities in material properties.

Experimental investigation and kinetic analysis of Al–Zn–Mg alloy coating

The hot-dip 55 wt%Al–Zn-1.6 wt%Si-(0–3)wt.%Mg alloy coatings were experimentally investigated, and the solidification behaviors and hot cracking susceptibility were simulated by means of CALPHAD (CALculation of PHAse Diagrams) method. The scanning electron microscopy (SEM), electron probe micro-analyzer (EPMA) and glow discharge spectrometer method (GDS) were utilized to determine the microstructures and the distribution of elements of the Al–Zn–Mg alloy coatings with different Mg contents. It is discovered that with the increase of Mg content, the percentage of the eutectic microstructure scales up, and the surface quality of the alloy coating is improved. Meanwhile, the bending properties of Al–Zn–Mg coatings with different Mg contents still requires further improvement according to the present bending test. Subsequently, the equilibrium solidification processes of the coatings were calculated using thermodynamic approach. In general, the calculated results reflect the solidified phases and the precipitated temperatures according to theory of equilibrium solidification. However, there still exist discrepancies between the thermodynamic calculation results and the observed experimental results during the practical galvanizing process, because the cooling rates were not taken fully into consideration. Consequently, the kinetic analysis was carried out to obtain the secondary dendrite arm spacing under different cooling rates. The cracking susceptibility index (CSI) was also calculated to predict the hot workability of the Al–Zn–Mg alloy coating. In summary, the appropriate increase of the cooling rate turns out be the effective approach to benefit the microstructure and the corrosion resistance of the Al–Zn–Mg coatings in the practical galvanizing process, and the coating is not suitable for the hot stamping process.

A new generation of metal chillers to control the solidification structure of Al-4.5 wt%Cu alloy

This paper introduces and examines a new generation of chillers for judicious control of the solidification structure of cast metals and alloys. This innovative chiller makes use of the absorption of the latent heat of melting of a Phase Change Material (PCM) incorporated in the chiller. In this work, Al-4.5 wt%Cu melt was cast in sand molds fitted with a traditional solid steel chiller as well as this new type of chiller consisted of a steel container filled with a given amount of pure zinc as PCM. Effects of the PCM fitted chiller on the thermal history, solidification and structure of the castings were studied by experimental and computer simulation investigations. The optimum casting parameters and mold and chillers dimensions were selected using ProCast simulation software. Use of the PCM fitted chiller resulted in faster columnar-equiaxed transition, 27 %, 54 % and 40 % reduction in the length of the columnar zone and the primary and the secondary dendrite arm spacings, respectively, and about 30 % improvement in the hardness. Thermal gradients and cooling rates at different points of the PCM fitted casting were generally more than those in the traditionally chilled casting. Use of the PCM fitted chiller eliminated the formation of the feathery grains and reduced the formation of the undesired Fe-rich phases close to the chiller due to different thermal history of the castings. Segregation pattern and change of Growth Restriction Factor (GRF) along the castings were studied and related to the cooling and growth conditions experienced by each casting.

Investigating the influence of thermal behavior on microstructure during solidification in laser powder bed fusion of AlSi10Mg alloys: A phase-field analysis

The utilization of the laser powder bed fusion (L-PBF) method in additive manufacturing experiments has revealed the intriguing potential to induce morphological evolutions within the solidification microstructure by manipulating the thermal conditions. Transitions of this nature can have a substantial impact on the ultimate texture and material properties of the product. This study utilizes numerical investigations to examine the microstructure evolution of the AlSi10Mg alloy, which is fabricated using the L-PBF process, under different thermal conditions. In order to investigate the changes in the microstructure, we employ a parameter phase-field (PF) model. This model effectively replicates the natural development of nuclei from inoculant particles and accurately simulates the transitions in the morphology. The PF model’s validity is determined through the numerical investigation of morphological transitions during directional solidification of the AlSi10Mg alloy. The model’s predictions are then compared to the analytical Hunt model. The formation of a columnar microstructure with a significantly reduced secondary dendrite arm spacing is observed when the ratio of the temperature gradient (G) to the solidification rate (R) is increased.

The Effect of the Distance between Ultrasonic Horn and Torch on the Microstructure of Ultrasonic-Assisted Gas Tungsten Arc Welded Inconel 690 Alloy Joint

The study focuses on investigating the relationship between the ultrasonic effect and microstructure of ultrasonic-assisted gas tungsten arc welding (UA-GTAW) Inconel690 alloy joints. The influence of ultrasonic vibrations on Inconel690 plates was examined, while also clarifying the distribution pattern of the ultrasonic effect across the plate. Furthermore, actual welding experiments were performed by varying the distance between the ultrasonic horn and the welding torch. The results revealed that there were changes in both grain growth direction within the weld zone and refinement effects achieved under different distances. The optimal refinement of primary and secondary dendrite arm spacing was observed at distances of 60 mm and 180 mm between the welding torch and ultrasonic horn. The hardness of weld zone reached 235HV1 when the distance between ultrasonic horn and welding torch is 180 mm.